Results of Chemical Cleaning the 242-16H (2H) Evaporator at the Savannah River Site

W. R. Wilmarth, C. J. Martino, J. T. Mills, and V. H. Dukes
Westinghouse Savannah River Company
Aiken, SC 29808

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The operation of the 242-16H (2H) Evaporator was curtailed in October 1999 due to the presence of an aluminosilicate scale that contained sodium diuranate with a uranium-235 enrichment of approximately 3 %. The scale had built to the point where steam lifting of the evaporator concentrates was ineffective. Work performed by SRTC during calendar years 1998-2000 had shown that dilute nitric acid was an effective chemical cleaning agent. An overall cleaning flowsheet was developed in calendar year 2000 that addressed numerous safety issues associated with cleaning the pot, neutralizing the uranium-bearing acid and discharging the neutralized solutions to a waste tank. Beginning in May 2001, a depleted uranium and nitric acid mixture was added to the 2H Evaporator pot and heated to elevated temperatures. As a result of this action, the pot was cleaned and returned to service as can be seen in Figure 1. The following summarizes the key conclusions from this work.

The Savannah River Site (SRS) stores high level nuclear waste in 49 underground storage tanks. The wastes are to be vitrified in the Defense Waste Processing Facility (DWPF) for permanent disposal. The available tank space must be managed to ensure viability of the separation canyon to support nuclear material stabilization and continued operation of DWPF. Under normal operations, the wastes are evaporated to reduce volume. The SRS has three operational high level waste evaporators. Two evaporators are located in H-Area and one is in F-Area. The 242-16H (or 2H) evaporator has not operated since October 1999 due to the presence of a large amount of sodium aluminosilicate scale that contained sodium diuranate. The scale is very similar to that observed in the aluminum and pulp paper industry^,, and was produced by reaction of the aluminate supplied by the canyons and the silicate from the DWPF recycle. The chemistry of high level waste with elevated silicon levels thermodynamically favors the formation of aluminosilicates.

The 2H Evaporator was scaled to the point that the concentrated evaporator bottoms could not be removed through normal steam lifting. Previous work by Wilmarth and others^, has shown that a dilute nitric acid cleaning solution is effective in dissolving the aluminosilicate scale and the sodium diuranate encrusted in the scale. A complete dissolution flowsheet was written for this operation by Boley, et al. The results of this cleaning operation and associated chemistry are present in this paper.

The cleaning process, as outlined in the operating plan, began during May 2001. The operational configuration is shown in Figure 2. The evaporator pot is 16.5 ft. tall and 8 ft. wide, and is cylindrical with a conical bottom section. Heat is normally supplied by a warming coil (25 lb. steam) and the horizontal tube bundle (150 lb. steam). The operating volume during caustic waste evaporation is approximately 1800 gallons and during acid cleaning the volume was raised to 2800 gallons. Figure 3 shows a schematic drawing of the evaporator internals. The flowsheet first required a water soak to remove soluble salts. Subsequently, dilute nitric acid (1.5 M free acid) containing 280 g/L depleted uranium, in the form of uranyl nitrate, was added and heated to around 90 ° C. The depleted uranium was added to ensure criticality safety in the neutralization tank prior to disposal in Tank 42H. An air lance in the evaporator pot provided agitation.

The Savannah River Technology Center (SRTC) analyzed liquid dip samples taken from the evaporator pot during the first acid strike and at the end of the second strike. Samples from H-canyon cleaning solution make-up tank and the acid unloading station were analyzed by SRTC and established the baseline characteristics of the acid cleaning solution. Blue label samples of the cleaning solution in the H-canyon make-up tank were qualified for proper uranium and acid composition by the F-area central laboratory (F-Lab). A sample of the loose solids that settled in the evaporator pot cone after the first acid cleaning was collected and analyzed by SRTC.

The pot dip samples were collected as previously stated by dipping a metal bottle (~ 80 mL) approximately 12 inches under the liquid surface. The air lance had been suspended and the pot contents had been allowed to settle for 30 minutes prior to the sampling. Thus, any solids or emulsions that are significantly more dense than the bulk cleaning solution had ample time to settle beneath the sampling zone.

Upon receipt, the acid samples were either placed in the shielded cells or taken to a radiochemical laboratory, depending on the dose rate of the sample. The samples were opened and, if solids were observed, the entire sample was passed through a 0.45 m m filter. The solid phase was collected and analyzed. The X-ray diffraction (XRD) patterns were obtained with Cu Ka radiation on a Bruker Axs, Inc. instrument with a Siemens D500 goniometer. Scanning electron micrographs (SEM) and energy dispersive spectra (EDS) were obtained using the following instruments: Cambridge Stereoscan 250 Scanning Electron Microscope, Tracor Northern Energy Dispersive X-ray Analyzer and Mirocspec Wavelength Disperive Analyzer. Portions of the solid samples were analyzed by Differential Scanning Calorimetry (DSC) and Thermal Gravimetric Analysis (TGA). Samples were placed in an Instrument Specialist Incorporated 550E DSC. About 10 to 20 mg of material was placed in the calorimeter and was heated at 10 ° C/minute from 25 ° C to 600 ° C. The temperature rise or depression in the sample was monitored and converted to energy via calibration standards. Over a similar temperature range, the weight loss of samples was determined in a DuPont V5.1A TGA equipment. About 20 to 40 mg of sample was placed in the TGA and it was heated 10 ° C/minute from 25 ° C to 1000 ° C. About 2 mg of sample was mixed with 0.2 grams of petroleum gel. The sample was mixed until a uniform color was achieved. The sample was squeezed between two potassium bromide plates until a film thickness of about 10 microns was achieved. The sample was in the sample compartment of a NICOLET 210 FT-IR spectrometer.

Elemental metals measurements were performed, based on atomic emission from excited atoms and ions, using Applied Research Laboratories, Model Number: 3580 inductively-coupled plasma atomic emission spectrometer (ICP-ES). Free hydroxide analysis was determined via an inflection point titration using a contained Radiometer "TIM 900" automated titration system. Tributyl phosphate analysis was performed by gas chromatography/mass spectrometry using a Hewlett Packard model 5973 mass selective detector with a model 6890 gas chromatograph. The n-Butanol analysis was performed by gas chromatography/mass spectrometry using a Hewlett Packard model 5971 mass selective detector with a model 5890 gas chromatograph. Carbon analysis was completed using a Tekmar-Dohrmann model DC-190 High Temperature Total Carbon Analyzer with an installed remote boat sampler for radiological samples.

Gamma analysis used an aliquot of the sample and was analyzed by gamma spectroscopy analysis using a high purity germanium detector. The gamma spectroscopy analysis uncertainties provided, which are based primarily on counting statistics, are 1 sigma. The results are background subtracted.

Strontium-90 separation and analysis, performed using an aliquot of the sample, was analyzed for Sr-90 using an Eichrom Sr-Spec based extraction procedure. A Sr-90 spiked blank, as well as a Sr-90 spiked sample, was analyzed with the sample batch to establish Sr-90/Y-90 counting efficiencies and Sr chemical recoveries. Once the extractions were complete aliquots of the resultant Sr-90/Y-90 containing extracts mixed with liquid scintillation cocktail were counted in the ADS Radiochemistry Counting Facility. The samples were counted on a Packard Instruments liquid scintillation counter along with an instrument blank. The instrument blank was counted first and was used to establish an instrument background that was subtracted from the count results for the samples. Uncertainties provided, which are based primarily on counting statistics, are 1 sigma.

The plutonium separation and analysis, performed using an aliquot of each sample, was subjected to a thenoyltrifluoroacetone (TTA) separation. An aliquot of each sample was initially spiked with a Pu-239 tracer. A second aliquot of sample was analyzed along with the spiked sample. All of the plutonium in the samples was reduced once using hydroxylamine. An anion complexing reagent (aluminum nitrate) was then added, and the solutions were oxidized with 4 M sodium nitrite. The plutonium was then extracted from the matrix using a TTA solution. The TTA layer was mounted on a counting dish, the mount was then analyzed by alpha spectroscopy. A blank sample was run with each sample set. The analysis results for the Pu-238 alpha peak were yielded using the Pu-239 recoveries from the Pu-239 traced sample separation. The uncertainties provided are given in a 1 sigma limit. The Pu-239 spike used has a small (<0.45%) component of Pu-238.

The following discussion is a chronology of significant events during the chemical cleaning of the 2H-evaporator. Many of these events are presented in Figure 4 and Figure 5, which track the evaporator pot temperature, the volume of cleaning solution in the evaporator pot, and the volume of overheads produced for the first and second acid strikes. Note that, as the pot contents reach the desired cleaning temperature, the pot volume decreases due to the evaporation of water from the pot and the collection of this water in the overheads system. There is good agreement between the volume decrease in the pot and the volume collected in the overheads tank. Table 1 provides a summary of the evaporator pot samples and values useful for the volume normalization of the components in these samples. Note that, in Table 1, the amount of cleaning solution charged to the pot was 2730 gallons for the first strike and 1760 gallons for the second strike. For upcoming analyses, the cleaning solution charged is taken to be at the composition of the baseline uranyl nitrate solution samples (shown later in Table 2).

Figure 4: Temperature Profile, Pot Evaporation, and
Overheads Production for the First Acid Strike.

The pot sample information is compiled from the 2H-evaporator chemical cleaning sample log, the sampling procedure records, and the engineering log. The sample time is an estimate rounded to the nearest half hour and has an uncertainty of about ±1 hour. The pot level, as measured from the dip tubes, has a short-term fluctuation of about ±2 in. The volume corresponding to each pot level is interpolated using the pot correlation, except for levels greater than 75 in, where Equation 1 is used.

Pot volume (gal) = 30.584 (gal/in) * Inches above 75 inch level (in) + 2653 (gal) [1]

Table 1. Listing of Evaporator Pot Liquid Samples Received during
Chemical Cleaning and the Corresponding Sampling Conditions.

Tank Farm Number	Date / Time	Sample Name	Temp. (° C)	Pot Level (in)	Pot Volume (gal)
First Acid Strike				80	2810^a
2H-CC-HTF-E-019	05-27-01 16:00	8-hr Pot	50	72	2560
2H-CC-HTF-E-029	06-04-01 11:30	16-hr Pot	87	62.5	2270
2H-CC-HTF-E-036 2H-CC-HTF-E-037	06-05-01 10:00	Post Cool Down	36	55	2050
Second Acid Strike				80	2810^b
2H-CC-HTF-E-073 2H-CC-HTF-E-074	07-10-01 23:30	Post Cool Down	35	47	1840

Although the trailer-acid sample filled the pot to the 80 inch level, corresponding to a volume of 2810 gal, the totalizer flow measurement of cleaning solution added to the pot was 2730 gal. The discrepancy in these two readings should correspond to the solids present in the evaporator pot, or 80 gal. This estimate, however, is substantially lower than the conservative estimate of 344 gal.

A water soak of the evaporator pot contents was performed in late April, 2001. A post soak inspection was performed on April 30, 2001. A thick layer of scale remained on exposed portions of the evaporator below the operating level. Other than the removal of some white salt deposits noted in October 2000, no significant changes were noted since the previous inspection. Due to the need for additional testing to lines, the pot was filled with water and emptied once more in the period leading up to the first acid strike.

The acid solution make-up occurred in the E3-2 tank of the H-canyon facility in April 2001. Canyons personnel prepared approximately 4500 gallons of the 1.5 M nitric acid/depleted uranium cleaning solution by combining a depleted uranyl nitrate waste stream with water and additional nitric acid. Samples of the original depleted uranyl nitrate solution and made-up cleaning solution were sent to F-Lab and SRTC for analysis. The cleaning solution was loaded into a tanker trailer and delivered to the 2H-evaporator system. F-Lab performed the blue label sampling for uranium required by the nuclear criticality safety evaluation (NCSE). SRTC analyzed a sample to provide a baseline for comparrison to subsequent pot samples.

On May 23, 2001, 2730 gallons of cleaning solution, as measured with a flow totalizer, was added to the evaporator pot. The addition, which took place over an 80 minute period and was completed by 19:00, brought the pot volume to 2810 gallons. The cleaning solution was sampled from the transfer line at 21:30 on May 23 and sample 2H-CC-HTF-E-018 was transferred to SRTC for analysis. The transfer line was flushed with water, resulting in a pot volume increase to approximately 2930 gallons. Approximately 10 mL of cleaning solution was spilled atop the trailer during its disconnection from the evaporator pot. The mitigation of this event, as well as changes to the pot heatup operating procedure, caused the heating of the cleaning solution to be delayed.

Heating of the cleaning solution, using the evaporator warming coils and tube bundle, was initiated at 02:23 on May 26, 2001. The temperature of the heating solution reached 87 ° C at 05:53 with little evidence of volume change due to thermal expansion. Heating was halted shortly after 06:00 due to a constant air monitor (CAM) alarm. As detailed in Appendix B.3, the CAM alarm was likely due to the release of radon from the scale as it dissolved. Heating with the warming coils was resumed at 10:00 and continued until a second CAM alarm was received shortly after 14:00. An additional problem was encountered as the pot pressure approached the Technical Surveillance Requirement (TSR) pressure limit, as detailed in Appendix B.2. The pot was allowed to cool back to room temperature as engineering developed solutions for the problems encountered. The first evaporator pot dip sample, 2H-CC-HTF-E-019, was pulled at 16:00 on May 27, 2001 and transported to SRTC for analysis.

A scheme was developed to resume heating of the pot contents slowly to potentially avoid exceeding allowable pressure limits. While the heating procedure was revised, the cleaning solution remained in the pot, allowing for an additional 120 hours of soak time. Heating was re-initiated at 1700 on June 2, 2001. On June 4, the pot temperature exceeded 80 ° C at 02:30 and exceeded 85 ° C at 06:30. The second pot dip sample, 2H-CC-HTF-E-029, was taken at 11:30 on June 4, 2001 and transported to SRTC for analysis. Heating was continued until 17:00, after which cooling was initiated. Samples were pulled on June 5 at 10:00, after the pot temperature had been brought below 40 ° C. One sample was sent to SRTC for analysis and one sample was sent to F-lab for titration.

On June 6, 2001 at 10:00, the pot contents were transferred from the pot to the neutralization tank. The evaporator pot was inspected on June 7, revealing that the majority of the deposits on the pot walls, warming coils, dip tubes, and supports had been removed during the first acid strike and that some loose solids were evident in the bottom of the cone. The loose solids were sampled on June 18 (2H-CC-HTF-E-051) and sent to SRTC for analysis. Details of the post-first-acid-strike pot inspection are presented in Appendix C.2. Figure 6 shows a dramatic comparison of videotape images taken before and after the chemical cleaning operation. Results from this inspection were used to estimate conservatively that only 40 gallons of the original 344 gallons of scale remained in the evaporator pot and West lift line.

On June 7, 2001 at 01:30, the addition of 710 gallons of 50 wt % (19 M) sodium hydroxide to the neutralization tank was initiated. As discussed in Appendix B.6, the evolution was halted after 444 gallons when instrumentation difficulties arose. The balance of the caustic, 266 gallons, was added on June 8 at 18:20. At 20:55 on June 8, shortly after the completion of the caustic addition, a leak from the neutralization tank recirculation system into the containment dike was recognized. As a result of this event, discussed in Appendix B.7, cleaning operations were suspended for about 2 weeks while the structural integrity of the neutralization tank system was assured and the dike area was brought to a safe condition. By June 12, 2001, most of the neutralization tank contents and material in the dike had been transferred to Tank 42.

From June 22 through June 27, 2001, a sub-contractor cleaned the interiors of the West lift line and the gravity drain line to Tank 38H with a high-pressure water lance. The gravity drain line to Tank 38H was cleaned successfully, but the upper part of the lift was only cleaned down to approximately the 78 inch pot level (see Appendix C.3 for details). Mechanical cleaning could not continue because the pot had accumulated water up to approximately the 58 inch pot level, filling the lift line to a level that interferes with mechanical cleaning. Management decided to perform another chemical cleaning strike before continuing to target the scale in the west lift with the hydro-lance. The 2140 gallons of liquid in the evaporator pot was sampled and determined to have a pH of 3 to 4. The fluid was pumped to the neutralization tank on July 5, neutralized with approximately 1 gallon of 50 wt % caustic, and transferred to Tank 42H.

On July 6, 2001 at 15:00, cleaning solution was again added to the evaporator pot. Limited by the size of the initial make-up tank, the amount of cleaning solution on-hand was not adequate to fill the pot to the planned 80 inch level. Thus only an estimated 1760 gallons of cleaning solution was charged to the pot. This was followed with 1080 gallons of water to attain the desired cleaning solution volume corresponding to the 80 inch pot level. The impact is that the second acid strike was more dilute in acid concentration, approximately 0.9 M nitric acid, with an identical dilution of uranyl nitrate.

A procedure was performed that allowed for the momentary venting of the catheter jumper plug to allow the cleaning solution to rise higher in the west lift. It was hoped that this would cover the approximately 1 gallon of scale resident within the lift line from the 60 inch to 78 inch pot level. Heating was initiated on July 8, 2001 at 01:30, again using only the warming coils due to pot pressure issues. On July 9, the pot temperature exceeded 80 ° C at 01:30 and exceeded 85° C at 10:30. Heating was continued until 11:30 on July 10, after which cooling was initiated. Samples were pulled on July 10 at 23:30, after the pot temperature had been brought below 40 ° C. One sample was sent to SRTC for analysis and one sample was sent to F-lab for titration.

On July 12, 2001 at 04:00, the pot contents were transferred from the pot to the neutralization tank. The evaporator pot was inspected on July 13, revealing that the majority of the remaining deposits had been removed (see Figure 6). There was no change, however, in the scale in the West lift line. The bulk of the remaining material could be classified as loose solids. Only about 10 gallons of material remained in the evaporator pot and lift line, far below the residual volume. Details of the post-first-acid-strike pot inspection are presented in Appendix C.4.

On July 14, 2001 400 gallons of 50 wt% caustic was added to the neutralization tank. As discussed in Appendix B.9, when the neutralization tank contents were sampled, the pH was 5. An additional 250 gallons of caustic was added to the neutralization tank, and the contents were transferred to Tank 42.

Canyons personnel sampled the uranyl nitrate canyon stream. These samples were sent to SRTC for organic analysis. At the time of cleaning solution makeup, two "blue label" samplesof the cleaning solution, as required by the NCSE, were sent to F-Lab for acid and uranium isotopic analysis. A sample of the cleaning solution was also sent to SRTC to establish the acid cleaning solution baseline. This sample, referred to as the "courtesy cleaning solution sample" was analyzed for organic constituents as well as radionuclides and elemental composition.

Additionally, after the cleaning solution for the first acid strike was transferred from the tanker car into the evaporator pot, operations personnel sampled the liquid in the transfer line. This sample, referred to as the "trailer acid sample" was analyzed by SRTC. The results for these sample analyses are presented in Table 2. The differences between the uranium isotope values reported by F-Lab and SRTC are due to the different analytical methods used in the different labs. F-Lab exclusively uses thermal ionization mass spectrometry for these samples, while SRTC, as outlined in Section 3, uses a combination of ICP-ES for total uranium and ICP-MS for uranium isotopics.

Table 2. Comparison of Analyses of Initial Cleaning Solution by F-Lab and SRTC.

Analyte	Blue Label Sample (F-Lab)	Courtesy Cleaning-Solution Sample (SRTC)	Trailer Acid Sample 2H-CC-HTF-E-018 (SRTC)
free acid	1.52 M	n.a.	1.4 M
total acid	4.48 M	n.a.	n.a.
density	1.43 g/mL	n.a.	1.39 g/mL
total U	283.2 g/L	256 g/L	251 g/L
U-234	6 mg/L	b.d.l.	b.d.l.
U-235	691 mg/L	653 mg/L	696 mg/L
U-236	25 mg/L	b.d.l.	b.d.l.
U-238	282.5 g/L	298 g/L	244 g/L
Org./aq.	0.017 %	n.a.	n.a.

Table 1 contains a listing of the liquid evaporator pot samples received during the first and second cleaning cycles. The samples, after filtering, were submitted for a number of analytes as specified in the Task Plan. The results are shown in Table 3. The main species that were targeted for monitoring scale dissolution were the bulk scale species (Na, Al, Si, and U) and other radionuclides trapped in the scale (Cs-137, Ce-144, Sr-90 and Sb-125) along with the free acid concentration. For direct comparison, the tank volumes must be normalized as the liquid evaporated over the duration at elevated temperature (Table 1).

For the major components, increased concentrations of sodium, aluminum and uranium were observed in the 8-hr. pot sample. However, silicon was not above the minimum detection level. The detection limit was high (338 mg/L) due to the spectral interference from the high uranium concentration. This behavior was not observed previously in laboratory dissolution of the scale even in the presence of large amount of depleted uranium. Therefore, it is concluded that the elemental interference was not the source of the silicon discrepancies. Laboratory testing only examined the stability of the acid solutions for short periods of time (< 8 hours). There are possible explanations that include the formation of high silicon to aluminum mineral phases such as mordenite. The results of the analysis of solids found in the evaporator pot and floating in the liquid samples are discussed below.

Shown in Figure 7 are the normalized concentrations of free acid, aluminum and sodium from the various samples taken during the initial acid strike. Volume normalization was performed by adjusting the data in Table 3 by the ratio of the pot volume at the time of sampling to the original volume of cleaning solution (volumes are contained in Table 1). The levels attained for sodium and aluminum plateau at the 8-hr sample through the post-cool down sample taken after approximately 24 hours. The normalized free acid concentration agrees well with the elemental data. The free acid is lowered to between 0.8 and 0.9 M in the three samples. As stated in Appendix B.3, CAM alarms ceased after several hours with the pot temperature near 85 ° C. The collection of the different data points indicates that the scale predominantly dissolved during the first 8 hours at pot temperatures near 85 ° C.

Figure 7. Plot of Various Normalized Analyte Concentrations for the 1st Cleaning Cycle

As the dip samples from the Evaporator pot were received, a small aliquot was originally poured into a glass vial to determine if solids were present. In each of the liquid samples from the Evaporator pot during the first acid cleaning operation, solids were observed and the entire liquid slurry was passed through a 0.45 m m filter.

Figure 8 shows a photograph of the solids observed from the first liquid pot sample. The material was yellow-reddish in color and floated on the surface of the uranium-nitric acid mixture. Portions of the solids were submitted for powder X-ray diffraction. The powder pattern exhibited peaks that corresponded to uranyl nitrate and did not contained peaks from other mineral phases.

Figure 9 shows a scanning electron mircoscope (SEM) image of the solids from the 8-hr pot sample and its associated energy dispersive spectrum (EDS). The particle morphology appears to show small aggregates of uranyl nitrate particles. The EDS spectrum shows the presence of sodium, aluminum and silicon. The relative ratios of the
sodium, aluminum and silicon peaks are not the same as the original pot scale samples from January 2000. This material appears to be enriched in silicon compared to previous samples.

Figure 8. Photograph of Solids from the
Evaporator Pot Liquid Sample, 1^st Acid Cleaning Cycle

The solid from the pot liquid sample was analyzed by Infrared (IR) spectroscopy and two thermal analyses (differential scanning calorimetry (DSC) and differential thermal analysis (TGA)). The IR spectrum of the solids recovered from the liquid, dip sample is shown in Figure 10. The spectrum shows no evidence of carbonate (peak position normally at 1570 cm^-1 adsorption), no ammonia ligand (absence of 2800 cm^-1 band) and definitely no hydrocarbons or carboxylates. The IR spectrum does contain water, hydroxyls, nitrates, silicates and predominantly the uranyl (UO₂) group. The lack of peak splitting at 950 cm^-1 assigned to UO₂ is an indication of no coordination to the nitrate groups. In addition, the broad adsorption of the hydroxyls and the nitrates indicates amorphous character of the solid. The very narrow peaks at 1470 cm^-1 is and the peak around 3000-2900 cm^-1 is due to the lubricant (hydrocarbon) gel use to suspend the sample.

The thermograms from DSC and TGA measurements are shown in Figure 11. The DSC measurement shows large endotherms associated with water loss between ambient temperature and 100 ° C and one centered near 200 ° C. Lastly, an endotherm from nitrate salt melting is observed at 105 and 325 ° C. The TGA measurement agrees well with the DCS measurements. In other words, the temperatures that endotherms observed in the DSC correspond to weight losses in the TGA measurement. Total weight loss upon heating to 900 ° C was 57.8 %.

Additionally, the solids from the liquid samples were analyzed after a fusion digestion was performed. The results of these analyses are shown in Table 4. The sample had a large amount of uranium, nearly 21 wt %. This along with the water detected in the DSC/TGA experiments and the nitrate associated with uranyl nitrate is the bulk of the sample composition. Silicon was detected at a concentration of 2.2 wt % but does not explain the fate of silicon in this dissolution process. Minor concentrations of other elements were detected and presented below.

Table 4. Analytical Results from Solids from the Evaporator Pot Liquid Sample

Al		0.2864%	Mo		0.0034%
B		0.0110%	Na		0.3774%
Ba		0.0011%	Ni		0.0234%
Ca		0.0004%	P	<	0.0112%
Cd		0.0028%	Pb	<	0.0233%
Co		0.0107%	Si		2.2247%
Cr	<	0.0232%	Sn		0.0245%
Cu		0.0207%	Sr		0.0019%
Fe		0.0737%	Ti		0.0047%
La		0.0160%	U		20.8299%
Li		0.0008%	V		0.0239%
Mg		0.0013%	Zn		0.0017%
Mn		0.0071%	Zr		0.0345%

After the first cleaning cycle was complete, High Level Waste personnel inspected the pot and found that the acid had substantially cleaned the evaporator pot. However, an accumulation of loose solids was observed in the evaporator cone. It is estimated that 9 to 18 gallons of solids remained in the evaporator pot after the cleaning solution was removed. A large (30 g) sample of solids was collected (2H-CC-HTF-E-051) and sent to SRTC for analysis.

An X-ray diffraction powder pattern was obtained from a portion of the sample and showed similar results to the solids recovered from the aqueous dip samples. The initial XRD analysis of the as-received sample indicated only uranyl nitrate. After washing with water or nitric acid, however, the XRD pattern indicated an amorphous material consistent with SiO₂ and a small amount of hematite (Fe₂O₃). The source of hematite is unknown. Although the solution phase concentration of silicon was low, these loose solids were enriched in silicon and are likely answer the fate of silicon in the cleaning process.

Table 5 contains the ICP-ES results for the digestions of the as received sample and the insoluble solids. Other compounds were noted to be present in some digestions at levels of less than 0.2 wt%. Table 6 summarizes the additional analyses performed on the as-received sample. During preparation of the dried as-received sample, the moisture content was determined to be 28%.

The solids washed with water and the solids washed with nitric acid left approximately the same insoluble material. Personnel observed that the solids did not significantly change in volume or appearance during washing. Uranium, aluminum, and sodium were removed during washing.

Table 5. ICP-ES Analysis of As-received and Washed Cone Solids Samples

Analyte	As-Received Sample	Dried As-Received Sample	Insoluble Solids H₂O Wash	Insoluble Solids 0.1M HNO₃ Wash
Al	0.75 wt%	1.2 wt%	0.23 wt%	0.21 wt%
Fe	0.50 wt%	0.71 wt%	1.4 wt%	1.8 wt%
Na	n.a.	1.2 wt%	0.094 wt%	0.12 wt%
Si	7.0 wt%	12.1 wt%	41.9 wt%	41.5 wt%
U	17.2 wt%	30.2 wt%	0.75 wt%	0.42 wt%

Table 7 contains additional analyses of the wet as received sample, which likely contained more than 28% water. The dried as-received and the washed insoluble solids samples were dried at 115° C before cesium hydroxide dissolution. Drying at this temperature would drive off the free water, but water would remain. The uranium analysis of the as-received sample indicates a U-235 enrichment of 0.23%, or approximately the same enrichment as the depleted uranyl nitrate cleaning solution.

After washing with water and acid, primarily SiO₂ remained as an insoluble material, which is likely the fate of the silicon during the cleaning process. Although no more than 18 gallons of this loose solid material was left in the evaporator after the first acid strike, it is expected that a significant amount of this material was transferred from the pot to the neutralization tank before the post-cleaning inspection

As discussed in Section 4.1, the first cleaning batch acid filled the pot to a volume of 2810 gallons, but only 2730 gallons of cleaning solution was used. The 80-gallon discrepancy between the pot level and the acid volume corresponds to the volume of scale and other material originally present in the evaporator pot. This scale volume estimate is substantially lower than the conservative estimate of 344 gal.

A mass balance was performed on sodium and aluminum in the cleaning solution samples. Using the liquid sample data in Table 3 for the first acid strike post-cooldown sample and normalizing using the volumes in Table 1 (2730 gallons reduced to 2050 gallons), the mass of scale dissolved during the first acid strike is estimated. Based on the observations of nearly complete scale removal during the first strike, this approach approximates the scale initially in the pot. The amount of aluminosilicate scale is between 320 and 350 kg, versus the original estimate of about 3500 kg. Thus, substantially less mass of scale was in the pot than the mass for which the cleaning plan was designed.

The cleaning data suggest that about 70 kg of total uranium was in the pot initially versus the flowsheet approximation of 300 kg. Based on the data, the weight percentage of uranium in the solids was about 18%, which is much higher than expected. Estimating the urainum in the scale by analyzing the cleaning solution data is a questionable approach, however, because the large concentration of uranium in the cleaning solution causes large uncertainties. For example, suppose that the final pot volume of 2050 gallons was off by ± 2.5%. With that small level of uncertainty in just one of the parameters, the calculated weight percentage of uranium in the scale ranges from 0% to 30% (0 kg to 140 kg).

As discussed in Appendix A.1, the conservative overestimate of the mass of scale in the evaporator pot is due to two factors: 1) the intentional over estimate of the scale volume from the pot inspection analysis, and 2) the use of scale density values that over estimate the relation between the mass and the bulk scale displacement.

It is not possible to precisely quantify the amount of loose solids that were present in the evaporator pot during the first acid strike. Assuming an initial 350 kg of scale and using the Si weight percentage in the wet as-received cone solids sample (see Table 5), the mass of siliceous solids present in the pot during the first acid strike is estimated to be 770 kg on a wet basis. These solids likely contained about 54 kg of Si, but the solid mass estimate is much larger due to the mass of water and the co-precipitated uranyl nitrate from the cleaning solution.

The operation of the 242-16H (2H) Evaporator was curtailed in October 1999 due to the presence of an aluminosilicate scale that contained sodium diuranate with a uranium-235 enrichment of approximately 3 % The scale had built to the point where steam lifting of the evaporator concentrates was ineffective. Work performed by SRTC during calendar years 1998-2000 had shown that dilute nitric acid was an effective chemical cleaning agent. An overall cleaning flowsheet was developed in calendar year 2000 that addressed numerous safety issues associated with cleaning the pot, neutralizing the uranium-bearing acid and discharging the neutralized solutions to a waste tank. Beginning in May 2001, a depleted uranium and nitric acid mixture was added to the 2H Evaporator pot and heated to elevated temperatures. As a result of this action, the pot was cleaned and returned to service.

From the results of sample analayses, the amount of aluminosilicate scale was over estimated. Original estimates were about 3500 kg. Based on elemental analysis of the dip samples taken from the pot, the amount of scale is between 320 and 350 kg. Thus, two acid batches, versus the five batches anticipated, effectively removed the scale. The original estimate of uranium was also high compared to cleaning data. The cleaning data suggest slightly less than 70 kg of total uranium was in the pot; whereas the flowsheet estimated approximately 300 kg. Additionally, the dissolution of the majority of the aluminosilicate scale appears to have been rapid and complete by the time the first samples were pulled for analysis (8-hr. sample).

Silicon was not observed to be measurable in any of the liquid samples taken from the 2H Evaporator pot. This phenomenon was not observed in any of the laboratory tests with either simulants or actual scale samples from the pot. However, laboratory tests did not replicate the time-temperature history as observed in the actual cleaning sequence. Silicon, however, was detected a solid phase discovered in the evaporator cone after the first cleaning cycle. Several operational difficulties were encountered during chemical cleaning including continuous air monitor alarms, high pot pressures, high mercury levels in the overheads, and chemical spills. The details and corrections made for each of these operational issues are summarized in appendices of this report. Appendices also contain estimates of the hydrogen generation and source term based on the pot sample analysis.

Steps are being taken to isotopically dilute uranium 235 in future supernates to be sent to the 2H evaporator system. This includes the feed tank, Tank 43H, and material recycled from the receipt tank, Tank 38H. An enrichment control program has been developed to assure that achieving nuclear criticality through the formation of sodium aluminosilicate scale with sodium diuranate is not credible. This program includes a monitoring regimen of feed tank samples.

The following is a cascade of recommendations for future cleaning assuming the success of the enrichment control program (as described in recommendation 1):

If a similar uranyl nitrate and nitric acid solution is required in future evaporator cleanings, the cleaning solution make-up plan should assure that enough cleaning solution is on hand to fill the pot to the desired level. Due to the volume of solution made-up for the chemical cleaning described herein, the second acid strike was insufficient to fill the pot.

The soak time and temperature profile required for heating should also be re-evaluated, since it is apparent from the "8-hour" heating sample that the majority of the dissolution achieved during the first acid strike had already occurred.

If there is a need to assess the mass of any future scale deposits, a more reasonable value for bulk density should be used. This is essential if an accurate estimate of the cleaning cycle requirements is to be made.

The authors sincerely appreciate the sample analysis efforts of the members of the SRTC Analytical Development Section, including C. J. Coleman, J. E. Young, J. C. Hart, S. L. Crump, C. C. Diprete, D. P. Diprete, and W. T. Boyce. Additional interpretation of sample analyses and cleaning operation events was assisted through consulting with the other researchers in SRTC Waste Treatment Technology, including F. F. Fondeur, C. M. Jantzen, and D. T. Hobbs.

The authors also wish to thank the contributions from HLW Engineering. C. S. Boley and B. L. Lewis were instrumental in the planning and implementation of the chemical cleaning process. J. C. Wittkop provided a compilation of overheads sample data, and information on the resolution of evaporator overheads and acidic cell sump issues. R. S. Waltz and W. R. West provided the evaporator pot interior photos included in the report body and the residual material observations compiled in Appendix C. In addition, reconstruction of the cleaning chronology (Section 4.1) was facilitated by the excellent notes of the engineers on shift.

The authors express appreciation to the many people that helped in this intense effort. We especially thank the members of the High Level Waste (HLW) Operations who actually worked in the field, the Analytical Development Section personnel that analyzed the samples and the Shielded Cells personnel that received and handled the samples from the field.

The authors also acknowledge the support of R. H. Young and the F-Lab staff for providing cleaning solution and titration analyses.

The analysis of the mass balance of the system in Section 4.3 shows that, although the deposits were removed from the evaporator, the sample analysis could not account for a large portion of the expected material. The discrepancy is likely caused by two factors: the initial overestimate of the scale volume and the failure to consider the porosity of the scale. Of concern is the disconnect between the visually estimated "bulk displacement" of the material and the true mass of the material. The visual volume estimate caused a great overestimation of the mass of scale in the evaporator pot. Use of literature values for the density of aluminosilicates (2.51 g/mL) and sodium diuranate (3.93 g/mL) without considering the porosity lead to this gross conservatism. The methods used for estimating the scale likely caused the expected mass of scale present to be 5 to 10 times larger than the actual mass present. This methodology can be refined in the future to yield a more representative estimate of the scale in the evaporator pot if the bulk scale density is determined experimentally.

The requirements for evaporator chemical cleaning include maintaining an air-lance flow rate of > 50 SCFM. The purpose of sparging the evaporator with the air lance is to provide agitation of the cleaning solution and to strip and purge any flammable volatile organics. Prior analyses defined the expected behavior of tributylphosphate (TBP), dibutylphosphate (DBP), monobutylphosphate (MBP), and n-butanol (BuOH) in the evaporator pot and overheads during chemical cleaning. Potentially flammable butanol vapors would be stripped out of the system. As expected, there was no evident buildup of n-butanol in the evaporator pot or overheads.

Safety concerns dictate the need for quantification of the hydrogen generation rate (HGR) from the radioisotopes contained in closed systems. Knowledge of the HGR allows for the proper mitigation of the flammability hazards with adequate ventilation. The HGR of the 2H-evaporator scale had been estimated prior to cleaning. Analysis of the samples collected during chemical cleaning will now be compared with the original estimate.

Table 8 contains a comparison of the original estimate for the HGR with the HGR values calculated from samples collected during cleaning. Nitrates present in the cleaning solution reduce the HGR. Results repotted for the situation " with scavengers" takes this HGR reduction into account, while the results reported as "without scavengers" ignores the affect of nitrates on the HGR. As noted earlier, the mass balance around the first strike can not be closed confidently due to the unknown amount of solids transferred out of the pot. Thus, the estimate of the HGR for the pot solids sample is on a per kg basis. Also, the nitrate concentration for the in situ HGR from the pot cone solids with scavengers assumes a nitrate concentration of the post-cool-down sample (4.7 M).

Table 8: Hydrogen Generation Rate for the
Original Scale and the First Acid Cleaning Batch.

Sample	HGR without Scavengers	HGR with Scavengers
Original scale	1.30 × 10^-2 ft³/hr	N/A
Based on 8-hour sample	3.78 × 10^-3 ft³/hr	4.12 × 10^-4 ft³/hr
Based on 16-hour sample	3.63 × 10^-3 ft³/hr	3.78 × 10^-4 ft³/hr
Based on post cool down sample	2.12 × 10^-3 ft³/hr	2.10 × 10^-4 ft³/hr
Pot cone solids	1.41 × 10^-6 ft³/hr/kg	1.39 × 10^-7 ft³/hr/kg

The 8 isotopes that were quantified plus the 2 daughter products that were estimated accounted for 97% of the original scale HGR estimate. Also, an estimated 90% of the scale was removed from the pot during the first acid strike. Thus, the value for the scale HGR should match the values for the cleaning solution and pot solids HGR.

The source term for the Pu-238 equivalent dose is contained in Table 9 for the cleaning solution samples by the method performed for the original evaporator scale.

The purpose of this section is to provide information on the operational and engineering problems encountered during the chemical cleaning process. The focus is on the operational difficulties that can be understood more clearly when given some technical background. This report will not attempt to address procedural issues. This information is used as a basis to provide process recommendations if the need for evaporator chemical cleaning should arise in the future. The discussion of these problems is presented in approximately the chronological order in which they arose.

During the water soak and the preparations for the start of chemical cleaning, a concern surfaced regarding the possibility of oil being introduced to the 2H-evaporator system from the air-lance air compressor. On May 15, three routine samples were taken from overheads tank 2 (2H-CC-HTF-E-007 in Table 11). One of the samples was observed to contain visible quantities of an oily material. This sample was analyzed by SRTC and shown to contain DexronÒ II. CSTE performed an analysis when the problem was encountered, and the investigation of the event identified a number of scenarios that could potentially result in oil reaching the overheads tanks. Each was assessed and, based on the analytical evidence, it was concluded that the source of the oil was an air compressor and that oil entered the overheads tank via the sample eductor. To preclude difficulties in dealing with DexronÒ II, it was recommended that a less volatile lubricant, such as RandoÒ HD 68. As a result, RandoÒ HD 68 replaced DexronÒ II in the air compressors used for the evaporator system.

After May 15, the total carbon (TC) and total organic carbon (TOC) measurements of the overheads samples during chemical cleaning, as reported in Appendix B.4, were close to or below the detection limits (from 10 to 60 ppm). In fact, the rainwater pumped from the overheads receiver cell sump accounted for all of the highest TC readings since the problem was recognized. Note that the high organics sample in question, contained primarily sump fluids even though it is identified as being plumbed to receive overheads. This supports a plausible transfer of residual oils from the overheads cell to overheads tank 2.

There was no discrepancy in the organics between the expectations and the in the overheads produced during acid boil-down. This is consistent with the absence of an air-compressor oil transfer path through the evaporator pot. Thus, the oil did not pose an additional evaporator pot deflagration hazard.

During initial heating of the first evaporator cleaning solution batch, the pressure in the evaporator increased to over 20 inches of water column. Because this pressure approaches the safety limit, it was necessary to heat the evaporator cleaning solution without such a pressure rise.

The evaporator pressure for the first heating period of the first acid strike is given in the upper portion of Figure 12. The pressure and temperature profiles for the remainder of chemical cleaning are given in the bottom portion of Figure 12 and in Figure 13. Before the first heating period of the first acid strike, the Evaporator pressure was 9 inches of water column (in. WC).

Beginning May 26 at 04:00, shortly after heating with the warming coils and tube bundle was initiated, the evaporator pressure increased steadily. On May 26 at 14:00, the pressure rose to 19.5 in. WC, the air lance was shut off, and the pot pressure dropped to 0 inWC. At 21:00, the lance air flow was restored and the evaporator pressure returned to 21.5 in. WC. The pot pressure slowly increased to 23.5 in. WC on May 27 14:00, where the air lance was again shut off and the pot pressure went to 0 in. WC. The lance air flow was restored at 17:00, and the pressure increased to 23.4 in. WC at 20:00, after which the lance air flow was again terminated. The pot was allowed to slowly cool over the next several days, but the pot pressure decline was slow while the air lance was engaged.

The cleaning of the evaporator differs from normal operation in several key ways, as illustrated in Table 10:

Table 10: Comparison of Evaporator Conditions
during Normal Operation and Chemical Cleaning

Normal Operation	Evaporator Cleaning
Temperatures of about 140° C	Temperatures up to 90° C
Highly-caustic concentrated HLW solution from tank farm	Depleted uranyl nitrate and 1.5 M nitric acid solution
Lance flow of 2000 SCFM steam	Lance flow of 50 to 100 SCFM air

During normal evaporator operation, the pot pressure rises to about 4 in. WC when 1000 SCFM steam is added. For cleaning, we observed a significantly higher pot pressure (over 20 in. WC) when a much lower flow rate (100 SCFM) is added to the pot. The main difference in the two modes of operation that would impact the pot pressure is the amount of non-condensable flow through the overheads. The steam used during normal evaporator operation has a very small non-condensable component, while the overheads created by the air used during chemical cleaning is almost entirely non-condensable.

It is suspected that the buildup of back-pressure is caused by some portion of the overhead system. Figure 14 illustrates the path that the overheads take in the 2H-evaporator system. Normally, the air from the lance is vented into the evaporator cell through the non-condensable line on the condenser. Until the mercury collection vessel (MCV) is filled, however, a potential pathway for non-condensable vent exists at the cesium removal column (CRC) tank vent line. The pressure behavior observed during the initial temperature increase and the delay in the slow return to normal pressure after heating is stopped can be explained by the removal of this alternate non-condensable flow pathway after the MCV has filled.

Thus, a likely contributor to this back-pressure problem is an undersized or obstructed non-condensable vent line. Under normal evaporator operation, there is a much larger flow out of the evaporator pot, through the demister, and into the condenser. The normal flow, however, is largely condensable water vapor, with only a small amount of non-condensables. In contrast, the flow in to the overheads during evaporator cleaning is mostly air. There is a smaller overall flow into the condenser during cleaning, but a much larger flow of non-condensables. This is the most likely explanation of why the cleaning process would have a higher pot pressure than encountered during normal evaporator operation.

Alternately, the higher pot pressure could be caused, wholly or in-part, by one of several potential problems caused by a blockage in the condenser. After an analysis of potential solids buildup in the condenser due to off-gassing and entrained cleaning solution, this was dismissed as unlikely given the evaporator pot contents and condenser geometry.

There was not a complete resolution of the cause of the pot pressure difficulties before heating of the cleaning solution was re-initiated. One potential solution involved the replacement of the restricting orifice in the air-lance line to reduce the air-lance flow rate while still remaining above 50 SCFM, the basis for the TSR limit. After careful evaluation, the judgement was made to continue using the same size orifice, and thus retaining the same air-lance flow rate. Instead, the procedures were revised to disengage the tube bundle and use only the warming coils for a slower and more controlled heating of the evaporator pot. As the second heating period of the first acid strike shows, the pressure did not increase to greater than 20 in. WC due to this change to the heating procedure. It is possible, however, that the lower volume in the pot rather than the reduced heating rate caused this pressure behavior during the second heating of the first acid strike.

As displayed in Figure 13, the problem of high pot pressure re-surfaced during the heating of the second acid batch. Again, the pot pressure rose to near the safety limit as the pot was heated, appeared to shadow the pot temperature while the air lance was engaged, and failed to quickly return to a lower pressure after cooling was initialed. In this batch, however, operation proceeded without delay due to the revised heating procedures put into place during the first batch.

Figure 12: Evaporator Pot Temperature and Pressure during the First Acid Strike.

Figure 13: Evaporator Pot Temperature and Pressure during the Second Acid Strike.

Figure 14: Rough Schematic of the Potential Vent
Paths in the 2H-Evaporator Overheads System (not to scale).

During the initial heating of the first acid strike, the continuous air monitor (CAM) alarmed twice. The first alarm occurred on May 26 at 06:02, shortly after the pot reached a temperature of 87° C. The air lance was placed in vent mode and the heating was halted while procedures were followed to mitigate the situation. Heating was re-initiated at about 09:30, and a second CAM alarm was received at 1410. Heating was halted and the air was temporarily turned off, and the pot slowly cooled. The air lance was re-initiated at 20:29, while the pot was still above 80 ° C. In order to alleviate the CAM alarms while still at this elevated temperature, the filter paper was replaced several times as the CAM level increased. The CAM alarm set point was 2700 cpm.

The situation surrounding the CAM alarms was investigated and the path forward was ultimately to raise the limit at which the CAM alarmed. Gamma scan by F-Lab of the filter paper indicates the presence of Bi-212, Pb-212, and Tl-208. An alpha scan by F-Lab showed Bi-212 and Po-212. It is postulated, based on the gamma and alpha scans, that the radionuclides are the daughters of thoron (radon-220), not transuranic nuclides.

The air lance operates as an efficient sparger at high temperatures. In addition to removing the traces of volatile organics from the pot, the air lance would be effective removing radon gas. Radon-220 and 222 was likely contained in the scale and cleaning solution, and subsequently stripped out of the liquid at high temperatures as the scale was dissolved. The release of these gases caused an accumulation of their particulate daughters on the CAM filter paper resulting in increased counts possibly exceeding the alarm threshold.

The CAM alarm set-point of 2700 cpm for the first heat up period of chemical cleaning was based on the worst case waste tank inventories which include transuranic nuclides. The isotopes that triggered the alarms were radon and thoron daughter products. Even though the release of these materials at the alarm set-point did not pose a personnel protection concern, the alarms were an operational nuisance. The CAM alarm set point was raised to 5000 cpm for the remainder of chemical cleaning to eliminate the alarms while preserving operational safety.

The CAM levels attained during the second heating period of the first acid strike did not exceed the 5000 cpm alarm threshold. CAM levels were not recorded during the second acid strike, and no alarms were received.

During normal operation, evaporator overheads are typically sent to the Effluent Treatment Facility (ETF). During chemical cleaning, the recycle route for the 2H-evaporator overheads to Tank 43H was not available. Additionally, the possibility of acidic overheads being sent directly to Tank 43H would have been a risk if that route were available. Thus, the plan was to send to ETF the overheads obtained during chemical cleaning. These overheads must therefore meet ETF’s waste acceptance criteria (WAC). The following sections contain an analysis of the sampling issues and explanations of the WAC deviations needed for transfer of chemical cleaning overheads to ETF.

During chemical cleaning of the 242-16H Evaporator, the evaporator overheads was sampled as an ETF WAC/WCP requirement. Table 11 contains the analytical results for the overheads tanks. Samples sent to ETF are analyzed for mercury, pH, and gross alpha. Samples sent to F-Lab are analyzed for nitrates and total carbon (TC). During the first batch of chemical cleaning, overheads samples were sent to SRTC for analysis of TBP, butanol (BuOH), and total organic carbon (TOC). In situations where no sample was sent to SRTC, ETF accepted TC as a conservative bound of TOC. Estimates of Cs-137 and Co-57 were obtained in the field.

Several complications in sampling of the evaporator overheads arose during chemical cleaning. The overhead tank sampler could not be used during chemical cleaning due to insufficient pressure to the sampling station and an apparent sample line pluggage. An alternate method sampling method was used to sample the overheads system via the recirculation line and a single recirculation pump.

During performance of the alternate sampling method, the overheads tank to be sampled should be recirculated. It was discovered the tanks were being recirculated from the line with a de-energized recirculation pump. This raises doubts about the accuracy of the samples taken using the alternate method prior to June 2, at which time corrective measures were taken. An evaluation of the alternate sampling method was completed and a recommendation was made to change recirculation time to > 30 minutes. The 5 minute recircluation time was only turning over ~ 22% volume of an overheads tank. The 30 minute recirculation time was equivalent to 1.3 turnovers of an overheads tank.

Table 3 reveals that the cleaning solution had elevated mercury concentrations (volume normalized concentrations of 50 to 75 mg/L) after scale was dissolved. During chemical cleaning of the 2H evaporator, mercury in the scale, either in elemental or oxide form, will react with the nitric acid in the cleaning solution in the evaporator pot to produce mercuric and mercurous ions. These ions have a low volatility and are not easily transferred into the evaporator overheads. Apart from physical entrainment, it is not likely that mercury entered the overheads from the evaporator pot during cleaning.

Table 11: Overheads System Sample Analysis During 2H-Evaporator
Chemical Cleaning (First batch or cleaning solution added to pot on May 23, 2001).

Sample

Date

OH
Tank

Contents

a
(dpm/ml)

Hg
(mg/L)

NO₃(mg/L)

Cs-137
(dpm/ml)

Co-57
(dpm/ml)

BuOH
(mg/L)

TOC
(mg/L)

TC
(mg/L)

2H-CC-HTF-E-

WAC Limits à

< 100

< 2

1 to 12.5

< 1600

< 1200

< 100

Analysis Lab à

ETF

F-Lab

pha

Pha

SRTC

F-Lab

001
002
003

4/29/01

OH1

< 1

9.732^a

6.98
7.31

273

248

n.a.

0.44

n.a.

005
006
007

5/15/01

OH2 ^d

n.a.

8.3

1038

n.a.

014
015

5/19/01

OH1

5.403^a

7.74
7.93

1114
1142

n.a.

< 2.5

016
017

5/23/01

OH1

0.44

7.32

51.85

408.9
477

n.a.

020
021
022

5/29/01

OH1

3.788^a

7.54

51.7

1868^a1863
1936

68.32

< 0.5

5.7

14.3

023
024
025

5/29/01

OH2

5.366^a

7.67

51.8

1355^a1804
1679

50.97

< 0.5

5.8

13.6

026
027
028

6/2/01

OH1^b

0.543

7.01

55.12

307

n.a.

030
031
032

6/4/01

OH1

0.342

6.41

60.015

244
324

n.a.

< 0.5

033
034
035

6/4/01

OH2

3888^a

23.531^a

2.27

482.93

1301^a1366

n.a.

038
039
040

6/6/01

OH2

3244^a

18.363^a

2.13

686.435

1954^a

n.a.

< 0.5

n.a.

041
042

6/13/01

OH1

379.9^a

24.89^a

2.62

341.4

891

n.a.

< 42

043
044

6/13/01

OH RS

n.a.

1.657

6.48

55.8

n.a.

< 42

045
046

6/14/01

OH1 ^c

38.918

14.356^a

6.46

62.6

n.a.

< 42

047
048

6/14/01

OH
RS ^c

2.74

1.355

7.13

53.1

n.a.

< 42

049
050

6/15/01

OH1

163^a

16.027^a

99.8

250
209

n.a.

< 42

052
053

6/20/01

OH1^c

495^a

70.882^a

2.24

570.63

1146

n.a.

< 42

055

6/26/01

OH1 ^c

256^a

25.493^a

3.00

n.a.

495

n.a.

056
057

6/27/01

OH2

1.23

6.4

59.98

219
206

n.a.

49.63

059
060

7/1/01

OH1 ^d

1.387

6.36

55.54

120

n.a.

< 42

061
062

7/2/01

OH1 ^d

2.977^a

6.23

56.55

284

n.a.

< 42

063
064

7/3/01

OH1

143^a

18.633^a

3.61

49.55

433

n.a.

< 42

065
068

7/3/01

OH2

132^a

18.283^a

3.57

49.72

254

n.a.

< 42

066
067

7/4/01

OH1

1.677

6.55

76.155

266

n.a.

42.17

069
070

7/9/01

OH2

2553^a

111.41^a

2.51

293.3

1468^a

n.a.

< 42

071
072

7/10/01

OH1

117^a

29.214^a

2.76

154.14

2817^a

n.a.

< 42

075
076

7/12/01

OH2

2.093

3.96

23.7

227

n.a.

< 42

077
078

7/13/01

OH1

1.25

4.12

12.4

172

n.a.

< 42

079
080
081

7/24/01

OH1

1.338

9.84

5.5

n.a.

58.53

084
085

7/28/01

OH1^e

COH

3.258^a

12^f

175.2

221

n.a.

< 42

086
087

7/29/01

OH2 ^e

COH

579^a

55.526^a

11.6^.f

8.4

661

n.a.

< 42

A walkdown and video did not reveal any indication of mercury in the overhead cell or sump, or any evidence of leaks. The MCV was drained just prior to cleaning, but difficulties were encountered due to a blockage in the ¼" line from the MCV to the sampling station. There was likely some residual elemental mercury in the MCV at the start of chemical cleaning.

The acidic conditions in the overheads could be a possible cause of excess mercury (> 2 mg/L) found in the overheads tanks during air sparging and chemical cleaning. Collection of elemental mercury in the MCV is the desired fate of mercury in the overheads during normal evaporator operations. At the neutral to slightly basic overheads conditions during normal operation, the elemental mercury will remain insoluble and be drained from the MCV. As seen in Table 11, however, the evaporator overheads produced during chemical cleaning routinely were acidic (pH 2 to 7). All of the liquid overheads must pass through the MCV. Any elemental mercury resident in the MCV would potentially dissolve in the acidic overheads by the same mechanism noted for the mercury in the scale. The aqueous mercury ions could be easily transferred with the liquid to the overheads collection tanks.

In Table 11, however, it is evident that elevated mercury levels in the overheads tanks had been encountered before the first chemical cleaning strike had begun (on May 23). Those overheads batches contained primarily rainwater pumped from the overheads cell sump. This supports the theory of mercury carryover into the overheads from elsewhere in the evaporator system.

Acidic vapors caused the CRC pump tank conductivity probe to alarm even though the tank level was well below its setpoint. While not out of the acceptable range for ETF acceptance, acid of pH 2 to 3 was regularly noted in the overheads system during chemical cleaning. Nitric acid has a vapor pressure slightly below that of water at the cleaning conditions, so some acid was expected to evaporate into the overheads during chemical cleaning. As noted earlier, this contributed to difficulties with dissolving residual elemental mercury that would likely have already been in the overheads system.

Probably the most significant of the problems related to sending chemical cleaning overheads to ETF was the elevated alpha radiation levels. As seen in Table 11, the overheads produced when the acid cleaning solution was heated contained alpha levels far above the ETF WAC limits (see samples 2H-CC-HTF-E- 033 through 035, 038 through 040, and 069 through 070). Several overheads batches had alpha levels from 2000 to 4000 dpm/ml, versus the ETF WAC limit of only £ 100 dpm/ml. The alpha was believed to be coming from legacy material in the evaporator and cleaning solution that was volatilized and introduced to the evaporator overheads system. Also, high alpha levels were observed when there was a sufficient amount of rainfall to create a liquid level in the evaporator overheads cell area. The overheads cell is pumped to the overheads sump, which in turn is pumped to the overheads tanks and transferred to ETF after meeting their WAC. This liquid released contamination that was settled in the corners and crevices and other areas in the overheads cell area. These two factors resulted in excessive amounts of alpha emitting materials in the overheads tanks. In addition to issuing a deviation, ETF required controls on the volume of high-alpha waste in order to assure proper dilution in their waste water collection tanks.

After the first period of heating during the first batch of chemical cleaning, several hundred gallons of water with a pH of 4 was discovered in the evaporator cell sump. This was determined to be consistent with rainwater, and authorization was given for a one-time transfer of this material to Tank 43H without affecting the chemistry control program.

After the second period of heating during the first batch of chemical cleaning, 65 gal. (246 L) of liquid was discovered in the evaporator cell sump. Through a test with litmus paper, the pH of this liquid was determined to be 1. This material was neutralized to a pH of 9 with the addition of 1 gallon of 50% caustic and a transfer to Tank 43H was performed.

From a material balance, the likely acid concentration in the sump fluid was 0.154 M. At the pot conditions, it is unlikely that nitric acid as concentrated as that observed in the sump would condense from nitric acid vapor in the overheads stream. If the acidic sump contents originated from the overheads, it was most likely caused by physical entrainment of an aerosol. If the acidic sump contents originated from a pump jumper leak, it would have been 1.8 gal. of leaked material diluted with 63.2 gal. of water.

The concern about the observation of this acid is the possible corrosion of the structural supports of the evaporator pot, carbon steel section of the evaporator cell ventilation, and the HEPA filter housings. Some of the supports for the evaporator vessel are constructed of A53 or A36 carbon steel, both of which are susceptible to severe corrosion when exposed to nitric acid. These supports are painted, however, which should mitigate acid attack. Also, some elements of the evaporator cell ventilation system contain galvanized steel, carbon steel, and aluminum. These components may experience some degradation if they were exposed to acidic vapors for a period of months.

An initial visual inspection of the evaporator cell after the first acid strike revealed no condensate on the evaporator supports and no apparent corrosion to evaporator supports. Inspection with an ultraviolet light source revealed no indication of uranyl nitrate leak sites. Before 2H restart, plans are in place to flush the evaporator pot supports with inhibited water. Operations inspected the cell ventilation system and found no evidence of corrosion, thus the evaporator cell HEPA filter was not replaced. The collection tank filters, however, were replaced.

During neutralization of the first batch of chemical cleaning solution, problems were encountered with the instrumentation on the neutralization tank. The pot contents, containing the nitric acid and uranyl nitrate cleaning solution, dissolved scale, and, potentially, siliceous solids, were transferred to the neutralization tank without incident. After about 440 gallons of 50 wt% caustic was added (out of the 710 gallons of planned caustic), the temperature and level readings in the tank began behaving erratically. Ultimately, infrared thermography was used to determine the tank temperature and ultrasound was used to determine the tank level. After two days, the remainder of the required caustic was added and the alternate instrumentation performed properly.

During neutralization, a complex mixture of solid uranium oxides are formed from the reaction of caustic with uranyl nitrate. The temperature is expected to rise during neutralization by 30 to 50 ° C. The neutralization tank is equipped with an impeller, which should adequately mix the tank contents and minimize the formation of large clumps of uranium-bearing solids. The neutralization tank temperature is measured with a thermocouple located near the tank bottom. Level indication is provided by dip tubes.

The instrumentation problem was encountered with temperature and level measurements almost simultaneously. The measured temperature rapidly increased from 30 ° C to 90° C, and a day later the measured temperature still had not decreased to below 70 ° C. Thermogrophy conducted 36 hours after the caustic addition was halted measured 45° C, while the thermocouple was reading 78° C. The erratic behavior of the temperature instrumentation has not been fully understood. Either there was a thermocouple malfunction and the temperature did not actually increase to near 90° C or there was a localized hot-spot in the tank. An analysis of the problem with the level indication suggests that one or more of the dip tubes may have been obstructed.

After the completion of the caustic addition to the neutralization tank contents for the first acid cleaning batch, fluid was discovered in the neutralization tank dike area. The pump was recirculating fluid in the neutralization tank when the leak was discovered. Visual surveillance could not determine the leak location due to insulation surrounding the piping.

There has been no official determination of the cause of the leakage. The pump will be tested to determine the cause of the leakage after decontamination of the dike area and removal of the pump.

To bring the evaporator back ready for service, the pot had to be filled, neutralized, and boiled down to the 48 inch level. Details of the caustic boildown are contained in Section B.10. On July 16, an evaporator pot sample was pulled in order to confirm that the 60 gallons of caustic was sufficient to bring the approximately 2800 gallons of pot contents to a pH of greater than 7. After the sample was taken, the sampling plug was re-installed and the pot air-lance flow was restored. Contaminated air leaked from the plug, contaminating the personnel in the hut and the evaporator cell sampling area. This was due to the failure of the seals on the Thaxton Plug, through which evaporator pot samples are taken.

In order to avoid future leaking through the sampling plug, the lance air flow rate was lowered significantly. Reducing the lance air flow was not a major issue at this juncture because the evaporator pot contained a lower-than-residual amount of scale and insignificant organics. During subsequent operation, there was only about 10% of the 50 to 100 SCFM that was used for the chemical cleaning. This impacted the caustic boildown, causing it to be extended over an entire weeks time when the expected time required was only about two days. Without the large air flow purging the evaporator vapor-space, there was little driving force to sweep the evaporating material into the overheads and reduce the pot liquid level.

This section explains the results, problems encountered, and potential problem solutions for the laboratory titrations involved with chemical cleaning.

There were no problems associated with the titration results for the first acid strike post cool down sample (2H-CC-HTF-E-036/037). The reason that the caustic was added in two stages had to do with the loss of level and temperature instrumentation in the neutralization tank. F-Lab reported the "total acid to pH 11" analysis as 6.6 N. Using standard methodology, CSTE calculated 710 gallons of 50 wt% caustic. That amount was adequate to neutralize to pH 11.

For the second acid strike post cool down sample (2H-CC-HTF-E-073/074), F-lab's initial titration result was 1.63N, corresponding to 160 gallons. This result was checked with an additional titration (after being questioned by the shift technical engineer and operations personnel), and ultimately revised to 4.1N, corresponding to 400 gallons. When 400 gal of 50% caustic was added to the neutralization tank, the pH was raised to only pH of 5. Based on 400 gallons raising the pH to 5, it would likely take only about 10 additional gallons to neutralize to pH > 11, but it could possibly be more (50 gallons or more) due to the non-ideality of the titration curve of our solution. Engineering recommended the addition of 220 additional gallons of caustic (total of 620 gallons), which was calculated as a conservative upper bound on neutralizing the pot contents. Actually, 250 extra gallons of caustic (total of 650 gallons) was added, raising the pH to an acceptable level.

The first titration result for the second acid batch (1.63N) was likely a gross error that could not be accounted for by just taking experimental uncertainties into account. As F-Lab suggests, this was likely a transcription error. This analysis was questioned and addressed in an error report by F-Lab.

The second titration result of the second acid batch (4.1N), however, may have been correct within experimental uncertainty. Based on the Year 2000 sample history data on the synthetic standards that F-Lab uses to track the standard deviation and bias of the "acid total to pH 11" method, the experimental uncertainty, or 95% confidence interval, based on 200 samples is roughly +/- 8%. This is reasonable considering the uncertainty involved with reading values off of a titration burette as well as ascertaining the exact pH stopping point. An 8% error corresponds to about 32 gallons in this case. Most of the quick calculations suggested that an additional 32 gallons would have likely brought the pH well above 11, but we can not be certain. Additionally, the volume to be neutralized has an uncertainty associated with it. If the evaporator pot level indication is off by +/- 2 inches (+/- 6 inches is used for safety), the volume to neutralize would be off by 60 gallons, or 3%. Potentially, another 12 gallons of caustic would be needed to neutralize. The calculation that is used to determine the amount of caustic to add takes into account neither the experimental uncertainty in the titration nor the uncertainty in the volume of material to neutralize. Instead, it uses the titration to a pH of 11 to be adequately conservative for achieving a pH of greater than 7. If needed in the future, this calculation should be edited to include both the experimental uncertainty in the titration and the uncertainty in the volume to neutralize. This would be sensible in this situation, where adding too much caustic is not a concern. Additionally, there is a chance that the result we obtained was due to an unrepresentative sample of the evaporator pot (as there were some loose solids present in the pot).

After the second acid strike, the pot met the residual limit for the amount of material remaining, so the evaporator pot was prepared for return to service. Following the operating plan, the pot was filled to the 80 inch level with water (2810 gallons). On July 16, 2 inches (60 gallons) of 50 wt% NaOH was added to the evaporator pot, bringing the pH to well above 11. On July 18, approximately 150 gallons was transferred from the pot to the neutralization tank, leaving the pot level at approximately 77 inches (2710 gallons). From July 21 to July 28, the pot was simmered until the final liquid level was 48 inches (1830 gallons). Although plans refer to this step as a boildown, boiling is not attainable at the temperature limits in place. Rapid evaporation at a temperature less than 92° C was the operational target. As stated in Section B.8, this boildown was performed over a much longer time period than expected due to the reduced air lance flow. Additionally, the mass of water leaving the pot and entering the overheads did not balance; there was a several-hundred gallon shortfall of condensate.

After the pot had reached nearly the target boildown level, the overheads tanks were sampled and sent to F-Lab and ETF for analysis. See samples 2H-CC-HTF-E-084 through 087 in Table 11 for the contents of these samples. Overheads tank 2 collected condensate during the initial portion of the caustic boildown, and overheads tank 1 contained rainwater plus material from the later portions of the caustic boildown. The pH in overheads tanks 1 and 2 was approximately 5 and 2.7, respectively. These had to be neutralized with the addition of approximately 1 liter of 50 wt % caustic to each tank.

Clearly, there was not a great amount of caustic material that entered the overheads during the caustic boildown period. Given the same conditions, caustic is much less likely to vaporize into the overheads than nitric acid. A good hope for caustic to be carried into the overheads is by significant amounts of physical entrainment. Additionally, the lance air flow rate was significantly less during boildown than during acid cleaning, reducing the likelihood of entrainment.

The overheads produced during the caustic boildown period was likely similar in pH to the overheads during typical evaporator operation, a pH of 8 to 10. Complicating matters, there was up to 160 gallons of acidic fluid remaining in the MCV. A significant amount of pH 8 to 10 overheads would be required to neutralize the MCV contents at pH 2 to 3. The MCV has subsequently been drained.

The following is a compilation of interoffice memoranda (from R. S. Waltz and W. R. West to B. L. Lewis) that contain observations of scale in the 2H-evaporator system during the cleaning process.

An inspection performed on 4/30/01 documented the conditions of the tube bundle, warming coil, thermowells, exposed piping, and the interior of the evaporator pot. This inspection is recorded on file tape 767.

The inspection of the interior of the vessel showed no significant changes since last inspected on 10/30/00. The white salt deposits that were present in October are no longer visible and were most likely dissolved when the water was added. No indications of these solids were visible at 86 inches (level in pot after water addition) in the pot and no apparent changes of the deposits on the upper regions of the vessel were observed. Portions of the vessel sidewalls, thermowells, warming coil, and other exposed piping below the operating limit remained incrusted with solids (sodium aluminosilicate). The intake of the lift line was not visible because it was extending beneath the liquid that remained in the pot. Approximately 9 inches of liquid remained in the pot after it was pumped out.

An inspection performed on 6/7/01 documented the interior of the evaporator pot. This inspection is recorded on file tape 776.

The inspection revealed that some scaling and a few small white deposits were still present in the upper regions of the vessel above 86 inches (operating level) and a thin scale on the sidewalls below this elevation with some areas of clean metal exposed. No deposits were observed on the thermowells, the exterior of the lift line, feed line or downcomer. The tube bundle had some small deposits at both ends, in the middle on the support plate, and a few deposits between some tubes. There are deposits up to eight inches in height remaining at approximately 16 inches (operating level) where the cone and sidewall are welded. However, the deposits on the sidewall are intermittent do not form a complete ring. This is the only location where any significant amounts of deposits remained. The warming coil has some dark loose solids on the last few coils that appear to have settled on the top of the coil as the liquid was removed.

A comparison with the pre-service inspection performed on 8/30/95 was made. The earlier inspection was made with a 500-watt light and a B/W camera. The inspection on 6/7/01 was performed using a color CCTV system with 24-watt lighting. The comparison showed several areas where the chemical cleaning had removed all deposits and the stainless steel surface was visible. There was still a thin scale on the vessel sidewalls and some of the service piping.

No liquid was observed above the bottom of the warming coil support collar, which is 8.5 inches above the bottom of the vessel. The bottom appeared to be covered with the same dark solids observed on the warming coil.

Video provided during sampling activities performed on 6/16 revealed approximately 3-5 inches of loose solids at the bottom of the vessel. These loose solids looked like coarse sand and were easily displaced by the sampling tool. The conical region was covered with a thin scale, which appeared to be < 0.0625 inches thick and was removed as the sampler came in contact with the vessel walls.

Inspections performed on 6/27/01 documented the interior of the GDL from COP #3 and from the N-3 nozzle. An inspection also documented the conditions of the West Lift Line.

From COP #3 towards the 2H evaporator the GDL was inspected for ~35 feet and for ~25 feet towards Tank 38H. This inspection revealed a thin scale on the bottom of the line and a few loose solids that have washed down from the mechanical cleaning performed earlier. No solids or deposits were observed attached to the walls of the line.

One small deposit was observed in the vertical section of the GDL just below nozzle N-3. This deposit protrudes out from the wall approximately 0.25 to 0.5 inches and is about 2 inches by 3 inches in surface area. Some deposits were observed at the bottom of the vertical section where the transition to the horizontal section begins. These deposits appear to be < 0.25 inch and are about 3 to 4 feet long. The deposits observed during this inspection are minor and this is the first time that this section of line has been this clean since sodium aluminosilicate deposits were observed.

Based on the observations from the COP and being able to look at 3-4 feet beyond the deposits at the base of the vertical section, I conclude that the horizontal section of the GDL is probably clean.

The inspection of the lift line revealed solids just beyond the last 45° bend as the line turns down in the pot. This deposit was approximately 18 inches long and at the thickest point it blocks about 70-75% of the line. The deposit was located from approximately 60 inches to 78 inches in the pot. The level in the pot was 58 inches and the camera was inserted below this elevation. All of the lift line from this point to a point a few feet below the 30° bend into the cone appears to be free of any solids and deposits. The line was not completely inspected to the cone, but based on observations of the line that was exposed to the acid. It is not expected that there were any further deposits below that point in the line. This line should have the deposits removed before returning the evaporator to service, and further engineering evaluations are required to determine how to best achieve this.

Inspections on 7/13/01 documented the interior of the 2H-evaporator pot and the lift line after the second acid cleaning. The lift line was pressure washed and re-inspected on 7/14/01. Evaluations are given below.

The inspection revealed that the acid cleaning had removed all of the remaining deposits from the sidewall. A thin scale remains on portions of the wall. The deposits observed at the ends of the tube bundle on 6/7/01 had been removed. Some of these settled on several of the tubes as loose solids. Small amounts of loose solids remain on the warming coils.

Approximately 4 inches of liquid and solids remained in the pot at the bottom of the cone. The solids had the appearance of coarse sand and were easily dislodged by a camera inserted into the liquid.

Inspection on 7/13/01 showed that the deposits observed on 6/27/01 just past the 45° bend at the top of the cone had not been removed by acid cleaning.

Pressure washing of the line with approximately 646 gallons of water was performed on 7/14/01. The line was re-inspected and the deposits had been cleaned, leaving only a thin scale on the pipe wall. The line was inspected to within 3 feet of the bottom of the pot. Based on the condition of piping inspected that was exposed to the acid, it is believed the piping not inspected (3 feet) is clean.

A review of the inspections performed on 8/8/01 and 8/9/01 after pressure washing on the inlet and outlet of the lift jumper/separator pot verified that the jumper is essentially clean.

The inspection on 8/8/01 of the outlet side revealed some loose solids and small deposits. The outlet side was cleaned and all loose solids and deposits were removed. Only a slight scale remains on the pipe walls. The outlet was inspected from the bottom of the Separator pot to the Hanford connector at the top of the Tank 38 GDL.

The inspection on 8/9/01 of the inlet side revealed only minor scaling with no deposits observed. The inlet was inspected from the Separator pot to the Hanford connector at the pot.

Compound	As-Received Sample	Dried As-Received Sample	Insoluble Solids H₂O Wash	Insoluble Solids 0.1M HNO₃ Wash
Al(NO₃)₃	8.7 wt%^b	9.5 wt%	1.78 wt%	1.63 wt%
Fe₂O₃	0.72 wt%	1.0 wt%	2.0 wt%	2.5 wt%
NaNO₃	2.8 wt% ^a	4.5 wt%	0.35 wt%	0.43 wt%
SiO₂	15.0 wt%	26.0 wt%	89.5 wt%	88.8 wt%
UO₂(NO₃)₂	36.3 wt%^b	50.0 wt%	1.2 wt%	0.69 wt%
Free H₂O	28 wt%	0 wt %	0 wt %	0 wt %
Total	91.4 wt%	91.0 wt%	94.9 wt%	94.1 wt%

Analyte	As-Received Sample
U-238	21.9 wt%
U-235	0.050 wt%
Hg	0.06 wt%
Sb-125	2.90´ 10⁷ dpm/g
Cs-137	2.54´ 10⁷ dpm/g
Sr-90	3.20´ 10⁷ dpm/g
Pu-238	1.90´ 10⁸ dpm/g
Pu-239/240	2.62´ 10⁶ dpm/g

Sample	Source Term
Original scale	9.28 × 10⁸ rem/gal of scale
8-hour sample	4.34 × 10⁷ rem/gal of solution
16-hour sample	4.59 × 10⁷ rem/gal of solution
Post cool down sample	2.93 × 10⁷ rem/gal of soltuion
Pot cone solids	3.94 × 10⁷ rem/kg of solids

BuOH	Butanol
CAM	Continuous Air Monitor
cpm	Counts per Minute
CRC tank	Cesium Removal Column feed tank
DBP	Dibutyl Phosphate
DSC	Differential Scanning Calorimetry
dpm	Disintegrations per Minute
DWPF	Defense Waste Processing Facility
EDS	Energy Dispersive Spectroscopy
ETF	Effluent Treatment Facility
F-Lab	F-area Central Laboratory (alternately C-Lab)
FT-IR	Fourier Transform Infrared Spectroscopy
GDL	Gravity Drain Line
HGR	Hydrogen Generation Rate
HLW	High Level Waste
ICP-ES	Inductively Coupled Plasma Atomic Emission Spectroscopy
ICP-MS	Inductively Coupled Plasma Mass Spectroscopy
in. WC	Inches of Water Column
MBP	Monobutyl Phosphate
MCV	Mercury Collection Vessel (alternately Mercury Removal Tank)
NCSE	Nuclear Criticality Safety Evaluation
SCFM	Standard Cubic Feet per Minute
SEM	Scanning Electron Microscopy
SRS	Savannah River Site
SRTC	Savannah River Technology Center
TC	Total Carbon Analysis
TBP	Tributyl Phosphate
TGA	Thermal Gravimetric Analysis
TOC	Total Organic Carbon Analysis
TTA	Thenoyl Trifluoro Acetone Separation
WAC	Waste Acceptance Criteria
WCP	Waste Compliance Plan
XRD	X-ray Diffraction