Comments for Review of NuMI Target Hall shielding July 27, 2001 from T. Leveling ------------------------ 1. Overall Remarks I was away from the laboratory during the formal presentation on July 27th, so my review is based on materials found at http://www-numi.fnal.gov:8875/numwork/reviews/july_27.html. Materials presented by Hylen and Stefanik were received through the mail on 8/17. Slides 15 - 21 in Grossman PP file were received 8/14. 2. Itemized suggestions, questions and concerns (1)Consideration of the shielding design for prompt and residual ionizing radiation appears to be comprehensive. The MARS calculations developed to understand residual dose rates in the NUMI target hall appear to work well for times greater than about an hour. Since it is improbable that target vault components can be removed within an hour of beam going off, the calculations should also be sufficient for purposes of this review. A waiting period of at least one hour should be imposed when the target hall be comes operational to preclude personnel access when dose rates are very high and not well understood. (2)The shielding calculation process is reasonably well understood and is fairly reliable at predicting actual conditions. However, a comprehensive measurement plan should be developed to check and confirm calculations when target hall operation begins. (3)Groundwater calculations and groundwater protection has been considered extensively. The RAW systems associated with the target hall will be a significant source of activated water. It would be more complete to include, at least peripherally, some mention of engineering controls to be used to preclude RAW system water from entering groundwater. (4)The Access portion of Grossman slides, includes the statement "RAW Room may have a locked door." The RAW Room appears in the list of NUMI spaces where beam on access is permitted. This is a little surprising. Even though the NUMI RAW room does not contain a beam dump cooling system, it seems probable that dose rates due to activated horn water would prohibit personnel access. Perhaps this room should be listed under "NO ACCESS" and should have a delay time after beam goes off before personnel access should be permitted. In addition, a remote monitoring system (e.g., chipmunk on MUX) should be used to determine radiation dose rates before permitting personnel access. (5)The shielding of the RAW room is not addressed in the target hall shielding presentation except for mention of a penetration. If not already done, the RAW room shielding needs to be addressed somewhere. (6)Target hall ventilation does not appear to be fully designed at this point. It would be prudent for NUMI to review air sample results of pbar vault air UPSTREAM of the HEPA filtered target vault exhaust. My recollection is that fairly significant airborne contamination (above and beyond PET isotopes C11, N13, etc.) exists in the vault upstream of the HEPA filter during beam operation due to activation of airborne dust, rust, etc. This source of contamination could be spread throughout the air cooling system resulting in contamination control requirements for the air cooling system maintenance. In addition, condensate drains in the system could become radioactive due to deposition of same materials on cooling system coils. Recent samples with beam off and beam on have been collected by the BD ES&H Department at pbar vault. If this is found to be a problem, NUMI should strongly consider the use of HEPA filters to remove particulates from the vault return air prior to cooling. (7)Removable radioactive contamination may be more of a concern at NUMI than at previous facilities due to intended beam power. Care needs to be taken in the facility design to provide for this (e.g., handling and storage of T blocks in manner that lower surfaces of blocks don't come in contact with uncontrolled surfaces.) (8)Comment on crane dose rates: mentioned 10 krad/year to crane bridge. Does this include any electronics, for example radio receiver, controls circuits? Upper limit for solid state components is about 10 krad. While not a concern for structural or electrical systems, electronic stuff begins to break down at this level. If gamma only, electronic stuff may be good for a factor of 10 higher integrated dose. (9)Operational aspects of target hall are not presented. It will be a major concern what modules will require removal and replacement and how all that is too be done. Facility design vv. ALARA and personnel exposure control needs to be addressed. (10)Personnel radiation exposure resulting from operation of this facility needs to be estimated and reviewed in context of annual exposure limits, ALARA, and DOE performance criteria.