APPENDIX A CRITERION BASIS STATEMENTS

1.2.1.1 Criterion Basis Statement

This criterion is needed to define the overall level of performance of the repository to which this system will be contributing. This criterion supports MGR RD 3.1.C, 3.2.P, and 10 CFR 63.113(b).

The performance parameters are taken from 10 CFR 63.113(b) and MGR RD 3.2.P.

1.2.1.2 Criterion Basis Statement

This criterion sets the design capacity for the MGR and flows from MGR RD 3.2.A and MGR RD 3.2.B. It should be noted that this design capacity, along with the required drift spacing, WP spacing, and WP capacity, effectively fixes the areal mass loading of the repository. Since the areal mass loading plays a significant role in the overall performance of the repository, this criterion also supports MGR RD 3.1.C and 3.2.P, and 10 CFR 63.113(b).

The MGR waste design capacites are taken from "Monitored Geologic Repository Project Description Document," Section 5.1.4.1 and 5.1.4.2. These design capacities correspond to the design capacities of MGR RD 3.2.A and 3.2.B.

1.2.1.3 Criterion Basis Statement

This criterion is needed to ensure the repository design is not precluded from accommodating an expanded inventory, as required by the "Monitored Geologic Repository Project Description Document," Section 5.1.4.2.

The expanded repository capacity is taken from the "Monitored Geologic Repository Project Description Document," Section 5.1.4.2.

1.2.1.4 Criterion Basis Statement

This criterion is needed to enhance the ability of the repository to shed thermally mobilized water from the repository horizon. A section of host rock, between emplacement drifts, that is below the water boiling temperature is believed to allow drainage of thermally mobilized water above the repository horizon toward the water table, whereas a host rock entirely above the water boiling temperature would inhibit that flow of water.
This criterion supports MGR RD 3.1.C, 3.2.M, 3.2.N, and 3.2.P, and 10 CFR 63.113(b). This criterion also supports "Monitored Geologic Repository Project Description Document," Section 5.1.1.3.

The temperature and rock mass limitations are taken from the "License Application Design Selection Report," p. O-15.

1.2.1.5 Criterion Basis Statement

This criterion is needed to permit the repository to be closed early, if so directed, as required by MGR RD 3.2.H. This criterion also serves the intent of "Monitored Geologic Repository Project Description Document," Section 5.1.1.1, as indicated by "Change to Requirement 5.1.1.1 in Monitored Geologic Repository Project Description Document, Rev 01, DCN 01."

The closure timing is taken from MGR RD 3.2.H.

1.2.1.6 Criterion Basis Statement

This criterion is needed to produce a uniform temperature distribution along the axis of an individual emplacement drift. This criterion also has the added benefit of reducing the cost of excavation (the space between WPs is reduced [compared to advanced conceptual and viability assessment designs]; therefore, less emplacement drift length is needed) and emplacement drift construction materials (materials used for ground support, drip shields, inverts, etc., are reduced proportionally with emplacement drift length reduction).
Line loading of emplacement drifts is driven by "Monitored Geologic Repository Project Description Document," Section 5.2.10.
This criterion supports MGR RD 3.1.C, 3.2.M, and 3.2.P; and 10 CFR 63.113(a) and 63.113(b).

The line loading parameters are taken from the "Monitored Geologic Repository Project Description Document," Section 5.2.10.

1.2.1.7 Criterion Basis Statement

This criterion is needed to establish the bounding fault standoff distance (i.e., the distance from any WP to the nearest fault) that protects the WPs from faults and splays (a minor fault that branches off of a larger fault) that represent potential preferential pathways.
This criterion supports MGR RD 3.1.C and 3.2.P, and 10 CFR 63.113(b).

The minimum distances between WPs and Type I faults and splays are taken from "Subsurface Facility System Description Document," Criterion Basis Statement 1.2.2.1.5.

1.2.1.8 Criterion Basis Statement

This criterion is needed to establish the system level of performance for draining free-liquid-phase water away from the emplacement drift to contribute to the long-term performance of WPs.
This criterion supports MGR RD 3.1.C and 3.2.P, and 10 CFR 63.113(b).

The water volume is taken from "Monitored Geologic Repository Project Description Document," CPA 040.
The 10,000-year timeframe is taken from 10 CFR 63.113(b).

1.2.1.9 Criterion Basis Statement

This criterion reduces the uncertainties associated with emplacement drift radionuclide transport, as compared to the other primary invert material candidate (concrete).
This criterion supports MGR RD 3.1.C and 3.2.P, and 10 CFR 63.113(b).

The invert material selection is obtained from "Monitored Geologic Repository Project Description Document," Section 5.2.8.

1.2.1.10 Criterion Basis Statement

This criterion is needed to establish one function of the invert ballast, to control the pH of water transporting radionuclides.
This criterion supports MGR RD 3.1.C and 3.2.P, and 10 CFR 63.113(a) and 63.113(b).

The 10,000-year timeframe is taken from 10 CFR 63.113(b), and is corroborated by Table 4 of "Manager System Requirements/System Description Documents." The upper pH bound is obtained from Table 4 of "Manager System Requirements/System Description Documents" (Invert Barrier Requirements). The lower pH bound is obtained from Table I of "Groundwater Chemistry Along Flow Paths Between a Proposed Repository Site and the Accessible Environment."

1.2.1.11 Criterion Basis Statement

This criterion reduces the uncertainties associated with emplacement drift radionuclide transport, as compared to the other primary invert material candidate (concrete).
This criterion supports MGR RD 3.1.C and 3.2.P, and 10 CFR 63.113(a) and 63.113(b).

The invert ballast material selection is obtained from "Monitored Geologic Repository Project Description Document," Section 5.2.8.

1.2.1.12 Criterion Basis Statement

This criterion is needed to ensure that the drip shield is designed with an operating life long enough to achieve the functions allocated to it.
This criterion supports MGR RD 3.1.C, and 3.2.P, and 10 CFR 63.113(a) and 63.113(b).

The 10,000 year timeframe is taken from 10 CFR 63.113(b), and is corroborated by the drip shield operating life in Table 4 of "Manager System Requirements/System Description Documents" (Drip Shield Barrier Requirements). The preliminary results transmitted in the "Manager System Requirements/System Description Documents" input transmittal indicate that additional performance is necessary over and above the 5,000 year life assigned to the drip shield in "Enclosure 2 - Guidelines for Implementation of EDA II," Section 9.0, which was transmitted by "Direction to Transition to Enhanced Design Alternative II" and baselined in "Interim Direction for Enhanced Design Alternative (EDA) II" (ECR No. E1999-0046).

1.2.1.13 Criterion Basis Statement

This criterion is needed to protect the WP from dripping water during its operating life.
This criterion supports MGR RD 3.1.C, 3.2.P, 10 CFR 63.113(a), and 63.113(b).

N/A

1.2.1.14 Criterion Basis Statement

This criterion is needed to establish one of the required functions of the drip shield, to protect the WP from rockfall during its operating life.
This criterion supports MGR RD 3.1.C, 3.1.G, 3.2.P, 3.3.I, 10 CFR 63.113(a), and 63.113(b).
This criterion is supported by guidance contained in the "Compliance Program Guidance Package for Ex-Container System," Guidance Statements 6.7g1 and 6.9g1.

The rockfall parameter is taken from "Rock Fall Calculations for Drip Shield," Item 3.

1.2.1.15 Criterion Basis Statement

This criterion is needed to establish one of the required functions of the drip shield, to protect the WP from rockfall during its operating life.
This criterion supports MGR RD 3.1.C, 3.1.G, 3.2.P, 3.3.I, 10 CFR 63.113(a) and 63.113(b).
This criterion is supported by guidance contained in the "Compliance Program Guidance Package for Ex-Container System," Guidance Statements 6.7g1 and 6.9g1.

The rockfall parameter is taken from "Rock Fall Calculations for Drip Shield," Item 3.

1.2.1.16 Criterion Basis Statement

This criterion is needed to preserve the functionality of the drip shield after a design basis earthquake during its operating life.
This criterion supports MGR RD 3.1.C, 3.1.G, 3.2.P, 10 CFR 63.113(a), and 63.113(b).
This criterion is supported by guidance contained in the "Compliance Program Guidance Package for Ex-Container System," Guidance Statements 6.7g1 and 6.9g1.

The specification of the design earthquake for this criterion is made recognizing that the Category 2 preclosure design basis earthquake has a recurrence interval of 10,000 years, which would indicate a probability approaching unity that such an earthquake would occur during the postclosure period (assuming the probability of such an earthquake remains constant over the entire postclosure period). Specification of design earthquakes normally gives some margin over and above earthquakes expected to occur, thus specification of the Category 2 earthquake is inadequate for postclosure purposes. Specification of the design earthquake in this criterion gives a recurrence interval of 100,000 years, which is one order of magnitude higher than the earthquake expected to occur. This value will be used (as TBV) until a better substantiated value is provided.

1.2.1.17 Criterion Basis Statement

This criterion is needed to preserve the functionality of the drip shield after a design basis earthquake during its operating life.
This criterion supports MGR RD 3.1.C, 3.1.G, and 3.2.P, and 10 CFR 63.113(a) and 63.113(b).
This criterion is supported by guidance contained in the "Compliance Program Guidance Package for Ex-Container System," Guidance Statements 6.7g1 and 6.9g1.

The specification of the design earthquake for this criterion is made recognizing that the Category 2 preclosure design basis earthquake has a recurrence interval of 10,000 years, which would indicate a probability approaching unity that such an earthquake would occur during the postclosure period (assuming the probability of such an earthquake remains constant over the entire postclosure period). Specification of design earthquakes normally gives some margin over and above earthquakes expected to occur, thus specification of the Category 2 earthquake is inadequate for postclosure purposes. Specification of the design earthquake in this criterion gives a recurrence interval of 100,000 years, which is one order of magnitude higher than the earthquake expected to occur. This value will be used (as TBV) until a better substantiated value is provided.

1.2.1.18 Criterion Basis Statement

This criterion is intended to ensure that the drip shield design will meet its other performance requirements.
This criterion supports MGR RD 3.1.C and 3.2.P, and 10 CFR 63.113(a) and 63.113(b).

The drip shield material and thickness is obtained from the "Monitored Geologic Repository Project Description Document," Section 5.2.11.

1.2.1.20 Criterion Basis Statement

This criterion is needed to establish the period of time that the system must physically support and maintain the WPs' as-emplaced position within an emplacement drift. The WP must be physically supported and maintained in the emplaced position to ensure that the emplacement, performance monitoring, possible retrieval, and closure activities can be performed with sufficient clearance around the emplaced WPs.
This criterion supports MGR RD 3.1.C, 3.1.G, 3.2.H, and 10 CFR 63.111(e)(1). This criterion also supports "Monitored Geologic Repository Project Description Document," Section 5.1.1.1.
This criterion is supported by guidance contained in the "Compliance Program Guidance Package for Ex-Container System," Guidance Statements 6.7g1 and 6.9g1.

The time period is derived from MGR RD 3.2.H.

1.2.1.21 Criterion Basis Statement

This criterion is needed to designate the invert and pallet's postclosure WP support performance. Degradation of the invert and WP may occur, but horizontal movement of the WP must be minimized to ensure that the WP does not contact the drip shield. Contact between the drip shield and the WP has the potential to cause adverse reactions between the SSCs. This criterion supports MGR RD 3.1.C, 3.2.P, and 10 CFR 63.113(b).

The 10,000-year timeframe is taken from 10 CFR 63.113(b).

1.2.1.22 Criterion Basis Statement

This criterion is necessary to ensure that the invert will be able to withstand its anticipated loading and still function to support WPs, performance-enhancing barriers, and emplacement and retrieval operations.
This criterion supports MGR RD 3.1.C, 3.1.G, 3.2.C, and 10 CFR 63.111(e)(1).
Backfill and the Backfill Emplacement System are included as a component to be included as a load, even though backfill is not part of the current design, because inclusion of these loads supports the physical installation of backfill, as required by the "Monitored Geologic Repository Project Description Document," Section 5.2.9.
This criterion is supported by guidance contained in the "Compliance Program Guidance Package for Ex-Container System," Guidance Statements 6.7g1 and 6.9g1.

N/A

1.2.1.23 Criterion Basis Statement

This criterion is needed to ensure that the WP is able to be safely lifted by the Waste Emplacement/Retrieval System. With the addition of the emplacement pallet to the reference design for Site Recommendation, the pallet assumed the responsibility for the lifting of the WP within the emplacement drift by the emplacement/retrieval gantry. This criterion supports MGR RD 3.3.A.

The factors-of-safety are obtained from Section 4.2.1.1 of the "American National Standard for Radioactive Materials - Special Lifting Devices for Shipping Containers Weighing 10000 Pounds (4500 kg) or More" (ANSI N14.6-1993).

1.2.1.24 Criterion Basis Statement

This criterion is needed to ensure that the WP is able to be safely lifted by the Waste Emplacement/Retrieval System. With the addition of the emplacement pallet to the reference design for Site Recommendation, the pallet assumed the responsibility for the lifting of the WP within the emplacement drift by the emplacement/retrieval gantry. This criterion supports MGR RD 3.3.A.

The factors-of-safety are obtained from Section 4.2.1.1 of the "American National Standard for Radioactive Materials - Special Lifting Devices for Shipping Containers Weighing 10000 Pounds (4500 kg) or More" (ANSI N14.6-1993).

1.2.2.1.1 Criterion Basis Statement

This criterion is needed to implement a portion of the safety strategy as described in "Decision Package Executive Summary, Strategy to Mitigate Preclosure Offsite Exposure," Description V of Options 1 and 2. The executive summary is an attachment to "Strategy to Mitigate Preclosure Offsite Exposure." A portion of that safety strategy is to not lift the WP above its design basis height. Lifts above the design basis drop height could result in a WP breach and subsequent exposure if dropped. This criterion will ensure that the emplacement hardware, primarily the WP pedestal, is not designed such that emplacement equipment is forced to lift the WP higher than its design basis drop height.

The lift height value is taken from "Waste Package Design Basis Events," Table 8-1. Implicit in the value identified is the concept that WPs will be emplaced in a horizontal position, which is consistent with the current design. In addition, the lift height value is identical to the horizontally-oriented drop height criterion baselined in the system description documents for the various disposal containers.

1.2.2.1.2 Criterion Basis Statement

This criterion is needed to ensure that the consequences of postclosure criticality events do not cause the repository to exceed the postclosure performance requirement of MGR RD 3.1.C and 3.2.P, and 10 CFR 63.113(b).

The timeframe used for the 10,000-year criticality control period is taken from 10 CFR 63.113(b).
The performance parameter for this criterion is chosen to implement the methodology of the "Disposal Criticality Analysis Methodology Topical Report" and be consistent with the criticality criteria for the disposal containers. The performance parameter basis for this criterion ensures criticality occurrences in the repository will not invalidate the total system performance assessment of expected annual dose to the critical group during the criticality control period. The 10 percent inventory increase is taken from the intermediate risk criterion of "Disposal Criticality Analysis Methodology Topical Report," Section 3.6.3, and is such that the intermediate criticality risk is less is less than the uncertainty in the total system performance assessment calculation of expected annual dose to the critical group.
Available for release (as used in the criterion) is defined in "Disposal Criticality Analysis Methodology Topical Report," Section 3.6.3, as radionuclide inventory from waste packages that have breached barriers and the waste form that have degraded sufficiently to expose the radionuclides to dissolving water.

1.2.2.2.1 Criterion Basis Statement

This criterion is needed to ensure that health and safety issues related to placement of the invert ballast materials are considered in the design.
This criterion supports MGR RD 3.3.A.

N/A

1.2.3.1 Criterion Basis Statement

This criterion is needed to establish the maximum temperature of the drift wall to limit the thermomechanical response of the host rock. Excessive near field temperatures (temperatures in excess of the temperature limit for this criterion) could result in local rock failure, which could make retrieval difficult during the preclosure period, and could have the potential to degrade the system's performance during the postclosure period. High temperatures (above the temperature limit for this criterion) can also create significant differential stresses between the drift wall rock and the drift wall ground support. This concern is described in detail in "Thermal Loading Study for FY 1996," Section 3.3.
This criterion supports MGR RD 3.1.C, 3.2.C, 3.2.M, and 3.2.P; and 10 CFR 63.111(e)(1) and 63.113(b).

The thermal limit value is taken from the recommendations given in "Thermal Loading Study for FY 1996" in Sections 3.3.3 and 7.

1.2.3.2 Criterion Basis Statement

This criterion is needed to preserve the ability of the zeolite layer beneath the emplacement area to act as a natural barrier to radionuclide migration. Temperatures above 90 to 100 degrees C may potentially alter the zeolite (e.g. clinoptilolite) layer to analcime, which has much poorer sorption properties for radionuclides than does clinoptilolite, as discussed in "Thermal Loading Study for FY 1996," Section 3.2.4.
This criterion also supports MGR RD 3.1.C, 3.1.G, 3.2.P, 10 CFR 63.113(a), and 63.113(b).

The zeolite temperature limit is taken from "Thermal Loading Study for FY 1996," Section 7.

1.2.3.3 Criterion Basis Statement

This criterion is needed to establish the bounds for limiting the temperature of the soil surface above the emplaced WPs and just below the soil surface. Soil temperature limits are necessary to limit the environmental impacts at the surface and reduce the potential for adverse changes to the geologic structures, which might increase water infiltration toward the repository emplacement structure.
This criterion supports MGR RD 3.1.C, 3.2.F, 3.2.P, 10 CFR 63.113(a), and 63.113(b).

The thermal bound on the soil temperature is provided by MGR RD 3.2.F.

1.2.3.4 Criterion Basis Statement

This criterion is needed to bound the temperature limits of the PTn geologic unit to limit the thermal, thermomechanical, and thermochemical response of the host rock. The effects of temperature changes in the PTn geologic unit have not been fully studied; however, it is speculated in the "Site Characterization Plan Thermal Goals Reevaluation," pp. 18 and 19, that the PTn could limit the amount of infiltrating water that could readily percolate to the repository horizon, and could act as a barrier against the release of radioactive carbon gas emanating from a breached WP.
This criterion supports MGR RD 3.1.C, 3.2.P, 10 CFR 63.113(a), and 63.113(b).

Although a PTn temperature limit is recommended in the "Site Characterization Plan Thermal Goals Reevaluation," p. 21 (recommendation 16), no quantitative limit is established as part of the recommendation. However, it is suggested on p.19 of the same document that an appropriate temperature limit for the PTn could be the boiling point of water. That suggestion forms the basis for establishing the 96 degrees C temperature limit in this criterion.

1.2.3.5 Criterion Basis Statement

This criterion is needed to preserve the integrity of the natural barrier, as discussed in the 'Assessment of Goals' section (p. 10) of the "Site Characterization Plan Thermal Goals Reevaluation." The following discussion is paraphrased from that document. The potential repository will initially be surrounded by relatively undisturbed rock formations. After waste emplacement begins, the repository will locally heat up and expand. If this expansion is sufficient, this can result in large horizontal stresses developing in the far field and an uplift in the repository region. If this uplift is large enough, it could cause the rock above the repository, especially the non-welded PTn units, to extend, resulting in fracturing of the units. This would damage the principal natural barrier above the potential repository, and could result in the opening of preferential pathways for water infiltration, or pathways for gas migration.
This criterion supports MGR RD 3.1.C and 3.2.P, and 10 CFR 63.113(a) and 63.113(b).

The thermomechanical unit uplift value for the TSw1 is taken from recommendation 3 listed in the 'Summary and Recommendations' section (p. 20) of the "Site Characterization Plan Thermal Goals Reevaluation."

1.2.3.6 Criterion Basis Statement

This criterion is needed to preserve the integrity of the natural barrier, as discussed in the 'Assessment of Goals' section (p. 10) of the "Site Characterization Plan Thermal Goals Reevaluation." The following discussion is paraphrased from that document. The potential repository will initially be surrounded by relatively undisturbed rock formations. After waste emplacement begins, the repository will locally heat up and expand. If this expansion is sufficient, this can result in large horizontal stresses developing in the far field and an uplift in the repository region. If this uplift is large enough, it could cause the rock above the repository, especially the non-welded PTn units, to extend, resulting in fracturing of the units. This would damage the principal natural barrier above the potential repository, and could result in the opening of preferential pathways for water infiltration, or pathways for gas migration.
This criterion supports MGR RD 3.1.C and 3.2.P, and 10 CFR 63.113(a) and 63.113(b).

The ground surface uplift rate above the repository is taken from recommendation 4 listed in the 'Summary and Recommendations' section (p. 20) of the "Site Characterization Plan Thermal Goals Reevaluation."

1.2.4.2 Criterion Basis Statement

This criterion is needed to establish the characteristics of WPs to be emplaced within the system.
This criterion supports MGR RD 3.3.A.

The WP characteristics are obtained from the "Monitored Geologic Repository Project Description Document," Sections 5.2.3 and 5.2.4.
The quantities of the waste packages for the Naval short canisters and the Naval long canisters come from Sections 5.1.4.1 and 5.1.4.2 of the "Monitored Geologic Repository Project Description Document." The Navy's position is that the maximum number of Naval short canisters is 200 and the maximum number of Naval long canisters is 100. The additional quantities provided in Sections 5.2.3 and 5.2.4 is not necessary for the Naval canisters. This Navy position is corroborated in "Information Requested by the Yucca Mountain Site Characterization Office For Use in the Repository Environmental Impact Statement."
The WP lengths are taken from "Revised Waste Package Lengths," Item 1.

1.2.4.3 Criterion Basis Statement

This criterion is needed to identify the maximum surface dose rate to be expected at the WP surface. Radiation fields have the potential to change the physical properties of materials and to alter physical processes over time.
This criterion supports MGR RD 3.3.A.

The surface dose rate is obtained from "Dose Rate Calculation for the 44-BWR UCF Waste Package," Table 25. The results from the calculation are conservatively converted from rem/hr to rad/hr and rounded up to the nearest 10 rad/hr for use in this system's design.

1.2.4.4 Criterion Basis Statement

This criterion is needed as an interface between this system and emplaced WPs. Maximum WP thermal output affects the thermal limitations placed on this system.
This criterion supports MGR RD 3.3.A.

The WP maximum thermal output is obtained from "Monitored Geologic Repository Project Description Document," Section 5.2.13.

1.2.4.5 Criterion Basis Statement

This criterion is needed as an interface between this system and the Subsurface Ventilation System. Removal of WP decay heat by the ventilation system affects the thermal limitations placed on this system.
This criterion supports MGR RD 3.3.A.

The WP heat removal percentage and timeframe is obtained from "Monitored Geologic Repository Project Description Document," Section 5.1.3.1.

1.2.4.6 Criterion Basis Statement

This criterion is needed as an interface with the Waste Emplacement/Retrieval System. Horizontal in-drift emplacement also affects the design of the Performance Confirmation Emplacement Drift Monitoring System and the Backfill Emplacement System.
This criterion supports MGR RD 3.3.A.

N/A

1.2.4.7 Criterion Basis Statement

This criterion is needed as an interface between this system and the Waste Emplacement/Retrieval System. This criterion is a quantification of the criterion to line load the WPs.
This criterion supports MGR RD 3.3.A.

The WP spacing is obtained from "Monitored Geologic Repository Project Description Document," Section 5.2.10.

1.2.4.8 Criterion Basis Statement

This criterion is needed as an interface with the Subsurface Facility System. Drift spacing affects the thermal limitations placed on this system. This criterion is a quantification of the criterion to preclude the merging of the pore water boiling fronts between individual emplacement drifts. This spacing is also intended to reduce the influence of one emplacement drift on another (as compared to subsurface facility designs with more closely spaced emplacement drifts).
This criterion supports MGR RD 3.3.A.

The drift spacing is obtained from "Monitored Geologic Repository Project Description Document," Section 5.2.1.

1.2.4.9 Criterion Basis Statement

This criterion is needed as an interface with the Subsurface Facility System. The excavated drift diameter affects the thermal limitations placed on this system.
This criterion supports MGR RD 3.3.A.

The drift spacing is obtained from "Monitored Geologic Repository Project Description Document," Section 5.2.5.

1.2.4.11 Criterion Basis Statement

This criterion is needed to establish the requirements for bounding the physical envelope available to the system, as an interface with the emplaced WPs, Ground Control System, Waste Emplacement/Retrieval System, Backfill Emplacement System, and the Performance Confirmation Emplacement Drift Monitoring System.
This criterion supports MGR RD 3.3.A, and "Monitored Geologic Repository Project Description Document," Section 5.2.9.

N/A

1.2.4.12 Criterion Basis Statement

This criterion is needed to ensure that the WP supports do not result in an adverse interaction between the WP outer barrier material and the support materials. In addition, it ensures that the SSCs that contact the WP will withstand the maximum WP external temperature.
The "Monitored Geologic Repository Project Description Document" constrains the disposal container design to use Alloy 22 for the outer barrier of the disposal container (Section 5.2.12). The emplacement of WPs on supports results in intimate contact between the WP outer barrier and the supports, and these areas of contact are potential crevice corrosion locations. As the relative humidity in the drift increases, galvanic reactions may take place in the crevice locations. When a corrosion resistant material (such as Alloy 22) is in contact with a less noble material (such as carbon steel), active corrosion of the carbon steel could occur generating hydrogen. This could potentially charge hydrogen into the nickel base alloys causing embrittlement of the WP outer barrier ("Metals Handbook," Volume 13 [Corrosion], p. 652). It is therefore important that dissimilar metal contacts at the WP surface are avoided. The WP support surfaces contacting the WP outer barrier should be fabricated from the same material as the WP outer barrier.
This criterion supports MGR RD 3.3.A.

N/A

1.2.4.13 Criterion Basis Statement

This criterion is needed as an interface with the Ground Control System. The use of concrete as the primary ground support material can have significant affects on the pH of water entering an emplacement drift. Elimination of concrete as the primary ground support material relieves the system (some portions of which are tasked to control the pH of water within emplacement drifts) of the need to compensate for substantial amounts of concrete in the emplacement drifts.
This criterion supports MGR RD 3.3.A.

The ground support material is obtained from "Monitored Geologic Repository Project Description Document," Section 5.2.6.

1.2.4.14 Criterion Basis Statement

This criterion maintains the near field environment interface between the system and the emplaced WPs. The system design determines many of the emplacement drift environment variables for which the disposal container will have to be designed.
This criterion supports MGR RD 3.1.C, 3.2.M, 3.2.P, and 3.3.A; and 10 CFR 63.113(a), and 63.113(b).

Environment parameters, with the exception of the lower pH bound, are obtained from Table 4 of "Manager System Requirements/System Description Documents."
The lower pH bound is obtained from Table I of "Groundwater Chemistry Along Flow Paths Between a Proposed Repository Site and the Accessible Environment."

1.2.4.15 Criterion Basis Statement

This criterion is needed to ensure that the design of the inverts includes consideration for the constructability of the inverts, such as loads placed on the inverts by the Subsurface Excavation System as the inverts are placed.
This criterion supports MGR RD 3.3.A.

N/A

1.2.4.16 Criterion Basis Statement

This criterion responds directly to MGR RD 3.3.C and supports MGR RD 3.1.C, 3.2.P, 10 CFR 63.113(a), and 63.113(b). This criterion is intended to be met in conjunction with a similar criterion levied upon the Subsurface Facility System.

The overburden depth is taken from MGR RD 3.3.C.

1.2.6.1 Criterion Basis Statement

This criterion ensures that the design complies with "Manual of Steel Construction, Allowable Stress Design" or "Manual of Steel Construction, Load and Resistance Factor Design."
This criterion supports MGR RD 3.1.G, and is supported by guidance contained in the "Compliance Program Guidance Package for Ex-Container System," Guidance Statements 6.7g1, 6.9g1, 7.1g1, and 7.2g1.

N/A

1.2.6.2 Criterion Basis Statement

The "Monitored Geologic Repository Project Description Document" allocates controlled project assumptions to systems. This criterion identifies the need to comply with the applicable assumptions identified in the subject document. The approved assumptions will provide a consistent basis for continuing the system design.

N/A

APPENDIX B ARCHITECTURE AND CLASSIFICATION

APPENDIX C ACRONYMS, SYMBOLS, AND UNITS

C.1 ACRONYMS

C.2 SYMBOLS AND UNITS

APPENDIX D FUTURE RevISION RECOMMENDATIONS AND ISSUES