Modified Waste Emplacement Mode Design Alternative Report
The alternative emplacement modes presented in this report provide potential conceptual design options to the VA design that enhance human access to the emplacement drift area during abnormal events. The alternative conceptual designs emplace waste packages in configurations that reduce the level of radiation exposure utilizing shield doors, shield plugs, and concrete slabs to allow for human access during off-normal events. The alternative emplacements modes rank slightly lower than the VA design when evaluated against the eight criteria (i.e., postclosure performance; preclosure performance; assurance of safety; engineering acceptance, construction, operations and maintenance; schedule; cost and environmental considerations) presented in Section 5. However, the alternative emplacement modes allow the waste packages to be more accessible for human access to perform infrequent and unplanned events. The alternative emplacement modes were evaluated by a team of experts in assessing the confidence level that would be presented by each one of the design emplacement mode concepts (See Appendix A). The experts ranked the alternative emplacement mode concepts on a scale from A to E (i.e., A represents a high level of confidence and E represents the lowest level of confidence). The criteria in which the alternative modes were evaluated include the following: postclosure performance; preclosure performance; assurance of safety; engineering acceptance; construction, operations and maintenance; schedule; and cost. The results of the evaluation concluded that the alternative emplacement modes have a moderate level of confidence when evaluated against the selected criteria. Overall, the average rankings for the alternative emplacement modes presented in this report score below the VA reference design when analyzed against the evaluation criteria. Some limited calculations for the postclosure performance criteria were generated to determine the TSPA for each alternative emplacement mode. Calculations to determine seepage rates from degraded waste packages, and therefore exposure rates to the environment over time, were not generated. Since total system performance is highly dependent upon waste package performance, additional calculations are required to determine the complete results of this evaluation. The TSPA calculations that were generated for the alternative emplacement modes were then compared with the results of the TSPA-VA. The short cross-drift and the borehole emplacement modes are similar to the TSPA-VA Base Case, and therefore, the waste package failure rates and the total system performance are also expected to be similar. Calculations for TSPA for the in-trench emplacement modes were not generated. However, preliminary analysis by the Performance Assessment organization provides some initial evidence that the total system performance is expected to be similar to the TSPA-VA Base Case. Hence, the alternative emplacement modes considered in this report are not expected to rate higher in postclosure performance when compared to the VA reference design. The alternative emplacement modes rate below or equivalent to the VA reference design in preclosure performance, assurance of safety, engineering acceptance, construction, operations and maintenance, schedule, cost and environmental considerations. Based upon these ratings, none of the alternative emplacement mode concepts appear superior to the VA reference design. Among the alternative emplacement modes, short cross-drift, which is the most similar to the reference emplacement mode appeared to rank highest, followed by in-trench emplacement, and then borehole emplacement. Although postclosure performance calculations have not been completed, none of the alternative emplacement modes are expected to perform superior to the VA reference design. Alternative emplacement modes, however, provide greater benefit to the VA design in allowing human access in the emplacement drift areas for infrequent, unusual or off-normal situations. Unless this benefit outweighs the lower ratings of the alternative emplacement modes to the emplacement mode used by the VA reference case, a recommendation to adjust the reference emplacement mode is not warranted.
- Research Organization:
- Yucca Mountain Project, Las Vegas, Nevada (US)
- Sponsoring Organization:
- US Department of Energy (US)
- DOE Contract Number:
- AC08-91RW00134
- OSTI ID:
- 759932
- Report Number(s):
- B0000000001717-5705-00110, Rev.00; MOL.19990621.0156, DC#21681
- Country of Publication:
- United States
- Language:
- English
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