Criticality evaluation and protocol for DOE-owned spent nuclear fuels
- and others
This report is a continuation of repository criticality evaluation work. Both the probability and consequences of a criticality were considered. A long-term, low-power, water-moderated criticality was the most likely of those considered. Its probability was low but not low enough to be dismissed. The governing regulation, 40 CFR 191, allows an event to be dismissed if it has less than one chance in 10,000 of occurring in 10,000 years. This implies a regulatory concern threshold of 10-8/yr. Even if such an event occurred, the repository inventory would still be dominated by the disposed fuel and waste and no significant additional releases would be expected. The major categories of criticality investigated were: water-moderated with fast or slow reactivity insertion, dry (hard-spectrum) with fast or slow reactivity insertion, water-moderated on the surface due to human intrusion, and far field. Fault trees were prepared to assess these scenarios. As a result of this study, the probability of a criticality in 10,000 years was revised from 3x10{sup -3} to 5x10{sup -4}, primarily through the elimination of conservatism and correction of assumptions. The presence of water is a major concern in criticality studies. The possibility of flooding due to water table rise had been dismissed in previous studies. Conservative models indicate that this is a defensible position. The possibility of a silica moderated criticality was considered briefly. The preliminary study identified isotopes of concern for release and these were verified by several comparative methods. Most isotopes had similar ratios across source categories and those that did not could be accounted for by fuel or waste characteristics. The ORIGEN2 code was validated to be sufficiently accurate for PA purposes for the low-power, long-term scenario considered in the criticality study.
- Research Organization:
- EG and G Idaho, Inc., Idaho Falls, ID (United States)
- Sponsoring Organization:
- USDOE, Washington, DC (United States)
- DOE Contract Number:
- AC07-94ID13223
- OSTI ID:
- 130638
- Report Number(s):
- INEL-94/0395; ON: DE96002193; TRN: 96:000096
- Resource Relation:
- Other Information: PBD: Sep 1995
- Country of Publication:
- United States
- Language:
- English
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