Results from past performance assessments for the Yucca Mountain disposal system for spent nuclear fuel and high-level radioactive waste

• Published in: Reliability engineering & system safety 2014-02, Vol.122, p.207-222
• Main Author: Rechard, Rob P.
• Format: Article
• Language: English
• Subjects: Activation; Assessments; Boundaries; High-level radioactive waste; Mountains; Parameter sensitivity; Performance assessment; Probabilistic risk assessment; Radioactive waste; Radioactive waste disposal; Repositories; Spent nuclear fuels; Viability; Yucca Mountain
• ISSN: 0951-8320; 1879-0836
• DOI: 10.1016/j.ress.2013.06.030

This paper summarizes the progression of results through four early performance assessments (PAs) conducted to support selection and to evaluate feasibility and three major PAs conducted to evaluate viability, recommend the site, and assess compliance of a repository for spent nuclear fuel and high-level radioactive waste at Yucca Mountain, Nevada. The early PAs in 1984, 1991, 1993, and 1995 evaluated cumulative release over 104yr at a 10-km or 5-km boundary as specified in the draft and final 1985 radiation protection standard, respectively. During the early PAs, the fission products 99Tc, 129I, and activation products 14C, and 36Cl were identified as important radionuclides at the beginning of the regulatory period. The actinide, 237Np, often dominated at the end of the regulatory period. Package and repository design options were evaluated during the early PAs but modeling did not identify strong preferences. In 1992 Congress mandated a change to a dose measure. Dose at a 20-km boundary from the repository was evaluated through 106yr for the undisturbed scenario class via the groundwater pathway for the Congressionally mandated viability assessment in 1998. For the assessment for the site recommendation in 2000, doses from igneous eruption dominated in the first ~3000yr, doses from igneous intrusion between ~3000yr and ~40,000yr, and doses from the undisturbed scenario class through 106yr. The 2008 compliance assessment for the license application incorporated the influence of the seismic scenario class on waste package performance. The compliance assessment found that doses from the igneous intrusive scenario class and the combined undisturbed and seismic scenario class were important contributors at the ~18-km boundary. In the compliance PA, 99Tc and 129I fission products and 14C activation product were important in the first 104yr. Beyond 104yr, actinides 239Pu, 242Pu, 237Np, and 238U decay product 226Ra were important. In all PAs, parameters of the natural barrier were important, but in the three latter PAs, the slow degradation of the large, in-drift container had an important role in explaining the uncertainty in the peak dose. •Progression of cumulative releases from four early PAs and doses from three major PAs are described.•Change in the contribution to dose from fission products, activation products, and actinides is described.•Change in the contribution of the various scenarios to dose is described.•Change in the important uncertain modeling