Preliminary evaluation of predicted peak release rates from the engineered barrier system for a potential repository at Yucca Mountain, Nevada

Any potential repository for the ultimate disposal of the nation`s high-level radioactive wastes is subject to meeting post-closure regulatory requirements as specified by the NRC. Three NRC sub-system performance measures are relevant to the evaluation of the Yucca Mountain site and possible engineered barriers. These performance requirements are specified in 10 CFR 60. These include the substantially complete containment requirement, the engineered barrier system (EBS) release requirement, and the pre-waste emplacement groundwater travel time requirement. The present paper documents an initial evaluation of the peak EBS release rates. A number of key factors significantly impact the maximum release rate from the engineered barrier system. The authors have conducted four simulations to approximate the effects of delaying and spreading out the failure distribution that are based on different thermal loads and criteria for the initiation of aqueous corrosion. Using an assumed outer barrier of 10 cm and an inner barrier of 0.95 cm and the Stahl model for aqueous pitting corrosion, they have analyzed the EBS release rates for thermal loads of 28.5, 57 and 83 kW/Ac using temperature as the corrosion limiting factor and at 57 kW/Ac for saturation limiting the initiation of corrosion. The later had the earliest failures and the most rapid failure rates observed in the TSPA-1993 analyses so provides the upper bound on the release rates