Screening Analysis of Criticality Features, Events, and Processes for License Application

The purpose of this analysis report is to evaluate the features, events, and processes (FEPs) associated with criticality and document the screening decision for either inclusion or exclusion of criticality in the Total System Performance Assessment for License Application (TSPA-LA). The FEPs associated with criticality address scenarios that include initiators of sequences of events or processes that could lead to configurations that have potential for criticality in the repository. Thus, criticality is a single event and a screening decision, either Included or Excluded for all criticality FEPs collectively, is based on the total probability of occurrence of configurations with potential for criticality for the repository rather than evaluating each FEP independently. The technical basis for each individual FEP is summarized in the conclusions for this analysis. This information is required by the U. S. Nuclear Regulatory Commission (NRC) as documented in 10 CFR Part 63 ([DIRS 180319], Section 102(j)) and § 63 (proposed rule) (70 FR 53313 [DIRS 178394]). Proposed amendments to the 10 CFR Part 63 to address a dose standard after 10,000 years are given in Implementation of a Dose Standard After 10,000 Years (70 FR 53313 [DIRS 178394]). The approach used for estimating the probability of postclosure criticality resulting from events occurring under conditions ranging from early failure of engineered barriers to disruptive geological environments makes use of various processes and tools for identifying potentially critical configurations (including probability of occurrence) and calculating the maximum effective neutron multiplication factor (keff) of configurations, if necessary.