Decommissioning Level 2 Probabilistic Risk Assessment Methodology for Boiling Water Reactors

This paper describes a methodology to evaluate the radiological risk of postulated accident scenarios during the decommissioning phase of commercial nuclear power plants. The fuel damage scenarios include those initiated while the reactor is permanently shut down and the spent fuel is initially located in the reactor pressure vessel and successively moved in the spent fuel storage pool. This paper focuses on the Level 2 PRA (post fuel damage) aspects of the analysis. The Level 2 decommissioning PRA uses event trees that assess the accident progression post spent fuel damage. Detailed deterministic severe accident analyses are performed to support the event tree development (e.g., success criteria and accident progression timings) and to provide source term information for the various release categories. Results are derived from the Level 2 decommissioning PRA event tree in terms of Large Release Frequency (LRF) and Large Early Release Frequency (LERF).