Reactor safety gap evaluation of accident tolerant components and severe accident analysis

The reactor accidents at Fukushima Daiichi have rekindled interest in Light Water Reactor (LWR) severe accident phenomenology. Post-event analyses have identified several areas that may warrant additional research and development to reduce modeling uncertainties and to assist the industry in the development of mitigating strategies and refinement of Severe Accident Management Guidelines to both prevent significant core damage given a beyond design basis event and to mitigate source term release if core damage does occur. On these bases, a technology gap evaluation on accident tolerant components and severe accident analysis methodologies has been completed with the goal of identifying any data andor knowledge gaps that may exist, given the current state of LWR severe accident research and augmented by insights gained from recent analyses for the Kukushima Daiichi accident. The ultimate benefit of this activity is that the results can be used as a basis for refining research plans to address key knowledge gaps in severe accident phenomenology that affect reactor safety and that arc not being directly addressed by the nuclear industry or by the US Nuclear Regulatory Commission. As a result of this study, thirteen gaps were identified in the areas of severe accident tolerant components and accident modeling. The results clustered in three main areas; namely, i) modeling and analysis of in-vessel melt progression phenomena, ii) Emergency Core Cooling System equipment performance under beyond-design-basis accident conditions, and iii) ex-vessel debris coolability and core-concrete interaction behavior relevant to accident management actions. This paper provides a high level summary of the methodology used for the evaluation, the identified gaps, and finally appropriate Research and Development that may be completed to address the gaps.