Multiphysics Analyses and Experiments for Safety of Advanced Light Water Reactor Fuels

The Fukushima Daiichi nuclear plant accident in 2011 triggered worldwide research and development initiatives to advance Light Water Reactor (LWR) fuel materials with excellent tolerance to high-temperature oxidation and deformation. Accident Tolerant Fuel (ATF) design concepts are expected to improve safety margin and extend coping time during severe accident progression, owing to their enhanced mechanical strength, oxidation, and degradation resistance. These concepts require a series of assessments to be licensed by the United States (US) Nuclear Regulatory Commission (NRC). In addition to enhanced safety from ATF materials, supported by the NRC, the US nuclear industry is seeking opportunities to increase economic competitiveness by extending the fuel burnup limit. Higher burnup is under-explored and requires high-fidelity assessments to build a robust technical basis for licensing. This dissertation leverages state-of-the-art experimental and computational methods to analyze the safety performance of the iron-chromium-aluminum (FeCrAl) cladding and higher burnup fuel during design basis accidents (DBAs). This dissertation aims to increase the knowledge base of considered advanced LWR fuel materials during transient scenarios to improve safety and competitiveness of LWRs.

Evaluation results highlight the pertinence of separate-effects tests for ATF safety assessments and the development of material models in advanced modeling tools. This dissertation presents and validates a novel correlation that improves the prediction of transient critical heat flux (CHF) and post-CHF thermal-hydraulics response in systems codes like RELAP5-3D. This dissertation validates BISON’s capabilities for modeling complex pellet-cladding mechanical interaction (PCMI) against high-fidelity strain data from the modified burst test (MBT) facility. Experimental comparisons of FeCrAl and Zircaloy cladding highlighted ATF candidate’s superior accident tolerance under high temperature dryout conditions simulating boiling water reactor (BWR) anticipated transient without SCRAM. A subsequent BISON analysis verified cladding mechanical responses and provided the reasoning behind this observation. A thermal-hydraulics loss-of-coolant accident (LOCA) analysis is conducted to provide realistic boundary conditions for high burnup fuel performance analysis investigating uranium dioxide (UO2) fragmentation and high burnup fuel integrity.