The potential impact of enhanced accident tolerant cladding materials on reactivity initiated accidents in light water reactors

Advanced cladding materials with potentially enhanced accident tolerance will yield different light-water reactor performance and safety characteristics than the present zirconium-based cladding alloys. These differences are due to cladding material properties, reactor physics, and thermal hydraulics characteristics. Differences in reactor physics are driven by the fundamental properties (e.g., neutron absorption cross section in iron for an iron-based cladding) and also by design modifications necessitated by the candidate cladding materials (e.g., a larger fuel pellet to compensate for parasitic absorption). This paper describes three-dimensional nodal kinetics simulations of a reactivity-initiated accident (RIA) in a representative pressurized water reactor with both iron-chromium-aluminum (FeCrAl) and silicon-carbide fiber silicon carbide ceramic matrix composite (SiC/SiC) materials. This study shows similar RIA neutronic behavior for SiC/SiC cladding configurations versus reference Zircaloy cladding. However, the FeCrAl cladding response indicates similar energy deposition but with shorter pulses of higher magnitude. This is due to the shorter neutron generation time of the core models based on FeCrAl cladding. The FeCrAl-based cases exhibit a more rapid fuel thermal expansion rate than other cases, and the resultant pellet-cladding interaction may occur more rapidly. The conclusions in this paper are based on a limited set of simulated super prompt RIA transients.