ANALYSIS OF SEVERE ACCIDENT PROGRESSION IN LWRS CONSIDERING POWER UPRATES AND ATF CLADDING MATERIALS

Abstract

Following the Fukushima Daiichi Nuclear Power Plant (NPP) accident in 2011, accident tolerant fuel (ATF) technologies have emerged as a key topic aimed at enhancing the resilience of light water reactors (LWRs) under severe accident conditions. Concurrently, power uprates have become increasingly attractive for nuclear power plant (NPP) operators due to economic benefits as well as widespread clean energy goals. Despite the growing relevance of both developments, the combined impact of ATF technologies and power uprates on severe accident progression remains unexamined. This study addresses that gap by investigating how ATF cladding materials combined with power uprates up to 20% affect accident progression and eventual consequences of severe accidents in both boiling and pressurized water reactors (BWR & PWR). A severe accident scenario is assigned to each of these representative LWRs and simulated using MELCOR (version r2025.0.0). Three candidate ATF cladding materials, chromium-coated zirconium (Cr-coated Zr), iron-chromium-aluminum alloy (FeCrAl), and silicon carbide (SiC) are evaluated against a conventional Zircaloy cladding baseline. Accident severity is assessed through a few primary metrics: the timing of core degradation and reactor pressure vessel (RPV) failure, fission product release from the core, and hydrogen generation due to oxidation processes. The results of this study emphasize the benefit of ATF cladding materials and expand the understanding of their impact on severe accident progression, for operating at uprated power conditions.