A comparative study of in-pile behaviors of FeCrAl cladding under normal and accident conditions with updated FROBA-ATF code

Abstract

Accident tolerant fuel (ATF) concepts are at present still in the engineering design stage. FeCrAl, which has great oxidation resistance in high temperature steam environment, is an ATF potential cladding material with higher research priority. However, considering its features, including high thermal expansion, low creep rate and strong absorption of neutron, further evaluation on its in-pile behaviors is still necessary for future industrial application. To address this issue, the self-developed fuel performance analysis code, FROBA, was further developed into a new version named FROBA-ATF. A transient heat transfer model was added into the code’s thermo-hydraulic module for transient simulation, the rigid mechanical model was rewritten into unrigid for ATF cladding and material properties of FeCrAl cladding were also added. These updated modules were introduced and the updated code was assessed in this paper. On this basis, a comparative study on in-pile behaviors of UO2-FeCrAl fuel rod and UO2-Zr4 fuel rod under normal and accident conditions were performed in this paper. Even through the performance analysis revealed that FeCrAl cladding could greatly reduce the oxidation thickness, the thermal performance of UO2-FeCrAl fuel rod was unsatisfactory due to its higher thermal expansion and lower creep rate, especially at beginning of life. With geometry optimization, the steady-state performance of UO2-FeCrAl fuel rod was enhanced. What’s more, the thermal and mechanical performance of the improved UO2-FeCrAl was evaluated and compared under Loss of coolant accident (LOCA) and Reactivity Initiated Accident (RIA) conditions. The results showed that the optimized ATF had better thermal performance, lower cladding hoop stress, and could provide more coping time under accident conditions.