Development of a transient module based on FROBA-ROD code and assessment for fuel rod performance under reactivity-initiated accident

By developing a reactivity-initiated accident simulation module, the steady-state fuel rod performance analysis code, FROBA-ROD, was updated and was capable of predicting the fuel rod behavior under a reactivity-initiated accident. The RIA simulation module was validated by comparing its results to an authoritative commercial code, FALCON, and to the experimental data of RIA simulation experiments performed on the NSRR in Japan. By using the new version of FROBA-ROD, a series of comprehensive calculations and analyses of fuel rod behavior under different RIA conditions were conducted. It is found that the cladding temperatures are at a low level in all the failure cases and the hydrogen concentration of the cladding is the key factor that effects the integrity of fuel rods under an RIA condition. And a PCMI cladding failure threshold equation was established for a better integrity estimate of fuel rod under RIA conditions in this study.