Simulation of IFA-650.10 Test Using a Modified Version of RELAP5/MOD3.1

In order to address the performance of the advanced cladding alloys under LOCA, especially at high burnup operation, the U.S.NRC has established newly revised LOCA acceptance criteria (10 CFR 50.46c) to ensure adequate safety margin. As the current LOCA methodology and related fuel rod model in the thermal-hydraulic system code, RELAP5, do not meet the revised criteria, code and methodology improvement reflecting the proposed acceptance criteria should be made. To make a fuel rod in RELAP5 calculations have the same initial conditions produced by ROPER, the rod initialization procedure was also developed. An assessment on the Halden IFA-650.10 LOCA test was conducted by the modified RELAP5 code and the ROPER code. To better simulate the fuel rod transient behavior, rod initialization procedure between ROPER and the modified RELAP5 code were established and developed respectively. Consequences are as follows. The clad surface temperature was predicted to be slightly higher than that of the measured data but the overall transient behavior of rod temperature was predicted very well. On the other hand, the predicted rod internal pressure was much higher before rod burst and its time is also earlier. This discrepancy is due to the over-prediction of rod plenum temperature