Numerical analysis on the cladding failure behavior of high burnup PWR fuels in NSRR experiments

Suzuki, Motoe

Numerical analyses were performed by using the RANNS code for the NSRR experiments VA-1, VA-2 (room temperature tests), VA-3 and VA-4 (high temperature tests) using high burnup PWR fuels. The fuel changes during base-irradiation were calculated a by the fuel performance code FEMAXI-6 and the results were fed to RANNS as initial conditions prior to the pulse irradiation tests. The RANNS analyses were conducted for the temperature, stress/strain and PCMI of pellet and cladding, and the fuel conditions at failure instant or internal pressure change in the non-failed VA-4 test were evaluated. These results were compared with the actual cladding rupture morphology and factors dominating cladding failure were discussed. Also, a simulation calculation was carried out with a widened pulse power which has the same integrated enthalpy as that of the original NSRR pulse power in the VA-3 test. This suggests no possibility of cladding failure.