Assessment of Refuelling Effects in High Power Channels on Fission Product Releases Following an End-Fitting Failure

Abstract

A more realistic fuel bundle power history considering the refuelling effect was used for the assessment of fission product releases during an end-fitting failure accident. The high power channels were selected as a conservative assumption, based on the instantaneous power/burnup distributions during 0 to 610 Full Power Days (FPDs) in the core, calculated from the fuel management study for Wolsong 2/3/4 plants. For each fuel bundle, the volume-average temperatures in the UO₂ pellets and fission product inventory distribution in the fuel elements were calculated by the ELESTRES code.

When compared with the case using the current overpower envelope based on the time average physics simulations, higher fuel temperature and more fission product inventory were predicted for the low power bundles located at bundle positions 1, 2, 11 and 12.However, the results for high power bundles at bundle positions 4 to 9, where the most fission products are released following an end-fitting failure event, confirmed the conservatism made in the current analysis methodology since they showed a very high fission product inventory.