Fission gas release and transport model for high-burnup PWR models

To minimize fuel cycle cost, Japanese utilities are planning to convert to extended burnup operation in the near future. However, there is concern that enhanced fission gas release will result in increased rod internal pressure. Some remedies for fuel pellets, such as large grain or doped pellets, are proposed and under examination to reduce fission gas release. To evaluate the effects of these improvements, we developed a diffusion based gas release and transport model that is applicable to the quantitative investigation of detailed phenomena at high burnup. These models are implemented in the IRON code and verified against its pressurized water reactor (PWR) fuel data base. This code is now applicable to the analyses for the extended burnup operation up to 55 MWd/kgU.