Modification of severe accident analysis code for accident tolerant fuel (ATF) applications

After the Fukushima nuclear accident, we gradually realized the safety issues of the traditional UO₂+Zr nuclear fuel system. Accident tolerance fuel (ATF) is a new generation fuel concept proposed to improve the performance of fuel elements against severe accidents, and can withstand the consequences of accidents for a long time while maintaining or improving their performance under normal operating conditions. Nowadays, the issue of the safe utilization of nuclear energy has attracted more and more attention. Reactor severe accident simulation and analysis for ATF has also become one of the important research directions. MELCOR is a fully integrated engineering-grade computer code which can model severe accidents phenomena in light water reactors. However, the existing MELCOR code is only applicable for the UO₂+Zr fuel system, and cannot simulate the behavior of the ATF. So it is necessary to modify the MELCOR code for ATF applications. Based on extensive investigation, multi-fuel and multi-cladding processing module and new physical properties of ATF are added to MELCOR. Also the heat transfer model, oxidation model and cladding failure model are modified, enabling the MELCOR code to calculate ATF behaviors. Afterwards, the model verification is carried out. Then the traditional UO₂+Zr and five ATF combinations are applied to the traditional three-loop PWR nuclear power plant to perform the safety analysis under large break loss of coolant accident (LBLOCA). The calculation results show that ATFs have better accident tolerance ability than UO₂+Zr fuel system used in the commercial PWR, and the temperature of the cladding rises more slowly. The cladding failure is also delayed to different extent. The ATF fuel system has a better performance under the severe accident condition.