Development of LOCA licensing calculation capability with RELAP5-3D in accordance with Appendix K of 10 CFR 50.46

In light water reactors, particularly the pressurized water reactor (PWR), the severity of a loss of coolant accident (LOCA) will limit how high the reactor power can operate. Although the best-estimate LOCA licensing methodology can provide the greatest margin on the PCT evaluation during LOCA, it generally takes more resources to develop. Instead, implementation of evaluation models required by Appendix K of 10 CFR 50 upon an advanced thermal–hydraulic platform also can gain significant margin for the PCT calculation. The compliance of the current RELAP5-3D code with Appendix K of 10 CFR 50 has been evaluated, and it was found that there are ten areas where code assessment and/or further modifications were required to satisfy the requirements set forth in Appendix K of 10 CFR 50. All of the ten areas have been further evaluated and the RELAP5-3D has been successfully modified to fulfill the associated requirements. To verify and assess the development of the Appendix K version of RELAP5-3D, nine kinds of separate-effect experiments were adopted. Through the assessments against separate-effect experiments, the success of the code modification in accordance with Appendix K of 10 CFR 50 was demonstrated. Another six sets of integral-effect experiments will be applied in the next step to assure the integral conservatism of the Appendix K version of RELAP5-3D on LOCA licensing evaluation.