1Submitted to the IRUG Annual Meeting of 2000 Development of LOCA Licensing Calculation Capability with RELAP5-3D in Accordance with Appendix K of 10 CFR 50

In light water reactors, particularly the pressurized water reactor (PWR), the severity of a 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 the 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 CFR50 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 the 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 the 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