Development and application of a deterministic-realistic hybrid methodology for LOCA licensing analysis

It is well recognized that a realistic LOCA analysis with uncertainty quantification can generate greater safety margin as compared with classical conservative LOCA analysis using Appendix K evaluation models. The associated margin can be more than 200 K. To quantify uncertainty in BELOCA analysis, generally there are two kinds of uncertainties required to be identified and quantified, which involve model uncertainties and plant status uncertainties. Particularly, it will take huge effort to systematically quantify individual model uncertainty of a best estimate LOCA code, such as RELAP5 and TRAC. Instead of applying a full ranged BELOCA methodology to cover both model and plant status uncertainties, a deterministic-realistic hybrid methodology (DRHM) was developed to support LOCA licensing analysis. Regarding the DRHM methodology, Appendix K deterministic evaluation models are adopted to ensure model conservatism, while CSAU methodology is applied to quantify the effect of plant status uncertainty on PCT calculation. Generally, DRHM methodology can generate about 80–100 K margin on PCT as compared to Appendix K bounding state LOCA analysis.

► A new LOCA licensing methodology (DRHM, deterministic-realistic hybrid methodology) was developed. ► DRHM involves conservative Appendix K physical models and statistical treatment of plant status uncertainties. ► DRHM can generate 50–100 K PCT margin as compared to a traditional Appendix K methodology.