Verification Of Licensing LOCA Analysis Program And Three-Dimension Effect Study

Licensing LOCA analysis is one of the important issues of Nuclear Power Plant (NPP) design and safety analysis. According to the related regulations, both conservative and best estimate (with uncertainty analysis) methodology can be used for licensing LOCA evaluation. In this thesis a relatively realistic technique have been adopted, and conservatism of a specific licensing LOCA analysis tool, which has been developed based upon the"advanced best estimate (BE) program platform + conservative evaluation model (EM)"technique, is assessed and verified with utilization of both separate effect test and integral test data. Moreover, three dimensional effects in LOCA analysis, by applying 3-D function of advanced best estimate program platform, are preliminarily discussed.In the thesis, following a brief introduction of the advanced BE platform and conservative EM recommended in Appendix K of 10CFR50.46, a detailed conservatism verification to the licensing LOCA analysis tool programmed through advanced BE platform + conservative EM methodology is carried out, through comparison with related separate effect test data. Also, a preliminary assessment on conservatism of the LOCA analysis program, which is based on the comparison of calculated data with those obtained in the LBLOCA test of LOFT facility, namely L2-5 test, is presented. It is demonstrated that the one dimensional calculation using the LOCA analysis tool can reasonably simulate the LBLOCA scenario and tendency, and conservative requirements of the related licensing LOCA analysis regulation are well complied.Furthermore, by utilizing the three-dimension function of the analysis tool, a three-dimensional input model of the annular downcomer of LOFT facility pressure vessel is established. By comparing the 1-D and 3-D calculation results of LOFT L2-5 test progress, related 3-D effects and its influence on such emergency core cooling progress as ECC bypass etc and that on the fuel peaking cladding temperature (PCT) is preliminarily investigated. Meanwhile, sensitivity of the downcomer 3-D control volume division is tentative studied, with a resulting suggestion of reasonably reflecting the 3-D effects by optimizing the control volume division in the three orthogonal directions. The author believes that, application of 3-D models might provide a possibility of developing LOCA analysis methodology and achieving further LOCA analysis thermal margin. However, there is a long way to go to make sufficient assessment, verification and study before its acceptably application in licensing LOCA analysis.