The design assessment of limiting transient event by RETRAN-02 and VIPRE-01 for Lungmen ABWR

Abstract

System thermal hydraulic and hot channel calculations are utilized in this paper to analyze the limiting transient event for Lungmen nuclear power plant (LMNPP). The difference of initial critical power ratio (ICPR) and minimum critical power ratio (MCPR), i.e., ΔCPR, is employed to quantify an impact caused by a transient to LMNPP. Based on the ΔCPR criterion, the Lungmen Preliminary Safety Analysis Report (PSAR) concluded that Load Rejection (LR) event was the most limiting event. However, Inadvertent Closure of One Turbine Control Valve (ICOTCV) event was specified as the most limiting core-wide transient event for LMNPP in the Lungmen Final Safety Analysis Report (FSAR). Moreover, the partial-arc TCV control mode is now applied for linear steam flow control, while the Lungmen FSAR utilized full-arc mode for ICOTCV transient analysis. Based on the above differences, it is necessary to re-analyze both LR and ICOTCV transient events for safety consideration. In this paper, ΔCPRs are calculated by the combination of RETRAN-02 and VIPRE-01 codes. The system transient parameters calculated by RETRAN-02 are furthermore submitted into VIPRE-01 for hot channel analysis. The hot channel model constructed by VIPRE-01 simulates the hottest fuel bundle. The critical heat flux (CHF) is calculated by a CHF correlation. Moreover, the different valve control modes are discussed to study the influence on ICOTCV transient. The analytic results by RETRAN-02 and VIPRE-01 are compared with Lungmen FSAR for assessment. The assessment result indicates that the RETRAN-02 and VIPRE-01 analytic modes applied in this paper are capable of simulating the transient behaviors reasonably. Based on the design changes mentioned above, the calculated maximum ΔCPRs are 0.18 and 0.20 for LR and ICOTCV by RETRAN-02 and VIPRE-01, respectively. It is concluded that, first, the impact caused by ICOTCV event is larger than that by LR event with the new fuel type design and full-arc control mode. Second, the adoption of partial-arc control mode is capable of controlling steam flow rate linearly. However it also increases the ΔCPR during ICOTCV transient. This issue should be highlighted after commercial operation.