Evaluation of the asymmetry effect on core thermal limit for the inadvertent cold coolant injection transient in Chinshan BWR-4 Plant

• The HPCI injection will result in an asymmetrical temperature distribution in lower plenum.
• The detailed CFD resolution can compensate the defect of RETRAN analysis.
• Spearman correlation coefficient method justifies the dependence among parameters.
• The inlet subcooling is in a medium to strong relationship to ΔCPR.
• 20% flow penalty can simulate the asymmetric HPCI event with enough conservatism.

The HPCI is designed to inject into one of the two feedwater lines, which eventually results in the uneven distribution of core inlet temperature. This paper develops a methodology to determine the penalty of HPCI flow to cover the defect of RETRAN computer code in the volume-averaged parameter and satisfy the requirement for a conservative analysis. The detailed inlet temperature calculated by CFD supports the determination of ΔCPR by using RETRAN hot channel model for the selected 56 potential channels.The Spearman rank correlation coefficient method is adopted to evaluate the dependence of the ΔCPR on the characteristics in the channel. Finally, the inlet subcooling in the channel is found to be in a medium to strong dependence on CPR change. The sensitivity studies verify that 20% penalty kept in HPCI flow covers 95% subcooling in all channels and the calculated ΔCPR has a rank of 54 (from low to high), which can cover 96.4% of CPR change in the 56 potential channels.