Abstract
A code for IVR (In-vessal Retention) analysis has been programmed based on a well-known IVR stable bounding computation methodology. The code has been verified by comparing the calculation results with ERI, DOE, and INEEL results for AP600 and AP1000. The motivation of this research work is to investigate the feasibility of adopting IVR strategy to mitigate the severe accident of a typical large-scale advanced PWR (power level is higher than 1400MWe). According to molten pool parameter analysis and uncertainty analysis, the probability of exceeding-CHF accident in large-scale advanced PWR is smaller than 7% if the flow path of ULPU-2000 configuration for vessel external flooding is used, but the probability that the largest melt thickness exceeds 15cm is very large. Heat flux distribution of the lower head of the pressure vessel plays the main role to influence the molten pool behavior. It is suggested to take engineering action to adjust the heat flux distribution for mitigating heat transfer crisis at the region near oxide zone and metal zone. The results obtained are encouraging for further study on IVR strategy to mitigate severe accident of large-scale PWRs.
