Study on the Calculation Method of Molten Pool Decay Heat Distribution under IVR Condition

Yisheng Hao,Xiaoyu Guo,Yuwen Hu,Shanfang Huang,Minyun Liu,Junyi Chen,Chuan Lu,Kan Wang,Houjun Gong,Yang Li,Hao Luo

doi:10.3389/fenrg.2021.677865

Abstract

As an important strategy to mitigate severe accidents, the in-vessel retention (IVR) technique has been applied to the new generation of pressurized water reactor (PWR). However, under IVR conditions, the decay heat distribution in the molten pool is very uncertain because of the complexity of the molten pool and the calculation method limitations. To explore the calculation method and distribution of the decay heat of lower head molten pool under IVR conditions, the decay heat calculation method is developed based on Reactor Monte Carlo Code (RMC). The verification results show that the relative error of calculation result is generally within ± 0.25%. In addition, geometric modeling for lower head molten pools has been carried out, and distribution of the decay heat in two-layer and three-layer structures has also been accurately calculated. The calculation results indicate that the decay heat power spatial distribution is relatively uniform in the two-layer molten pool structure. The decay heat power at the center of the lower head decreases from 0.71°W/cm3 to 0.023°W/cm3 within 1d-5d. In the three-layer molten pool structure, the spatial distribution of the decay heat power is severely uneven due to the precipitation of heavy metal uranium. Besides, in actual engineering calculations, it should lay emphasis on the heat transfer characteristics and design margin of the upper part of the heavy metal layer and the lower part of the oxide layer because the maximum decay heat power appears at these two positions.

Highlights

In-Vessel Retention (IVR) technology is an important strategy for serious accident mitigation
Because of the common decay heat calculation requirements in reactor shutdown and molten pool scenarios, this paper proposes the corresponding decay heat calculation method based on the DEPTH program coupled with the Monte Carlo code Reactor Monte Carlo Code (RMC), which enriches the functional modules of the RMC program
To solve the above problems, the decay heat calculation module is developed based on DEPTH coupled with RMC, and its functional verification is carried out

Summary

Introduction

In-Vessel Retention (IVR) technology is an important strategy for serious accident mitigation. It arrests relocated molten core materials in the vessel during the severe accident and has been singled out as an appealing accident management approach to many reactors(Theofanous, 1989; Su, 2016). The specific process of IVR technology is as follows. During the severe accident in PWR, the core melts if it cannot be effectively cooled. The melting core relocates to the lower head of the pressure vessel and forms a liquid molten pool with a variety of pool configurations. Since the IVR strategy confines all the fission products in the vessel, complex ex-vessel severe accident phenomena can be avoided

Methods

Results

Conclusion