Neutronic modeling of a subcritical system with corium particles and water (from international benchmark)

Abstract

After the accident at the Fukushima Daiichi NPP, the attention of the scientific community is riveted on how the consequences are being eliminated. Removing corium – a lava-like resolidified mixture of nuclear fuel with other structural elements of the reactor – remains the most difficult task, the solution of which can take several decades. It is extremely important to exclude the occurrence of any emergency processes during the removal of corium. The purpose of this work was to solve a coordinated hydrodynamic and neutronic problem characterized by a large number of randomly oriented and irregularly located corium particles in water as part of the development of a benchmark for this class of problems. Monte Carlo-based precision codes were used to perform a neutronic analysis. The positions of corium particles were determined from the numerical simulation results. The analysis results obtained using the codes involved showed good agreement for all the states considered. It was shown that the modern neutronic codes based on the Monte Carlo method successfully cope with the geometric formation and solution of the problem with a nontrivial distribution of corium particles in water. The results of the study can be used to justify the safety of corium handling procedures, including its extraction from a damaged power unit.

Monte Carlo codes benchmarking on sub-critical fuel debris particles system for neutronic analysis

“…There is no significant difference between eigenvalues obtained with all three codes. This is a current research progress since paper [7] that reported MCU results differing by more than a percentage point for 0.1 s timepoint. Improvement of the results was achieved by correcting calculation model in MCU.…”

“…This article continues a series of papers in which detailed benchmark description and results of preliminary explicit effective multiplication factor calculations were presented [7,8], and also developed programming tool for visualizing the calculation results was introduced [9]. Current paper focuses on more accurate calculation results of several parameters such as neutron fluxes, reaction rates, and relative FOM (Figure of Merit) as well as improved effective multiplication factor calculation results (results improvement was achieved by correcting calculation model in MCU).…”

The Development of a Multiphysics Coupled Solver for Studying the Effect of Dynamic Heterogeneous Configuration on Particulate Debris Bed Criticality and Cooling Characteristics

“…The CFD solver, DEM solvers, and the sub-models for evaluating momentum/energy exchange between fluid-particle phases were executed via the commercial code of STAR-CCM+ (Version 2020.3) [32], a general-purpose tool allowing the processing of three-dimensional calculation among multi-phases with high fidelity and flexibility. The MCN solver can be conducted on the in-house code of MVP3, developed by the JAEA [33] and validated via conducting benchmarking on the debris particles system with two other Monte-Carlo-based codes (Serpent and MCU), showing that the three modern codes are capable of performing neutronic analysis for the fuel debris particles system without significant discrepancy and with high accuracy [34]. The interface, which is liable for exchanging information and the workflow control between STAR-CCM+ and MVP3, was originally created in this research to realize the automated multi-physics-concerning function in the coupled CFD-DEM-MCN solver.…”