Verification for Flow Analysis Capability in the Model of Three-Dimensional Natural Convection with Simultaneous Spreading, Melting and Solidification for the Debris Coolability Analysis Module in the Severe Accident Analysis Code ‘SAMPSON’, (I)

Abstract

The debris coolability analysis module in the severe accident analysis code 'SAMPSON' has been enhanced to predict more mechanistically the safety margin of present reactor pressure vessels in a severe accident. The module calculates debris three-dimensional natural convection with simultaneous spreading, melting and solidification using the 'debris spreading-cooling model' in combination with the temperature distribution of the vessel wall and it evaluates the wall failure. Debris spreading is solved by the free surface calculation method in which the height function is applied. The model makes possible a multiplex heat and mass transfer analysis with flow spearhead and melt front transportation for a single-phase flow analysis code through the resetting of two types of mesh attributions and re-arrangement of the pressure matrix at each time step. The results calculated with the present model are compared with the results from a water spreading experiment. The comparisons verify the model capability for predictions of debris flow in the spreading process. The module provides a good tool for prediction of the reactor safety margin in a severe accident through the three-dimensional natural convection analysis of debris with simultaneous spreading, melting and solidification.

Verification for Flow Analysis Capability in the Model of Three-Dimensional Natural Convection with Simultaneous Spreading, Melting and Solidification for the Debris Coolability Analysis Module in the Severe Accident Analysis Code 'SAMPSON'. (II).

“…5) The flow analysis capability with energy transportation and solidification analysis is verified by comparing with results from a thermalhydraulic experiment for spreading of a stainless steel melt in the present study.…”

“…The heat transfers obtained by procedure (1) are used as the boundary conditions. (3) Energy Transportation after Resetting of Mesh Attribution After the energy conservation calculation and resetting the mesh attribution in the free surface tracking method, 5) the energy transportation between the debris pool or the crust and the free surface mesh on the debris is calculated, except for the wall top meshes. The heat transfers are calculated as they reach thermal equilibrium immediately.…”

“…In the melting and solidification analysis of natural convection, generally, the crust is handled as an unmovable object; however, the wall boundary condition without movability is unsuitable since the crust movement has freedom and uncertainty above the debris pool. The following methods and assumptions are used in the model 5) to simulate the phenomena more realistically and to obtain the calculation stability.…”

“…The model makes possible a multiplex heat and mass transfer analysis with flow spearhead and melt front transportation in open spaces through the resetting of two types of mesh attributions and re-arrangement of the pressure matrix at each time step. 5) Though the energy conservation equation was shown, the spreading was calculated for constant temperature and property of the working fluid and the flow analysis capability of the model without energy transportation analysis was verified using a water spreading experiment 10) in Part (I). The method of energy transportation during the spreading process in addition to the solution of the energy conservation equation should be clarified, while the verification for the thermal-hydraulic analysis capability with energy transportation, melting and solidification analysis has also remained as undone work.…”

“…The debris spreading-cooling model of the debris coolability analysis module, [1][2][3][4][5] in the SAMPSON code [6][7][8][9] was developed for the thermal hydraulic analysis of core melt debris relocated onto the reactor pressure vessel (RPV) head. The model makes possible a multiplex heat and mass transfer analysis with flow spearhead and melt front transportation in open spaces through the resetting of two types of mesh attributions and re-arrangement of the pressure matrix at each time step.…”