2001 Fiscal Year Final Research Report Summary
Study on Molten Core Behavior in Severe Accidents using Particle Method
| Project/Area Number |
11480120
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| Research Category |
Grant-in-Aid for Scientific Research (B)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Nuclear engineering
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| Research Institution | The University of Tokyo |
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Principal Investigator |
OKA Yoshiaki Graduate School of Enginnering, The University of Tokyo, Professor, 大学院・工学系研究科, 教授 (40011225)
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| Co-Investigator(Kenkyū-buntansha) |
MUKOHARA Tami Graduate School of Enginnering, The University of Tokyo, Research Associate, 大学院・工学系研究科, 助手 (90292763)
KOSHIZUKA Seiichi Graduate School of Enginnering, The University of Tokyo, Associate Professor, 大学院・工学系研究科, 助教授 (80186668)
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| Project Period (FY) |
1999 – 2001
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| Keywords | Particle Method / MPS / Severe Accident / Molten Core / MCCI / Crust / Debris Bed / Vapor Explosions |
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| Research Abstract |
Test experiments, SWISS-2 and MACE-MO, of molten core-concrete interaction (MCCI) were analyzed by a particle method. In both cases, crust was formed at the top of the melt pool and the heat removal to the upper water pool was suppressed. The heat removal to the water pool and the ablation speed in the concrete agreed well between the calculations and the experiments in two cases. An unlimited geometry was also analyzed. The upper crust was formed and the heat removal was suppressed as well. However, the heat removal was enhanced when the crust was broken by the dissolved gas release and the old crust sank in the melt pool.
Formation of the molten core debris was analyzed by the particle method. This is an additional subject which had not been described in the initial research plan. Behavior of a single droplet of the melt in water was investigated. Neglecting the vapor film, we could reproduce the critical Weber number which had been obtained in experiments without the phase change. If the vapor film was considered, the critical Weber number increased and the droplet size was enlarged. The critical heat flux of the debris bed was assessed as IMW/m^2, which showed enough capabilities of the decay heat removal.
Pressure wave propagation processes in vapor explosions were analyzed using a one-dimensional finite volume method considering water, steam, melt droplets and fragments. Based on the past studies using the particle method, a thermal fragmentation model for the melt droplets was developed and incorporated into the code. The mechanical energy conversion ratio achieved 5 % when the thermal fragmentation took place, while it remained less than 1% when the hydrodynamic fragmentation took place. In large-scale vapor explosions, the hydrodynamic fragmentation becomes dominant, so that 1 % is proper to employ as the conversion ratio.
As described above, the present study progressed beyond the initial goal as well as reached it.
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