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Effect of Debris Bed Pressure, Particle Size, and Distribution on Degraded Nuclear Reactor Core Coolability

D. Squarer, A. T. Pieczynski, L. E. Hochreiter

Nuclear Science and Engineering / Volume 80 / Number 1 / Pages 2-13

January 1982

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In the worst hypothetical accident of a light water reactor (LWR), when all protection systems fail, the core could melt and be converted to a deep particulate bed as a result of molten-fuel-coolant interaction. The containment of such an accident depends on the coolability of the heat generating particulate bed. This paper summarizes published theoretical analyses that may predict bed dry out. In three of the analyses, the fluid flow in the heat generating particulate bed is considered to be laminar (Darcy's law), whereas in one study the fluid flow is solved for both the laminar and the turbulent flow regimes and is affected by capillary forces. The theoretical studies are compared with our recent data and with other recently published data covering a range of parameters that is expected in an LWR accident. An extension of the analysis and the experiments to a mixture of particle sizes is presented. The scaling of the dry out data to high pressures, which may be encountered during the course of an accident, is accomplished by multiplying the experimental bed dryout heat flux by the ratio of dry out flux at pressure to the dryout flux at atmospheric pressure. This ratio was calculated with the theoretical model, which agreed best with the experimental dryout data at atmospheric pressure. Based on the pressures and particle sizes expected in a pressurized water reactor core melt, it is concluded that stable (self-cooled) debris bed formation will occur if sufficient water is available.

 
 
 
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