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首页> 美国政府科技报告 >An Assessment of Fuel Melting, Radial Extrusion, and Cladding Thermal Failure during a Power-Cooling-Mismatch Event in Light Water Reactors
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An Assessment of Fuel Melting, Radial Extrusion, and Cladding Thermal Failure during a Power-Cooling-Mismatch Event in Light Water Reactors

机译：轻水反应堆功率冷却失配事件中燃料熔化，径向挤压和包层热失效的评估

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Fuel conditions during a hypothesized power-cooling-mismatch (PCM) accident in LWRs are characterized with regard to pellet cracking and fuel melting. Melting of UO2 fuel at the center of the pellet during a PCM accident in which film boiling is present at the cladding surface, is assessed by employing a simplified steady state analysis. The induced pressure at the center of the pellet due to fuel melting fission gas release, and UO2 fuel vapor may force molten fuel to penetrate through radially open cracks in the outer unmelted portion of the pellet and relocate in the fuel-cladding gap. The contact of molten fuel with zircaloy cladding, which is at high temperatures during film boiling, may initiate cladding melting at its inside surface and eventually result in a thermal failure of the cladding. An analytical model is developed to study the transient freezing of a superheated liquid penetrating an initially empty crack, maintained at a constant, subfreezing temperature. The analysis is presented in a dimensionless form, demonstrating the effect of the governing parameters; namely, the driving pressure, crack shape, crack length, liquid flow conditions, thermophysical properties, and the temperature of the liquid and the crack walls. The calculational results are applied to the radial extrusion of molten UO2 fuel, observed in some in-pile tests in which PCM conditions were simulated. Conditions for potential melting of the zircaloy cladding upon being contacted by the extruded molten fuel are investigated analytically. The analytical predictions are consistent with the experimental results from PCM in-pile tests.

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