Numerical Simulation of Water Temperature in a Spent Fuel Pit during the Shutdown of Its Cooling Systems

概要

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In order to evaluate the heat loss and water temperature in a spent fuel pit (SFP) after the shutdown of its cooling systems, three dimensional thermal hydraulic behavior was calculated using the CFD software, FLUENT 6.3.26. In the calculations, the decay heat calculated by using the burn-up calculation software, ORIGEN 2.2, and the previously proposed correlation for evaporation heat fluxes from the water surface to air flow were used. Water temperatures were almost uniform in the SFP, and this indicated that one-regional calculation model might be able to obtain an average water temperature accurately. Comparisons of calculated results with measured temperatures showed that ORIGEN 2.2 gave good prediction of the decay heat for fuel assemblies with large decay heat which had been taken relatively recently from the shutdown reactor core. But ORIGEN 2.2 overestimated for longtime cooled fuel assemblies with small decay heat. The previously proposed evaporation heat flux correlation overestimated the temperature increasing rate of the SFP water.