Abstract
A key issue contributing to the success of NPP technology is the safe handling of radioactive waste, particularly spent nuclear fuel. According to the IAEA safety standard, the spent fuel must be stored in interim wet storage for several years so the radiation and the decay heat of the spent fuel will decrease to the safe limit values, after which the spent fuel can be moved to dry storage. In this study, we performed a theoretical analysis of heat removal by natural convection airflow in spent nuclear fuel dry storage. The temperature difference between the air inside and outside dry storage produces an air density difference. The air density difference causes a pressure difference, which then generates natural airflow. The result of the theoretical analysis was validated with simulation software and experimental investigation using a reduced-scale dry storage prototype. The dry storage prototype consisted of a dry cask body and two canisters stacked to store materials testing reactor (MTR) spent fuel, which generates decay heat. The cask body had four air inlet vents on the bottom and four air outlet vents at the top. To simulate the decay heat from the spent fuel in the two canisters, the canisters were wrapped with an electric wire heater that was connected to a voltage regulator to adjust the heat power. The theoretical analysis results of this study are relatively consistent with the experimental results, with the mean relative deviation (MRD) values for the prediction of air velocity, the heat rate using natural airflow, and the heat rate using the thermal resistance network equation are +0.76, −23.69, and −29.54%, respectively.
Highlights
Introduction iationsA central issue of the nuclear power plant (NPP) program is the generation of radioactive waste
The temperature measurement was taken at several points on the outer surface of the canister, in the air gap, in the outlet vents, and in the airconditioned laboratory room where thethe dry storage prototype was placed
The differences between the predicted and experimental values of air velocity in the air gap, the heat rate using the natural airflow equation, and the heat rate using thermal network resistance were relatively good (MRD = +0.76, −23.69, and −29.54%, respectively). These two negative mean relative deviation (MRD) values are quite high because the calculations carried out on these two values used several measurement data, each of which has uncertainties
Summary
Introduction iationsA central issue of the nuclear power plant (NPP) program is the generation of radioactive waste. The safe handling and management of radioactive waste is very important. The most high-risk and dangerous radioactive waste is spent nuclear fuel because of the risk of a self-sustaining chain reaction (criticality), the very high radioactivity, and the high decay heat. There are several studies on the handling and storage of spent fuel [1,2,3,4,5,6,7,8,9,10]. After remaining in interim wet storage for more than 4 years, spent fuel can be moved to dry cask storage. An important research topic related to spent fuel dry storage is the removal of spent fuel decay heat. The dry storage must be designed in such a way that an optimal heat flow is obtained so the temperature of the spent fuel in dry storage does not exceed the Licensee MDPI, Basel, Switzerland
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