Study on shortening vacuum drying time by heating with external heater

Before transport or storage of spent fuel by transport/storage cask, it is necessary to dry the cask cavity. Vacuum drying is one of the methods to dry. The vacuum drying equipment developed by OCL can be designed to reduce residual moisture below limit in helium filling state by continuous 8 hours operation, as long as the residual water after drainage can be kept at approximately 50°C or more. However, when the quantity of decay heat of the spent fuel is low or the initial temperature of the cask is low, the supply of latent heat necessary for evaporation of residual water is insufficient. Therefore the preparation time is prolonged. In order to improve this, it is necessary to continuously supply heat to the residual water and its surroundings. And as one of the means, we propose heating from the outside of the cask by the additional heating device. In consideration of devise handling, cask safety, and efficient supply heat to the residual water, we designed the external heater (see fig.1). And we conducted thermal analysis with the quantity of decay heat of the spent fuel and the initial temperature of the cask as parameters. As a result, it is expected that by using the external heater, it is possible to drastically shorten the preparation time.