An Experimental Investigation of Thermal Stratification in Water-Filled Flasks

Transport flasks are often filled with water as it provides both good cooling and shielding for irradiated fuel. However, during a fire, thermal stratification may occur, potentially leading to significant pressurisation of the flask from the vapour pressure of the water. A series of 12 experimental tests into thermal stratification have been carried out, based upon the NEACRP thermal benchmark problem UK-4. The results show that under the conditions of the test, with the dry vessel walls above the water being heated, strong thermal stratification occurs and high internal pressures are generated. The vapour pressure inside the vessel is demonstrated to be related to the temperature of the water surface. The agreement with the calculated results of the benchmark problem is reasonably good, demonstrating that the methods used in the benchmark exercise can be used to adequately model thermal stratification in water-filled flasks.