BENCHMARK CALCULATIONS FOR EVALUATION METHODS OF GAS VOLUMETRIC LEAKAGE RATE

A containment function of radioactive materials transport casks is essential for safe transportation to prevent the radioactive materials from being released into environment. Regulations such as lAEA standard determined the limit of radioactivity to be released. Since it is not practical for the leakage tests to measure directly the radioactivity release from a package, a gas volumetric leakage rates are usually measured instead. Methods of evaluating gas volumetric leakage rates are proposed in ANSI N14.5 and ISO standards. In our previous works, gas volumetric leakage rates for several kinds of gas from various leaks were measured and two evaluation methods, \"a simple evaluation method\" and \"a strict evaluation method\", were proposed based on the results. The simple evaluation method considers the friction loss of laminar flow with expansion effect. The strict evaluating method considers an exit loss in addition to the friction loss. In this study, four worked examples were completed for on assumed large spent fuel transport cask (Type B Package) with wet or dry cavity and at three transport conditions; normal transport with intact fuels or failed fuels, and an accident in transport. The standard leakage rates and criteria for two kinds of leak test were calculated for each example by each evaluation method. The followings observations are made based upon the calculations and evaluations: • The choked flow model of ANSI method greatly overestimates the criteria for tests. • The laminar flow models of both ANSI and ISO methods slightly overestimate the criteria for tests • The above two results are within the design margin for ordinary transport condition and all methods are useful for the evaluation. • For severe condition such as failed fuel transportation, it should pay attention to apply a choked flow model of ANSI method.