EXPERIMENTS TO QUANTIFY POTENTIAL RELEASES AND CONSEQUENCES FROM SABOTAGE ATTACK ON SPENT FUEL CASKS

On behalf of the German Federal Ministry of Environment, Nature Conservation and Nuclear Safety (BMU) an experimental program was performed in 1992 to quantify the potential release from a CASTOR type spent fuel cask following attack by a conical shaped charge. Salient features of these experiments were: · a very close approximation of real conditions by using a cask which was in all essential aspects identical to a real CASTOR cask; · the cask was loaded with 9 fuel elements filled with depleted uranium pellets as surrogate material instead of irradiated spent fuel; the fuel elements being internally pressurised to simulate conditions after burn-up; · the airborne release of material through the penetration channel of the shaped charge jet was retained in an aerosol chamber and directly analysed by applying a specially developed in-situ classification with respect to the amount and aerodynamic particle size distribution of the ejected dust up to an aerodynamic diameter of 100 mm. The main features and results of the experiments will be reviewed. The transfer of the results obtained with depleted UO2 as surrogate material to the conditions of a cask with spent fuel is discussed. On this basis potential airborne releases of radioactive material can be estimated for a real spent fuel cask and resulting radiation exposures be calculated. An advanced atmospheric dispersion model in connection with statistical data on atmospheric dispersion conditions is applied to derive probability distributions of ground-level air concentration, depositions levels and resulting potential radiation exposures of persons.