ASSESSMENT OF THE CONSEQUENCES OF ACCIDENTAL BURIAL INTO SOFT GROUND OF A SPENT FUEL TRANSPORT CONTAINER

When it is accidentally buried into soft ground, a spent fuel package can lose its heat dissipation capability, as a result of the gradual drying of the ground into which it is buried. Overheating of sensitive components can result, notably those which contain the radioactivity. The study focused on the transport of spent fuel by rail in France, taking into account derailment causing a package to fall into a marshy area. The probability of a derailment, causing a package to fall into a marsh is low but not negligible and therefore, in accordance with the safety principles applied to nuclear activities (the concept of defence in depth)\", a deterministic study was carried out under upper bound conditions. The results of thermal calculations indicate that partial sinking into this marsh, of less than half the package, will not induce overheating of the sensitive components and has no noteworthy effect on safety. Thus, action to extract the package, even if protracted, could take place without the use of special cooling facilities. If, on the other hand, the package sinks completely, it may be necessary to introduce some means of emergency cooling, within a period of not more than two days. Studies are in progress to illustrate that the necessary means can be deployed within this time. A study of this accident scenario effectively illustrates that the safe transport of radioactive materials depends on the following three factors: - reliable transport systems, which reduces the probability of accidents, -the design margins of the packages, which allow sufficient response time, - the effectiveness and rapidity of the response.