SEAWATER CORROSION OF RADIOACTIVE MATERIAL TRANSPORT PACKAGES

The transport of radioactive materials by sea is estimated to 255 shipments on average each year in France. To these movements may be associated the risk of immersion of a ship's cargo by accident. In this case, the packages of radioactive materials immersed in this way can lie at different depths and suffer seawater corrosion. This study estimates in a conservative manner the minimum time for the loss. due to corrosion. of watertightness or strength of the constituents of the packages. The recovery of packages immersed may thus be organised and carried out in satisfactory conditions, as regards contamination problems, if within this minimum time. The most toxic radioactive materials likely to be involved include : PuO,, high-activity vitrified waste, UF6 and irradiated fuel. The types of packaging studied, are those most frequently used for the maritime transport of the materials dispatched or received by France. Seawater is a particularly aggressive environment for the majority of metallic materials which constitute these packages and their immersion in a marine environment can set up strong galvanic interaction between the different materials, which accelerates corrosion. Two types of phenomena can be identified : • phenomena of generalised corrosion, which are slow-acting and involve the overall weakening of the structure, culminating in large leaks and contamination, either in solution or in suspension, • phenomena of localised corrosion, quick-acting but not accompanied by loss of strength, and culminating in a large number of minor leaks and thus the rapid entry of water, but without any serious transfer outside of the package. The dispersed contamination should thus be low. Three phases may thus be defined : • a destruction phase : at the end of this phase, destruction of the package caused by generalised corrosion will occur, implying the probable ejection of the materials, • a shorter, penetration phase : at the end of this phase, penetration of water caused by localised corrosion of the structure of package will probably occur, • a phase of loss of watertightness, also shorter : at the end of this phase, a loss of watertightness caused by localised corrosion of the sealing surfaces will occur