Rejets en mer des eaux résiduaires faiblemhent radioactives du centre de la Hague

Chef du Bureau Recherches et Développement au C.E.A., Centre de La Hague.

Résumé

The construction of a large chemical treatment plant for radioactive Electricité de France reactor fuel has brought with in an effluent disposal problem, for which the possibility of disposal of slightly radioactive decontaminated effluent at sea has been investigated in the absence of a big river carrying a regular flow. The attractive feature about the selected dumping area off Cap de la Hague is its powerful Raz Blanchard current which it was thought could be relied on to rapidly disperse the radioactive elements within a very substantial body of sea water. The project authorities considered it desirable to aim at minimum possible specific sea water contamination in the immediate vicinity of the disposal channel outlet. This meant studying contaminated water movements and establishing the safety margin attached to the scheme by tracing the radioactive effluent's route back to Man and calculating likely radiation therefrom. This safety margin was found to be very high. A further purpose of the preliminary studies was to deterrnine the optimum site for the channel outlet and appropriate times at which to discharge the effluent (3 hours during each tide.) The disposal duct runs overland for a short distance, followed by an underwater run 5,500 m in length. Technical design and pipe-laying problems have all been solved, especially as associated with the altitude of the Centre, the ground features and the strong local sea currents. Despite all the difficulties encountered, the undersea duct was laid in six months. An original experiment with dye designed to simulate normal operating conditions during a fortnight was carried out as a check on the accumulation possibilities observed on the model. Thus, the general problem was dealt with by alternating model and real-life tests, which seemed to be the only way to do the job in view of the very numerous parameters on which dispersion depends in this region. The experimental data were found to agree very closely with the initial data observed in real life, Careful systematic supervision of the area is ensuring that contamination of the sea water within the limits laid down by the local authorities (which are based on the preliminary studies carried out on site) does not endanger human life, i.e.that it is well within the limits specified by the International Commission for Protection against Radiation.