Shielding Designs for Pressurized Water Reactors in France

Abstract

The efforts made by Electricité de France to reduce exposure from the two-component neutrongamma radiation fields inside the pressurized water reactor (PWR) building are described. Most of the attention has been focused on the problem of neutron exposure relative to the problem of achieving a highly efficient confinement within the reactor cavity and the state of the art of personnel neutron dosimetry. A description of the general neutron calculation scheme that links the characteristics of the neutron fields escaping from the reactor vessel to the dose equivalent rate cartographies inside the reactor building is provided. Numerous measurements have been carried out to check the reference radiation sources involved in the calculation scheme and its predictions, increasing confidence in the calculational results. During the design of neutron shielding, it is necessary to take into account many requirements, particularly those of accessibility, safety, and normal operation. Some shielding materials commonly used on French PWRs are presented. The emphasis placed on the evolution of shieldings designed to prevent irradiation through the three main weaknesses of the primary concrete shield (access pit, primary bunkers, and refueling pool bottom) shows that they should become increasingly sophisticated. A comparison between the former shielding designs for three-loop PWRs and the latter for four-loop PWRs is made for this purpose.