Radiation damage to the permanent and semi-permanent structures of the commercial fast reactor

The design of the fast reactor is affected by the need to reduce the radiation damage in the structures near the core which it is not intended to replace on a routine basis. High levels of irradiation cause degradation in material properties and also swelling and the irradiation dose must be kept low enough to ensure that the structures can perform their functions for the whole of the reactor life (30 years). In the CDFR the design is such that all the highly irradiated regions such as the sub-assemblies, leaning posts etc, are replaced on a routine basis. The surrounding regions such as the above core structures, core restraint system, and core support of sub-assembly carrier and diagrid cannot easily be designed to be replaceable and so shielding must be put between the core and these components to reduce the damage rates to tolerable levels. This paper discusses the choice of materials to be used as shielding from the point of view of ease of use and effectiveness, and what form the shielding should take. An example of a calculation to find the damage rate on the sub-assembly carrier and diagrid is described. (author)