Auswirkungen des Strukturmaterialschwellens auf den Entwurf Schneller Reaktorkerne

Abstract

The concept of “radial core constraint” is described in the light of a survey of the changes in structural materials expected in a high fast-neutron flux environment together with the attendent problems arising for sodium-cooled fast breeder reactors. This formulation results in the construction concept of “plane of radial constraint” whose characteristics are outlined in some detail. As a result of these ideas, reactor-core design criteria are deduced for the core constraint principle. Some simplifications and assumptions for design and optimization calculations are briefly explained and the most important results are indicated. This is followed by suggestions for the design and construction of the core restraint. Because of radiation induced swelling and creeping of structural materials, no supporting structures must be located in the region of high neutron fluxes. This, together with the primary requirement of negative reactivity coefficients of thermal fuel element bowing and following the required minimization of stresses on materials, results in the establishment of two planes of radial core constraint above the reactor core proper. It is suggested that the fuel element boxes should be reinforced against tranverse pressure loads in the planes of radial constraint and should be made flexible against pressure loads acting from all sides. The decisive influénce of the very high friction coefficients in sodium will be removed changing to rolling friction. These measures make the planes of radial constraint calculable. Moreover, low-pressure hydraulic elements (sodium) can be used for outer core restraint which, just as the fuel elements proper, can be exchanged.