Limiting conditions for structural integrity of components under fast breeder reactor core environment

Limit analyses of structures generally focus upon the influence of a uniquely defined loading condition or set of conditions upon the integrity of the structure. Components of a fast breeder reactor core may reach the limits of their structural integrity during normal reactor operation as a result of experiencing loads which may be significantly lower than the limit loads obtained from limit analyses. The primary reasons for this are (i) the change in the material properties as a function of fast neutron irradiation; (ii) structural deformations resulting from irradiation-induced creep and swelling, and (iii) residual stresses set up in a component as a result of interaction with adjacent structure undergoing differential deformations. The present study focuses upon the influence of the fast breeder reactor core environment on the resultant useful service life and load carrying capability of core components of Experimental Breeder Reactor II (EBR-II). Specific examples selected are: (i) the dynamic response of a single hexagonal subassembly can to a potential pressure pulse resulting from a failed fuel element cladding; (ii) interaction between a fuel element cluster and its surrounding subassembly can; (iii) the interaction between adjacent subassemblies, and (iv) the influence of swelling and pressure induced stresses on the grid plenum assembly. Results of core surveillance efforts, experimental investigations, and analyses completed to date by several EBR-II investigators are presented. The study demonstrates the significance of fast breeder reactor core operating conditions in determining the safe limiting conditions for core structural components