Stress analysis of a nuclear reactor grid plenum assembly and its application to the EBR-II

A structural model is presented to predict the stress and deformation of a nuclear reactor grid plenum assembly. The model consists of two circular grid plates on top of one another which are interconnected by a large number of tubes, a perforated cylindrical shell and a cylinder at the outer edge of the plates. During normal reactor operation and shutdown the grid plenum assembly is subjected to both external and internal loads, in which the external load is due to the dead weight of the subassemblies resting on the upper grid plate and the coolant pressure, while the internal load is due to the temperature gradient and irradiation swelling in the grid plates accumulated through the life of the reactor. The structure is divided into many annular regions implying an axisymmetric treatment. The solution of the structural system is obtained by solving the equilibrium equations of the individual tubes, plates and shells, and satisfying the compatability condition at the boundary of each region. The swelling strain in the grid plates is treated analogously to that of thermal strain in the elastic region. The numerical results of the problem are obtained by means of a computer code which uses a matrix-inversion technique to solve the simultaneous algebraic equations involved. (Auth.)