ANALYSIS OF STRESSES AND DEFLECTIONS IN TOP SUPPORT GRID, PWR REACTOR. Final Report

The top grid of the PWR reactor core assembly is treated as a simply supported circular plate. The theory of plate is applied to the grid umder mechanical loads. The thermal stress problem is analyzed by treating the plate as under combined action of a laterally distributed load and forces in the middle plane of the plate. The load distribution is calculated from the temperature variation over the grid. The thermal stress problem then is equivalent to two problems: one, of bendimg of plate; and, the other, a plane stress problem. The theoretical formulation for plates under nonuniform heating is developed by neglecting the effect of uneven expansion in the direction perpendicular to the plane of the plate. In replacing the partial dffferential equations by difference equations, the latter are modified to take into account the change in tbickmess and spacing of the grid webs near the boundary. Twentythree difference equations for the twenty-three stations in one octant of the grid are obtained for each second order partial differential equation. The difference equations are solved by assuming that the twisting moments and shearing stresses in the plane of the grid vanish at the boundary. The stresses and deflections due to mechanical loads and thermal expansion are then superposed. (auth)