Thermal and structural analysis of the support region of an LMFBR reactor vessel

The stainless steel reactor vessel of a Pool-Type LMFBR is suspended from an extension of the carbon steel deck structure through a bimetallic weld. Maximum deck temperature is 1250F (520C) while the temperature of the vessel at the sodium level is about 7000F (3710C). The thermal stresses resulting from this temperature difference, for various assumptions of vessel thermal insulation characteristics, were investigated. Steady-state vessel temperature distributions were calculated for several assumed values of the thermal insulation conductivities. The shape of the outside vessel insulation was varied to achieve an approximately linear temperature gradient in the vessel. Other conditions investigated included the effect of natural convection cooling in the top 3 feet (0.9 m) section of the vessel, and complete removal of the outside vessel insulation. The effect of raising the sodium level above the nominal 3 feet (0.9 m) and attaching the vessel at a lower elevation was also investigated. Calculated thermal stresses were combined with primary stresses resulting from deadweight and operating basis earthquake seismic loads. Results show that the proposed reactor support design appears feasible from a thermal and structural point of view. (orig.)