Experimental and analytical studies of the K-reactor moderator flow patterns and neutron poison distribution

Effects of buoyancy forces and transient flow conditions on injected neutron poison [Gadolinium poison solution (GPSI)] is of interest in the safety analysis of the K reactor following a loss-of-alternating-current-power transient. During this scenario, the safety and control rods are assumed to fail, with reactor shutdown accomplished by injection of GPS. In the reactor, the radial pressure drop is sufficiently larger than the vertical pressure drop to create an up and over moderator flow pattern. At shutdown the fuel assemblies effluent temperatures decrease (in response to the power decrease) to a value approaching the reactor inlet temperature. This decrease in exit temperatures, may affect the normal moderator flow patterns due to thermal stratification from buoyancy forces. To validate the code, individual and integrated thermal stratification and transient flow tests were conducted at the Idaho National Engineering Laboratory (INEL).