Thermal hydraulic aspects of an unconventional liquid-metal reactor

The Trench Reactor (TR) is a liquid sodium cooled fast power reactor. The reactor core is fueled with U-Pu-Zr metal fuel and generates 800 MW of thermal power. The core is located in a sodium pool which is contained in a thin and deep rectangular vessel. Also located in the pool are the two intermediate heat exchangers (IHX) and the two primary pumps. The liquid sodium exists the core at 485 degree C and is pumped through the IHXs where it is cooled to 343 degree C and enters the core through an inlet plenum. The reactor building atmosphere is nitrogen which circulates through the guard tank and reactor vessel. The secondary sodium enters the IHXs at 294 degree C and exits at 465 degree C. It then is used to generate steam at 425 degree C and 15 MPa. The electric power output of the plant is 300 MWe. TR has the advantages of a small plant. The current technology can be applied to build the main components of the reactor system. The initial margins to failure are large and the failure mechanisms are slow. The use of metal fuel and the large sodium pool enhance the safety of the reactor. The major design changes introduced are the elimination of heat capacity effects associated with the core inlet temperature and the rectangular shape of the reactor vessel and the core. The former helped to improve the response of the TR to a wide range of accidents by enabling the effects of core inlet temperature changes to be felt early in the transients. The latter resulted in a simpler core design and control. The TR response to unprotected loss of heat sink, loss of flow, positive reactivity insertion and overcooling accidents is favorable