PHYSICS CHARACTERISTICS OF A LARGE, PASSIVE, PRESSURE TUBE LIGHT-WATER REACTOR WITH VOIDED CALANDRIA

A light water cooled and moderated pressure tube reactor concept has b een developed that can survive loss-of-coolant accidents (LOCAs) witho ut scram and without replenishing primary coolant inventory, while mai ntaining safe temperature limits on the fuel and pressure tube. The re actor employs a solid SiC-coated graphite fuel matrix in the pressure tubes and a calandria tank containing a low-pressure gas, surrounded b y a graphite reflector. This normally voided calandria is connected to a light water heat sink. The cover gas displaces light water from the calandria during normal operation, white during LOCAs it allows passi ve calandria flooding. It is shown that such a system, with high void fraction in the core region, exhibits a high degree of neutron thermal ization and a large prompt neutron lifetime, similar to D2O moderated cores, although light water is used as both coolant and moderator. Mor eover, the extremely large neutron migration length results in a stron gly coupled core with a flat thermal flux profile and inherent stabili ty against xenon spatial oscillations. The heterogeneous arrangement o f the fuel and moderator ensures a negative void coefficient under all circumstances. Flooding of the calandria space with light water resul ts in redundant reactor shutdown. Use of particle fuel allows attainme nt of high burnups.