Loss Of Heat Sink Accident Research Articles

ICONE15-10397 ANALYTICAL EVALUATION OF REACTOR COOLABILITY FOR SODIUM COOLED SMALL FAST REACTOR (4S) : Investigation of RVACS Performance under Loss of Stacks Condition

The 4S (Super-Safe, Small and Simple) reactor is a sodium-cooled fast reactor aiming at an application to dispersed energy source and multi-purpose use. Its electrical output is 10MW or 50MW and the core lifetime can be varied from 10 to 30 years without refueling. An introduction of RVACS (Reactor Vessel Auxiliary Cooling System) can enhance the passive decay heat removal capability. In the present study, the RVACS performance in 4S reactor (10MWe, pool-type) was analytically evaluated under the functional loss of RVACS stack condition, which is considered as a beyond design basis event. A protected loss of heat sink accident was selected and simulated to evaluate the capability of RVACS to cool the plant under such an unusual condition. The three-dimensional thermal hydraulic analysis was conducted by PHOENICS code. Analytical results show that the functional loss of air outlet stack has more effect on RVACS performance than that of air inlet stack. The air flow rate in RVACS under the functional loss of one out of two outlet stacks decreases up to approximately 60% and the heat removal rate approximately 70%, comparing with those under the normal stack condition. However, the maximum hot plenum temperature is low enough to satisfy the safety criteria.

Large Passive Pressure Tube Light Water Reactor with Voided Calandria

A reactor concept has been developed that can survive loss-of-coolant accidents (LOCAs) without scram and without replenishing primary coolant inventory while maintaining safe temperature limits on the fuel and pressure tube. The proposed concept is a pressure tube reactor of similar design to Canada deuterium uranium reactors but differing in three key aspects. First, a solid silicon carbide-coated graphite fuel matrix is used in place of fuel pin bundles to enable the dissipation of decay heat from the fuel in the absence of primary coolant. Second, the heavy water coolant in the pressure tubes is replaced by light water, which also serves as the moderator. Finally, the calandria tank, surrounded by a graphite reflector, contains a low-pressure gas instead of heavy water moderator, and this normally voided calandria is connected to a light water heat sink. The cover gas displaces the light water from the calandria during normal operation while during a LOCA or loss of heat sink accident, it allows passive calandria flooding. Calandria flooding also provides redundant and diverse reactor shutdown. The fuel elements can operate under post-critical-heat-flux conditions even at full power without exceeding fuel design limits. The heterogeneous arrangement of the fuel and moderator ensures amore » negative void coefficient under all circumstances. Although light water is used as both coolant and moderator, the reactor exhibits a high degree of neutron thermalization and a large prompt neutron lifetime, similar to D{sub 2}O-moderated cores. Moreover, the extremely large neutron migration length results in a strongly coupled core with a flat thermal flux profile and inherent stability against xenon spatial oscillations.« less