Feasibility study of a gas cartridge loop for the versatile test reactor

Abstract

A feasibility study of a Gas Cartridge Loop (GCL) for the Versatile Test Reactor (VTR) was carried out to determine the performance requirements of major components and evaluate the performance during normal operation and transient conditions. The major components consist of a circulator/motor, a heater, a test article, a flow guide and a pressure vessel. The pressure vessel incorporates a pressurized, flowing helium loop with capability to test heat-producing test articles up to a 200 mm length of Energy Multiplier Module (EM2) fuel rod at a linear heat rate of 55 kW/m. The heat is rejected to VTR primary coolant sodium flowing along the outside of the GCL pressure vessel. For the baseline design, the helium temperatures at the test article inlet and outlet are 650 °C and 850 °C, respectively, when the mass flow is ~0.01 kg/s. The circulator inlet temperature is 362 °C and the motor power is 11.9 W. An electric heater power is 15.8 kW which is required to maintain the inlet temperature of the test article. Under the normal operating condition, the estimated fuel and cladding temperatures are 1233–1610 °C and 917–1219 °C, respectively.The controllability of the GCL was evaluated for the operational transients during a single fuel cycle by maneuvering either the motor or heater power to keep the test article outlet temperature at 850 °C. For an estimated perturbation of the test article power by ±3.5%, the required motor or heater power variations are ± 4.1% or ± 2.4%, respectively. The safety feature of the GCL was evaluated for the postulated accidents initiated by the VTR and GCL itself under the assumption that the helium flow is pseudo-steady. For the reactivity-initiated accident (RIA) like transient overpower (TOP) of the VTR, the simulation predicted that the margin to fuel melting is 24% and 5% for the protected and unprotected TOP, respectively. For GCL-initiating accidents, the simulation predicted the fuel reaches its melting point when the system loses mass flow by 52% with the nominal heater power or when the system pressure drops by 56% with the nominal motor and heater power level. For both the loss-of-flow and loss-of-pressure cases, the system shall terminate the heater and fission reaction at pre-determined set points. For the loss-of-power case, the GCL requires coastdown capability of the motor for at least several seconds to avoid the test article failure due to fuel melting.