Control-rod, Pressure and Flow-Induced Accident and Transient Analyses of a Direct-Cycle, Supercritical-Pressure, Light-Water-Cooled Fast Breeder Reactor

摘要

The features of the direct-cycle, supercritical-pressure. light-water-cooled fast breeder reactor (SCFBR) are high thermal efficiency and simple reactor system. The safety principle is basically the same as that of an LWR since it is a water-cooled reactor. "Maintaining the core flow" is the basic safety requirement of the reactor, since its coolant system is the one through type. The transient behaviors at control rod. pressure and flow-induced abnormalities are analyzed and presented in this paper. The results of flow-induced transients of SCFBR were reported at ICONE-3, though pressure change was neglected. The computer code has been improved to handle the pressure change inducing the pressure regulation system using the turbine control valve. The change of fuel temperature distribution is also considered for the analysis of the rapid reactivity-induced transients such as control rod withdrawal. Total loss of flow and pump seizure are analyzed as the accidents. Loss of load (with and without opening turbine by-pass valves), control-rod withdrawal from the normal operation, loss of feedwater heating, inadvertent start of an auxiliary feedwater pump, partial loss of coolant flow and loss of external power are analyzed as the transients. The behavior of the flow-induced transients is not so much different from the analyses assuming constant pressure. Fly wheels should be equipped with the feedwater pumps to prolong the coast-down time more than 10s and to cope with the total loss of flow accident. The coolant density coefficient of the SCFBR is less than one tenth of a BWR in which the recirculation flow is used for the power control. The over pressurization transients at the loss of load is not so severe as that of a BWR. The power reaches 120%. The minimum deterioration heat flux ratio (MDHFR) and the maximum pressure are sufficiently lower than the criteria; MDHFR above 1.0 and pressure ratio below 1.10 of 27.5MPa, maximum pressure for operation. Among the reactivity abnormalities, the control rod withdrawal transient from the normal operation is analyzed. The maximum fuel enthalpy is 104.9cal/g and the smallest MDHFR is 1.66 which are sufficiently lower than the criteria; fuel enthalpy below 170cal/g and the MDHFR above 1.0. In conclusion, all the transients and accidents satisfy the safety criteria.