Research On Group Operation Mode Of Once-through Steam Generator

The inherent safety systems employed in new designed integral pressurized water reactor(IPWR) can satisfy the inherent safety demand due to the compact configuration, small size andlight weight. Hence, they can particular used in small-scale nuclear power plants and marinenuclear power systems. Casing once-through steam generators, which are generally used inIPWR, are suitable for nuclear power plants because of their simple structure, strong heattransfer capability and fast load tracking ability. However,intense phase-change processusuallyexists in heat transfer tubes of once-through steam generator,especially in start-up, shutdownand low-load operation conditions when the reactor power load changes quickly. Furthermore,the flow rate of feed water in once-through steam generator is small and single-phase regions ofonce-through steam generator tube is short, which will results in many kinds of two-phase flowinstability.When IPWR operates at low load conditions, less steam will be generated. Meantime,OTSG also operates under low load conditions and flow instability will exist in the tubes,which affects the operation safety, so we should take measure to avoid flow instability.In this paper, self-designed integrated reactor IP200is used as the model. Relap5is used toset up the model and conduct simulation. Based on the above, factors and initial load affectingflow instability in IPWR is discussed. Moreover, group operation mode of OTSG based on theideal steady-state programming, which can effectively avoid flow instability and ensure stableoperation at low load conditions is proposed. At the same time, RELAP5/MOD3.4is coupledwith ANSYS, in which temperature from RELAP5/MOD3.4is applied in finite elementanalysis module of ANSYS which calculates the thermal stress.After comparing the two kindsof results which satisfy the requirements of thermal stress for pipes and stable operation rangeto avoid flow instability, the group operation mode is modified. In the end, according to thecharacteristics of natural circulation, a completely set of design parameters and operationscheme which can ensure IPWR stable operation at low load conditions is proposed.