Modeling And Accident Simulation Of The Primary Circuit System Of One 3rd Generation Nuclear Power Plant Based On RELAP5 Code

At present, Chinese nuclear power has entered into a period of accelerated construction. Most of the nuclear power units under construction and planning are the 3rd generation pressurized water reactors. In the context of the international community, the Chinese government and the social public put forward higher requirements and expectations on the safety of nuclear power plants, to build a credible primary circuit thermodynamic system model, simulate and analyze the transient response of primary circuit thermohydraulic condition under various accidents is an important task in the construction and operation of 3rd generation nuclear power plants.The main content of this research has two parts:(1)In this work, we took “Hualong No.1” as reference, which is so far the only generation 3 nuclear power unit with complete intellectual property rights of our country;used RELAP5 as modeling tool; divided the primary circuit system into four independent function modules: pressure vessel, steam generator, pressurizer,reactor coolant pump;carried out the analysis and calculation of parameters, the simplification and equivalence of the modules; then integrated the modules to the primary circuit system. The results showed that the deviations of the steady-state calculation results and the design parameters of "Hualong No.1" were less than 0.5%, which proved the reliability of the model.(2)Based on the steady state model of primary circuit system, the study established the models of the accumulation injection system,the reactor protection system and the pressurizer overpressure protection system; then simulated three typical accidents by RELAP5: loss-of-coolant-accident, loss-of-flow-accident and loss-of-heat sink-accident. In accident analysis, the deterministic safety basic assumptions were applied. The simulation results of three kinds of accidents were evaluated by the safety acceptance criterions of pressurized water reactor.Based on the results, this study analyzed the situations and reasons of temperature,pressure, mass flow, core void fraction, fuel shell temperature and other parameters changing in various steps of the accidents, reflected the whole thermohydraulic condition of the accidents as possible. From the analysis of the accident process, the following conclusions were drawn : cooling means under high pressure and long-term effectivewater charge means are essential in the small-loss-of-coolant-accident; In the loss-of-flow-accident, the process of the accident is determined by decrease of both of the coolant flow rate and the core power; The consequence of partial loss of flow accident compared to that of total loss of flow accident may be more serious; In the loss-of-heat sink-accident, the system can enter the safe state without operator intervention, and the core structure can maintain the acceptable cooling characteristics under the condition of the steam turbine trip.Steady state model and accident model established in this study showed that RELAP5 is suitable for numerical simulation of the primary circuit thermal system of 3rd generation nuclear power plants. Meanwhile, it provides the basis for full scale modeling and safety analysis of the "Hualong No.1" nuclear power system.