Study On The Method Of Source Term Assessment Based On Monitoring Data Of NPPs

In the case of a severe accident at a nuclear power plant with the containment failure,a large amount of radioactive fission products will release into the environment,causing serious harm to society,humans and the environment.Therefore,determining the source term under severe accidents can provide data support for severe accident management and off-site radioactive transport.At present,there are two methods for calculating the accident source term.One is integrated severe accident code,and the other is parameter source term,but each of them is a kind of prediction for the accidents that haven’t happened using known parameter such as the plant module or power.In an actual accident,there will be a series of real-time monitoring data in the nuclear power plant to characterize the state of the core or containment.If these monitoring data are combined with existing source term calculation methods,it will provide a novel post-accident way to get source term.In this paper,a 600 MW PWR is selected as the research NPP.Based on the monitoring data of the nuclear power plant in a severe accident,the source term is calculated by combining the integrated severe accident analysis program MELCOR and the core damage assessment method.First of all,use MELCOR to establish a CNP600 severe accident analysis model,then write an interface program to achieve an integrated code source term evaluation based on the monitoring data of the power plant;And use the core outlet thermocouple temperature,containment monitor reading,water level of the vessel,and containment hydrogen concentration for evaluating the core damage phase.Finally,the accident source term will be calculated based on NUREG-1465 report,which defines the relationship of release phase and fraction of core activity inventory in PWR.The results show that the interface program of monitoring data and MELCOR achieve the joint calculation of the monitoring data of the nuclear power plant and the MELCOR code.The monitoring data has played a role in the calculation of the severe accident process and the source term.These monitoring data include the core hot-leg temperature,the reactor vessel level,core outlet thermocouple temperature;the source term based on the core outlet thermocouple temperature,the containment monitor reading,the reactor vessel level,and the containment hydrogen concentration are more conservative than the MELCOR calculation results,and the calculation process is more faster which can provide a reference for emergency response in the event of a nuclear power plant accident.