Research On The Reflooding Heat Transfer Model For Reactor Loss Of Coolant Accident In COSINE Software

Energy is the foundation of national development and plays an irreplaceable role.Nuclear energy,as a clean energy source with good economic benefits and strong stability,has been widely used in developed countries such as the United States,France,Japan,etc.China is also actively developing the nuclear power industry.In the process of vigorously developing nuclear power,nuclear safety is of utmost importance.In order to ensure nuclear safety,an excellent nuclear power safety design and thermal hydraulic analysis program are crucial.COSINE is the first thermal hydraulic software in China that fully possesses independent intellectual property rights.Large break LOCA is a typical pressurized water reactor design basis accident and also the most serious hypothetical reactor accident.It plays a very important role in the reactor safety analysis.The re flooding stage is an important stage in the LOCA to derive the core residual heat and ensure the core safety,which has important research significance.Therefore,this project analyzed and validated the cosSyst reflooding heat transfer model of the COSINE software package hydraulic system program,and explored the influence of parameters such as flow rate,pressure,and power on re submergence heat transfer.This article selects multiple experimental conditions from the FLECHT SEASET experiment and the FEBA experiment,and applies the cosSyst program’s optimal estimation model and conservative model for modeling and calculation.Through sensitivity analysis,appropriate control volume numbers and time steps are selected.Taking into account the comprehensive consideration of the two experiments,24 node axial node modeling and 40 node axial node modeling are used for subsequent reflooding calculation verification.The time steps are determined as the minimum time step size of 10^-5 and the maximum time step size of 10^-3.The calculation results of the cosSyst program’s optimal estimation model are in good agreement with experimental data,proving the rationality of the cosSyst program’s optimal estimation model.The conservative model calculation results of the cosSyst program show a higher peak temperature compared to experimental data,and the position of the quenching front lags behind,which effectively proves the conservatism of the cosSyst program conservative model.And the most widely used thermal hydraulic system program RELAP5 was selected as a comparison,and the calculation results were analyzed and compared with the cosSyst program.The calculation results showed that the cosSyst program and RELAP5 calculation trends were consistent,and the results were in good agreement.This article uses the cosSyst program to model and calculate the optimal estimation model,and explores the influence of parameters such as coolant inlet flow rate,system pressure,initial shell temperature,and heating rod power on the re flooding process.The results indicate that an increase in coolant inlet flow rate will increase the advance rate of the quenching front and reduce the achievable peak temperature.The increase in pressure will increase the advance rate of the quenching front,but it has almost no effect on the peak temperature that the heating rod can reach.Moreover,as the pressure increases,the sensitivity of the heating rod cladding temperature to pressure decreases.An increase in coolant temperature will reduce the advance rate of the quenching front and lower the peak temperature reached by the heating rod.As the initial temperature of the heating rod cladding increases,the advancing rate of the quenching front will decrease but the change is not significant,and the maximum temperature rise of the heating rod will decrease.An increase in the power of the heating rod will reduce the advancing rate of the quenching front and increase the peak temperature that the heating rod can reach.