Transport Simulation Study On ¹³N And ¹⁸F In Nuclear Containment

Pressure boundary leakage monitoring of nuclear power plant primary circuit is the core component of nuclear power plant containment monitoring,which is related to the safe operation of nuclear power plant.The ¹³N or ¹⁸F isotope can be used as a leak tracer to monitor the leakage of high temperature and high pressure water in the primary circuit.However,the specific transport diffusion and concentration distribution of ¹³N or ¹⁸F in the containment are relatively vague in the actual use process.At the same time,the existing radiation monitors cannot give the leakage point information.Therefore,it is a great significance to study the transport and concentration distribution law of ¹³N or ¹⁸F in the containment for ¹³N or ¹⁸F monitors that which can provide information about the leakage point to play the role of primary radiation monitoring better.In this paper,numerical simulation calculation method is adopted,and the transport situation of ¹³N and ¹⁸F in the nuclear power plant containment is simulated by Fluent software.Assume that the two locations which are the reactor body and the No.2 steam generator primary circuit connection pipe,the cloud chart of ¹³N concentration distribution,the cloud chart of velocity distribution and the change of ¹³N concentration at the sampling point with time are obtained.Distribution cloud chart of ¹⁸F concentration,velocity cloud chart and sample point ¹⁸F concentration change with time;The transport mechanism and concentration distribution of ¹³N and ¹⁸F are analyzed,and the concentration ratio of ¹³N/¹⁸F at the sampling site is calculated according to the time of ¹³N and ¹⁸F from the leakage point to the sampling site,which provides theoretical reference data for the information of the leakage point.The results show that:When reactor leak of ontology,¹³N and ¹⁸F in high-speed jet form into the containment vessel in free space,the main vertical upward flow in the direction of the velocity,the ventilation system,under the action of change over time,spread to the reactor dome and agglomeration,and then along the containment domes to spread around,part of the containment dome ¹³N and ¹⁸F mixed with air in the space below,the last ¹³N and ¹⁸F and air to achieve dynamic circulation state,¹³N and ¹⁸F gradually evenly distributed throughout the containment vessel,but the whole in the upper space above the containment of the ¹³N and ¹⁸F concentration is slightly higher than the lower space.It can be calculated that when running at full power,the concentration of ¹³N in the primary water is 4.522×10¹⁶ cm^-3,and the concentration of ¹⁸F is 2.520×10¹⁵/cm³,and the initial source term concentration ratio of leakage is ¹⁸F/¹³N=5.57%.When the reactor body leaks,the concentration ratio of ¹⁸F/¹³N is C₁=34.20%C₀.When the no.2steam generator leakage occurs at the pipe connection of the primary circuit,the concentration ratio of ¹⁸F/¹³N is C₂=45.40%C₀.Under the two working conditions,the concentration ratio of ¹⁸F/¹³N has a concentration ratio difference of 10%,and the difference is obvious.By measuring the concentration ratio of ¹⁸F/¹³N in the field experiment and comparing with theoretical value,the leakage location can be preliminarily determined.