Simulation Study On Cladding Tubes Emissivity Test System Of Nuclear Power Station

When the coolant of the nuclear power plant reactor is lost,the cladding tube is likely to rupture under the condition of high temperature and high pressure,resulting in a nuclear fuel leakage accident.In this case,the cladding tube mainly transfers heat by radiation,and the emissivity is an important parameter of radiant heat transfer.Therefore,measuring the emissivity of the cladding tube can analyze its heat dissipation under accident conditions,and then explore the method for reducing cladding tube rupture.It has very important realistic meanings.However,the high temperature water vapor in the reactor has a great influence on the measurement of the emissivity of the cladding tube.This thesis presents a simulation model optimization method for detection technology of cladding tube emissivity measurement in water vapor environment,to explore the influence of water vapor environment on cladding tube emissivity test,and to provide key technical support for the realization of emissivity measurement technology under water vapor environment.The emissivity of the cladding tube in the system is difficult to measure mainly in two aspects: first,water vapor has a strong absorption and scattering effect on radiation,and water vapor easily enters the detector,the temperature of the sensor is increased,and the phenomenon of temperature drift is generated,which affects the measurement result;second,the vision of the infrared radiation sensor is difficult to cover due to the small diameter of the cladding tube,so that background radiation easily enters the sensor,resulting in measurement errors.This thesis analyzes the transmission rate of water vapor to different wavelengths of thermal radiation,and uses air cooling in the mechanical design of the detector,which reduces the temperature of the sensor and reduces the water vapor entering the detector to solve the first problem;for the second problem,a method for measuring the normal emissivity of a thin-diameter cylinder is proposed,and the mechanical design of the detector using a cladding insulator and collimator tube to reduce the background radiation.The effect can solve the problem of emissivity measurement in this case.Finally,based on the measurement principle of the emissivity of the cladding tube,the finite element analysis method is used to construct a simulation system for the emissivity test of the cladding tube.The test temperature range is 350 ～ 800 ℃.The effect of different gaseous medium on the emissivity test of cladding tube is explored.The functional relationship between the temperature of the cladding tube and the radiant flux received by the detector and the emissivity is fitted.The fitting degree reaches 0.99,which has a good fitting effect.Based on the above relationship,the emissivity calculation formula of the test simulation system is derived.Simultaneously,the oxidation reaction of the cladding tube during the emissivity test is simulated.The emissivity of the oxidation model is compared with the theoretical value calculated by the derivation formula.The relative error is about 5%.After the cladding tube is completely oxidized,the relative error will decrease.When the reaction proceeded to 60 min,the relative error dropped to 2.4%.It is proved that the formula can approximate the oxidation model,and the feasibility of the simulation model and system design is verified.