Research On Condensation Characteristics Of Steam Jet Through Multi-hole Nozzle

In the Third Generation advanced PWR AP1000,Automatic Depressurization System(ADS)is introduced.When the system was triggered,high temperature and high pressure steam was directly sprayed into In-containment Refueling Water Storage Tank(IRWST)through a multi-hole sparger,and condensed with the sub-cooled water of IRWST.It passively removes heat from the primary loop and achieves the purpose of rapidly cooling down and depressurization in the primary loop,which plays an important role in preventing core melting when the pressure is high in reactor accident conditions.In addition,the steam jet condensing effect directly determines the pressure relief rate of the primary loop.If the steam is insufficiently condensed,the steam escapes into the containment,which may cause instantaneous overpressure in the containment and affect its integrity.Therefore,whether the high temperature and high pressure steam in the ADS can effectively condense plays an important role in ensuring safe and reliable operation of the reactor.For the Automatic Depressurization System,the current research mainly pays attention to the overall reliability of the system operation and the overall flow characteristics of the IRWST during the steam jet,as well as the steam jet condensation characteristics through single-hole nozzle,without the experimental research on the steam jet condensation characteristics through multi-hole nozzle.And some numerical simulations show that steam jet condensation through multi-hole nozzle is significantly different from steam jet condensation through single-hole nozzle,which has obvious inter-hole effect.The inter-hole effect affects the heat transfer coefficient of steam jet condesnation.In the nuclear power plant AP1000,the ADS sprayer is a multi-hole nozzle.For the thermal parameters of the new component during operation,it is urgent to carry out research on the model for the condensation and the calculation of the heat transfer coefficient.Based on the above considerations,this paper takes the steam jet condensation as the prototype,and bulids the corresponding experimental bench to study the condensation characteristics of the steam jet through the multi-hole nozzle under different test conditions and spargers' parameters.In the experiment,advanced measurement equipment such as thermocouple array,high-speed camera and particle image velocimetry(PIV)were employed to capture key parameters such as temperature field,flow pattern and velocity field.The experimental results show that the steam jet through multi-hole nozzle is significantly different from steam jet through the single-hole nozzle,which appears new condensation characteristics.When the water temperature is high,the steam plumes between adjacent nozzles interact and are combined to each other as the water temperature gradually approaches the saturation temperature,so that the heat transfer area increases.And the temperature of beginning steam plume combination effect reduced along with the reduction of the hole center distance.In addition,the heat transfer efficiency of steam jet condensation is high.The axial temperature of the nozzle center is rapidly decreased within a very short distance,and the fluid flow velocity near the nozzle is large.In the tail of steam plume,the maxmuim is as high as 3.5 m/s.Finally,the condensation heat transfer coefficient of single-hole and two-hole steam jet is calculated in the range of 0.5-2.5MW/m2K,and the results show that the heat transfer efficiency of the multi-hole nozzle is reduced due to the steam plume combination effect.Therefore,this paper clarifies the combination effect of the adjacent steam plume in steam jet through multi-hole nozzle,analyzes its influence on the condensation characteristics,and obtained key thermal parameters,which is of great significance for the design and improvement of sprayers.