Research On Gap-to-coolant Release Of Fission Gas In Pressurized Water Reactor Under The Condition Of Fuel Cladding Breach

During the operation of reactor,fuel cladding failure is possible due to physical causes and chemical causes.The defect needs to be determined when cladding failure occurs,and accident severity needs to be predicted.To improve accuracy and promptness of prediction,release mechanism of fission gas during initial stage of fuel cladding failure needs to be revealed.But it’s still unclear,further research is needed.This thesis is aimed to research effect of loop pressure,loop temperature and defect size on gas release by simulation experiment,and reveal release mechanism of fission gas.To achieve this goal,this thesis analyzes release process of fission gas in pressurized water reactor,experiment apparatus is designed according to a subchannel of pressurized water reactor.Influence of defect size loop pressure and temperature is investigated in a subchannel.Detailed release process at the defect is observed by visualization method.Results indicate that there is negative correlation between escape rate and loop pressure,but there is positive correlation between escape rate and loop temperature,also for defect size.Results of visualization experiments indicate that there are two release mechanisms for gas,one is convective mass transfer,and the other is formation of gas bubbles.And there is a jet flow of gas in the initial stage of fuel cladding failure,but it has no impact on long-term release process.According to CFD simulation,results of simulation experiments apply to Pressurized Water Reactor.