Study On The Technology And Application Of UO₂ Pellets Prepared By Dry Powder With Returned Powder

Pressurized Water Reactor（PWR）is the main type of commercial nuclear power reactor.The core of PWR is nuclear fuel,and UO₂ is the most commonly used ceramic fuel.The domestic production of UO₂ powder is widely used in large-scale industrial production mainly by the IDR（Integrated Dry Route）Dry process and the ADU（ammonium diurate）process,with continuous improvement of equipment and process in domestic nuclear fuel plants,the IDR dry process is generally used to produce UO₂ powder at present,but a wet recovery line is still retained.The IDR dry process has the advantages of short process flow and very little waste water,but the loose density of the powder is low,the fluidity is poor,and the rate of finished products is low,the bulk density and fluidity of the powder produced by wet process were obviously better than those by IDR process.Based on the significant difference between IDR dry powder and return powder in formability and sintering performance,theoretically speaking,by adding return powder to IDR dry powder,it should not only be able to solve the problem of poor pellet density caused by poor sintering activity of return powder,but also improve the formability of IDR dry powder and the strength of green compact,reducing the defect rate of core block dropping and improving the appearance quality of core block.In this thesis,the effect of UO₂ powder technology on the properties of UO₂ powder and the properties of UO₂ pellets was studied.Firstly,the feasibility of this technology and its effect on the properties of UO₂ powder and pellets were analyzed by experimental research,the results of previous tests show that the properties of UO₂ pellets prepared by IDR dry process are greatly affected by the addition of recycled powder.The sintered density of UO₂ pellets is stable and controllable,and the microstructure is good,it is feasible to adopt this technology.Further production and application tests are carried out in a proven nuclear fuel production line.The results of experiment and production show that the mixed powder has a good mixing effect,and the powder produced by IDR dry process and recycle process can be mixed in a certain proportion,the main physical and chemical properties of the mixed powder meet the requirements of technical documents.The mixed powder has the basis of pressing and forming UO2 pellets.The performance of mixed UO2 powder is better than that of IDR dry powder,and the strength of green body is better,the sintering property is better,the density of pellets is stable and controllable,the appearance quality is better,and the yield is higher than that of IDR dry powder.