SOLID SOLUTION CONCENTRATION ADJUSTMENT METHOD FOR CRYSTAL GRAIN BOUNDARY AND PERIPHERY OF CRYSTAL GRAIN BOUNDARY OF HETEROGENEOUS ADDITIVE ELEMENT, AND METHOD OF MANUFACTURING NUCLEAR FUEL SINTERED BODY HAVING LARGE CRYSTAL GRAIN USING THE SAME

摘要

PROBLEM TO BE SOLVED: To provide a method of controlling a concentration at which an additive agent is solved at a crystal grain boundary in sintering of a uranium-based oxide compact which varies in solid solution concentration in uranium-based oxide according to oxygen partial pressure of sintering gas, and contains an additive agent element, and to provide a method of manufacturing a nuclear fuel sintered body which has large crystal grains.SOLUTION: There is provided a crystal grain boundary solid solution concentration adjustment method for a heterogenous additive element which keeps a crystal grain boundary solid solution concentration of the heterogeneous additive agent element at a certain level during sintering of the uranium-based oxide compact containing additive agent powder of a heterogenous element by changing the oxygen partial pressure in stages during isothermal sintering when the uranium-based oxide compact is sintered. Further, there is provided a method of manufacturing a nuclear fuel sintered body which has large crystal grains including a stage of preparing mixed uranium oxide powder of the additive agent, a stage of forming a mixed uranium oxide compact of the additive agent using the mixture, a heating stage of raising temperature of the compact to the sintering temperature of the compact under a gas atmosphere of low oxygen partial pressure, and a stage of sintering the compact by changing a sintering gas atmosphere so as to raise the oxygen partial pressure in stages at the isothermal sintering temperature.