| 摘要 |
PROBLEM TO BE SOLVED: To reduce the production cost while maintaining the soundness of fuel and to achieve a high degree of burnup by encapsulating a nuclear fuel pellet having a mean grain size within a specified range and helium (He) gas having pressure within a specified range in a fuel rod. SOLUTION: A lower end plug 6 is welded to a fuel cladding tube 3 made of a zirconium alloy which is then filled with a plurality of uranium pellets 4 having a mean grain size of 30-60μm. In a welding chamber, He gas 1 is substituted for the gas, e.g. air, in the fuel cladding tube 3 and pressurized to 1-8atm. In the chamber filled with He gas of that pressure, an upper end plug 5 is welded to the fuel cladding tube made 3 while pressing the uranium pellet 4 by means of a plenum spring 7 thus sealing the inside of fuel rod 2 hermetically. The lower the encapsulation pressure of He at the time of producing fuel rod, the higher the pressure of gaseous fission product and the index of soundness of fuel rod, i.e., the inner pressure of fuel rod at the end of service life, is increased.
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