Fuel elements

Porpose: To maintain the safety of fuel elements with no excess distortion in cladding tubes even for long time burn-up in the reactor core. Constitution: Cylindrical fuel pellets made of sintered uranium dioxide charged in a cladding tube are formed with central apertures respectively. The radius r (cm) for the aperture and the uranium dioxide density rho (ratio to the theoretical density) are selected so as to satisfy the relationships: (rho - 2.11)2 + 4(r - 0.432)2 <= 2.091, rho(0.492 - r2)/0.492 >= 0.7 and rho < 0.95. Since the fuel pellets are formed with apertures and the uranium dioxide density is set lower than the theoretical density (95%), the burning shrinkage of the fuel pellets is increased, the absorption volume of fission products in the fuel pellets is increased and the expansion of the fuel pellets due to irradiation swelling can be minimized. (Moriyama, K.)