Prevention of segregation of pore former by granulating with MOX powder in low density pellet fabrication for fast breeder reactors

Murakami, Tatsutoshi ; Aono, Shigenori

Japan Atomic Energy Agency has been working to advance fabrication technology of mixed plutonium-uranium oxide fuel pellets for fast breeder reactors. In brief, the usual fabrication method of MOX pellets for FBRs consists of granulating raw MOX powder by a tabletting method, followed by pressing into compacts. Then, the compacts are sintered to get the MOX pellets. For the FBR "MONJU", MOX pellets having low density are required as the fuel pellets. The low density pellets are fabricated by adding an organic additive called a "pore former" to the MOX powder. The pore former is thermally decomposed and pores are incorporated into MOX pellets by sintering the compacts containing the pore former. In the past, the pore former was blended with the granulated MOX powder after the granulation process. But the pore former became segregated from the granulated MOX powder during feeding to the press machine, because the specific gravity of pore former is significantly lower than that of granulated MOX powder. In order to solve the problem, blending the raw MOX powder with the pore former was carried out before the granulation process to keep the pore former in the granulated MOX powder. As the result, segregation of pore former was prevented.