Mitsubishi Nuclear Fuel CO.,LTD.

UO2 powder (uranium dioxide)

Low-enriched uranium hexafluoride, the starting material for the chemical conversion process, is vaporized. This gaseous uranium hexafluoride is then absorbed by pure water to produce uranyl fluoride solution. Ammonium hydroxide is added to this solution and ADU (ammonium diuranate) is precipitated. Further, through processes of dewatering, drying, calcinations / reduction, and milling, uranium dioxide powder is manufactured from ADU.

UO2 pellets (uranium dioxide)

UO2 (uranium dioxide) powder is slugged and granulated in order to obtain flow-able granules. Then green pellets are pressed by a rotary press. Green pellets are sintered at a temperature higher than 1,700 oC in a continuous sintering furnace, to obtain UO2 pellets. Sintered pellets are ground to the specified dimensions.

Fuel rod

UO2 pellets are loaded into a Zircaloy-tube. Then a pellet-hold-down spring is inserted from one end, and end plugs are pressed into place at both ends. Top and bottom end plugs are alternately welded to the fuel tube. Helium gas is pressurized through a vent hole in the top end plug and the vent hole is then seal-welded. Thus, a four (4) meter length fuel rod is produced.

Fuel assembly

Fuel rods are inserted into six to nine grid assemblies. Guide thimble tubes are mechanically joined to grid assemblies and top and bottom nozzles are attached, completing fuel assembly fabrication.