Equipment for Pressing Mixed Nitride Uranium-Plutonium Fuel Pellets
The area for pressing mixed nitride uranium-plutonium (MNUP) fuel pellets is part of the fuel fabrication/re-fabrication plant of the pilot demonstration energy complex (PDEC) being established at Siberian Chemical Combine (SCC). After sintering and machining, the pellets will be loaded into the fuel rods of the future fuel assemblies. An air-tight shielded glovebox with inert atmosphere housing the pellet pressing equipment is the main unit of the area.
Uranium mononitride and plutonium mononitride powder with required granulometric composition are the input material for the pellet pressing unit.
Pressing is the critical step in pellet-making, for it is density of the fuel composition that determines the advantages of the nitride fuel over the oxide one. Pellet pressing provides prerequisites for further successful sintering of fuel composition particles. As a result, a pellet density of 12 g/cm3 is achieved.
The pellet pressing unit is equipped with an electromechanical press consisting of a powder supply assembly, a shoe and pressing tools with three punches. The powder is supplied to the unit by gravity via a tube and reaches the throttle that regulates the powder level. The automatic control system opens and closes the throttle to supply the powder batches into the supply assembly located beneath. The hopper of the supply assembly moves radially over the shoe surface and fills three slots on its way with the powder. The shoe moves in the horizontal plane and fills the inner volume of three matrices with the powder from the powder supply assembly and at the same move pushes the pressed pellets off the lower punches. After the shoe returns into its initial position, the three upper punches descend into the matrices and compress the powder under the pre-set force.
The unit is equipped with a pick-and-place system to accurately arrange the pellets one by one in a few layers in a boat. The pneumatic gripper has a vacuum cup to take a pellet by its upper end avoiding the damage and to load the pellets into the boat as close to each other as possible. The unit has two weigh modules and a laser micrometer to measure the weight and the height of the pellets. The density of the pellets is calculated automatically from the measurement results, and this data is the basis for adjustment of the unit parameters. Each glovebox is equipped with the vacuum cleaner with accumulated powder control.
During the design phase, special attention was paid to nuclear and radiation safety assurance, as well as mechanical strength.
The pressing equipment was designed and developed by Sosny R&D Company and CHAMPALLE (France). The factory acceptance testing of the unit was performed on the production site in Dimitrovgrad, using mock-up powder.
General supervision over the project was exercised by TVEL and PRORYV Innovation Center. SCC is the general customer and the end user of the equipment. VNIINM, SverdNIIkhimmash and ATOMPROEKT contributed to the designing of the equipment.
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