The equipment for sintering mixed uranium-plutonium nitride (MUPN) fuel pellets is part of the fuel production line of the Fabrication/Recycling Facility of the Pilot Demonstration Energy Complex (PDEC) being established at the Siberian Chemical Combine (SCC).
Sintering is the final stage of the fuel pellet consolidation. The sintering process determines the final composition, structure and properties of the fuel. The optimal parameters (i.e. isothermal holding temperature and atmosphere composition) of the MUPN fuel have been determined experimentally. The pellets are heated and cooled down in the argon atmosphere.
The equipment consists of the following main components:
- Dispatch glovebox to receive, to weigh and to identify the number of the boat filled with pellets. Here the boat is put on a tray and transferred to the input glovebox of the sintering furnace;
- Input glovebox where the atmosphere is changed and the filled boat on its tray enters the input channel of the pusher sintering furnace;
- Pusher sintering furnace consisting of pre-sintering, sintering and cooling modules. The furnace has heaters, gas injection and suction equipment, instruments to control gas pressure and flow rate. The furnace is equipped with inlet and outlet bellows to compensate seismic impact and thermal expansion;
- Output glovebox to change the gas atmosphere once more;
- Return glovebox to receive the boat with sintered pellets. The boat returns to the dispatch glovebox on the conveyor. Here the boat is separated from its tray, the unique boat number is identified and the boat is weighed.
The sintering plant also includes a gas treatment unit. It is an air-tight glovebox with two parallel lines of furnace gas cooling and treatment to provide non-stop operation by swapping the lines in case of maintenance of one line is needed. The gas treatment unit is equipped with sensors and mechanisms to monitor the environment inside glovebox and in the off-gas pipe. All the sintering unit components are bound together with a transport system of an original design that consists of a series of conveyors and pushing mechanisms with different travel length.
The equipment safety analysis was prepared at the design phase. Certified up-to-date software was used to confirm nuclear safety and to justify the strength of the equipment components. The seismic analysis results confirmed that the bodies of the input and output gloveboxes belong to safety class 2N, and the furnace body and the bellows between the furnace and the gloveboxes - to 3N according to NP-016-05.
The developer of the MUPN fuel technology put forth strict requirements to the sintering parameters, namely to the isothermal time of the pellets in the high-temperature zone and to the volumetric concentration of the mixed gases in different zones of the furnace tunnel. Thus the task to provide and control gas distribution under working temperatures required modeling the furnace with Ansys Fluent software of computational fluid dynamics. To verify the model, a full-scale mockup was created to simulate the geometry of the furnace tunnel and to allow determination of the gas composition in the selected points of the tunnel under the room temperature. The optimal mode of gas supply to the furnace tunnel was calculated.
The control system of the sintering furnace is a distributed automated human-machine interface that monitors and controls the equipment of the sintering gases, input and output gloveboxes. It includes the systems for regulation of the gas temperature and pressure, boats transport, gas and water supply, moisture and oxygen concentration monitoring in argon and nitrogen-hydrogen mixture.
The control system is based on up-to date high-precision and reliable measurement instruments. They are certified to be used at nuclear fuel cycle facilities and are well-proven in the nuclear industry. The control means are certified and registered in the Russian National Register of Measuring Equipment. The software has been developed by the experts of the Sosny R&D Company in compliance with the requirements of the European standards.
All components of the pellet sintering facility, except for the pusher furnace, ware developed and fabricated at the Sosny R&D Company. The pusher furnace was fabricated by the ECM Technologies (France) and the Sosny R&D Company. The designing and fabricating of the facility was carried out under the scientific supervision of VNIINM and with active participation of SverdNIIkhimmash, SCC, TVEL and PRORYV Innovation Center.
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