Technologies and Equipment for Reprocessing the VVER Spent Fuel at the Experimental Demonstration Center of the Mining and Chemical Combine
To improve technologies for reprocessing the VVER-1000 spent fuel, the Experimental Demonstration Center has been built at the site of the Mining and Chemical Combine. This Center includes:
- A complex of research cells to try out the innovative technologies for any spent fuel reprocessing which capacity is up to 5 tons of spent fuel per year, and
- A main process line to perform the whole procedure for reprocessing the VVER-1000 spent which capacity is up to 400 tons per year.
Since 2015 Sosny R&D Company has been proactively involved in development of the in-cell process equipment and auxiliary equipment for the research complex and the main process line of the Experimental Demonstration Center.
In 2015 the specialists of Sosny R&D Company developed the Fuel Assembly Cutting Hot Cell and all the associated in-cell equipment which is a part of the complex of research cells.
In 2017-2019 Sosny R&D Company developed and fabricated the equipment for the following three divisions of the main process line at the Experimental Demonstration Center:
- Fuel Assembly Cutting and Fuel Voloxidation Division,
- Spent Fuel and Radioactive Waste Handling Division, and
- The 1st Extraction Cycle Division.
EQUIPMENT FOR THE FUEL ASSEMBLY CUTTING AND FUEL VOLOXIDATION DIVISION
This division is intended to perform the incoming visual inspection of the fuel assemblies and to determine the spent fuel burnup and the isotopic composition. After that the top and bottom nozzles of the fuel assembly shall be cut out, and the fuel rods enclosed in a fuel assembly skeleton shall be cut into fragments using the mechanical cutting upper pressure technique. Then the mechanical mixture of structural materials and spent fuel shall be transferred for the oxidative recrystallization (voloxidation).
The voloxidizer is designed for decladding the voloxidized spent fuel in process of the fuel volume oxidation supporting simultaneous localization of the released volatile fission products, tritium and iodine in the main gas purification system. After that the mechanical mixture of fuel powder and fragments of the fuel rod claddings, spacer grids and guide channels shall be transferred to the sieving machine. The voloxidized fuel powder separated from the structural materials shall be transferred for subsequent cooling and dissolving (leaching) to the Spent Fuel Dissolution Division while the structural elements shall be transferred for additional extraction of the fissile material to the special machine for washing the structural materials in the Spent Fuel and Radioactive Waste Handling Division.
To carry out the processes above, the following equipment has been designed and fabricated:
- Equipment for incoming visual inspection of the fuel assemblies and determination of spent fuel burnup and isotopic composition,
- A facility for fuel assembly cutting and fragmentation (GIT-1000), and
- A voloxidation facility.
The equipment for the Fuel Assembly Cutting and Spent Fuel Voloxidation Division has been designed and fabricated supported by all needed design safety analyses, including the nuclear safety analysis and the radiation safety analysis. The positive expert assessments from the IPPE's Nuclear Safety Department have been received.
Equipment for incoming visual inspection and determination of fuel burnup is intended to check the exterior of the spent fuel assemblies received from the storage, to identify and keep records of the fuel assembly serial numbers, and to determine the fuel burnup for fissile material control and accounting, and for the nuclear safety assurance. Also, it can be use for visual monitoring the fuel assembly gripping and position during the transport activities.
VVER MKS-01 Facility made by Kvant R&D Company is intended to determine the nuclear fuel burnup and the fuel assembly isotopic composition. This facility can be operated underwater in the cooling pool for VVER-100 spent fuel assemblies. Based on the fuel burnup measurement results, the isotopic composition and decay heat of the nuclear fuel can be determined.
The fuel burnup can be measured in the range from 10 to 70 МW·day/kg and the fuel assembly cooling period from 10 days to 50 years. This equipment includes the gamma detectors and the neutron detectors, both dosimetric and spectrometric.
Facility for fuel assembly cutting and fragmentation has been designed and fabricated jointly with the Design and Engineering Branch of Lavrentyev Institute of Hydrodynamics of the Siberian Branch of the Russian Academy of Sciences and VARIANT-999 Company. It is intended to cut out the top and bottom nozzles of the fuel assembly, to cut the fuel rod bundle together with the guide channels and spacer grids with a given pitch (not more than 40 mm), to remove dust from the cutting equipment and to load fragments of the fuel assembly into the loading tube.
This facility includes:
- a tilter,
- a fuel assembly feeder,
- a fuel assembly nozzles cutter,
- a fuel assembly cutter,
- a sorting unit with a slave electromechanical manipulator,
- a loading tube with a rotary gate,
- a power manipulator with a protective enclosure, and
- a local control system.
Since the chopping blades were replaced by the special design cutting blades, the mass and size of the facility have reduced. The adjustment of the cut pitch can extend the blade service life. The remote replacement of the blade assembly significantly reduces the downtime.
Voloxidation facility is intended to perform the fuel volume recrystallization by a reagent gas at the temperature not more than 550°C, to distillate the volatile fission products, to separate the spent fuel powder and fuel rod structural fragments by sieving, to filtrate light fractions of the voloxidized fuel powder in order to prevent their ingress to the gas purification system, to cool and transfer the fuel to the dissolver, and to transfer the structural elements to the associated washing machine.
The voloxidation facility has been designed and fabricated by Sosny R&D Company only. This facility includes:
- a voloxidizer,
- a sieving machine,
- a voloxidized fuel powder cooler with a rotary gate,
- a local control system, and
- mounting tools and accessories.
The main components of the voloxidation facility can be handled using a power manipulator and auxiary tools designed by Sosny R&D Company. A sieve of the sieving machine is designed for the long-term service and can be replaced remotely using a power manipulator.
All electric drives are arranged outside the radiation hazardous zone for the purpose of their maintenance. In case the main rotation drive fails, an additional drive with a lantern gear will ensure the operability of the facility.
Key advantages of our voloxidation facility:
- Possibility to load all fragments of one fuel assembly at once,
- Nuclear safe geometry of the facility,
- Removal of voloxidized spent fuel from the fuel rod fragments by mechanical activation, and
- Use of original sealing at the rotation shaft designed for the long-term service.
EQUIPMENT FOR SPENT FUEL & RADIOACTIVE WASTE HANDLING DIVISION
All the equipment for the Spent Fuel & Radioactive Waste Handling Division has been designed and fabricated by Sosny R&D Company supported by all needed design safety analyses, including the nuclear safety analysis and the radiation safety analysis. The positive expert assessments from the IPPE's Nuclear Safety Department have been received.
This division is a site where a whole procedure for handling the solid radioactive waste of the main process line at the Experimental Demonstration Center can be implemented.
Structural material washing machine with tanks, pumps and auxiliary equipment. This machine is designed for additional extraction by leaching of those fissile materials which are remained on the fuel rod cladding fragments and on the structural material fragments after their separation in the sieving machine. Its functions:
- accept the fragments of the fuel rod claddings, spacer grids and guide channels with residual fissile material after their separation in the sieving machine (capacity is all fragments of one fuel assembly),
- dissolve the spent fuel remained on the fuel rod claddings in the nitric acid solution at the temperature of 115 °C with the solution agitation by partial decantation in the interim tank,
- unload the clean structural material into the tank for solid waste, and
- transfer the fuel solution to the dissolution division for the main dissolution of the voloxidized fuel.
The design of the cladding washing machine has been developed to prevent intensive evaporation during the acid supply by cooling the structural material fragments with residual fissile material down to the required temperature, and to heat and maintain the operating temperatures of the nitric acid and the scrub solutions.
Solid waste drying machine is intended to remove water and drip aerosols from the tank with clean fragments of the fuel rod claddings, spacer grids and guide channels of the fuel assembly, and insoluble residuals of the structural materials received from the clarification division. The drying is performed to prevent accumulation of hydrogen and ensure explosion safety during the lo9ng -term storage of the radioactive waste.
In addition, the Spent Fuel &Radioactive Waste Handling Division houses the following equipment:
- Hoisting and transport equipment for loading the spent cartridges of the gas purification system into the tank for solid waste,
- A tank welding facility which is intended to seal the tank lid by welding and to test weld for leaks with a helium probe,
- A tank decontamination facility which is intended to decontaminate the tank filled with solid waste up to the level needed for its safe preparation for transportation to the high-level waste storage volt at the Experimental Demonstration Center,
- A transport system which includes the lifting equipment, hoisting and rotation equipment, carriages and associated rails, and full tank reloading modules. This system supports the whole procedure for continuous handling the radioactive waste within the period of up to 300 days per year, and
- A system for local control of the machines and facilities in the Spent Fuel & Radioactive Waste Handling Division.
EQUIPMENT FOR THE 1st EXTRACTION CYCLE DIVISION
The 1st Extraction Cycle Division is the key division of the Experimental Demonstration Center intended to extract fuel components from the clarified solution of spent fuel, to fraction the target product streams and to purify them from fission products and impurities.
It includes the following equipment:
- an extraction pulse annular continuous column,
- centrifugal extractor units,
- mixer-settler units,
- separators for fine extractor cleaning from the emulsion aqueous entrainment,
- uranium catalytic recovery columns with platinum catalysts,
- tanks and vessels,
- heat exchangers,
- metering pumps and force pumps,
- auxiliary equipment,
- mounting tools and accessories, and
- a local control system including the process control and monitoring equipment, and the equipment needed to ensure safe operation of the extraction facility.
The innovative decision was to use the centrifugal extractor units and the extraction pulse annular continuous column. The centrifugal extractors allow to increase the production capacity of the 1st Extraction Cycle Division. As the irradiation time of the organic extracting agent becomes significantly less, its degradation will be much smaller. The extraction pulse annular column allows not to use the electromechanical drives which require regular maintenance and replacement thus significantly reducing the operating costs. The extractors can be operated in parallel mode or in serial mode.
The problem related to the vibration resistance of the centrifugal extractors has been successfully solved. Moreover, the working sections of the extractors can be remotely dismantled and removed to the maintenance area for replacement. All drives of the equipment are also mounted outside the radiation hazardous area.
In process of the equipment designing, the issues related to selection of structural materials resistant to corrosive environment, assurance of sealed interface, maintainability and interchangeability of standard assemblies located in the canyons and hot cells were addressed.
The works on creation of the equipment for the Experimental Demonstration Center are still ongoing.
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