TUE Re-Extraction Equipment

The equipment for re-extraction of transuranium elements (TUE) is part of the Fabrication/Refabrication Plant (FRP) of the Pilot Demonstration Energy Complex (PDEC) at the Siberian Chemical Combine (SCC). The process equipment is compiled into a facility to implement the chain of operations to extract TUE from liquid radioactive waste (LRW). The facility offers after-treatment of pre-evaporated LRW to separate actinides (uranium, plutonium, and americium) and to reduce waste activity.

The inputs for the facility are:

• acid and alkali solutions arising from decontamination of the glove boxes and process equipment of the FRP,
• sludges from the LRW treatment evaporator,
• spent process solutions from the analytical laboratory,
• decontaminants from the analytical laboratory.

The facility generates the following outputs:

• a pulverized mixture of uranium, plutonium, and iron to be taken for interim storage,
• alkaline LRW with the maximum activity of 1.9·10⁶ Bq/L with the plutonium content of not more than 15 μg/L or americium content of not more than 1.8 μg/L to be fed to the grout treatment facility.

The processing of the pre-evaporated LRW from the FRP includes precipitation in alkaline solutions, clarification, drying, and calcination of the resulted solids, followed by safe storage of the obtained mixed powders. This process flow reduces the loss of fissile material down to 0.1 % of its total amount in the production cycle in of MUPN fuel fabrication.

In 2020, Sosny R&D Company developed a preliminary design of a facility comprising the following process equipment:

• a vertical decanter centrifuge with scroll discharge of precipitate from the rotor to separate the solids,
• an ultrafiltration unit to trap fine solids from the centrate by ceramic filters and to obtain the retentate by clarification method,
• vessels and tanks, including nuclear safe ones, to receive, correct, and precipitate initial solutions, to collect centrates and permeates,
• pumps to feed the solutions at a preset flow rate,
• centrifugal pumps to stir and transfer the solutions,
• tanks to feed the required agents,
• an electric furnace to dry and calcinate the precipitate,
• a dry precipitate glove box,
• a sampling glove box,
• a receiving hopper,
• a cooling screw conveyor,
• a local gas purification system,
• a video surveillance system,
• a local control system,
• electric equipment,
• biological shielding,
• piping, valves, monitoring instruments.

Facility specifications:

In 2021, Sosny R&D Company manufactured the equipment described below.

The initial solution receiving tank receives the incoming liquids, heats, stirs and cools them, forms batches and dispenses them for the following separation of TUE. The tank is a heat-insulated toroidal vessel of Type К 1–80 to OST 95 407–95 with a heating (cooling) jacket. A neutron-absorbing insert is installed inside the tank. The working volume of the tank is 0.8 m³, the height is 3040 mm, the diameter is 1940 mm. Safety class to NP-016−05 is 2N.

The tank is has a bubbler for stirring, a level indicator, a temperature transmitter, level switches, and a pressure transmitter. An industrial pH meter measures the activity of hydrogen ions in the solutions.

The vertical setting centrifuge separates the solid phase (precipitate) from the liquid one (centrate) after the suspension sedimentation under the acceleration force created by the rotor. The solids deposit on the inner wall of the rotor, and the scroll conveyor carries them to the solids outlet. The remaining fine particles suspended in the supernatant are removed by precipitation on the discs. The centrifuge design enables its flushing by feeding a cleansing liquid into the rotor and subsequently removing the cleansing liquid through the centrate removal line.

The instruments to measure vibration velocity, the rotation frequencies of the rotor and scroll conveyor, the temperature of the upper support bearings, and motor input power monitor the health of the centrifuge in operation.

Specifications of the centrifuge:

The top-driven continuous air-tight horizontal furnace is designed to dry and calcinate the precipitate obtained in the centrifuge. Wet solids are unloaded directly from the centrifuge rotor to the furnace rotating plate, where they are pre-dried, crushed with the blades, and forced through the holes in the rotating plate down to the hearth. The product is calcinated while moving across the hearth surface from the center to the periphery till it enters the cooling screw conveyor.

Specifications of the furnace:

Filtering unit. The filtering unit includes centrate receiving tanks, membrane filters, centrifugal pumps, and other equipment. Centrate leaves the centrifuge and enters the centrate receiving tank of the filtering unit. Membrane filters trap the remaining TUE from the centrate. Clarified liquid (permeate) is removed from the filtering unit to the permeate receiving tanks, while retentate (radioactive alkaline slurry) is fed to the settlers for additional sedimentation. The centrifugal pump enables the slurry circulation in the centrate receiving tanks, the slurry supply to the membrane filters, and the slurry discharge.

Specifications of the filtering unit:

The dry precipitate glove box is designed to receive dry powder, take samples, weigh samples and discharge the powder for further storage.

The glove box equipment includes:

• inlet, exhaust, and maintenance vents,
• TV camera mounting fixtures,
• LED lights,
• negative pressure and temperature measuring transmitters,
• a cyclone dust collector,
• scales.

The glove box design provides the space to install and connect a manual station for sending samples via pneumatic tube capsules.

A bag port to remove decontaminated objects, a drain, a sample outlet, and a container port are designed at the bottom of the glove box. The bag port design provides for attaching plastic bags. A height-adjustable table on the base frame under the bag port facilitates the bag-out of the objects from the glove box. The glove box accessories include a sample carrying container.

A cyclone dust collector with a nuclear-safe catch-pot unified for in-box application in the FRP is utilized for dry cleaning.

The glove box is supplied with a sampling kit, including a sampler, a tray, a scraper, a wide trowel, a narrow trowel, a mortar, a pestle, and a funnel.

The receiving hopper fills a can with dry powder. A sample is taken from the can, and sampled powder is sent in a specialized container via pneumatic tube to the laboratory. Upon the availability of the sample analysis results, the can is loaded into a TUK-30М2 container through the airlock. The container is tightly attached to the airlock to maintain the glove box containment.

The sampling glove box is designed to take and prepare samples of the process media from the equipment of the TUE extraction facility to be sent to the analytical laboratory.

The glove box equipment includes:

• inlet, exhaust, and maintenance vents,
• a transfer airlock to connect to the dry precipitate glove box,
• an antechamber to post in the tools and chemical agents,
• negative pressure and temperature measuring transmitters,
• a LED light,
• a drain.

Dry cleaning of the glove box is carried out, if necessary, with the cyclone dust collector located in the dry precipitate glove box.

The sampling from the equipment of the TUE extraction facility is remote and initiated by the operator’s command from the local I&C workplace. The liquids from the extracting equipment are fed via the sampling line to the glove box, where the operator takes the samples by manually opening the valves. Then, the samples are sent to the analytical laboratory.

The shielding wall is mounted in front of the glove boxes and receiving hopper to protect the personnel against ionizing radiation. The thickness of the biological shielding is 40 mm of steel and 20 mm of polyethylene. The windows are made of ТФ 5 plate with a thickness of 36 mm and polycarbonate panel with a thickness of 10 mm. The height of the shielding wall is 2 meters from the floor level. The shielding below the table level is sliding to provide access to the space under the box.

The local gas purification system offers pre-treatment of the off-gases coming from the extraction facility equipment before discharging to the centralized FRP gas purification system.

The local gas purification system consists of an off-gas flue, a gauze filter, a cooling condenser, an aerosol filter, a receiver. The off-gas flue is electrically heated and heat-insulated to prevent the condensation of the steam-gas mixture coming from the furnace. All off-gas streams enter the cooling condenser, where they are dehumidified and cooled, then filtered and discharged into the centralized FRP gas purification system. The volumetric activity of sols is monitored. 

Specifications of the gas purification system:

The drain montejus receives, stores, and discharges any process and non-process solutions coming from the main process equipment of the TUE extraction facility, including drains and leaks from the pits. The drain montejus is a toroidal vessel of Type К 1–80 to OST 95 407–95 with a mixing device at the bottom. A neutron-absorbing insert is installed inside the montejus. The montejus is has a bubbler for stirring, a level indicator, a temperature transmitter, level switches, and a pressure transmitter.

The vacuum trap separates the liquid phase from the pumped-out gas. The operating medium is nitric acid solutions, alkaline solutions. The vacuum trap retains operating solutions along the vacuum line when vacuuming the process tanks during the transfer of the operating solutions and discharge to the drain montejus.

The metering pump is designed to transfer, meter, and discharge the slurry from the settlers to the centrifuge. A hydraulic cylinder and a plunger are the main elements of the pump. The operating principle of the metering pump is based on the periodical creation of negative pressure in the pumping chamber and, then, overpressure is created. The plunger strokes are simultaneously rotational and reciprocating and are provided by a profiled cam and a magnetic coupling.

A frequency converter of the pump motor regulates the slurry flow by the rotation and reciprocating movement frequency of the plunger.

Specifications of the metering pump:

The video surveillance system offers remote monitoring of the facility location, personnel activity, and equipment operation. The equipment of the video surveillance system comprises a control cabinet and twelve IP cameras.

The system software supports the following operations:

• real-time remote surveillance,
• simultaneous video recording from all cameras, and from selected ones,
• full-screen and multiple-screen viewing options,
• digital zoom in/out of the image for each camera,
• switching to stored records viewing and back.

The lighting system of the TUE area includes primary and emergency lights, a control cabinet, and distribution boxes. 230 V 50 Hz power supply to the cabinets from two independent external sources is available corresponding to primary and emergency lighting.

During normal operation of the electrical equipment, the lighting is provided with primary lights installed in the following zones:

• Zone 1 - the space within the shielding structure of the TUE area,
• Zone 2 - sanitary barrier rooms of the TUE area,
• Zone 3 - glove-box room of the TUE area.

Independent control over switching on/off the lights for each of the above-mentioned zones is available in the control cabinet.

Emergency lights turn on automatically in case the main power line and, thus, the primary lights, are off or failed.

The local control system is designed to measure and control the process variables, and to control the actuators of the following equipment in the TUE area:

• the settler pumps,
• the dry precipitate glove box,
• the cooling condenser,
• the drying and calcination furnace,
• the centrifuge,
• the filtering unit,
• the initial solution receiving tank
• the sampling glove box,
• the pumps of the clarified solution receiving tanks,
• the drain montejus,
• the vacuum trap,
• the local gas purification system.

The local control system is configured of ten Rittal VX cabinets (bays) and two Provento MPS cabinets which are earthquake-resistant, support access from one side, power and signal cable infeed from above via cable entries.

The signals from the lower level equipment are transmitted to the LCS middle level in the TUE area. Unified signals 4…20 mA, Pt100 are used as analog signals transmitted to the control system. Physical RS-232/485 interface with Dibus and Modbus RTU protocols is available for data transfer.

A local area network to Industrial Ethernet standard (S7\ProfiNet protocol) on industrial Ethernet Siemens SimaticNET Scalance X100 switches is implemented in the LCS.

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