Development Programme for Retrieval of Stored Secondary Waste from the Sellafield Ion Exchange Plant - 22217

The Site Ion exchange Plant at Sellafield has operated since 1985 to treat effluent water from fuel storage ponds and waste silos before sea discharge. Solid particles are removed by deep bed filtration, and radioactive cesium and strontium are removed by ion exchange. Secondary waste from the process is currently stored in large tanks pending implementation of facilities for retrieval and treatment. Waste includes spent filter sand and used ion exchange medium (clinoptilolite), as well as magnesium hydroxide sludge solids from corrosion of Magnox fuel cladding which is stored separately. Studies to consider options for SIXEP Waste Management have been conducted since the implementation of the plant, designs have been prepared and technologies have been tested for both retrieval and treatment. As plans for waste treatment processing infrastructure for the wider Sellafield site have developed the concepts and options for SIXEP Waste Management have evolved. A 3 phased approach is now planned, additional storage and a route to treatment will be provided in the phase 1 SIXEP waste management receipt facility. Technology development is required to select the processes for phase 2 retrieval of historic waste and phase 3 waste treatment. Retrieval of waste from the historic storage tanks is constrained by the geometry of the 1000 m³ tanks, with limited access through one central and four peripheral vertical down comers in the top of the tank, and a reach of up to 20 m from the operating area through the biological shielding to the waste. Technologies are required for the mobilization of the waste, pumping from the tank, transport to the treatment process, separation of solids from the transport fluid, and treatment of the fluid. Technology options include submerged water jets, fluidic pulse jets, centrifugal and jet pumps, exposed bed sluicing, reeling drums, telescopic mast, remote operated vehicle and pneumatic transfer systems. The SIXEP waste will be processed, packaged into a form suitable for the UK Geological Disposal Facility and interim stored. Treatment options will be selected within the context of the Sellafield Integrated Waste Management strategy. Complex plans already exist for processing facilities, transport infrastructure and waste stores, prioritized to reduce hazard at the site as quickly as possible. Alternatives for the SIXEP waste range from extending use of existing treatment and encapsulation plants to construction of new facilities. The benefits of treatment by vitrification in a new 'thermal' processing plant is also being considered. Initial focus of the retrieval development work program is on selecting technologies for exporting waste from the new phase 1 storage tanks. As these are still at concept stage it is possible to design the tanks with less constraints, and additional processes can be considered for waste transfer, including preinstalled facilities. (authors)