Composition Changes and Future Challenges for the Sellafield Waste Vitrification Plant
- PDF / 322,019 Bytes
- 7 Pages / 595 x 841 pts Page_size
- 4 Downloads / 184 Views
Composition Changes and Future Challenges for the Sellafield Waste Vitrification Plant A. Riley1, S. Walker 1, Nick R. Gribble 2 1 Sellafield Ltd, Sellafield, Seascale, Cumbria, CA20 1PG, Cumbria, UK 2 National Nuclear Laboratory, Sellafield, Seascale, Cumbria, CA20 1PG, Cumbria, UK ABSTRACT The Sellafield Waste Vitrification Plant (WVP) immobilises highly active liquors produced during reprocessing of spent nuclear fuel by bonding the fission products as metal oxides into a borosilicate glass matrix. This provides a stable and durable waste form suitable for safe long term storage and ultimate disposal. WVP was commissioned with feed from reprocessing of Magnox reactor fuel. This material is relatively low in fission product content per tonne of fuel, but contains significant Al and Mg from fuel cladding. WVP also routinely treats a blended feed made from a mixture of Magnox and Oxide reprocessing products. The Oxide fuel from Light Water Reactor (LWR) and Advanced Gas Cooled (AGR) power stations is of higher burnup and contains more fission products per tonne of fuel, also Gd and other process additives. Blending allows 25% incorporation of waste oxides by weight in glass to be achieved routinely. Recent programmes of development work in WVP have been aimed at increasing incorporation rates for these feeds, to reduce the number of waste containers produced for disposal. Work has also focussed on increasing the throughput of WVP, to more rapidly treat current stocks of liquid reprocessing waste, both by increasing the feed rate and by improving the lifetime of key components to improve plant availability. Future challenges for WVP include flowsheet changes to treat historic stocks of reprocessing wastes containing high U, Fe and Cr. Washout of solids from the base of waste storage tanks in preparation for decommissioning is also likely to give high Mo feeds. Development of flowsheet and glass formulation to accept these changes in feed composition will be a key objective of future work. INTRODUCTION Reprocessing of spent Magnox nuclear fuel has been carried out at Sellafield in the UK for over 4 decades, and Oxide fuel has been reprocessed in the Thermal Oxide Reprocessing Plant (THORP) for 15 years. The resulting High Level radioactive Waste (HLW) streams from these processes are concentrated by evaporation and stored as a nitric acid solution of fission product and other metal nitrates prior to being treated in the Sellafield WVP. WVP immobilises HLW by bonding the fission products as metal oxides into a borosilicate glass matrix. This provides a robust waste with a low leach rate, suitable for safe long term storage and ultimate disposal. The vitrification plants in the UK use a two-stage vitrification process to incorporate the Highly Active Liquor (HAL) into glass. An overview of the key vitrification equipment is shown in Figure 1. The HAL, along with other calcination additives, is fed into a rotating kiln furnace known as a calciner to evaporate the liquor and de-nitrate the resulting solid thus producing a
Data Loading...
