Composition Changes and Future Challenges for the Sellafield Waste Vitrification Plant

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.

Radioactive waste (RAW) conditioning, immobilization, and encapsulation processes and technologies: overview and advances

“…Joule heated melters are relatively intolerant of crystal growth in the melt which causes slag formation. [161] Recently, Sellafield has shown the ability to go to 38 wt% waste loading [162] from 25 wt% waste loading [163] by allowing spinel formation in the melt but the Sellafield melter is induction heated not a JHM design. However, 1-2% crystallization of spinels is planned for Hanford's HLW AJHM and it is anticipated that the spinel crystals will stay buoyant from the melt pool agitation afforded by the bubblers.…”

Calcination and vitrification processes for conditioning of radioactive wastes

“…The AVM process has been operated successfully in France for 30 years and three vitrifi cation plants based on this process have been constructed at Marcoule and La Hague. A similar plant also been constructed at Sellafi eld, UK (Riley et al, 2009). …”