The Nuclear Decommissioning Authority

 

UKAEA Ltd is carrying out a detailed study of graphite – a fundamental component of Magnox and Advanced Gas-cooled Reactors (AGRs) – to assist in understanding the options for its treatment and disposal across the UK.

Graphite is a form of carbon that occurs naturally in the environment and can also be manufactured. For the UK Magnox reactors, graphite is manufactured in the form of bricks, which surround the fuel and are used to moderate or slow down the nuclear reaction.

With more than 99,000 tonnes (79,000m3), the UK has the largest graphite inventory in the world. Categorised as Intermediate Level Waste, the waste arises from operational and reactor decommissioning activities.

Compared to other forms of ILW, graphite waste is stable and relatively low hazard, though long-lived. Once packaged, it is currently destined for burial in the Geological Disposal Facility (GDF) where it will account for 33% of the available space.

The Government's Committee on Radioactive Waste Management has, however, recommended that alternatives to geologicial disposal should be examined for graphite.

Lisa Hughes, Reactor Decommissioning Waste Project Manager, explained that an in-depth understanding of graphite characteristics was key to exploring alternative treatment and disposal options. She added:

"This work is a key contributor to exploring alternative management routes for reactor graphite which was a major commitment in the NDA's 2006 strategy. By improving our confidence in the graphite inventory we will be able to understand whether alternative management options are feasible."

The NDA-funded programme is being delivered by UKAEA Ltd, on behalf of NDA, with an extensive supply chain including Manchester University, Galson Sciences Limited and the National Physical Laboratory. The aims are to increase the certainty of the NDA's graphite inventory and clarify its consistency across the NDA estate.

UKAEA has reused archived graphite samples originally extracted from operating reactors as well as un-irradiated samples of graphite which have been stored since the reactors were constructed. The original chemical composition of un-irradiated samples is being investigated because it has a critical influence the composition of irradiated graphite.

The campaign to analyse the un-irradiated graphite samples is ongoing. However, the early results are extremely promising, demonstrating that the computer modelling process developed by UKAEA provides accurate results and can be used with confidence to predict the characteristics of irradiated graphite.

In the longer term, an accurate inventory will enable different, more appropriate treatment and disposal methods to be developed that are potentially more cost-effective, while avoiding taking space in the GDF that could be used for higher-hazard waste.

The programme will be complete by March 2011 with a full set of irradiated graphite sample results, confirmation of un-irradiated graphite quantities, and the impact of these results on the model predictions.