Graphite Decommissioning: Options for Graphite Treatment, Recycling, or Disposal, Including a Discussion of Safety-Related

Although graphite is not a major waste form in LWR reactors it nevertheless represents a verysignificant problem in nuclear plant decommissioning for many of EPRI’s internationalmembers. Graphite is used as a moderator material in many reactor types, particularly the gascooled reactors in UK and France. It is also used for minor components such as fuel elementsleeves. In all there are about 250,000 tonnes of graphite waste to be dealt with indecommissioning worldwide. Although there are some examples of successful graphite disposition (most notably at Fort StVrain in the US), not much progress has been yet been made with graphite managementelsewhere. This is due to a combination of “SAFESTORE” policies, concerns relating to safetyof handling and disposal and absence of suitable disposal facilities. In most cases graphitemoderators of retired reactors have simply been left “in-situ” whilst graphite fuel sleeves havebeen deposited in silos which are not suitable environments for long-term disposal. However,several countries (including the UK and France) have changed their policies and now wish to seereactors and their graphite moderators and components appropriately dispositioned as soon aspossible. The methodology and safety of dismantling, and waste disposition of graphite havethus rather suddenly become important topics. Graphite has particular characteristics that make it a very special waste form. The phenomenonof stored “Wigner energy”, which contributed to the Windscale reactor fire in 1957, theperceived possibilities of conventional fire and dust explosion, and the problems associated withisotope inventories of carbon-14 and chlorine-36, are some of the issues. For disposal there arethe possibilities of conventional burial, oxidation to the gas phase and release as carbon dioxide(with radionuclide retention as appropriate) or recycling into new graphite or carbon products.In particular, new high-temperature reactors will require graphite, which should ideally bemanufactured with a proportion of recycled waste graphite if possible. This report discusses all the issues relating to handling and disposal of graphite in depth. Itconcludes as follows:1. Adequate information exists to enable graphite moderators to be safely dismantled andprocessed.2. Concerns about Wigner energy are limited to the minority of reactors in which the moderatoroperated at low temperature. The phenomenon is well understood, and appropriateprecautions can be defined to avoid unacceptable energy release.