Guide to nuclear decommissioning

Transcription

1 Guide to nuclear decommissioning Contents: What is decommissioning? Stages of decommissioning Site restoration Waste management The UK decommissioning industry The international picture What is decommissioning? There comes a time in the life of any power station nuclear, coal or oil-fired when age takes its toll and it becomes uneconomic to run any longer. Once this stage has been reached the decision has to be taken to shut it down. Eventually the plant is taken to pieces to remove any hazardous material, the debris disposed of and the site left in a safe condition which is visually acceptable. This is called decommissioning. Each project is treated on its merits; actions can range from simply closing the facility to dismantling and restoration of the land for other use. Decommissioning is not unique to the nuclear industry. For example, chemical companies use similar practices to dismantle and dispose of obsolete plants which have been used to handle hazardous compounds. In the course of restoring a nuclear site, a variety of facilities need to be decommissioned. Reactors, support laboratories and plants used for fuel and waste storage and treatment all present challenges involving many different types of contaminated material. The overriding approach with any decommissioning project is to ensure safety and protection for the environment. UKAEA has carried out more nuclear cleanup work than any organisation in Europe, dismantling 15 reactors and over 40 major radioactive facilities. Today, new nuclear plant is designed with decommissioning in mind. However, many of the facilities removed by UKAEA were experimental devices built in the early days of the nuclear industry. UKAEA has proved largely through innovative use of existing technology that such facilities can be removed safely, predictably and costeffectively. Reactor decommissioning at Harwell

2 Stages of decommissioning There are three stages of decommissioning a nuclear facility: 1. Initial decommissioning Reactors are defuelled and the fuel usually moved away from the reactor. All non-fixed contaminated components are removed. For non-reactor facilities, all radioactive sources and readily removable equipment are taken out. The structure is maintained intact and the atmosphere inside the containment building and enclosures are controlled. This stage is sometimes referred to as post operational clean-out (POCO). 2. Decontamination and dismantling Contaminated equipment is dismantled in carefully planned steps. This involves decontamination to minimise the amount of radioactive waste which is generated. Once a building is stripped of all its internal equipment, it is carefully surveyed to determine the extent of contamination in the building fabric. Simple processes of washing and scabbling are generally sufficient to decontaminate the building. 3. Demolition Once all radioactive and other hazardous material (such as asbestos or mercury) have been removed, the building is refurbished for alternative uses or demolished if no longer required. Demolition is carried out in the same way as for any industrial building, although stringent controls are applied to monitor for the possible presence of radioactivity. The land is then remediated and returned to a condition where no radioactive hazard remains. In some cases the stages will follow directly one after the other. However, they are often separated by periods of care and maintenance to allow for radioactive decay.

3 Site restoration Restoring the environment of a whole nuclear site involves integrating a large range of individual projects within an overall programme. UKAEA has led the development of site restoration plans that prioritise these projects based on safety, environmental and cost considerations. The end-point for decommissioning a site depends on the potential for its future use. Ideally the site will be restored for unrestricted alternative use. However, our overriding consideration is whether it is the Best Practicable Environmental Option (BPEO). The BPEO assessment takes account of the needs of the environment, safety of workers and the local community, and the practicability of the clean-up operations. Consulting our stakeholders is an integral part of the BPEO assessment process. Where the assessment decides that release of land for unrestricted use is the BPEO, UKAEA seeks regulatory approval to delicense or remove it from nuclear site restrictions. This involves remediating the land and carrying out extensive environmental surveys to demonstrate to the regulators that there is no danger from ionising radiation. Restored nuclear sites can often be regenerated for the benefit of local communities. UKAEA has successfully established business centres at its Harwell and Winfrith sites, and sold former research sites at Risley and Culcheth for commercial development. 1. New business premises at the Harwell site 2. The site of a major plutonium facility at Winfrith has been restored to greenfield

4 Waste management Decommissioning nuclear facilities can generate large amounts of radioactive waste. Much of this waste is no more harmful than Brazil nuts, coffee or garden fertiliser, which are naturally radioactive. UKAEA has experience in managing a wide variety of waste types safely and securely. In each case we assess all relevant options, so that the chosen strategy represents the best balance of environmental, safety, economic and community considerations. UK radioactive wastes are classified into a number of categories, as follows. Very low-level waste (VLLW) Waste which can be safely disposed of with ordinary refuse, each 0.1 m 3 of material containing less than 400 kbq of beta/gamma activity or single items containing less than 40 kbq of beta/gamma. Comprises of demolition rubble and similar materials. Low-level waste (LLW) Wastes containing radioactive materials other than those acceptable for disposal with ordinary refuse, but not exceeding 4 GBq/te alpha or 12 GBq/te beta/gamma activity. LLW accounts for by far the largest volume of waste from nuclear activities almost 90%. The waste includes anything from contaminated tools and equipment to rubble from demolished facilities. - Solid LLW at our English sites is mainly sent to the LLW disposal facility at Drigg in Cumbria. Dounreay LLW is held on the site pending a longer-term disposal solution. - Liquid LLW at UKAEA sites is treated to remove as much of the radioactivity as possible before discharging the treated liquid within stringent authorised limits. Separated solids containing the radioactivity are immobilised and managed with other solid wastes on the sites. Intermediate-level waste (ILW) Wastes with radioactivity levels greater than LLW, but which do not require heating to be taken into account in the design of storage or disposal facilities ILW. Material can vary from solid reactor components to liquid coolants and sludges from treatment processes. There is no UK disposal facility for ILW and the Government is consulting on a long-term national strategy for managing it. - UKAEA policy is to condition solid and liquid ILW in a passively safe form and store it securely until a permanent disposal route is available. High-level waste (HLW) The temperature of this waste can rise significantly as a result of its radioactivity, so this factor has to be taken into account in designing storage or disposal facilities. HLW arises from the reprocessing of spent nuclear fuel. - UKAEA sites do not have any HLW. For more information on radioactive waste, please see

5 The UK decommissioning industry The Nuclear Decommissioning Authority (NDA) is responsible for overseeing the 48 billion restoration of the UK s 20 civil nuclear sites, including those operated by UKAEA. The NDA provides national co-ordination and ensures that best practice and value for money is being achieved. It contracts out the management of its site clean-up programmes UKAEA is a contractor for management of the Dounreay, Harwell, Windscale and Winfrith sites. The NDA monitors site clean-up progress against Near Term Work Plans showing the detailed scope of work for the first three years and long-range Lifecycle Baseline plans covering the entire restoration process. They are available at UKAEA s decommissioning operations in the UK are regulated by the Nuclear Installations Inspectorate part of the Health and Safety Executive and by the Environment Agency (Dounreay is subject to regulation by the Scottish Environment Protection Agency). The regulators must be satisfied that all relevant health, safety and environmental considerations are being met before projects can be carried out. The international picture Around the world, nuclear clean-up is becoming a major growth industry, with over 400 reactors being decommissioned or awaiting decommissioning. UKAEA s work in cleaning up UK nuclear sites has set international standards. Pioneering decommissioning projects such as the Windscale Advanced Gas-cooled Reactor have attracted interest from organisations facing similar challenges in other countries. We are therefore well placed to advise on best practice, and so far we have supplied consultancy services to decommissioning agencies in over a dozen countries including South Africa, Australia, Denmark and Canada. We also help raise global understanding of decommissioning issues through collaboration agreements with France's Commissariat a l'energie Atomique (CEA), the Idaho National Engineering and Environmental Laboratory in the USA, Italian Government Agency SOGIN and Electricité de France. Decommissioning the Windscale Advanced Gas-cooled Reactor