Decommissioning of Nuclear Power PlantsCase Study:Dounreay Nuclear FacilitySamuel ChapmanHeriot-Watt University
Dounreay siteOpened in 1955Developing Fast Breeder Reactor Technology (FBR)Operated by United Kingdom Atomic Energy Authority (UKAEA)Site has three nuclear reactors
LocationSites of UKAEA
Three ReactorsDounreay Materials test reactor (DMTR)1958 - 1969Dounreay Fast Reactor (DFR)On-line November 1959Supplied National Grid from 1962Taken off-line for decommissioning, 1977Supplied 600 million kWh during lifespanPrototype Fast Reactor (PFR)Supplied grid from 1975 - 1994
1994: end of nuclear power generation at site
Subsequent ActivityReactors have all been shut downCare and maintenance of old plant and decommissioning activities have meant that large work-force retained. Commercial reprocessing of spent nuclear fuel and waste stopped by the UK government in 1998.Some waste is still accepted from other nuclear facilities in special circumstances
Future of SiteOn 1 April 1995 the Nuclear Decommissioning Authority (NDA) became the owner of the siteUKAEA remaining as operator.Decommissioning of Dounreay is planned to bring the site to an interim care and surveillance state by 2032. Brown-field site by 2336, at a total cost of 2.9 billion (~2.18 billion)
Apart from decommissioning the reactors, reprocessing plant, and associated facilities;there are five main environmental issues to be dealt with:
Irradiated nuclear fuel particles on the seabed near the plant, estimated about 10,000 in number. Some are being washed ashore, including as of 2006 about 70 smaller particles on the public Sandside Bay beach and one at a popular tourist beach at Dunnet. The way these particles escaped the site has not been determined, there are several plausible possibilities. The risk to the public is considered low.1
18,000m3 of radiologically contaminated land, and 28,000m3 of chemically contaminated land.
1,350m3 of high and medium active liquors and 2,550m3 of unconditioned intermediate level nuclear waste in store.
1,500 tonnes of sodium, 900 tonnes of this radioactively contaminated from the Prototype Fast Reactor.
A 65m deep shaft used for intermediate level nuclear waste disposal.Shaft never designed as waste depository and was used on a very general and poorly monitored basis. Relic of a process by which a waste-discharge pipe was constructed, designed to discharge into sea. Historic use of the shaft as waste depository has resulted in one hydrogen gas explosion. At one time it was normal for workers to fire rifles into the shaft to sink polythene bags floating on water.5
In 2007 UKAEA pleaded guilty to four charges under the Radioactive Substances Act 1960 relating to activities between 1963 and 1984.One of disposing of radioactive waste at a landfill site at the plant between 1963 and 1975 and, three of allowing nuclear fuel particles to be released into the sea, resulting in a fine 140,000.
Current State of ShaftMore than 11,000 disposals took place until 1977. A wide variety of radiologically contaminated material was dumped in Shaft. Since then, environmental legislation has been tightened.UKAEA are now required to remove all the waste from the Shaft.
A 16 million contract to isolate the Shaft was awarded in October 2004 to Ritchies, the specialist geotechnical division of Edmund Nuttall Ltd.
Contents of Shaft
Hydraulically Isolating Shaft Isolating the Shaft involves building a raised working platformDrilling up to 400 boreholes and injecting grout into rock fractures and the liquid effluent discharge tunnel Restricts water movement to and from the ShaftCreates a stable environment for waste retrieval in the future
Working PlatformTo allow the boreholes to be drilled requires use of raised working platformConstructed by placing a concrete core within a structural concrete facingBuilt up from the height of the existing Dounreay foreshore to the height of the existing Shaft building.
Contruction Phases of Raised Concrete Platfrom
Natural state of proposed location
Construction ProblemsCoastal Situation
Commencing of Borehole Drilling
Locations of initial sealing of outflow pipe
Future?Complete decommissioning of the site
Removal of three reactors, waste from shaft and construction materials
Still nowhere yet for permenant storage of waste!Stored at Dounreay, above ground stores pending a national policy for the management of intermediate-level waste.
Thanks for your Attention!
BibliographyUKAEA websitehttp://www.ukaea.org.ukDecommissioning factsheetShaft project updatesShaft isolation Project_Raised Platform ConstructWikipediaDounreayGoogle Images