David Griffiths from the Environment Agency's Nuclear Regulation Group was our guest at the spring 2011 NAG meeting to reveal the untold story of how radioactive discharges from the Atomic Weapons Establishment (AWE) have reduced over the last forty years. Using data from AWE and the Ministry of Defence which has never before been presented in public, David gave a fascinating presentation about efforts to drive down the levels of radioactive material released from AWE sites. (A copy of the Powerpoint slideshow with graphs and illustrations used during the talk is available to download at the bottom of the page).
David began by explaining that the Environment Agency has the responsibility of regulating discharges from nuclear licensed sites in England and Wales, but that at many of these sites there are as many non-nuclear environmental hazards posed by chemicals and wastes as there are nuclear hazards. These are also controlled by the Environment Agency, which also has a role to play in advising site operators on construction programmes, flooding issues, and reducing resource usage.
The Agency's aim is not just to ensure that site operators comply with permitted discharge limits, but also to drive down the quantity of radioactive materials released to the environment by securing improvements to production processes and equipment. AWE has made good progress in this respect over recent years and, according to David, “is probably the closest to achieving zero discharges than any other operator in the sector”. Since the 1960s the nuclear industry has changed from being largely unregulated to a very heavily controlled and closely monitored industry, with pressure for improvements in recent years driven by the European Union, the Ospar Treaty, and a 'best practicable environmental option / best available technology' approach to regulation.
The discharge profiles at both AWE sites reflect the evolving approach taken to environmental regulation over the decades, although the two sites have different discharge profiles. Radioactive discharges from Aldermaston reflect the production and manufacturing nature of the site, in contrast to the Burghfield site where discharge levels are lower and of less interest. Aqueous and airborne discharges from both sites show peaks and troughs which reflect events in the UK's nuclear weapons programme and also events at the sites themselves.
For many years aqueous radioactive wastes from Aldermaston were discharged to the River Thames through the Pangbourne Pipeline. Discharges from the pipeline show peaks in alpha radiation in 1956 and in beta radiation in 1965, with a very significant drop in discharge levels from the mid 1970s until the pipeline's closure in 2005. Improvements in process management, a reduction in the volumes of liquid volumes used, and efforts to prevent the ingress of rainwater into contaminated areas led to a large reduction in the volume of effluent generated at Aldermaston, allowing the pipeline to be closed and replaced by a reverse osmosis treatment plant. Radioactive contaminants from the plant are concentrated in sludges which are then solidified and cemented and stored as low level radioactive ease, meaning that liquid alpha and beta discharges from the site have been reduced to a very low level.
Discharges of tritium through the Pangbourne Pipeline showed large peaks in 1974, 1982, and 1990, the last of which coincided with closure of the Herald research reactor and drainage of reactor coolant, with a much smaller peak in 2004 coinciding with work to decommission the reactor.
Rainwater and trade waste from AWE Aldermaston were discharged to a sewer for treatment at Silchester sewage treatment works, and since the closure of the Pangbourne Pipeline in 2005 all effluent from the site has been discharged through this route. The alpha and beta content of these discharges show a number of historical peaks but drop significantly from the early 1990s onwards.
Tritium discharges from Aldermaston remain an issue, largely because of its highly soluble nature and its ability to leach into a variety of substances. Under some circumstances tritium gas discharged as air emissions can dissolve in rainfall and be precipitated back onto a nuclear site as surface water. Explosives components of nuclear weapons which are contaminated with tritium are burnt at the explosives burning ground at Aldermaston and larger volumes of explosives and radioactively contaminated substances may also be burnt at the Qinetiq site at Foulness, although this option is not currently used.
Tritium levels in the Aldermaston stream, which receives surface water run-off from AWE Aldermaston, are higher than expected, and this is believed to be due to leaching from a buried source of tritium-contaminated material, suspected to be an old tip area. As levels of tritium in the stream are below World Health Organisation standards for drinking water and are gradually reducing, the Environment Agency considers there is no benefit in investigating the matter further. AWE Aldermaston site has also suffered from chemical solvent contamination in the Paices Hill area, and a reasonably successful programme to decontaminate groundwater in the area has now been concluded.
Effluent discharges from AWE Burghfield into the Burghfield Brook have historically been much lower than discharges from Aldermaston. No liquid discharges have been made from Burghfield for many years, and liquid wastes, if they arise, are now collected on site and tankered to Aldermaston for treatment.
As with effluent discharges, atmospheric discharges from AWE sites show a number of historical peaks reflecting activities taking place on the site at the time, with much lower levels of emission over recent years. Beta emitters in airborne discharges from Aldermaston show a large spike in the mid 1960s, coinciding with work on the Polaris warhead programme, with tritium emissions showing peaks in the early 1970s, dropping substantially at the end of the 1980s but with smaller peaks over the period 2001-5 coinciding with decommissioning of AWE's old tritium facility, which has been replaced by a new facility with efficient tritium capturing facilities allowing the gas to be retained and re-used.
Alpha emissions to air from AWE Burghfield reflect the nature of the assembly operations at the site, with no smelting or metalworking processes undertaken. Emissions levels are close to the limit of detection and in the Environment Agency's view there is no real need for a discharge limit to be set for the site, although AWE has requested that a limit has been set so that it can demonstrate that the site is complying with legal standards. There have been no tritium discharges from Burghfield since 2000.
The future of the Pangbourne Pipeline is currently under consideration, with AWE and the Ministry of Defence working to identify whether their preferred option for the pipeline is to leave it in situ, remove it, or remove certain sections. The Ministry of Defence claims to have the money available to decommission the pipeline and would apparently prefer to dismantle the entire pipeline to limit legacy liabilities, but landowners for some sections of the route have said they do not wish the pipeline to be removed.
Further information about radioactive discharges from AWE sites is gathered from monitoring programmes conducted by the Food Standards Agency and other authorities and is available in a number of published reports.
We would like to thank David Griffiths for attending the meeting as our guest speaker, and also to staff at AWE and the Ministry of Defence for preparing the data used in the presentation.
You can download a copy of David's presentation here: