Report of the RPII Visit to BNFL Sellafield

Transcription

1 RPII 05/01 Report of the RPII Visit to BNFL Sellafield P.A. Colgan D. Pollard C. Hone C. McMahon A.T. McGarry

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3 Report of the RPII Visit to BNFL Sellafield Report of the RPII Visit to BNFL Sellafield P.A. Colgan D. Pollard C. Hone C. McMahon A.T. McGarry April 2005

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5 Report of the RPII Visit to BNFL Sellafield Contents 1. Introduction 1 2. Summary of Operations at BNFL Sellafield Introduction Reprocessing at BNFL Sellafield The Magnox Operating Plan (MOP) 4 3. Site Visits The Magnox Fuel Storage Pond and Decanning Facility The Solid Active Waste Storage Facility The Medium Active Concentrate (MAC) Storage Tanks The Highly Active Liquor Evaporation and Storage (HALES) Plant The Waste Vitrification Facility The Thermal Oxide Reprocessing Plant (THORP) Emergency Planning Arrangements at BNFL Sellafield The BNFL Sellafield Reference Accident Structure of Emergency Response The Sellafield District Control Centre (DCC) Security Issues post 9/ Conclusions Plant Operations Radioactive Discharges Emergency Preparedness Terrorist Threats References 16 ANNEX 1 17 ANNEX 2 21 ANNEX 3 28

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7 Report of the RPII Visit to BNFL Sellafield 1 1. Introduction In 2002 the Irish Government initiated international legal proceedings against the United Kingdom (UK) under the United Nations Convention on the Law of the Sea (UNCLOS) in relation to the Sellafield MOX Plant. The Tribunal in the case issued an Order on 24 June 2003 after hearing an application by Ireland for Provisional Measures. The Provisional Measures Award recommended inter alia that Ireland and the UK enter into dialogue to improve cooperation and consultation between the two Governments. As part of this process the Irish Government expressed an interest in further visits to BNFL Sellafield by officials of the Radiological Protection Institute of Ireland (RPII). A previous factfinding visit had taken place in February Written proposals for a visit were presented to the UK in January In their response to the proposals, the UK invited the RPII, together with relevant officials from the Department of the Environment, Heritage and Local Government, to a background briefing at the headquarters of the Health and Safety Executive in Bootle in advance of a visit to BNFL Sellafield. The background briefing, conducted over two-and-a-half days, was comprehensive and contributed significantly to understanding the regulatory approach by both the Health and Safety Executive s Nuclear Installations Inspectorate (NII) and the Environment Agency (EA) and the regulatory regime currently in place at BNFL Sellafield. The briefing also addressed the current principal regulatory issues at BNFL Sellafield including details of a revised Discharge Authorisation to be issued by the Environment Agency to take effect in October 2004 and the considerations underpinning the current regulatory obligations imposed by the NII on the BNFL Sellafield site in relation to the reduction of the Highly Active Liquor (HAL) stocks to buffer stock levels by The facilities included as part of the visit were: The redundant Magnox Fuel Storage Pond and Decanning Facility; The Solid Active Waste Storage Facility; The Medium Active Concentrate (MAC) Storage Tanks; The Highly Active Liquor Evaporation and Storage (HALES) Plant; The Waste Vitrification Facility (WVF); and The Thermal Oxide Reprocessing Plant (THORP). Throughout the visit representatives of BNFL, the NII and the EA accompanied the RPII delegation. The RPII met key BNFL personnel in each of the areas visited as well as representatives of the main worker unions. On the second day of the visit the RPII discussed on-site and offsite emergency arrangements with staff of BNFL Sellafield and the emergency planning officer of Cumbria County Council responsible for the BNFL Sellafield site. A summary of the regulatory activities of the NII and of the EA can be found in Annexes 1 and 2 respectively. General information on emergency response planning and procedures in the UK can be found in Annex 3. Five members of staff of the RPII visited BNFL Sellafield over the period September The purpose of the visit was to see at first-hand a small number of on-site facilities of particular interest and concern to Ireland and to explore the changing nature of operations at the site. Issues of security were outside the scope of the visit.

8 2 Report of the RPII Visit to BNFL Sellafield 2. Summary of Operations at BNFL Sellafield 2.1 Introduction BNFL Sellafield is a 700-acre nuclear site in Cumbria in the North West of England. The site is located close to the Irish Sea and at its closest point (Clogher Head, Co. Louth) is approximately 112 miles from the Irish coastline. In the late 1940s work commenced at the site on the construction of two nuclear piles for the production of plutonium for military use. These are commonly referred to as the Windscale piles. Electricity production commenced at the site in 1956 when the first of four Calder Hall nuclear reactors came into operation. The last of these closed down in March Sellafield was also the site of an experimental reactor, the Windscale Advanced Gas-cooled Reactor (WAGR), which is being decommissioned presently. Today the main activities at BNFL Sellafield include the storage and reprocessing of spent nuclear fuel 1, the storage of plutonium and uranium, the fabrication of mixed oxide (MOX) fuel and decommissioning activities. Previous non-commercial operations that have ceased have resulted in large amounts of radioactive waste being stored in various buildings around the BNFL Sellafield site. These are often referred to as legacy wastes 2. The clean-up 3 of these facilities represents a major challenge that has begun to be addressed and will be the primary focus of future activities at BNFL Sellafield once commercial reprocessing operations come to an end. 2.2 Reprocessing at BNFL Sellafield After being removed from a nuclear reactor, the spent nuclear fuel still contains approximately 96% uranium. The remainder consists of plutonium (1%) and a number of other highly radioactive materials collectively called fission products. Spent fuel is highly radioactive and generates a large amount of heat; it therefore needs to be managed very carefully to protect both man and the environment. One way of managing spent nuclear fuel is by separating it into its constituent parts. This is called reprocessing. Reprocessing was first developed to provide plutonium for military purposes. Plutonium can also be used in a modern reactor design called a fast breeder reactor but there is currently little interest in developing this type of reactor. One further use for plutonium is in the manufacture of mixed oxide (MOX) fuels for burning in some commercial nuclear reactors. The majority of UK nuclear reactors are not suited to the burning of MOX fuel. UK nuclear reactor sites are shown in Figure 1. There are two reprocessing plants on the BNFL Sellafield site. One of these, the Magnox reprocessing plant, reprocesses spent fuel from Magnox reactors. Magnox technology was developed in the UK and is principally confined to the UK. The Thermal Oxide Reprocessing Plant (THORP), which came into full operation in 1995, reprocesses uranium oxide fuel used in several different types of nuclear reactors in the UK, Europe and Japan. Figure 2 shows the various steps in the reprocessing of spent nuclear fuel through THORP. Following delivery to the BNFL Sellafield site for reprocessing, the spent fuel is stored in cooling ponds, often for several years, in order to allow some of the heat to dissipate and the amount of radioactivity present to reduce by natural decay. The spent fuel is then chopped into small pieces and dissolved in hot nitric acid 4. The casing is segregated and stored as intermediate-level radioactive waste. A solvent is then added that separates out the uranium and plutonium for purification and storage. What remains is high or medium-level radioactive waste in concentrated liquid nitric acid. 1 Conventional nuclear fuel consists of a mixture of uranium-235 and uranium-238. This is used in a nuclear reactor to produce energy. Spent nuclear fuel is nuclear fuel that has been removed from a nuclear reactor. Spent nuclear fuel contains uranium-235, uranium-238, plutonium and a number of highly radioactive materials collectively referred to as fission products. 2 In the 2002 UK White Paper on managing the nuclear legacy (DTI, 2002), legacy wastes are defined in the following terms those nuclear sites and facilities now operated by the United Kingdom Atomic Energy Authority (UKAEA) and British Nuclear Fuels plc (BNFL), which were developed in the 1940s, 50s and 60s to support the Government s research programmes, and the wastes, materials and spent fuel produced by those programmes; and the Magnox fleet of nuclear power stations designed and built in the 1960s and 70s and now operated on the Government s behalf by BNFL, plant and facilities at Sellafield used for the reprocessing of Magnox fuel and all associated wastes and materials. 3 clean-up is defined as the decontamination and decommissioning of a nuclear licensed site. 4 The casing of Magnox fuel is removed before the fuel is dissolved. In the case of oxide fuels processed through THORP, the fuel and its casing are chopped into small pieces. The nitric acid dissolves the fuel but not the casing, which is then segregated for storage as intermediate-level waste.

9 Report of the RPII Visit to BNFL Sellafield 3 Figure 1 Location of BNFL Sellafield and UK Nuclear Reactor Sites Hunterston A & B Torness Chapelcross Hartlepool Sellafield/ Calder Hall Wylfa Heysham I & II Trawsfynydd Sizewell A & B Berkeley Oldbury Bradwell Hinkley Point A & B Dungeness A & B

10 4 Report of the RPII Visit to BNFL Sellafield Figure 2 Reprocessing of Spent Nuclear Fuel through THORP Reactor Solid Waste Store Discharges of Gases to Air High-Level Waste Storage Tanks Shipment of Spent Reactor Fuel Spent Reactor Fuel THORP Storage Pond Fuel Assemblies THORP Liquid Waste EARP Plutonium Oxide Uranium Oxide Liquid Discharges Liquid Discharges Discharges to Air & Sea Plutonium Store Uranium Store IRISH SEA Reprocessing generates large amounts of radioactivity for which there is no end use. This waste material is classified according to its radioactive content as high-, intermediate- or low-level waste. Highlevel liquid radioactive wastes are stored in the Highly Active Storage Tanks (HASTs) before being incorporated into glass blocks (a process known as vitrification) for long-term storage. Intermediate-level radioactive waste is stored on-site at BNFL Sellafield while low-level radioactive waste produced at BNFL Sellafield is disposed of at a nearby waste repository called Drigg. Reprocessing also gives rise to liquid radioactive discharges into the Irish Sea and gaseous radioactive discharges to the environment. These discharges are classified as low-level radioactive wastes. Reprocessing at BNFL Sellafield evolved into a commercial activity in the 1980s, providing uranium and plutonium for reuse in the manufacture of nuclear fuel. However, given the current low world price for uranium it is cheaper to mine and mill fresh uranium than to re-use uranium recovered during reprocessing. In the absence of a fast breeder reactor programme the only alternative to longterm storage or disposal of plutonium is the manufacture of MOX fuel in the Sellafield MOX Plant. The plutonium is mixed with uranium and the MOX fuel can be used in certain nuclear reactors to generate electricity. There are currently no plans to produce MOX fuel from the UK s own plutonium stocks but some contracts do exist with BNFL s overseas customers for the conversion of their plutonium into MOX fuel for burning in nuclear reactors in their own countries. On 1 April 2005 a new Nuclear Decommissioning Authority (NDA) takes over responsibility for the management of all legacy wastes at designated sites (NDA, 2004) as well as current and future decommissioning programmes in the UK. The NDA also assumes responsibility for the commercial activities on the BNFL Sellafield site, namely the reprocessing operations at THORP and the manufacture of MOX fuel. 2.3 The Magnox Operating Plan (MOP) The UK s nuclear power programme, announced in 1955, called for 5,000 megawatts of generating capacity through the construction of a series of Magnox reactors across the country. The fuel used in Magnox nuclear reactors consists of natural uranium encased in magnesium alloy. When stored underwater, Magnox spent fuel undergoes corrosion, initially of the magnesium alloy cladding and subsequently of the uranium metal within. Dry storage has also been considered but is not a proven long-term management option, although interim storage of

11 Report of the RPII Visit to BNFL Sellafield 5 Magnox spent fuel does take place at the Wylfa nuclear power plant. According to the UK Radioactive Waste Management Advisory Committee even if dry stored [Magnox spent fuel] would need to be in a carefully controlled environment and would not be in line with the concept of passivity. If a policy of deep disposal were ultimately pursued, the fuel would also then subsequently have to be suitably conditioned, given that it would still be reactive in a geological environment. Currently, no industrial-scale process exists to do this, other than reprocessing itself. It is therefore rational to continue to reprocess the [Magnox] spent fuel (RWMAC, 2000). Thus the UK s policy for managing Magnox spent fuel is based primarily on the reactivity of the fuel and the fuel cladding, which in turn makes it unsuitable for ultimate disposal unless it is reprocessed. The only Magnox stations still operating are in the UK, where they produce approximately 8% of the UK s electricity. Previously, Magnox power stations operated at Latina in Italy and Tokai Mura in Japan. In May 2000 BNFL announced the planned closure dates for its remaining Magnox reactors. Following a number of safety-related incidents at both Calder Hall and Chapelcross, the closure dates for these reactors were brought forward as their continued operation could not be justified economically. The UK Strategy for Radioactive Discharges (DEFRA, 2002) also brought forward the closure dates for Oldbury and Wylfa (previously 2013 and 2016/2021 respectively). The most up-to-date timetable for closure, defuelling and decommissioning of the Magnox stations is given in Table 1. The Magnox Operating Plan (MOP) places priority on the reprocessing of Magnox spent nuclear fuel. OSPAR Contracting Parties, including the UK, undertook in 1998 to reduce radioactive discharges so that, by 2020, the additional concentrations in the marine environment above historic levels, arising from such discharges, are close to zero (OSPAR, 1998). This goal is to be achieved through progressive and substantial reductions in radioactive discharges. The Magnox reprocessing plant is due to cease operation by the end of This date is consistent with the closure date for the final Magnox station (Wylfa) in 2010 and the NII specification to reduce HAL volumes in the HASTs by 2015 (HSE, 2000a). To achieve the 2012 operational deadline requires approximately eight years of good operation of all plants including the liquid effluent treatment plants - linked to the Waste Vitrification Facility. Procedures are in place to monitor the implementation of the MOP so that steps can be taken if problems arise. If the HAST specification is not complied with, then the NII has the authority to close the Magnox stations at an earlier date or to constrain the operation of THORP so as to give priority to Magnox reprocessing. Restricting the operation of THORP would still allow the 2015 specification to be met but would extend the time period over which THORP reprocessing would take place. Table 1 Current Status of UK Magnox Reactors Station Commissioned Current Status Berkeley 1962 closed 1989 being decommissioned Hunterston A 1964 closed 1989 being decommissioned Trawsfynydd 1965 closed 1991 being decommissioned Hinkley Point A 1965 closed 2000 being defuelled Bradwell 1962 closed 2002 being defuelled Calder Hall 1956 closed 2003 awaiting defuelling (2005) Chapelcross 1958 closed 2004 awaiting defuelling (2005) Dungeness A 1965 to close 2006 Sizewell A 1966 to close 2006 Oldbury 1967 to close 2008 Wylfa 1971 to close 2010

12 6 Report of the RPII Visit to BNFL Sellafield 3. Site Visits 3.1 The Magnox Fuel Storage Pond and Decanning Facility The Magnox Fuel Storage Pond and Decanning Facility came into operation in Its principal role was to receive and store irradiated spent fuel from Magnox reactors and to remove the fuel cladding (a process called decanning ) prior to the fuel being reprocessed. Initially a wet decanning process was used but later a dry decanning facility was added. A new Magnox Fuel Handling Plant was commissioned in 1986 and a phased handover to the new plant took place in the early 1990s. The Magnox spent fuel is stored underwater in a pond that is exposed to the open air. The pond is approximately 60 m in length and 12 m in width. The casing of Magnox fuel is subject to corrosion and this limits the amount of time for which it can be stored underwater to approximately one year. Around 1974 a reprocessing shutdown led to the accumulation of spent Magnox fuel in the storage ponds; this started to corrode and leak, making it almost impossible, with the technology available at the time, to recover and reprocess the contents. Over the years this has resulted in the accumulation of highly radioactive spent fuel in the form of sludge on the bottom of the storage ponds, which by the mid 1980s meant that it was no longer feasible to operate the plant reliably. This sludge contains uranium, plutonium and a range of fission products. Around this time the ponds were also used to store other radioactively contaminated material generated in the plant. This includes material such as iron bars, pumps, solid material contaminated as a result of routine operations, etc. The total inventory of contaminated material and its radioactive content is not accurately known and this adds to the complexity of the clean-up operations. The NII regards the clean-up of this facility as one of the major onsite priorities and it has specified a date of August 2010 by which 90% of the sludge in the tanks must be removed. A further specification requires that at least 80% of the total volume of all sludges originating from operations prior to 1 August 2000 and which have been accumulated as radioactive waste shall be stored in a passive form by Material retrieved from the ponds will be classified as intermediate-level waste i.e. it will be encased in concrete, placed in metal drums and stored on the BNFL Sellafield site. BNFL has put in place a project team with an annual budget of 150 million to decommission the facility. While considerable advances have been made in improving the building condition, developing contingency plans and retrieving some of the wastes, there are many unknowns and unforeseen problems arise on a regular basis (Travis, 2003). The dose rates inside the plant present a major constraint on working times and mean that much of the work has to be done remotely. Dose rates along the south wall of the pond, for example, are as high as 1 Sievert per hour in places. This compares with the annual dose limit for a radiation worker of 0.02 Sievert. On-going work is necessary to upgrade basic safety facilities and to stabilise and make safe the structures in order that the decommissioning work can continue. These factors greatly increase the technical complexity of the decommissioning operations. After the NDA takes over responsibility for clean-up operations at several UK sites, including BNFL Sellafield, in April 2005, it will have available to it an annual budget of 1.2 billion for each of the first three years of its operation. While the NDA is free to set its own priorities for the clean-up of the UK s nuclear sites, there is confidence that the current clean-up and decommissioning programme for this plant will continue. The water in the pond serves the dual purpose of cooling the pond contents while also acting as a shield to reduce radiation doses to workers. These waters are routinely transferred to the Site Ion Exchange Effluent Plant (SIXEP), where they are treated to remove radionuclides prior to discharge, and replaced by fresh uncontaminated water. As part of the new EA Discharge Authorisation for BNFL Sellafield, which came into force on 1 October 2004, BNFL is required to estimate the actual discharges from all of its major operations. The clean-up and decommissioning of the Magnox Fuel Storage Pond and Decanning Facility is regarded as one such major operation. Estimated discharges for current operations must be submitted to the EA on an annual basis with the first such submission required at the end of June 2006.

13 Report of the RPII Visit to BNFL Sellafield The Solid Active Waste Storage Facility The Solid Active Waste Storage Facility was commissioned in 1952 for the dry storage of intermediate-level waste, principally the casings that had been removed from spent fuel. The facility is a reinforced concrete structure sub-divided into a number of compartments, normally referred to as silos. Routine tipping of waste into these silos ceased in However small quantities of miscellaneous beta/gamma wastes were placed in the silos up to In addressing the on-going maintenance and eventual decommissioning of the facility there are two principal issues. The first is the potential for a fire and/or explosion from Magnox casings stored in a dry environment. This risk was previously evaluated by BNFL and considered unacceptable with the result that the building is now maintained in an argon-rich environment. Argon is an inert gas that significantly reduces the risks of fire from dry storage of fuel cladding. To ensure an uninterruptible argon supply, back-up safety systems have been installed and are regularly tested. The second issue is the very high radiation levels present. These are due to a combination of, the small amounts of spent fuel that remained attached to the casing at the time of mechanical separation, irradiation products and the miscellaneous beta/gamma emitters referred to above. Waste material from the facility is classified as intermediate-level waste. As with the sludges and other waste materials arising from the clean-up operations at the Magnox Fuel Storage Pond and Decanning Facility, this waste will be retrieved, packaged and stored on-site in metal drums. However the timescale for these activities has yet to be established. 3.3 The Medium Active Concentrate (MAC) Storage Tanks The MAC storage tanks were built in the late 1940s and are used to store liquid wastes generated by Magnox reprocessing before being sent to the Enhanced Actinide Removal Plant (EARP). In EARP, chemical treatment of the wastes removes much of the strontium-90, caesium-137, americium-241 and plutonium prior to discharge to the Irish Sea. Since March 2004, the chemical tetraphenylphosphonium bromide (TPP) has been added to MAC as it passes through EARP and this removes the bulk of the technetium-99 present in this waste stream, resulting in a significant reduction in discharges of technetium-99 into the Irish Sea. Current and future arisings of MAC are diverted directly to the HALES building where they are added to high-level radioactive wastes prior to vitrification. The NII has expressed its concern about the prolonged use of..[the tanks].. to store MAC because of the age of the tanks (built in the late 1940s) and the deteriorating condition of the building structure 5. Specifically the NII cited that the roof of the building could collapse, damaging the tanks and leading to a release of radioactivity to the environment. The NII is satisfied that the tanks are structurally sound up to The current discharge strategy will see the tanks emptied by this date and this will further reduce the overall hazard on the site. Over the past year approximately 65% of the stored MAC has been removed from the tanks. The BNFL Sellafield discharge authorisation issued by the EA will allow the contents of the MAC storage tanks to be emptied within the timescale acceptable to the NII. At present the EA is considering a request from BNFL to accelerate the treatment and discharge of MAC. If this proceeds, the on-site hazard will be reduced more quickly than is presently foreseen. MAC is normally stored for a period of three years in order to allow the ruthenium- 106 content to reduce by radioactive decay. A change to the present timetable will reduce the storage time to less than three years and this will result in a small increase in the quantity of this radionuclide discharged to the Irish Sea 6. Ruthenium-106 is not presently detected in the Irish marine environment and it is unlikely that the small increased discharges resulting from the earlier emptying of the MAC storage tanks will change that. However, in future years BNFL Sellafield is likely to handle spent fuels which have spent longer times in the reactor and which are stored for shorter periods prior to reprocessing. These two factors could potentially further increase the discharges of ruthenium- 106 to the Irish marine environment if no abatement is applied. 5 Letter to Rt. Hon. Margaret Beckett, M.P. from Laurence Williams, NII Chief Inspector dated 13th January Ruthenium-106 has a half-life of approximately one year and therefore prolonged storage can significantly reduce the amount present. EARP does not remove ruthenium-106 from MAC prior to discharge.

14 8 Report of the RPII Visit to BNFL Sellafield 3.4 The Highly Active Liquor Evaporation and Storage (HALES) Plant The HALES Plant contains over 90% of the on-site radioactivity in the form of waste and is where the Highly Active Storage Tanks (HASTs) are located. The HASTs contain high-level liquid radioactive wastes, commonly referred to as Highly Active Liquors (HAL), awaiting vitrification. On arrival, waste streams sent to the HALES plant are evaporated to reduce the volume of material that has to be managed. There are two evaporation plants one for Magnox wastes and one for THORP wastes and a third (back-up) evaporator has recently been recomissioned. The volume reduction achieved by evaporation is typically a factor of 125. The waste is then transferred to one of the HASTs and different tanks are used for Magnox and THORP wastes. There are 21 HASTs, all of which are located in the HALES building. The first eight HASTs were commissioned in 1955 and brought into active use between 1955 and 1970 as the volume of waste produced increased. Each of these has a working volume of 70 cubic metres. The remaining 13 HASTs were built during the 1970s and 1980s and each has a working volume of 145 cubic metres. For safety reasons, a policy of keeping one tank empty for every three in use has always been maintained in the event that one of the other HASTs needs to be emptied at short notice. The HASTs are housed in thick reinforced concrete cells. Because of the very significant heat generating capacity of the waste (up to several kilowatts per cubic metre) the tanks require continuous cooling to prevent evaporation and, ultimately in the case of those tanks with the larger radioactive inventories, boiling and release to atmosphere of their contents. For safety reasons the HASTs are also segregated into cells to provide isolation from the other tanks. The first eight tanks were installed two per cell while the remaining 13 tanks were installed one per cell. Most of the waste stored in the HASTs consists of long-lived radioactive materials. The most important of these is caesium-137, which accounts for about 10% of the total inventory. The next most important radionuclides (in terms of quantity stored) are strontium-90, caesium-134 and ruthenium-106. Because the stored wastes are derived from reprocessing, much of the plutonium has already been removed and only trace amounts are present in the HASTs. RPII staff previously examined safety documentation relating to the HASTs, the Continued Operation Safety Report (COSR) over a two-week period in February 2000 (Turvey and Hone, 2000). The main conclusions of that examination were that the risk of damage from a severe earthquake had not been fully analysed and that, while the probability of an accident leading to a significant release of radioactivity was low it could be reduced further through the implementation of certain measures including, in particular, increasing the level of independence of the cooling water supplies. These issues were discussed with appropriate personnel during the course of the site visit. The RPII team was advised that the safety case relating to severe earthquake damage, much of which would also apply to a terrorist attack involving the intentional crashing of a heavy aircraft into the building, has been completed and that the NII accepts that no further structural modifications are required. The team were also advised that the level of independence of the different cooling water supplies has been increased since the February 2000 visit. The issue of the detection of spikes or hot-spots of activity in the cooling jacket in HAST 13 as referred to in the RPII Annual Report and Accounts 2003 was discussed in detail. At the time of our visit we were advised that, while the source of the contamination had not been fully identified, it was believed to have originated from cross contamination from cooling water in an internal cooling coil. (The cooling coils and cooling jackets share a common water supply). Minor cracks in internal cooling coils do occur from time to time and while the pressure in the cooling coils is kept higher than the pressure of the HAL to prevent HAL entering a damaged cooling coil, some transfer of radioactivity through mixing is a possibility.

15 Report of the RPII Visit to BNFL Sellafield 9 The Institute was subsequently advised by the NII that the spike in activity in the cooling jacket in HAST 13 is now believed to be due to a microscopic fissure in the tank wall, as a result of stress corrosion of the steel, which has allowed nanolitre quantities of HAL to leak out. While there are no immediate safety concerns, further studies are being conducted by BNFL and the NII is monitoring this work and considering the implications for storage of HAL. This incident is clearly of greater significance than if the activity in the spike was due to cross contamination resulting from a leaking internal cooling coil and provides further evidence that the long-term storage of highlevel radioactive waste in liquid form is not sustainable. The NII recently advised the Institute that a small activity spike, at too low a level to characterise, has been detected in HAST 12. An enhanced surveillance programme has been put in place to monitor this HAST. The activity spikes in both HASTs are under active investigation by both BNFL and the NII. The NII has acknowledged that these events are a safety concern, as well as potentially an additional constraint on the efficiency of operations (HSE, 2005). The NII has specified that BNFL must reduce the volume of HAL stored in the HASTs to a buffer volume of 200 m 3 by The NII believes that this requirement is necessary to reduce overall hazard at the BNFL Sellafield site (HSE, 2001). In specifying this requirement, the NII has taken into account the need to reduce the volume of stored HAL as quickly as possible while still ensuring that the stocks of spent fuel currently in storage on site and awaiting reprocessing are dealt with in a timely manner. The NII believes that the current arrangements are the best solution for dealing with the many hazards that are present on the site. The current volume of HAL in the HASTs is approximately 1400 m 3. To meet the NII requirements, this volume must be reduced by 35 m 3 per year for the next number of years and this is currently being achieved. Once THORP and Magnox reprocessing end in 2010 and 2012 respectively there will be a significant reduction in the volume of HAL generated and this will allow the rate of volume reduction in the HASTs to be increased. The NII is on record as saying that, if there are indications that these deadlines will not be met, it will use its regulatory powers to instruct BNFL to cease temporarily the reprocessing of oxide spent nuclear fuel through THORP. This is consistent with the Magnox Operating Plan (MOP), which places priority on the reprocessing of Magnox spent nuclear fuel. This is discussed in greater detail in Section The Waste Vitrification Facility In the early years of Magnox reprocessing research was carried out into the treatment and long-term management of the HAL stored in the HASTs. However, it was subsequently decided to invest in a vitrification process developed in France and in 1990 a Waste Vitrification Facility (WVF) came into operation. This facility encapsulates the HAL in glass blocks for long-term storage. The WVF had two vitrification lines but these failed to operate at full capacity due to operational difficulties associated in part with the very high temperatures of the materials passing through the plant. In January 2002 the commissioning of a third vitrification line commenced and this came into full operation in July There are many factors to consider when dealing with the vitrification and storage of HAL: it is highly radioactive; it contains acids that are corrosive in nature; it generates considerable amounts of heat and it contains different mixes of radionuclides depending on whether it originated from Magnox or THORP reprocessing. The process of vitrification involves the blending of wastes from the different HASTs in order to minimise the number of glass blocks that have to be produced and maximising the amount of radioactivity in each, while at the same time taking account of the chemical nature of the different liquors. Following blending, the waste is sent by pipe to the WVF. On arrival at the WVF, the HAL is passed through a calciner to transform it into powder form. Glass-making substances are added and the material is heated and melted to form a viscous liquid that is then poured into stainless steel containers. The glass cools and solidifies, thereby binding the radioactivity into a structure that is chemically inert and shows long-term resistance to leakage. The stainless steel containers are transferred to a shielded storage area that has the capacity for 8,000 containers. Presently the store is less than half full. BNFL s current overseas contracts will generate approximately 3,000 containers and from 2007 onwards these will be returned to the customer by ship. BNFL s reprocessing contracts with its UK customers are expected to generate considerably less than 8,000 containers.

16 10 Report of the RPII Visit to BNFL Sellafield No decision has been made on the long-term storage or disposal of high-level radioactive waste in the UK. However, the UK recently established an independent body, the Committee on Radioactive Waste Management (CoRWM) to review the available options and to provide its recommendations to Ministers by July The current inventory of radioactive waste at BNFL Sellafield is given in Table The Thermal Oxide Reprocessing Plant (THORP) In March 1977 BNFL applied to Cumbria County Council for approval to construct THORP. Following a public inquiry, THORP was approved in 1978 and subsequently built at a total cost of 2.8 billion. Commissioning of THORP commenced in 1994 and the plant came into full operation in early Table 2 Current Inventory of Radioactive Waste at BNFL Sellafield 1 Radioactive Waste Form Volume (m 3 ) High Level Waste HASTs (liquid) Vitrified Waste (solid) Intermediate Level Waste 4 75,400 Low Level Waste 5 1 x based on April 2001 values given in DEFRA (2001). 2 value as of end December it is estimated that the total volume of vitrified waste generated from current reprocessing contracts will be 1510 m 3, of which approximately 400 m 3 belongs to BNFL s overseas customers (CoRWM, 2004). 4 the majority, but not all, of this waste originates at BNFL Sellafield. 5 low-level radioactive waste produced at BNFL Sellafield is disposed of at Drigg, approximately 6 km south of the BNFL Sellafield site. This disposal is controlled through authorisations issued by both the NII and the EA. Efficient operation of the WVF is the key to volume reduction of HAL in the HASTs. If the vitrification throughput is reduced, this in turn limits the allowable production of HAL (as the volume in the HASTs must decrease rather than increase) and could impact significantly on THORP reprocessing. This is also discussed in some detail in Section 2.3. For this reason considerable effort is being put into upgrading the first two vitrification lines in an effort to process the volume of HAL in storage in the HASTs at a faster rate than that specified by the NII. Neither the operations in the Waste Vitrification Facility or HALES give rise to liquid discharges to the environment. All such waste streams are recycled to the evaporators in the HALES building. The reasons for Magnox and THORP reprocessing are fundamentally different. Originally Magnox reprocessing was undertaken to produce plutonium for the UK s nuclear weapons programme. At present, the reprocessing of Magnox spent fuel is seen as the best management option for a material that is reactive and unstable when stored under water or in open air for prolonged periods. Conversely, THORP reprocessing was set up as a commercial venture to provide operators in the UK and abroad with a spent fuel management route and/or to extract reusable uranium and plutonium from their spent uranium oxide fuel. THORP reprocesses spent fuel used in several different types of nuclear reactor including advanced gas cooled reactors and light water reactors. In terms of tonnage, THORP s main customer is Japan, followed by British Energy. Its principal European customer is Germany but contracts also exist with utilities in Switzerland, Italy, Spain, Sweden and the Netherlands. THORP is in stark contrast to the older plants visited. It is clearly more modern and has a greater degree of automation. The aerial and liquid discharges from THORP are also less than those from Magnox reprocessing for the same throughput of spent fuel. The mix of radionuclides discharged and their relative percentages are also different from those discharged as a result of Magnox reprocessing. The future planned throughput of spent fuel through THORP would result in all existing reprocessing contracts being completed by However, additional reprocessing contracts may be entered into, but only with the consent of the UK Government. Presently, any requests for approval of such contracts are made by BNFL to the UK Government, its sole shareholder. As of 1 April 2005 these submissions, should any arise in respect of new contracts, will be made by the NDA.

17 Report of the RPII Visit to BNFL Sellafield Emergency Planning Arrangements at BNFL Sellafield 4.1 The BNFL Sellafield Reference Accident All nuclear sites in the UK are required by law to define a bounding reference accident scenario for the purposes of off-site emergency planning. The reference accident must be based on the concept of the worst credible accident, which is reasonably foreseeable at the site, taking into account all of the facilities on the site (see Annex 3). The NII must approve the reference accident for each nuclear site and this is then used as the basis for deciding the size of the Detailed Emergency Planning Zone (DEPZ). Within the DEPZ detailed plans must be prepared for the implementation of applicable off-site countermeasures. Formerly the reference accident for the BNFL Sellafield site was based on the Calder Hall reactors. Since the closure of these reactors in 2003, the reference accident has been based on a leak into the coolant circuit in one of the Highly Active Storage Tanks (HASTs) leading to an environmental release via one of the HAST cooling towers. While precise information on the reference accident source term or amount of radioactivity likely to be released is not made publicly available by the UK authorities for security reasons, it is possible, on the basis of the size of the DEPZ to make a crude estimate of the size of the source term. This was found to be equivalent to a small percentage of the inventory for one of the older HASTs or less that 1% for one of the newer HASTs, based on the HAST inventories previously reported by the RPII (Turvey and Hone, 2000). While the hypothetical release is somewhat smaller for the HASTs than was the case for the reference accident based on the Calder Hall reactors, the difference is small and the NII decided to leave the size of the DEPZ unchanged at 2 km. However, since the current reference accident does not involve any release of iodine-131 and since there is no longer a source of iodine-131 at BNFL Sellafield, the distribution of stable iodine tablets as a countermeasure for the site is no longer warranted and has been discontinued. The decision to implement a particular countermeasure (such as sheltering or the administration of stable iodine) in a given set of circumstances is generally based on consideration of the benefits (in terms of reduction in radiation exposure) and the risks (disruption to normal living) associated with the countermeasure. In order to assist decision makers radiation doses known as an Emergency Reference Level (ERL) have been defined in advance, at which the benefits are likely to outweigh the detriment associated with implementing the countermeasure. 4.2 Structure of Emergency Response The emergency planning infrastructure in place on the BNFL Sellafield site includes a site emergency response centre equipped with the necessary communications infrastructure and access to site monitoring systems and other response resources. This centre is at all times manned by the BNFL Sellafield duty site supervisor. The key facilities of the emergency response centre are duplicated at a second facility on the site remote from the first. The site emergency response centre manages all communications between the site and outside agencies such as the NII, DTI and the local authority. In addition to the site emergency response centre there is a network of 12 local response centres located around the BNFL Sellafield site for the management of emergencies at facility level. All of the local response centres are identically equipped and are used regularly for drills and response training. There are three classifications of emergency for the BNFL Sellafield site, namely a facility emergency, a site emergency and a nuclear emergency. A facility emergency is defined as an emergency confined to a single facility and which does not have implications for the wider site. The response to a facility emergency is managed by the facility management from a local response coordination centre; A site emergency is defined as an emergency, which affects more than a single facility but does not have any off-site implications. The site management manages the response to a site emergency. Coordination of the initial response is the responsibility of the duty site supervisor. The site response is managed from the site emergency control centre, where a site response coordination team is assembled. Management of the response at a facility level, however, continues to be the responsibility of the management for the affected facilities; and A nuclear emergency is defined as an emergency with off-site consequences. The on-site response is coordinated from the site emergency control centre while the off-site response is coordinated from the off-site facility (OSF), which in the BNFL Sellafield emergency plan is referred to as the District Control Centre (DCC).

18 12 Report of the RPII Visit to BNFL Sellafield The site emergency planning officer has responsibility for on-site planning and coordination with the local authority, Cumbria County Council. A detailed programme of exercises and emergency response training is in place for coordination teams, fire fighters, monitoring teams, etc. 4.4 Security Issues post 9/11 As indicated in the Introduction, discussion of security measures was not included in this visit. However, since the RPII last visited the BNFL Sellafield site in 2000, it was evident that a number of security enhancements have been introduced. Some of the more obvious manifestations of this enhanced security include: 4.3 The Sellafield District Control Centre (DCC) The Sellafield DCC is a purpose-built facility located approximately 10 km from the BNFL Sellafield site. This facility is managed by Cumbria County Council but is resourced by BNFL. The BNFL Sellafield emergency plan envisages that in the event of an emergency each of the agencies with responsibility for offsite measures would send a representative to the DCC for the purpose of coordinating the interagency response. Each agency is allocated a room with basic IT and communications facilities and a central area is designated for coordination group meetings. An IT based information management system is used so that all groups are kept up to date with developments. A media briefing centre has been established at a Whitehaven school located approximately 4 miles from the DCC. The key DCC facilities are duplicated at a second site. The upgrade of fire fighting facilities to deal with the impact of a major air crash on the site. This has included the procurement of two airport foam fire tenders and associated equipment and training; The introduction of enhanced perimeter security including anti-ramming barriers at gates and the use of an increased number of armed guards; The introduction of physical barriers and access restrictions around individual facilities; The construction of heavy barriers around more vulnerable facilities; and The introduction of increased security for visitors to the site.

19 Report of the RPII Visit to BNFL Sellafield Conclusions 5.1 Plant Operations BNFL Sellafield is an extensive and complex site and there are several significant hazards present on it. These include, but are not limited to, the liquid radioactive wastes stored in the Highly Active Storage Tanks (HASTs), the spent nuclear fuel in storage awaiting reprocessing and the legacy wastes present in a number of facilities across the site. The approach being adopted by the nuclear regulator, the Health and Safety Executive s Nuclear Installations Inspectorate (NII), to reduce overall hazard at the site is to address hazards in parallel. Thus reprocessing and the management of legacy wastes are continuing while at the same time the volume of liquid radioactive waste in storage in the HASTs is being progressively reduced. The NII requires BNFL to prioritise the reprocessing of Magnox fuels over oxide fuels. This is because of the instability of Magnox fuel, particularly under wet storage conditions. If the timetable set by the NII for completing Magnox reprocessing is interrupted, the reprocessing of oxide fuels through THORP will be delayed, thereby extending the lifetime of that plant. The option of further reprocessing contracts for THORP has not been ruled out but such a decision is no longer in the hands of BNFL and can only be taken by the UK Government. The schedule for the completion of the current reprocessing contracts is 2010 for oxide fuels and 2012 for Magnox fuels. These dates are linked to the planned closure programme for Magnox reactors and the existing reprocessing contracts that BNFL has entered into with both its UK and overseas customers. Compliance with these deadlines will require ongoing reliable throughput of both fuel types at the rates that are only now being achieved. On the basis of information supplied to the Institute, it is difficult to see how this can be achieved without also increasing some radioactive discharges to the environment. While reprocessing continues, the NII has also stipulated that the volume of liquid waste stored in the HASTs is to be progressively reduced at an annual rate of 35 m 3 up to 2010 and at a faster rate thereafter. By July 2015 the volume stored must be reduced to 200 m 3 or less. The content of the HASTs currently represents over 90% of the inventory of radioactivity in the form of waste on the BNFL Sellafield site. The recent identification of spikes or hot-spots of activity in HASTs 12 and 13 is a matter of concern. While the leaks involve minute volumes of liquid and have not resulted in a release of radioactivity to the environment, they do call into question the long-term integrity of the tanks and underline that the storage of high-level radioactive waste in liquid form is not sustainable. The vitrification plant plays a key role in the ability of BNFL Sellafield to meet its targets over the next few years. If this plant fails to meet programme requirements, the volume of radioactive waste in storage in the HASTs can only be controlled by reducing reprocessing, which in turn means that the 2010 and 2012 deadlines will be at risk. A possible option would be to close down the remaining Magnox stations prematurely but as time passes this would have a progressively smaller impact on the volume of fuel to be reprocessed. This is because the amount of Magnox fuel already in reactors or in storage awaiting reprocessing greatly exceeds the amount of new fuel that will be placed in reactors between now and the end of the Magnox generating programme in At present the major challenge at the BNFL Sellafield site is the management of legacy wastes. Already the clean-up and decommissioning of the Magnox Fuel Storage Pond and Decanning Facility is a significant technical and engineering challenge with anticipated expenditure up to 2020 of the order of 150 million per year. The extent to which these operations will give rise to radioactive discharges has not yet been quantified and it is too early to say whether future discharges will be greater or less than those attributable to reprocessing. The UK has indicated that it will be reviewing its Discharge Strategy (DEFRA, 2002) to take account of the management of legacy wastes. Once reprocessing comes to an end and the legacy wastes have been treated, decommissioning of the BNFL Sellafield site will be the main on-site activity. The extent of the challenges facing BNFL and its UK regulators should not be underestimated. Decommissioning, by its nature, is a slow process that extends over several decades and current estimates are that decommissioning and final site remediation of BNFL Sellafield will not be completed until about 2150 (i.e. 150 years from now). Ensuring that the resources necessary to support this work are maintained over this timescale will clearly be a significant challenge. Decommissioning will also give rise to as yet unspecified radioactive discharges.