Peter E. Vickery
British Nuclear Fuels Limited

The paper concerns the evolution and implementation of a strategy for the recovery of 16,000 m³ of radioactive material accumulated in storage ponds and silos at Sellafield during 30 years of active operations.

The paper details how the wastes were accumulated and then how they were characterised so that possible techniques for recovery, treatment and disposal could be examined. The disposal forms and the specific techniques for recovery and treatment are described, and the means by which decisions were reached are discussed. Emphasis is placed on the benefits of a clearly defined and agreed methodology in reaching such decisions. The solutions adopted make maximum use of existing facilities at Sellafield for the treatment of current operational arisings, and the paper describes the projects necessary for the task to be accomplished.

The paper summarises the lessons learnt from the experience to date, in particular the need for a comprehensive overview of the waste arisings to be accommodated in such an undertaking and for a detailed understanding of their nature and accessibility prior to making investment decisions. Finally, the importance of involving customers, plant operators and regulators from as early as possible in the decision making process is emphasised.

Operations at Sellafield from 1952 onwards were centred on the development of the fuel cycle process. This programme initially involved the production and reprocessing of fuel which consisted of metallic uranium clad with aluminium, using graphite as a carrier for the fuel assemblies. As a result of reprocessing operations, significant quantities of radioactive waste associated with these materials were produced. This solid waste was accumulated in a purpose built silo, the Dry Silo, made up of six compartments. The contents comprise around 3200 m³ of magnox, aluminium, graphite, miscellaneous waste, fragments of fuel and fuel element furniture.

From 1957 onwards, activity at Sellafield was concentrated on the Magnox fuel programme. This concerned the reprocessing of several million fuel elements irradiated in the Magnox reactors at several sites throughout the UK, Italy and Japan. As with the earlier fuel, material was reprocessed by removing the cladding and exposing the uranium so that it could be fed forward for chemical reprocessing. The redundant cladding was then stored in a silo complex, the Wet Silos, eventually comprising 22 water filled compartments which now, after 35 years of operations, contain some 11,000 m³ of material. This consists of Magnox swarf arisings from the decanning operation, some fragments of fuel carried over as a result of this process, the fuel element furniture in the form of springs and end fittings, some residues from experimental operations carried out in the laboratories and miscellaneous items of scrap associated with the fuel handling process. These items vary in size from particles of a few microns through to items of equipment several metres long.

Magnox alloy fuel cladding degraded under the prevailing storage conditions in the pond. This produced insoluble corrosion products comprised of magnesium hydroxide, Magnox metal, uranium and other fuel derived constituents. Over many years of operations, knowledge of the corrosion process increased. It was observed that, under certain storage conditions, enhanced corrosion excursions occurred, leading to the generation of large quantities of hydrogen and heat. The compartments were built in four phases over more than twenty years and, as knowledge increased, the design evolved from a single skin concrete structure with limited ventilation and no cooling provisions, to a double skinned structure with a high integrity ventilation system, nitrogen inerting provisions and cooling systems which maintain a safe environment at all times. The material stored in the later compartments therefore varies greatly from material accumulated in the early sixties.

Prior to reprocessing, irradiated fuel was received into and stored in purpose built ponds to allow for cooling to take place. Two such ponds were constructed during the early years of Sellafield operations prior to the opening of the current facility, the Fuel Handling Plant (FHP), in 1986. These are Pond 1, which stored the aluminium clad fuel irradiated in the Windscale piles, and Pond 2 which stored the fuel from the Magnox programme. Both ponds comprise single skin reinforced concrete storage ponds linked to underwater decanning bays. Of the two structures, Pond 2 poses the greater challenge, due firstly to the longevity of its operational life (early sixties through to the present day) and secondly to the presence of sludge arising from the corrosion of stored Magnox fuel.

Initially fuel was stored in Pond 2 only for short periods following irradiation until radioactive decay had allowed cooling to a sufficient level to allow reprocessing to proceed. During the seventies, however, a number of interruptions to reprocessing operations resulted in fuel being stored in the pond for extended periods. This resulted in gradually rising levels of activity in the pond. These levels, and the loss of visibility resulting from the suspension of the sludge in the pond water, led to challenging operating conditions. Interim measures were employed to treat the pond water using ion exchange. Sludge removal was also attempted so as to improve visibility for fuel handling operations. Initially, sludge was managed within the pond, but subsequently a settling tank was constructed in the vicinity of the pond which enabled both the pond water to be purged and the sludge exported by pipeline to bulk storage tanks at the new Site Ion Exchange Plant (SIXEP). Despite these measures, it was eventually decided to cease operations in Pond 2 as part of the main Magnox reprocessing route, and it was replaced by FHP in 1986.

The wastes held up in both ponds therefore comprise sludge, with high levels of activity resulting from the release of fuel and fission products, items of contaminated operational waste and items of redundant pond equipment. The total sludge inventory is currently estimated at 1700 m³.

Taken with the contents of the two silos, the wastes in the two fuel storage ponds make up the major component of the historic inventory at Sellafield, the recovery of which is covered by an Intermediate Level Waste strategy. The volumes and characteristics of the waste generated from these four sources is summarised in table I.

In the early years of reprocessing, options for the long term treatment and disposal of Intermediate Level Wastes were being developed, and therefore, wastes were accumulated in bulk form on nuclear sites in facilities such as the ponds and silos already described. Pending the satisfactory resolution of the disposal issues, care was taken not to foreclose future options and no treatment was carried out other than to maintain acceptable and safe operating conditions

Throughout the 1980s work went on to develop products for deep disposal. This was achieved by a programme of waste characterisation and the evaluation of possible product formulations. This eventually led to the selection of the preferred option of encapsulation in cement prior to deep disposal. This programme was undertaken jointly by the nuclear industry across the United Kingdom.

During the 1980s, the behaviour of the waste stored in the Wet Silos and the developments in design of the facility, led to a change in policy. The quantities of hydrogen and heat generated by the underwater corrosion of Magnox, as already described, led to the design of compartments of ever increasing complexity and cost, both to construct and to operate. This was considered by the company and the Nuclear Installations Inspectorate (NII) not to be the best practicable means for long term operations, given that the Magnox programme would not be completed until 2008/9. It was therefore agreed to move from ongoing bulk storage to the direct encapsulation of current arisings. To this end the first encapsulation plant on the site, the Magnox Encapsulation Plant (MEP), was constructed and came into operation in 1990.

The decision to construct MEP coincided with a wholesale re-evaluation of the storage of Intermediate Level Waste on the Sellafield site. This resulted from the industry-wide agreement on the generic waste forms for final disposal. A policy of direct encapsulation of current arisings would be central to any future strategy. A complete inventory of all waste forms arising from past, current and future operations was established and studies initiated to bring forward schemes for the processes and facilities necessary to accomplish this task.

In order to set out a clear basis for the management of future waste retrieval schemes, it was agreed that the historic arisings, and any subsequent accumulations to the bulk storage facilities, would be retrieved and processed against an agreed set of policy statements. These form the basis of the Company's Waste Management Plans Review (WMPR) and are:

• To maintain the health and safety of the workforce
• To meet existing regulatory requirements
• To minimise environmental impact
• To achieve minimum overall lifetime cost
• To minimise waste volumes
• To produce a product compatible with deep disposal.

By lifetime cost is meant the total of development, capital, operational and decommissioning costs associated with any facility. It was therefore readily apparent that to achieve minimum overall lifetime cost, it would be highly desirable to maximise the use of any infrastructure being constructed for current arisings in the processing of the historic waste inventory, and in particular to treat waste streams in parallel. The subsequent development of strategies and programmes for the recovery of the historic waste inventory was driven by this principle.

As an example, MEP was given the capability of handling any waste retrieved from the Wet Silos which had not been subject to excessive corrosion. Similarly, a second encapsulation plant, the Waste Encapsulation Plant (WEP), which was built as part of the Thermal Oxide Reprocessing Plant (THORP) project in 1994, was given sufficient capacity to accommodate the encapsulation of all sludge arisings from Pond 1, Pond 2 and the wet silos. Two stores were constructed to store the drums arising from the operational and retrieval programmes. The first Encapsulated Product Store (EPS1) came into use in 1990 and the second in 1997 (EPS2).

Summarising the above, the starting point for consideration of the historic inventory was that the best possible use of the available infrastructure at Sellafield should be made in its recovery and treatment . This inventory, as described, was associated with some old buildings and comprised waste forms which were heterogeneous in nature and difficult to access. Furthermore, although product forms compatible with final disposal had been identified for the majority of wastes, there were no given processes for the conversion of the wastes as recovered, into these forms.

The infrastructure, and in particular the two encapsulation plants, had been designed against well defined waste streams from current operations. The fact with the historic inventory was that storage conditions had altered, and would continue to alter, the characteristics of the wastes. This meant that treatment processes to condition the wastes for encapsulation would have to be considered. Against this background, the strategy and the projects necessary for its implementation could only be developed against two sets of information, namely what was the starting point (i.e. the characteristics of the wastes) and what was the end point (i.e. the product forms for final disposal).

The first requirement of the strategy was therefore to establish a comprehensive and detailed characterisation of the waste inventory. This was undertaken over a number of years by a dedicated task force. Their remit was to obtain representative samples and characterise them in sufficient detail to support the design, safety and disposal work which had to be undertaken. This also encompassed the specification of inactive simulant materials which would be used in inactive trials supporting process development work.

As a further output from the characterisation work, an inventory database was created which pulled together the information. This was used for many purposes, but primarily to support the many projects which have been initiated to implement the overall strategy. To ensure that the comprehensive nature of the strategy is sustained, each of the building owners on the Sellafield Site is involved by means of questionnaires, interviews and the annual update of the waste inventory in his care. The database is updated by this means and is a source of basic data in support of the development of planned retrieval and treatment processes.

Similarly, the second requirement of the strategy was that there had to be clear end points in terms of approved product formulations on which retrieval and treatment projects could base process design studies. Again, a dedicated task force has been in place over many years to identify appropriate product forms and to resolve issues concerning long term storage and deep disposal.

In order to direct and co-ordinate the evolution of the strategy, the Company, as described, had instigated an annual review. This has the purpose of ensuring that projects evolve as part of a larger picture rather than as the resolution of a series of individual problems. The annual review updates the lifetime costs and programmes associated with the processing of all waste streams, past present and future, on the Sellafield site as well as the key risks associated with the implementation of the work.

The following paragraphs describe how projects undertaken in support of the strategy are developed. Individual projects are the responsibility of different business units on the site. The annual review forms part of the business planning cycle and ensures that all relevant information is brought together in a consistent fashion. It also forms the basis of allocating the costs associated with the strategy to the Customers whose financial liability the wastes are.

Each waste retrieval project is one item in the overall strategy to be undertaken as part of the recovery of historic waste accumulations. It is essential that overlaps and omissions do not occur if the strategy is to meet the policy directives stated above. This requires that individual projects are extremely rigorous in their early "front end" stages regarding the agreement of their scope and that they share their findings with one another. This is accomplished through "optioneering" studies, described below, such that each project, as well as every waste in the inventory, will eventually have an associated history of optioneering decisions leading to the chosen processing routes.

In order to generate viable options for waste retrieval and treatment in the context of this overall site strategy, BNFL has adopted the use of Value Engineering techniques. This process includes the use of workshops involving all those, from plant operators through to senior managers and Customers, with a stake in the final outcome. It is important to emphasise that these workshops pull in people both from across the Company and from outside. This ensures that the scope of projects has wide support, that imaginative solutions are considered and that projects do not work in isolation. This approach clearly demonstrates that marginal increases in the investment in one project can allow the inclusion of a number of waste streams, with substantial savings to the Company and its Customers.

The use of value engineering enables projects to bring forward comparable schemes for evaluation without wasting money on excessively detailed "front end" design work . The design process is progressed to a point where alternative options can be defined in sufficient detail to allow them to be compared. A multi attribute decision analysis approach is then employed, utilising success criteria based on the list of policy statements above, to select preferred schemes. These are then progressed to the point where capital sanction can be sought to bring the designs to the point where they can be put out to tender for design and supply.

As the optioneering process proceeds, the uncertainties associated with each project are managed by means of conventional risk management techniques such that the proposed processes are defined by a work breakdown structure and, by means of workshops, risk registers are established and the risks fed into risk management models. These are used to monitor the mitigating actions which are undertaken by means of the project development work, the results of which are fed through to the design of the project as it proceeds.

The risk management process is primarily used by individual projects to control programme and expenditure. It is also used to "post" certain risks which, by agreement, are outside the scope of the project and remain with the Company to mitigate by other means. The annual review is used to bring these risks together and give direction as to their mitigation. As the strategy develops, this list decreases and is evidence of its success.

As a result of the optioneering process, the recovery of the historic waste inventory has evolved over the past 10 years into a series of interdependent projects summarised in Figure 1.

There are essentially two main treatment routes for the historic ILW depending on the level of sludge held up with specific wastes. The Box Encapsulation Plant (BEP) will treat solids from The Dry Silo, Pond 1 and Pond 2 which are essentially sludge free, but comprise either irradiated fuel cladding wastes or contaminated items of operational scrap. The Wet Silo wastes and pond sludges (which are routed via SIXEP), will all be treated in the Sellafield Drypac Plant (SDP). This plant is designed to handle radioactive wastes dominated by magnox cladding sludges but which may contain solid wastes of widely differing characteristics.

The following paragraphs look in more detail at various aspects of this strategy and the challenges being addressed. The areas covered are:

• The Retrieval projects for the recovery of solids and sludges
• Transfer issues (skips and pipelines)
• The new treatment plants for ILW (SDP & BEP)
• Encapsulated product storage

Retrievals projects are in many respects more technically challenging than the new treatment plants. This is because the recovery of material from the old buildings presents design and operational problems of a unique nature. Not only are the wastes heterogeneous in nature which presents challenges to mechanical handling equipment, but the buildings are old and built to design standards different to those now in force. Therefore, the fitting of new plant to such buildings requires careful evaluation of a number of aspects, in particular the radiation dose received by those installing and operating the retrieval equipment.

The Dry Silo is one of the older buildings on site and presents all these challenges. It is not only approaching its fiftieth year, but retrieval methods are hindered by other buildings, pipebridges and the site railway adjacent to it. The chosen retrieval process reflects these difficulties , and includes new buildings such as a process building to house ventilation systems, a waste sorting and export facility, and two new Argon plants. The silo itself will be contained by an overbuilding to house retrieval equipment.

The retrieval method will involve side entry to compartments using manipulators to retrieve the waste into buckets. The buckets are then transported through the building, and the waste transferred into transport skips in the sort cell which are then flasked out to the Box Encapsulation Plant for subsequent encapsulation of the waste.

The Wet Silo will use four mobile caves from which retrieval equipment will be deployed. The first of these, the Swarf Retrieval Facility (SRF) is operating and successfully recovering swarf for encapsulation in MEP. It was designed as a demonstration facility for retrievals from this silo. The differing inventory of the compartments (total 22) means that whilst the SRF grabbing technique can be retained, three larger Silo Emptying Plant (SEP) mobile caves are required which incorporate limited size reduction capability. These mobile caves will allow the retrieval of the bulk contents and their loading into skips for subsequent transfer in flasks to SDP. To allow for the installation of the caves (which weigh approx. 370 Te each) on top of the silos, extensive preparatory work is being undertaken This includes structural steelwork strengthening and the installation of rail beams to support the caves.

The number of mobile caves for the Wet Silo is a compromise between the capital spent on retrieval equipment against the time taken to process the material at SDP. The optioneering process concluded that it is more economical to use three caves over a shorter time frame than one in isolation, as the major cost is associated with the lifetime operating costs of the downstream processing plants.

The old storage ponds, Ponds 1 and 2, require general structural refurbishment to maintain them in an operable state, with further repair, maintenance and new pieces of equipment for waste retrieval and export operations. For solid waste retrievals from Pond 2 as an example, this will involve the installation of a shielded working platform and a 2.5 te monorail hoist for the transfer of wastes into areas of the pond from which they can be recovered.

The other main element of the retrievals strategy is the recovery of the sludges from Ponds 1 and 2 and their subsequent transfer, via the settling tank adjacent to Pond 2, to bulk storage tanks at SIXEP before export to and treatment at SDP. In total some 2,000 m³ of sludge will have accumulated at SIXEP by 2002. Sludge recovery has necessitated the development of a variety of ingenious methods, since sludge accumulations vary in their physical form and are located in parts of the ponds which are often difficult to access. The choice of technique is dictated by a number of parameters such as the physical dimensions of the bay or pond, and any physical obstructions. Two examples are as follows.

Tank Emptying Facility (TEF) - This equipment is being deployed in a Settling Tank that adjoins Pond 2, and has achieved bulk desludging of the main tank. The building is divided into a number of open water-retaining chambers of varying depth (4 to 8.5m)with sludge close to the surface of the pond. The solution adopted was to use a combination of pumps to disturb the sludge and transport the sludge down a pipeline to a new Buffer Storage Tank. The use of a desludging head inside a containment module that prevented the release of contamination from the surface of the tank.

Bay Sludge Retrieval Facility (BSRF) - This equipment is being deployed in Pond 2, D Bay. This is a ventilated and shielded bay, approximately 5.5 metres in depth. It contains deep and compact sludge. There is also solid debris in the bay, and ongoing corrosion resulting in the release of hydrogen from the sludge bed. The retrieval method uses redistribution pumps to direct the sludge towards the desludging pump, for resuspension and hydraulic transfer to the Buffer Storage Tank. The method differs to that for the Settling Tank, as the bay is covered with concrete shield blocks and the debris and items in the bay prevent the use of a desludging head.

Pond 2 requires the use of various methods for sludge retrievals. The pond is approximately 100m long, with sludge in places up to 2 metres deep containing debris and others items, such as flexible hoses and fuel rods. A bucket grab has been used to pick up the bulk sludge and large items, but this could not effectively cope with the thinner layers of fine material, as more would fall through than be retrieved. The current reference scheme is the Pond Sludge Retrieval Facility (PSRF), a desludging head unit which is to be transported around the pond by a handler.

The construction of bulk storage tanks at SIXEP to accommodate arisings of sludge was mentioned earlier. These represent an interim storage capability of high integrity which has enabled the retrieval of historic sludge arisings from Pond 2 and elsewhere to proceed in advance of downstream treatment facilities being available. It is planned to recover the sludge accumulated in the tanks, using a combination of pumping and grabbing techniques, for transport to SDP in concentrated campaigns. This project is known as the SIXEP Export Facility (SEF).

Waste transfers are a key element in the strategy. Sellafield has developed over the years into an extremely complex and crowded site. This has particularly affected the transfer of wastes from the point of recovery to downstream treatment and storage plants. Transfers are achieved by either flasking the waste or the use of pipelines

Flasks - Flexibility is a key issue due to the uncertainties which will still be associated with certain waste streams even after extensive characterisation and which may require re-routing from one facility to another. To this end, a common container, or skip, is used in which to transfer the bulk of the retrieved wastes. It has a capacity of 1.5 cubic metres. The flask in which the skips are transported, originally designed for Wet Silo retrievals only, has become the adopted flask for the major retrieval projects and the new downstream treatment facilities (SDP and BEP). This is a bottom opening flask weighing in the region of 55 te, which will be maintained in a dedicated facility within SDP, and transported using the existing site railways, with a new flatroll system. Existing cuboid flasks are being re-deployed for waste transfers between Pond 2 and BEP. The cuboid flask and the associated handling equipment are a standardised transport system, having been used both internally and externally to Sellafield in Italy (Latina), Japan (Tokai Mura) and other UK facilities for the transfer of all Magnox fuel over the last 40 years.

Pipelines - The Settling Tank adjacent to Pond 2, as already described, was originally built to transfer Pond 2 sludges to the Bulk Storage Tanks at SIXEP. This necessitated the construction of a pipebridge between the settling tank and SIXEP some 800 metres long. Since then, additional lines into the settling tank have enabled the retrieved sludges to be transported to SIXEP. A considerable design capability for the transport of magnox sludges by pipeline has been built up over many years in tackling these projects.

Pond 2 has a number of complicating factors which constrain not only retrieval options, but also the ability to transport the sludge away. These include high radiation levels around sludge accumulations and an adjacent drain trench with vulnerable cast iron pipework filled with active liquor and sludges. Options vary from installation of new pipelines to the re-use of existing ones. In one case, a 75mm coaxial pipe has been fed into an existing unused length of ducting, as its 150 mm bore was too large for adequate sludge transfer velocities to be maintained. This choice was identified as the best practicable means, as it avoided the major problems of radiation and any installation work around the drain trench.

Two new ILW treatment plants are required to convert the wastes as retrieved into encapsulated product forms compatible with deep disposal. The first, SDP, converts sludge-dominated wastes into a product, contained in 500 litre drums, which can be encapsulated at WEP. The second, BEP, encapsulates solid wastes which are substantially free from sludge directly into boxes of 3 cubic metres capacity.

The SDP process involves sorting and screening of the wastes, with the sludge and undersize items being loaded directly into cans and dried before undergoing high force compaction. The oversize waste is size reduced as necessary before undergoing compaction. High force compaction (2000 Te) significantly reduces the waste volume, with typically 3 or 4 compacted waste cans being loaded into each product drum prior to transfer to WEP.

In BEP, solid wastes from the Dry Silo, Pond 1 and Pond 2 will be tipped, inspected and sorted. Gamma cameras will be used to sentence waste and establish box loading, any high emitters will be removed with a manipulator and dealt with as appropriate. The boxes will then be filled with the waste prior to further monitoring and grouting. After curing, capping, lidding and final monitoring, the boxes are transferred to the product store.

The two existing stores (EPS1 and EPS2) will be full by 2005 as the retrieval of historic wastes reaches its peak. A further two stores are planned to accommodate approximately 30,000 m³ of additional product from the historic inventory. They will be based upon the design which has evolved for the current arisings, but the store adjacent to BEP will be able to hold both 3m³ boxes and stillages (4x500 litre drums), which have the same envelope for mechanical handling purposes. This again sustains the flexibility essential to the success of the overall strategy.

With the main elements of the strategy set in place, it is now important to focus on the recovery of residual materials from the bottom of the ponds and silos and the final clean up of structures. The economies of recovering the bulk contents over a short time frame will be lost if the downstream treatment plants have to stay open to process small quantities of material which may prove difficult to recover effectively. It is therefore important that the bulk retrieval processes encompasses as far as possible the recovery of these residual materials. Much effort is now being expended to bring imaginative solutions to this issue.

As an example, at the bottom of the dry silos there is material of a fine or gravelly nature which is not going to be consistent with BEP but which may need to be exported to SDP. Another example is the removal of residual liquors from the wet silos once the solid material has been recovered. This will be achieved by routing the liquor via the settling tank adjacent to Pond 2 and then to SIXEP, both of which trap any residual solid material and remove the activity associated with the liquor.

A number of plants have been or are to be constructed for the recovery of the historic waste. The SRF is already operational and was commissioned in 1993. MEP and WEP are already operational for the encapsulation of current waste arisings and two encapsulated product stores are operational. A number of schemes, such as TEF and BSRF, at the storage ponds have enabled sludge from Pond 2 to be recovered to SIXEP.

The remaining facilities key to the execution of the strategy are due to come on line from 2002 onwards and are:

• The three SEP mobile caves which will recover the swarf and associated material from the majority of the Wet Silo for transport to SDP;
• The SEF facility which covers the export of sludges from SIXEP to SDP
• The Waste Retrieval Plant (WRP) will recover material from the Dry Silo for transport to BEP;
• Further schemes at Ponds 1 and 2 to allow the recovery of sludge and solids;
• SDP, BEP and the associated encapsulated product storage capacity.

The bulk of the historic waste inventory has yet to be retrieved. However, substantial quantities have already been recovered, giving additional confidence to the performance of future plant and equipment. In summary, approximately 1,000 m³ of swarf has been recovered to date from the wet silos. Over 250 m³ of sludge have been recovered using TEF and BSRF, and in excess of 700 m³ of from other areas of Pond 2.

The major undertaking over the next few years is the construction and bringing into operation of the facilities described above. In addition, further development work will be required, due to remaining uncertainties regarding the nature of the material to be retrieved. It is not necessary to resolve all of these prior to the start of retrieval operations though, which means that machinery and plant need to be flexible in their operation, while retaining the simplicity essential for effective retrieval.

Further work is associated with the final clean up of the ponds and silos to prescribed endpoints. This will involve the incorporation of new pieces of equipment on to the existing retrieval machines as the programmes near completion. The eventual decommissioning of the facilities will be a phase of work to be undertaken on a site-wide basis rather than by treating them individually. It is therefore necessary to get all the plants to a point where they can be maintained at a low, ongoing, annual cost prior to the start of decommissioning.

To ensure that later phases do not require expensive downstream facilities, such as those associated with bulk waste recovery, it is important that retrievals of residual materials are accomplished, where possible, in parallel with the bulk wastes and therefore within the operational windows of the main processing plants. Any arisings which remain will then be minor and can be safely dealt with on a plant-by-plant basis as part of decommissioning.

The evolution of this strategy and the development of the associated projects has been the result of many years of work by BNFL staff, both at Sellafield and elsewhere.

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