RADIATION PROTECTION DURING THE EARLY STAGES OF SITE DECOMMISSIONING AT THE UKAEA'S DOUNREAY SITE

P.J. Thompson*, W. Sinclair+, D. Mowat+, S. White*, R. Kerr*, T. Chalmers+ and S.M. Calder*

* The United Kingdom Atomic Energy Authority, Dounreay, Thurso, Caithness, KW14 7TZ. + RWE NUKEM Ltd., Dounreay, Thurso, Caithness, KW14 7TZ.

In 1998 the United Kingdom Government announced that the United Kingdom Atomic Energy Authority (UKAEA) site at Dounreay in northern Scotland would no longer be seeking further commercial reprocessing contracts. This decision laid down the foundations for the UKAEA to focus firmly on the task of decommissioning the UKAEA’s site at Dounreay. Fifty to sixty years has been identified as the period in which to decommission the site and restore its environment. The business of decommissioning at Dounreay presents a number of interesting challenges that need to be addressed. There are a number of complex and unique projects that must be undertaken including the decommissioning of the early fast reactors, a materials test reactor, metallurgical laboratories (housing fume cupboards, glove boxes and shielded cells) and novel fuel reprocessing plants. This paper discusses the experience gained during the various stages of decommissioning in the fast reactors and nuclear fuel cycle reprocessing plants, focusing on the Dounreay Fast Reactor, the Prototype Fast Reactor, a criticality test facility, fuel reprocessing plants, laboratories and associated environment. The UKAEA at Dounreay is dedicated to restoring the environment both safely and cost effectively. This paper discusses the practical radiation protection issues that have been encountered during the early stages of a number of decommissioning projects on the site. The conference presentation will give an update on our experience and discuss lessons learnt.

INTRODUCTION The United Kingdom Atomic Energy Authority (UKAEA) site at Dounreay was opened in 1955, and was built on a former Admiralty airfield and adjacent farmland. Dounreay was instrumental in developing the United Kingdom’s knowledge of fast reactors. It is home to both the Dounreay Fast Reactor (DFR) and the Prototype Fast Reactor (PFR). The DFR went critical in November 1959, supplying electricity power for commercial use from October 1962 and the Prototype Fast Reactor (PFR) went critical in 1974. PFR was the postulated forerunner of large-output commercial fast reactors and an important facility within the European collaborative programme.

Figure 1: Dounreay Fast Reactor (DFR) and the Prototype Fast Reactor (PFR)

A third reactor on the site, the Dounreay Materials Test Reactor (DMTR) went critical in May 1958. The associated infrastructure, such as reprocessing plants, metallurgical laboratories and examination facilities were completed subsequent to this.

Figure 2: Dounreay Material Test Reactor (DMTR)

The DMTR, DFR and PFR closed in 1969, 1977 and 1994 respectively. As a consequence, work at Dounreay continued primarily focussed on commercial fuel reprocessing contracts and to a certain extent decommissioning.

Figure 3: The Dounreay Fuel Cycle Area (FCA) There are many books available on the history of Dounreay and the UKAEA’s web site (http://www.ukaea.org.uk) provides further interesting information. In 1998 the United Kingdom (UK) Government announced that Dounreay would no longer be seeking further commercial reprocessing contracts. This decision has enabled the UKAEA to focus firmly on the task of decommissioning the site. A period of between fifty and sixty years has been identified to decommission and restore the environment of the site. The Dounreay Site Restoration Plan (DSRP1) details the proposal, which is supported by the Health and Safety Executive2 (HSE) and Scottish Environment Protection Agency (SEPA) in their close out report3 to the 1998 Safety Audit4.

THE DOUNREAY SITE RESTORATION PLAN (DSRP) The UKAEA’s business at Dounreay is now one of decommissioning, environmental remediation and site restoration. An ambitious, but achievable plan has been formulated detailing how this will be achieved and the timetable involved. A copy of the DSRP1 can be downloaded from the UKAEA’s web site, and an overview of the rational behind the DSRP and the challenge it poses were given in ‘People, plants and Projects: the challenges at Dounreay’5. To aid restoration of the site a number of new plants will be required to support the decommissioning infrastructure and provide temporary waste storage capabilities. These plants will be constructed in parallel to certain decommissioning activities, with their availability being pivotal to the DSRP’s success. Managing the interdependencies of decommissioning, construction, land remediation and site restoration is complex, and the DSRP will be a “living document” that will be continuously reviewed and modified as required. The DSRP has been divided into five sections, each of which reflects a consecutive time period of between ten and fifteen year’s duration. Summarised details are provided in figure 4.

Period 1 Up to twenty new plants will be constructed for waste treatment and processing of nuclear material, to put them in a suitable condition for long term storage or disposal. A small number of existing plants will be upgraded to support continued operations to treat waste and fuels. Coincidental with this work, decommissioning will continue on a number of redundant facilities and dealing with contaminated land. Period 2 Waste will be retrieved from the shaft and silo and the remaining nuclear materials will be processed. As operations in plants are completed they will start to undergo decommissioning. At the end of this section of the DSRP the major radiological hazards on the site will have been removed. Period 3 Primarily the decommissioning of fuel processing and handling plants. Work will also start on decommissioning redundant high-level waste treatment and storage facilities. Period 4 The decommissioning of the DFR, DMTR and PFR will have been completed, whilst the decommissioning of redundant waste facilities will continue. Post Operative Clean Out (POCO) and the decommissioning of the remaining redundant facilities will commence. Period 5 By the end of this period all redundant facilities will be dismantled and the wastes appropriately treated. Environmental remediation will be completed and although some areas of site will require continuing “control and surveillance”, the risk to the public and environment will be minimal.

Figure 4: Summarised stages of the DSRP

Figure 5 depicts the changing landscape of Dounreay during the DSRP.

Figure 5: Changes to the Dounreay site during implementation of the DSRP

DUE PROCESS – SAFETY JUSTIFICATIONS The UKAEA has a strong safety and environmental management system, supported by UKAEA Safety and Environment Procedures (USEPs) and lower tier site-specific derivatives, called Dounreay Procedures (DPs) at Dounreay. These documents specify the requisite due process for decommissioning projects (and other activities), including the requirement for project sanctioning and the production of Project Safety Cases as detailed below. Project Project Project Project Project Plant Initiation Development Design Construction Commissioning Operation

Safety Case Preliminary Pre- Pre- Pre- Strategy Safety Report Construction Commissionin Operational Overview (PSR) Safety Report g Safety Safety Report Report describes the (PCSR) Report (POSR), is (SCSOR), safety describes how (PCmSR), this based upon informs principles and the facility covers both “as built” stakeholders standards to will address non-active and plant (such as the be employed and meet the active (from a information to Nuclear in the work principles radiological confirm that it Installations described in perspective) is now ready Inspectorate the PSR. commissionin for operation. and the Issues such as g works. Scottish planning Approval Environment permission allows a Protection and ‘licence Agency) of conventional instrument’ to the steps that safety will be granted and will be gone also be the release of through, key addressed at “hold points”. safety this stage Authorisation documents of discharges that will be under the produced and Radioactive “hold points”.

Figure 6: Safety Case Documentation at the various Project Stages

The Pre-Commissioning Safety Report (PCmSR) and the Pre-Operational Safety Report (POSR) are not always appropriate for decommissioning projects. They may, however, be necessary for decommissioning “pre-works” projects (electrical and ventilation upgrades, etc.). A well-established system of document peer review and then committee review by suitably qualified, experienced, competent and trained personnel will be used for any safety case with a significant hazard category, or a project that is considered novel or potentially contentious. The Nuclear Installations Inspectorate (NII) and possibly SEPA will also review high hazard category safety cases.

DOSIMETRY The UKAEA, with its appointed Approved Dosimetry Service (ADS) [RWE Nukem Ltd.], operates a robust and demonstrable system for the selection and adoption of appropriate personal dosimetry commensurate with project hazards. These requirements are formally reviewed at least annually and at key project phases, to ensure their continued suitability for the particular workforce. These reviews are conducted by the UKAEA Management, the UKAEA appointed Radiation Protection Adviser (RPA) (and on occasion the contractor’s RPA) and a senior member of the ADS. Further details of the arrangements are provided in reference 6. The minimum dosimetry for access to controlled areas at Dounreay is a body dosemeter. This may be supplemented by personal air sampling, electronic real time alarming dosemeters, neutron dosimetry, extremity dosimetry, biological monitoring, accident dosimetry, etc., dependent upon the findings of a suitable and sufficient risk assessment for the work being conducted. To supplement routine radiological surveys, workplace monitoring systems, such as alarming air samplers and gamma detectors are situated within the radiological designated areas commensurate with the hazards and risk. UKAEA is currently considering formal arrangements for pre- and post-project dosimetric assessment for peripatetic workers, to demonstrably show the adequacy of the stringent radiation protection standards being implemented on the Dounreay site.

HISTORY The Dounreay Fast Reactor The Dounreay Fast Reactor (DFR) was constructed between 1955 and 1958. Until it’s closure in 1977 it played an important part in fast reactor research by developing fuel design, coolant technology, efficient reprocessing techniques and nuclear waste management. The success of DFR’s design, together with the demonstration that a high burn-up could be achieved, gave confidence not only within the fast reactor project, but also to the UK Government when sanction was sought for the construction of the Prototype Fast Reactor (PFR). The secondary sodium-potassium (NaK) coolant circuits have been removed, but the primary coolant circuit contains high levels of caesium. Following this the remaining NaK coolant will be treated using “Water Vapour Nitrogen” techniques and then ion exchange, in a plant currently being constructed. Projects in progress at DFR include: S Electrical supply system upgrade, to support decommissioning activities. S Ventilation system upgrade to modern standards, including monitoring equipment for alpha, beta, gamma and tritium. S Pond decommissioning - removal of pond water, sludge and contaminated pond wall surfaces. S Construction of a NaK disposal plant (NDP). Stage one decommissioning of DFR is planned for completion by 2016, when the remaining coolant and about 1000 breeder fuel elements (some of which are jammed) will have been removed.

The Prototype Fast Reactor The Prototype Fast Reactor (PFR) was a 250 MW(e) pool type sodium cooled fast reactor using mixed uranium and plutonium oxide ceramic fuel clad in stainless steel. The core was immersed in a pool of sodium and the heat generated (600 MWth) transferred from the primary circuit to the steam generators via three non-active secondary sodium loops, significantly confining activity to the primary circuit. A single large main building provides secondary containment for the reactor, the irradiated fuel cave and all the major plant items. Post-Operative Clean Out (POCO) of PFR was undertaken following its closure. This involved removing the fuel and other tasks, which significantly reduced the immediate hazards and maintenance requirements. New plant has had to be designed and built to assist in the safe decommissioning of the PFR nuclear legacy. This has necessitated significant “pre-works” activity before physical decommissioning can be initiated, including: S Installation of HEPA filtered ventilation systems that comply with modern standards. S Upgrading the monitoring and sampling systems for atmospheric discharges. S Upgrading environmental monitoring systems. S Building waste handling plants for solid and liquid waste. S Up grading electrical supplies. Currently, the major decommissioning task at PFR is the disposal of the liquid metal inventory of approximately 1500 tonnes of sodium (Na) [300 tonnes of which was from PFR research support conducted elsewhere on site] and a small amount of sodium-potassium (NaK).

The Dounreay Materials Test Reactor The Dounreay Materials Test Reactor (DMTR) went critical in 1958 and ceased operations in 1969. Consequently, its operational life was significantly shorter than similar reactors at the UKAEA Harwell site. Certain decommissioning activities were conducted following closure, including removal of the fuel and the heavy water. DMTR was then placed under a ‘Care and Maintenance’ regime. The plant is currently being prepared for a further stage of long term ‘Care and Maintenance’, with the condition of the plant being greatly improved, and some periphery plant services and equipment either being upgraded or removed. The DMTR will be under this new ‘Care and Maintenance’ regime starting in the summer of 2002.

Fuel Cycle Related Plant Decommissioning Projects The Pulsed Column Laboratory The Pulsed Column Laboratory (PCL) was involved in the development of solvent extraction equipment and “Flow Sheet” trials, using pulsed columns as a replacement for “mixer settler” solvent extractors. It houses the Pulsed Column glove box (PCG) which is approximately ten metres high and the Centrifugal Contactor glove box (CCG), added after initial commissioning of the PCG, which is approximately three metres high. Following completion of experimental work on pulsed column solvent extraction processes within the PCL in 1991, activities ceased, after a certain amount of POCO. The PCL is now ready for decommissioning and awaits regulatory consent to proceed. To put the PCL in a suitable position for decommissioning, a number of pre-work activities were required and these included: S Construction of a new entrance to the PCL, including the installation of a new change room and barrier. S Installation of glove box impact protection. S Strip out of redundant electrical and mechanical equipment, external to the glove boxes. S Upgrade of the Static Air Sampler monitoring system. S Removal and replacement of the ventilation system. S Installation of internal contamination barrier in the laboratory. S Physical isolation (dependence) of the PCL from the building it is connected to. S Installation of a stand-alone modern standards ventilation system, for decommissioning. The radiological protection aspects of progress towards physical decommissioning of the Pulsed Column Laboratory have been discussed elsewhere7 and lessons learnt summarised to the end of this report. This work is now complete and authorisation for active discharges to the environment from the ventilation system is awaited prior to the commencement of physical decommissioning. It is anticipated that some contract specific pre-works will be necessary prior to actual decommissioning commencing.

Decommissioning of D1200 Redundant Laboratories The D1200 Laboratory facility was commissioned in the late 1950s to provide general analytical services, including metallurgical analysis work in support of fuel experiments in DMTR, DFR and PFR. This metallurgical analysis work ceased with the end of the UK’s Fast Reactor programme and the laboratories performing this function were placed under care and maintenance in 1993. This facility still provides chemical analysis in support of the environmental discharge monitoring program, calibration facilities for Non Destructive Assay (NDA) equipment and other radiometric and periphery work. The redundant laboratories house various facilities ranging from fume cupboards to shielded cells. The decommissioning strategy for the redundant laboratories is based on the removal of redundant plant and equipment to leave the rooms free from contamination. At a later stage the D1200 complex, as a whole, will be decommissioned and the building demolished to leave a ‘brown field’ site. Decommissioning activities are not new to this facility, as a number of laboratories have previously undergone decommissioning and some of them refurbished. Current decommissioning work is focussed on the redundant laboratories containing glove boxes and fume cupboards. Work to remove the fume cupboards has started and is currently on going. This work includes size reduction of components to fit into standard site radioactive waste bins. During this work, the adjacent glove boxes have been shielded to prevent accidental damage and multi-staged ventilated temporary containments (tents), dependent upon assessed hazard, used to contain this work.

Criticality Test Facility Decommissioning The Criticality Test Facility was a plutonium laboratory built in the late 1950s to provide data on both solid and liquid plutonium criticality, in support of reprocessing plant design. The laboratory had four main areas: 1. The solid fuel process line in which a solid plutonium mixture was handled in a number of glove boxes. 2. The solution preparation room, in which solutions of plutonium nitrate were prepared. This area contained glove boxes, an evaporator and solution storage tanks. 3. A pressure (containment) vessel area in which solid plutonium experiments were carried out in the PUMA (plutonium moderated assembly) and plutonium nitrate experiments in the PANTHER (plutonium nitrate thermal reactor) rigs. 4. The administration area. The facility operated from 1960 to 1963, when it was then segregated into inactive and active (with a residual plutonium inventory and plutonium contamination) sections. The ‘non active’ part of the facility was converted to office space. From 1963 until 1967 the facility underwent some POCO and decommissioning, with the removal of the panther rig and the plutonium inventory. The facility was then placed in ‘Care and Maintenance’ until 1987 when extensive decommissioning work took place8. Prior to this work a new building was constructed adjoining the active section, incorporating changeroom and office accommodation for the project. Following an entry to the building in October 1987, to review the situation, the ventilation and electrical services were refurbished before any further decontamination work took place. The proposed decommissioning project was broken down into three phases: Phase 1 - Decontamination of the solid fuel process area: In December 1987, the physical decommissioning commenced. The programme to decontaminate the area started with the solid fuel process area and associated glove boxes. Phase 2 - Decontamination of the solution preparation room: The next stage of the project involved the disposal of glove boxes and removal of redundant services from the solution preparation room, as well as a cell that contained eleven storage tanks. Phase 3 - Decontamination of the pressure vessel: At this stage, in 1995, the project was stopped. Unfortunately some of the previously generated waste was put in the pressure vessel to be sentenced at a later date. Work resumed again in 1999 and will continue to brown field status without further prolonged intermissions. Prior to entry into the containment vessel the ventilation system was serviced and steps were made to improve the number of air changes in the building. This was done, primarily, by sealing routes where air could pass between outside and the building. The changeroom was also refurbished and the liquid discharge system to the site low active drain was reinstated. A ventilated modular containment unit was built to act as a dressing/undressing area and access point for entry to the pressure vessel. The higher risk decommissioning activities are now complete, with low-level residual radioactive contamination remaining.

The Research Reactor Fuel Reprocessing Plant The Research Reactor Fuel Reprocessing Plant, as its name identifies was involved in the reprocessing of fuel from research reactors, including DMTR and others at home and abroad. It was initially involved with reprocessing fuel from DMTR, but was refurbished to reprocess similar types of fuel. Decommissioning has been started on the plant, with pre-works to make the plant fit for decommissioning and consistent with modern standards (where feasible). This has included new access control, sub-changeroom facilities, and the replacement of the ventilation, electrical and activity in air monitoring systems. A significant part of this pre-work, which has necessitated some low risk physical decommissioning tasks, is now nearing completion and further physical decommissioning will start in the near future.

The Post Irradiation Examination – Remote Handling Plant The Post Irradiation Examination (PIE) – Remote Handling Plant contains a U-shaped suite of cells used initially for PIE of DMTR and DFR fuel, and then support of PFR operations. The U-shaped cells within the facility are currently being emptied of waste and this is significantly reducing the radioactive inventory. A further cell, the Pressurised Tube Measurement Facility (PTMF), is currently having plans for assessment of its internal radiological conditions and decommissioning developed.

The Fast Reactor Fuel Reprocessing Plant The Fast Reactor Fuel Reprocessing Plant was built to reprocess fuel from DFR and was subsequently refurbished to allow dissolution and reprocessing of Mixed Oxide Fuel from PFR. The produce from this plant was plutonium nitrate, uranyl nitrate and raffinates (containing the fission products) for export, conversion and storage respectively. However, in 2001 the UK Government announced that this plant would not be dealing with the fuel legacies on the Dounreay site and consequently the plant is now to undergo imminent decommissioning.

Land remediation, including Dounreay castle Due to historical practices and legacies, radioactive contamination exists on and around the Dounreay Site. This contamination may have arisen from the following sources: S Accidental leakages and spillages of radioactive material (for example from tanks or pipes, drains, and during the storage and transport of radioactive material). S Disposal of waste material. S Deposition from aerial stack emissions. S Decommissioning and/or decontamination of buildings that have contained radioactive material. S Movement of contaminated ground water. S Return from the sea as spume. Site wide radiological surveys during 1995 and 1996 identified several areas of radioactive contamination that had previously not been identified. The location of each contamination find was recorded and discrete spots of surface contamination removed. Areas with significant detectable radiological contamination have been barriered and designated in accordance with UK legislation (the Ionising Radiations Regulations 1985 and now 1999) and the UKAEA’s system. In light of changing legislative and UKAEA requirements, the designation of barriered areas (former and existing) has been reviewed. Many of the barriered areas have been surface remediated, declassified and the barriers removed. Radiological monitoring is performed in the existing and former barriered areas, so that the radiological conditions can be kept under review. This monitoring has, on occasion, found low levels of beta and gamma contamination in areas that had been previously surface remediated. These contamination finds are of concern, but tend to be of low radiological hazard significance. The NII has stated that radioactively contaminated land on a licensed site is an accumulation of radioactive waste and that “Safety cases will be needed for contaminated land”. UKAEA has put considerable effort into developing contaminated land safety cases. The UKAEA has undertaken some large-scale remediation projects to date and plans further remediation projects to reduce it’s contaminated land liabilities. UKAEA has been, and still is, working to characterise the contamination on site, such as investigating the depth of contamination. The Dounreay Castle and Foreshore was remediated in 19989. The target remediation levels for this project were set at 4 Bq.g-1 beta and gamma, and 1 Bq.g-1 man-made alpha activity. These levels were based on the practical detection limits of the instrumentation in the environment, the background activity levels and the requirement to maintain exposure to ionising radiations at a level that is As Low As Reasonably Practicable. An area of 900 m2 was excavated down to a maximum depth of 3 m, resulting in a total of 1540 tonnes of low- level waste (LLW). Some material with contamination above the target remediation level was left in place, because it was not practicable to excavate rock beneath the Castle/Cottage wall or on the foreshore. A separation membrane was laid over the remaining contaminated areas to avoid cross contamination of the clean backfill material except for the foreshore area, due

to the erosion prone environment.

Figure 7: Dounreay Castle

LESSONS LEARNT AND RE-AFFIRMED The lessons learnt and re-affirmed during decommissioning on the Dounreay site to date fall into two time frames, that is historical and the present. The historical lessons are simple, but are none the less pertinent to all nuclear liabilities as they near the end of their useful life.

Historical based lessons 1. Design plants with decommissioning, as well as operations, in mind and adequately maintain their safety infrastructure, especially ventilation (dynamic containment). 2. Don’t leave plants in care and maintenance regimes for longer periods than necessary before beginning decommissioning, because: S Knowledge and experience of the plant may be lost, and these attributes are paramount to straightforward, safe and cost effective decommissioning. Wherever possible the people who operated the plant should play a major role in its decommissioning, especially during POCO and the development or validation of the decommissioning plan. This has the advantages of: S Plant knowledge (of spills, incidents and inventories) and experience being retained. S Utilising site knowledge. S Retaining the motivation and continuity of workers. S Continued employment for personnel who operated the plant. S The support of the local community. S Long decay half-life isotope plants, particularly actinide ones, can develop a number of problems. The most significant being the increase in radiation dose rates due to the in-growth of americium-241. S Tie-down coatings and other temporary remedial works may deteriorate/degrade. S Physical containment’s deteriorate and require their conditions to be kept under review.

Present Timeframe Lessons Learnt 1. Obtaining Radiation Protection Adviser (RPA) and other specialist support to decommissioning activities is best done at conception and maintained throughout the whole work programme. 2. Expect the unexpected, and then be pleased if it doesn’t happen. 3. It is best from a project time line perspective to implement controls early on in a project if a hazard is reasonably foreseeable, as it becomes more difficult and time consuming to do this as a retro fit later. A good example of this is the improvement of glove box containment prior to ‘pre-works’ projects and extended periods of ‘Care and Maintenance’. 4. Soil and land remediation is problematic, areas that have been surface remediated may initially show no signs of residual elevated radioactivity, but may over time manifest a residual hazard. 5. Soil chemistry and hydrogeology can have significant effects on the localisation and migration of radionuclides in the environment. For example, in cases where strontium- 90 and caesium-137 contamination was deposited simultaneously, over time the two radionuclides can separate out depending on the local soil chemistry and hydrogeology. In some excavations, a layer of 90Sr has been found with little 137Cs present and in other areas 137Cs can be found with no 90Sr. More information on the soil chemistry of 90Sr and 137Cs is available in the literature10, 11. 6. An elevated internal dose was identified for a peripatetic worker on the Dounreay site, involved in decommissioning. It is unlikely that the dose was accrued on the Dounreay site, with the stringent control measures being implemented, however due to limited supporting dosimetric evidence the dose was attributed to work at Dounreay. UKAEA is currently re-considering dosimetric arrangements for this group of workers to remove any future difficulties. 7. As is to be expected12, dust generated during certain decommissioning tasks adversely affects the detection efficiency, especially for alpha emitting radioactive contamination. This is due to the dust masking or attenuating the emissions. This dust can also cause alpha in air detection equipment to alarm, due to attenuating naturally occurring radon daughter alphas into the man-made radiation energy detection region7.

RECOMMENDATIONS AND ACTIONS FROM LESSONS LEARNT 1. Prior to closing nuclear facilities, all process plant and equipment should be decontaminated (so far as reasonably practicable). 2. Components that may perish (rubber seals etc) should be decontaminated, replaced (if appropriate) and not left for periods of time, unless appropriately inspected and maintained. 3. Consideration should be given to secondary containment (such as “top hats”) and protective sealant coatings on glove ports and seals, etc. 4. Staff involved in running plants should be involved in the POCO and decommissioning plan preparation as a minimum. 5. Modern plants should be designed and built to modern standards, where decommissioning is an integral part of the plant design. For example active plant and equipment should be segregated and contained within appropriately shielded containments, within suitably ventilated buildings. Thus the radiation and contamination hazards controlled by engineered design solutions, so far as reasonably practicable. The Sodium Disposal Plant (SDP) and Caesium Removal Plant (CRP) at Dounreay are good examples of this being appropriately implemented. 6. Minimisation of maintenance in new plants should be a key consideration, with items being replaced as units as opposed to intricate time-consuming work in high radiological hazard areas. For example at Dounreay, entry to the SDP will only be performed using written (risk assessed) maintenance instructions under a ‘Permit To Work’, once the sodium filters have been backwashed and the systems in the cell have been drained of active material. Before breaking the primary containment, the aqueous plant will be washed through with water. It is not anticipated that any plant will break down and require replacement during commissioning. Any plant that does need to be replaced will be removed at appropriate points and replaced by appropriately tested new plant. Any new welds will undergo one hundred per cent radiography following completion of the work. 7. Consideration should be given to formal arrangements for pre- and post-project internal dosimetric assessment for peripatetic workers, to demonstrably show the adequacy of the radiation protection standards being implemented. 8. Work is needed to accurately determine the impact of dust on the detection efficiency of radiological protection instrumentation and identify appropriate correction factors, to ensure that a suitable level of protection is always maintained during decommissioning activities.

THE FUTURE On 28th November 2001 the United Kingdom Government announced that nuclear liabilities, such as those owned by the United Kingdom Atomic Energy Authority (and British Nuclear Fuels plc.) would come under the auspices of a new Liabilities Management Authority following an Act of Parliament. The LMA will oversee the care, maintenance and timely decommissioning of these facilities. The UKAEA will continue to progress decommissioning in line with project plans and the DSRP, utilising in house resources and contract support as necessary. A significant amount of decommissioning work has been conducted and will be necessary on the Dounreay site as a prelude to site restoration. It is likely that these projects will be discussed in greater detail in future reports to be produced by the UKAEA. ACKNOWLEDGEMENTS We wish to thank the United Kingdom Atomic Energy Authority for supporting the production and presentation of this paper. We would also like to thank our colleagues who have assisted with critical appraisal of this paper and the provision of information. Finally, we owe a debt of gratitude to the Decommissioning and Waste Management Groups staff at Dounreay who have and are still performing the decommissioning work, and without whom progress towards site restoration would not be happening.

DISCLAIMER Any views, opinions or endorsements expressed within this paper are solely those of the Authors and do not necessarily reflect the views or policies of the UKAEA.

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