RWMAC's Advice to Ministers on the Restoration of the UKAEA Dounreay Nuclear Site

6. Radioactive wastes

The Dounreay Radioactive Waste Management Document

6.1 The Dounreay Radioactive Waste Management Document (DRWD) - volume 4 of the DSRP - is designed to provide a single comprehensive source of authoritative information on radioactive waste management at Dounreay, e.g., technical details, strategies for individual waste streams, waste routes and facilities.

6.2 The DRWD describes the content, role, and maintenance of the Dounreay Radioactive Waste Inventory (DRWI). This will ultimately be used as the basis for supply of data to the UK Radioactive Waste Inventory. Currently, the DRWD and the DRWI cover more than 100 waste streams. Dounreay, having undertaken work on highly specialised research reactors and the reprocessing of specialist experimental fuels, has produced many different waste streams and sub-streams, some of which could, potentially, pose unique or difficult management problems. Development Requirements Documents (DRDs) will also be produced to highlight all the potential development work required to support the processes for packaging waste, including development work on retrieval of waste, waste treatment and packaging, and compliance with Nirex disposal requirements. The DRDs will also be used to cover all associated research work.

6.3 Overall, RWMAC is strongly supportive of the concept of the DRDW, the DRWI and the DRDs, as a systematic and sensible approach to the issue of waste accounting and planning for its treatment. The Committee believes that, if properly constructed and managed, these documents should provide a sound basis for future radioactive waste management at Dounreay.

6.4 The DRWD also describes the strategies leading to disposal of the wastes (and the threats to those strategies), the treatment processes needed, and the status of the Letter of Comfort (LoC) approval needed from Nirex to confirm that a particular waste form is (currently) acceptable for disposal in a national repository.

6.5 The DRWD draws attention to the potential conflict between early waste conditioning and storage of untreated wastes with the minimum packaging required for safety. For each waste stream, the aim is to maximise the safety benefit achieved. Where a LoC has been obtained, the policy is for the wastes to be conditioned for long term storage, giving priority to those where the most safety benefit can be achieved (e.g., immobilisation of liquid wastes) through analysis of each waste stream. Otherwise, the balance between the safety gain that can be delivered through early waste conditioning, compared to the advantages of not foreclosing future management options, is considered by UKAEA for each waste stream. The timescale for conditioning of a particular waste stream is influenced by a number of factors, notably the availability of suitable plant.

6.6 In this context, RWMAC supports the principle of passively safe storage of radioactive waste, while acknowledging that not all the defining criteria of passivity have been finally established. The Committee is not in favour of wastes being left in mobile form for long periods except in cases where this can be demonstrated to be unavoidable, for example if treatment plant has yet to be developed. In any instance where there is an assertion that waste cannot be put in a passively safe storage state because of option foreclosure, that assertion needs to be reviewed vigorously and critically to ensure that it is completely valid. RWMAC's view is that, in general, conflict between achieving passivity and unduly foreclosing options is liable to be more asserted than real. These observations on securing passive storage apply to all HLW and ILW at Dounreay and are reflected in the discussion of specific waste streams in the following paragraphs.

HLW

6.7 The only HLW that has been generated at Dounreay is the liquid waste stream (termed "raffinates") arising from the reprocessing of PFR fuel. The UKAEA reference strategy is to vitrify the raffinates within steel containers on the Dounreay site, as a prelude to their storage pending eventual disposal. Currently, the raffinates are held in tanks in the Dounreay high active liquor (HAL) store. In RWMAC's view, this arrangement ranks highly as a potential risk, because of the hazard posed by the activity and mobility of HAL, and the technology required for checking the integrity of the storage tanks.

6.8 While the Dounreay HAL has some distinctive chemical characteristics, RWMAC understands that UKAEA has conducted considerable research into the vitrification of fast reactor raffinates, including the availability of "off-the-shelf" plant, which could provide proven vitrification technology.

6.9 In its most recent study on Dounreay ⁴, RWMAC questioned the timeframe for the vitrification programme, suggesting that it should be possible to bring forward the start-time from 2008. The DSRP confirms the intention to construct a Vitrification Plant and Vitrified Product Store,the indicative timeframe for operation of which remains 2008. RWMAC reiterates its view that, given the hazard posed by HAL, there is a need for UKAEA to maintain good progress with its research and planning for implementation of the HAL vitrification programme.

ILW

6.10 A wide variety of Dounreay wastes are classified as ILW, including DFR and MTR reprocessing raffinates, resins and sludges, and solid wastes; the last are divided into contact-handling and remote-handling categories. Some solid ILW is already stored in drums; decommissioning of the ILW Disposal Shaft and the Wet Silo will create further arisings.

6.11 New facilities (the Waste Treatment Plant; WTP) are planned to treat the solid ILW, including its sorting and repackaging into Nirex-approved containers, for storage pending a permanent management route. Final or conceptual Letters of Comfort (LoCs) have been obtained for cementation of the ILW raffinates, although vitrification remains an option for the DFR streams. Nevertheless, questions of the timing of the cementation programme, and consideration of the alternative option of vitrification, do not appear to have been finally resolved. Cementation of MTR raffinates was halted in 1998 when NII required operations in the Dounreay Fuel Cycle Area to shut down (except for those required for the maintenance of safety).

6.12 In 1999 ⁴, RWMAC said that "management of ILW streams is adequately documented". The Committee welcomes the further advances made, apparent from volume 4 of the DSRP, in developing plans for the treatment and storage of ILW. This seems to be reinforced by Nirex's view of the Dounreay ILW streams. While the particular contents of the Shaft, and to a lesser extent the Wet Silo, pose characterisation problems, UKAEA's general forward management planning for radioactive materials and wastes associated with fast reactor decommissioning (while these are unusual and varied), has been aided by the robust R&D culture at Dounreay. In essence, the difficulties associated with granting Nirex LoCs for Dounreay waste forms are understood to be challenging but achievable.

6.13 Concerns are raised by the continuing presence of wastes in two sub-standard ILW facilities - the Shaft and the Wet Silo. These two facilities are different in both concept and use. The Shaft was excavated to allow the vertical removal of spoil during construction of the Dounreay effluent discharge system and was later (1957) authorised for the disposal of ILW, while the Silo is a purpose-built store.

6.14 Earlier in this report, RWMAC questioned whether sufficient priority was being given to the Shaft waste retrieval programme. The programme incorporates the hydrogeological and geotechnical investigation projects necessary to characterise the ground conditions around the Shaft, and especially around the plug at its base, as a precursor to containment and eventual waste retrieval works.

6.15 In paragraph 4.53 of its 1999 report ⁴, RWMAC stated that "these timescales imply that the first retrievals of waste will not take place until 2011. In RWMAC's view, this time frame is difficult to defend". Section 4 of the present report has already noted critically that current plans do not foresee removal of waste starting until 2014. The lengthy timeframe is despite the fact that UKAEA advertised for companies to express an interest in tendering for retrieval work in July 2000.

6.16 Although there were delays in placing contracts, a new phase of below-ground surface characterisation works in the area of the Shaft was scheduled to begin in June 2001. Borehole drilling, and associated investigation and testing, intended to provide information for isolation and containment project design work, will be carried out.

6.17 In the Committee's view, there is also scope for some investigation studies to be undertaken in parallel with retrieval plant design and shaft-head engineering works. UKAEA's plans for regular public announcements about the timing of both the characterisation studies and the tendering for retrieval plant design contracts - so as to firmly establish future timescale objectives against which progress can be monitored and assessed - are helpful. Generally, however, RWMAC remains concerned about the lengthy, possibly over-protracted, timeframe for the Shaft remediation programme.

6.18 It is well known that the Shaft is located close to the edge of the sea cliffs at Dounreay. The risk of cliff erosion that would expose part of the shaft, and disturb its contents, as part of a "catastrophic" event, is remote. Even so, the DSRP appears to give no analysis of the timescale over which the Shaft might be affected by erosion or the occurrence of abnormal sea incursions - matters that would reasonably be raised in any public debate. This issue needs to be addressed and clarified.

6.19 The retrieval strategies proposed for these facilities are well integrated into overall site ILW management plans which envisage that the WTP will condition and package all remote-handled ILW. A new WTP store will, similarly, be the sole Dounreay facility for storage of future arisings of remote-handled ILW, once conditioned and packaged, including the immobilised ILW raffinates.

6.20 While issues of risk, the extent of practical experience that can be gained, and transferred, between projects, and efficiency savings, all have to be considered, it would appear logical for work on the Shaft to begin first, with waste retrieval from the Silo following on.

LLW

6.21 In the past, solid LLW arisings at Dounreay were disposed of to a facility known as the "LLW pits". This is now effectively full and no further wastes are being consigned there. Solid LLW continues to arise at Dounreay, however, and will continue to do so, almost certainly at steadily increasing rates, as decommissioning progresses. The issues associated with future arisings, and those associated with the existing LLW facility, are addressed, in the following paragraphs, in turn.

6.22 The management of future Dounreay LLW arisings is very important because, in the absence of any further capacity offered by the pits, a waste management route must be found, notably for decommissioning LLW. This has two implications. The first is for Dounreay itself. A replacement disposal facility, which is only a possibility at this stage, must be a number of years off and, meanwhile, there is a need to condition and store waste safely on the site. This presents a challenge for UKAEA management to develop suitable LLW treatment and storage facilities. The second implication is for the Government, since the effective loss, in capacity terms, of one of the UK's two authorised LLW repositories (the other being the BNFL site at Drigg in Cumbria) will inevitably have implications for the UK's national LLW management policy. This, in RWMAC's view, is something that needs to be addressed as part of the forthcoming Government consultation on future policy even if, on the face of it, historic LLW buried at Dounreay need not be an early concern.

6.23 The DSRP includes a flow diagram setting out the elements of a strategy for managing future solid LLW at Dounreay. It is clear that ability to handle these arisings is one of the most crucial aspects to successful delivery of the DSRP, and yet this is an area of the Plan where there is little detailed coverage of the potential implications of the possible options. It is also a politically sensitive area. RWMAC's view is that, as a matter of general principle, UKAEA needs to take action, at a pace commensurate with proper consideration of the issues, and in conjunction with other relevant parties, to ensure that arrangements for the management of present and future LLW arisings are put in place without undue delay.

6.24 Volume 1 of the DSRP - its Introduction and Overview - states:

"The long-term strategy and associated facilities to manage all existing and future LLW arising from the Dounreay site will be determined by carrying out a Best Practicable Environmental Option Study. In the meantime, without prejudice to the outcome of the study and solely for evaluation purposes, the Plan assumes a new LLW facility built in the vicinity of Dounreay".

6.25 Volume 4 of the DSRP - the Dounreay Radioactive Waste Management Document - talks of a "reference strategy" - for LLW. This is for the wastes, compacted or otherwise, to be placed in half-height ISO containers for interim storage (pending establishment of a long-term management route) in a facility known as Whatlings Hangar (DN016). There is also a temporary store for solid items of LLW. Plans are in place to construct a further interim store (D3110) - it is understood that this is consistent with the local Development Plan. The reference strategy statement closes by saying that "UKAEA is developing plans to provide a long-term management solution that will accommodate all future solid LLW arisings from Dounreay".

6.26 Commencement of the operation of the new LLW facilities is rightly identified as a key output of the restoration programme, that needs to be achieved between 2010 and 2015. Few specific details of how this is to be progressed are, however, given in the DSRP.

6.27 The key to these questions about future LLW management appears to lie, to a considerable degree, in the BPEO study proposed by UKAEA. There are, however, difficulties associated with this. They concern the various options likely to emerge, the practical arrangements for carrying out the study, and the relationship of the BPEO study to the Government's forthcoming consultation on the management of the UK's solid radioactive wastes.

6.28 The most obvious management options for consideration are provision of a new LLW disposal facility in the vicinity of Dounreay, disposal of Dounreay LLW to the Drigg site in Cumbria in England, or long term storage on the Dounreay site.

6.29 Considerations of these options will not only be contentious, but will also raise radioactive waste management issues of UK significance. For instance:

• any proposal to site another LLW disposal facility at Dounreay will inevitably lead to objections. There will be major regulatory and planning issues (e.g., inclusion in the local plan, environmental assessment) associated with it. These issues are likely to take a considerable time and effort to resolve;
• if Dounreay LLW was to be transferred to Drigg, it would use up part of a scarce UK resource. Since Dounreay LLW has never been taken account of in Drigg plans, it would also bring forward the date for which a replacement for the Drigg facility would need to be found. It would necessitate the movement of waste across the national boundary (while this already takes place, the volumes would be greatly increased);
• at the moment, virtually all LLW is subject to early disposal. In RWMAC's view, storage would not constitute a long-term solution for the management of Dounreay's LLW.

6.30 Against the same background, there are issues of who should carry out the BPEO exercise and who should be involved as part of it. The Committee questions whether it is sensible for this to be left to UKAEA alone, given the sensitivity and potential wider implications of the work. There are also issues of who should be consulted, e.g., is it a matter purely for those living in the vicinity of Dounreay, or should those as far away as Drigg be included? RWMAC believes that, as one of the first steps, the implications of all the options need to be examined in the context of a UK-wide debate on LLW management (see below).

6.31 For the above reasons, RWMAC does not believe that the status of current UKAEA consideration of plans for LLW management at Dounreay is adequate. Solid LLW is an issue that must to be given high priority in both developing the DSRP and taking it forward. But it is equally important that its wider implications are exposed in a national debate. RWMAC does not believe that the extant statements of Government policy on this issue, notably the Cm 2919 White Paper ³, are any longer sufficiently informative or transparent to support the debate. The forthcoming Government consultation on solid radioactive wastes must, in RWMAC's view, address future LLW management arrangements on a UK-wide basis, taking into account the interests and views of the devolved administration in Scotland.

6.32 It is vital, therefore, that the Government's consultation on solid radioactive wastes should seek to identify and assess all the options for management of solid LLW and, ultimately, lead to the adoption of a clear policy covering the whole of the UK.

6.33 There is, similarly, some lack of clarity in the DSRP concerning the future of the existing disposal facilities (the LLW pits). For instance, Volume 2 (Schedule 1, Zone 9) assumes the application of ongoing management control up to the decommissioning endpoint, between 2050 and 2060, by which time the pits will have been closed off with an engineered mound, covered with topsoil and landscaped. On the one hand, this could mean that emptying the pits, and transferring the waste elsewhere (termed by RWMAC "decanting"), has been ruled out. On the other, Volume 3 (page 68) observes that "the contents of the existing LLW pits will be the subject of option assessment to determine the optimum action to be taken towards the end of the Site Decommissioning Phase". From statements elsewhere, it is clear that it is the BPEO exercise which is to assess the benefits and disadvantages of the various options.

6.34 The location of the existing disposal facilities, the design and engineering of some of the pits, and uncertainties about the inventory of their contents, may not pose significant practical problems except in the significantly longer term. It is not clear at present, however, whether a post-closure safety case can be made for the facility. If it can, there is no obvious reason why consideration of these historic arisings should need to form part of the DSRP-based debate on a new facility. But if the retention of waste in the pits is not sustainable, this will have implications for the provision of future facilities at Dounreay or elsewhere.

6.35 Thus, there is a need to look much more critically, than appears to have been achieved during preparation of the DSRP, at the sustainability of the existing LLW pits. In doing so, various questions need to be addressed, including : can their location and condition sustain a rigorous post-closure safety assessment; what is the timeframe for the hazard posed by their contents relative to the risk that they could eventually be affected by coastal erosion or abnormal sea incursion, and, if so, to what possible timescales; what is the likelihood that the existing pits may need to be decanted and, if so, what are the implications for the wider Dounreay LLW strategy?

6.36 Issues of LLW at Dounreay will remain contentious, and there are understandable public concerns. If LLW, whether historic or future arisings, cannot, for whatever reason, be managed at Dounreay, it still needs to be managed somewhere, for example at Drigg. This would involve the transport of large volumes of radioactive material, possibly over long distances. The benefits and detriments of this option would need to be judged in the same way as all others. The Committee is clear, however, that it should not be chosen simply in order to avoid facing up to difficult issues at Dounreay. It would need to be demonstrated to be the best option.

VLRM

6.37 UKAEA characterises Very Low Radioactive Material (VLRM) as decommissioning wastes and excavation arisings in the range from 0.4 Bq/g to approximately 40 Bq/g beta-gamma equivalent. The DSRP states that UKAEA is currently developing plans for the safe and cost-effective management of VLRM arisings. Characterisation and accumulation of VLRM as proposed in the DSRP is predicated on the 0.4 Bq/g level contained in the Substances of Low Activity Exemption Order as an appropriate level for site decontamination. More is said of this in section 8.