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

7. Nuclear fuels

7.1 The Nuclear Fuels Inventory and Management Plan - Volume 6 of the DSRP - describes the fissile material inventory at Dounreay and, at the time of publication of the draft Plan in October 2000, the range of strategies for its reduction. It includes information relating to the quantities, nature, and possible methods of treatment for the different fuel types, with preferences indicated.

7.2 Volume 6 states that a dedicated system, the Dounreay Nuclear Fuels Inventory, has been produced by UKAEA to record progress in reducing the inventory of fissile material and review and report on the availability of preferred methods of treatment.

7.3 It should not be forgotten that the Dounreay fuels are not conventional in kind and cannot easily be treated by conventional procedures in existing plants elsewhere. It is noted that the availability of some options, notably on-site reprocessing in custom-built Dounreay facilities, may be time-limited for reasons of political and public acceptability, rather than the life-span of the plant (although this could also be significant).

7.4 The Nuclear Fuels Inventory and Management Plan relates to, and references, two other sets of documentation - the documents making up the "Making the Right Choice" consultation exercise run by the DTI during 2000 in relation to PFR fuel at Dounreay, and the analogous exercise to determine the BPEO for all fuels that are a liability of the DTI. The Plan makes clear that the BPEO study for PFR fuels, set out in "Making the Right Choice", drew on the "All Fuels" BPEO.

The "Making the Right Choice" consultation

7.5 In June 2000, RWMAC responded to the "Making the Right Choice" consultation on the PFR fuels ⁸. Three options were put forward :

• a "Dounreay strategy", in which both irradiated and unirradiated PFR fuels would be reprocessed at Dounreay;
• a "hybrid strategy", in which the irradiated PFR fuel would be reprocessed in the Sellafield THORP plant and the unirradiated fuel reprocessed at Dounreay or overseas;
• a "minimum treatment" strategy, in which all the PFR fuels would undergo treatment at Dounreay to put them into a form suitable for interim storage, pending future decisions on their possible deep underground disposal.

7.6 RWMAC's view was that, at the time, the options had been insufficiently defined to allow a meaningful choice to be made. It noted that two of the options - "Minimum Treatment" and "Hybrid" involved unproven technology while the third, involving the recommencement of reprocessing at Dounreay, posed the prospect of an uncertain public response, as well as potential regulatory difficulties in the context of both national policy on discharges and plant safety (since some of the plant had been non-operational for four years). Following subsequent discussion, including sight of the regulators' responses, RWMAC inclined more towards the Dounreay option, noting the advantages of using proven technology to reduce technical risks, promote the safety of operations, and secure regulatory consents (subject to factors such as demonstration of BPM, any safety case improvements required, etc.).

7.7 The text of RWMAC's responses to the "Making the Right Choice" consultation and a discussion of them are given in the Committee's 20^th Annual Report ⁹.

The All Fuels BPEO

7.8 The final version of the All Fuels BPEO was published in January 2001. Its aim was to consider the optimum strategies for dealing with all the fuels held at Dounreay. This was the final version of a document that, in an earlier draft stage, had informed preparation of the "Making the Right Choice" documents.

7.9 The All Fuels BPEO report is a complex technical document that will not be easily understandable to the non-expert. Its structure is analogous to that used for the PFR fuels, although the way in which its conclusions were arrived at is, in RWMAC's view, more clearly stated.

7.10 Not all the constituents of the fissile material inventory were addressed to the same extent in the study, the starting point for which was consideration of the principal groups of fuel materials in isolation (DFR and PFR materials). In each case, a range of possible treatment methods was considered. The aggregate output from these individual BPEOs was then used to eliminate options "not worthy of further consideration" in the formulation of an "all fuels strategy". UKAEA argued that evaluation of options for each group of fuel materials in isolation did not provide adequate information for decisions - because it would not take account of interactions. In RWMAC's view, this was sensible.

7.11 The practical treatment options for some other groups of materials were very restricted and had no effective impact on the assessment of options.

Results of the BPEO

7.12 The overarching aim of the strategy is the retrieval, characterisation and treatment of the Dounreay fuels to prepare them for safe, long-term, storage. "Do-nothing" was not an option considered as part of the BPEO since deterioration in the condition of the fuels, and also in available treatment plant, would progressively limit the options.

7.13 Using the results for the PFR and DFR materials, together with the practicable options for other materials, a simplistic view (since there were a number of variants within these strategies) of three representative treatment options, similar to those identified for the PFR fuels, emerged :

• a Dounreay strategy, in which all fuel materials would be treated in new or existing refurbished plant at Dounreay;
• a hybrid strategy, in which as many fuel materials as possible would be treated at Sellafield and the remainder treated at Dounreay;
• a minimum treatment strategy, in which all fuel materials would undergo minimum treatment at Dounreay.

7.14 All three options contained a significant minimum treatment element and all had common elements in that new plants for carbide fuel oxidation, characterisation of unirradiated fuels, and fuel repackaging, would be required, as well as the existing Dounreay vitrification and cementation plants. The emphasis on minimum treatment was indicative of the fact that conventional treatment routes are not always available. Thus, the element of risk posed by unproven technology remained.

7.15 While no clear BPEO emerged from this part of the study, the Dounreay strategy scored high relative to the others (i.e., in relation to those attributes where the difference in scores is largest) for technical robustness and feasibility, regulatory matters, and cost.

7.16 Further work was then carried out in relation to the irradiated DFR breeder fuel and PFR fuel and related materials. The work also reflected the need, as part of any reprocessing strategy, to reprocess some irradiated enriched uranium and plutonium/uranium oxide items. The work complicated, and blurred, to a degree, the results of the BPEO, but was suggestive of UKAEA's willingness to respond to external concerns. It also brought in the option of reprocessing some DFR fuel through the Sellafield Magnox reprocessing plant, and, therefore, timing uncertainties associated with the future of that facility.

7.17 The second phase of the all fuels work served to shed further light on the results of the PFR BPEO study, but only to the extent of, in RWMAC's view, further equalising the options. Further decisions, possibly in conjunction with public consultation, were necessary in relation to the possible need for new or refurbished plant at Dounreay, including the contentious issue of the future, and possible uses, of the D1206 irradiated PFR fuel reprocessing plant.

7.18 The results from this second phase of the study did not change the conclusion that there was no clear BPEO strategy for all the Dounreay fuel materials. Nor did they alter the conclusion that there would be 38 tonnes of fuel materials that would need to undergo minimum treatment, whatever strategy was chosen.

Observations on the way forward

7.19 The form of the All Fuels BPEO was similar to that used for the PFR assessment, for both the range of attributes and the weightings applied. In its June 2000 response to the "Making the Right Choice" consultation ⁸, RWMAC commented that the use of large numbers of attributes appeared to lead to a lack of sensitivity and an element of convergence, with none of the three options emerging clearly. In this respect, the results of the All Fuels exercise had a strong resemblance to that of the PFR fuels, i.e., the signals about preferred options were relatively weak, and the exercise thus failed to identify an optimal strategy. Thus, there was no favoured option for a management strategy for the DTI liability fuels.

7.20 The limitations of the analysis notwithstanding, the conclusions of the BPEO exercise gave a very even-handed review of the outcome. Coupled with the commitment to greater openness in carrying out the assessment, it demonstrated that considerable effort was being made by UKAEA to provide an objective basis for taking decisions forward.

7.21 Given the absence of a clearly identified BPEO, RWMAC's view was that the decision concerning the way to proceed would have to be made primarily on the basis of what was known about existing, or could be judged about future, technology and attendant risk, the impact of regulatory approval, or non-approval, and the degree of acceptability of the favoured strategy to those most affected by it. Whatever the decision, however, and whatever criteria were used in making it, the important thing was that the issues should be brought out fully and openly.

7.22 The Minister for Energy, Brian Wilson, said in his 18 July 2001 announcement about the decision to end reprocessing of PFR fuel at Dounreay:

"It is important to get on with the job of the environmental restoration of Dounreay. This decision gives the workforce and management a clear way forward to complete this nationally important task. UKAEA welcome this clear focus for all involved.

I have considered carefully the advice and comments I have received for dealing with this fuel. Following an extensive consultation it is clear that refurbishing the reprocessing facilities at Dounreay risks diverting valuable resources from the restoration of the site.

I have taken full account of UKAEA's work to identify the best environmental option during the public consultation".

7.23 UKAEA's BPEO work did not identify a preferred management strategy for the fuel. Although the Minister's statement does not indicate the present state of thinking on how the fuel may now be dealt with, it represents a clear advance that enables UKAEA to embark on the first step towards final decommissioning - post-operational clean out of D1206 and the associated Residues Recovery Plant. Following the decision, more detailed planning is now required of the way in which all the nuclear fuel materials held at Dounreay are to be managed, including the provision of any treatment facilities that are necessary.