RWMAC's Advice to Ministers on the Radioactive Waste Implications of Reprocessing

6. MATERIAL TREATMENT, STORAGE AND DOWNSTREAM HANDLING IMPLICATIONS

This section considers the issue of how spent fuel and the products of its reprocessing are handled at the Sellafield site. This is done through reference to descriptions of the major waste conditioning plants and storage facilities at the Sellafield site given in Annexes 5 and 6. In doing so, it touches on several key points relating to the issue of passivity, essentially the holding or storing of radioactive materials in a passively safe form.

6.1 The concept of passivity

Storage in a passively safe form is one of the principles of radioactive waste management set out in the last Government’s Cm2919 White Paper³ and one on which RWMAC understands the Nuclear Installations Inspectorate (NII) is laying increasing emphasis, for example through development of guidance for its inspectors. RWMAC welcomes this, particularly in the current absence of an agreed long-term policy for the management of any of the UK’s HLW, ILW and spent fuel following the 1997 collapse of the Nirex ILW repository programme. Hopefully, the forthcoming UK Government consultation on its future radioactive waste management policy will in due course resolve this.

RWMAC takes the concept of passivity to be broadly the holding of radioactive materials in a passively safe form with a minimal need for active control systems or human intervention. A key emphasis is on the waste form, which should be immobile, physically and chemically stable and resistant to significant deterioration or reaction with its environment over a reasonably foreseeable storage period. But the requirements for its storage surroundings are also important. In practice, implementation of the concept will raise some complex issues. For example, there is currently a policy presumption against treatment of ILW and LLW which might foreclose future management options, although this can be relaxed where there are clear safety or economic benefits (ref Cm2919¹³, para 113). Additionally, there are likely to be timing constraints on the application of the concept. Quite simply, while it may be possible to design a store for the passive storage of wastes or other materials for a period of 100 years, this would, at first sight, appear unlikely to be possible over the many thousands of years it might take for radioactivity to decay to safe levels. The forthcoming review of radioactive waste management policy should also, in RWMAC’s view, seek to promote the formulation of a full and operational definition of the concept of passivity, which pays due regard to these wider considerations. The Committee discusses several issues that are clearly related to the concept of passivity in the remainder of this section.

6.2 Materials treatment routes and facilities at Sellafield

The routes and facilities available for the treatment of both Magnox and THORP reprocessing material arisings are described in Annex 5. BNFL have stated to RWMAC that the existing or currently planned facilities will be sufficient to deal with any of the scenarios considered by RWMAC, except in the case of the Waste Vitrification Plant (WVP) where a fourth vitrification line would be needed to deal with the "Combined Extended" scenario (see section 4.2).

One of the most sensitive issues relating to spent fuel treatment at Sellafield, which again relates to the concept of passivity, is the storage of liquid HLW, or HAL, reprocessing product. This liquid HLW, or HAL, is produced from current operations and has also accumulated since the 1950s from earlier reprocessing. It is currently produced by both Magnox and THORP reprocessing activities, and is stored in building B215 on the Sellafield site.

The holding of this HAL on site is clearly not in accord with the concept of passively safe storage. HAL generates heat and therefore needs to be continuously cooled. The B215 tanks contain different types of HAL which have different characteristics and hence their behaviour on loss of cooling is different. For the older HAL, the loss of cooling has no significant consequences. However, for the later tanks, total loss of cooling would eventually lead to the HAL boiling with potential increase in mobility as vapour and condenses. The NII has been aware of the potential risks associated with the storage of HAL at Sellafield for a number of years. In a 1995 report¹⁷, the NII set an objective of reducing the stocks of HAL to an unspecified buffer volume by around 2015. In February 2000, the NII reported a further safety review of HAL storage at Sellafield to review¹⁸ progress since 1995.

Whilst stating the belief that the arrangements for liquid HLW storage at Sellafield remain acceptably safe, the February 2000 report noted that BNFL’s HAL stock provisions did not show any reduction in the storage levels until about 2004. However, the NII itself concluded that this downturn in 2004 was itself sensitive to BNFL’s assumptions of achieving the stated throughput from the new third WVP line, improved performance from the two existing vitrification lines and reduced fuel reprocessing business in the period 2004-2015¹⁸. Figures given in the NII report showed that the two existing vitrification lines had substantially under-performed their original design intent since commencement of operation.

Because of this, the NII stated in their February 2000 report¹⁸ that they remained unconvinced that BNFL will achieve the aim to reduce their HAL stocks to a buffer volume by around 2015. Failure to achieve the required reduction in HAL stocks, would leave BNFL with the following options to avoid regulatory intervention:

• improve vitrification throughput rates in WVP lines 1, 2 and 3

• voluntarily reduce THORP throughput

• close some Magnox generation capacity earlier than planned to reduce Magnox HAL arisings

• construct additional vitrification plant capacity i.e. line 4

The choice of which option to adopt would be a matter for BNFL and may involve some combination of the above. The NII¹⁸ stated that they would not hesitate to use their regulatory powers to ensure that the necessary HAL stock reductions were achieved. In practice, the lesser the ongoing reprocessing requirement, the greater the chances of reducing the HAL stocks to the requisite buffer levels by 2015.

RWMAC also sees the reduction of the HAL stock to be important both for safety and public reassurance reasons. The Committee therefore recommends that progress towards this objective be kept under close review and published on a year by year basis.

6.3 Reprocessing timescales

BNFL’s revised Magnox station lifetime strategy statement made in May 2000 said that this would allow the Magnox reprocessing plant, B205, at Sellafield to close, once all Magnox fuel had been reprocessed, sometime around 2012, although acknowledged that this could be later depending on the throughputs achieved.

The figures for amounts of Magnox fuel to be reprocessed given in Table 3 together with consideration of the rates of throughput likely to be achievable by the B205 facility can be used to assess the likelihood of this objective being achieved. Figure 1(a) gives the results of such an analysis. It should be noted that, for the purposes of this evaluation, an "updated" Reference Scenario of 12,000 tHM has been used, this being the 10,500 tHM shown in Table 3 for the Reference scenario, M2, plus the additional 1,500 tHM that will need to be reprocessed under BNFL’s revised Magnox business plan (see section 4.2). The analysis, on the basis of an average throughput, may be considered simple, when, in practice, throughputs may vary over time. Nevertheless, the fact remains that a suitable average will need to be maintained over the relevant period to achieve the reprocessing required.

What figure 1(a) shows is that an average throughput rate of about 1,000 tHM per annum would need to be achieved for the "updated" Reference, i.e. 12,000 tHM, scenario in order to allow the B205 facility to be closed by around 2012. However, Magnox reprocessing throughputs over the past three years have averaged about 500 tHM per annum. This compares to the B205 lifetime annual average throughput of 1084 tHM per annum. This suggests to RWMAC that BNFL will have to elevate recent throughputs back to the significantly higher earlier levels in order to achieve closure of B205 against their revised Magnox business plan by around 2012. Continuing at an average Magnox throughput of 500 tHM per annum would mean that B205 would need to operate to about 2023 to deal with the amount of spent fuel to be generated under BNFL's latest Magnox business plan. It is inevitable that as plants get older the need for maintenance and refurbishment increases.

Figure 1. Estimates of reprocessing timescales for different rates of throughput

BNFL have informed RWMAC that B205 operational capacity is constrained by the fuel decanning activity in its Fuel Handling Plant and that since 1995 this plant has been run with only one of the two decanners operating at any one time. They said that they intended to change the operating regime soon by increasing manning levels, which would enable both decanner lines to be operated thereby increasing Magnox reprocessing throughput.

Nevertheless, RWMAC believes that, given the sensitivity of the issue, it is important that any statement made by BNFL concerning future reprocessing activity timescales should be well-founded. The Committee therefore recommends that BNFL reviews its revised May 2000 business plan statement to ensure that it is realistically commensurate with the closure of B205 by around 2012, to be clear how progress towards this goal will be monitored and to declare what its strategy would be if the necessary throughput is not achieved. Analysis considered in Section 7.5 of this report indicates that the future timescales of Magnox reprocessing are liable to be a critical element in the achievement of the UK’s OSPAR objectives.

THORP reprocessing requirements can also be analysed in similar fashion. Figure 1(b) sets out the results of such an analysis. Footnote (d) to Table 3(b) indicates that the THORP reprocessing plant has reprocessed 2,800 tHM since it opened in 1994. Amounts have increased from 65 tHM in the first year up to 830 tHM in the year ending 31 March 2000⁶. Its currently intended throughput is 800-900 tHM per annum.

What figure 1(b) indicates is that, unless substantial new contracts are won, THORP reprocessing will come to an end between about 2008 and 2010, given an average reprocessing throughput from now on of between 800 and 1,000 tHM per annum. This in turn would mean that, if the use of Magrox fuel is to be contemplated for Oldbury and Wylfa (see section 4.2), the possibility of its subsequent storage, as opposed to reprocessing, also needs to be considered and evaluated by BNFL. Conversely, if substantial contracts were won, THORP reprocessing, e.g. under the Extended scenario, might be extended to 2021 to 2025 for average throughput rates of 800 -1,000 tHM per annum.

6.4 Storage requirements

An analysis of the storage requirements associated with the various scenarios considered by RWMAC is set out in Annex 6. The conclusions concerning whether there would be additional requirements or potential savings in stores relative to the "Combined Reference" scenario case is as summarised in Table 8.

Table 8

Additional requirements or savings in stores relative to Combined Reference scenario

Additional storage space could be provided either by building one or more new stores, or extending an existing one or, possibly, building a single larger new store. Store savings are only possible when a proposed additional store would not need to be built. Annex 6 gives further details.

Interim storage of HLW, ILW, reprocessed uranium and separated plutonium may be regarded as proven technology (LLW already being disposed of to Drigg). There is therefore no reason to believe that provision of additional interim storage for these materials would give rise to any real practical difficulty over the shorter term.

Very much more careful consideration would need to be given to this issue over the longer term, particularly if the concept of passivity is developed as is suggested in section 6.1. This could be particularly important in respect of RepUO₃ and SepPuO₂ if some or all of the stocks held came to be regarded as wastes.

Currently regarded by the industry as a resource rather than a waste, these materials, which currently exist in a powdered oxide form, might be considered to be unsuitable for longer-term passive storage (see section 6.1). Notably, as powders, these materials could, potentially, be dispersible if the integrity of their containers is not maintained. In the case of plutonium, the stored containers must also be cooled and the hazard increases with time as a result of the in-growth of the more radiologically significant americum-241. In comparison, uranium oxide powder is relatively benign and easy to store. However, their powder form may be taken to indicate a need for further conditioning of these materials, particularly SepPuO₂. It is a matter of judgement as to whether these characteristics provide sufficient reason for relaxing any presumption against treatment which might foreclose future management options. Ensuring the necessary level of security of these materials could also, potentially, become increasingly difficult the longer they have to be stored.

The High Level Waste and Spent Fuel Disposal Research Strategy Project commissioned by the Department of the Environment, Transport and the Regions from QuantiSci^19,20 considered the possible implications of ultimately regarding RepUO₃ and SepPuO₂ as wastes and including them in any future disposal strategy (more is said of this in section 6.6). This included brief reference to development of appropriate waste forms. There have been various past studies of this issue²¹, some now dated, that would need to be thoroughly reviewed and evaluated if some or all of the current stocks of RepUO₃ and SepPuO₂ came to be classified as waste.

Conversely, options involving the early termination of reprocessing will lead to more fuel that must be stored, presumably either at power stations or at Sellafield, in addition to the 2,900 tHM AGR and 1,200 tHM Sizewell B fuel currently not covered by reprocessing contracts. For the pursuit of such options, the industry would need to develop and maintain a robust storage plan which satisfies the fuel volumes envisaged and uses storage methods which are appropriate to the timescales defined by developing radioactive waste management policy.

6.5 The prospects for uranium and plutonium recycling

An important question to contemplate in respect of the UK’s holdings of civil uranium and plutonium, is whether UK stocks might be reduced in the foreseeable future through recycling as nuclear fuel. In RWMAC’s view the signs are that they will not for several reasons.

In respect of uranium, BNFL’s construction of a facility to convert reprocessed uranium into uranium hexafluoride prior to enrichment and fuel fabrication was suspended due to the lack of demand for the manufacture of reprocessed uranium fuel. BNFL’s position is that completion of the facility is dependent on sizeable customer commitments.

The situation is unlikely to change in the foreseeable future. For example, in 1996 the Recycling Working Group of the Uranium Institute (UI)²² reported that: "So far, only utilities in Belgium have begun to make routine use of reprocessed uranium fuel, in line with a commitment to fully utilise arisings of reprocessed uranium from existing reprocessing contracts by 2003. In other countries the use of reprocessed uranium from LWR spent fuel reprocessing has been restricted to relatively small-scale trials, and utilities have not set a firm schedule for the large-scale use of reprocessed uranium". However, BNFL have informed RWMAC that since the UI report was published reprocessed uranium has been used by a number of other countries.

In its review of the UK position, the UI Working Group explained that although reprocessed uranium fuel from Magnox stations has been recycled in AGRs in the past, recent market prices for fresh uranium had made its use uneconomic. It added that in principle reprocessed uranium from oxide fuel could be used in AGRs, but handling difficulties caused by the level of radioactivity in the reprocessed uranium would be likely to limit its use²². During the course of the current study British Energy (BE) informed RWMAC that its current position was that "in principle reprocessed uranium from oxide fuel could be used in AGRs but its economics would depend on whether any additional costs for reprocessing this uranium and minimising exposure to operators outweigh the savings on purchases of uranium and uranics services". BE is currently evaluating the economics of such recycle. RWMAC observes, however, that it is at least a possibility that the extra incentive provided by declaration of any of the existing stocks of reprocessed uranium as waste, and the need to minimise the net costs of treatment, could relax or remove such limitations of its use.

In respect of plutonium it is noted that:

• BE’s position on the potential use of MOX in the UK was set out in a letter to the House of Lords Science and Technology committee in September 1998²³. This stated that utilisation in AGRs has been reviewed but was not considered practicable. With regard to the PWR, Sizewell B, it added that the company would consider in due course whether to use MOX, subject to demonstrating its safety, reliability and economics. BE added that "at current prices for uranium and taking account of the premium for MOX fuel fabrication and all other costs and benefits, the economics of MOX use in Sizewell B are not currently competitive with uranium fuel^"23.
• even if they were to adopt the use of MOX fuel in substantial amounts, many of the more important overseas customers will have stocks of plutonium already in the UK from reprocessing of their own fuel. This would presumably be used before any UK-owned plutonium, therefore the UK-owned stockpile would not be reduced.
• the apparently unfavourable economics of MOX fuel relative to conventional uranium fuels could potentially be modified by a declaration of any existing plutonium stocks as a waste liability, as the comparison would then need to include the economics of plutonium immobilisation.

RWMAC would not wish to assert those circumstances may not change nor, the Committee acknowledges, is it well placed to say if and when this might happen. However, to reiterate, there are no obvious signs that UK stockpiles of civil uranium and plutonium can be significantly reduced in the foreseeable future through recycling as nuclear fuel.

Some would claim a case for looking to increased use of nuclear power in the future to help to achieve greenhouse gas objectives. This, and increases in fossil fuel prices, could potentially be seen to make nuclear power more attractive. Others would see increased use of nuclear power to be unacceptable until the problems of its high capital construction cost and associated waste management are solved. They would also argue that there are other alternatives (e.g. more efficient energy use) for addressing the greenhouse gas problem. Fuller discussions of this particular issue are given in the joint Royal Society and Royal Academy of Engineering report on "Nuclear Energy – the Future Climate"²⁴ and in the Royal Commission on Environmental Protection report "Energy – the Changing Climate"²⁵ .

6.6 Possible disposal implications

Operation of the Drigg disposal facility has demonstrated the feasibility of surface disposal of LLW. Some countries also use such facilities for the disposal of short-lived intermediate level waste. BNFL currently believe that, on the basis of a projected remaining disposal volume of about 850,000 m³, Drigg will be able to accept the great majority of the UK’s LLW up until about 2050 (there are, however, some LLW waste streams that will have to be excluded either because they are unsuitable for disposal at the site or due to their disproportionate use of its radiological capacity). A replacement facility for Drigg will therefore need to be found for the remainder of the LLW predicted in Table 7. The House of Lords Select Committee on Science and Technology concluded⁵ that plans should be made for the establishment of a new LLW disposal facility, to open before Drigg closes. RWMAC fully endorses this conclusion.

UK Nirex Ltd (Nirex) had responsibility for development of a repository for deep disposal of the UK’s ILW and LLW unsuitable for disposal at Drigg until the programme was suspended in 1997, as a result of the company’s failure to secure planning permission to allow construction of a Rock Characterisation Facility (RCF, essentially an underground laboratory) at Longlands Farm near Sellafield. Nirex continues to maintain a watching brief on disposal issues. Their current estimate of the cost of developing, constructing, operating and closing such a repository for a volume of ILW similar to the 209,000 m³ forecast in Table 7 is of the order of £5,100 - £5,800m at 1999 values depending on whether a period for possible retrieval is required prior to closure²⁶. Construction of such a repository would of course ultimately be dependent on all the necessary planning and regulatory permissions being obtained.

The research and development programme needed to support underground disposal of HLW, spent fuel and other materials was also explored in the study of a research strategy for the disposal of HLW and spent fuel undertaken by QuantiSci for the Department of the Environment, Transport and the Regions (DETR)^19,20. Nirex believe that the underground disposal of the other materials recorded in Table 7 – VHLW, spent fuel, reprocessed uranium and separated plutonium is also potentially possible, provided the materials can be conditioned to a suitable form. During the course of this study Nirex provided RWMAC with some of their initial ideas for this²⁶, based on both the concepts of separate and co-disposal. Again, such disposal would be dependent on obtaining all the necessary planning and regulatory permissions.

A key consideration in contemplating the possible underground disposal of these other materials – VHLW, spent fuel, reprocessed uranium and separated plutonium – either co-disposed with or separate from ILW, is the potential repository volume implication. For VHLW and spent fuel, the required repository volume would be determined not simply by the physical volume of the wastes, but by their heat outputs which, in the case of VHLW and spent fuel, are similar. If plutonium were ever to be disposed of, criticality and security considerations would also need to be taken into account. Quite apart from being likely to increase the repository volume requirements compared with that required for ILW alone, the underground disposal of these other materials is likely to be politically much more sensitive.

RWMAC thus believes that the volumes and forms of wastes to be disposed of would have major implications for the potential siting of any future disposal facilities. The rejection of the RCF at Sellafield has raised doubts about the suitability of a site in the locality. Yet, the fact remains, that, while reprocessing continues, the bulk of wastes will continue to be stored at Sellafield in addition to the historic wastes already in store there. With or without reprocessing, it will be difficult to achieve a site elsewhere and will involve the transhipment of large volumes of wastes from Sellafield.