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

5. SOLID MATERIALS

5.1 Amounts of spent nuclear fuel to be reprocessed

The amounts of spent fuel that BNFL estimate would need to be reprocessed from 1 April 2000 onwards under each of the scenarios set out in Table 1 are given in Table 3.

It subsequently became clear that there were some differences in the information provided by BNFL to RWMAC and numbers appearing in the House of Commons Select Committee on Trade and Industry report on BNFL⁶ published in May 2000. The differences were primarily in THORP post-baseload figures. These differences were drawn to the attention of BNFL, who confirmed the numbers given to RWMAC were the correct figures from their viewpoint. They added that they had not supplied the figures quoted by the Select Committee. RWMAC have therefore proceeded on the basis of the BNFL figures, but remain concerned that two such important studies have led to publication of apparently contradictory figures.

The working assumption used for the analysis reported subsequently here, which is considered by RWMAC to be sufficiently accurate for its purpose, is that all the reprocessing of UK spent fuel was of Magnox and AGR spent fuel (i.e. overlooking the SGHWR spent fuel) and all reprocessing of overseas spent fuel was of LWR spent fuel (i.e. overlooking the Magnox spent fuel from Tokai Mura).

There are also 4,100 tHM of forecast UK spent fuel arisings that are not included in any of the scenarios considered. This is made up of about 1,200 tHM of Sizewell B LWR fuel (for which there are currently no plans for reprocessing) and 2,900 tHM of AGR fuel. The 2,900 tHM of AGR fuel are beyond the THORP "Extended" scenario and could potentially be treated in a number of ways. BNFL indicated to RWMAC that this could include reprocessing in a third decade of THORP reprocessing if there proved to be sufficient work to sustain plant operation for this long. (Note that this figure of 4,100 tHM for Sizewell B and AGR fuel beyond the scenarios considered of is an update of an earlier figure of 3,300 tHM given in reference 9).

In order to simplify the analysis, it has been assumed that the conditioning and direct disposal of spent fuel would not give rise to any secondary waste forms. In practice, however, the amounts of secondary wastes would not be negligible. For the purpose of this report, RWMAC has not attempted an analysis of the implications of spent fuel conditioning and disposal, other than to note the comparison in volumes of material arisings.

Table 3

Amounts of fuel to reprocessed from 1 April 2000 by scenario expressed in terms of tonnes of heavy metal, tHM

(Source: BNFL)

a) Magnox (uranium metal fuel)

b) THORP (uranium oxide fuel)

5.2 Rates of material arisings per tonne of spent fuel heavy metal reprocessed

The reprocessing of spent nuclear fuel gives rise to HLW, ILW, LLW reprocessed uranium and separated plutonium. Reprocessed uranium and separated plutonium are produced and stored in an oxide form, and so will be designated as RepUO₃ and SepPuO₂ from hereon, (where UO₃ and PuO₂ are the appropriate chemical formulae for the uranium and plutonium oxides produced).

The figures for amounts of materials arising from the reprocessing of one tHM of spent nuclear fuel are given in Table 4. These are based on information provided by BNFL at RWMAC’s request. The figures for HLW, and ILW were used in the analysis reported by BNFL’s stakeholder Waste Working Group⁹.

The HLW from reprocessing is first produced in a highly radioactive liquid (HAL) form. It is subsequently transformed into a solid vitrified form in the Waste Vitrification Plant at Sellafield (more is said of this in section 6.2). The volume figures quoted in Table 4 are for the vitrified form of the waste, and are therefore designated as VHLW. Any spent fuel which is not reprocessed, and for which no future use is foreseen, would also, in practice, need to be regarded as another form of HLW.

Materials generation rates may be expressed in various ways e.g. volumes, weight or, potentially, activity. However this is done, the results arrived at are usually required as a means of indicating the potential management requirements and costs associated with the materials. In reality, these management requirements and costs may depend in differing ways on the particular characteristics of the material concerned. For example, whereas volume may be the primary consideration in contemplating the storage and/or disposal of LLW, heat generation will be important in the case of HLW. RWMAC has presented its own results in a manner that it sees to be appropriate for this study. However, the Committee warns that, for the above reasons, simply adding weights or volumes across various types of material, a practice that has sometimes been adopted in the past, does not necessarily give a good indicator of the overall difficulty of dealing with that particular combination of materials. In reality, the specific requirements for each type of material need to be evaluated separately.

Table 4

Rates of materials arisings from reprocessing of one tonne of spent nuclear fuel heavy metal, tHM (Source: BNFL)

5.3 Estimated material arisings per scenario

The figures given in Tables 3 and 4 have been used to estimate the various amounts of materials arisings for each of the scenarios considered. Table 5 below gives a summary of the solid materials predicted to be produced for each of the scenarios from 1 April 2000 onwards. The arisings are presented separately for the different Magnox and THORP scenarios. In practice, the way these arisings are treated and stored subsequently will be, to a degree, interdependent.

Table 5

Quantities of solid material arisings per scenario after 1 April 2000 (Source: BNFL, figures derived from Tables 3 and 4)

a) Magnox (uranium metal fuel) scenarios

b) THORP (uranium oxide fuel) scenarios

total amounts produced in the UK

amounts remaining in UK after return of products from reprocessing overseas spent fuel with no substitution

amounts remaining in UK after return of products from reprocessing overseas spent fuel with substitution

For the THORP scenarios, the three figures given are for : (i) amounts of material to be produced from reprocessing from April 2000 onwards; (ii) the amounts of that material remaining in UK after products from reprocessing of overseas spent fuel have been returned with no substitution; and (iii) the amounts of that material remaining in the UK after products from reprocessing overseas spent fuel have been returned with substitution allowed (see section 2.2 for an explanation of the meaning of substitution). In deriving the figures allowance has been made for the fact that there are early reprocessing contracts covering 1,500 tHM of overseas LWR spent fuel that did not include return of waste clauses.

The substitution calculations applied assume the return of additional HLW in return for ILW being left within the UK. For the purpose of the Table 5(b) analysis it is assumed that all the LLW generated by THORP reprocessing will remain in the UK, because of the availability of the Drigg LLW disposal facility. In practice, any effect on the amount of HLW returned overseas will be effectively negligible due to the relative activities of HLW and LLW.

Table 5 shows that the scenarios involving an early end to reprocessing also lead to an increase in the amount of unreprocessed spent fuel that would need to be managed as an additional form of HLW. RWMAC has concluded that all committed Magnox fuel will need to be reprocessed (see section 4.2). For the AGR spent fuel recorded in the table, RWMAC analyses have suggested that, the volume: weight equivalence would range between 0.4 m³/tHM (dismantled pins, wet storage) and 1.1 m³/tHM (stored as elements, dry). Conditioning for disposal would be expected to increase volumes at least from the minimum quoted above. For LWR spent fuel, the volume: weight equivalence would be about 0.4 m³ /tHM for storage as elements, with conditioning for disposal increasing volumes to between 0.9 and 1.5 m³/tHM.

Given that one tHM of AGR and LWR spent fuel are equivalent to about 0.08m³ of VHLW – see Table 4 – it may be said that reprocessing reduces the total volume of HLW to be dealt with

5.4 Combined scenario arisings in the context of total UK radioactive waste generation

Table 6 has used the figures given in Table 5 to estimate the total materials arisings from reprocessing for the various combined scenarios discussed in Section 4.2 – Combined Early Termination, Combined Reference and Combined Extended. Figures are given for (i) substitution not allowed and (ii) with substitution allowed.

Table 6

Future UK product arisings for various combined Magnox and THORP scenarios (Source: BNFL figures derived from Table 5)

no substitution

substitution

These estimates, of the total amounts of materials to be produced from future reprocessing, need to be set within the context of the amounts already held and the amounts eventually forecast to be generated by the current UK nuclear programme. This can be done using the outcome of the most recent UK Radioactive Waste Management Inventory¹³ and the latest annual estimates of civil plutonium and uranium stock figures published in the Department of Trade and Industry (DTI)¹⁶. The 1998 study by the Royal Society of the Management of Separated Plutonium⁴ also provides relevant background material. The Inventory information was based on a scenario equivalent to the RWMAC study’s Combined Reference scenario. The outcome of this analysis is set out in Table 7.

It must be emphasised that the current holdings and forecast total waste arisings given in Table 7 for the current UK nuclear programme are only estimates. This is because they are based on 1998 UK Radioactive Waste Inventory¹³ and 1999 DTI civil uranium and plutonium holdings¹⁶ figures which have been broadly estimated forward to 1 April 2000. Also some allowance has had to be made for the future return of overseas-owned reprocessing products which is not allowed for in the Inventory data.

Taking the various materials in turn, Table 7 shows that decisions on the future reprocessing of UK spent fuel are liable to have a marked impact on the amount of VHLW held by the UK in future. This is because VHLW comes almost exclusively from reprocessing. Current stocks of UK-owned VHLW of about 720m³ would be increased by between about 20 and 105 per cent depending on the extent of future reprocessing. This VHLW is produced initially as HAL which has to be processed through Sellafield’s Waste Vitrification Plant (see section 6.2).

Table 7 also shows that the Combined Early Termination scenario leads to an increase in the amount of unreprocessed spent AGR fuel that would need to be classified and managed as an additional form of HLW. The 4,400 tHM shown in Table 7 would be in addition to the 4,100 tHM – 2,900 tHM AGR fuel and 1,200 tHM Sizewell B fuel - not committed to reprocessing (see section 5.1). The volume: weight ratios given in section 5.3 indicate that this additional 4,400 would be equivalent to between 1,760 m³ (if wet stored, dismantled) and 4,840m³ (if dry stored as elements).

Table 7

Predicted UK-owned reprocessing conditioned materials arisings against current and forecast holdings

Effects on the generation of ILW are less marked and on LLW less marked still. Future reprocessing would add between about 10 and 35 per cent of currently held UK stocks of ILW and between about 5 and 10 per cent of total forecast arisings. Future LLW arisings from reprocessing would be at most of the order of 10 per cent of arisings to date and no more than 5 per cent of the total LLW that will eventually either have been disposed of or held. This is because substantial amounts of ILW and LLW also arise from activities other than reprocessing e.g. day-to-day nuclear power generation, decommissioning etc. Increased LLW generation places additional pressure on the Drigg disposal facility.

As is the case with VHLW, reprocessed uranium and separated plutonium come solely from reprocessing. Thus, reprocessing of UK spent fuel continues to have a marked effect on the amounts of these materials held and owned by the UK. Table 7 shows that current holdings of uranium could be increased by up to about 30 per cent and current plutonium holdings could be more than doubled by the Combined Extended scenario.

Thus, whilst the effects of the different reprocessing scenarios on the amounts of ILW and LLW held are not large in percentage terms, there will be substantial impacts on the relative amounts of VHLW, spent fuel, reprocessed uranium and separated plutonium that need to be managed.

5.5 Materials arisings and other implications of the reprocessing of overseas spent fuel

The figures set out in Table 7 refer to the materials arising from the reprocessing of UK spent fuel, i.e. materials which are UK-owned.

Future Magnox reprocessing will apply solely to UK spent fuel, with the exception of the 250 tHM of fuel from Tokai Mura in Japan. However, a large proportion of THORP work consists of commercial reprocessing of overseas spent fuel.

On the one hand it may be seen to be potentially possible to set aside consideration of the reprocessing of overseas-spent fuel in contemplating the longer-term implications for the UK. This is on the grounds that the reprocessing products will be returned (although as section 5.3 has indicated, this does not apply to some 1,500 tHM of spent fuel covered by some early THORP reprocessing contracts). On the other hand, such reprocessing gives rise to discharges, needs for the interim handling of materials and, potentially, shifts in the balance of wastes remaining in the UK if substitution (see section 2.2) is allowed, all of which need to be suitably weighed against any commercial profit. In addition, it needs to be borne in mind that little, if any of the products of the reprocessing of overseas fuel, have actually been returned to date. Thus the timing issue comes into play.

RWMAC recommends that, in future, there should be greater transparency concerning holdings of overseas material within the UK and the proposed schedule for, and progress made towards, their return. Policy set out in the Cm2919 White Paper³ is that "the wastes resulting from foreign spent fuel should be returned to the country of origin, and the HLW should be returned as soon as practicable after its vitirification". In this context, also, RWMAC notes that the UK Radioactive Waste Inventory¹³ does not distinguish between future arisings that are covered by return clauses and those that must continue to be held within the UK, either because they are UK-owned or were not the subject of contractual return provisions. The Committee recommends that this be rectified in future Inventories.