Management and Disposition of Excess Weapons Plutonium Reactor-Related Options (1995) / Chapter Skim
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Chapter 5: Disposal of Plutonium Without Irradiation
Chapter 5: Disposal of Plutonium Without Irradiation
Pages 214-249
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From page 214... ...
This case was chosen as the baseline, not as the result of a detailed comparison of alternative waste forms by the panel, but because, after decades of such comparisons for the mission of disposal of HEW, borosilicate glass has been chosen as the waste form of choice for the HLW disposal mission in the 214
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From page 215... ...
for the plutonium disposition mission to make use of existing processes, approaches, and facilities to the extent practical, a logic that focuses attention on the borosilicate glasses already scheduled to be produced (A brief discussion of a few of the alternative waste fonns that have been proposed for this mission is also provided.) As discussed in this chapter, plutonium could also be incorporated in glass without fission products, but we do not believe this would provide a large enough barrier to reuse in weapons to be satisfactory as a final disposition option.
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From page 216... ...
Once produced, the glass logs incorporating plutonium and fission products would be stored until a nuclear waste repository became available, at which time they would be emplaced in the repository as waste without making use of the energy value of the plutonium.' Once the glass is produced, it is well within current technical capabilities to handle and store the plutonium-laden glass safely from the perspectives of worker safety, environmental contamination, and criticality. The basic waste vitrification device is a melter, into which a glass powder, known as glass frit, is continuously fed, along with whatever is to be dissolved in the glass.
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From page 217... ...
. To incorporate large quantities of fission products (whether in glass or other waste forms)
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From page 218... ...
The choice of borosilicate glass is based on several favorable properties (Marples 1988~: it can incorporate almost all of the important radioactive fission products dissolved as oxides; it can contain waste at levels as high as 20 or even 25 percent by weight; it is tolerant of widely varying waste compositions; it is reasonably resistant to leaching by water; it is relatively resistant to radiation damage; it can accommodate the chemical changes that occur when the waste impurities decay radioactively; and the production process is relatively simple and reliable, with a reasonably low formation temperature, and with a glass product that is not corrosive to the process equipment, unlike phosphate and lead phosphate glasses.2 Providing a sufficient radiation barrier to meet the spent fuel standard for 50 tons of plutonium will require tens or hundreds of millions of curies of radioactivity, a small but significant fraction of the total amount of separated radioactive fission products currently stored in the United States. Hence, incorporating these fission products with plutonium into waste forms other than the borosilicate glasses on which the HLW disposal program is now centered would represent a substantial modification of that program, with the attendant potential for delays and uncertainties for both the HLW disposal program and the WPu disposition program.
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From page 219... ...
The choice of borosilicate glass was based on a number of technical issues related to synroc that have not been resolved, including the larger amount of hot-cell processing required to produce the synroc, and the greater flexibility of glass in incorporating a wide range of wastes. The latter concern might not be a serious problem in the case of plutonium disposition, if the radiation barrier were to be provided by fission products such as the cesium137 stored at Hanford, rather than by HLW combining a range of products.
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From page 220... ...
For WPu disposition, the concept is to use the pyroprocessing approach to reduce a mixture of oxide spent fuel and WPu to a metal fond; in this case, for maximum proliferation resistance, the fission products from the spent Fuel would not be separated but would remain in the metal product.3 This approach has several disadvantages that the panel believes effectively rule it out as a serious competitor for the near-term plutonium disposition miss~on: . First, to meet the spent fuel standard would require the plutonium to be mixed with a large amount of material (roughly 1,000 tons for 50 tons of plutonium, if the product was to be 5-percent WPu by weight)
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From page 221... ...
Characterization and certification of waste forms for radioactive isotopes that will last many thousands of years is a lengthy and painstaking process that would almost certainly introduce additional delays. It appears unlikely that a metal matrix such as that produced by the pyroprocessing would be a suitable waste form for the chemical environment of Yucca Mountain: the metal, once exposed to water, would be expected to undergo both hydration and oxidation reactions, breaking down its structure and releasing the radioactive materials it contained.
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From page 222... ...
As with spent fuel, the chemical processes needed to extract plutonium from glass are not especially difficult or obscure. The primary difficulty arises from coping with the radioactivity of the fission products also embedded in the glass.
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From page 223... ...
The large glass logs to be produced in vitrification operations at the Savannah River and Hanford sites, about 3 m and over 2 tons each, cannot easily be moved. Especially when combined with radioactivity sufficient to require remote handling, size can be a substantial handling problem for at least some potential parties wishing to reuse the WPu.
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From page 224... ...
By contrast, if the logs contained some 20 kg of plutonium (roughly 1 percent by weight for a 2-ton log like those to be produced at the Savannah River Site tSRS] , comparable to the percentage of plutonium in spent fuel)
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From page 225... ...
Many of these costs and risks, however, will have to be borne in any case to dispose of the existing fission products at DOE sites; the important questions in this case are the net additional costs and risks that would be associated with adding plutonium to the HLW vitrification campaigns that will be .
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From page 226... ...
For example, substantial quantities of plutonium are now stored in forms that are not suitable either for long-term storage or for transport; vitrifying these forms of plutonium at the sites where they are now stored in order to produce a safe form for transport to another site where they could be revitrified with fission products could be an attractive disposition approach for these materials. Indeed, in some circumstances it might be judged desirable to undertake a relatively rapid campaign to vitrify all of the WPu without any other radioactive species, thereby inexpensively and rapidly transforming the existing metallic WPu pits and ingots into a glass form, but with a second follow-on vitrification step clearly in mind in which the WPu-laden glass would be revitrified later with highly radioactive species included to provide the desired deterrent.
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From page 227... ...
. By contrast, if the plutonium is to be added to HLW glass logs already 6 A security advantage enjoyed by the glass logs over much spent fuel is that the major vitrification operations and the interim storage of the glass logs prior to emplacement in a geologic repository would be at major nuclear weapons complex sites.
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From page 228... ...
, and the suitability of the glass product for geologic disposal. Westinghouse Savannah River Company (WSRC)
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From page 229... ...
Handling Plutonium in Upstream Processing and in the Melter The chemical processing involved in preparing HLW for vivification is quite complex, and the intense radioactivity of the HLW complicates the problem further. (Indeed, discover of a series of difficulties with the flow-sheet for chemical preprocessing of wastes at Savannah River has delayed the DWPF project there by several years.)
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From page 230... ...
For the WPu disposition mission, large melters have the additional major disadvantage that a very large amount of plutonium would be in the melter at any one time, increasing criticality concerns. In the DWPF, for example, if the plutonium were 1 percent by weight in the glass, the melter would contain well over 100 kg of plutonium at any one time.
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From page 231... ...
The issues in developing such a design are technically challenging and have only begun to be explored, but there do not appear to be any inherent technical obstacles.8 A melter designed for WPu vitrification would probably be smaller (perhaps with more than one melter operating in parallel) and designed specifically to ensure criticality safety (perhaps with an "inherently safe" geometry that would prevent criticality)
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From page 232... ...
All of these issues must be, and are being, addressed for the spent fuel that would be the Yucca Mountain repository's principal waste form, including criticality. In that sense, there is nothing unique about plutonium-laden glass.
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From page 233... ...
But as noted earlier, if the glass is not an acceptable waste form for geologic disposal, some form of further plutonium processing would be necessary at some unknown time in the future, involving additional costs and risks.
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From page 234... ...
Once vitrified onsite, this plutonium would be in a form sufficiently stable to ship elsewhere for revitrification with fission products if desired. ASSESSMENT BY KEY CRITERIA Facility Options and Schedule As noted elsewhere in this report, the schedule for WPu dispositionincluding both when a campaign could begin and when it could be finished is a major component of the security criterion for comparing options.
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From page 235... ...
Sc`:vannah River Facility Vitrification technology is highly developed at DOE's Savannah River Site, and an advanced facility, the Defense Waste Processing Facility, has been under construction for several years there with the goal of vitrifying much of the highlevel radioactive waste in the 30 million gallons currently stored there in tanks (McKibben et al.
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From page 236... ...
This estimate was made when the planned DWPF startup was still in 1994, but the initial steps are primarily analysis, design, and regulatory ones in which the status of the DWPF would not play a major role. If DWPF was still not operating in the mid-2000s, however, a WPu disposition mission relying on that facility could be delayed.
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From page 237... ...
The WVDP melter design has about half of the capacity of the DWPF melter and its technology is similar. It would be possible to vitrify some part of the WPu at West Valley with the fission products located there.
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From page 238... ...
If HWVP could be designed from the outset for WPu, and began operations in the mid-2000s time frame envisioned for the start of WPu vitrification at Savannah River, waiting for HWVP might impose only a modest delay on initiating WPu vitrification operations. Foreign Vitrification Facilities Significant vitrification capability exists abroad (Odell 1992)
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From page 239... ...
The glass produced has somewhat higher loadings of radioactivity than are planned at Savannah River. Nearly 700 million curies of HEW remain in waste tanks at this site, similar to the holdings at Savannah River and somewhat more than the amount at Hanford.'3 As noted earlier, the phosphate-glass composition employed at this facility is less appropriate for WPu disposition than borosilicate glass.
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From page 240... ...
Although construction of a special-purpose facility might simplify the task of vitrifying the plutonium, the total costs would be higher, because all the costs of production, handling, and disposal of this waste form (including the potentially substantial costs of providing and operating facilities capable of handling the highly radioactive materials that might be added to it) would have to be charged to the plutonium disposition mission, rather than only the net additional costs of adding plutonium to a previously planned HLW vitrification campaign.
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From page 241... ...
All of the planned capacity in the Yucca Mountain repository will be filled by wastes already scheduled to be produced. Therefore production of additional waste products specifically for WPu disposition (rather than piggy-backing on planned HEW vitrification campaigns)
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From page 242... ...
Vitrifying the WPu pits themselves without fission products does not seem to the panel to be worthwhile; however, neither the security nor the safety benefits seem to be substantial enough to justify the costs and risks, except perhaps as a step in the process of vitrifying the material in a form incorporating fission products. Late in its deliberations, the panel learned that options are being considered to vitrify actinides now stored in solution at the F-canyon at Savannah River, as part of the clean-out of that facility.
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From page 243... ...
Siting approval and licensing for a vitrification facility dedicated solely to plutonium disposition would probably be more protracted than for an approach piggybacking on already scheduled HLW vitrification campaigns. Certification of the plutonium-bearing glass as a suitable waste form for emplacement in a geological repository, including resolution of the long-term criticality issue, would be the highest hurdle.
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From page 244... ...
For those options that would incorporate WPu in HLW glass that would be produced in any case, it is important to focus on the net additional cost of adding the WPu, as in those cases the total cost of the vitrification operation cannot be charged to the WPu disposition mission. For all cases, it is important to separate the various preprocessing costs before vitrification begins from the costs of vitrification itself, as these preprocessing costs are similar to those that must be borne by other options as well.
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From page 245... ...
Also, the WPu vitrification cost will depend almost inversely proportionally on how much WPu loading by weight can be safely and economically added to the vitrified glass, unless the WPu campaign fits well into a previously planned campaign to vitrify HLW, such as the currently planned DWPF campaign to vitrify HLW at SRS. The only detailed cost estimates that have been available to the panel were prepared by Westinghouse Savannah River Company, for vitrification at Savannah River Site.'4 The estimated cost for vitrification with HLW in the DWPF is approximately $600 million, plus approximately $400 million to carry out the preliminary steps, including pit processing (which would also be required for the reactor options)
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From page 246... ...
Of course, some plutonium-contaminated waste streams, including contaminated equipment, will require subsequent LLW handling and disposal. These waste streams (besides the glass product itself)
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From page 247... ...
"Radioactive Waste Solidification at the West Valley Demonstration Project." In "Proceedings of the Third International Conference on Advances in Fusion and Processing of Glass," Ceramic Transactions 29, American Ceramics Society, 1993. Lyman 1994: Edwin S
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From page 248... ...
McKibben and G Wicks, Westinghouse Savannah River Company.
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From page 249... ...
Wicks 1993: G Wicks, Westinghouse Savannah River Company.
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