Nuclear Wastes Technologies for Separations and Transmutation (1996) / Chapter Skim
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2 SUMMARIES OF S&T PROPOSALS AND RADIONUCLIDES RELEASE SCENARIOS IN REPOSITORY
2 SUMMARIES OF S&T PROPOSALS AND RADIONUCLIDES RELEASE SCENARIOS IN REPOSITORY
Pages 21-36
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From page 21... ...
These fissions will almost all take place inside the uranium dioxide fuel. There are several hundred different fission products produced by these reactions which cause the spent reactor fuel to be highly radioactive and generate substantial amounts of decay heat.
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From page 22... ...
4C, a long-lived acti vation product of concern in some waste disposal circum stances. The actinides, fission products, and activation products taken together are the radioactive waste that must be se questered in some way so that they do not enter the bio sphere in unacceptable concentrations.
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From page 23... ...
There are two fission products that are a principal concern because of their substantial thermal impact on the repository as opposed to posing a potential health risk: 90Sr and i37Cs. These two radionuclides, which could pose a health risk in an early intrusion scenario, are dominant contributors to the heat released by spent fuel or HLW during at least the first several decades (see Appendix Figure G-S)
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From page 24... ...
This would involve reprocessing spent LWR fuel to recover the radioelements containing these nuclides in relatively pure form, fabricating them into targets, irradiating the targets to destroy part of the radionuclides, and recovering the untransmitted radioelements and recycling them in new targets. The second method of reducing potential releases of these radionuclides is to incorporate them in a waste form specifically tailored to retain them, which would then be 24 TABLE 2-1 Properties of Selected Fission Products of Interest in Spent Fuel and HLW Half-Life Nuclide (years)
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From page 25... ...
For comparison, the ingestion toxicity of the fission products is also shown. As can be seen, the long-term toxicity of spent fuel is dominated by the actinides such as 237Np, 234 236U, and TABLE 2-2 Properties of Actinides in Discharged Uranium Fuela Elemental Boiling Radionuclide Half-Life kg Ci Temperature, oCb 234u 2.47 x 105 yr 3.14 1.94 x 10~ 23su 7.1 x 108 yr 2.15 x 102 4.61 x 10-t 236u 2.39 x 107 yr 1.14 x 102 7.22 237u 6.75 days 9.15 x 10-7 7.47 x 10 23su 4.51 x 109 yr 2.57 x 104 8.56 Total 2.60 x 104 a3.56 x 10 ~4,135 ,B7.47 x 10i 237Np 2.14 x 106 yr 2.04 x 10 ~1.44 x 10i 239Np 2.35 days 2.05 x 10-6 4.78 x 102 Total 2.04 x 10i al.44 x 10i p4.78 x 102 236pu 2.85 yr 2.51 x 10-4 1.34 x 102 23spu 86 yr 5.99 1.01 X 105 239pu 24,400 yr 1.44 x 102 8.82 x 103 24opu 6,580 yr 5.91 x 10 ~1.30 x 104 24~pu 13.2 yr 2.77 x 10 ~2.81 x 106 242pu 3.79 x 105 yr 9.65 3.76 x 10i Total 2.46 x 102 al.23 x 105 3,508 p2.81 x 106 24lAm 458 yr 1.32 4.53 x 103 249mAm 141 yr 1.19 x 10-2 yr 1.16 x 102 243Am 7,950 yr 2.48 4.77 x 102 Total 3.81 aS.01 x 103 2,880 ,B1.16 x 102 242cm 163 days 1.33 x 10- ~4.40 x 105 243cm 32 yr 1.96 x 10-3 9.03 x 10~ 244cm 17.6 yr 9.11 x 10-i 7.38 x 104 245cm 9,300 yr 5.54 x 10-2 9~79 246cm 5,500 yr 6.23 x 10-3 1.92 Total 1.11 aS.14 x lOs TOTAL 2.63 x 104 a6.42 x 105 ,B2.81 x 106 aUranium-fueled 1,000-MWe POOR, 150 days after discharge.
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From page 26... ...
. If it were to be recovered during spent fuel reprocessing operations, the only possible recourse would be to immobilize it in a specially tailored waste form for repository disposal.
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From page 27... ...
An LWR transmutation system could use the most wellknown approach to reprocessing based on aqueous separations technology. A new generation of reprocessing plants could be applied to existing spent LWR fuel and could support subsequent application of more advanced transmutation concepts.
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From page 28... ...
compared to about 30% for the ALMR metallic fuel. Pyroprocessing requires considerable further development and scale-up with full pilot-plant demonstration, especially for spent LWR fuel application to commercial processing.
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From page 29... ...
. Separations Technology and Commercial Spent-Fuel Reprocessing At present, there are the only four industrially demonstrated separations processes applicable either to DOE defense reactor wastes or to meeting the needs of transmutation of TRUs and fission products in spent LWR fuel.
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From page 30... ...
has a pyroprocessing development effort for ALMR spent-fuel reprocessing under way; an extension of that process is being studied by ANL for possible employment in the reprocessing of LWR spent fuel. The transmutation concepts being proposed require headend treatment of spent LWR fuel to chop and dissolve the fuel, followed by separation of the TRUs and selected fission products.
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From page 31... ...
Such an LWR could also transmute the long-lived 99Tc and HI fission products if separated and recycled. Of course, the big cost is that of spent LWR fuel reprocessing and the all-remote fabrication of plutonium-bearing recycle fuel.
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From page 32... ...
DOE currently plans to package spent LWR fuel rods in sealed containers for placement in the repository. To satisfy code of NRC regulations 10CFR60, the containers must have high integrity during emplacement and for the decades or so that the repository is being filled, such that the containers could be removed safely if the repository were found to be defective.
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From page 33... ...
For the Yucca Mountain site, there is no reason to think or assume that 23~Pa would be any less important for luff than for granite, given the different conditions of the formations. Thus, Papa is likely to be the radionuclide of significance for the dissolution-and-migration scenarios, if the long-lived fission products were greatly reduced.
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From page 34... ...
Although spent fuel does not have a large curie inventory of ~4C, the calculations assume that essentially all of it would be released as a gas during a few thousand years under oxidizing conditions such as in the unsaturated luff at the Yucca Mountain site. The dose to an individual living on the surface would be small, but under the original standard, the calculated probabilistic cumulative release was considered important.
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From page 35... ...
However, as noted in Chapter 6, Impact of S&T on Waste Repository, there is no evidence from the assessment to date of repository risk that S&T systems and/or optimized waste forms are actually needed to improve nuclear waste disposal relative to the once-through LWR fuel cycle. REFERENCES Croff, A.G., R.L.
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