Actinides wastes

Mclsaac, L. D., Baker, J. D., Krupa, J. F., Meikrantz, D. H., and Schroeder, N. C., "Flowsheet Development Work at the Idaho Chemical Processing Plant for the Partitioning of Actinides from Acidic Nuclear Waste," Actinide Separations Symposium, ACS Pacific Chemical Conference, Honolulu,... 

Type of Resin MSE Waste Actinide in Feed Actinide Recovery+... 

The used fiiel elemmts may later be reprocessed to recover the remaining amount of fissile material as well as any fertile material or regarded as waste fertile atoms are those which can be transformed into fissile ones, i.e. " Th and U, which through neutron capture and jS-decays form fissile and Pu, respectively. The chemical reprocessing removes the fission products and actinides other than U and Pu. Some of the removed elements might be valuable enough to be isolated although this is seldom done. The mixed fission products and waste actinides are stored as radioactive waste. The recovered fissile materials may be refabricated (the U may require re-enrichment) into new elements for reuse. This "back-end" of the nuclear fuel cycle is discussed in Chapter 21. 

It has been suggested that the most hazardous actinides be removed from the reprocessing waste and stored separately. The advantage is (i) to eliminate all actinides from the HAW, so that its hazardous potential follows that of Sr, Cs and Tc, by which the main hazard is gone in about 400 years, and completely in about 100 000 y (ii) to reduce the waste actinides to a small volume, 1/100 to 1/1000 of that of the HAW (and, of course, even much less when compared to the volume of the spent fuel elements), which will simplify the storage problem. For example, such actinide waste could be stored uniquely in very deep bore holes in the ground, eventually in the earth s molten interior. A similar procedure seems possible also for the Sr+Cs fraction. 

Table 1 provides a listing of the current Saltstone waste acceptance criteria (WAC) for 90Sr and selected alpha-emitting radionuclides. These limits establish the target concentrations that the process used in the SWPF for 90Sr and actinide removal must meet. 90Sr removal performance originally served as the chief criterion for selection of MST for use in radiochemical separations at the SRS. With increased characterization of SRS wastes, actinide removal performance has increased in importance. 

Thorium, uranium, and plutonium are well known for their role as the basic fuels (or sources of fuel) for the release of nuclear energy (5). The importance of the remainder of the actinide group Hes at present, for the most part, in the realm of pure research, but a number of practical appHcations are also known (6). The actinides present a storage-life problem in nuclear waste disposal and consideration is being given to separation methods for their recovery prior to disposal (see Waste treati nt, hazardous waste Nuclear reactors, waste managet nt). 

Dioxygea difluoride has fouad some appHcatioa ia the coaversioa of uranium oxides to UF (66), ia fluoriaatioa of actinide fluorides and oxyfluorides to AcF (67), and in the recovery of actinides from nuclear wastes (68) (see Actinides and transactinides Nuclear reaction, waste managel nt). 

Potential fusion appHcations other than electricity production have received some study. For example, radiation and high temperature heat from a fusion reactor could be used to produce hydrogen by the electrolysis or radiolysis of water, which could be employed in the synthesis of portable chemical fuels for transportation or industrial use. The transmutation of radioactive actinide wastes from fission reactors may also be feasible. This idea would utilize the neutrons from a fusion reactor to convert hazardous isotopes into more benign and easier-to-handle species. The practicaUty of these concepts requires further analysis. 

The throwaway fuel cycle does not recover the energy values present ia the irradiated fuel. Instead, all of the long-Hved actinides are routed to the final waste repository along with the fission products. Whether or not this is a desirable alternative is determined largely by the scope of the evaluation study. For instance, when only the value of the recovered yellow cake and SWU equivalents are considered, the world market values for these commodities do not fully cover the cost of reprocessing (2). However, when costs attributable to the disposal of large quantities of actinides are considered, the classical fuel cycle has been the choice of virtually all countries except the United States. 

The primary issue is to prevent groundwater from becoming radioactively contaminated. Thus, the property of concern of the long-lived radioactive species is their solubility in water. The long-lived actinides such as plutonium are metallic and insoluble even if water were to penetrate into the repository. Certain fission-product isotopes such as iodine-129 and technicium-99 are soluble, however, and therefore represent the principal although very low level hazard. Studies of Yucca Mountain, Nevada, tentatively chosen as the site for the spent fuel and high level waste repository, are underway (44). 

Nuclear Waste Reprocessing. Liquid waste remaining from processing of spent reactor fuel for military plutonium production is typically acidic and contains substantial transuranic residues. The cleanup of such waste in 1996 is a higher priority than military plutonium processing. Cleanup requires removal of long-Hved actinides from nitric or hydrochloric acid solutions. The transuranium extraction (Tmex) process has been developed for... 

Despite the problems of direct experimental evaluation of plutonium stability constants, they are needed in modeling of the behavior of plutonium in reprocessing systems in waste repositories and in geological and environmental media. Actinide analogs such as Am+3, Th+, NpOj and UOj2 can be used with caution for plutonium in the corresponding oxidation states and values for stability constants of these analogues are to be found also in reference 20. 

Peters, R.D. Diamond, H. "Actinide Leaching from Waste Glass Air-Equilibrated versus Deaerated Conditions", Report PNL-3971, Battelle Pacific Northwest Laboratory, 1981. 

Figure 3 shows a flowsheet for plutonium processing at Rocky Flats. Impure plutonium metal is sent through a molten salt extraction (MSE) process to remove americium. The purified plutonium metal is sent to the foundry. Plutonium metal that does not meet foundry requirements is processed further, either through an aqueous or electrorefining process. The waste chloride salt from MSE is dissolved then the actinides are precipitated with carbonate and redissolved in 7f1 HN03 and finally, the plutonium is recovered by an anion exchange process. 

Waste Handling for Unirradiated Plutonium Processing. Higher capacity, better-performing, and more radiation-resistant separation materials such as new ion exchange resins(21) and solvent extractants, similar to dihexyl-N,N-di ethyl carbamoyl methylphosphonate,(22) are needed to selectively recover actinides from acidic wastes. The application of membranes and other new techniques should be explored. 

High-Level Waste Hydrated iron oxide (so-called "sludge") precipitates when NaOH is added to HLW and carries down almost all the plutonium and most of the other actinides in the HLW. 

Gray, L. W. Radke, J. H., in "Actinide Recovery from Waste... 

Bray, L. A. Ryan, J. L. in "Actinide Recovery From Waste... 

Boyd, T. E. Kochen, R. L. Ferrite Treatment of Actinide Waste Solutions A Preliminary Study, U.S. DOE Rept. RFP-3299, Rockwell International, Golden, Colorado, July 30, 1982. 

Molten salt extraction residues are processed to recover plutonium by an aqueous precipitation process. The residues are dissolved in dilute HC1, the actinides are precipitated with potassium carbonate, and the precipitate redissolved in nitric acid (7M) to convert from a chloride to a nitrate system. The plutonium is then recovered from the 7M HNO3 by anion exchange and the effluent sent to waste or americium recovery. We are studying actinide (III) carbonate chemistry and looking at new... 

Waste Treatment. Figure 2 outlines the current waste recovery and treatment processes, and proposed changes. Acid waste streams are sent through nitric acid and secondary plutonium recovery processes before being neutralized with potassium hydroxide and filtered. This stream and basic and laundry waste streams are sent to waste treatment. During waste treatment, the actinides in the aqueous waste are removed by three stages of hydroxide-iron carrier-flocculant precipitation. The filtrate solution is then evaporated to a solid with a spray dryer and the solids are cemented and sent to retrievable storage. 

A ferrite waste treatment process is being investigated to determine if it can more effectively remove actinides from waste solution with less solid waste generation than the flocculant precipitation method presently used (18). 

Mullins, L.J. Christensen, D.C. Babcock, B.R. "Fused Salt Processing of Impure Plutonium Dioxide to High Purity Metal", Los Alamos Nat. Lab. Report LA-9154-MS also Symposium on Actinide Recovery from Waste and Low Grade Sources, ACS, New York City August 23-28, 1981 (in press). 

The above information was used to develop conceptual flowsheets for the extraction of all of the actinides (U, Np, Pu, Am, and Cm) from high-level liquid waste from PUREX processing using 0.4 M 0fuel using 0.8 M DHDECMP in DEB. In both flowsheets, no oxidation state of Pu is necessary since the III, IV, and VI state extract into the organic phase. 

Conceptual flowsheet for the extraction of actinides from high-level liquid waste using 0.4 M 0<)>D[IB]CMP0 in DEB. 

Storage, nuclear waste, x-ray photoemission spectroscopic study of actinides in silicate-based... 

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