Plutonium processing production

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... 

An overview is presented of plutonium process chemistry at Rocky Flats and of research in progress to improve plutonium processing operations or to develop new processes. Both pyrochemical and aqueous methods are used to process plutonium metal scrap, oxide, and other residues. The pyrochemical processes currently in production include electrorefining, fluorination, hydriding, molten salt extraction, calcination, and reduction operations. Aqueous processing and waste treatment methods involve nitric acid dissolution, ion exchange, solvent extraction, and precipitation techniques. 

A. Process Schematic. A schematic of the main process sequence for the conversion of plutonia scrap to high-purity metal is shown in Figure 2. Plutonia scrap is fed to both the direct oxide reduction (DOR) process and the plutonium tetrafluoride production/ reduction process. 

The fission product and encapsulation plant (FPCE) to be built by Isochem, Inc.y in Washington state will produce fully encapsulated fission products for the commercial market. Among these, all of which are extractable from Hanford s plutonium process residues, is cesium-137, a 600-kv. gamma emitter of interest to the process irradiation industry. Isochem will offer cesium in large production quantities and low cost to irradiators of foods, woods, chemicals, etc. Its 30-year half-life promises economies in source array replenishment to compensate for decay. Cesium thus becomes an economic contender for current and planned irradiation applications. 

An optimum molten salt extraction process at Rocky Flats would use the minimum amount of salt required to obtain (1) a desired removal of americium, (2) a minimum transfer of plutonium to the salt, and (3) a minimum take-up of magnesium by the plutonium metal product. The product salt must be compatible with subsequent chemical processes for the recovery of americium and plutonium contained in the salt. To minimize the number of glove-box operations, time in the gloves, and operator radiation exposure, the operations must be simple and easy to conduct. By using the minimum amount of salt feed, a minimum amount of waste will be generated that ultimately must be sent to long-term storage. 

In April of 1955, a facility utilizing the Recuplex solvent extraction process(2j was installed in the 234-5Z Building at Hanford. This facility provided the capability of recovering plutonium from unirradiated plutonium scrap from Hanford plutonium processing operations. By 1960, the Recuplex facility was inadequate with respect to contemplated production loads, shielding requirements, and criticality prevention safety. A project was authorized in March 1961 to provide a new facility for the adequate reclamation of plutonium from both wet and dry plutonium scrap generated from both on and offsite operations. This facility, the 236-Z Building, was completed in June 1964 and is referred to as the PRF. Details on the new plant were first published in 1967.(2)... 

Fig. 21.17. Uranium metal reduction process a similar process is used for plutonium metal production. (Courtesy USDOE.)...

The scraps which arise during the fabrication of plutonium-containing nuclear fuels are collected and stored for some time before they are processed to recover the plutonium. Due to the decay of Pu-241, considerable amounts of Am-241 may build up in the stored material. At the Alkem company, plutonium is recovered from the scrap by anion exchange the americium which is not sorbed on the resin is collected in the combined effluents from the loading and wash steps. The effluents are concentrated by evaporation besides americium, the concentrated effluents contain major amounts of uranium, plutonium, corrosion products, and residues from chemical reagents. A typical composition is given below ... 

The effect of plutonium recycle is to increase the production of higher-mass isotopes of plutonium and of americium and curium, because the recycled plutonium is exposed to neutrons throughout the entire irradiation cycle. The actinide quantities calculated [PI] for the same 1000-MWe reactor operating on an equilibrium fuel cycle with self-generated plutonium recycle are shown in Table 8.5. The alpha activity of the plutonium processed yearly is increased by a factor of 14 by plutonium recycle, the americium activity is increased by a factor of 5, and the curium activity by a factor of 7. 

Direct calcination of Pu(N03)4 involves no chemical separations that could remove impurities, so a highly pure plutonium nitrate feed solution is required. The plutonium dioxide product can be hydrofluorinated to PUF4, or it can be used as a feed for the formation of PUCI3. Direct calcination has received less industrial-scale application than the precipitation processes described above [C2]. 

Specifications for plutonium product call for less than 100 ppm of uranium, a total gamma activity less than 40 iCi/g plutonium, and a zirconium-niobium activity less than 5 /uCi/g plutonium. Plutonium nitrate product 3PC, stream 55, meets the total activity specification but does not quite meet the zirconium-niobium specification with the hi burnup, 40,000 MWd/MT, feed used in this process example. 

The pure plutonium nitrate product from the solvent extraction process was concentrated in a titanium evaporator and conditioned with respect to nitric acid concentration and the plutonium IV valency state to reduce radiolytic off-gas production before loading to the transport flask for shipment to BNFL Sellaiield. 

Isotopes of curium are also found in waste streams from plutonium-239 production, but in amounts smaller than those of americium. Curium is produced by the beta decay of Am and Am formed by neutron capture in Am and Am. The amount of curium-244 accumulated in process wastes and in unprocessed irradiated fuel elements as of 1985 is estimated at more than 100 kg [5]. Separation and purification of curium and americium is best carried out by the ion-exchange procedures described below (see Section 14.3.5). 

Nuclear wastes are classified according to the level of radioactivity. Low level wastes (LLW) from reactors arise primarily from the cooling water, either because of leakage from fuel or activation of impurities by neutron absorption. Most LLW will be disposed of in near-surface faciHties at various locations around the United States. Mixed wastes are those having both a ha2ardous and a radioactive component. Transuranic (TRU) waste containing plutonium comes from chemical processes related to nuclear weapons production. These are to be placed in underground salt deposits in New Mexico (see... 

These variations permit the separation of other components, if desired. Additional data on uranium, plutonium, and nitric acid distribution coefficients as a function of TBP concentration, solvent saturation, and salting strength are available (24,25). Algorithms have also been developed for the prediction of fission product distributions in the PUREX process (23). 

Uranium. The uranium product from the PUREX process is in the form of uranyl nitrate which must be converted to some other chemical depending on anticipated use. One route to MO fuel is to mix uranium and plutonium nitrates and perform a coprecipitation step. The precipitate is... 

By-Products. The PUREX process is efficient at separating uranium and plutonium from everything else in the spent fuel. Within the high level waste stream are a number of components which have, from time to time, been sufficiendy interesting to warrant their recovery. The decision to recover a particular isotope is usually based on a combination of market incentives and desired waste reduction. 

The Natural Reactor. Some two biUion years ago, uranium had a much higher (ca 3%) fraction of U than that of modem times (0.7%). There is a difference in half-hves of the two principal uranium isotopes, U having a half-life of 7.08 x 10 yr and U 4.43 x 10 yr. A natural reactor existed, long before the dinosaurs were extinct and before humans appeared on the earth, in the African state of Gabon, near Oklo. Conditions were favorable for a neutron chain reaction involving only uranium and water. Evidence that this process continued intermittently over thousands of years is provided by concentration measurements of fission products and plutonium isotopes. Usehil information about retention or migration of radioactive wastes can be gleaned from studies of this natural reactor and its products (12). 

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