Plutonium processing Water

WATER, VARIOUS LOCATIONS Hanford, Washington plutonium processing waste ponds ... 

Like microflltration, ultraflltration process can also be used in conjunction with chemical precipitation techniques to improve decontamination factors. Ultrafiltration processes could be useful for decontaminating alpha wastes from laundry and washing water streams of plutonium-processing plant on a large scale [15,16]. 

The important chemical transformation process in surface water is the oxidation or reduction of plutonium. In waters with low suspended solids, plutonium is generally found in oxidized forms, dissolved in the water. In waters with high suspended solids, plutonium is generally reduced and sorbed onto either suspended solids or sediments (Choppin and Morse 1987 Higgo and Rees 1986 Nelson etal. 1987). 

An EPA-approved procedure for the analysis of plutonium in water is listed in Table 6-2. In addition, the following ASTM standard methods relate to the measurement of plutonium in water D 3648, D 3084, D 3972, and D 1943 (ASTM 1981, 1982a, 1982b, 1987). Recent work has focused on more rapid analytical methods in order to determine monitor plutonium levels in waste process streams at nuclear facilities. For example, Edelson et al. (1986) have investigated the applications of inductively-coupled plasma-atomic emission spectrometry (ICP-EAS) to routinely analyze water samples. 

A fast breeder reactor offers one approach to getting more power out of existing uranium sources and potentially reducing radioactive weiste. This type of reactor is so named because it creates ( breeds ) more fissionable material than it consiunes. The reactor operates without a moderator, which means the neutrons used are not slowed down. In order to capture the fast neutrons, the fuel must be highly enriched with both uranium-235 and plutonium-239. Water cannot be used as a primary coolant because it would moderate the neutrons, and so a hquid metal, usually sodimn, is used. The core is surrounded by a blanket of iucmium-238 that captmes neutrons that escape the core, producing plutonium-239 in the process. The plutonium can later be separated by reprocessing and used as fuel in a future cycle. 

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... 

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). 

When the water becomes stagnant, the particulate matter settles as bottom sediments. In this process it carries with it considerable amounts of plutonium, if any has been dissolved in the watter (see Table I). 

Research into the aquatic chemistry of plutonium has produced information showing how this radioelement is mobilized and transported in the environment. Field studies revealed that the sorption of plutonium onto sediments is an equilibrium process which influences the concentration in natural waters. This equilibrium process is modified by the oxidation state of the soluble plutonium and by the presence of dissolved organic carbon (DOC). Higher concentrations of fallout plutonium in natural waters are associated with higher DOC. Laboratory experiments confirm the correlation. In waters low in DOC oxidized plutonium, Pu(V), is the dominant oxidation state while reduced plutonium, Pu(III+IV), is more prevalent where high concentrations of DOC exist. Laboratory and field experiments have provided some information on the possible chemical processes which lead to changes in the oxidation state of plutonium and to its complexation by natural ligands. 

Ground-Water Composition and Its Relationship to Plutonium Transport Processes... 

These processes do not operate independently for example, the behavior of plutonium in step 3 will be greatly dependent on the species formed as a result of solution-phase reactions in step 2. However, from a chemical standpoint, we have found that consideration of these processes individually is a useful aid to understanding the transport of plutonium in a ground-water system. 

PUREX process, recovery of uranium and plutonium, in this case from the SC-C02 phase, would be accomplished simply by contact of the phase with water. 

Utilization of plutonium in early research and commercial orders to fabricate thermal recycle and fast breeder fuels did not coincide in timing with Pu availability from different sources. The plutonium comes mainly from high-exposure light-water reactor fuel reprocessing extended storage of this Pu as a nitrate solution leads to 241 contents up to 3%. For hands-on operation with this material it is necessary to reduce the Am content to about 0.5%. It was also necessary to minimize the liquid waste streams from the plant. In designing a technical-scale process, it was... 

Plutonium-239 and tritium for use as military explosives are the two major transmutation products. The nuclear process for Pu-239 production is the same as for energy generation, but there are some differences (a) metallic natural uranium clad with aluminum facilitates later dissolution for plutonium recovery, and the reactor operates at a relatively low temperature because of the aluminum clad and better heat transfer (due to the metallic natural uranium) (b) the irradiation cycle is limited to a few months to minimize the Pu-239 conversion to Pu-240 and Pu-241 and (c) a carbon or a heavy water moderator is used to increase the neutron efficiency. 

A variety of methods have been used to characterize the solubility-limiting radionuclide solids and the nature of sorbed species at the solid/water interface in experimental studies. Electron microscopy and standard X-ray diffraction techniques can be used to identify some of the solids from precipitation experiments. X-ray absorption spectroscopy (XAS) can be used to obtain structural information on solids and is particularly useful for investigating noncrystalline and polymeric actinide compounds that cannot be characterized by X-ray diffraction analysis (Silva and Nitsche, 1995). X-ray absorption near edge spectroscopy (XANES) can provide information about the oxidation state and local structure of actinides in solution, solids, or at the solution/ solid interface. For example, Bertsch et al. (1994) used this technique to investigate uranium speciation in soils and sediments at uranium processing facilities. Many of the surface spectroscopic techniques have been reviewed recently by Bertsch and Hunter (2001) and Brown et al. (1999). Specihc recent applications of the spectroscopic techniques to radionuclides are described by Runde et al. (2002b). Rai and co-workers have carried out a number of experimental studies of the solubility and speciation of plutonium, neptunium, americium, and uranium that illustrate combinations of various solution and spectroscopic techniques (Rai et al, 1980, 1997, 1998 Felmy et al, 1989, 1990 Xia et al., 2001). 

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