Plutonium uranium dioxide

Fuel type Cylindrical fuel elements with pellets of plutonium-uranium dioxide fuel in steel claddings... 

Several components are required in the practical appHcation of nuclear reactors (1 5). The first and most vital component of a nuclear reactor is the fuel, which is usually uranium slightly enriched in uranium-235 [15117-96-1] to approximately 3%, in contrast to natural uranium which has 0.72% Less commonly, reactors are fueled with plutonium produced by neutron absorption in uranium-238 [24678-82-8]. Even more rare are reactors fueled with uranium-233 [13968-55-3] produced by neutron absorption in thorium-232 (see Nuclear reactors, nuclear fuel reserves). The chemical form of the reactor fuel typically is uranium dioxide, UO2, but uranium metal and other compounds have been used, including sulfates, siUcides, nitrates, carbides, and molten salts. 

One of the most Important thermophysical properties of reactor fuel In reactor safety analysis Is vapor pressure, for which data are needed for temperatures above 3000 K. We have recently completed an analysis of the vapor pressure and vapor composition In equilibrium with the hypostolchiometric uranium dioxide condensed phase (1 ), and we present here a similar analysis for the plutonium/oxygen (Pu/0) system. 

Since the water movement will be very slow compared with the rate at which the wastes dissolve, we are concerned first and foremost with equilibrium solubility. Also, if only to relate behaviour on the geological time scale to that on the laboratory time scale, we will need to know about the mechanisms and kinetics of dissolution and leaching. The waste forms envisaged at present are glass blocks containing separated fission products and residual actinides fused into the glass and, alternatively, the uranium dioxide matrix of the used fuel containing unseparated fission products and plutonium. In the... 

Knighton, J.B. Baldwin, C.E. Pyrochemical Coprocessing of Uranium Dioxide-Plutonium Dioxide LMFBR Fuel by the Salt Transport Method, Rocky Flats Report RFP-2887, CONF-790415-29 (1979). 

Pyrochemical Coprocessing of Uranium Dioxide-Plutonium Dioxide LMFBR Fuel by the Salt Transport Method... 

We have determined that plutonium dioxide does not react with molten nitrates under the same conditions that uranium dioxide does. We have also determined that plutonium dioxide is not soluble in molten nitrates with the addition of 100% nitric acid vapor under conditions which did produce soluble uranium. This observation must be further verified under the various conditions which can produce the soluble uranium species. 

Another important consideration is the problem of dissolving the mixed-oxide fuel for subsequent reprocessing and plutonium recovery after the irradiated mixed-oxide fuel has been discharged from the reactor. When plutonium dioxide is in solid solution with uranium dioxide at low concentrations, as in the case of plutonium created during the irradiation of uranium dioxide... 

When plutonium dioxide is mixed uniformly with uranium dioxide containing 0.71 w/o or less the subcritical limits for infinite water-reflected cylinders or slabs are greater than... 

Pyrometallurgical processes investigated include slagging of molten irradiated uranium, plutonium extraction by silver, plutonium volatilization, and fused-salt extraction (78). Interest in these approaches ended with the selection of uranium dioxide as the CANDU fuel. 

A suitable fuel, used in the Galileo Jupiter explorer, which was finally destroyed in 2003, is the isotope Pu. This is an a-emitter, which provides about 0.5 Wg . The half-life is 87.4 years. The fuel is the solid oxide plutonium dioxide, Pu02. Chemically, it is similar to the uranium dioxide used in thermal reactors, and adopts the same fluorite (Cap2) crystal structure, similar to that of calcia-stabiUsed zirconia and UO2. This structure is inert chemically and stable up to the melting point of approximately 2500 °C. The oxide is pressed and sintered into pellets under conditions that lead to high density and low, but not zero, porosity. This is to ensure dimensional stability of the pellets over the lifetime of the spacecraft because, as Pu is an a-emitter, the resulting helium gas must be allowed to escape. 

The fuel in fast-breeder reactors is an oxide, as with a thermal reactor. The material chosen is a solid solution of uranium and plutonium dioxides, U tPU -jC)2. This material shares the same fluorite (Cap2) structure-type as uranium dioxide and plutonium dioxide. 

Plutonium dioxide (PUO2) is the most common form used as a reactor fuel. PUO2 is not used alone as a reactor fuel it is mixed with uranium dioxide. This mixture ranges from 20% plutonium dioxide for fast reactor fuel to 3% to 5% for thermal reactors. 

Oxide fuels have demonstrated very satisfactory high-temperature, dimensional, and radiation stability and chemical compatibility with cladding metals and coolant in light-water reactor service. Under the much more severe conditions in a fast reactor, however, even inert UO2 begins to respond to its environment in a manner that is often detrimental to fuel performance. Uranium dioxide is almost exclusively used in light-water-moderated reactors (LWR). Mixed oxides of uranium and plutonium are used in liquid-metal fast breeder reactors (LMFBR). 

The application of the mixed uranium-plutonium fuel in power reactors requires assurance of safe transport of semifinished items, fuel elements, and fuel bundles (FB). To research various aspects of safety, it is necessary to take into account that the thermal and radiation characteristics and criticality parameters of MOX fuel are higher than the characteristics of fuel on a basis of uranium dioxide. 

Spent fuel bundles with fuel from power (i.e., reactor-grade) plutonium, which were stored for 1-3 years, are characterized by a heat release approximately 70% higher than those with uranium dioxides. The heat release from fuel bundles made of weapon plutonium is approximately 30% higher than that of FB with uranium [1]. 

Fuil A mixture of plutonium 120%) and uranium dioxides in Stainless steel cans. 

BFS-1 critical facility was used to continue studies on the characteristics of fast reactor cores designed for the weapons grade plutonium utilization and minor actinides burning, for instance, the effect of neptunium introduction into fuel. The first stage of these studies made on the insert of the BN-800-Superphenix reactor fuel with up to 14% of depleted uranium dioxide replaced by neptunium dioxide was accomplished in 1995 (BFS-67 critical assemblies set). 

Uranium dioxide dissolves more rapidly than plutonium dioxide or thorium dioxide. Irradiated fuel dissolves faster, probably because of cracking during irradiation. 

Fuel material - the material from which the fuel elements are made. Typical fuel materials are uranium metal and uranium dioxide however, the material could also be a mixture of uranium dioxide and plutonium dioxide or thorium dioxide. Data providers should choose the appropriate option from the multiple-choice menu U metal, UO2, UO2/PUO2, U02/Th02, UO2/MOX, U02/Er203. 

The fuel is uranium dioxide mixed with plutonium dioxide (U02 - Pu02). It is contained in 103 subassemblies, each containing 217 pins, which in turn consist of a stack of sintered oxide pellets, S.S mm in diameter, in stainless steel cladding. The pins are assembled in clusters in a stainless steel outer shell, which also contains the upper and lower fertile blanket pins (depleted uranium oxide) and the upper neutron shielding. 

The fiiel is plutonium uranium mixed dioxide with 27.2% weight percentage of PuOa. The uranium will be enriched to 30%. 

After working with beryllium I moved on to study nuclear reactor fabrication. In this study I worked on determining the surface area, size and shape distributions of uranium dioxide and plutonium dioxide powders used to fabricate fuel rods. Looking back I see that my initiation into powder technology was a baptism of fire since all of these powders were extremely toxic and dangerous. The technology that I studied in those years is currently very applicable to the study of modern ceramic materials and powder metallurgical routes to finished products [1,2]. 

Usami, T., Kurata, M., Inoue, T. et al. (2002) Pyrochemical reduction of uranium dioxide and plutonium dioxide by hthium metal. J. Nucl. Mater., 300, 15-26. 

Mhere materials are labelled with an asterisk, a large number of powders were successfully deposited using the suspension medium described. Mizuguchi et al included alumina barium, strontium and calcium carbonates magnesia, zinc oxide, titanium dioxide, silica, indium oxide, lanthanum boride, tungsten carbide, cadmium sulfide and several metals and phosphors. The list of materials described by Gutierrez et al included several metals carbides of molybdenum, zirconium, tungsten, thorium, uranium, neptunium and plutonium zirconium hydride, tantalum oxide and uranium dioxide. In addition, many metallic and oxide powder suspensions in alcohols, acetone and dinitromethane were studied by Brown and Salt ... 

The many possible oxidation states of the actinides up to americium make the chemistry of their compounds rather extensive and complicated. Taking plutonium as an example, it exhibits oxidation states of -E 3, -E 4, +5 and -E 6, four being the most stable oxidation state. These states are all known in solution, for example Pu" as Pu ", and Pu as PuOj. PuOl" is analogous to UO , which is the stable uranium ion in solution. Each oxidation state is characterised by a different colour, for example PuOj is pink, but change of oxidation state and disproportionation can occur very readily between the various states. The chemistry in solution is also complicated by the ease of complex formation. However, plutonium can also form compounds such as oxides, carbides, nitrides and anhydrous halides which do not involve reactions in solution. Hence for example, it forms a violet fluoride, PuFj. and a brown fluoride. Pup4 a monoxide, PuO (probably an interstitial compound), and a stable dioxide, PUO2. The dioxide was the first compound of an artificial element to be separated in a weighable amount and the first to be identified by X-ray diffraction methods. 

Plutonium has a much shorter half-life than uranium (24.000 years for Pu-239 6,500 years for Pu-240). Plutonium is most toxic if it is inhaled. The radioactive decay that plutonium undergoes (alpha decay) is of little external consequence, since the alpha particles are blocked by human skin and travel only a few inches. If inhaled, however, the soft tissue of the lungs will suffer an internal dose of radiation. Particles may also enter the blood stream and irradiate other parts of the body. The safest way to handle plutonium is in its plutonium dioxide (PuOj) form because PuOj is virtually insoluble inside the human body, gi eatly reducing the risk of internal contamination. 

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