Neptunium alloys

In research at the Institute of Radiochemistry, Karlsruhe, West Germany, during the early 1970s, investigators prepared alloys of neptunium with indium, palladium, platinum, and rhodium. These alloys were prepared by hydrogen reduction of the neptunium oxide in (he presence of finely divided noble metals. The reaction is called a coupled reaction because the reduction of the metal oxide can be done only m the presence of noble metals. The hydrogen must be extremely pure, with an oxygen content of less than 10 25 torr. 

In the transthorium elements (with Z above 90) there was around 1955 a controversy 16 17) whether some 6 d electrons might occur, rather than a partly filled 5 f shell in agreement with Eqs. (4) and (5). The situation seems quite complicated in alloys of protactinium, uranium and neptunium with other metals, whereas plutonium may choose between 5 f4 Pu[IV] and 5 fs Pu[III] in the individual alloys or modifications of the element. On the other hand, americium and curium seem al-... 

Early Work. The irradiated fuel, upon discharge from the reactor, comprises the residual unbumt fuel, its protective cladding of magnesium alloy, zirconium or stainless steels, and fission products. The fission process yields over 70 fission product elements, while some of the excess neutrons produced from the fission reaction are captured by the uranium isotopes to yield a range of hew elements—neptunium, plutonium, americium, and curium. Neutrons are captured also by the cladding materials and yield a further variety of radioactive isotopes. To utilize the residual uranium and plutonium in further reactor cycles, it is necessary to remove the fission products and transuranic elements and it is usual to separate the uranium and plutonium this is the reprocessing operation. 

In 900MWe units, the capsules are irradiated along the outer surface of the thermal shield assembly. In 1300 and 1450 MWe units, the capsules are directly attached to the core barrel. In the case of Chooz-A, the thermal shield assembly was removed in 1970 and the surveillance capsules were then located under the core. The capsules are equipped with neutron dosimeters and thermal monitors, with some variations according to the reactor series. In all cases, activation dosimeters of nickel, copper and cobalt, as well as fissile dosimeters of uranium-238 and neptunium-237 are used. This instrumentation is complemented by iron and cadmium-shielded cobalt dosimeters in most cases and, in the most recent plants, also by niobium dosimeters. Each capsule contains temperature detectors based on eutectic alloys with melting points generally of 304 and 310 °C. 

The uranium-neptunium and uranium-plutonium alloys show a total miscibility in the liquid phase and in the A2-solid solution, moreover they exhibit phases with structures different from those of the pure components in a rather large range of composition in the middle of the phase diagram. 

Neck, V., W. Runde, and J.I. Kim. 1995. Solid-liquid equilibria of neptunium(V) in carbonate solutions of different ionic strengths II. Stability of the solid phases. J. Alloys Comp. 225 295-302. 

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