Nuclear fuel pellets

Example 7.5 Cooling nuclear pellets Spherical nuclear fuel pellets generate heat at a rate per unit volume, q, and being cooled at the boundary by convection heat transfer. For a single pellet on start up, we have... 

UO2 is a non-stoichiometric compound. Freshly reduced with hydrogen, it has the composition UO2.0, but in air it takes up oxygen and the composition varies with the partial pressure of O2 between UO2.0 and U02.25- For use as nuclear fuel, pellets of UO2 about 1 cm in diameter and 1 cm in height are produced. By sintering at 1600-1700 °C in hydrogen, the content of excess oxygen in UO2+X is reduced to x < 0.03 and about 98% of the theoretical density is obtained. 

The nuclear fuel pellets are generally filled in thin-walled cladding tubes to hinder leaching by coolant in the reactor core and to prevent release of fission products into the coolant circuit. In light-water reactors, for example, zirconium alloy (zirkaloy) cladding is used. 

What is now called sol-gel technology was originally developed by mineralogists for the preparations of homogeneous powders for use in studies of phase equilibria (72-74), by chemists for manufacturing nuclear fuel pellets (75, 76), and by ceramists for the preparation of advanced ceramic materials (77, 78). 

A batch of nuclear fuel pellets was weighed to determine if they fell within control guidelines. The weights were 127.2, 128.4, 127.1, 129.0, and 128.1 g. Calculate (a) the mean, (b) the median, and (c) the range. 

Uranium extraction from UO2 has been demonstrated using a high pressure mixture of TBP-HNO3-H2O-CO2 (10). The UO2 powder was prepared by grinding mechanically the UO2 nuclear fuel pellet using a vibrating sample mill (Tl-lOO,... 

Layers of pure pyrolytic boron nitride are generally prepared by thermally induced chemical vapor deposition (CVD) on graphite substrates. In most cases the reaction is performed using BCI3, NH3, and N2 (sometimes at about 0.5 to 50 Torr) and working at deposition temperatures of 1800 to 2000°C [97 to 111]. The same process is used at lower temperatures (600 to 800°C) for the coating of nuclear fuel pellets with boron nitride [112]. The thermally induced CVD of BN in such systems is not restricted to the formation of boron nitride layers but can be used to prepare compact boron nitride articles such as crucibles [113 to 121]. 

Stacks of completed nuclear fuel pellets being moved in a fuel fabrication facility. 

Wear-resistant, semiconducting films neutron-absorbing layers on nuclear fuel pellets. Niobium monoboride... 

Bulk and grain-boundary diffusion coefficients were measured for Gd diffusion in nuclear fuel pellets. Between 1500 and 1703C, in a hydrogen atmosphere, the bulk diffusion coefficient could be described by ... 

One of the routes to dense, fine-microstructured, polycrystaUine abrasive minerals considered by 3M at that time (-1974) was sol-gel technology. Prior to work on abrasives, 3M s Dr. Harold Sowman had been successful utilizing sol-gel approaches for the synthesis of nuclear fuel pellets and production of ceramic fibers. He, along with Dr. Melvin Leitheiser, initiated an effort to develop new aluminous abrasive minerals based on sol-gel technology. They focused their effort on the conversion of colloidal boehmite, y-AlOOH, into dense, polycrystalline alumina. Since that time, boehmite has become, not only the precursor of choice for sol-gel abrasive grains, but the precursor of choice for virtually every sol-gel alumina process. 

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