Nuclear fuels and development of nuclear fuel elements

Abstract

The importance of nuclear energy in meeting future energy demands has been well-recognlsed and a variety of nuclear reactor systems have been developed. Inherent characteristics of nuclear technology like neutron economy and neutron irradiation-induced degradation in properties of materials require stringent control of material purity and necessarily limit the choice of candidate materials. Hence safe, reliable and economic operation of nuclear fission reactors, the source of nuclear power at present, requires judicious choice, careful preparation and specialised fabrication procedures for fuels and fuel element structural materials. These aspects of nuclear fuels (uranium, plutonium and their oxides and carbides), fuel element technology and structural materials (aluminium, zircaloy, stainless steel etc.) are discussed with particular reference to research and power reactors in India, e.g. the DHRUVA research reactor at B~c, Trombay, the pressui'ised heavy water reactors (PHWR) at Rajasthan and Kalpakkam, and the Fast Breeder Test Reactor (FBTI~) at Kalpakkam. Other reactors like the gas-cooled reactors operating in UK are also mentioned. Because of the limited uranium resources, India has opted for a three-stage nuclear power programme aimed at the ultimate utilization of her abundant thorium resources. The first phase consists of natural uranium dioxide-fuelled, heavy water-moderated and cooled PHWR. The second phase was initiated with the attainment of criticality in the FSTR at Kalpakkam. Fast Breeder Reactors (FBR) utilize the plutonium and uranium by-products of phase 1. Moreover, FBR can convert thorium into fissile U-233. They produce more fuel than is consumed-hence, the name breeders. The fuel parameters of some of the operating or proposed fast reactors in the world are compared, rBTR is unique in the choice of mixed carbides of plutonium and uranium as fuel. Factors affecting the fuel element performance and life in various reactors e.g. hydriding of zircaloys, fuel pellet-cladding interaction etc. in PHWR and void swelling, irradiation creep and helium embrittlement of fuel erement structural materials in FBR are discussed along with measures to overcome some of these problems.

Molecular dynamics study of the point defects in bcc uranium

“…Thus, the equilibrium volumes and hence formation and binding energies of point defects in bcc uranium obtained from our molecular dynamics simulation are more reliable than those from the shell method. Further, the bulk moduli of U 126 M 1 II). This is acceptable because such binding energies in bcc iron [18] are generally higher than −1.5 eV and because our binding energies are similar to the He-binding in tungsten [59].…”

“…Fundamental limitations of UO 2 such as the low uranium density and poor thermal conductivity have nevertheless driven the development of advanced fuels such as UC, UN, and metallic alloys of uranium. Fast reactor fuel elements made of metallic alloys of cubic uranium, with enhanced dimensional stability over time, enable high burn-up and breeding besides the possibility of concurrent burning of radioactive minor actinides and fission products [1][2][3][4][5][6][7][8]. In a nuclear reactor, the fuels experience the most severe temperatures, irradiation damage, and chemical transmutation environment.…”

Phase decomposition of γ-U (bcc) in U-10 wt% Mo fuel alloy during hot isostatic pressing of monolithic fuel plate

“…Orthorhombic α-, tetragonal βand body-centered cubic (BCC) γ-phases are stable up to 667°C, between 667° and 771°C, and above 771°C, respectively [14][15][16][17]. The α-U has undesirable characteristics as a nuclear fuel such as low hardness, rapid oxidation, low corrosion resistance and anisotropic irradiation behavior [18][19][20][21].…”

“…The α-U has undesirable characteristics as a nuclear fuel such as low hardness, rapid oxidation, low corrosion resistance and anisotropic irradiation behavior [18][19][20][21]. A single crystal of α shortens in a-axis and extends in b-axis, and there is no significant change in c-axis during irradiation under 500˚C [16,22], leading to dimensional instability [23,24].…”

The Fate of Sulfur in Mild Gasification Liquids

“…Also, while techniques have been proposed [3][4][5][6][7] to reduce the sulfur content of volatile products, thc effects of such methods on sulfur distribution have not been investigated.…”