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After four decades and hundreds of billions of dollars spent on the buildup of nuclear weapons, the United States and the Russian Federation have taken a bold step to convert deadly instruments of the Cold War into peaceful and productive resources. The United States and Russia are implementing a historic agreement whereby the United States is purchasing material recovered from dismantled Soviet weapons for use in commercial electricity production. By purchasing Russian highly enriched uranium (HEU), the United States is helping to ensure that it will be used solely for peaceful purposes.

The objective of the nuclear industry is to produce energy in the forms of heat from either fission reactions or radioactive decay and radiation from radioactive decay or by accelerator methods. For fission heat applications, the nuclear fuel has a very high specific energy content that currently has two principal uses, for military explosives and for electricity generation, mainly in light water reactors (LWRs) operating between 250 and 350 °C. While higher-temperature reactors, mainly high-temperature gas and sodium reactors have been available for over 60 years, they have been shown to not be economically competitive with LWRs. For radiation applications, the emissions from radioactive decay of unstable nuclides are employed in research, medicine, and industry for diagnostic and measurement purposes. Radioactive decay heat is also employed to generate electricity from thermoelectric generators for low-power applications in space or remote terrestrial locations. Radiation produced from accelerator-based sources is used for geologic investigation (e.g., identifying oil deposits), materials modification, and contrast imaging of dense media (e.g., security inspections in commercial shipping). Fuel from the first atomic pile is shown in Fig. 1.

The graphite-moderated reactor has a longer history than any other type, since the first critical assembly constructed under the direction of Enrico Fermi at Chicago in December 1942 was a natural uranium, graphite- moderated reactor. The principal use of graphite-moderated reactors for power generation, however, has been in the United Kingdom and France. In both cases, the original motivation was the advantage of constructing a system combining natural uranium fuel with a readily available and relatively inexpensive moderator.

An assessment of the concept to dispose of spent, irradiated nuclear fuel in an underground repository requires information on the rates of radionuclide leaching from the fuel matrix and of fuel matrix dissolution.

Early in 1950, the Norwegian physicist Gunnar Randers found himself in a predicament: he was in charge of the construction, already at an advanced stage, of one of the first nuclear reactors to be made outside the Anglo-Saxon world, but he had not managed to find the requisite uranium. Indeed, it had been on his instigation that the Norwegian government, encouraged by its national production of heavy water (the first such industrial production in the world), had granted just after the war the appropriations required for the construction of a heavy-water research reactor of low power, quite reasonably assuming that the uranium needed for its operation would be found on Norwegian territory in the course of the few years required to build the reactor.

Natural uranium dioxide nuclear fuel for irradiation in CANDU reactors is manufactured by General Electric Canada. To ensure the fuel does not rupture,pellet chipping and cracking is controlled. While not apparent in the green compact stage chips and cracks are readily observed after sintering and are generally located at the ends of the pellets

Following the discovery of the neutron, detailed measurements of the effect of bombarding elements with neutrons were carried out, notably by Enrico Fermi and his collaborators in Rome. Among the large number of elements investigated was the heaviest naturally occurring element, uranium. As with many of the other elements, the bombardment of uranium led to the production of induced β activity. At least four different β-active isotopes, of different half-lives and disintegration energies, were detected.

The long-term incentive for the development of breeders is well known: better use of natural uranium in order to extend the potential of nuclear energy by a factor of 50 with given uranium resources, and in fact by a much larger factor, since also uranium resources from low-grade ores can be used economically in breeder reactors. Nuclear energy without breeders represents a relatively modest contribution to the world’s total energy supply; with breeders, it allows thousands of years of high energy consumption.

The feasibility of the fission track registration technique to investigate the natural uranium concentration in petroleum is examined. The application of this technique to petroleum is briefly described and discussed critically. The results obtained thus far indicate uranium concentrations in samples of brazilian petroleum which are over the detection limit of the fission track technique.

My purpose today is to give a brief overview of the technology of the nuclear fuel cycle. I shall describe briefly the processes which are now being used and shall venture some opinions about future trends.

The nuclear industry of the U.S., and most of the world, is based on light-water reactors (LWRs). These reactors were developed in America, where we had the capacity to enrich natural uranium slightly. Using slightly enriched uranium as fuel made it possible to use ordinary water as reactor coolant and moderator for power reactors. This, in turn, permitted us to use well-known steam technology in designing the reactor system. The resulting reactors turned out to be cheaper than their main competitors and quite reliable.

Much of the early development work on power reactors concentrated, of necessity, on the use of natural uranium. This demanded the selection of high-grade moderator, of low-neutron cross section, either graphite, as in the United Kingdom magnox system, or heavy water, as in the Canadian CANDU reactor. The United States, on the other hand, had available from an early date adequate supplies of enriched uranium from the diffusion plants constructed for military purposes. The high specific fission cross section of the enriched fuel enabled an adequate thermal utilization to be achieved even when a relatively low-grade moderator of high absorption cross section, such as ordinary water, was used. Having chosen water as moderator on account of its excellent moderation properties and ready availability, it was natural to employ it also as the coolant, because of its good heat transfer properties. Reactor development in the United States over the past two decades has been largely devoted to the water-moderated, water-cooled type of reactor, and the last few years have seen an increasing installation of this type in other countries. As of 1980, the 142 light water reactors in operation were producing a total annual output of 109 GWe, out of a total world nuclear generating capacity of about 130 GWe.

The incentive to use heavy water as moderator arises from the excellent neutron economy made possible by the low neutron cross sections of both deuterium and oxygen (0.5 and 0.27 mb, respectively). In combination with its slowing-down power of 0.175 cm-1, the low cross section of D2O leads to a moderating ratio of 6000, making heavy water, by a wide margin, the most desirable moderator on purely theoretical grounds. The fast and slow leakages from a heavy water reactor tend to be roughly equal, in contrast to the situation for a light water system, where the fast leakage is much the greater.

Deuterium, a heavy hydrogen isotope, is used in certain bubble chambers and also for experiments in nuclear fusion. However, the greatest demand for deuterium is associated with nuclear reactor technology, particularly for reactors of high power output. These reactors have attained importance because they can use natural uranium. This makes them attractive in those countries that have no U-235 enrichment plants or that prefer natural uranium for other reasons and is one reason why the demand for heavy water is increasing.