专业英语教材

LESSON ONE

The peaceful uses of nuclear energy: technologies of the front and back-ends of the fuel cycle

Jacques Percebois

Abstract

The principal peaceful application of nuclear energy is that of electricity generation. The nuclear industry is a young one, which is today confronted with difficult choices, essentially because this activity generates fear. This fear is partly related to the generation of electricity in power plants but is particularly present in relation to the transport, reprocessing, management and underground disposal of nuclear waste. This paper examines, respectively, the nuclear technologies available today (1), the future perspectives for nuclear energy on a worldwide basis (2) and the controversial question of the management of nuclear waste (3). Nuclear energy can be considered as an alternative to fossil fuels in the context of policies to reduce emissions of greenhouse gases. The potential technological progress is a key element of the future of nuclear energy; but the crux of the problem remains the long-term management of waste.

Keywords: Nuclear technologies; Perspectives of nuclear energy; Management of nuclear waste 1. Nuclear technologies

1.1. The principle of nuclear fission (see Percebois, 1989)

The cohesion of an atomic nucleus is obtained by the binding energy emitted by each nucleon making it up. However, this binding energy is not the same for all nuclei: it is weak for light nuclei, strong for medium-sized nuclei and average for heavy nuclei. Therefore, if a heavy nucleus is split, the two nuclei resulting from this fission have a total binding energy greater than that of the original nucleus. Thus, during this transformation, a certain quantity of energy is emitted, as it is now necessary to provide more energy to dissociate the two new nuclei rather than to dissociate the initial heavy nucleus: part of the weight of the initial nucleus is in fact transformed into energy (Einstein’s law). The energy thus emitted is kinetic energy of the two resulting nuclei. The situation is the same if, instead of splitting a heavy nucleus, we re-bond two light nuclei: the binding energy of the nucleus resulting from this fusion is greater than that of the original nuclei.

Fission takes place when a heavy nucleus absorbs a neutron (a non-electrically charged sub-atomic particle), thereby creating an unstable edifice which splits into two lighter nuclei by emitting 2 to 3 neutrons which in turn can cause fission. During fission, if at least one neutron emitted is absorbed by a new fissile nucleus thereby instigating further fission, then there is said to be a “chain reaction”.

However, few elements are naturally fissile. Most natural substances are capable of capturing neutrons without there being either fission or emission of energy: they have simply become radioactive. Naturally, fissile elements are to be found at the top of Mendeleev’s table, i.e. beside the heaviest and therefore most unstable atoms. The most important of the fissile isotopes is U-235