Chicken Nuclear Power Hazard Control Policy

1. Auflage 2013
ISBN: 978-1-4831-5463-3
Verlag: Elsevier Science & Techn.
Format: EPUB
Kopierschutz: 6 - ePub Watermark

E-Book, Englisch, 282 Seiten

Nuclear Power Hazard Control Policy presents an analysis of the factors that appear to have influenced the formation and form of nuclear power hazard control policy in Britain. Particular attention is directed to those political groups that have developed a special interest in the problems of nuclear power, and to the interplay between organized groupings and public opinion generally. The metamorphosis of these groupings is traced from the origins of the nuclear industry in World War II to their prominent role during the Windscale Inquiry. This volume is comprised of nine chapters and begins with a simple account of the technical nature of nuclear hazards and of the legal and administrative framework that has been developed to control them. The subsequent chapters concentrate primarily on the influence exerted by social and political factors. Throughout the study, emphasis is given to the policy constraint imposed by increased expectations in the form of demands for higher standards of living, as well as improvements in the quality of the environment. The final chapter describes a model of the policy-making system that takes account of the consequences of variation with time in the environment surrounding the system. Appendices are included to provide a chronology of the relevant events and a summary of the administrative arrangements that various countries have made to control the safety of nuclear reactors. This monograph will be of value to policymakers concerned with the hazards of nuclear power and how to control them.

Autoren/Hrsg.

Chicken, John C.

Leseproben

CHAPTER 2

The Nature of Nuclear Power Hazards

Publisher Summary

This chapter discusses the nature of nuclear power hazards and provides a sound basis for the analysis of nuclear power hazard control policy and how these nuclear hazards may be controlled. The primary hazards from nuclear power are the various types of radioactive radiations that may cause somatic and genetic damage. By careful design and operation of the associated plant and equipment, nuclear power hazards may be controlled in such a way that their impact on society is restricted to an acceptable level. The significance of nuclear hazards can be expressed in quantitative terms, thus allowing decisions regarding what is an acceptable level of hazard to be made more rationally. The indications are that nuclear power hazards are less than those of coal-fired power stations and some other industries.

In order to provide a sound basis for the analysis of nuclear power hazard control policy this chapter outlines the nature of these hazards. The principal aim is to explain the nature of the problem to the non-specialist reader and to identify the ways in which these nuclear hazards may be controlled.

The major hazards associated with nuclear reactors are the radiations emitted from the materials used in and generated by the nuclear fission process. In addition, as with any industrial process, there are hazards of a more general kind which are common to most working environments. These industrial hazards, which include such risks to employees as being hurt by falling objects, by falls, or by being caught in machinery, are not considered further in this study since they have no special significance in the nuclear power context.

The nuclear power industry embraces a broad spectrum of activities which include the mining of uranium, the fabrication of nuclear fuel, the construction and operation of nuclear reactors, the removal of used nuclear fuel from the reactors, the storage and reprocessing of used nuclear fuel, and the safe storage and dispersal of radioactive waste generated. In the following summary of nuclear power hazards, the significance of the radiation hazards at each stage of the nuclear power process from mining to the disposal of radioactive waste will be considered. No consideration is given to the radiation hazards which are associated with other uses of radioactive materials such as radioactive isotopes used for radiotherapy and radiographic examinations.

The description of the nature of nuclear power hasards that follows is divided into five stages: (a) a description of the various forms of radiation, (b) an outline of the ways radiation arises, (c) an evaluation of the harm that radiation can do, (d) an examination of the way protection can be provided against harm from radiation, and (e) a comparison of the hazards associated with nuclear reactors with hazards from other sources.

FORMS OF RADIATION

The following summary of the various forms of radioactive radiation associated with nuclear power reactors is based, to some extent, on the more detailed accounts given by Eichholz (1) and in the sixth report of the Royal Commission on Environmental Pollution. (2) The two basic types of radiation that have to be considered are particulate, and electro-magnetic radiations. Particulate radiations are those consisting of the streams of particles that are constituents of individual atoms. The particles may be the relatively heavy positively charged protons, or neutrons which have a similar mass to protons but are electrically neutral, or the very light electrons, or positrons. Electrons have a negative charge, and positrons have a positive charge. The magnitude of the charge possessed by positrons and electrons is equal in magnitude to that possessed by protons, but in the case of electrons the charge is negative. If the proportion of protons, neutrons, positrons and electrons in a particular atom is such that their charges do not balance the atom will be unstable. An unstable atom will radiate particles or energy or both until an equilibrium state is achieved. In this unstable state an atom is referred to as being radioactive. Some of the energy given out by an unstable atom may be used to propel the particles emitted, and some of the energy may take the form of electromagnetic radiations, known as gamma radiations. These gamma radiations are similar to x-rays.

The main ways an unstable atom may decay to a stable state are as follows:

(1) a decay in which an atom emits an a particle. An a particle is the same as the nucleus of a helium atom, and consists of two neutrons and two protons.

(2) ß decay in which either a neutron changes to a proton or a proton changes to a neutron. In this form of decay a ß particle is given out. If a neutron becomes a proton the particle given out is an electron, but more rarely if a proton becomes a neutron the positive analogue of an electron, that is a positron, is given out. Positrons and electrons tend to annihilate each other and in doing so emit electromagnetic radiation in the form of ? rays.

(3) If energy is released by the process some will be used to propel any neutrons or a or ß particles emitted and the rest will be emitted as ? rays.

(4) An unstable very heavy element may move to a more stable state by spontaneous fission into two large fragments (fission products). The fission process is accompanied by release of a very large amount of energy and a few neutrons.

It is a controlled fission process which is harnessed in a nuclear reactor to generate power. At the heart of a reactor is an assembly containing heavy metals, such as Uranium 235. The assembly is designed so that fission may be induced by the heavy metal being struck by and capturing a neutron. To start the process a source of neutrons may be required, but once the process is started in an appropriate assembly of fissionable materials it generates sufficient neutrons to keep the process going. The fission products generated by the process may be isotopes of any of about 38 elements, some of which may be radioactive. Those that are radioactive may decay to other more stable isotopes. In addition to the radioactive materials generated as fission products, the transformation of uranium metal to other elements has to be considered. For example, the Uranium 235 present in the fuel may transform to Uranium 239 by neutron capture, and Uranium 239 will decay to Neptunium 239 and then to Plutonium 239.

There are several characteristics of these radioactive fission products that are important to this study. These characteristics include their abundance, their radioactivity, how quickly they decay, and how volatile they are. The last two characteristics need a little explanation. All radioactive materials lose their radioactivity with time as they decay to a more stable state. The rate at which they lose their radioactivity is measured in terms of “half lives”. “Half life” is the time taken for the radioactivity to fall to ha f its original value. Half lives vary from seconds to years depending on the isotope. The longer the half life the longer the hazard associated with the material will last. The volatility of a radioactive isotope is important as it gives an indication of how easily a particular isotope could escape and cause a hazard beyond the confines of the reactor. In the Windscale incident in 1957, the only British reactor accident resulting in release of significant quantities of fission products* to the atmosphere, most of the radioactivity released was in the form of Iodine131 (3). Iodine131 is volatile, it has a half life of eight days and it is easily taken into the body either by inhalation or ingestion.

In the major study of nuclear risks undertaken by Rasmussen**, for the United States Nuclear Regulatory Commission, 246 activation products, 461 fission products and 82 transuranic nuclides were considered. Not all these substances were radioactive. By eliminating those nuclides that were not radioactive, had half lives shorter than 25 minutes, and were of low activity, the list still contained 54 nuclides that were considered to warrant further examination.(4) The nuclides that have to be considered as a hazard in accident conditions vary and are, to some extent, determined by the specific circumstances of a particular accident. The accidents which give rise to the greatest concern are those in which radiation and radioactive nuclides may escape from the reactor to the atmosphere. How the escaping radioactivity interacts with people that are exposed to it then becomes the key question, and this is discussed below***. It is sufficient to say at this stage that people in the vicinity may be subject to radiation in three ways, by direct radiation from the radioactivity released, internal exposures to radiation by radioactivity that enters the food chain, and internal exposure to radiation resulting from radioactivity being inhaled.

Some means of measuring the dose received from the various forms of radioactivity is required. The amount of activity is conventionally measured in curies****, one curie corresponding to the activity displayed by one gram or radium. This in itself is not adequate, since it is the dose absorbed by the target material that is of most interest, and this varies with each substance. The unit of absorbed dose is the rad, where 1 rad = 100 erg/gram. The concept of the...