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Risk assessment*

Published online by Cambridge University Press:  05 December 2011

J. H. Gittus  and
M. R. Hayns
J. H. Gittus
Affiliation:
Safety and Reliability Directorate, United Kingdom Atomic Energy Authority, Wigshaw Lane, Culcheth, Warrington WA3 4NE, U.K.
M. R. Hayns
Affiliation:
Safety and Reliability Directorate, United Kingdom Atomic Energy Authority, Wigshaw Lane, Culcheth, Warrington WA3 4NE, U.K.
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Synopsis

Risk involves consideration both of the consequences of accidents and the frequency with which the accidents occur. Indeed formally risk is equal to the product of frequency and consequences. The important question of the perception of risk by the public and by the professional is first addressed. Two tenets are proposed as being a suitable summary of the public requirement:

1. If it can happen, then it must not matter.

2. If it matters, then it must not happen.

A mathematical interpretation is placed upon these tenets and is shown to be consistent with various professional safety targets. The tenets do not indicate what numerical values for risk would be acceptable to the public but they do show how the consequences of accidents should diminish as the frequency or likelihood of a particular accident increases. It is argued that the best way of determining what level of risk the public accepts is to be guided by statistics for man-caused accidents. These, it transpires, pose risks which are considerably greater than those implied, for example, by the professional targets for nuclear reactors. The risk posed to the public by two energy installations is summarised. The one installation, situated on Canvey Island, exports energy in the form of gas, some of which (methane) is pumped into a national gas grid. The other installation, the Sizewell “B” Pressurised Water Reactor nuclear power station has not yet been constructed, but a comprehensive risk assessment has been undertaken, the results of which are summarised. The two installations are comparable in the sense that each exports a power of the order of a million kilowatts (in the form of gas in the one case and electricity in the other). Both have been the subject of Public Inquiries. The risks posed by the Canvey installations are accepted, since they only constitute a small fraction of the risks which the public run in any case during the course of their everyday lives. The predicted risks for the PWR are smaller still. The form taken by the risks posed by both installations corresponds broadly with the two tenets. That is to say the greater the consequences the lower should be the frequency of a particular accident.

Type
Research Article
Information
Proceedings of the Royal Society of Edinburgh, Section B: Biological Sciences , Volume 92 , Issue 1-2: Scotland's Energy Future , 1987 , pp. 139 - 154
Copyright
Copyright © Royal Society of Edinburgh 1987

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Footnotes

*

Note added in proof: This paper was written, and presented, well before the accident at the Chernobyl nuclear power plant in Russia. The paper considers the risk posed by nuclear power plants and the targets used by both the regulators and the industry. It deduces that it will add negligibly to the existing societal risks. The fact that the very large accident happened does not change our conclusions. Firstly because the process of risk assessment is not a prediction of the future and because an accident occurs it does not mean that the risk changes. Secondly, all the analysis upon which the conclusions are based are concerned with plant built and operated in the west. The information given by the Russians in Vienna (both authors were members of the United Kingdom delegation) has re-inforced the view that a reactor of the type involved in the accident (the “RBMK”) would not be acceptable in the United Kingdom—it would not meet the basic professional safety targets. It is now apparent that a combination of human error, operator malpractice and design faults caused the accident; the professional safety targets described in this paper guard against such occurrences in this country.

References

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