Page 5, 16th May 1986

16th May 1986
Page 5
Page 5, 16th May 1986 — Questions requiring answers after Chernobyl

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Locations: Chernobyl


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Questions requiring answers after Chernobyl

Oxford don Dr Peter Hodgson sets the agenda

AFTER the Chernobyl disaster, any decisions that are made concerning our own power programme must be based not on emotional reactions but on a careful quantitative assessment of the risks and hazards not only of nuclear power but also of the possible alternatives. Only in this way can we ensure that our power needs are met in the most efficient, safe and economical way.

Rather few facts are at present available about the Chernobyl accident, but making use of the general principles of reactor design it is possible to make some reasonable speculations that serve to underline areas where more information must be obtained.

To set the discussion in its wider context, the Soviet Union, like all other countries, is faced with the problem of meeting increasing demands for more electric power. It is fortunate in having huge deposits of coal, oil and minerals, but these are mostly in the Urals, thousands of miles away from the centres of population and heavy industry in the west.

The Soviet Union therefore went ahead with what is now the world's largest nuclear power programme using a standardised reactor type.

Already the Ukraine gets about 40% of its electricity from nuclear reactors, much of it from the complex at Chernobyl. For the Soviet Union, the Chernobyl accident is an economic disaster of the first magnitude.

It would be prudent to shut down or at the very least to reduce the power level of all reactors of the same type until the cause of the accident is established and the necessary action taken. If it is a design fault that can easily be corrected, well and good, but if it should transpire that the design of the reactors is unsafe, then the whole nuclear programme will have to be reorganised.

The Chernobyl reactor is of the water-cooled, graphitemoderated uranium type. The uranium undergoes fission and the heat produced is carried away by the water and used to generate electricity. If one of the pipes carrying the cooling water breaks, then the reactor is no longer cooled and its temperature rises rapidly.

This is immediately detected by safety devices that activate control rods that stop the nuclear reaction. Even if these safety devices were also to fail; there is no possibility of a nuclear explosion; the uranium is not sufficiently concentrated for that to happen.

However even when the nuclear reaction has stopped, the radioactive fission products in the reactor continue to give out heat, and so the reactor gets hotter and hotter until the reactor vessel ruptures. This exposes the uranium and graphite to the air, whereupon they catch fire and burn fiercely.

The smoke from this fire carries away with it radioactivity from the fission products in the reactor and if it is not stopped by the outer containment shield of the reactor building it can rise to a great height and be blown by the prevailing vitinds over a wide area, depositing radioactivity. Most of this comes down fairly near the reactor, but some may be carried thousands of miles. It seems likely that this is what happened at Chernobyl, though it is essential to find out in much more detail what went wrong. Was the design of the reactor unsafe, as had been claimed in the west? Was the operating temperature too high? This would increase the power output, but also the risk of fire if an accident happened.

Were the cooling circuits duplicated and triplicated and so designed that even if one of them failed the others could keep the reactor safely under control? Why was there no outer containment building of thick reinforced concrete to keep the radioactivity within the building in the event of an accident?

Most important of all, was the reactor constructed according to specifications, and to the highest building standards?

It is worth noting in this connection that an article in the March 27 issue of Literaturnaya Ukrainia criticised the poor standard of the construction work at Chernobyl, mentioning in particular defective materials, poor organisation and morale among the builders and defects in the structure.

We will soon have accuarate measurements of the radioactivity deposited in western Europe, and it seems likely that this will not constitute a serious health hazard. This may not be the case in eastern Europe, and particularly in the region to the northwest of the reactor itself. The vital question is how much of the radioactivity in the reactor escaped.

It is imperative that measurement of radiation levels be made and the results published as soon as possible. It would be more credible if these were made by representatives of the International Atomic Energy Authority.

It will take much longer to establish the cause of the accident. It is in everyone's interest that this should be done as soon as possible, and Governments should be pressing for the establishment of an international commission of reactor experts with full access to the Chernobyl reactor, its design specifications and its operating records and charged with the responsibility to make a full report as soon as possible.

Until a full report is available, it would be premature to draw any conclusion for our own nuclear power programme. Nuclear reactors are of many different types, and if one type is proved unsafe it does not follow that other types are also unsafe.

It is more than ever necessary at this time to emphasise that the right decisions can only be taken on the basis of careful quantitative assessments of the safety, capacity and economy of the various possible means of generating the electic power that we need to sustain our lives.

Those who propose the abandonment of nuclear power must consider in detail the implications of either living without so much power, or of using more coal or oil. It is not responsible to propose a course of action without facing the consequences. Present assessments strongly favour nuclear power and this must stand until convincing counter arguments are produced.

There are many important questions to be discussed, but the essential prerequisite is that those taking part in the debate inform themselves about the basic scientific, technical and economic facts.

Dr Peter Hodgson is a lecturer in Nuclear Physics at Oxford University and a fellow of Corpus Christi College.

Next week nuclear physicist Chris Feetenby will reply. '

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