THE fifth anniversary of the Chernobyl disaster provides an opportunity for an assessment of the consequences both for the inhabitants of the surrounding area and for the future of nuclear power.
It was, without any doubt, a major disaster. Indeed in a recent Oxford lecture Zhores Medvedev, the Russian dissident and one-time Head of the Institute of Radiological Biology in Obninsk, said that it was one of the main factors leading to the collapse of the Soviet Union. A short time before Chernobyl, Mr. Gorbachev's energy policy for the Soviet Union put increasing reliance on nuclear power. After Chernobyl, local anti-nuclear pressure stopped nearly all further construction and thus gravely exacerbated the economic difficulties that already faced him.
Around the time of the fifth anniversary, the media were filled with stories about the consequences of the accident for the people in the surrounding regions, giving substantial figures for the death toll, and for the expected numbers of cancer deaths. It is important to assess the actual evidence, and this can only be done on the basis of detailed measurements of the radioactive contamination. This information is now available from several surveys carried out by international organisations.
The workers in the immediate vicinity of the reactor at the time of the accident received large radiation doses, and 31 died soon after. In addition, there are 145 people who received large but not lethal doses; they are being carefully monitored and it is likely that some of them will develop cancers over the coming years.
After the initial power surge, the reactor caught fire and large amounts of radioactivity were released. Depending on the prevailing winds, some of this was deposited on the ground in the region surrounding the reactor, and some was carried large distances and was detected in many European countries. To minimise the danger to their health, the authorities evacuated over a hundred thousand people from the region extending about thirty kilometres around the reactor, and they have still not returned.
There are thus two questions to be addressed. Firstly, how seriously is the surrounding region contaminated, and will it ever be safe for the inhabitants to return? Secondly, what will be the effects of the much smaller doses received throughout Europe and elsewhere?
It is easy to detect the radioactive decay of a single nucleus, so exceedingly minute amounts of radioactivity can be measured. It is therefore already well-known that practically everything is radioactive to some extent, including our own bodies. We are continuously irradiated by the cosmic radiation from outside the earth, and by the radioactivity in the ground. This constitutes the natural background of radiation, and provides a standard with which to assess the likely effects of any additional radiation due to the nuclear industry, to medical irradiation and to accidents like Chernobyl. Furthermore, the natural background varies very markedly from place to place, depending on the geology of the region. In Cornwall, for example, the natural background is over twice the average for Britain, due to the granite rocks that contain uranium.
Measurements of the radiation levels around Chernobyl show an excess over the natural level attributable to the accident. Detailed maps have been made, and show a very irregular distribution, impossible to summarise concisely. All that can be done is to give a few numbers to indicate the general levels found. All the following numbers are for levels of radiation expressed in terms of the unit microsieverts per hour:
The highest readings were of course near the reactor itself, being 30-50 at 300 metres. Further away, in the town of Pripyat, they were 0.5 to 0.9, and at the edge of the 30 km zone around the reactor, 0.7. In an administration building 18 km from the reactor, 0.2. For comparison, the Swedish scientists who made these measurements in September 1990 found 1. …