Extinguishing the fire and deployment of liquidators

Fig. 8: From 27 April to 5 May, more than 30 military helicopters flew over the burning reactor. They tried in vain to put out the fire with 2400 tonnes of lead and 1800 tonnes of sand. © Chernobyl Interinform Sources (3.9)  Wolfgang Botsch: Untersuchungen zur Strahlenexposition von Einwohnern kontaminierter Ortschaften der nördlichen Ukraine, Universität Hannover, 2000, p. 16 (26.1)  United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR): Source and Effects of Ionizing Radiation, UNSCEAR 2000 Report to the General Assembly, Annex J, New York, 2000, p. 455 (36.1)  www:Medicine Worldwide, Tschernobyl, p. 2 www.onmeda.de Documents Movie showing the first cleanup activities in the reactor in April and May 1986 (17.5 MB), © Agentur ChernobylInterinform, (You need a Real-Player to view this. You can download it from http://www.real.com). Glossary Pressurized-Water Reactor (PWR) Boiling-water reactor Reactor Radiation and radioactivity Sievert Further information Acute effects of radiation on human health

What technical measures were taken to extinguish the fire in the reactor?
What technical measures were taken to extinguish the fire in the reactor?To put out the fire and thus stop the release of radioactive materials, firefighters pumped cooling water into the core of the reactor during the first ten hours after the accident. This unsuccessful attempt to put out the fire was then abandoned. From 27 April to 5 May, more than 30 military helicopters flew over the burning reactor. They dropped 2400 tonnes of lead and 1800 tonnes of sand to try to smother the fire and absorb the radiation.

These efforts were however unsuccessful. In fact they made the situation worse: heat accumulated beneath the dumped materials. The temperature in the reactor rose again, and thus also the quantity of radiation emerging from it. In the final phase of firefighting, the core of the reactor was cooled with nitrogen. Not until 6 May were the fire and the radioactive emissions under control (3.9; 26.1).

The 600 men of the plant's fire service and the operating crew, who were employed in firefighting, were the most severely irradiated group. 134 of them received doses of radiation between 0.7 and 13 sieverts (Sv). This means that within a few hours they received a quantity of radiation up to 13 000 times higher than 1 millisievert: in the European Union, 1 millisievert per year is the maximum effective dose of radiation to which individuals in the population near a nuclear power station should be exposed.

31 workers died shortly afterwards. A total of around 800 000 men were involved in the clean-up operations in Chernobyl up until 1989. Today, they are still suffering from the damage to their health. 300 000 of them are believed to have received doses of radiation of more than 0.5 Sv. How many of them have died to date from the effects is a controversial question. According to government agencies in the three former Soviet States affected, about 25 000 "liquidators" have so far died (36.1). Estimates provided by the liquidator associations in the three countries are well in excess of the official figures. The Chernobyl Forum's 2005 Report on the other hand attributes a far lower number of liquidator deaths to the reactor disaster.

These discrepancies in numbers are due to different methods of assessment. The Chernobyl Forum bases its assessment on the assumption that a dose of under 500 mSv cannot result in death. Applied to the Hiroshima-Nagasaki data, however, this assumption would lead to an entirely new appraisal of the internationally recognised consequences of the two atom bomb explosions. Besides, the liquidator statistics (number of casualties and amount of radiation received) were deliberately and accidentally distorted by the Soviet authorities, something which is nigh to impossible to rectify this stage.