MOSCOW--For the past 3 decades, rumors have circulated here that in the early 1970s an accident at the Kurchatov Institute of Atomic Energy, in a residential suburb of Moscow, released a cloud of gas that drifted over the city, exposing the population to potentially harmful radiation. Late last month at a nuclear safety conference in France, a senior Kurchatov researcher discussed these events in public for the first time: There were two blasts at the institute in the early 1970s, which killed two people, he said, but as far as Kurchatov scientists could tell, no radionuclides were released over the city. According to Stanford University historian David Holloway, author of the book Stalin and the Bomb, "Secrecy was such in the 1970s that it would have been covered up."
The Kurchatov Institute was at the heart of the Soviet Union's atomic weapons program in the 1940s, but it moved over to civilian research in the 1950s. Today, it is one of Russia's State Research Centers. Dmitry Parfanovich, a leading researcher at the Kurchatov, told the International Conference on Nuclear Criticality Safety in Versailles that the most serious blast occurred on 26 May 1971. At the time, Parfanovich was working in the research area close to one of the institute's critical nuclear assemblies--a basic feature of a nuclear reactor. "It all happened because the structure of the critical assembly was very fragile," Parfanovich told Science.
At about 4:00 p.m., experiments at this reactor had been completed and researchers were in the process of shutting it down. This involved draining the assembly of water, which was used as a moderator. Standard procedure required the water to be drained slowly and carefully, but on that day, Parfanovich recalls, the workers were in a hurry and they used a large emergency drain at the bottom of the tank. The rapid removal of the water moderator caused the structure to heat up, creating excess pressure that buckled the base of the reactor. As a result, uranium rods came out of their sockets and dropped out of the bottom of the assembly onto the floor below, where they created a critical mass. There was a flash of radiation, the rods melted and changed their configuration, so the reaction stopped again.
Although the blast lasted only milliseconds, Parfanovich said a technician standing nearby received a dose of direct radiation amounting to 6000 roentgens. He died the next day of a heart attack. A researcher received more than 2000 roentgens and died 2 weeks later. Another two researchers received 800 to 900 roentgens and were saved through extensive medical treatment, but their health suffered as a result. Other staff members were protected by a concrete shield and received insignificant doses.
All personnel working in the building were evacuated, and routine radiation checks revealed that some had radioactive iodine on their clothing. Vladimir Asmolov, head of the Institute for the Control of the Safe Use of Nuclear Energy (a part of the Kurchatov center), recalls that some young researchers who had contaminated clothes deliberately evaded the security and simply waited for the level of radioactivity to go down. They went drinking in an apple orchard on the grounds of the institute, which had been planted by its founder, Igor Kurchatov, "father" of the Soviet bomb. (Kurchatov liked to demonstrate the safety of his institute by eating apples from the trees.) Despite the rumors of radioactive clouds floating across downtown Moscow, Parfanovich said no emissions were traced outside the research area.
The whole incident was kept secret, even from researchers in other branches of the institute. Most knew that an explosion had taken place but had no idea of its severity. Similarly sketchy details had leaked out of another weaker blast which had happened about 3 months earlier. In this case researchers were unaware there was anything wrong with the reactor until they noticed a blue light illuminating the ceiling. Parfanovich reported that two researchers received a dose of about 1000 roentgens, and one of them later had his feet amputated.
Parfanovich told the Paris meeting that there were a total of five such blasts in research centers during the Soviet era. Asmolov thinks that the atomic research institutes and the nuclear power industry that grew out of them nevertheless had a good safety record, but that standards are now slipping. "Greater openness now about the past serves as a signal that they are trying to address safety issues seriously today," says Holloway. However, safety concerns now keep all the research reactors at the Kurchatov idle, and even the director of the institute, Evgeny Velikhov, favors moving them outside Moscow.