On Monday 28 April 1986, two days after the Chernobyl accident, we were gathered at the Swedish Nuclear Power Inspectorate at midday as an ad hoc group of five inspectorate employees, completely unaware of what had happened earlier. We had an hour to identify the cause of the contamination at the Forsmark nuclear power plant, located 150km north of Stockholm. After some telephone calls, we found out that other Swedish nuclear sites were also contaminated. The contamination levels were not as high, but these other plants are located west of Forsmark. It became clear that the easterly wind blew in the radioactivity from a nuclear accident.

The isotopes analysed by a research laboratory in Stockholm indicated that no ship reactor was involved. The cladding of the damaged fuel did not contain stainless steel – there was no trace of cobalt. Much later the laboratory was able to find graphite particles in the air.

Our immediate conclusion was that a major reactor accident happened east of the Baltic Sea but it was hard for us to reach that conclusion: The Soviet Union’s might was only just past its zenith and in Sweden, only the harm the Swedish reactors could cause in neighbouring countries was debated in the political arena – it was not appropriate to consider the other way around.

At once, the Swedish scientific attaché in Moscow and the International Atomic Energy Agency (IAEA) were informed. The Swedish mass media became increasingly interested during the afternoon and after an evening announcement from the Soviet Union, it became the hottest story for practically all newspapers, radio and TV stations all over the world.

Over the past two decades, a large amount of money was spent on the exchange of experts mainly between Lithuania and Sweden and also Russia. Millions more has been spent on safety-related improvements at the Ignalina nuclear power plant in Lithuania, but after that country entered the European Union, direct cash contributions from Sweden ceased. Now the support money is directed to the Leningrad plant, located west of St Petersburg on the Finnish Gulf, by and large on the opposite Baltic coast to Stockholm.

Organisations such as the IAEA and the World Association of Nuclear Operators (WANO) were invited to send expert groups to the different RBMK plants to examine and suggest improvements to operational practice. The International Electrotechnical Commission (IEC) issued a report on the instrumentation and control (I&C) aspects of the RBMK reactors.

Undoubtedly the plants are now less vulnerable than they were 20 years ago. In addition to the physical improvements, the theoretical understanding of the operational characteristics has also been enhanced. The main control rooms have been modernised and new I&C systems have been installed. The greatly improved use of computers has increased the quality of information to the operators. The fuel enrichment was also increased and the resulting harder neutron spectrum helped to lower the notorious positive void coefficient.

As time goes by, the scenario is drastically changing and so are attitudes. Sweden’s two-unit Barsebäck plant, located 25km from Copenhagen (the capital of anti-nuclear Denmark), has recently been closed at a cost of €2 billion. The power outputs of the remaining ten reactors in Forsmark (three units), Oskarshamn (three units) and Ringhals (four units) have been substantially uprated and further increases are anticipated. These plants account for about half of the Swedish electricity consumption. The official nuclear phaseout policy has been postponed to a distant future.

The Nordic grid is integrated into continental Europe and in the winter, Sweden imports a lot of electricity. The Swedish heavy industries – iron, paper and manufacturing – are large consumers of electricity. To protect themselves from the enormous money transfer to the electric utility industry they decided to form their own electric power company named Basel.

Basel is looking eastwards for its supplies, towards the other side of the Baltic Sea, where many different thermal power plants are located. Among them there are the Leningrad and Ignalina nuclear plants. To import 1000MWe from Russia to Sweden, a direct cable connection through Finland is planned to be built in three years. Also a different direct cable connection is planned between Sweden and Lithuania.

At present, RBMKs are operating in Russia: Kursk (4), Smolensk (3) and Leningrad (4). In Lithuania there is Ignalina (1), but closure is planned for 2009. Assuming no further accidents, it looks as though the RBMK reactors – against all the odds and in spite of vehement opposition from anti-nuclear organisations – have been given a second chance to continue operation.

Author Info:

Frigyes Reisch, Associate Professor, Nuclear Power Safety, KTH Engineering Sciences, Royal Institute of Technology, Stockholm, Sweden