Monday 28 April 1986 did not turn out quite as Claes-Göran Runermark, then operations manager at Forsmark 2, had imagined.
The day had started as any other day at the Forsmark nuclear power plant. During the previous weekend, it had rained over parts of Sweden and the prevailing winds had blown south-easterly.
What no one knew at that time was that reactor number four at the nuclear power plant of Chernobyl in the then Soviet Union had exploded two days earlier and parts of the reactor core had shot high up into the atmosphere.
The rain and winds carried the radioactive fallout over parts of Sweden.
At half past seven on Monday morning, information reached Claes-Göran Runermark that a final monitoring frame at the entrance to Forsmark 3 had indicated radioactivity on an employee’s shoes.
The radiation protection team determined very quickly that the radiation had not come from inside the plant.
“We were sitting in a production meeting together with the power plant manager when he received a call that the radiation protection team had detected radiation in the area. The meeting was concluded and we were all asked to check that the radiation was not coming from anywhere else within Forsmark,” says Runermark.
When the source of the radiation had still not been localised that morning, power plant manager Karl-Erik Sandstedt decided to increase the standby level, which meant that everyone, some 800 people, with the exception of the operating personnel and the emergency and standby teams, was to leave Forsmark and assemble at a site six miles away.
“Everyone was then checked over, and some people had to leave their contaminated shoes behind and leave the site in plastic overboots,” says Claes-Göran Runermark,” smiling at the memory.
What was the mood like at Forsmark?
“As I recall, it was quite calm, as in that situation everyone knew that the radiation did not come from within Forsmark. Many people thought it was plain silly to have to go home.”
At lunchtime, an analysis of the radioactive substances showed that they had come from a nuclear power plant and not from nuclear weapons.
A retrospective analysis of weather data showed that the radiation had been carried to Sweden via winds from the east.
“We then understood that something must have happened in the Soviet Union during the weekend.”
On Monday afternoon, Forsmark returned to its normal status and by evening the Soviet Union confirmed that a serious nuclear accident had occurred in Chernobyl on 26 April.
It was during the night of 26 April that Chernobyl’s engineers had started an experiment in reactor number four. The aim was to determine whether the cooling system could be operated solely with power from the reactor if the external power supply were to fail. To run the test, a number of safety systems were deactivated.
Just before the clock struck half past one that night, the reactor’s output suddenly rocketed to about a hundred times its normal level. An emergency shutdown of the reactor was attempted, but by then it had exploded. As there was no internal reactor containment, the roof of the building was blown off and parts of the reactor core shot up into the atmosphere and spread over large parts of Europe and the northern hemisphere.
What was it like to work at Forsmark when you discovered the radiation spike?
“It was quite clearly special. My wife rang me as soon as she heard on the radio that something had happened. With hindsight we might well call it a sort of live-fire exercise, but not of the sort that I had already experienced several times compared with the routine exercises that we have here.”
How were things at Forsmark after Chernobyl?
“We had to undergo tightened-up procedures to enter and be able to work at the plant. For example, we were not allowed to come in with our own shoes and clothes. But I wouldn’t say that Chernobyl led to any immediate changes here.”
The big lesson that the international nuclear power industry took away from Chernobyl was the creation of a stricter safety culture and safety awareness. The World Association of Nuclear Operators (WANO) was set up as a direct consequence of Chernobyl.
The year after Chernobyl, the Swedish parliament decided to introduce a law that prohibited all preparations for building new nuclear power plants in Sweden. The law was not repealed until 2010.
The Chernobyl accident did not lead to any drastic measures in Sweden, such as instructions to stay indoors, evacuation of areas or taking iodine tablets. However, the authorities did introduce limits for caesium in food, and informed the public of the risks of radiation.
In those regions of Sweden that received the most fallout, agriculture was hit during the first few years. This was due largely to the persistence of radioactive iodine and caesium in cow’s milk for months after the accident.
In 1986, 78 per cent of Swedish reindeer meat had to be discarded, which was a catastrophe for the herders. A higher safety limit was introduced the following year, which improved the situation of the reindeer owners.
“I can recall that there was a hefty discussion about elk and reindeer meat, mushrooms and parsley. Whether they could be eaten, and if so how much,” says Claes-Göran Runermark.
“I personally took a Geiger counter home and checked the children’s sand box, which led to them not being allowed to play there for a few days. I also measured the level in the street at home when the winter grit was being swept up. It was apparently intended to be used as filling material, but my counter reacted strongly, so that I had to point out that it would be unsuitable to use it.”