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Mysterious radiation leak traced to paper mill in central Finland

The caesium-137 leak detected by the Finnish radiation watchdog last week was traced to another tenant in its building – and from there to a UPM mill in Jämsä.

STUK -kyltti säteilyturvakeskuksen seinässä.
Image: Yle

The Finnish Radiation and Nuclear Safety Authority (STUK) has finally isolated the source of heightened radioactive caesium-137 measurements it detected in Helsinki in early March.

On Tuesday, STUK said the radioactivity had originated from the basement and garage of the authority's own headquarters in Helsinki's Roihupelto industrial area.

STUK shares those parts of the building with Suomen Nukliditekniikka, a company that processes small amounts of radioactive waste. On Thursday STUK confirmed that the radiation was coming from the firm's storage area.

The caesium levels measured in the air above the building last week were about a thousand times higher than normal – but, STUK says, only one-millionth of the level that would pose a health threat to humans.

Trail leads to Jämsä

After the caesium source was pinpointed and isolated on Wednesday evening, STUK asked Nukliditekniikka to ascertain the item's origin. The damaged and leaking device was traced to forest products company UPM's Kaipola paper mill in Jämsä, central Finland. It was a measurement device often used in industry, one of thousands such items used in Finland.

"These radiation sources have shields that normally prevent the source from being damaged. For reasons that still remain unclear, this source was however damaged," Eero Kettunen, Director of STUK's Department of Radiation Practices Regulation, told Yle.

STUK and UPM then checked the Kaipola plant but found no unusual radiation levels in initial testing. The radiation watchdog pledges to completely investigate the chain of events in hopes of preventing such incidents in the future. It has also asked Nukliditekniikka to come up with a plan for cleansing its facility and rendering the damaged device harmless.

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