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Sweden: New owner to invest in remaining Oskarshamn reactor

Nuclear Monitor Issue: 
Charly Hultén ‒ WISE Sweden

Uniper Sweden, which holds a majority stake in the operator OKG (Oskarshamn Kraft Grupp), committed SEK 865 million (€94m, US$105m) to safety improvements in O3, the single remaining reactor at Oskarshamn. The decision was a long time coming.

As reported earlier (Nuclear Monitor #807, #846), Sweden's nuclear park is shrinking. Twelve reactors will soon be only six. O1 and O2, small and chronically ailing reactors at Oskarshamn, have now been taken off-line, while two similarly small and ailing reactors at Ringhals are on track to shut down within the next two years. For reasons of public safety, two reactors at Barsebäck, directly across The Sound from metropolitan Copenhagen, were the first to go, in 1999 and 2005.

The fate of the remaining reactor at Oskarshamn has been hanging in the balance since mid-2015, when then-majority owner EON announced it would divest itself of all nuclear holdings in favor of renewable energy sources. Two clouds combined to darken O3's horizon: an EU requirement that all reactors in the Union be equipped with independent core cooling by 2020 implied major investments, just as electricity prices in Europe fell into a protracted slump.

Now, the new majority owner is unreservedly optimistic. In conjunction with the announced investment, Roger Strandahl, spokesperson for Uniper Sweden, said that OKG intends to operate O3 until 2045 – at which point the reactor will be 60 years old.

'Independent core cooling' is shorthand for a reserve system for cooling the fuel core that will operate regardless of the state of the reactor. The requirement was issued after the disastrous tsunami crippled reactors at the Fukushima Daiichi plant in Japan in March 2011, resulting in multiple meltdowns.

SSM, Sweden's Radiation Safety Authority, has specified what the system has to be able to withstand. The list includes more extreme external factors than have been analyzed to date, for example earthquakes and flooding with total loss of power from external networks and scenarios where normal access to water from the Baltic has been cut off.

The chosen solution is considerably simpler than earlier proposals. For one thing, it is a low-pressure solution. In the event of total power failure, pressure in the reactor tank will be reduced by transferring steam to the condensation pool via the reactor's RAMA filter.

The system consists of two pumps, each powered by its own diesel motor. The larger pump will start whenever the water level in the reactor tank reaches a predefined level. It has the capacity to fill the reactor tank with water from the central pool within one hour. The need for water is presumed to decline as the decay power in the fuel subsides. The lesser pump will start up after about two hours and cool the core as long as is necessary using water from the central pool, the firefighters' water system and, if needed, water from a nearby reservoir.

The switch to a low-pressure solution means that the new facility can be less complex and will require less space. Reliance on the reactor's RAMA filter to remove heat affords a substantial simplification of the electrical system. The proposed solution was approved by the Radiation Safety Authority earlier this year. According to plan, it will be in operation by the end of 2020.

The prospect of a tsunami in the Baltic Sea is hardly a real concern, but many Swedes recall an incident at Forsmark, north of Stockholm. There, in 2006, the reserve cooling system failed because of a partial power outage in the control room of a reactor. Subsequent analyses suggest that the reactor was about 20 minutes from a meltdown by the time reserve power could be put in place. The incident reportedly caused Swedish authorities to revise the estimated risk of reactor meltdown upwards by factor 780. In other words, the EU requirement comes none too soon.

Is this the classic happy ending? No, it is rather only a beginning, and some major questions remain unanswered. Will, for example, O3 last the full 60-year stretch and pay off its owners' investment? Will the electricity market support the reactor's production costs? Will Swedes find the risks associated with such an aged reactor acceptable? There are no guarantees.


Press release (English), 19 Aug 2017, 'OKG. Multi-million SEK investment to secure long-term power supply from Oskarshamn 3',

News articles in Östra Småland, 19 and 24 August 2017.

A document (in Swedish) on OKG's site describes the safety system: