(Bloomberg) -- Two unplanned outages at key reactors in Sweden and Finland sent Nordic power prices to their highest levels since March, just as a cold snap engulfs the region. 

Vattenfall AB’s Ringhals-4 nuclear reactor shut early Wednesday after a failure, while Teollisuuden Voima Oyj’s Olkiluoto-3 went offline during testing in the afternoon, according to regulatory filings with the Nord Pool exchange. 

The jump in prices offers a stark reminder of the vulnerability of Europe’s energy markets even after the worst of last year’s crisis has passed. Electricity costs have already been on the rise recently due cold weather spreading across northern Europe, with temperatures in Helsinki plunging to -7.5C on Thursday, according to forecaster Maxar Technologies Inc. 

The outages are likely to translate to higher energy bills for some consumers and businesses whose contracts are tied to wholesale pricing.

Ringhals-4, which has a capacity of 1,130 megawatts, is expected back on the grid at midnight on Thursday at the earliest, operator Vattenfall AB said in a filing. It shut after a deviation in one of the facility’s three steam generators, it said in a follow-up statement. 

The average day-ahead price for Thursday in the Nordic market soared to its highest since March 5 in an auction on Wednesday. 

TVO said electricity production at its 1,600 megawatt Olkiluoto-3 nuclear reactor was interrupted on Wednesday at 1:35 p.m. Helsinki time due to a fault ride-through test at the turbine plant, according to a statement. 

Vattenfall only recently returned its Forsmark-3 reactor outside Stockholm to the grid after an outage from Saturday to Monday. The firm operates five of Sweden’s six reactors, which supply about a third of the country’s power, and is looking into building more units as power demand is poised to double in the next two decades. 

(Updates with Finnish reactor halt in second paragraph.)

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