Searching for more info I found an related article from early January. Apparently Sweden has an extra set of mothballed plants for really cold winters with low water levels and offline nuclear. Here is some experts:

Elpaniken tvingar fram dyr oljekraft - Ny Teknik		Electricity panic forces expensive oil power
Den statliga myndigheten Svenska Kraftnät har nu aktiverat all den reservkraft på 1 300 MW som energibolagen mot betalning håller i beredskap om det blir en så kallad tioårsvinter då den vanliga elproduktionen inte räcker.		The governmental authority Swedish National Grid has now enabled all of the back up of 1 300 MW that energy companies - against payment - has on standby if there is a so-called tenth winter when the normal electricity generation is not enough.
Svenska Kraftnäts generaldirektör Mikael Odenberg tvingades i går också ringa till Vattenfall och stoppat planerna på att lägga oljekraftverken i Stenungsund i malpåse.		Swedish Kraftnäts General Mikael Odenberg was forced to call Vattenfall and halt plans to have oil plants in Stenungsund mothballed.
Var på väg att läggas ned Så sent som i början av december meddelade det statliga energibolaget Vattenfall att man lägger ned de oljeeldade reservkraftverken i Stenungsund och Marviken.		Was about to be closed As late as early December the state energy company Vattenfall announced that the oil-fired back-up power plants in Stenungsund and Marviken would be closed.
Under stora delar av hösten 2009 var bara hälften av den svenska kärnkraftskapaciteten igång.		During much of the autumn of 2009 was only half of the Swedish nuclear power capacity up and running.
Och nu, när den arktiska kylan dragit ned över Sverige, har Vattenfall, Eon och Fortum ännu inte fått ordning på sina kärnkraftverk. Fortfarande är drygt en fjärdedel av kapaciteten ur drift.		And now, when the Arctic cold drawn down over Sweden, Vattenfall, Eon and Fortum have not yet sorted out their nuclear power plants. Still more than one quarter of the capacity out of service.

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