Reactor 3 had to be shut down because of a problem with the water cooling system. The power company OKG, which runs the nuclear plant, says to news agency TT it will be supplying electricity at its usual level by Thursday.
Currently only one of the three reactors at Oskarshamn nuclear plant is working.
Reactor 1 is out of action while its security system is updated and will not re-start until Summer 2015.
Power company OKG says it normally supplies ten percent of Sweden's electricity generation.