The fire broke out when performing a pressure test of the reactor's containment on May 10. Someone forgot to remove a wet vacuum cleaner from the premises, which then caught on fire.
"Those items aren't supposed to be left in the containment, when testing," said energy company Vattenfall's nuclear power head Peter Gango to SVT.
"It was a human error, and those shouldn't occur in our power plants."
Cleaning and reparation of the reactor is expected to take at least seven months, meaning that management is hoping to get the reactor started sometime in mid-December. The long down-time has caused a loss of profit of 1.8 billion kronor, which hits state-owned Vattenfall hardest, as the energy company owns 70 percent of the Ringhals power plant.
The calculations on profit loss from the fire have been made by broker firm Bergen Energi for SVT.
Right now all of Ringhals's four reactors are turned off, according to SVT. The power plant's management is hoping to get two of the reactors started next week.