Two of the three reactors at Forsmark were taken off-line earlier this month after one of them showed damage to a rubber seal.
That reactor cannot be restarted until the Swedish Nuclear Power Inspectorate gives a green light.
The agency on Wednesday said the second reactor could not be restarted either until Forsmark officials present a thorough report on the safety controls at the power plant, 100 kilometres north of Stockholm.
According to an agency spokesperson, ”we want to ensure that there are no deficiencies in the safety routines in the other reactors. This could be a one-off (incident), but it could also be generic.”
The third reactor is still online, but the inspectorate ordered plant officials to review controls at that reactor, too, and present a report by February 28.
If Forsmark fails to reply before that date, it could lose its operating permit.
Wrong Readings of Radioactive Particles
In a related story, instruments used to show how many radioactive particles are released by Forsmark have been giving wrong readings since 2004, and in fact levels were three to four times greater than previously believed.
Staff have only just noticed the errors and have informed the Swedish Radiation Protection Authority.
It says the increased amounts are still within safety guidelines, but says it is worrying that it has taken so long for the problem to come to light.