Two reactors at the Forsmark plant, 60 miles north of Stockholm, were shut down in July after two backup generators malfunctioned during a power failure.
They went back on the grid two months later after security upgrades.
In its complaint to prosecutors, the Swedish Nuclear Power Inspectorate said plant managers acted too slowly in cooling down one of the reactors after the incident. Such a decision was not made until one day after the July 25 incident, the inspectorate said.
Prosecutors will now review the complaint and decide whether to press charges against the operator, Forsmarks Kraftgrupp AB, for nuclear safety violations. The company is controlled by state-owned energy group Vattenfall AB.