According to the Ringhals power station, the stop in one reactor was to adjust instruments after anomalous readings. The other reactor has been closed since Monday after a problem in the cooling system.
The move came the same day it was revealed the Swedish Nuclear Power Inspectorate has filed police complaints against another nuclear station for safety violations. A leaked internal report criticised the operators of the Forsmark station, north of Stockholm, in connection with a power outage in July.
One of the Ringhals reactors is expected to return to service on Friday.