The operator of the crippled Fukushima No. 1 nuclear power plant said Tuesday a power outage halted some systems but that no problems were detected in the cooling of the three melted-down reactors.

Machinery affected included cooling equipment for an underground ice wall, which is being set up around four reactor buildings in a bid to restrict the flow of groundwater beneath them.

Tokyo Electric Power Co. said an alarm sounded at 3:40 a.m. Tuesday, and workers found a unit that filters radioactive cesium from contaminated water had shut down.

The Nos. 1 to 3 reactors, which suffered meltdowns in the 2011 crisis, are currently being kept cool by having water poured into them every day.

Tepco said no abnormalities were detected with this equipment or in the surrounding environment.