At 11:34 p.m., right after the first quake struck off the coast of Fukushima Prefecture, the coolant pump automatically halted for the spent fuel pool in the No. 5 reactor building at the stricken Fukushima No. 1 nuclear power plant, TEPCO said.
Pump operations were restored about four and a half hours later.
The cooling facilities in the No. 2 reactor building also stopped running at around midnight because the water level in the tank connected to the spent fuel pool had dropped. The facilities were restarted about seven and a half hours later.
TEPCO also confirmed that water inside the spent fuel pools spilled out at the No. 5 and No. 6 reactor buildings but remained within the structures.
In addition, a TEPCO official said a quake slightly shifted the position of a tank storing contaminated water in the compound of the plant.
The company said the quake’s intensity in the area of the No. 1 plant was a lower 6 on Japan’s seismic scale of 7.
A lower 6 intensity also rocked TEPCO’s Fukushima No. 2 nuclear power plant, where decommissioning work started in June last year.
The coolant pumps for spent fuel pools were shut down at the No. 1 and No. 3 reactor buildings.
Pump operations were recovered after 40 minutes at the No. 3 reactor building and after two hours at the No. 1 reactor building.
The quake also apparently warped a panel opening in a door at the No. 1 reactor building that releases pressure in emergencies to prevent hydrogen explosions.
The deformity created a fist-sized space in the panel opening, but no radioactive substances were confirmed to have leaked, TEPCO said.
The Onagawa nuclear power plant in Miyagi Prefecture, operated by Tohoku Electric Power Co., also recorded an intensity of lower 6.
The coolant pump for the spent fuel pool stopped at the building housing the No. 1 reactor, which is currently being decommissioned.
Operations were restored around 12:30 a.m., the utility said.
(This article was written by Yu Fujinami and Tsuyosi Kawamura.)