A drop in the water levels in the reactor containment vessels of units 1 and 3 at the Fukushima Daiichi plant in Japan has been detected, Tokyo Electric Power Company (Tepco) has announced. The utility said the decreased levels probably indicate that existing damage to the units' containment vessels has been exacerbated by the recent earthquake that struck the region, allowing more water to leak from them.
A 7.1 magnitude earthquake occurred at a depth of 60 km, some 90 km off the coast of Fukushima Prefecture at 11:08pm on 13 February. Tepco reported shortly afterwards that the Fukushima Daiichi plant had not sustained any further damage due to the quake, but noted about 160 ml of water had spilled from the used fuel storage pool at unit 1, which had no impact on the cooling of the pool.
Since the March 2011 accident at the Fukushima Daiichi plant, Tepco has been pumping cooling water into the leaking reactor vessels of units 1 and 3 in order to maintain the water levels within them.
However, on 19 February Tepco announced the water level in the reactor containment vessels of both unit 1 and 3 "is on a downward trend".
Tepco spokesman Keisuke Matsuo was cited by the Associated Press as saying the cooling water level dropped up to 70cm in the primary containment vessel of unit 1 and by about 30cm in unit 3. He said the company was not able to determine any decline in the water level in unit 2 as measuring instruments have been removed to prepare for the removal of melted fuel debris.
"The cause may be a change in the situation of the damaged part of the reactor containment vessel due to the earthquake, but we will continue to closely monitor the parameters," Tepco said in a statement.
It added: "No significant changes were observed in the reactor pressure vessel bottom temperature, the containment vessel gas management system radioactivity (including monitoring of rare gases), site boundary radiation monitoring, and on-site radiation monitoring. We have determined that there will be no impact."
The leaked water is believed to have remained inside the reactor buildings. "At present, no significant fluctuations have been confirmed in the water level of the reactor buildings, but detailed evaluation and monitoring of the parameters will be carried out," Tepco said.