At around 12:30 pm on May 11, 2011, a worker, who was working on blockage
of a vertical shaft, found the water flowing into the pit (vertical shaft
made of concrete) through the duct electric wires were in near the water
intake of Unit 3.
As a result of our investigation of the possibility of the leakage of
radioactive water off the site, outflow of the water from the pit to sea
was confirmed at around 4:05pm.
After that, we inserted fabrics to the duct leading to the pit and filled
concrete inside the pit. We confirmed that outflow was stopped at 6:45pm
on the same day.
We will monitor the condition of water stop and, will also analyze sea
water sampled at the water intake of Unit3 as well as the routes of inflow
and outflow and their condition.
(Previously announced on May 11, 2011)
On the same day we received the following verbal instructions from Nuclear
and Industrial Safety Agency (NISA);
· to check whether there is any impact on the ocean,
· to take measures immediately to stop the leakage, and
· to identify the inflow/outflow routes and their condition urgently and
We compiled preventive measures and countermeasures to prevent scattering
to the outside of harbor, in addition to the condition of inflow/outflow
routes and the impact on the ocean as instructed. Yesterday we reported
them to NISA.
Appendix: Countermeasures to outflow of radioactive water off the site
near water intake of Unit 3 at Fukushima Daiichi Nuclear Power
Station(overview) (PDF 99.0KB)
Reference 1-3: Trench for sea water pipes at Unit 3 (PDF 60.5KB)
Reference 4: Method taken to estimate amount of flow (PDF 25.8KB)
Reference 5.1-5.3: Reinforcement to prevent scattering liquid containing
radioactive materials (PDF 114KB)