At around 11:07 AM on September 22, during debris removal from the upper part of Unit 3 Reactor Building, a steel beam (approx. 300mmx200mmx7m, approx. 470kg) which had been on the side of the spent fuel pool (SFP) and found to be unstable slipped and fell into the pool when a worker was trying to grab it using an oil-pressure fork attached to the head of a crane. Then at around 11:45 AM on the same day, it was confirmed that there was no problem with the operation status of the spent fuel pool alternative cooling system and the skimmer surge water level. As a result of the radioactivity density analysis of the spent fuel pool water*1, no significant change was found before and after the incident (by comparing the results obtained after the incident and the most recent results before the incident). In addition, no significant change was found with the monitoring post data, the atmosphere dose rate measured near the spent fuel pool and the spent fuel pool water level.
From September 24, the conditions of the inside of the spent fuel pool (location where the steel beam fell into, conditions of the spent fuel and storage rack, soundness of the pool, etc.) have been investigated using an underwater camera. As a result, no problem was found with the upper part of the spent fuel and storage rack as well as the pool wall in the area captured by the underwater camera. During the investigation conducted today, the location of the steel beam which had fallen into the pool was identified.
Today, we received a directive document*2 "A steel beam falling into Unit 3 spent fuel pool at Fukushima Daiichi Nuclear Power Station (Direction)" from the Nuclear Regulatory Authority. In accordance with the direction given, we will promptly implement necessary measures and report the results.
End
*1 Radioactivity density analysis results
As a result of radioactivity density analysis of Unit 3 spent fuel pool water, no significant change was found comparing before and after the incident.
*2 Directive document
"A steel beam falling into Unit 3 spent fuel pool at Fukushima Daiichi Nuclear Power Station (Direction)"
The aforementioned document is available only in Japanese. We apologize for the inconvenience this may cause.
