Surveys above and below

25 April 2012

A visit from the Japanese prime minister's cabinet office senior vice minister Ikko Nakatsuka to the Fukushima Daiichi site prompted a trip to the unit 4 reactor well and spent fuel pool.

Visit to Fukushima Daiichi unit 4 reactor well
Visit to Fukushima Daiichi unit 4 reactor well

Nearby, TEPCO has launched two surveys to find leaks in the primary containment vessels of Fukushima Daiichi units 2 and 3. Before TEPCO can begin to remove the fuel, it must flood the PCVs with water; doing that requires finding, and fixing, the leaks. The unit 2 survey did not find any leaks, but the unit 3 survey did.

A remote-controlled robot sent around the Fukushima Daiichi unit 2 torus (wet well) found no obvious leaks. The survey, on 18 April, found radiation levels around the torus up to 118 mSv/hr. It also photographed some damaged pipe covers above the walkway around the torus.

The lack of evidence of leaks in the torus is surprising, given the amount of water (9m3/hr) being injected into the reactor. The US blogger Leslie Corrice speculates that the leak might be in feedwater piping outside of containment (scroll to April 20 entry on

It was a different story in the unit 3 survey. An endoscopic survey behind the unit 3 primary containment vessel hatch, behind the shield plug, detected the presence of water on the floor that could indicate a leak. Results from the quick survey, which took less than five minutes to minimize radiation doses, will be reviewed, TEPCO said.

Seeping water found in Fukushima Daiichi unit 3 PCV hatch
Seeping water found in Fukushima Daiichi unit 3 PCV hatch could be a path for leaks

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