Power Transmission Tower for Fukushima I Nuke Plant Fell Because Drain Pipe Wasn't Installed When the Site Was Prepared in 1960s

A mountain stream used to flow near the site for the power transmission tower for Fukushima I Nuclear Power Plant. They dumped a lot of soil and filled the stream to create the embankment, and built the power transmission tower. They thought the water would naturally flow underground at the old surface level. Well it didn't.

From Jiji Tsushin (2/17/2012):

東京電力福島第１原発事故の際、５・６号機に外部電源を供給する電線の鉄塔が倒れたのは、隣接地の沢を１９６０年代後半に埋めた時に排水管を設置しなかったため、盛り土が巨大地震の強く長い揺れで崩れたことが原因と分かった。東電が１７日、経済産業省原子力安全・保安院に報告した。

The power transmission tower for Reactors 5 and 6 at Fukushima I Nuclear Power Plant fell because the embankment collapsed from the intense and long shaking from the mega earthquake. In late 1960s the nearby mountain stream was filled but a drain pipe was not installed. TEPCO reported the findings to the Nuclear and Industrial Safety Agency on February 17.

　５・６号機は鉄塔倒壊で電線が切れて外部電源が失われたが、非常用発電機の一部が機能し原子炉を冷却できた。１～４号機は別ルートの鉄塔や電線が無事だったが、配電設備や非常用発電機が津波被害を受け、冷却電源を完全に失った。

Reactors 5 and 6 lost external power when the tower fell and the electricity supply was cut off when the power lines were severed. But one of the the emergency power generators worked, and the reactors were cooled. For Reactors 1 through 4, the other tower and the power lines remained intact, but the power distribution equipment and the emergency power generators were damaged by the tsunami, resulting in the complete loss of power for the cooling systems.

　報告書によると、鉄塔付近では昨年３月１１日午後２時４８分すぎに最も強く揺れ、同４９分すぎに鉄塔が倒れ電線が切れた。６６年当時の工事図面などによると、鉄塔建設地に向かって沢が流れており、盛り土をした後は地下水の流れとなった。この流れの位置は旧表土層から約２メートル上になり、盛り土の中を通る形になっていた。

According to the report. the strongest shaking near the tower from the quake occurred at 2:48PM on March 11, 2011. At 2:49PM, the tower fell and the power lines were severed. According to the blueprint from 1966, there was a mountain stream flowing toward the site for the power transmission tower. After the embankment was built, the stream went underground. The underground stream then flowed at about 2 meters above the old surface, flowing right through the embankment.

　東電の松本純一原子力・立地本部長代理は記者会見で、「沢を埋めた際、地下水は旧表土層に沿って流れるとみていた」と説明した。

TEPCO's Matsumoto explained in the press conference, "When the stream was filled, we assumed that the underground water would flow along the old surface level."

The general contractor who built Fukushima I Nuclear Power Plant is Kajima, who should have known better. The company was, and still is, the first and foremost general contractor in Japan in huge civil engineering projects. I would give them some slack though, as building something that would withstand Magnitude 9 earthquake may be near-impossible.

TEPCO's report to NISA is in Japanese only, and it is not known if NISA will ever provide the English translation. If you read Japanese, the report is here.

The report says the tower fell 30 seconds after the maximum acceleration.

From the report, it looks a large tree jammed into the tower:



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