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» NRA determined Fukushima nuclear disaster caused by tsunami, not earthquake

The Nuclear Regulation Authority says the Fukushima nuclear disaster in 2011 was almost certainly triggered by towering tsunami generated by the Great East Japan Earthquake.

NRA said key equipment and emergency power systems at the Fukushima No. 1 nuclear power plant failed due to damage from the tsunami instead of the magnitude-9.0 earthquake that preceded the deluge.

The NRA endorsed the view in an interim report draft on the nuclear disaster released July 18.

Its findings are expected to influence the evaluation by the International Atomic Energy Agency due out by the end of the year.

Experts have been divided over whether the massive earthquake was responsible for the failure of key equipment and emergency power sources at the No. 1 reactor building.

Workers at the plant at the time of the disaster reported that water was already leaking on the fourth floor of the No. 1 reactor building before the tsunami inundated the plant.

The fourth floor housed isolation condensers that cool steam from the reactor’s pressure vessel and condense the steam into water and return the cooling water into the reactor.

The condensers were supposed to kick in during an emergency even without a power source, but it was discovered that they barely functioned, leading to a meltdown earlier than anticipated.

A Diet investigative committee pointed out the possibility that water leaked because isolation condenser pipes were damaged by the quake. It also said that emergency power sources for the No. 1 reactor could have been lost before the tsunami struck the facility on the basis of its assessment of when the tsunami hit the plant.

The NRA, however, concluded that the leaking water that the workers saw was overflow from the spent fuel storage pool nearby.

It also determined that emergency power sources were lost due to the tsunami, based on data released in May 2013 by TEPCO, and other sources.

Whether the isolation condensers were already damaged by the quake is an issue of significant implications, raising the question of the adequacy of anti-quake preparedness measures at the Fukushima plant and other nuclear facilities.
<Media Report>
NRA blames tsunami for equipment failure at Fukushima plant (Asahi Newspaper)

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