Fukushima: Earthquake not a factor, Tsunami the 'direct cause'

The tsunami of 11 March was actually the 'direct cause' of the accident at the Fukushima Daiichi nuclear power plant, concluded an official investigation report. It dismissed the idea that earthquake damage was a major factor in the accident.

As we can see the figure above the Fukushima Nuclear Power Plant geography is situated near the first earthquake point [1]. A safe emergency shutdown was achieved within seconds of the magnitude 9.0 earthquake, said the Fukushima Nuclear Accident Investigation Commission composed of experts independent of plant owner Tokyo Electric Power Company. Control rods were fully inserted within seconds and all 13 diesel generators started as per design when tremors disconnected the grid connection. Instrumentation was working correctly, as were cooling systems.

Fukushima's coastal position in the Japanese north-east left it exposed to the full force of the tsunami 

Photograph: The Tokyo Electric Power/EPA [3].

Shaking recorded at the site was around the maximum that the plant was designed to cope with and still maintain nuclear safety but walk-down checks by plant staff showed no indication of significant damage to coolant systems.

Within an hour of the earthquake, however, almost the entire site was submerged to a depth of up to nine metres by a series of tsunami waves. Over about ten minutes these flooded six of the diesels and ruined the supporting equipment of another six. Only one diesel unit survived and this was used alternately to maintain essential systems at units 5 and 6 - using one of only three power distribution panels that had not been submerged. Some 36 other distribution panels throughout the emergency diesel generator system were made useless by water.

     Before and after tsunami: Fukushima Dai-ichi nuclear comples. Pic: AP [4].

This situation was noted as the 'direct cause' of the accident. The lack of emergency power and the inability to restore it eventually led to the loss of four reactor units and a significant release of radioactivity.

The report was based in part on analysis of observable factors at the site - such as high-water marks and physical damage - in addition to reams of hard data produced by reactor control systems up to the time they lost power. This report was an interim publication, running to hundreds of pages, and was released for comment while the investigating commission promised to report again as more information comes to light [2].

More info here: Earthquake not a factor

References:

1. http://gruntdoc.com/2011/03/fukushima-nuke-plant-geography.html

2. http://www.worldnuclearnews.org/RS_Earthquake_not_a_factor_in_Fukushima_accident.html

3. http://www.guardian.co.uk/world/2011/mar/11/japan-earthquake-evacuate-nuclear-plant

4. http://asiancorrespondent.com/50356/japanese-ordered-indoors-in-radiation-leak-crisis/

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What is Nuclear Power?

Nuclear power is the use of sustained nuclear fission to generate heat and do useful work. Nuclear power plants provide about 6% of the world's energy and 13-14% of the world's electricity [1] with US, France and Japan together accounting for about 50% of nuclear generated electricity [2]. In 2007, the International Atomic Energy Agency (IAEA) reported there were 439 nuclear power reactors in operation in the world [3] operating in 31 countries [4]. Also, more than 150 Naval vessels using nuclear propulsion have been built.

There is an ongoing debate about the use of nuclear energy [5]. Proponents,such as the World Nuclear Association and IAEA,contend that nuclear power is a sustainable energy source that reduces carbon emission [6].Opponents ,such as Greenpeace International and NIRS, believe that nuclear power poses many threats to people and the environment [7]

Nuclear power plants accidents include the Chernobyl disaster(1986), Fukushima Daiichi nuclear disaster (2011), and the Three Mile Island accident (1979) [8]. There have also been some nuclear power submarine mishaps [9]. However, the safety record of nuclear power is good when compared with many other energy technologies. Research into safety improvements is continuing and nuclear fusion may be used in the future.

China has 25 nuclear power reactors under construction,with plans to build many more [9],while in the U.S the license almost half its reactors have been extended to 60 years, and plans to build another dozen are under serious consideration.However. Japan's 2011 Fukushima Daiichi nuclear disaster prompted a rethink of nuclear energy policy in many countries. Germany decided to close all its reactors by 2022, and Italy has banned nuclear power [10]. Following Fukushima, the International Energy halved its estimate of additional nuclear generating capacity to be built by 2035.

References

1. World Nuclear Association.Another drop in nuclear generation World Nuclear News, 5 May 2010

2. Key world energy Statistics 2007. International Energy Agency 2007. Retrieved 2008-06-21

3. U.S Energy Legislation May Be 'Renaissance'for Nuclear Power

4."Nuclear Waste Pools in North Carolina". Projectcensored.org. Retrieved 2010-08-24

5.The worst Nuclear Disasters

6. Strengthening the safety of radiation sources

7.World Nuclear Association (December 10,2010) , Nuclear Power In china

8.Sylvia westall and Fredrik dahl (June 24,2011). "IAEA Head Sees Wide for Stricter Nuclear Plant Safety". Scintific American. 

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