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Safety Moment #58: Fukushima-Daiichi – Two Too Many Common Causes

July 1, 2020

Common Cause Event at Fukushima-Daiichi

Almost a decade ago, one of the most serious industrial incidents ever to have occurred took place at the Fukushima-Daiichi nuclear power plant in Japan. The event gets little publicity now, even though it is still not known exactly what happened, and even though radioactive materials continue to leak into the surrounding sea water.

One of the themes of the posts at this blog is that we in the process and energy industries can learn a lot from other industries, just as they can learn from us (see Safety Moment #8: “But We’re Different, You Know” in the ebook 52 Process Safety Moments).

The FD event illustrates how supposedly redundant safety systems turn out not be redundant after all. To summarize:

  1. Nuclear power plants must always maintain a flow of cooling water to the reactors following an emergency shutdown.
  2. The 2011 subsea earthquake caused extensive damage to four of the reactors at FD.
  3. The facility went into an emergency shutdown, as designed.
  4. Emergency diesel-powered pumps started and then maintained the flow of water to the reactors. Therefore, even though the damage was extensive, the reactors were in a safe condition.
  5. Then a tsunami that had been created by the subsea earthquake came ashore. It overwhelmed the sea walls protecting the water pumps.
  6. The pumps failed.
  7. The reactors overheated, thus creating a series of meltdowns and fires that released large quantities of radioactive materials into the sea, sky and ground.
  8. The common cause in this event was “subsea quake”. First, it wrecked the reactors, then it destroyed the safety backup systems.

Common Cause Event at Fukushima-Daiichi

Common Cause Event at Fukushima-Daiichi

There are two lessons from this event for those working in the process and energy industries.

  1. Always be on the lookout for difficult-to-spot common causes, and
  2. Recognize that independent safety systems may not actually be fully independent from one another.

Further analysis of this event using Fault Tree methodology is provided in Safety Moment #58: Fukushima-Daiichi – Two Too Many Common Causes.

  1. Lyndon Pousson Sr. permalink

    My hindsight is perfect. Are there any ongoing studies regarding the building of nuclear power plants in close proximity to the ocean?

    • Not that I know of. In the U.S. it seems as if the number of nuclear power plants is going down. When all the environmental and permitting issues are considered, they are very expensive. And we still don’t have a way of storing high level waste.

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