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Vol.3 No.4 previous GA19
General Articles
GA19
 

An International View of the Fukushima Accident, Japanese Response, Japan’s Post Accident Situation and Needed Actions

 
Douglas M. Chapin
MPR Associates, Inc.
 
 

1. Introduction

This paper represents the personal views and opinions of the author and does not reflect the views of the United States government or any official organization. In developing these views and opinions, the author has devoted considerable time to the study of a wide variety of information about the Fukushima accident. In addition, the paper reflects insights based on over 30 years of experience in working on nuclear power technology in Japan and almost 50 years of experience in the nuclear power field.

2. Scope

The scope of the paper covers:
  • A brief discussion of the Fukushima accident sequence.
  • The major lessons the author draws from the accident.
  • Strength and weaknesses of the Japanese accident response.
  • Actions suggested to prevent recurrence of events like Fukushima in the future.

3. Accident Sequence

At 2:46 pm on March 11, 2011, Japan time, a magnitude 9 earthquake occurred about 24 km off the Oshika Peninsula and at a depth of about 24 km. This resulted in an earthquake acceleration level at the Fukushima Daiichi site of about 0.5 g which slightly exceeded the design basis. A tsunami was initiated at the same time and first waves reached Fukushima Daiichi about 3:30 pm. The maximum wave height was about 14 m and greatly exceeded the design basis.

At the time of the event, Fukushima Daiichi units 1, 2, and 3 were at 100 percent power and units 4, 5 and 6 were shut down. Unit 4 reactor was empty, preparing for core shroud replacement. All unit 4 fuel was moved to the spent fuel storage pool in the reactor building. Units 5 and 6 had fuel in the reactor vessels.

In passing, and in view subsequent events and the lessons the author draws from the Fukushima accident, one should note that core shroud replacement is expensive and time-consuming. However, it probably does not increase safety and in that sense, it represents a large diversion of resources from matters of much larger safety significance such as protection against tsunami. Core shroud replacement is essentially unique to Japan and is driven by regulatory requirements that are not risk-informed and to satisfy the need for local technical approval, perhaps to demonstrate attention to safety by making large investments.

The Fukushima site sustained relatively minor damage from the earthquake especially to the buildings and equipment needed to assure safety and protect the public and operators. There was extensive damage in office buildings on the site, not designed to resist large earthquakes, and this demonstrates the effectiveness of the Japanese approach to seismic design used for safety systems and buildings. As a result, the post-earthquake Fukushima site operating status was normal:
  • Units 1-3 were tripped by earthquake sensors and shut down.
  • The earthquake caused a loss of off-site power.
  • Emergency diesels started and supplied power to units 1-6.
  • Safety systems operated normally and units 1-3 began cool-down.
  • Post - earthquake procedures began, personnel mustered at designated locations. With a tsunami expected, precautions began and personnel moved to higher evaluations.
The tsunami struck the Fukushima Daiichi site in several waves, the biggest about 14 meters, and inundated the Fukushima Daiichi site. Even on the land side the plant water levels reached 6 meters or more and extensively damaged the site from both flooding and dynamic effects of the waves.

In particular, the tsunami flooded and disabled the emergency diesel generators and much of the low-lying, unprotected in-plant electric distribution system. The emergency diesel generators were made inoperable for a long period since the tsunami washed away the associated fuel tanks and cooling system. Only the large on-site batteries remained and they had a limited life since there was no ability to recharge them without on-site power. Heroic and clever actions by the operators and staff conserved the batteries so the limited power lasted many hours, even days longer than expected; but power was insufficient to operate all critical equipment. The result was total, extended station blackout (SBO). These conditions further greatly impeded needed operations and despite the heroic efforts, major damage including core melts and major hydrogen explosions occurred and resulted in uncontrolled releases of radioactivity off-site. Units 1-4 were extensively damaged.

As of March 2012, the current conditions at Fukushima Daiichi are that Units 1-4 are severely damaged, probably beyond repair. The plant conditions are stable with cooling systems in operation and temperatures of the reactors and containment are quite low. The major effort is focused on eliminating off-site radiation releases and restoring reasonable working conditions on-site. A restricted access zone around the plant remains in effect and the conditions and schedule for full return of people to work-sites and homes is not yet determined. On-site recovery is progressing slowly as is expected under the conditions remaining after the earthquake, tsunami and resultant core melts and hydrogen explosion’s accidents.

4.Major Lessons

I believe the major lessons to be learned from Fukushima Daiichi are that the accident was an inevitable result of the Japanese approach to regulation and operation of nuclear plants, NOT the inevitable result of nuclear power technology. Japanese nuclear plant operations and safety activity are incorrectly focused at the plant, vendor and regulatory levels. The current Japanese approach must be extensively revised to become risk-informed and operation-based. It must change from the current emphasis on form and passing tests, often meaningless, rather than assessing and assuring safety.
    I can cite many examples; here are three:
    – Tsunami protection design basis.
    – Emergency power system design basis testing.
    – Emergency preparedness and training.
First, the tsunami protection design basis is not risk-informed. Specifically, the design basis wave-height is not based on the historical record (See figure, slide 16 from lecture). The design basis does not call for protection against attendant effects such as flooding for critical equipment. Finally, there is a “cliff-edge” to major damage with no protection if the actual wave exceeds the design basis height.

Note this is very different from the established, effective earthquake design basis which has repeatedly demonstrated the ability to protect safety systems in Japanese nuclear power plants.

Second, the emergency power equipment design basis and testing is flawed. The emergency diesel testing is invalid and misleading as a 100% success rate is required. This makes the testing unrealistic and it does not provide actual data on the performance of the units or issues affecting performance. Further, as can be seen from the previous item and the results of the tsunami at Fukushima, the emergency power system is not protected against the dominant risk, that is, tsunami flooding of the low-lying emergency power supply system. Finally, this issue is not limited to only the electrical systems but to other important systems needed after an emergency such as communications, and the infrastructure to bring needed equipment to the site. This was not addressed in Japanese licensing and safety programs, even though there was an earlier ‘near-miss” event that showed similar effects after the large earthquake near the Kashiwazaki-Kariwa site.

The third example illustrating the need for sweeping changes to the Japanese approach to nuclear plant safety is inadequate emergency preparedness and training. There is essentially no realistic planning and preparation for major accidents. There were no meaningful on-site drills other than personnel evacuations. The chain-of-command authority and responsibility assigned is not consistent with the quick time response required for actions to protect the public and safety systems. Operators are not familiar with the use of safety systems in emergency, off-normal conditions and apparently did not recognize the critical dependence on speedy response to depressurize the reactor containment and inject coolant. Finally, safety systems were not readily usable in off-normal conditions.

5. Strengths and Weaknesses of the Accident Response

The overall weakness in the inadequate emergency preparedness is discussed above. Another major weakness in the accident response was the post - accident distribution of information. The information provided by government and utility authorities was inaccurate, incomplete, disjointed and inconsistent, both off-site and on-site. The on-site communications system was disabled in the accident, significantly impeding needed actions. This resulted in needed actions not being taken in some cases and improper action being taken in other cases. The wide-spread failure of communications resulted in a loss of credibility with the Japanese public and the International Community.

A major strength was prevention of radiation effects despite significant, uncontrolled releases of radiation from the combination of severe fuel damage and hydrogen explosions. There are no health-threatening effects from off-site radiation. No radiation-induced fatalities have occurred, nor are any projected. Good control of food contamination was maintained. Off-site doses are low and continue to fall. Radiation levels off-site are such that there is a scientific basis for allowing the evacuees to return home now.

An important point to note is that the Fukushima events demonstrated the robustness of water-cooled plants to inherently limit off-site radiation releases despite devastating damage.

6. Action to Prevent Recurrence

Based on the author’s understanding of the events at Fukushima, the major lessons learned are:
  • The chain-of-events was not the inevitable result of using nuclear power.
  • The chain-of-events was the inevitable result of the Japanese Safety Approach.
As a result, the key improvements needed are directed at making major changes to the Japanese Safety Approach. Specifically the revised approach must:
  • Assure external events used for design basis at specific sites are truly bounding.
  • Had no effective emergency preparation.
  • Had no effective measures to prevent or mitigate accidents.
So the Japanese public asks: “Why should I trust you to safely operate in the future?”

    My suggestions for the basic features of the sweeping and for-reaching action required are:
  • Clearly assign responsibility for safety to utilities operating the plants.
  • Establish an independent, competent and adequately funded regulator to assure the utilities meet their safety responsibility.
  • Establish a clear chain-of-command for accidents with clearly defined responsibilities at each level, and assure that responsibility is backed up by competence.
  • Bring in full and effective international participation at the outset of developing Japan’s recovery plan.
    However, accomplishing these actions requires overcoming “excuses”. For example:
  • Excuse:
    – This will take a long time, Japanese culture requires we move solely.
  • Response:
    – It is like planting a tree: the best time to plant is long ago, the next best time is now. Moving slowly cannot be used as a basis for doing nothing.
  • Excuse:
    – International input can be obtained at the end of a Japanese–only “Nemawashi” process.
  • Response:
    – Consensus must be built among all participants from the beginning. Further, the international participants bring new ideas and alternate approaches that must be addressed and considered before it is “too late to change”. My personal experience in Japan is that reviews at the end of the consensus building are a waste of time and resources.
  • Excuse:
    – Japanese nuclear plants and operating/safety culture are “different”. Therefore, international norms and best practices do not apply, we must continue to do things the Japanese way.
  • Response:
    – Japanese plants are not different. Further, the Japanese way has been proven to be ineffective in achieving safety and reliable operation. The Japanese must adopt the performance-based, risk-informed approach.

7. Closing Thoughts

Here are the two quotations to carefully consider. The first:

    “Those who cannot remember the past are condemned to repeat it.”
    – George Santayana
And the second is from Albert Einstein:

    “Without changing our pattern of thought, we will not solve the problems we created with our current pattern of thought.”
The horrible remains of the mangled plants at Fukushima Daiichi are the creation of our current pattern of thought. We must change to assure such an accident NEVER HAPPENS AGAIN!