Lessons Learned from Fukushima: part I – the Technical

I’ve spent some time over the last few weeks talking about “lessons learned from Fukushima” to several different audiences. There are many different ways to look at this event and many different “lessons” that are to be taught. However, I think it is useful to consider those lessons in about three different general classes.

1)     Technical Lessons

These are internal lessons about what equipment or systems worked in what ways at the plant. There are some very specific lessons that all nuclear facilities should be looking at and learning from

2)   Corporate Lessons

Corporate lessons are the business responses that TEPCO had to the event. These are also internal to companies that are managing nuclear facilities, but could be learned by any corporation operating large industrial facilities.

3)   Political Lessons

It is always hard to take lessons at the political level, but understanding how the interactions between corporations, regulators, and government, both nationally and globally worked is critical in improving emergency response.

Each should be examined for what worked, what didn’t, and why. In the next three weeks, we will examine each. Whether or not people have died in this event, the terrible toll being paid by the evacuated people and the workers at the plant site and the immense cost of response require that we look at what happened and try to determine ways to prevent it from happening ever again.

Technical

Let’s look at things in the order of occurrence, as a sort of step through the defense-in-depth features of these plants.

1)     Natural disasters

The specific events (earthquake and tsunami) shouldn’t be the question. I have had a number of people asking me if they should be worried about the plants in their neighborhood (like Iowa or North Carolina). My stock answer has been “If you have a 9.0 subsidence earthquake and a 15 meter tsunami in Iowa, we have WAY more to worry about than the nuclear facility.” In other words, we need to look at each facility site and understand the risks and potentials for natural and man-made disasters at that facility.

In the U.S. this is an ongoing effort. Every time something happens through the INPO reporting systems and the NRC assessments, the entire industry looks at each facility and assesses any lessons learned or changes that need to be made.However, it is clear that we need to remain vigilant against complacency while balancing cost vs. risk assessments of these potentials.

2)   Long term Station Blackout (SBO)

Generally two issues stand out. Either the possibility of common cause failure needs to be eliminated, or the facility needs to be able to manage for a longer period before regaining power. The inherent issue here is how long is long enough and the fact that batteries aren’t really a practical option for driving pump power.

3)   Ultimate Heat Sink

The underlying issue of SBO is one of maintaining the ultimate heat sink during those early critical hours when the decay heat in the reactor is significant and can cause major fuel failure. Loss of the heat sink is the ultimate reason for the catastrophic failure of the fuel in core. Whether a solution separate from the SBO issues is required isn’t clear, but the issue is one to consider.

4)   Spent Fuel Pools

The issues with the spent fuel pools are still evolving. Claims made internationally regarding the status of the pools in the early days of the event have been clearly proven false. However, at a minimum these pools represented a significant diversion of resources for TEPCO that could have been better spent elsewhere.

5)    Hydrogen

aside: I’ve been told that many believe that hydrogen explosion to be like a hydrogen bomb. That is not the case. The explosion we’re talking about here is that of hydrogen and oxygen recombining rather violently to make water. It is the same mechanism that caused the explosion of the Challenger Shuttle in the 1980’s :end aside.

Much speculation has been made as to the sources of the hydrogen that caused the explosions in units 1, 3, and 4. The only thing we KNOW at this point is that the unit 4 pool was NOT the source of the hydrogen in that explosion. I explained this in more detail in a prior entry (Nuclear Power and the Witch Hunt). Given everything else, it is reasonable to assume that the hydrogen came from the zirconium cladding inside the reactor cores of units 1, 2, and 3.

How that hydrogen migrated to places where it could freely combine with oxygen is not understood at this point. Having that knowledge is absolutely necessary to determine appropriate mitigation. Until that is understood, comments about hydrogen recombiners or hardened vents or other issues and or solutions are mere speculation and do not serve to improve plant safety.

We can go on forever in considering possible technical issues and actions to prevent or mitigate them. As this event stabilizes and more time can be given to expert review of the equipment and events, knowledge will be gained. That knowledge will be used to make plants in the US safer and more secure.

Next week, corporate lessons learned.