Friday, July 15, 2011

Post-Fukushima Findings:

The Origins of the Problem begin to Emerge

Ground zero: Bulldozers (top) take the top off a 35-meter bluff to prepare the site for the Fukushima No. 1 nuclear plant in the late 1960s in this image taken from the documentary "Reimei" ("Dawn"). Left: The construction site is seen after the leveling work. Right: An excavated area where the emergency diesel generators were installed is seen at the construction site.
Tokyo Electric Power Co. via Japan Times

Until now, our understanding of the Fukushima accident has been focused on information that was immediately available in its aftermath--the size of the earthquake and subsequent tsunami, the location of the emergency diesel generators, the loss of all onsite and offsite power, etc.

Recently, some new information has begun to emerge, information that may further inform what else needs to be examined at other nuclear power plants, especially in Japan, and what safeguards need to be put in place for the future.

One Japan Times article points to the huge irony that Fukushima Dai-ichi was built on a hill that had been cut down in an effort to make the plant more secure against earthquakes! It is a well accepted practice in earthquake areas to anchor building structures in bedrock in order to increase the stability of the building in case of a severe earthquake. Coupled with the facts that have already come out about how the potential magnitude of the maximum possible tsunami was grossly underestimated, it probably seemed like a reasonable engineering tradeoff at the time. And the subsequent cost tradeoffs also seem rational in that light. Although we cannot know for certain today what damage the plant might have suffered from the earthquake had it not been built in the bedrock, clearly, the decision to level the hill exacerbated the effects of the tsunami.

Like many others, I'm still puzzled that there was not earlier recognition of the earlier large tsunami in that region of the country, but I am not a seismologist, and only know by what I've been reading when and how such information was understood.

A second Japan Times article indicates that the decision on where to place the diesel generators was made by GE, and that some TEPCO engineers are now saying that they had concerns about this decision but that it was the long-standing policy at Japanese utilities (pre-dating nuclear power) not to make alterations to imported designs. What is not clear yet is if anyone at TEPCO or the regulatory authority at the time voiced these concerns.

Surely, this is the first of a lot more of the history of the design and construction of the Fukushima plant that will emerge in coming months. I hope that the outcome will not degenerate into finger pointing. The damage has been done. What is needed now is to learn from it so that no similar events ever happen again anywhere in the world.


1 comment:

  1. As with almost all major disasters, it is usually a combination or chain of events that result in catastrophe. In hindsight (only!) one can say that, if any one link in the chain of circumstances hadn't happened, then the consequences would have been avoided or greatly lessened. The same I would submit is true at Fukushima. It wasn't a single decision that ended up in the mess that exists today. Yes it is true that the hill was shaved, but that is only on link in the chain. Yes it is true that the DC batteries and the generators were located in the basement, but each of these is also just one link in the chain. There are critical additional links not mentioned in the articles.

    First, it is my understanding that the electrical panels were also located in the basement and were also flooded with seawater. That made restoring power with generators brought in after the tsunami almost impossible as seawater and electrical panels with very high voltages are a deadly combination.

    However, even if the hill hadn't been shaved so much and the generators, dc batteries and electrical panels hadn't been flooded, the disaster would have happened anyway, because of two other critical links. First are the seaside pumps mentioned in the article. Some genius decided to put in water-cooled generators, so when the tsunami came in, the seaside pumps were taken out and, not only was cooling water for the primary reactor cooling circuits cut off, but it is my understanding that water to cool the generators was also cut off. IIRC, there was only one of 12 or so generators that was air-cooled and it I believe was the one that saved units 5 and 6, which IIRC were also a few meters higher than units 1 to 4.

    Second, Fukushima Dai-Ichi (Fuku I) was connected to grid power through a conventional above-ground power line. TEPCO owned apparently one and only one transmission tower of the many that carried the power line. Unfortunately, this single trasmission tower was taken out by a landslide caused by the earthquake. The final and deadly link.

    It is my understanding that Fukushima Dai-Ni (Fuku II) also suffered many of the same failures as Fuku I, but it apparently was built a little higher up. Second, although it IIRC lost its seaside pumps and its generators and its electrical panels were also flooded, I am not sure but they may have had a second set of panels above the flood level. Most importantly, however, it never lost grid power. You may remember that there was a 10 km evacuation around Fuku II also, because it came very close to disaster as well, but the 10 km zone around Fuku II was almost entirely within the 20 km zone around Fuku I.