No strong conclusions can yet be drawn on the Fukushima Nuclear Crisis, because so much detail and hard data remains unclear or unavailable. Indeed, it will probably take years to piece the whole of this story together (as has now been done for accidents like TMI and Chernobyl [read this and this from Prof. Bernard Cohen for an absolutely terrific overview]). Still, it will definitely be worth doing this post-event diagnostic, because of the valuable lessons it can teach us. In this spirit, below an associate of mine from the Science Council for Global Initiatives discusses what lessons we’ve learned so far. This is obviously a huge and evolving topic that I look forward to revisiting many times in the coming months…
Guest Post by Dr. William Hannum. Bill worked for more than 40 years in nuclear power development, stretching from design and analysis of the Shippingport reactor to the Integral Fast Reactor. He earned his BA in physics at Princeton and his MS and PhD in nuclear physics at Yale. He has held key management positions with the U. S. Department of Energy (DOE), in reactor physics , reactor safety, and as Deputy Manager of the Idaho Operations Office.
He served as Deputy Director General of the OECD Nuclear Energy Agency, Paris, France; Chairman of the TVA Nuclear Safety Review Boards, and Director of the West Valley (high level nuclear waste processing and D&D) Demonstration Project. Dr. Hannum is a fellow of the American Nuclear Society, and has served as a consultant to the National Academy of Engineering on nuclear proliferation issues. He wrote a popular article for Scientific American on smarter use of nuclear waste, which you can download as a PDF here.
On 11 March 2011, a massive earthquake hit Japan. The six reactors at Fukushima-Dai-ichi suffered ground accelerations somewhat in excess of design specification. It appears that all of the critical plant equipment survived the earthquake without serious damage, and safety systems performed as designed. The following tsunami, however, carried the fuel tanks for the emergency diesels out to sea, and compromised the battery backup systems. All off-site power was lost, and power sufficient operate the pumps that provide cooling of the reactors and the used-fuel pools remained unavailable for over a week. Heroic efforts by the TEPCo operators limited the radiological release. A massive recovery operation will begin as soon as they succeed in restoring the shutdown cooling systems.
It is important to put the consequences of this event in context. This was not a disaster (the earthquake and tsunami were disasters). This was not an accident; the plant experienced a natural event (“Act of God” in insurance parlance) far beyond what it was designed for. Based on the evidence available today, it can be stated with confidence that no one will have suffered any identifiable radiation-related heath effects from this event. A few of the operators may have received a high enough dose of radiation to have a slight statistical increase in their long term risk of developing cancer, but I would place the number at no more than 10 to 50. None of the reports suggest that any person will have received a dose approaching one Sievert, which would imply immediate health effects.
Even ignoring the possibility of hormetic effects, this is approaching the trivial when compared with the impacts of the earthquake and tsunami, where deaths will likely come to well over 20,000. Health impacts from industrial contamination, refinery fires, lack of sanitation, etc., etc. may reasonably be supposed to be in the millions. Even the “psychological” impacts of the Fukushima problems must be seen to pale in contrast to those from the earthquake and tsunami.
The radiological impact on workers is also small relative to the non-radiological injuries suffered by them. One TEPCO crane operator died from injuries sustained during the earthquake. Two TEPCO workers who had been in the turbine building of Unit 4, are missing. At least eleven TEPCO workers were take to hospital because of earthquake-related physical injuries.
TEPCO has suffered a major loss of capital equipment, the value of which is non-trivial even in the context of the earthquake and tsunami devastation. They also face a substantial cost for cleanup of the contamination which has been released from the plants. These are financial costs, not human health and well being matters.
The Sequence of Events
Following the tsunami, the operators had no power for the pumps that circulate the primary coolant to the heat exchangers. The only way to remove the decay heat was to boil the water in the core. After the normal feed water supplies were exhausted, they activated the system to supply sea water to the core, knowing this would render the plant unfit to return to operation. In this way, the reactors were maintained in a relatively stable condition, allowing the water to boil, and releasing the resulting steam to the containment building. Since this is a Boiling Water Reactor (BWR), it is good at boiling water. Operating with the water level 1.7 to 2 meters below the top of the core, they mimicked power operation; the core normally operates at power with the water level well below the top of the core, the top part being cooled by steam. Cold water in, steam out, is a crude but effective means of cooling.