The following is a reply to an inquiry we received about the accident at the Mihama-3 nuclear reactor, which occurred on the 59th anniversary of the dropping of the atomic bomb on Nagasaki (9 August). We thought that it might be of general use to other readers of our web site.
Dear Reader,
Firstly I would suggest that you keep an eye on our website. I gather that you have already checked it, but just in case, the following page will take you to information about the recent accident at the Mihama-3 nuclear reactor:
http://cnic.jp/english/news/index.html
Secondly, in response to your question about radioactivity, we believe that a small amount of radiation could possibly have leaked out. If so, it would most likely have been in the form of tritium. We would not expect it to have been a large amount, because in Pressurized Water Reactors such as Mihama-3 the secondary coolant system, where the accident occurred, does not pass directly through the reactor itself. Rather there is a primary coolant circuit which passes through the reactor and the heat from this is then transferred to the secondary coolant circuit at a place outside of the reactor itself. This process generates the steam which drives the turbines which produce the electricity.
However there are often small leaks in the primary coolant circuit and the liquid in the secondary circuit can also be made radioactive by neutrons which pass through the pipes. Kansai Electric Power Company says no radiation was recorded on their monitors. We are currently seeking more information about this and other issues.
In Boiling Water Reactors steam is piped directly from the reactor to drive the turbines, so a similar accident would lead to a much larger release of radiation.
The biggest risk in this accident was the possibility of it leading to a Loss of Coolant Accident. In a worst case scenario, if various emergency systems had failed, this could have led to a reactor core meltdown such as occurred in the Three Mile Accident in the US. In the Mihama-3 accident the auxiliary feedwater system operated successfully at the time of the accident, so this nightmare scenario didn't eventuate. However after the situation had been stabilised the auxhiliary feedwater pump was tested once again and on this occasion it failed. There were still other emergency systems available, but since these systems are rarely activated, they are quite prone to failure.
It is when various systems fail simultaneously that the most destructive accidents occur. As much as governments and the nuclear industry might like to deny it, simultaneous failures can and do occur. Over the next few million years that the materials contained in nuclear reactors remain dangerous, who is to guarantee that these materials will not be released into the environment?
I hope this helps you with your research.
Philip White
International Liaison Officer
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