March 24, 2011

ongoing rapid reaction – Fukushima nuclear incident

Further comments on the nuclear emergency in Japan.

Prof Richard Wakeford, Dalton Nuclear Institute and Visiting Professor in Epidemiology, University of Manchester said:

“There seems to be some confusion in the media about radioactive contamination. The below may assist and you can use as you see fit.

“The radioactive iodine and caesium that have been found in environmental media near the Fukushima site were produced when the three reactors were operating (i.e. before the reactors were automatically shut down at the time of the earthquake). Once the reactors shut down, production of these radioactive elements stopped.  This is important for radioactive iodine-131, which has a half-life of 8 days (over half of the iodine-131 originally present in the three reactors at the time of the earthquake has now decayed away), and iodine-131 is the most important consideration for radiological protection in the short-term because of its concentration in the thyroid gland. So, in around three months, the iodine-131 will be gone because it has decayed away, and it is not a long-term problem. It is radioactive caesium that is likely to be the main consideration in the long-term because caesium-134 has a half-life of 2 years while caesium-137 has a half-life of 30 years – it is caesium-137 that remains the principal concern around Chernobyl (and even in some parts of upland Britain). It will largely be the levels of radioactive caesium around Fukushima that will determine what restrictions (e.g. food bans) need to be kept in place.”

Prof Steve Jones, independent nuclear and environmental consultant, said:

“Much more technical information is now coming forward on levels of radioactivity in Japan. This includes radiation dose rate measurements, measurements of radioactivity deposition, and simulations of the movement of radioactive plumes from national institutes in Canada, Austria, and France. The effects on the Japanese mainland appear to be greater than those that resulted in the UK from the 1957 Windscale Pile Fire, but much lower than those in the Ukraine following the Chernobyl accident. However the plume simulations indicate that much of the radioactivity was dispersed over the Pacific Ocean and, but for that, the effects may have been much greater. It is likely that there is some continuing release of radioactivity from the Fukushima reactors, albeit probably at a lower rate than that which has occurred already.”

Dr Jim Smith, Reader in Environmental Physics at the University of Portsmouth said:

“The U.S. DoE aerial monitoring survey carried out 17-19 March is a very important development in helping us begin to determine the magnitude and consequences of radionuclide releases from Fukushima. It seems from these data that radiation dose rates in a relatively narrow area of land extending about 15 miles (25 km) to the northwest of the plant are above 12.5 mR/hr (equivalent to 125 uSv/h for beta/gamma radiation). Importantly, no dose rates are reported above 30 mR/hr (300 uSv/h for beta/gamma radiation).

“I am relieved to see the results of this initial monitoring. The external dose rates measured imply that the deposition of radionuclides to land around Fukushima, in the early phase of the accident, was very much lower than the levels seen shortly after Chernobyl. The external dose rates observed are, however, high enough to cause significant doses to people occupying these areas for extended periods of time. The recent results from the IAEA/Japanese monitoring teams, also showed some areas (not covered in this aerial survey) of relatively high dose rate at greater than 58 km from the plant. I would expect that any areas above 125 uSv/h radiation dose would likely require temporary evacuation of the population. The length of time these areas will remain contaminated depends on the radionuclide composition: if a significant proportion is radiocaesium, food bans and, potentially, evacuation may be long-term.”