March 18, 2011

ongoing rapid reaction – Fukushima nuclear incident

Further reaction to the situation at the nuclear power plant in Fukushima, Japan.

Tony Ennis, Fellow of the Institution of Chemical Engineers and independent environmental safety consultant, said:

“There are several key factors in the dispersion.  If the vertical velocity of the plume is low then it would tend to stay near the ground.  If the vertical velocity is high then particles may get pulled into the jetstream and travel large distances.  Generally, the heavier particles will fall to ground near the plant whilst the micron-sized ones will tend to travel further.

“Also, whilst the reactor core remains stable and the containment intact, then most of the radioactivity will be released with the steam being vented. This will probably by Iodine, Caesium and Argon.  Since Argon is a gas, this will disperse easily. Iodine 125 has a half-life of 59 days and hence is only a problem in the short term.  Caesium has a half-life of 30 years and is obviously more of an issue.

“A serious release could occur if:

1.  There is a reactor meltdown & loss of containment (Chernobyl scenario).  This may result in a fire of the reactor core fire in which case the heat released would carry particles up in the fire plume and these particles would potentially be carried for long distances.

2.  The fuel rod storage tanks lose water in which case the rods will overheat.  The Zirconium alloy melts at ~1200°C and this could result in a meltdown of the rods within the cooling tank.  This could result in very high temperatures and a nuclear reaction within the tanks.  This would result in a lot of radioactivity being released.  If there is also a fire or there is a lot of heat from the reaction then again, particles may be carried very high into the atmosphere.

“In terms of winds, a low wind speed would result in high concentrations of radioactive fallout close to the reactors, whilst high winds would dilute the plume but spread it over a larger area.  Rain would tend to scrub the radioactive particles out of the plume and bring them down to ground with the raindrops.”

Prof Paddy Regan, Professor of Nuclear Physics at the University of Surrey, said:

“There have been a lot of questions about the amount of radioactivity that those working at the nuclear plant are being exposed to and the effects of this exposure on those individuals.  We know they are not being exposed to over 20 Sv of whole body gamma-ray dose because they would collapse due a breakdown of the central nervous system; if they were exposed to more than 1-2 Sv whole body gamma-ray dose they would be too sick to work.

“Reports say that on site workers are being exposed to up to 250 mSv (=0.25 Sv) of total additional radiation.  Assuming this refers to ‘whole body gamma-ray dose’, the most recent International Commission on Radiological Protection (ICRP) report, ICRP 103, suggests that this dose of radiation would constitute an increase in cancer risk over a lifetime of approximately 1% (one per cent).  In the average population, risk of a terminal cancer over a lifetime is about 25%, so the additional risk of getting a cancer induced from this level of radiation exposure would be expected to increase by around 1%.”

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

“There seem to be some erroneous perceptions about the Fukushima emergency workers. This brief note may help.

“Comparisons have been made between the emergency workers at Fukushima and those at Chernobyl, 28 of whom died of the immediate effects of high levels of exposure to radiation (doses of several thousand millisieverts). The radiation doses received by the heroic emergency workers at Fukushima are being carefully monitored by specialist radiation protection staff – usually to a cumulative dose limit of 100 millisieverts, but under these conditions probably to a limit of 250 millisieverts.  These limits, although higher than would normally be permitted in the workplace (20 millisieverts per year) will prevent any serious early health effects (e.g. radiation sickness) in the workers.  Late effects, primarily cancer, will also be controlled by these emergency dose limits – a worker receiving a dose of 100 millisieverts from these emergency operations will have a future risk of a serious cancer from this dose of less than 1%, which compares to a background risk of cancer mortality in the absence of this radiation exposure of around 20-25%.”

NB. Sv = sieverts, mSv = millisieverts