[ RadSafe ] Iodine Chemistry of nuclear reactors in emergency cases

[Franz Schönhofer]

Dan et al.,

I never thought that I would use again all the vast knowledge I had to
acquire during the Chernobyl accident and its aftermath not only in Austria
but also in practically all of Europe. I have refrained from weighing in on
the discussions going on on RADSAFE, because most of the postings are
citations of - very often - dubious sources, mere speculations and hear-say.
This is also associated with the fact, that obviously some RADSAFErs,
especially those who send mails with four and five letter words to my
private e-mail address, do not appreciate a non-US-citizen, even more living
outside the USA, to have some knowledge about those relevant facts. (I hope
I will not again be "monitored" because of this comment.)

Now let us go to the facts about iodine: 

Being a chemist originally I can tell all of you, that "iodine" may be
emitted during normal operation and of course even more during an emergency
in several chemical ways. Unfortunately it has become common in
environmental surveillance to neglect the chemical forms of radionuclides.
So people put their samples (filters, water, precipitation etc.) on their
Germanium detectors and measure ("iodine"), some even go so far to
distinguish between I-131 and I-132. For the dose estimation and the
contamination of food, water, as well as the transfer etc. the chemical
speciation would be of importance. 

One of the chemical speciations is "volatile" iodine, which simply is
molecular iodine, chemically characterized as I2 (two atoms form a
molecule). This is actually very volatile and if I want to smell iodine I
only need to open a semi antique powderflask with elemental iodine - it does
not boil at ambient pressure, but sublimates, which means it transfers from
solid phase directly to gaseous phase. In fact I need not open the flask,
only the glass window to the cupboard where I store it, because it is so
easily volatile.

Two other ones are the ionic forms of iodide I- and less frequently
occurring iodate IO3-. Those are less volatile, but occur in a nuclear
reactor.

On the long term the organic species like methyl iodide will be formed and
they have a very different impact on the ecosystem.

The ratio of these species is reactor specific and very significant. Studies
exist for BWR, PWR etc. since decades. 

Molecular iodine will be mostly transported as a gas (like the rare gases),
iodide and iodate will be carried exclusively by aerosols. This might
already give you a coarse information about the different ways "iodine"
impacts.

As for your questions: Molecular Iodine might be effectively removed from
water by boiling, because it is volatile. My guess is that it will be for
the most part already have been converted to iodide. The ionic Iodide cannot
be removed by physical methods like boiling. 

Your second question is also easy to answer: Any additional stable iodide
(not molecular iodine!) uptake will help to block the thyroid. BUT!!!! The
amount of iodide to be used in an emergency case is very well investigated
and has been optimized. There are a lot of caveats in taking "iodine"
prophylaxis: First of all it is potassium iodide (remember that potassium is
radioactive......), secondly some people are allergic to iodine and this
might result in shocks, thirdly the age of people plays a big role. In
Europe (or at least in Austria), people above a certain age (I do not
remember because I am without doubt above this age limit) are sincerely
discouraged to take KI - first of all because of the higher sensitivity to
iodine. Secondly I know I am very nasty and political incorrect, but their
chance to develop thyroid cancer and die from it is rather small, because
they might die before of other natural reasons......

There have been fierce discussions in the past about adding iodine to table
salt. This addition was not to protect people from radioactive fallout, but
to protect them from goiter (struma). Since the iodine concentration in
natural water supplies varies so much within very small areas, the
individual dosage would be impossible to establish. So this is probably not
a good idea... Think of the still ongoing discussion about fluorination of
drinking water. And if you happen to know this very great and very old film
"How I learnt to love the bomb" with the great Peter Sellers, you will know,
that fluorination might lead to the nuclear destruction of this world!

I am open for any questions and any discussion and would appreciate them.

Best regards,

Franz



Franz Schoenhofer, PhD
MinRat i.R.
Habicherg. 31/7
A-1160 Wien/Vienna
AUSTRIA


-----Ursprüngliche Nachricht-----
Von: radsafe-bounces at health.phys.iit.edu
[mailto:radsafe-bounces at health.phys.iit.edu] Im Auftrag von Dan W McCarn
Gesendet: Mittwoch, 23. März 2011 21:18
An: 'The International Radiation Protection (Health Physics) MailingList'
Betreff: [ RadSafe ] Iodine Chemistry & Geochemistry

Dear Group:

I have been going through the geochemistry of iodine for the last couple of
hours, but cannot find a couple of items.  When I cook with iodized salt, I
notice that I can easily smell the iodine released in the boiling water.  

Likewise, iodine preferentially partitions from seawater over Cl and I can
smell the iodine from seawater for miles.  Groppel and Anke (1986) note that
the iodine concentration of crops and grasses was influenced by distance
from the sea.