RADSAFE digest 1572 -Reply

[George Cicotte <GCICOTTE@GW.ODH.STATE.OH.US>]

Dear Franz,

I'll include excerpts, based on my best recollection from various trade
publications and bulletins I've seen.  Consider this to be opinion based on
information, and greatly subject to revision/correction:
The article mentioned that "in the JET experiment in 1991 1.8 MW were
created during a few seconds". Can anyone tell me, what really
happened - I think to remember that the time the reaction could be held up
was by orders of magnitude lower. 

The "few seconds" refers to the length of the experiment.  Most of the
1.8 MW would have been produced during several milliseconds, but it
takes a finite and measurable amount of time for power to rise and fall,
even in a fusion experiment.

It was stated in the article, that the TFTR-experiment in 1993 created 6.0
MW. Any information?

I don't know this one at all.

In the article it was mentioned that there was a "low risk" associated
with fusion. If "all of the radiating tritium would be liberated the maximum
radius of danger would be 300 m. As a comparison: During the accident
at Chernobyl in 1986 the radioactive particles were distributed almost
over the whole continent". Does anybody have an idea, where the 300 m
zone might come from? I did not know that tritium would decay that
fast.........

That's not the point.  The "maximum radius of danger" refers to
"dangerous" levels of tritium, which would be determined based on
distance, weather, and source term (H3 inventory at time of
occurrence), and of course on the fact that H3 has a 0.050 MeV beta. 
Also, the term, "dangerous," refers to the intensity of the hazard.  There
was a recent incident in our state of New Jersey where a young student
(who was apparently skipping school, instead of where he was
supposed to be) found an "exit" sign illuminated with about 740 Gbq of
H3.  He broke the chamber open, releasing all the gas, while eating lunch.
 His estimated whole body dose was around 100 uSv (100 mrem).

I quote: "Also fusion creates radioactivity, but far less than the risky
nuclear fission, the technique used in Chernobyl." What I remember is
that the neutrons would give rise to a terrible amount of activation
products, not to talk about the problem of mechanical degradation of the
structure material. Is it possible that the fast neutrons will only produce
very short lived activation products which might not be of concern? 

The term isn't "terrible."  It's "extensive."  Most of the activity IS
short-lived, but the biggest factors are selection of materials resistant to
activation [by virtue of small activation cross-sections], geometry
[happenstance - containment is through magnetic flux, so most of the
neutrons don't escape to activate materials], etc.

Please don't post these to RADSAFE unless you verify them.

Respectfully,

George R. Cicotte
Health Physicist III
Ohio Dept. of Health, Bureau of Radiation Protection
Nuclear Material Safety Section
gcicotte@gw.odh.state.oh.us

DISCLAIMER:  The Governor and I don't agree on evertthing, and this may
be one of those times. . . unofficial unless notified otherwise.