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While I'm satisfied as to the strength and integrity of the
Type B containers used to transport spent nuclear fuel in the UK I'm not
absolutely convinced that a) an accident involving spent fuel containers could
not occur, and b) that this would not result in a release of activity to the
environment. One of the reasons for this is that the largest number of
fuel movements involves MAGNOX fuel. This fuel consists of a rod of
natural Uranium metal encased in a magnesium alloy can. This type of
fuel cladding is not once it has been irradiated and then placed in a
cooling pond. The chemistry of cooling water is very important
to minimise the corrosion of the fuel clad. In addition the
corrosion products themselves increase the rate of corrosion of the MAGNOX
cladding. The end result is that once these fuel elements have been
discharged to the cooling pond they begin to degrade. This is the
primary reason why reprocessing must continue in the UK at least until all
the Magnox reactors have ceased operation and all spent fuel has been
reprocessed. Returning to the issue, this results in the
operators wishing to retain spent fuel for as short a time as
possible. The minimum period that Magnox fuel can be transferred for
reprocessing is 90 days this is to ensure that high levels of radioiodines are
not released at Sellafield during the de-canning process. While very
little fuel is transferred this quickly, the fuel is unlikely to remain at the
power plant for the several years that you mentioned. In addition to
this the fuel remains inside the reactor for long periods of time, at the Magnox
power plant that I worked at the fuel would remain in the reactor for
approximately 7 years this results in greater amounts of Pu, Am and Cm in
the fuel than would occur in a typical 3 x 12 month PWR operating
cycle. Another important issue is that natural Uranium metal
undergoes a phase change at a relatively low (compared to PWR fuel)
temperature. The best guess that I can recall is about 600 to 700 deg.
centigrade. During this phase change the metal swells
and the clad will rupture. In addition the Magnox cladding will
ignite at lower temperatures than Zircalloy. A Magnox fire is
also very aggressive and cannot be extinguished with water of other normal fire
fighting methods as the fire can utilise the oxygen present in water
etc. Special fire fighting products such as Graphex have to
used. All of the above would appear to paint a much bleaker picture than I
intended, however as I haven't been involved in a safety cases for these types
of movements I don't know whether they fall into the "outlandish scenarios" that
you indicated or not. I certainly feel that the transport of PWR fuel that
has been stored for long periods prior to transport which uranium dioxide
ceramic pellets and zircalloy clad will have am much theoretical risk of a
radiological release than Magnox fuel.
What impressed me the most about the GLA report was the
approach that if there was a credible accident scenario then there were
improvements that should be made to the emergency arrangements and the training
of the emergency service personnel and not a, we cannot accept this here and we
must rouse the population of London to prevent these movements approach. I
would say that I did not agree with all that was said in the report, but that I
could see where the authors were coming from and that their responses were both
reasoned and reasonable.
I am certainly in agreement with you that the nuclear industry
has to be realistic when undertaking its safety assessments. I
would suggest that most individuals on this list have probably come across
assessments where a number of unlikely events have been strung together to
create a significant event which can't be any means be described as
credible. Sometimes these seem to be driven by an industry desire to
demonstrate that it is doing everything possible to prevent event the most
"incredible" event. On other occasions they seem to be driven by the
regulator who wishes to be seen to do everything possible to safeguard the
public. Neither of which succeed, because as you lend credence to ever
more unlikely events those opposed to the nuclear industry will then add some
other unassessed risk in an attempt to discredit the industry.
The focus for the industry these days seems to be on finding
the ideal way of explaining relative risks to the public. Unfortunately
although I accept and support this work and do everything I can when discussing
these issues with those outside the industry to put these risks into
context, there are days when I feel that it makes little difference. For
the majority of the public as long nuclear power is cheap and efficient doesn't
have a significant incident (with or without any consequential release of
activity) and most importantly is nowhere near them it is not a significant
issue. This is why the nuclear industry is in an industrial equivalent of
the doldrums. Even if we succeed in educating the general public about the
actual risks of nuclear power and how they compare with other risks they
encounter in everyday life we will only move from being an industry where the
status quo is tolerated to one where everyone thinks it is a good idea as long
as we don't have one built near us. This is the same status as wind
turbines and mobile phone masts (cell phone antenna?).
Now having thoroughly depressed myself I'm going to do
something else instead.
regards
Julian
Ginniver
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