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RE: Pu contact dose rates
Franz,
I'll reply to RADSAFE as well, so that we can close this issue publicly. I
apparently misunderstood your comments, so please accept my apology.
I have perceived that there have often been suggestions on this list that
people are using it as a means of avoiding doing the work themselves. While
this may happen sometimes (which would iritate me too), I don't believe that
to be the normal case. Furthermore, DOE has been the object of many jokes,
and perhaps that has heightened my frustration level. Since I was directly
named in your message, along with my association to DOE, I felt compelled to
respond, although perhaps it was in error.
As for the questions I originally asked, they are for real. As I originally
mentioned, there have been many measurements and calculations published of
contact radiation dose rates for gammas, betas, and low-energy x-rays from
plutonium. However, what I found is that since the alphas are easily
shielded by gloves and the dead layer of skin, the contact alpha dose rates
were apparently not as well documented, because they were not deemed as
important, since they were easily shielded (this is not to be confused with
internal doses, which are well documented, but addressed in a different
manner). The application that I am looking at is one of material damage
resulting from direct exposure to plutonium, either as contamination or as
solid material. While the damage mechanisms from photons and neutrons have
been well studied, the surface damage from alphas are much less well known.
This is important when the material is being used as a sealing surface, such
as polymers used as valve seats. DOE experienced a significant Pu-238
release and subsequent worker uptakes at one of our facilities a couple
years ago, partially due to failure of a valve seat, and I have the task of
recommending an approach for how we will deal with these applications in the
future. I would be happy to forward you a copy of the accident
investigation report, as it may be of interest to you and others.
As it turns out, current research indicates that the damage mechanism is
much different for alphas than for penetrating radiations, and we are still
trying to evaluate the significance of that fact for our facilities. I can
readily calculate the alpha dose rates (technically, what I am looking for
is the energy-deposition rate from alphas in various plastics), but I was
hoping to find a published method or results that I can compare my results
against, to provide a technical basis for a future DOE standard on this
issue. (Note, this research is still in the pre-publication stage, so I'm
sorry that I cannot share all of it at this time.)
There is no scandal here, we do understand plutonium very well. This is a
situation where DOE was bitten by a low probability event that has raised
some questions that were not previously recognized.
I hope this better explains what the original posting was all about, and
again, I apologize if I misunderstood your comments.
Doug Minnema, PhD, CHP
National Nuclear Security Administration, US DOE
<Douglas.Minnema@nnsa.doe.gov>
-----Original Message-----
From: Franz Schoenhofer [mailto:franz.schoenhofer@chello.at]
Sent: Monday, June 17, 2002 5:25 PM
To: Minnema, Douglas; radsafe@list.vanderbilt.edu
Subject: Re: Pu contact dose rates
Doug,
Since you posted to RADSAFE, I post to RADSAFE as well.
-----Ursprüngliche Nachricht-----
Von: Minnema, Douglas <Douglas.Minnema@nnsa.doe.gov>
An: radsafe@list.vanderbilt.edu <radsafe@list.vanderbilt.edu>
Datum: Montag, 17. Juni 2002 20:38
Betreff: RE: Pu contact dose rates
>Franz,
>
>At one time, as I recall, this list server was intended to allow us to ask
>questions of one another in a civilized manner. I was not aware that this
>focus had changed.
If you reread my posting you probably will discover that the main part of my
contribution was, that I did not know, who was posting it. Emil Kerrembaev
posted a nice and humorous comment on my mail, which I really appreciated.
---------------------------------
I will be happy to post my full qualifications, if that
>is necessary in order for you to appreciate that this question has been
well
>researched before it was asked. However, I did not, and still do not feel
>that to be necessary.
-----------------------------------------
What should this be good for?
---------------------------------------
>
>Yes, the DOE is the place for me. Regardless of public opinion, it is
still
>the place where serious questions are raised, researched, and answered, and
>we still have a tremendous pride in our work.
--------------------------------------------------------------------------
Since I am non-American I can hardly be accused that I joined the common
attitude of bashing federal US agencies and departments. I do it in my own
country. Again, please do not tell me, that DOE and associated laboratories
or contractors never have looked into the question of doses from direct
contact with plutonium. I have no idea, how many people have worked during
the last almost 60 years with plutonium in DOE facilities, but I guess there
must have been at least tens of thousands. So please do not tell me and
other RADSAFErs, that no data are available about doses from direct contact
with Pu. If these considerations have not been done, I would regard this as
an incredible scandal.
In the course of the discussion about depleted uranium used in the Gulf war
and in Kosovo, enough knowledge should have been accumulated in order to be
able to draw conclusions for plutonium as well. The alpha-energies are much
to similar. And the DOE has no data available? You are kidding.
>
>Actually, Franz, you would be surprised at the number of questions that
>still exist in both DOE and the rest of the world, simply because
previously
>the answers were not deemed necessary for the work at hand.
If tens of thousands of people have worked with plutonium and even more on
uranium, nuclear fuel, reprocessing etc. then these answers were necessary
and please do not tell me, that these questions were not asked and not
answered.
----------------------------------------------------------------
Now, the nature
>of the work has changed, and the questions need to be re-asked. Such is
the
>case here.
----------------------------------------------------------
Not only at your place. Six years ago I was at Mururoa and we were among
many other sample taking duties looking for hot particles. We isolated one
particle which according to gamma-spectrometry had a Pu-239 activity of more
than 1MBq. I handled it with my hands. Please could you inform me of how
many milliseconds of my life I lost?
------------------------------------------------------------------
But don't worry too much, because in this case some of our
>esteemed RADSAFE colleagues have already offered valuable assistance, and I
>have what I need. To them I am very grateful.
----------------------------------------------------------------------------
---
I do not worry, because I regard the dose from direct contact with Pu-metal
to be ridiculously low, compared with the dose from Rn-222 in indoor air. If
you have reliable answers to your question, please share them with
RADSAFE!!!
This message seems to be typical. Whenever one dares to make a pointed
comment, people, who like in this case are not even be addressed, feel
vulnerated. Why? Is this a follow up of the NY-incident?
Regards,
Franz
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