[ RadSafe ] Tritium contamination
Olsson Mattias :MSO
mso at forsmark.vattenfall.se
Wed Nov 2 03:41:45 CDT 2011
It is exactly how Franz describes it. The concern is not about health, it is about being able to show that materials that are measured for free release are below the limits of free release for the nuclides that are present in the potential contamination. If materials are let out from a nuclear facility after a free release measurement and it then turns out that it was done against government regulations you would certainly have some cause for concern.
There have been several private post about this being a silly problem or of no concern, but I have also got some background information that will allow me to deal with the issue. I thank you all for the commitment and for offering your input! The list has been helpful again. :)
I ask the list because experience on how to build a nuclide vector for free release measurements would be relevant no matter what the limits for free release are. The purpose of the vector is to estimate the relationship between the radioactivities of the nuclides that are expected to be present. In any case (and this has no real bearing on the problem, it's just information for the possibly interested) the regulation I am working against has nuclide specific release limits for a large number of nuclides. The materials that are measured for free release have to be sampled according to a separate paragraph. For example, any form of dilution is not allowed. Not that it matters, but for tritium, the limit that I need to work against for solid materials is 100 Bq/g. That is the name number as is given in the proposed update of the Euratom Basic Safety Standards Directive.
All the best,
Från: radsafe-bounces at health.phys.iit.edu [mailto:radsafe-bounces at health.phys.iit.edu] För franz.schoenhofer at chello.at
Skickat: den 1 november 2011 21:50
Till: Jerry Cohen; The International Radiation Protection (Health Physics) MailingList
Ämne: Re: [ RadSafe ] Tritium contamination
Jerry et al.,
Probably the concern is, what maximum permisible contaminant levels are prescribed by authorities - whether they make sense or not, they have to be fulfilled. Your comment, Jerry, is fully justified, but does not help when it comes to legislation.
I am somewhat surprised that Martin (hej!) asks RADSAFE for advice since he is dealing with a Swedish problem. I would be very surprised if limits and legislation in Sweden would be the same as in the USA. I know to well that US persons tend to assume that their national legislation is applicable and valid all over the world, which it is clearly not!
I have been working in a group of the Austrian Standardisation Institute on decontamination of surfaces. The problem in this tritium case is not to the surface. Anyway I refused to support the groups conclusions, because this is such an unbelievable difficult and complex question that it cannot be easily solved by just a few simple tests, even for common radionuclides. To many parameters!!!! We did not even touch the question of tritium.
---- Jerry Cohen <jjc105 at yahoo.com> schrieb:
> Based upon any credible exposure scenario, Tritium is simply not a
> health threat.
> So, why the concern?
> From: Scott Davidson <bsdnuke at gmail.com>
> To: The International Radiation Protection (Health Physics) Mailing
> <radsafe at health.phys.iit.edu>
> Sent: Mon, October 31, 2011 8:26:21 AM
> Subject: Re: [ RadSafe ] Tritium contamination
> You seem to be on the right track. Unless the material is porous or
> has a particular affinity for tritium, then when it is dry, the
> tritium will be gone.
> Porous is on atomic/molecular level where tritium can permeate the
> material. This would be evident if wipes came up contaminated after
> decontamination (weeping). This was the classic "re-appearium" that
> occurred on casks that were used in spent fuel pools and can occur
> from many radionuclides. The NRC has some old guidance on cask
> Materials with an affinity for tritium include some metals that form
> hydrides and things with hydrogen in them. Some metal hydrides will
> be stable and not release their hydrogen (tritium) readily. But if
> the tritium concentration is high, some exchange will occur and be
> well fixed. Likewise for plastics or other polymers that might
> exchgange a hydrogen for tritium.
> There is a lot of information in chapter 5 of DOE Handbook 1129 a
> portion a different section is shown as "19-26" but I am not sure how
> much you want to make this a science project.
> On Mon, Oct 31, 2011 at 11:03 AM, Olsson Mattias :MSO
> <mso at forsmark.vattenfall.se> wrote:
> > Dear Radsafers,
> > I am playing around with a nuclide vector that I hope to be able to
> > apply for free release measurements. The assumption is that the
> > contamination comes from BWR reactor water, and at least Co-60 is
> > measurable with a gamma detector. I want to use Co-60 as a key
> > nuclide to estimate the amount of a whole array of other nuclides by
> > using the known composition of the activity in reactor water.
> > To set this up is not very difficult, and I also add a function to
> > let the nuclide vector "age" for the cases where it is known that
> > the contamination occured some time ago.
> > The thing is that the free release measurements will be done on dry
> > materials. That means that the tritium, which is fairly abundant in
> > the reactor water, will no longer be there during the measurement. I
> > suppose
> > *some* tritium will be retained on the materials, though. Surfaces are
> > somewhat prone to exchange protons in an aqueous environment, if nothing
> > else. Anyway... What I wonder is if there is any experience on here on
> > how much tritium will stay as contamination on a surface if the surface
> > is first splashed with tritiated water and then allowed to dry. I
> > imagine this would depend on a number of factors (type of surface, ratio
> > between available surface and the amount of tritiated water etc) that
> > would make a general statement hopeless, but if there are any practical
> > examples I would love to hear about them! It could lead me towards a
> > conservative reasonable assumption.
> > All the best,
> > Mattias Olsson, Sweden
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Franz Schoenhofer, PhD, MinRat
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