Re: Skin Dose Assessment from Whole Body Contamination Meters

[Mike Lantz <mlantz33@cybertrails.com>]

As Tosh said (thanks Tosh), I wrote a paper in 1991
in Radiation Protection Management (Nov/Dec 91) that details a simple process
for the determination of skin dose from noble gases.  It does not
rely on the measurement of gas concentrations in the area and timekeeping
- we found that to be notoriously problematic.  Often, we'd find people
encountering much higher concentrations of gas than the samples indicated
(and therefore incurring higher doses than calculated) because they were
close to leaks or at the opening of systems (Pressurizer, Steam Generators,
pressurizer safetys) - significant puffs.  Representative samples
are extremely difficult to obtain in this case.  Or we'd find the
tracking to be very poor (too high) as for example when a tech would be
going in and out of containment, or a worker signing in and waiting outside.

With some analysis of "tons" of data, I discovered a simple, but effective relationship between the retention of noble gases in body fat and the cumulative exposure to the cloud, and therefore, the skin dose.  I described it in several meetings as the first time an internal measurement could be used to determine an external dose!   As Stu Bland suggested, the retention of gases are complex - but we see that complexity only early on - as noted when people reach that contamination monitors and could set off the friskers with their breath (early, quick release through the lungs).  After an hour or so, I found that Xe-133 (and the others should follow similar pathways) was retained at approximately 0.3%, or the simple number - 100 nCi per mrad of beta skin dose.  This would be corrected with a 6 hour half-life after that.  Lots of data available, and an interesting evaluator of body fat (friends, who ten years ago, were below the 100 nCi/mrad model when they rode bikes all the time who have now aged like me with a little spare tire - and match well).

We just reanalyzed this in our previous outage and it worked to a tee after a noble gas release into containment.  But additionally this time, I had the excitement of seeing confirmation of the information that I had written about.  With our new PCM-2's that show clearly (with a body map) where the activity was, ALL of the activity was in body fat - almost nothing in the legs, head or arms.  That was wonderful to see because even today I get some strange looks when I say that the monitor alarm is caused by 80 keV photons being emitted from inside the person, and not beta contamination on the outside.

Well, I hope this helps.  If anyone wants a copy, I can send it to them.  As advertisement, I will have this process as part of my 8-hr AAHP class at the Midyear and we can talk about it more.

Mike Lantz, CHP
Palo Verde Nuclear Generating Station
623 393 5200

Tosh Ushino wrote:

John,

San Onofre Nuclear Generating Station (SONGS) has been using whole-body counter
result to calculate skin dose from noble gas for several years. It is based on
the paper in Radiation Protection Management written by Mike Lantz et. al. of
Palo Verde.

I'd suggest you contact someone at Health Physics Engineering at SONGS or Mike
Lantz at Palo Verde for the procedure. Depending on your particular situation or
the type of whole-body counter you use, you will probably have to develop your
own site-specific conversion factor.

Good luck!
Tosh Ushino
--------------------------------------------------------------------------
Toshihide "Tosh" Ushino, CHP                  Tel: (800) 548-5100 x2413
Product Development Manager                   Fax: (714) 668-3149
Dosimetry Div., ICN Biomedicals, Inc.         Email:  tushino@icnpharm.com
3300 Hyland Ave., Costa Mesa, CA  USA 92626           tushino@hotmail.com

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