RE: "Hot Particle"

[CHASE John -NUCLEAR <john.chase@ontariopowergeneration.com>]

I gave a presentation at the American Radiation Safety Conference and
Exposition this June in Denver entitled, "VARSKIN Mod 2 - Anomalies and
Remedies." I and three student interns have been working with Jim Durham,
the author of VARSKIN Mod 2, to address a number of problems we have
identified with the code. We are currently testing modifications and hope to
be able issue a beta version in a few weeks. When this is ready, I will post
a note on RADSAFE. I will be able to send out a compiled version and a set
of notes on what the problems are that we have identified with VARSKIN. Jim
has already approached the NRC for funding to make this and other upgrades
to the code.

The particular problem with point and small 2D and 3D disks is that the
numerical integration ignores a central cylinder with a radius of 0.27
microns. The point source and the smallest 2D disks have a radius of 1
micron. The omission of the central cylinder results in the dose rate being
7.3% less than what it would be for a larger 2D disk. A similar problem
results for the 3D disk. Here, however, the smallest 3D disk has a radius of
0.5 microns, and the dose rate is correspondingly underestimated by 29%.
This particular problem can be identified by calculating the dose rate to 1
cm2 for various disk diameters with the same total activity. As long the
disk diameter does not get too close to 0.564 cm (the radius of a 1 cm2
circle), the dose averaged over 1 cm2 should be independent of the source
disk size.

For typical dose calculations normally used to assess dose from skin and
clothing contaminations, the problems are unlikely to cause errors larger
than about 15%. As such, the errors are well within the accuracy tolerance
for typical skin dose calculations. Errors that are larger than 15%, such as
large fluctuations in the results from volume averaging, are easily
recognized.

If anyone needs guidance for a specific case, E-mail or call me.

John Chase
Sr. Specialist, Dosimetry
Health Physics Laboratory Department
Ontario Power Generation
905 430-2215, ext. 3242

	----------
	From:  Gv1@aol.com [SMTP:Gv1@aol.com]
	Sent:  Tuesday, August 08, 2000 2:47 PM
	To:  Multiple recipients of list
	Subject:  Re: "Hot Particle"

	It was mentioned that the code under responds by 7%.  What is this
compared 
	to, measurements, other theoretical codes?  Is there a mathematical
error in 
	the code or do you not feel comfortable with some of the fundamental

	assumptions?  A lot of regulatory related calculations are performed
with 
	this code and it essentially has been approved by the NRC in the
form of a 
	NUREG document...

	Now everyone is in a position where there is question concerning an
industry 
	standard code nobody really knows what is wrong with it.  It sounds
like skin 
	dose calcs will stop for some time.  If there is a real problem, the
code 
	writers definitely need to get into the communication channels with
INPO or 
	the NRC to communicate the need to stop using the codes or issue new

	limitations for the use of the code with nuclear power plants as
well as 
	every other imaginable type of user.  

	Glen Vickers
	Nuclear Power HP
	glen.vickers@ucm.com
	
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