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RE: "Hot Particle"

Mr. Chase

I was perusing some old e-mail messages that I had set aside for later view
and came across your message regarding a VARSKIN  revision.  

Would it be possible to obtain a copy of your presentation ?

Also, would it be possible to obtain a copy of the program, when available ?

Thank you for your time and consideration.

Ron LaVera
Lavera.r@nypa.gov

		-----Original Message-----
		From:	CHASE John -NUCLEAR
[mailto:john.chase@ontariopowergeneration.com]
		Sent:	Wednesday, August 09, 2000 5:39 PM
		To:	Multiple recipients of list
		Subject:	RE: "Hot Particle"

		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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information can be accessed at http://www.ehs.uiuc.edu/~rad/radsafe.html