RE: Absence of radionuclides

[Robert_A_Jones@RL.gov]

MDC is not the lowest amount you can detect.  I believe that you want to
use the DL (decision level) value for this - it essentially is the level
at which you can distinguish measurements above background.  You should
not report "<MDC" as equivalent to radionuclide free.  Your MDC does
have to be equal to or less than the limits in whatever table you use.
Beyond this, a measurement less than MDC or MDA does not mean that you
have demonstrated the absence of radionuclides.  This is done, in part
by the DL (it is the 5% false positive calculation - I am not
remembering the other names for it).

  Robert A. Jones		Robert_A_Jones@rl.gov
Health Physicist 			phone: (509)376-8528
PFP Radiological Control 		fax: (509)373-4274
Hanford, WA				Hanford Pager: 85-6559 


	-----Original Message-----
	From:	The Turners [SMTP:dwturners@earthlink.net]
	Sent:	Tuesday, June 30, 1998 9:24 PM
	To:	Multiple recipients of list
	Subject:	Re: Absence of radionuclides

	Hi Claude,
	For nuclear power plants many of the licensee's use the minimum
detectable
	concentration values in their Offsite Dose Calculation Manual to
	demonstrate a specific isotope is "not present".  This allows
establishing
	a counting time for the specified percent uncertainty.
Procedures or
	Technical specifications at older reactors sometimes designate a
specific
	gross activity such as less than 100 ccpm with a thin window GM
or
	equivalent as "no detectable activity".

	Doug Turner <dwturners@earthlink.net>

	At 11:36 AM 6/30/98 -0500, you wrote:
	>The old 10CFR20 had a method in Appendix B to determine the
absence of any
	>radionuclides in a mixture.  If each 'absent' radionuclide was
less than
	10% of
	>it's MPC and the sum ratio of 'absent' radionuclides to their
respective MPCs
	>were less than 25%, than those radionuclides were absent from
the mixture.
	 The
	>new Part 20 requires that the absence of the radionuclides be
demonstrated. 
	>These appears to be another case of "if it's detectable, it's
there."
	Have any
	>NRC licensees had to 'demonstrate' the absence of radionuclides
in a
	mixture? 
	>If so, how?
	>
	>Claude Flory
	>Northeast Utilities
	>floryca@gwsmtp.nu.com   
	>
	>