# [ RadSafe ] Stack Emission Limits - Clarification

Wesley wesvanpelt at verizon.net
Tue Feb 13 10:58:05 CST 2007

```Barbara,

Thanks for your several updates to the stack emission limit discussion. As

Indeed, your example shows that even for a very short release time (1
minute) the annual average concentration is the critical calculation.

Your calculation indicates that, at an annual average concentration at the
air effluent concentration limit, the dose is 50 mrem. This is exactly the
dose that the NRC Part 20, Appendix B, Table 2 values are calculated to
give.

The ability to average over a year is based on the "0.1 rem in a year" dose
limit in 20.1301 for members of the public.

And I want to be very clear on how one can physically achieve the annual
average when there is only a very short emission time during the year.
Consider the radionuclide concentration at the exit point of a stack or
duct. If there is no radionuclide emission, the concentration is ZERO
whether there is a volume flow of air or not. Thus, one can turn off the
exhaust fan for 364 days if the radionuclide emission is confined to less
than one day.

Thanks for listening.

Best regards,
Wes
Wesley R. Van Pelt, PhD, CIH, CHP
Wesley R. Van Pelt Associates, Inc.

-----Original Message-----
Of BLHamrick at aol.com
Sent: Saturday, February 10, 2007 3:32 PM
Subject: [ RadSafe ] Stack Emission Limits - Clarification

To all,

A kind, brave soul pointed out that in my earlier message, I had relied on
the wrong ALI for Cs-137.  I kept thinking something was wrong, and
re-checked
the math, but never went back to the source.  I had pulled out  the
ingestion
ALI, not the inhalation ALI.

So (recognizing the limitations of converting ALI's to dose), indeed you
cannot meet the time-averaged annual concentration limit in 10 CFR 20,
Appendix
B and exceed a 100 millirem dose to a member of the public:

(2E-4 uCi/ml x 1 min) + (0 uCi/ml x 525,599 min)]/525,600 min (per  year) =

3.8E-10 uCi/ml, which exceeds  the 10 CFR 20, Appendix B  effluent limit for

Cs-137 (which is 2 E-10 uCi/ml).

Now that I think about it, Otto's question may have been more along the
lines of this:

Say, I release 2E-4 uCi/ml x 1 min, at an exhaust rate of V/min, so I
release 2E-4 x V uCi total.  Then, I run my exhaust the rest of the year
with no
releases at a rate of U/min, such that the final "annual" concentration  is:

(2E-4 x V)/[(V x 1 min) + (U x 525,599 min) < 2E-10 uCi/ml, which will  be
true if my ratio of U/V is high enough.

I thought there was language in the regulations about using the
"time-averaged" annual concentration, but I can't seem to find it.   That
would prevent
the "bulk" averaging of total activity over total air volume  that would
result
in Otto's original point.

Thanks for listening.

Barbara L. Hamrick

```