NUREG-1400 Release Fractions -Reply

[Stephen McGuire <SAM2@nrc.gov>]

It has been almost 3 weeks since the questions was posted, but perhaps an answer is
better late than never.

The question concerned the release fractions and intake fractions in NUREG-1140
and NUREG-1400 and how they relate to Brodsky's magic number of 10-6.

First note that NUREG-1140 considers dose outside a building having an accident and
NUREG-1400 deals with worker doses inside abuilding.

Brodsky's 10-6 for outside a building is based on meteorological considerations.  He
proposed that no one outside of a building would be likely to have an intake exceeding
10-6 of the material released.  NUREG-1140 evaluated that, found it to be a valid
assumption, build further upon it, and then added a release fraction to determine how
much might become airborne.  Sorensen referenced the DRAFT NUREG-1140.  The
final NUREG-1140 (January 1988) explained the release fractions in much greater
detail than the draft.

For worker dose inside buildings, Brodsky also found 10-6 to be a valid fraction. 
However, the measurements supporting the conclusion were based on iodine, which is
very volatile.  He provided no data on non-volative materials.  NUREG-1400 expanded
the Brodsky proposal to non-volatiles.  Considering that there are similarities in the
mechanisms of how materials are suspended and become airborne in both accidents
and in workplace activities, it is reasonable that the airborne fractions should not be
totally dissimilar.  This was supported by some other data including a thesis by Scott
Pennington at Georgetown Univeristy, who looked at uranium processing and found
that a fraction of 10-9 provided a good fit with the data (10-6 x 0.001). 

I hope this is useful.

Stephen McGuire, sam2@nrc.gov

>>> "Sorensen, Scott" <ssorensen@doeal.gov> 01/06/98 12:06pm >>>
Greetings!

NUREG-1400, Air Sampling in the Workplace (Sept. 1993), adopts the use
of Allen Brodsky's "Magic Number" of 1e-6 in its methodology for
evaluating potential annual intake from airborne hazards.  However, the
"Magic Number" is then modified by release fractions from NUREG-1140, A
Regulatory Analysis on Emergency Preparedness for Fuel Cycle and Other
Radioactive Material Licensees (June 1985).  These release fractions are
based on "severe facility fire" scenarios.  NUREG-1400  states that
their use is "generally suitable for releases to air in the workplace."

Does anyone know what is the basis behind this statement?  It appears to
me that the NUREG-1140 release fractions were intended to be used in
accident analyses without modification by the Magic Number.  As such,
why is it appropriate to modify the Magic Number by these values when
used to guestimate the need for air sampling at facilities operating
under normal conditions?  Please note that NUREG-1400's use of release
fractions result in a less conservative guestimate.

Appreciate your thoughts...

Scott A. Sorensen
ssorensen@doeal.gov