Re: Pipes & ducts, surveys of

[jgbarnes@ix.netcom.com (JAMES BARNES)]

Dear Paul,

For what it's worth, here are my comments:

You wrote (regarding surveys of pipes and ducts): 

>1. What instruments, commercially available or otherwise, have you
>used? Any comments, good or bad?

We characterize the isotopes of concern either by gamma-spec'ing a 
sample of the duct (or filter), or by performing a process history 
analysis for the duct.  We look specifically for readily detectable 
isotopes, then scale the process mixture to this isotope (usually 
Cs-137 is used as the "detectable.")  In our case, the mixtures are 
predominantly Cs-137, with other isotopes forming a small fraction of 
the total activity.  Because of this, we have found if the Cs-137 is 
not detectable, then other isotopes are also not detectable.

Because of the levels of Cs-137, we have generally been able to use 
standard hand-held pancake friskers.  We sometimes mount them on 
extendable poles for reach.  Be careful of cable length; if it's too 
long, you'll lose signal and get spurious reads.

Similarly, we use hand-held alpha survey meters.  We have sometimes 
manufactured custom probes for specific geometries.

We have also toyed with using NaI detectors inserted into piping.  It 
is very difficult to do quantative work with this, however, as the 
geometry problems are nearly insurmountable.  It will help find hot 
spots, and can be used to locate hot sections of piping.

We have also used portable MCAs with NaI to get a rough spectrum of 
isotopes.  We met with limited success as the resolution of NaI was not 
that great.

>2. If it was done quantitatively, how did you determine the
>efficiencies?

We use the standard calibration against check sources.  We rarely use a 
"field" calibration.

For "special" probes, we generally avoid the problem by only using them 
for "go/no go" qualitative evaluation.

>3. Any general thoughts on this subject e.g. problems, good
>references etc?

NRC Reg Guide 1.86.



Jim Barnes, CHP
RSO
Rockwell International, Rocketdyne Division