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Re[2]: Contamination Control? (Ref: 49CFR173.443)
I'd like to thank Judd Sills for the info regarding the methods of
assessment in obtaining wipe samples. I was confusing "detection
equipment efficiencies" with "wipe/smear sampling efficiencies". I am
including his reply to me for all to see and decipher.
______________________________ Reply Separator _________________________________
Subject: Re: Contamination Control? (Ref: 49CFR173.443)
Author: sillsj@GAT.COM (Judd Sills) at Internet
Date: 10/12/95 4:14 PM
You asked:
> I may be missing something in the wording of this part of the Code but
> I've been wondering what "Other methods of assessment of equal or
> greater efficiency" means? And further, why does there seem to be a
> kind of "allowable range [Table 10 limit - up to 10 times the limit]"
> when using the "Other method of assessment?
>
> You can respond to me directly via e-mail since this may not be
> relevant to the majority of the RADSAFERS unless they're actively
> receiving/shipping radioactive materials.
The following excerpt is from NRC Information Notice 85-46 (subject title is
"CLARIFICATION OF SEVERAL ASPECTS OFREMOVABLE RADIOACTIVE
SURFACE CONTAMINATION LIMITS FOR TRANSPORT PACKAGES", which should answer
your question about the vague reference to "other methods of
assessment". If you need a copy of the entire Information Notice, please
feel free
to give me a call.
"USE OF HIGHER EFFICIENCY WIPE SAMPLES
As is stated in 173.443(a): "Other methods of assessment of equal or greater
efficiency may be used. When other methods are used, the detection
efficiency of
the method used shall be taken into account and in no case shall the nonfixed
contamination on the external surfaces of the package exceed ten times the
limits stated in Table 10." NRC also queried DOT on this matter, as follows:
We understand that DOT considers that the reference in 173.443(a) stating that
'other methods of assessment of equal or greater efficiency may be used,' may
include other wipe sampling methods wherein the efficiency has actually been
demonstrated to be greater than 10 percent. Therefore, in effect, the wipe
sample
limits stated in 173.443(a) and (b) and Table 10 therein, are limits "by
default"
which do not take advantage of utilizing an efficiency which has been
demonstrated to be greater than 10 percent. In our evaluations of licensees'
package surveys, we therefore plan to accept assessments based on efficiencies
which have been appropriately demonstrated to have a higher than 10 percent
efficiency.
The reply by DOT on the usage of higher efficiency wipe samples was as follows:
It is our interpretation of this section that wiping methods with a
demonstrated
efficiency greater than 10 percent may take this greater efficiency into
account. As
you point out, the higher efficiency must be documented and in no case may the
removable levels exceed 10 times the values in Table 10.
It should be understood that where the term "detection efficiency" is used,
it refers
to the efficiency of alternate methods for quantifying the amount of removable
contamination on a package surface. It does not refer to the laboratory term
relating to instrument effectiveness for counting analyses.
An additional clarification also was received from DOT relative to use of
contamination assessment techniques with greater than 10% efficiencies in
exclusive-use vs. nonexclusive-use shipments. It stated that "the provision
for using
higher efficiency techniques, described in 49 CFR 173.443(a) may also be used
when operations are being performed in accordance with 173.443(b)."
An acceptable method of demonstrating wipe (smear) efficiency is repetitive
wiping of a portion of the package surface. The demonstrated wipe efficiency is
the ratio of the initial smear activity to the summation of activity on all
the wipes of
the designated portion of the package surface. For the purpose of this
calculation,
one can assume all activity is removed when two consecutive wipes show less
than 10% of the activity of the initial wipe. Because of variation in package
surfaces and contamination characteristics, care should be taken
to ensure
that the demonstrated wipe efficiency is representative of the wipes to
which it is
applied. This will normally require delaying package decontamination until
after
conduct of wipe efficiency determinations if an efficiency greater than 10% is
used. In no case, however, may the removable contamination levels exceed ten
times the Table 10 limits for packages in exclusive-use shipments when no
consideration is given to a demonstrated higher wiping efficiency. Upon such an
appropriate demonstration, however, removable contamination may not exceed
100 times the Table 10 limits, as would be the case for a wiping method
demonstrated to have been 100% efficient.
In general, licensees may only utilize demonstrations of high smear collection
efficiencies which have been determined by smear results taken on the same cask
for which the initial smears (using the assumed 10% efficiency) indicated the
regulatory limit was exceeded. Licensees will not be allowed to use the generic
collection efficiencies obtained on one specific cask for other future cask
shipments."
End of Quotation.
Good Luck
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Contents of this message are not reviewed or approved by General Atomics
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J. M. Sills
(619)455-2049
General Atomics, Room 14-152 Fax:(619)455-3181
3550 General Atomics Court
San Diego, CA 92121