Information Notice No.NO. 93-30: NRC Requirements for Evaluation of Wipe Test Results; Calibration of Count Rate Survey Instruments
UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF NUCLEAR MATERIAL SAFETY AND SAFEGUARDS
WASHINGTON, D.C. 20555
April 12, 1993
NRC INFORMATION NOTICE NO. 93-30: NRC REQUIREMENTS FOR EVALUATION OF WIPE
TEST RESULTS; CALIBRATION OF COUNT RATE
SURVEY INSTRUMENTS
Addressees
All U.S. Nuclear Regulatory Commission Licensees
Purpose
The U.S. Nuclear Regulatory Commission (NRC) is issuing this information
notice to alert NRC licensees to the following:
a. NRC requirements for evaluation of wipe test results
b. Calibration of count rate survey instruments based on the use of
the instrument.
It is expected that recipients will review this information for applicability
to their facilities and consider actions, as appropriate, to ensure
instruments used for contamination surveys are properly calibrated. However,
suggestions contained in this information notice are not new NRC requirements;
therefore, no specific action or written response is required.
Description of Circumstances
Licensees have recently been cited for failure to properly calibrate
instruments used to evaluate wipe tests and survey instruments used for
contamination surveys.
Some licensees are evaluating wipe samples with wipe test counters without
determining the instrument sensitivity or efficiency. The licensee must
demonstrate that the instrument is calibrated to make measurements and
sufficiently sensitive to meet the applicable regulatory requirements in
10 CFR Parts 20, 34 and 35.
Also, NRC inspections have revealed that many count rate survey instruments
used exclusively with pancake probes for measuring surface contamination are
not being calibrated with procedures established for this use. The
instruments have been calibrated following the procedures outlined in
Appendix B of Regulatory Guide 10.8, Revision 2, "Model Procedure for
Calibrating Survey Instruments." This procedure provides guidance for
calibrating survey instruments used for dose rate measurements, not
contamination levels.
9304070022.
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Discussion
The following provide examples of NRC regulations that include specific
performance criteria: 10 CFR 20.205(b)(2) requires a minimum detection limit
of 0.01 microcurie per 100 square centimeters of package surface, when
monitoring the external surfaces of incoming packages; 10 CFR 34.25(c) and
10 CFR 35.59 (c)(3) require that a leak test be capable of detecting the
presence of 0.005 microcurie of removable contamination on a sealed source;
10 CFR 35.70(f) requires that a medical use licensee conduct the surveys
required by 10 CFR 35.70(e) so as to be able to detect contamination on each
wipe sample of 2000 disintegrations per minute (dpm), 9.01E-4 microcurie;
10 CFR 35.315(a)(7) requires that rooms used by patients undergoing
radiopharmaceutical therapy not be reassigned until removable contamination
levels are less than 200 dpm per 100 square centimeters; and 10 CFR 35.70(h)
requires that survey records for removable contamination in each area be
expressed in dpm per 100 square centimeters.
Calibration information can be found in the instrument manufacturer's guidance
or the following references for calibrating instruments to detect surface
contamination:
1) National Council on Radiation Protection and Measurements (NCRP)
Report No. 112, Calibration of Survey Instruments used in
Radiation Protection for the Assessment of Ionizing Radiation
Fields and Radioactive Surface Contamination (see Attachment 1 for
address)
2) American National Standards Institute, Inc. (ANSI) ANSI N323-1978,
Radiation Protection Instrumentation Test and Calibration (see
Attachment 1 for address)
3) NUREG-1156, Accuracy and Detection Limits for Bioassay
Measurements in Radiation Protection, Statistical Consideration
(see Attachment 1 for address)
4) NUREG/CR-4007, Lower Limit of Detection: Definition and
Elaboration of a Proposed Position for Radiological Effluent
Environmental Measurements, September 1984 (written by the
National Bureau of Standards, now the National Institute of
Standards and Technology) (see Attachment 1 for address)
I. Wipe Test Counters
The licensee, not the instrument manufacturer, is responsible for
demonstrating that the instrument and method used are sensitive enough to
meet NRC regulatory requirements.
The efficiency and sensitivity of the instrument are a function not only
of the physical components of the device, but also of the methodology of.
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the survey and the counting procedures. The counting procedures need to
address the time of counting, the background count, the energy spectrum
and emission rates of the isotope, and the desired accuracy of the
measurement.
An efficiency must be determined for each isotope used, and normally the
isotope with the lowest efficiency is assumed to be the isotope detected
until the emission spectrum of the sample can be analyzed.
The sensitivity, or minimum detectable activity (MDA), defines the minimum
activity which will produce counts above the background for a specific
counting time that will yield the true count rate within a predetermined
degree of accuracy.
The MDA may be set by the regulations governing the licensed activity, for
example, 2000 dpm may be chosen to comply with 10 CFR 35.70(f). Licensees
must, at a minimum, choose a measurement system with an MDA equal to, or
less than, that required by applicable NRC regulations. Licensees may
either develop their own procedure or follow the manufacturer's
instructions for the calibration of the wipe test counter and the check of
the MDA.
If the background is too high to accurately count the required MDA, the
instrument may need to be moved to a lower background area or serviced.
II. Count Rate Survey Instruments
Count rate survey instruments (those with a counts per minute (cpm) scale)
using pancake probes are routinely used to detect and measure surface
contamination. Pancake probes are thin window Geiger-Mueller probes which
typically have an active face area of about 15 square centimeters.
Pancake probes are most efficient for detecting and measuring energetic
beta radiation from radioactively contaminated surfaces. The measured
activity is commonly expressed in units of disintegrations per minute
(dpm).
To obtain uniform radiation fields, calibrations are commonly made with
the detector window nearly in contact with large area, flat, uniformly
distributed sources such as planchet sources. The American National
Standard Institute (ANSI) N323-1978, Radiation Protection
Instrumentation Test and Calibration, specifies that calibration
shall be performed with a standard source or sources providing radiation
fields similar to those for which the instrument is used (Section 4.3.2).
For example, the proper beta radiation response of an instrument would be
determined with a source of beta radiation of similar properties to the
radioisotopes in use.
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This information notice requires no specific action or written response. If
you have any questions about the information in this notice, please contact
the technical contacts listed below or the appropriate regional office.
ORIGINAL SIGNED BY
Richard E. Cunningham, Director
Division of Industrial and
Medical Nuclear Safety
Office of Nuclear Material Safety
and Safeguards
Technical contacts: Jim Smith, NMSS
(301) 504-2613
Torre Taylor, NMSS
(301) 504-2611
Attachments:
1. Addresses of Organizations
2. List of Recently Issued NMSS Information Notices
3. List of Recently Issued NRC Information Notices
.
Attachment 1
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ADDRESSES OF ORGANIZATIONS
1. NUREG Documents:
The NRC Public Document Room
2120 L Street, N.W., Lower Level
Washington, D.C. 20555
2. NCRP Publications
P.O. Box 30175
Washington, D.C. 20014
3. ANSI
1430 Broadway
New York, NY 10018
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