ASTM C1169-97

Standard Guide for Laboratory Evaluation of Automatic Pedestrian SNM Monitor Performance

SCOPE
1.1 The requirement to search pedestrians for special nuclear material (SNM) to prevent its theft has long been a part of both United States Department of Energy and United States Nuclear Regulatory Commission rules for the physical protection of SNM. Information on the application of SNM monitors to perform such searches is provided in Guide C1112. This guide establishes a means to compare the performance of different SNM pedestrian monitors operating in a specific laboratory environment.  The goal is to provide relative information on the capability of monitors to search pedestrians for small quantities of concealed SNM under characterized conditions. The outcome of testing assigns a sensitivity category to a monitor related to its SNM mass-detection probability; the monitor's corresponding nuisance-alarm probability for that sensitivity category is also determined and reported.
1.2 The evaluation uses a practical set of worst-case environmental, radiation emission, and radiation response factors so that a monitor's lowest level of performance in a practical operating environment for detecting small quantities of SNM is evaluated. As a result, when that monitor is moved from laboratory to routine operation, its performance will likely improve. This worst-case procedure leads to unclassified evaluation results that understate rather than overstate the performance of a properly used SNM monitor in operational use.
1.3 The evaluation applies to two types of SNM monitors that are used to detect small quantities of SNM. Both are automatic monitors; one monitors pedestrians as they walk through a portal formed by the monitor's radiation detectors (walkthrough or portal monitor), and the other monitors pedestrians who are stationary for a short period of time while they are monitored (wait-in monitor). The latter can be a portal monitor with a delay mechanism to halt a pedestrian for a few seconds or it can be an access-control booth or room that contains radiation detectors to monitor a pedestrian waiting for clearance to pass.
1.4 The values stated in SI units are to be regarded as standard.
1.5 This standard does not purport to address the safety problems, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.

General Information

• Status: Historical
• Publication Date: 09-Jun-1997
• Technical Committee: C26 - Nuclear Fuel Cycle

Relations

• Replaced By: ASTM C1169-97(2003) - Standard Guide for Laboratory Evaluation of Automatic Pedestrian SNM Monitor Performance
• Effective Date: 10-Jun-1997
• Referred By: ASTM C1189-11(2018) - Standard Guide to Procedures for Calibrating Automatic Pedestrian SNM Monitors
• Effective Date: 10-Jun-1997

Standards Content (Sample)

NOTICE: This standard has either been superceded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information.
Designation: C 1169 – 97
Standard Guide for
Laboratory Evaluation of Automatic Pedestrian SNM Monitor
Performance
This standard is issued under the fixed designation C 1169; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (e) indicates an editorial change since the last revision or reapproval.
1. Scope contains radiation detectors to monitor a pedestrian waiting for
clearance to pass.
1.1 The requirement to search pedestrians for special
1.4 The values stated in SI units are to be regarded as
nuclear material (SNM) to prevent its theft has long been a part
standard.
of both United States Department of Energy and United States
1.5 This standard does not purport to address the safety
Nuclear Regulatory Commission rules for the physical protec-
concerns, if any, associated with its use. It is the responsibility
tion of SNM. Information on the application of SNM monitors
of the user of this standard to establish appropriate safety and
to perform such searches is provided in Guide C 1112. This
health practices and determine the applicability of regulatory
guide establishes a means to compare the performance of
limitations prior to use.
different SNM pedestrian monitors operating in a specific
laboratory environment. The goal is to provide relative
2. Referenced Documents
information on the capability of monitors to search pedestrians
2.1 ASTM Standards:
for small quantities of concealed SNM under characterized
C 859 Terminology Relating to Nuclear Materials
conditions. The outcome of testing assigns a sensitivity cat-
C 993 Guide for In-Plant Performance Evaluation of Auto-
egory to a monitor related to its SNM mass-detection probabil-
matic Pedestrian SNM Monitors
ity; the monitor’s corresponding nuisance-alarm probability for
C 1112 Guide for Application of Radiation Monitors to the
that sensitivity category is also determined and reported.
Control and Physical Security of Special Nuclear Material
1.2 The evaluation uses a practical set of worst-case envi-
C 1189 Guide to Procedures for Calibrating Automatic
ronmental, radiation emission, and radiation response factors
Pedestrian SNM Monitors
so that a monitor’s lowest level of performance in a practical
operating environment for detecting small quantities of SNM is
3. Terminology
evaluated. As a result, when that monitor is moved from
3.1 Definitions of Terms Specific to This Standard:
laboratory to routine operation, its performance will likely
3.1.1 confidence coeffıcient—the theoretical proportion of
improve. This worst-case procedure leads to unclassified
confidence intervals from an infinite number of repetitions of
evaluation results that understate rather than overstate the
an evaluation that would contain the true result.
performance of a properly used SNM monitor in operational
3.1.1.1 Discussion—In a demonstration, if the true result
use.
were known the theoretical confidence coefficient would be the
1.3 The evaluation applies to two types of SNM monitors
approximate proportion of confidence intervals, from a large
that are used to detect small quantities of SNM. Both are
number of repetitions of an evaluation, that contain the true
automatic monitors; one monitors pedestrians as they walk
result. Typical confidence coefficients are 0.90, 0.95 and 0.99.
through a portal formed by the monitor’s radiation detectors
3.1.2 Confidence Interval for a Detection Probability—An
(walkthrough or portal monitor), and the other monitors
interval, based on an actual evaluation situation, so constructed
pedestrians who are stationary for a short period of time while
that it contains the (true) detection probability with a stated
they are monitored (wait-in monitor). The latter can be a portal
confidence.
monitor with a delay mechanism to halt a pedestrian for a few
3.1.2.1 Discussion—Confidence is often expressed as
seconds or it can be an access-control booth or room that
100*the confidence coefficient. Thus, typical confidence levels
are 90, 95 and 99 %.
3.1.3 detection probability—the proportion of passages for
This guide is under the jurisdiction of ASTM Committee C-26 on Nuclear Fuel which the monitor is expected to alarm during passages of a
Cycle and is the direct responsibility of Subcommittee C26.12 on Safeguard
particular test source.
Applications.
Current edition approved June 10, 1997. Published May 1998. Originally
published as C 1169 – 91. Last previous edition C 1169 – 92.
Note that this is a laboratory evaluation and is not designed for routine in-plant
use. A separate guide, C 993, is available for verifying routine in-plant performance. Annual Book of ASTM Standards, Vol 12.01.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
NOTICE: This standard has either been superceded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information.
C 1169
TABLE 2 Mass Detection Sensitivities in Pedestrian Neutron
3.1.3.1 Discussion—Although probabilities are properly ex-
A
Monitors
pressed as proportions, performance requirements for detection
B
Category Description Plutonium (g)
probability in regulatory guidance have sometimes been ex-
pressed in percentage. In that case, the detection probability as NI Standard Neutron 250
NII Improved Neutron 100
a proportion can be obtained by dividing the percentage by
NIII High Sensitivity 30
100.
Neutron
3.1.4 detection sensitivity category—specified in terms of a
A
In a nominal 20 μR/h background intensity using standard metallic test sources
test source mass for which the monitor has a 0.50 or greater
and procedures described in 11.2.
B
Low-burnup plutonium as described in 8.5. For monitors having gamma-ray
detection probability, as measured by a test procedure having a
sensitivity in addition to neutron sensitivity the plutonium must be shielded in 5-cm
95 % confidence coefficient for its result. The specified 0.50 or
thick lead.
greater detection probability is a very convenient one for
testing. The limited number of test source masses used to
should be in as many layers as local rules require of a
define sensitivity categories (see Table 1 and Table 2) ad-
non-radioactive material such as aluminum (#0.32-cm thick)
equately describe the performance of SNM monitors that can
or thin (#0.16-cm thick) stainless steel or nickel to reduce
detect small quantities of SNM.
unnecessary radiation absorption.
3.1.5 nuisance alarm—a monitoring alarm not caused by
3.1.9.3 standard uranium source—a metallic sphere or cube
SNM but by one of two other causes, which are statistical
of highly-enriched uranium (HEU) containing at least 93 %
variation in the measurement process or natural background
U and less than 0.25 % impurities. Protective encapsulation
intensity variation. Other contributors to nuisance alarms, such
should be thin plastic or thin aluminum (#0.32-cm thick) to
as interfering radiation sources and equipment malfunction,
reduce unnecessary radiation absorption in the encapsulation.
should not be present during testing.
No additional filter is needed.
3.1.6 radiation intensity—expressed as the number of pho-
tons or neutrons emitted by a material per second or as the
4. Summary of Guide
environmental background radiation dose rate.
4.1 Evaluation follows a sequence of steps, each of which
3.1.7 SNM (special nuclear material)—plutonium of any
should reach an acceptable outcome before the next is begun.
isotopic composition, U, or enriched uranium as defined in
The steps are: placing the monitor into operation; determining
Terminology C 859. This term is used here to describe both
nuisance alarm probability; determining detection probability;
SNM and strategic SNM, which is plutonium, uranium-233,
and categorizing the results.
and uranium enriched to 20 % or more in the U isotope.
4.2 The monitor is put into operation in a nominal 20 μR/h
3.1.8 SNM monitor—a radiation detection system that mea-
(5.2 nC/kg h or 1.43 pA/kg) background environment. The
sures ambient radiation intensity, determines an alarm thresh-
manufacturer’s instructions are followed to assemble, calibrate
old from the result, and then, when it monitors, sounds an
(see Section 10), and begin using the monitor.
alarm if its measured radiation intensity exceeds the threshold.
4.3 Nuisance alarm probability is determined (see Section
3.1.9 standard SNM test source—a metallic sphere or cube
11) by automatic data collection with a system that cycles the
of SNM having maximum self attenuation of its emitted
monitor alternately through a group of simulated pedestrian
radiation and an isotopic composition to minimize that emis-
passages and a background update while recording the back-
sion as described below. Encapsulation and filtering also affect
ground intensity and each of its alarms.
radiation intensity, and particular details are listed for each
4.4 Detection probability is determined (see Section 12) by
source.
transporting SNM test sources through the monitor’s least
3.1.9.1 standard plutonium source—a metallic sphere or
sensitive region, which is determined as part of the evaluation.
cube of low-burnup plutonium containing at least 93 % Pu,
Different individuals transport the SNM at their accustomed
less than 6.5 % Pu, and less than 0.5 % impurities.
pace but in a specified manner. Results (number of detections
3.1.9.2 Discussion—A cadmium filter can reduce the impact
and passages) are analyzed as a binomial experiment to give a
of Am, a plutonium decay product that will slowly build up
confidence interval for the probability of detection that may
in time and emit increasing amounts of 60-keV radiation.
place the monitor in a sensitivity category. If the monitor can
Begin use of 0.04-cm-thick cadmium filter when three or more
be operated in different modes or at more than one spacing
years have elapsed since separation of plutonium decay prod-
between its detectors, it should be evaluated in each mode and
ucts. If ten or more years have elapsed since separation, use a
at each spacing that is expected to be used operationally.
cadmium filter 0.08-cm thick. The protective encapsulation
4.5 The sensitivity category of a monitor is determined (see
A Section 13) by the smallest test source for which the monitor
TABLE 1 Mass Detection Sensitivities of SNM Monitors
has a 0.50 or greater detection probability with 95 % confi-
B C
Category Description Uranium (g) Plutonium (g)
dence at an acceptable nuisance alarm probability.
I Standard Plutonium 64 1
II Standard Uranium 10 0.29
5. Significance and Use
III Improved Sensitivity 3 0.08
IV High Sensitivity 1 0.03
5.1 SNM monitors are an effective and unobtrusive means
A
In a nominal 20 μR/h background intensity using standard metallic test sources
to search pedestrians for concealed SNM. Nuclear facility
and procedures described in 11.2.
security plans often include SNM monitors as one means to
B
HEU as described in 8.4.
C
Low-burnup plutonium as described in 8.5. help prevent theft or unauthorized removal of designated
NOTICE: This standard has either been superceded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information.
C 1169
quantities of SNM from access areas. This guide describes a grounds from other than natural causes are present. A simulated
way to evaluate and categorize the relative performance of high intensity background produced by point sources is unsuit-
available SNM monitors that might be considered for use in a able.
security plan. 6.2 Parts of the evaluation use specific values or measure-
5.2 The significance of the evaluation for monitor users is ments that can alter the testing outcome if not done properly.
that evaluated monitoring equipment has a verified capability. For example, an improperly measured background intensity
Unexpected deficiencies such as low sensitivity for highly (see 7.1) that is actually much higher or lower than stated in 6.1
self-absorbing forms of SNM, lower than expected sensitivity will bias the results toward a lower or higher sensitivity
in areas having high natural background intensity, or a high category. Similarly, inattention to test source specification,
nuisance-alarm probability from electronic noise or faulty method of carrying test sources through the monitor, and
alarm logic often can be detected during evaluation and improper interpretation and reporting of results will bias the
corrected before a monitor is placed in operation or further outcome. Other possible errors and biases in the evaluation
marketed. results are discussed in Section 13.
5.3 The significance of the evaluation for monitor manufac-
7. Apparatus
turers is that it may disclose deficiencies in design or construc-
7.1 Measuring the gamma-ray background intensity re-
tion that, when corrected, will improve the product. A monitor
quires a precision ion chamber or similar environmental
verified to be in a particular sensitivity category will be a
radiation measurement device that is calibrated to provide
product that customers who need that level of performance can
gamma-ray dose rate. For neutron monitors, the background
purchase in good faith.
intensity is inferred from the more readily measured gamma-
5.4 The established sensitivity categories for evaluated
monitors will provide information to regulatory agencies on the ray intensity because the cosmic-ray and terrestrial factors that
lead to high natural gamma-ray intensity are the same ones that
performance range of monitoring equipment for detecting
small quantities of SNM. produce high natural neutron background intensity.
7.2 The presence of unnatural sources of background during
5.5 Independent monitor evaluation will encourage monitor
manufacturers to provide appropriate documentation for cali- nuisance alarm testing can be discovered by recording the
output of a background monitor or the output of the monitor’s
brating and operating their monitors to obtain the best possible
performance for detecting SNM. radiation detection circuits. A strip-chart recorder, data logger,
and computer-generated display are convenient ways to record
5.6 The underlying assumptions in this guide are that SNM
background data.
monitors are applied in a wide range of background environ-
7.3 Alarms also must be recorded during nuisance alarm
ments at facilities that process a variety of chemical and
testing. For example, an event marker could record alarms on
physical forms of SNM. The operational expe
...