ASTM C1455-00
(Guide)Standard Guide for Nondestructive Assay of Special Nuclear Material Holdup Using Gamma-Ray Spectroscopic Methods
Standard Guide for Nondestructive Assay of Special Nuclear Material Holdup Using Gamma-Ray Spectroscopic Methods
SCOPE
1.1 This guide addresses methods used to prepare for and to perform, using gamma-ray measurements, the nondestructive assay (NDA) of radioisotopes, for example, 235U, or 239Pu, remaining as holdup in nuclear facilities. Holdup occurs in facilities where nuclear material is processed. This guide includes the measurement of holdup of Special Nuclear Material (SNM) in places where holdup may occur, such as in process equipment, and in exhaust ventilation systems. This guide includes information useful for management planning, selection of equipment, consideration of interferences, measurement program definition, and the utilization of resources.
1.2 The measurement of nuclear material help up in process equipment is both an art and a science. It is subject to the constraints of politics, economics plus health and safety requirements, as well as to the laws of physics. The measurement process often is long and tedious and is performed under difficult circumstances of location and environment. The work combines the features of a detective investigation and a treasure hunt. Nuclear material held up in pipes, ductwork, gloveboxes, heavy equipment, and so forth, usually is distributed in a diffuse and irregular manner. It is difficult to define the measurement geometry, identify the form of the material, and measure it without interference from adjacent sources of radiation. A scientific knowledge of radiation sources and detectors, calibration procedures, geometry and error analysis also is needed ().
This standard does not purport to address all of the safety concerns, 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.
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Designation:C1455–00
Standard Guide for
Nondestructive Assay of Special Nuclear Material Holdup
Using Gamma-Ray Spectroscopic Methods
This standard is issued under the fixed designation C 1455; 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 Dispersive X-Ray Fluorescence (XRF) Systems
C 1009 Guide for Establishing a Quality Assurance Pro-
1.1 This guide addresses methods used to prepare for and to
gram for Analytical Chemistry Laboratories Within the
perform, using gamma-ray measurements, the nondestructive
235 239
Nuclear Industry
assay (NDA) of radioisotopes, for example, U, or Pu,
C 1030 Test Method for Determination of Plutonium Isoto-
remaining as holdup in nuclear facilities. Holdup occurs in
pic Composition by Gamma-Ray Spectroscopy
facilities where nuclear material is processed. This guide
2.2 ANSI Standards:
includes the measurement of holdup of Special Nuclear Mate-
ANSI N15.37 Guide to the Automation of Nondestructive
rial (SNM) in places where holdup may occur, such as in
Assay Systems for Nuclear Materials Control
process equipment, and in exhaust ventilation systems. This
ANSI/ASME NQA-1-1983 American Nuclear Society Re-
guide includes information useful for management planning,
quirements for Nuclear Power Plants
selection of equipment, consideration of interferences, mea-
2.3 U.S. Nuclear Regulatory Commission Regulatory
surement program definition, and the utilization of resources.
Guides:
1.2 The measurement of nuclear material help up in process
Regulatory Guide 5.23, In Situ Assay of Plutonium Re-
equipment is both an art and a science. It is subject to the
sidual Holdup
constraints of politics, economics plus health and safety
Regulatory Guide 5.9, Rev 2, Guidelines for Germanium
requirements, as well as to the laws of physics. The measure-
Spectroscopy Systems for Measurement of Special
ment process often is long and tedious and is performed under
Nuclear Material
difficult circumstances of location and environment. The work
combines the features of a detective investigation and a
3. Terminology
treasure hunt. Nuclear material held up in pipes, ductwork,
3.1 Definitions:
gloveboxes, heavy equipment, and so forth, usually is distrib-
3.1.1 absorber foils, n—thin foils, usually of copper, tin,
utedinadiffuseandirregularmanner.Itisdifficulttodefinethe
cadmium, or lead, used to intentionally attenuate the gamma
measurement geometry, identify the form of the material, and
flux reaching a detector. Absorber foils, typically, are used to
measure it without interference from adjacent sources of
reduce the counting rate from low-energy gamma rays not
radiation. A scientific knowledge of radiation sources and
needed for the measurement.
detectors, calibration procedures, geometry and error analysis
2 3.1.2 attenuation, n—reduction of measurable gamma-ray
also is needed (1).
flux due to the interaction of gamma rays with the container,
1.3 This standard does not purport to address all of the
holdup and other material between the source of the gamma-
safety concerns, if any, associated with its use. It is the
rays and the detector.
responsibility of the user of this standard to establish appro-
3.1.3 attenuation correction, n—a correction to the mea-
priate safety and health practices and determine the applica-
sured count rate that enables one to make an estimate of the
bility of regulatory limitations prior to use.
actual gamma-ray emission rate from the holdup, thereby
2. Referenced Documents correcting for the attenuation effects of the measurement
situation.
2.1 ASTM Standards:
3.1.4 background, n—any count in a gamma-ray peak,
C 982 Guide for Selecting Components for Energy-
which did not originate as a gamma ray at the assay energy in
This guide is under the jurisdiction ofASTM Committee C-26 on Nuclear Fuel
Cycle and is the direct responsibility of Subcommittee C26.05 on Methods of Test. Annual Book of ASTM Standards, Vol 12.01.
Current edition approved Jan. 10, 2000. Published March 2000. Available from American National Standards Institute, 11 W. 42nd St., 13th
The boldface numbers in parentheses refer to the list of references at the end of Floor, New York, NY 10036.
this standard. Available from the U.S. Nuclear Regulatory Commission, Washington, DC,
20555.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
C1455
the sample or item being measured, can be considered back- 3.1.16 shielded detector, n—a detector surrounded on all
ground. The three main contributors to background are as surfaces but one with material that provides significant attenu-
follows:
ation of gamma-rays.
3.1.4.1 Compton scattering, v—which produces a con-
3.1.17 transmission correction, n—an attenuation correc-
tinuum under the peak of interest due to scattering of higher
tion is determined using a gamma-ray emitting source, some-
energy gamma rays;
times a transmission source is used, placed behind the holdup
3.1.4.2 Peaked background—Gamma rays of the assay
with respect to the detector.
energy, which originate in sources other than the holdup being
3.1.18 working source, n—an item containing, in a fixed
measured; and,
geometry, a fixed quantity of a radioisotope to be measured.A
3.1.4.3 Summed background, n—Nonpeaked counts under
working source can be used for routine measurement control
the peak of interest that result from the summing of lower
checks if the gamma-ray emission rate is well characterized.
energy gamma rays, or Compton events, or both.
3.1.5 collimated detector, n—a detector surrounded by a
4. Summary of Guide
shield that imposes a directional response on the collimated
4.1 Introduction—Holdup measurements range from the
detector. The shield, called a collimator, generally is a cylinder
assay of a single item to routine measurement of a piece of
of high-Z material, for example lead, tungsten) mounted
equipment, to an extensive campaign of determining the total
coaxially to the detector and extending over the detector and
SNM in-process inventory for a processing plant. Holdup
beyond the detector face. Since a collimator is designed to be
measurements differ from other nondestructive measurement
used with and affects the calibration of a specific detector, it is
methods in that the assays are performed in situ on equipment
appropriate to refer to the unit as a detector-collimator assem-
associated with the process. Often, the chemical form and
bly.
geometric distribution of the SNM are not known. These
3.1.6 contact measurement, n—a special case of a near-field
unique challenges require for each measurement a specific
measurement in which measurements are made with the
definition of what is expected from the assay, specific infor-
detector assembly in contact with the item, for example, tank,
mation about the item or items to be assayed, design of the
pipe, ductwork, being assayed.
assay, and special preparation for the assay. The amount of
3.1.7 far-field measurement, n—measurement with a detec-
effort expended and level of detail attained for each of these
tor and collimator such that the assumptions for a generalized
preparatory activities is dependent on both assay requirements
geometry assay are valid (1).
and available resources.
3.1.8 field of view, n—the entire range encompassed by the
4.2 Definition of Requirements—Definition of the holdup
collimated detector when it is trained in a particular direction.
measurement requirements should include, as a minimum,
3.1.9 holdup, n—residual special nuclear material in pro-
measurement goals, for example, criticality control, SNM
cessing or support equipment areas.
accountability, security, time constraints for the measurements,
3.1.10 infinite thickness, n—the thickness of material
resources available, for example, personnel, equipment, fund-
throughwhichthegammaraysofthedesignatedenergycannot
ing, and desired measurement sensitivity, accuracy, and uncer-
penetrate (2); however, for the purposes of this guide, the
tainty.
thickness through which 99.9 % of the gamma rays of the
4.3 Information Gathering and Initial Evaluation—
designated energy cannot penetrate, will be used.
Information must be gathered concerning the item or items to
3.1.11 isotopic mapping, v—use of high resolution gamma-
be assayed and the level of effort needed to meet the holdup
ray spectrometry to identify gamma-ray emitting isotopes and
measurement requirements. Preliminary measurements may be
interfering gamma rays at representative locations on the
needed to define the location and extent of the holdup, to
measurement items.
determinetheSNMisotopiccompositionorenrichment,andto
3.1.12 near-field measurement, n—measurement made at a
identify potential interfering isotopes. Factors to be considered
detector to holdup distance such that the far-field assumptions
include the geometric configuration of the item or process
are not satisfied.
equipment to be assayed, location of the equipment in the
3.1.13 scan method, n—rapid, that is, short-count time,
facility, attenuating materials, sources of background or inter-
measurement at specific locations or movement of a gamma-
ferences, safety considerations (both radiological and indus-
ray count rate meter along process equipment to qualitatively
trial) associated with the assay, plus the personnel and equip-
identify the presence of radioactive material above a predeter-
ment needed to complete the assay. Sources of information
mined activity level (“hot spots”). It can be used to map the
mayincludeavisualsurveyoftheitems,engineeringdrawings
extent of areas with a similar activity level or to identify an
of the item and other equipment in the vicinity, process
area of maximum activity.
knowledge, and prior assay documentation.
3.1.14 self attenuation, n—attenuation of gamma rays pro-
duced within the holdup by the holdup itself. 4.4 Task Design and Preparation—The initial evaluation
3.1.15 shadow shield, n—attenuating material placed be- serves as the basis for choosing the quantitative method, assay
model, and subsequently, leads to determination of the detec-
tween the shielded detector and radiation sources not part of
the assay item so as to limit the contribution from those tion system and calibration method to be used. Appropriate
standards and support equipment are developed or assembled
extraneous sources to the observed measurement or back-
ground count rates. for the specific measurement technique. A measurement plan
C1455
should be developed. The plan may outline required documen- isotopically homogeneous, the measured isotopic composition
tation, operating procedures, including background measure- will not be a reliable estimate of the bulk isotopic composition.
ment methods and frequencies, plus training, quality and 5.3.1 Enrichment Measurements—A special case of the
measurement control requirements. Necessary procedures, in- determination of isotopic abundance is the measurement of the
cluding those for measurement control, should be developed, ratio of two isotopes. Generally, this is applied to uranium.
documented, and approved. 5.4 Quantitative Measurements—These measurements re-
4.5 Measurements—Perform measurements and measure- sult in quantification of the mass of SNM in the holdup. They
ment control as detailed in the measurement plan or procedure. typically include all the corrections, such as attenuation, and
4.6 Evaluation of Measurement Data—Appropriate to the descriptive information, such as isotopic composition, that are
quantitative method chosen, corrections are made for gamma- available concerning the holdup.
ray attenuation effects, for example, the container, item matrix, 5.5 Spot Check and Verification Measurements—Periodic
absorbers, and measured background. These corrections are measurement of holdup at a defined point can be used to detect
applied in the calculation of the assay value. Measurement or track relative changes in the holdup quantity over time.
uncertainties are established based on factors affecting the Either the scan method or a quantitative method can be used.
assay. 5.6 Indirect Measurements—Quantificationofanisotopeby
4.6.1 Converting measurement data to estimates of the measurementofadaughterisotopeorofasecondisotopeifthe
quantity of nuclear material holdup requires careful evaluation ratio of the abundances of the two isotopes is known. This can
of the measurement against calibration assumptions. Depend- be used when there are interfering gamma rays or when the
ing on the calibration and measurement methods used, correc- parent isotope does not have a sufficiently strong gamma-ray
tions may be necessary for geometric effects (differences signal to be readily measured. If this method is employed, it is
between holdup measurement and calibration geometries), important that the ratio of the two isotopes be known with
gamma-ray attenuation effects, background, and interferences. sufficient accuracy to meet the holdup measurement quantifi-
Measurement uncertainties are estimated based on uncertain- cation requirements.
ties in assay parameters, for example, holdup distribution, 5.7 Mathematical Modeling—An aid in the evaluation of
attenuation effects, measured count rates. complex assay situations. Actual measurement data are used
4.6.2 Resultsshouldbeevaluatedagainstpreviousresultsor with a mathematical model describing the physical location of
clean out data, if either is available. If a discrepancy is evident, equipment and materials.
an evaluation should be made. Additional measurements with
6. Interferences
subsequent evaluation may be required. The assay should be
6.1 Peaked and Compton Background—Background can
documented.
cause problems in several ways.
4.7 Documentation—Measurement documentation should
6.1.1 Peaked backgrounds that fluctuate, for example, a
include a description of measurement parameters considered
cyclical process or a rotating attenuator, which shields some
important to the calibration and measurement techniques used,
source of background, during the measurements will cause
estimated precision and bias, and comparison to other mea-
surement techniques. biased results.
6.1.2 If a background activity (peaked or Compton) is large
5. Significance and Use
relative to the gamma-ray flux from the holdup, the overall
5.1 The following methods assist in demonstrating regula-
assay sensitivity will be reduced and uncertainty increased.
tory compliance in such areas as sa
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