ASTM C1493-01
(Test Method)Standard Test Method for Non-Destructive Assay of Nuclear Material in Waste by Passive and Active Neutron Counting Using a Differential Die-Away System
Standard Test Method for Non-Destructive Assay of Nuclear Material in Waste by Passive and Active Neutron Counting Using a Differential Die-Away System
SCOPE
1.1 This test method covers a system that performs nondestructive assay (NDA) of uranium or plutonium, or both, using the active, differential die-away technique (DDT), and passive neutron coincidence counting. Results from the active and passive measurements are combined to determine the total amount of fissile and spontaneously-fissioning material in drums of scrap or waste as large as 208 L. Corrections are made to the measurements for the effects of neutron moderation and absorption, assuming that the effects are averaged over the volume of the drum and that no significant lumps of nuclear material are present. These systems are most widely used to assay low-level and transuranic waste, but may also be used for the measurement of scrap materials. While this test method is specific to the second-generation Los Alamos National Laboratory (LANL) passive-active neutron assay system, the principle applies to other DDT systems.
1.1.1 In the active mode, the system measures fissile isotopes such as 235U and 239Pu. The neutrons from a pulsed, 14-MeV neutron generator are thermalized to induce fission in the assay item. Between generator pulses, the system detects prompt-fission neutrons emitted from the fissile material. The number of detected neutrons between pulses is proportional to the mass of fissile material. This method is called the differential die-away technique.
1.1.2 In the passive mode, the system detects time-coincident neutrons emitted from spontaneously fissioning isotopes. The primary isotopes measured are 238Pu, 240Pu, and 242Pu; however, the system may be adapted for use on other spontaneously-fissioning isotopes as well. The number of coincident neutrons detected is proportional to the mass of spontaneously-fissioning material.
1.2 The active mode is used to assay fissile material in the following ranges.
1.2.1 For uranium-bearing items, the DDT can measure the 235U content in the range from 0.02 to over 100 g. Normally, the assay of items bearing only uranium is performed using matrix-specific calibrations to account for the effect of the matrix on the active signal.
1.2.2 For plutonium-bearing items, the DDT method measures the 239Pu content in the range between 0.01 and 20 g.
1.3 The passive mode is capable of assaying spontaneously-fissioning nuclei, over a nominal range from 0.05 to 15 g of 240Pu, or equivalent. The passive mode can also be used to measure large (for example, kg) quantities of 238U.
1.4 This test method requires knowledge of the relative abundances of the plutonium or uranium isotopes to determine the total plutonium or uranium mass.
1.5 This test method will give biased results when the waste form does not meet the calibration specifications and the measurement assumptions presented in this test method regarding the requirements for a homogeneous matrix, uniform source distribution, and the absence of nuclear material lumps, to the extent that they effect the measurement.
1.6 The complete active and passive assay of a 208 L drum is nominally 10 min or less.
1.7 Improvements to this test method have been reported (1,2,3 ,4 ). Discussions of these improvements are not included in this test method.
1.8 This standard may involve hazardous materials, operations, and equipment. 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. Specific precautionary statements are given in Section 8.
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Designation: C 1493 – 01
Standard Test Method for
Non-Destructive Assay of Nuclear Material in Waste by
Passive and Active Neutron Counting Using a Differential
Die-Away System
This standard is issued under the fixed designation C 1493; 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 formed using matrix-specific calibrations to account for the
effect of the matrix on the active signal.
1.1 This test method covers a system that performs nonde-
1.2.2 For plutonium-bearing items, the DDT method mea-
structive assay (NDA) of uranium or plutonium, or both, using
sures the Pu content in the range between 0.01 and 20 g.
the active, differential die-away technique (DDT), and passive
1.3 The passive mode is capable of assaying spontaneously-
neutron coincidence counting. Results from the active and
fissioning nuclei, over a nominal range from 0.05 to 15 g
passive measurements are combined to determine the total
of Pu, or equivalent. The passive mode can also be used to
amount of fissile and spontaneously-fissioning material in
measure large (for example, kg) quantities of U.
drums of scrap or waste as large as 208 L. Corrections are
1.4 This test method requires knowledge of the relative
made to the measurements for the effects of neutron modera-
abundances of the plutonium or uranium isotopes to determine
tionandabsorption,assumingthattheeffectsareaveragedover
the total plutonium or uranium mass.
thevolumeofthedrumandthatnosignificantlumpsofnuclear
1.5 This test method will give biased results when the waste
material are present. These systems are most widely used to
form does not meet the calibration specifications and the
assaylow-levelandtransuranicwaste,butmayalsobeusedfor
measurementassumptionspresentedinthistestmethodregard-
the measurement of scrap materials. While this test method is
ing the requirements for a homogeneous matrix, uniform
specific to the second-generation Los Alamos National Labo-
source distribution, and the absence of nuclear material lumps,
ratory (LANL) passive-active neutron assay system, the prin-
to the extent that they effect the measurement.
ciple applies to other DDT systems.
1.6 The complete active and passive assay of a 208 L drum
1.1.1 In the active mode, the system measures fissile iso-
235 239
is nominally 10 min or less.
topes such as U and Pu. The neutrons from a pulsed,
1.7 Improvementstothistestmethodhavebeenreported(1,
14-MeV neutron generator are thermalized to induce fission in
2, 3, 4). Discussions of these improvements are not included
the assay item. Between generator pulses, the system detects
in this test method.
prompt-fission neutrons emitted from the fissile material. The
1.8 This standard may involve hazardous materials, opera-
number of detected neutrons between pulses is proportional to
tions, and equipment. This standard does not purport to
the mass of fissile material. This method is called the differ-
address all of the safety concerns, if any, associated with its
ential die-away technique.
use. It is the responsibility of the user of this standard to
1.1.2 In the passive mode, the system detects time-
establish appropriate safety and health practices and deter-
coincident neutrons emitted from spontaneously fissioning
238 240
mine the applicability of regulatory limitations prior to use.
isotopes. The primary isotopes measured are Pu, Pu,
Specific precautionary statements are given in Section 8.
and Pu; however, the system may be adapted for use on
otherspontaneously-fissioningisotopesaswell.Thenumberof
2. Referenced Documents
coincident neutrons detected is proportional to the mass of
2.1 ASTM Standards:
spontaneously-fissioning material.
C 859 Terminology Relating to Nuclear Materials
1.2 The active mode is used to assay fissile material in the
C 986 Guide for Developing Training Programs in the
following ranges.
Nuclear Fuel Cycle
1.2.1 For uranium-bearing items, the DDT can measure
C 1009 Guide for Establishing a Quality Assurance Pro-
the U content in the range from 0.02 to over 100 g.
gram for Analytical Chemistry Laboratories within the
Normally, the assay of items bearing only uranium is per-
Nuclear Industry
This test method is under the jurisdiction ofASTM Committee C26 on Nuclear
Fuel Cycle and is the direct responsibility of Subcommittee C26.10 on Non-
The boldface numbers given in parentheses refer to a list of references at the
Destructive Assay.
end of the text.
Current edition approved Feb. 10, 2001. Published May 2001.
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.
C 1493
C 1030 Test Method for Determination of Plutonium Isoto- 3.1.2 (alpha, n) reactions, n—occur when energetic alpha
3 18
pic Composition by Gamma-Ray Spectrometry particles collide with low atomic number nuclei such as O, F,
C 1068 Guide for Qualification of Measurement Methods or Mg producing single neutrons. Neutrons produced in this
by a Laboratory within the Nuclear Industry manner are not correlated in time and are a source of
C 1128 Guide for the Preparation of Working Reference accidentals in passive mode and background in active mode.
Materials for Use in the Analysis of Nuclear Fuel Cycle
3.1.3 coincidence gate length, n—the time interval follow-
Materials
ing the detection of a neutron during which additional neutron
C 1156 Guide for Establishing Calibration for a Measure-
counts are considered to be in coincidence with the original
ment Method used to Analyze Nuclear fuel Cycle Materi-
neutron. Coincidence gate lengths are generally determined by
als
the die-away time of the detector package. The gate length for
C 1207 TestMethodforNondestructiveAssayofPlutonium
ashieldeddetectorpackageisnominallybetween35and70µs.
in Scrap and Waste by Passive Neutron Coincidence
The gate length for a bare detector package is nominally 250
Counting
µs.
C 1210 Guide for Establishing a Measurement System
3.1.4 coincident neutrons, n—two or more neutrons emitted
Quality Control Program for Analytical Chemistry Labo-
simultaneously from a single event, such as from a nucleus
ratories within the Nuclear Industry
during fission.
C 1215 Guide for Preparing and Interpreting Precision and
3.1.5 combined passive and active, n—amethodwhichuses
Bias Statements in Test Method Standards used in the
passive and active modes to determine the spontaneously-
Nuclear Industry
fissioning and fissile mass components of the waste form,
2.2 ANSI Standard:
respectively.
ANSI N15.20 Guide to Calibrating Nondestructive Assay
3.1.6 depleted uranium, n—uranium containing less than
Systems
the naturally occurring fraction of U isotopes (< 0.7 weight
2.3 U.S. Government Documents:
percent).
DOE Order 435.1 (supercedes DOE Order 5820.2A Radio-
3.1.7 die-away time, n—the average lifetime of the neutron
active Waste Management
population in an NDAassay system as measured from the time
DOE Order 474.1 (supercedes DOE Order 5633.3B) Con-
of emission to detection, escape, or absorption. The average
trol and Accountability of Nuclear Materials
lifetime is the time required for the neutron population to
DOE Order 5630.2 Control and Accountability of Nuclear
decrease by a factor of 1/e. It is a function of several
Materials, Basic Principles
parameters including chamber design, detector design, assay
DOE /WIPP-069 Waste Acceptance Criteria for the Waste
item characteristics, and neutron energy.
Isolation Pilot Plant
3.1.8 early gate, n—the time interval during which the
10CFR71 Packaging and Transport of Radioactive Materi-
thermal-neutron induced prompt-fission neutrons are mea-
als
sured.Typically,thistimeintervalbegins0.4to0.9msafterthe
40CFR191 Environmental Radiation Protection Standards
initiating neutron generator pulse and is 2 to 4 ms in duration.
for Management and Disposal of Spent Nuclear Fuel,
This gate is used only during the active mode. Fig. 1 indicates
High-Level, and Transuranic Radioactive Waste
the approximate delay and length of the early gate in reference
USNRC Regulatory Guide 5.11 Nondestructive Assay of
to a generator pulse.
Special Nuclear Materials Contained in Scrap and Waste
USNRC Regulatory Guide 5.53 Qualification, Calibration,
3.1.9 fissile isotopes, n—isotopes that can be induced to
and Error Estimation Methods for Nondestructive Assay
fission by neutrons with thermal kinetic energy, about 0.025
233 235 239 241
electron volts. U, U, Pu, and Pu are the most
3. Terminology
common fissile isotopes.
3.1 Definitions—The following definitions are needed in
3.1.10 flux monitors, n—detectors in the measurement
addition to those presented in Terminology C 859.
chamber. There are two types of flux monitors:
3.1.1 active mode, n—determines total fissile mass of the
3.1.10.1 cavity flux monitor, n—bare neutron detectors used
assayed item through thermal neutron interrogation and sub-
to monitor the intensity of the interrogating thermal neutron
sequent detection of prompt-fission neutrons released from
flux in the chamber.
induced fission. A 14-MeV neutron generator is pulsed at a
3.1.10.2 drum flux monitors, n—bare neutron detectors
nominal rate of 50 Hz. The pulsed neutrons rapidly thermalize
placed close to the drum and collimated with cadmium to
in the chamber and in the assay item. Thermal neutrons are
measure the thermal neutron flux emitted from the drum.
captured by fissile material which then fissions and immedi-
3.1.11 late gate, n—the time interval during which the
ately releases more neutrons which are detected prior to the
active neutron background is measured. Typically, this time
initiation of the next pulse. The prompt-neutron count rate is
interval begins 8 to 18 ms after the initiating neutron generator
proportional to the mass of fissile material.This mode is called
pulse. Refer to Fig. 1.
the differential die-away technique (DDT). Refer to Fig. 1.
3.1.12 lump, n—that contiguous mass of nuclear material
that is sufficiently large to affect the measured signal. In the
activemode,self-shieldingofthethermalneutroninterrogating
Available from American National Standards Institute, 11 W. 42nd St., 13th
Floor, New York, NY 10036. flux results in an underestimation of the fissile mass. In the
C 1493
FIG. 1 Time History of an Active Assay of Plutonium Using the Differential Die-Away Technique
passive mode, self-multiplication leads to an overestimation of cadmium. These packages measure the neutrons produced by
the spontaneous-fissioning mass. nuclear interactions and are relatively insensitive to thermal-
3.1.13 matrix, n—the material which comprises the bulk of ized neutrons.
the item, except for the assay isotopes and the container. 3.1.17 neutron moderators, n—materials which slow down
3.1.14 matrix-specificcalibration,n—usesacalibrationma- neutrons through elastic scattering interactions. Materials con-
trix for both passive and active assays similar to the matrix to taining large amounts of low atomic weight materials, for
be measured. No matrix correction factors are used. This example, hydrogen, are highly moderating.
calibration is generally not appropriate for other matrices. 3.1.18 passive mode, n—a technique used to determine the
3.1.15 neutron absorbers, n—materials which have rela- spontaneously-fissioning mass in the measured item through
tively large thermal-neutron capture cross-sections. Absorbers the detection of coincident neutrons. The coincident neutrons
withthelargestcapturecross-sectionsarecommonlyknownas are prompt neutrons.
240 240
neutron poisons. Some examples are boron, cadmium, gado- 3.1.19 Pu-effective mass, m , n—the mass of Pu that
eff
linium and lithium. would produce the same coincident neutron response in the
3.1.16 neutron detector package, n—a bundle of two or instrument as the assay item. It is a function of the quantity of
three, 2- or 3-ft long neutron proportional detectors (for even mass isotopes of plutonium in the assay item and
example, Hetubes)surroundedbypolyethylene.Theoutputof fundamental nuclear constants.
thedetectorsfromonepackageiscombinedintoonesignaland 3.1.20 prompt neutrons, n—neutrons released within ap-
-14
processed by a single preamplifier/amplifier/ discriminator. proximately 10 s of the fissioning event. For example, on
235 239
Neutron detector packages are of two types: average, U and Pu emit 2.41 and 2.88, respectively,
3.1.16.1 bare detector package, n—neutron detectors sur- promptneutronsperneutron-inducedfissionevent. Puemits
rounded by polyethylene, but not shielded with cadmium. on an average of 2.16 neutrons per spontaneous fission event.
These packages provide a better efficiency for thermal neu- 3.1.21 pulsed neutron generator, n—a device which can
trons, thus providing a better passive sensitivity when a small supplyapulsedfluxofneutrons.Awidelyusedgeneratoristhe
amount of nuclear material is present. zetatron which produces 14-MeV neutrons via the deuterium-
3.1.16.2 shielded detector package, n—neutron detectors tritium interaction. Zetatrons generate a 10 to 20 µs pulse at a
surroundedbypolyethyleneandshieldedbyathinwrappingof frequency of 50 Hz.
C 1493
3.1.22 spontaneously-fissioning nuclei, n—those nuclei for individual radionuclides, the active and passive modes can
which do not require an external neutron source to undergo be used to give independent measurements of the total pluto-
238 240 242
fission. The most common isotopes are Pu, Pu, Pu, nium mass.
244 252
Cm and Cf. 4.1.2 The system can also be operated only in the passive
mode to measure the plutonium content of scrap or waste, or
3.1.23 totals, n—total number of individual neutrons de-
only in the active mode for measurement of uranium.
tected during the count time, t.
4.1.3 For waste containing both uranium and plutonium,
3.1.23.1 bare totals, n—is the sum of neutrons detected
determination of the mass of the fissile materials is performed
from all bare detector packages.
outside of the standard DDT code.
3.1.23.2 shielded totals, n—is the sum of neutrons detected
4.1.4 In all modes, the relative abundances of the plutonium
from all shielded detector packages.
and uranium isotopes are required to determine the total
3.1.23.3 system totals, n—isthesumofneutronsdetectedin
plutonium and/or uranium mass.
both the bare and shielded detector packages.
4.2 The active assay is performed using the differential
3.1.24 transuranic waste, TRU waste,
...
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