ASTM C1458-00
(Test Method)Standard Test Method for Nondestructive Assay of Plutonium, Tritium and 241Am by Calorimetric Assay
Standard Test Method for Nondestructive Assay of Plutonium, Tritium and <sup>241</sup>Am by Calorimetric Assay
SCOPE
1.1 This test method describes the nondestructive assay (NDA) of plutonium, tritium, and 241Am using heat flow calorimetry. For plutonium the range of applicability corresponds to 1 g to > 2000 g quantities while for tritium the range extends from 0.001 g to > 10 g. This test method can be applied to materials in a wide range of container sizes up to 50 L. It has been used routinely to assay items whose thermal power ranges from 0.001 W to 135 W.
1.2 This test method requires knowledge of the relative abundances of the plutonium isotopes and the 241Am/Pu mass ratio to determine the total plutonium mass.
1.3 This test method provides a direct measure of tritium content.
1.4 This test method provides a measure of 241Am either as a single isotope or mixed with plutonium.
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:C1458–00
Standard Test Method for
NondestructiveAssay of Plutonium, Tritium and Am by
Calorimetric Assay
This standard is issued under the fixed designation C 1458; 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 ANSI N15.22 Plutonium—Bearing Solids–Calibration
Techniques for Calorimetric Assay
1.1 This test method describes the nondestructive assay
ANSI N15.54 Radiometric Calorimeters–Measurement
(NDA) of plutonium, tritium, and Am using heat flow
Control Program
calorimetry. For plutonium the range of applicability corre-
sponds to < 1 g to > 2000 g quantities while for tritium the
3. Terminology
range extends from 0.001 g to > 10 g. This test method can be
3.1 Definitions—Terms shall be defined in accordance with
applied to materials in a wide range of container sizes up to 50
Terminology C 859 except for the following:
L. It has been used routinely to assay items whose thermal
3.1.1 baseline—the calorimeter output signal with no heat-
power ranges from 0.001 W to 135 W.
generating item in the calorimeter sample chamber.
1.2 This test method requires knowledge of the relative
3.1.2 basepower—a constant thermal power applied in a
abundances of the plutonium isotopes and the Am/Pu mass
calorimeter through an electrical resistance heater with no
ratio to determine the total plutonium mass.
heat-generating item in the sample chamber.
1.3 This test method provides a direct measure of tritium
3.1.3 calorimeter—a device to measure heat or rate-of-heat
content.
generation.
1.4 This test method provides a measure of Am either as
3.1.4 calorimetric assay—determination of the mass of
a single isotope or mixed with plutonium.
radioactive material through the measurement of its thermal
1.5 This standard does not purport to address all of the
power by calorimetry and the use of nuclear decay constants
safety concerns, if any, associated with its use. It is the
and, if necessary, additional isotopic measurements.
responsibility of the user of this standard to establish appro-
3.1.5 effective specific power—the rate of energy emission
priate safety and health practices and determine the applica-
per unit mass of plutonium at the time of measurement.
bility of regulatory limitations prior to use.
3.1.6 equilibrium—thepointatwhichthetemperatureofthe
2. Referenced Documents calorimeter measurement cell and the item being measured
stops changing.
2.1 ASTM Standards:
3.1.7 heat distribution error—the bias arising from the
C 697 Test Methods for Chemical, Mass Spectrometry, and
location of the heat source within the calorimeter chamber.
Spectrochemical Analysis of Nuclear-Grade Plutonium
3.1.8 heat-flow calorimeter—a calorimeter so constructed
Dioxide Powder and Pellets
2 that the heat generated in the calorimeter flows past a tempera-
C 859 Terminology Relating to Nuclear Materials
ture sensing element, through a thermal resistance, to a
C 1009 Guide for Establishing a Quality Assurance Pro-
constant temperature heat sink.
gram for Analytical Chemistry Laboratories Within the
3.1.9 passive mode—amodeofcalorimeteroperationwhere
Nuclear Industry
no external power is applied to the calorimeter except the
C 1030 Test Method for Determination of Plutonium Isoto-
current needed to excite the Wheatstone Bridge circuit.
pic Composition by Gamma-Ray Spectrometry
3.1.10 sensitivity—the change in calorimeter response per
2.2 ANSI Standards:
Watt of thermal power (usually in units of micro Volts per
Watt) for a heat flow calorimeter.
ThistestmethodisunderthejurisdictionofASTMCommitteeC-26onNuclear
3.1.11 servo control—a mode of calorimeter operation
Fuel Cycle and is the direct responsibility of Subcommittee C26.10 on Nondestruc-
where a constant applied thermal power is maintained in a
tive Analysis.
calorimeter measurement chamber through the use of an
Current edition approved Jan. 10, 2000. Published March 2000.
Annual Book of ASTM Standards, Vol 12.01.
electric resistance heater in a closed loop control system.
Available from American National Standards Institute, 11 W. 42nd St., 13th
Floor, New York, NY 10036.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
C1458
3.1.12 specific power—the rate of energy emission by 5. Significance and Use
ionizingradiationperunitmassofanisotope,suchas Amor
5.1 This test method is presently the most accurate NDA
tritium.
technique for the assay of many physical forms of plutonium.
3.1.13 thermal diffusivity—the ratio of thermal conductivity
Isotopicmeasurementsbygamma-rayspectroscopyordestruc-
to the heat capacity. It measures the ability of a material to
tive analysis techniques are part of the test method when it is
conduct thermal energy relative to its ability to store thermal
applied to the assay of plutonium.
energy.
5.1.1 Calorimetry has been applied to a wide variety of
3.1.14 thermal resistance—ratio of the temperature differ-
Pu-bearing solids including metals, alloys, oxides, fluorides,
ence at two different surfaces to the heat flux through the
mixed Pu-U oxides, mixed oxide fuel pins, waste, and scrap,
surfaces at equilibrium.
for example, ash, ash heels, salts, crucibles, and graphite
3.1.15 thermal time constant—an exponential decay con-
scarfings) (2,3). The test method has been routinely used at
stant describing the rate at which a temperature approaches a
U.S. and European facilities for plutonium process measure-
constant value.
ments and nuclear material accountability for the last 30 years
3.1.16 thermel—theTHERMal ELement of the calorimeter,
(2-6).
including the sample chamber, and temperature sensor.
5.1.2 Plutonium-bearing materials have been measured in
3.1.17 traceability—relating individual measurements
calorimeter containers ranging in size from 0.025 to 0.30 m in
through an unbroken chain of calibrations to U.S. or interna-
diameter and from 0.076 to 0.43 m in height.
tional primary reference materials or to accepted values of
5.1.3 Gamma-ray spectroscopy typically is used to deter-
fundamental physical constants.
mine the plutonium isotopic composition and Am/Pu ratio
(see Test Method C 1030). Isotopic information from mass
4. Summary of Test Method
spectrometry and alpha counting measurements may be used
(see Test Method C 697).
4.1 The item is placed in the calorimeter measurement
5.2 The test method is the most accurate NDA method for
chamber and the total heat flow at equilibrium, that is, the
themeasurementoftritium.Formanyphysicalformsoftritium
thermal power, from the item is determined by temperature
compounds calorimetry is the only practical measurement
sensors and associated electronic equipment.
technique available.
4.2 The thermal power emitted by a test item is directly
5.3 Unlike other NDA techniques no physical standards
related to the quantity of radioactive material in it. The total
representative of the materials being assayed are required for
power generated by ionizing radiation absorbed in the item is
the test method.
captured by the calorimeter.
5.3.1 The test method is largely independent of the elemen-
4.3 The mass of plutonium, tritium, or Am (m) is calcu-
tal distribution of the nuclear materials in the matrix.
lated from the measured thermal power of an item (W) using
i
5.3.2 The accuracy of the method can be degraded for
the following relationship:
materials with inhomogeneous isotopic composition.
W
i
m 5 (1)
5.4 The thermal power measurement is traceable to the U.S.
P
eff
or other national measurement systems through electrical
where:
standards used to directly calibrate the calorimeters or to
P 5 the effective specific power calculated from the
eff
calibrate secondary Pu heat standards.
isotopic composition of the item (see Appendix X1
5.5 Heat-flow calorimetry has been used to prepare second-
for details of the calculation of P for plutonium).
eff
ary standards for neutron and gamma-ray assay systems (7).
4.3.1 For tritium the measured thermal power can be di-
5.6 The calorimetry measurement times are typically longer
rectly transformed into mass using the specific power of
than other NDA techniques. The thermal diffusivity of the
tritium, P 5 0.3240 6 0.00045 (SD) W/g (1).
eff
matrix of the item and its packaging will determine the thermal
4.3.2 For Am as a single isotope the measured thermal
time constant for heat transfer from the item and hence the
power can be directly transformed into mass using the specific
measurement time.
powerof Am, P 50.1142 60.00042(SD)W/g(seeTable
eff
5.6.1 Calorimeter measurement times range from 20 min-
X1.1).
utes (8) for smaller, temperature-conditioned, containers up to
241 241
4.3.3 For Am mixed with plutonium, the Am mass,
24 h for larger containers and items with long thermal-time
M , is determined by
Am constants.
M 5 R M (2)
5.6.2 Measurement times may be reduced by using equilib-
Am Am Pu
rium prediction techniques, by temperature preconditioning of
where:
the item to be measured, or operating the calorimeter using the
R 5 the mass ratio of Am to Pu, and
Am
servo-control technique.
M 5 the mass of plutonium.
Pu
6. Interferences
6.1 Interferences for calorimetry are those processes that
would add or subtract thermal power from the power of the
The boldface numbers in parentheses refer to the list of references at the end of
this standard. radionuclides being assayed.
C1458
6.2 Interferences can be phase changes or endothermic or 7.1.6 Heat Standards—Thermal power standards are re-
exothermic chemical reactions, such as oxidation. quired to calibrate the calorimeter and may be used as
measurement control standards to check the stability of calo-
6.3 Undetected heat-generating radionuclides would add
additional thermal power to the measurement. rimeter performance (9-12).
7.1.6.1 Radioactive heat standards, typically powered
by Pu, also may be used to calibrate calorimeters over a
7. Apparatus
rangeofthermalpowers.Thesestandardsarecalibratedagainst
7.1 Calorimeters are designed to measure different sizes and
electrical standards traceable to the national measurement
quantities of nuclear material. Different types of heat-flow
system.
calorimeter systems share the common attributes listed below.
7.1.6.2 Removable electrical heaters may be used to cali-
7.1.1 Measurement Chamber—Heat flow calorimeters have
brate calorimeters. For this type of standard the power gener-
a cylindrical measurement chamber from which all of the heat
ated by the heater must be measured with electrical equipment
flow generated by radioactive decay is directed through tem-
regularly calibrated against standards or standard methods
perature sensors.
traceable to a national measurement system. The power sup-
7.1.1.1 Anelectricalheatermaybebuiltintothewallsorthe
plied to the electrical calibration heater may be varied over the
base of the chamber to provide measured amounts of thermal
range of calibration.
power into the calorimeter well.
7.1.7 Wheatstone Bridge—When temperature sensitive re-
7.1.1.2 Insulationisusedtoshieldthechamberfromoutside
sistance wire is used as the sensor, it usually is arranged in a
temperature variations that would influence the thermal power
Wheatstone Bridge configuration shown in Fig. 1.
measurement.Typically,aninsulatedplugisinsertedabovethe
7.1.8 Data Acquisition System—Calorimeter data collection
item container inside the calorimeter. For some calorimeter
is performed using computer-based data acquisition systems.
types an insulating plug is installed permanently below the
Thesystemshouldbeabletoreadsignalvoltagesorresistances
measurement chamber.
at a fixed time frequency and be able to calculate and report a
7.1.2 Calorimeter Can—The item to be measured may be
power value from the item using software that detects equilib-
placed in a special can that is designed to be inserted and
rium. Graphics and numerical data indicating system power
removed easily from the calorimeter. It will have only a small
and temperatures may be displayed to aid the operator.
air gap to provide good thermal conductivity between the outer
7.1.9 Adapters—Cylindrical metal adapters may be fabri-
surface of the can and the inner surface of the measurement
cated to accept smaller calorimeter containers in the calorim-
chamber.
eter well, and thus, provide good thermal contact between the
7.1.3 Temperature Sensors—Temperature sensors consist of
outer container surface and calorimeter inner wall. Heat-
commercially available thermistors, thermocouples, tempera-
conducting metal foil or metal gauze fill material, typically Al
ture sensitive resistance wire, or thermopiles.
or Cu, or metal shot can be used in place of machined metal
7.1.4 Thermal Sink—The temperature increases due to heat
adapters. Smaller items may be placed in the calorimeter
flows generated by items are measured against a reference
container and the void space inside the container may be filled
temperature of a thermal sink. The thermal sink could be a
withmetalfillmaterialorshottoprovidegoodthermalcontact.
water bath or air bath or a metal block maintained by a
7.1.10 LoadingApparatus—Ahoistorassistmaybeusedto
thermoelectric cooler/heater. In the case of servo-controlled
loadandunloaditems.Roboticloadingsystemsmaybeusedto
calorimeters, the measurement chamber is maintained at an
handle the items.
elevated temperature compared to the reference temperature.
8. Heat-Flow Calorimeter Systems
7.1.5 Electrical Components—Sensitive, stable electronic
components are required for accurate calorimeter measure-
8.1 Equilibrium—A heat flow calorimeter consists of a
ments.
sample chamber thermally insulated from a constant tempera-
7.1.5.1 High precision voltmeters are required to measure
ture environment by a thermal resistance. When an item is
the voltage changes generated from the temperature sensors.
placed in the calorimeter the temperature difference across the
The resolution of the voltmeters should be better than one part
thermal resistance is disturbed and the difference changes with
per million of the voltage range.
time until it converges to a constant value and equilibrium is
7.1.5.2 Stable power supplies are necessary to provide
achieved. The magnitude of the shift in the measured voltage
constant current to resistance sensors and calorimeter heaters.
(passive mode) or supplied power (servo mode) is used to
7.1.5.3 Precision resistors with certified resistances trace- determine the thermal power of the ite
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