1、Designation: C 1458 00Standard Test Method forNondestructive Assay of Plutonium, Tritium and241Am byCalorimetric Assay1This standard is issued under the fixed designation C 1458; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the
2、year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.1. Scope1.1 This test method describes the nondestructive assay(NDA) of plutonium, tritium, and241Am using heat flowcalor
3、imetry. For plutonium the range of applicability corre-sponds to2000 g quantities while for tritium therange extends from 0.001 g to 10 g. This test method can beapplied to materials in a wide range of container sizes up to 50L. It has been used routinely to assay items whose thermalpower ranges fro
4、m 0.001 W to 135 W.1.2 This test method requires knowledge of the relativeabundances of the plutonium isotopes and the241Am/Pu massratio to determine the total plutonium mass.1.3 This test method provides a direct measure of tritiumcontent.1.4 This test method provides a measure of241Am either asa s
5、ingle isotope or mixed with plutonium.1.5 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory li
6、mitations prior to use.2. Referenced Documents2.1 ASTM Standards:C 697 Test Methods for Chemical, Mass Spectrometry, andSpectrochemical Analysis of Nuclear-Grade PlutoniumDioxide Powder and Pellets2C 859 Terminology Relating to Nuclear Materials2C 1009 Guide for Establishing a Quality Assurance Pro-
7、gram for Analytical Chemistry Laboratories Within theNuclear Industry2C 1030 Test Method for Determination of Plutonium Isoto-pic Composition by Gamma-Ray Spectrometry22.2 ANSI Standards:3ANSI N15.22 PlutoniumBearing SolidsCalibrationTechniques for Calorimetric AssayANSI N15.54 Radiometric Calorimet
8、ersMeasurementControl Program3. Terminology3.1 DefinitionsTerms shall be defined in accordance withTerminology C 859 except for the following:3.1.1 baselinethe calorimeter output signal with no heat-generating item in the calorimeter sample chamber.3.1.2 basepowera constant thermal power applied in
9、acalorimeter through an electrical resistance heater with noheat-generating item in the sample chamber.3.1.3 calorimetera device to measure heat or rate-of-heatgeneration.3.1.4 calorimetric assaydetermination of the mass ofradioactive material through the measurement of its thermalpower by calorimet
10、ry and the use of nuclear decay constantsand, if necessary, additional isotopic measurements.3.1.5 effective specific powerthe rate of energy emissionper unit mass of plutonium at the time of measurement.3.1.6 equilibriumthe point at which the temperature of thecalorimeter measurement cell and the i
11、tem being measuredstops changing.3.1.7 heat distribution errorthe bias arising from thelocation of the heat source within the calorimeter chamber.3.1.8 heat-flow calorimetera calorimeter so constructedthat the heat generated in the calorimeter flows past a tempera-ture sensing element, through a the
12、rmal resistance, to aconstant temperature heat sink.3.1.9 passive modea mode of calorimeter operation whereno external power is applied to the calorimeter except thecurrent needed to excite the Wheatstone Bridge circuit.3.1.10 sensitivitythe change in calorimeter response perWatt of thermal power (u
13、sually in units of micro Volts perWatt) for a heat flow calorimeter.3.1.11 servo controla mode of calorimeter operationwhere a constant applied thermal power is maintained in acalorimeter measurement chamber through the use of anelectric resistance heater in a closed loop control system.3.1.12 speci
14、fic powerthe rate of energy emission byionizing radiation per unit mass of an isotope, such as241Am ortritium.1This test method is under the jurisdiction of ASTM Committee C-26 on NuclearFuel Cycle and is the direct responsibility of Subcommittee C26.10 on Nondestruc-tive Analysis.Current edition ap
15、proved Jan. 10, 2000. Published March 2000.2Annual Book of ASTM Standards, Vol 12.01.3Available from American National Standards Institute, 11 W. 42nd St., 13thFloor, New York, NY 10036.1Copyright ASTM, 100 Barr Harbor Drive, West Conshohocken, PA 19428-2959, United States.3.1.13 thermal diffusivity
16、the ratio of thermal conductivityto the heat capacity. It measures the ability of a material toconduct thermal energy relative to its ability to store thermalenergy.3.1.14 thermal resistanceratio of the temperature differ-ence at two different surfaces to the heat flux through thesurfaces at equilib
17、rium.3.1.15 thermal time constantan exponential decay con-stant describing the rate at which a temperature approaches aconstant value.3.1.16 thermelthe THERMal ELement of the calorimeter,including the sample chamber, and temperature sensor.3.1.17 traceabilityrelating individual measurementsthrough a
18、n unbroken chain of calibrations to U.S. or interna-tional primary reference materials or to accepted values offundamental physical constants.4. Summary of Test Method4.1 The item is placed in the calorimeter measurementchamber and the total heat flow at equilibrium, that is, thethermal power, from
19、the item is determined by temperaturesensors and associated electronic equipment.4.2 The thermal power emitted by a test item is directlyrelated to the quantity of radioactive material in it. The totalpower generated by ionizing radiation absorbed in the item iscaptured by the calorimeter.4.3 The ma
20、ss of plutonium, tritium, or241Am (m) is calcu-lated from the measured thermal power of an item (Wi) usingthe following relationship:m 5WiPeff(1)where:Peff5 the effective specific power calculated from theisotopic composition of the item (see Appendix X1for details of the calculation of Pefffor plut
21、onium).4.3.1 For tritium the measured thermal power can be di-rectly transformed into mass using the specific power oftritium, Peff5 0.3240 6 0.00045 (SD) W/g (1).44.3.2 For241Am as a single isotope the measured thermalpower can be directly transformed into mass using the specificpower of241Am, Peff
22、5 0.1142 6 0.00042 (SD) W/g (see TableX1.1).4.3.3 For241Am mixed with plutonium, the241Am mass,MAm, is determined byMAm5 RAmMPu(2)where:RAm5 the mass ratio of241Am to Pu, andMPu5 the mass of plutonium.5. Significance and Use5.1 This test method is presently the most accurate NDAtechnique for the ass
23、ay of many physical forms of plutonium.Isotopic measurements by gamma-ray spectroscopy or destruc-tive analysis techniques are part of the test method when it isapplied to the assay of plutonium.5.1.1 Calorimetry has been applied to a wide variety ofPu-bearing solids including metals, alloys, oxides
24、 fluorides,mixed Pu-U oxides, mixed oxide fuel pins, waste, and scrap,for example, ash, ash heels, salts, crucibles, and graphitescarfings) (2,3). The test method has been routinely used atU.S. and European facilities for plutonium process measure-ments and nuclear material accountability for the l
25、ast 30 years(2-6).5.1.2 Plutonium-bearing materials have been measured incalorimeter containers ranging in size from 0.025 to 0.30 m indiameter and from 0.076 to 0.43 m in height.5.1.3 Gamma-ray spectroscopy typically is used to deter-mine the plutonium isotopic composition and241Am/Pu ratio(see Tes
26、t Method C 1030). Isotopic information from massspectrometry and alpha counting measurements may be used(see Test Method C 697).5.2 The test method is the most accurate NDA method forthe measurement of tritium. For many physical forms of tritiumcompounds calorimetry is the only practical measurement
27、technique available.5.3 Unlike other NDA techniques no physical standardsrepresentative of the materials being assayed are required forthe test method.5.3.1 The test method is largely independent of the elemen-tal distribution of the nuclear materials in the matrix.5.3.2 The accuracy of the method c
28、an be degraded formaterials with inhomogeneous isotopic composition.5.4 The thermal power measurement is traceable to the U.S.or other national measurement systems through electricalstandards used to directly calibrate the calorimeters or tocalibrate secondary238Pu heat standards.5.5 Heat-flow calor
29、imetry has been used to prepare second-ary standards for neutron and gamma-ray assay systems (7).5.6 The calorimetry measurement times are typically longerthan other NDA techniques. The thermal diffusivity of thematrix of the item and its packaging will determine the thermaltime constant for heat tr
30、ansfer from the item and hence themeasurement time.5.6.1 Calorimeter measurement times range from 20 min-utes (8) for smaller, temperature-conditioned, containers up to24 h for larger containers and items with long thermal-timeconstants.5.6.2 Measurement times may be reduced by using equilib-rium pr
31、ediction techniques, by temperature preconditioning ofthe item to be measured, or operating the calorimeter using theservo-control technique.6. Interferences6.1 Interferences for calorimetry are those processes thatwould add or subtract thermal power from the power of theradionuclides being assayed.
32、6.2 Interferences can be phase changes or endothermic orexothermic chemical reactions, such as oxidation.6.3 Undetected heat-generating radionuclides would addadditional thermal power to the measurement.4The boldface numbers in parentheses refer to the list of references at the end ofthis standard.C
33、 145827. Apparatus7.1 Calorimeters are designed to measure different sizes andquantities of nuclear material. Different types of heat-flowcalorimeter systems share the common attributes listed below.7.1.1 Measurement ChamberHeat flow calorimeters havea cylindrical measurement chamber from which all
34、of the heatflow generated by radioactive decay is directed through tem-perature sensors.7.1.1.1 An electrical heater may be built into the walls or thebase of the chamber to provide measured amounts of thermalpower into the calorimeter well.7.1.1.2 Insulation is used to shield the chamber from outsi
35、detemperature variations that would influence the thermal powermeasurement. Typically, an insulated plug is inserted above theitem container inside the calorimeter. For some calorimetertypes an insulating plug is installed permanently below themeasurement chamber.7.1.2 Calorimeter CanThe item to be
36、measured may beplaced in a special can that is designed to be inserted andremoved easily from the calorimeter. It will have only a smallair gap to provide good thermal conductivity between the outersurface of the can and the inner surface of the measurementchamber.7.1.3 Temperature SensorsTemperatur
37、e sensors consist ofcommercially available thermistors, thermocouples, tempera-ture sensitive resistance wire, or thermopiles.7.1.4 Thermal SinkThe temperature increases due to heatflows generated by items are measured against a referencetemperature of a thermal sink. The thermal sink could be awate
38、r bath or air bath or a metal block maintained by athermoelectric cooler/heater. In the case of servo-controlledcalorimeters, the measurement chamber is maintained at anelevated temperature compared to the reference temperature.7.1.5 Electrical ComponentsSensitive, stable electroniccomponents are re
39、quired for accurate calorimeter measure-ments.7.1.5.1 High precision voltmeters are required to measurethe voltage changes generated from the temperature sensors.The resolution of the voltmeters should be better than one partper million of the voltage range.7.1.5.2 Stable power supplies are necessar
40、y to provideconstant current to resistance sensors and calorimeter heaters.7.1.5.3 Precision resistors with certified resistances trace-able to a national measurement system may be used withcalibrated voltmeters to accurately determine electrical powerdelivered to heaters in the calorimeter chamber.
41、 If radioactiveheat standards are used as part of the measurement controlprogram the calorimeter voltmeters need not be calibrated, norare precision resistors required.7.1.5.4 For a calorimeter operated in the servo (powerreplacement) mode digital-to-analog controller units are usedto supply power t
42、o an internal resistance heater to maintain aconstant temperature differential across thermal resistances.7.1.6 Heat StandardsThermal power standards are re-quired to calibrate the calorimeter and may be used asmeasurement control standards to check the stability of calo-rimeter performance (9-12).7
43、1.6.1 Radioactive heat standards, typically poweredby238Pu, also may be used to calibrate calorimeters over arange of thermal powers. These standards are calibrated againstelectrical standards traceable to the national measurementsystem.7.1.6.2 Removable electrical heaters may be used to cali-brate
44、 calorimeters. For this type of standard the power gener-ated by the heater must be measured with electrical equipmentregularly calibrated against standards or standard methodstraceable to a national measurement system. The power sup-plied to the electrical calibration heater may be varied over ther
45、ange of calibration.7.1.7 Wheatstone BridgeWhen temperature sensitive re-sistance wire is used as the sensor, it usually is arranged in aWheatstone Bridge configuration shown in Fig. 1.7.1.8 Data Acquisition SystemCalorimeter data collectionis performed using computer-based data acquisition systems.
46、The system should be able to read signal voltages or resistancesat a fixed time frequency and be able to calculate and report apower value from the item using software that detects equilib-rium. Graphics and numerical data indicating system powerand temperatures may be displayed to aid the operator.
47、7.1.9 AdaptersCylindrical metal adapters may be fabri-cated to accept smaller calorimeter containers in the calorim-eter well, and thus, provide good thermal contact between theouter container surface and calorimeter inner wall. Heat-conducting metal foil or metal gauze fill material, typically Alor
48、 Cu, or metal shot can be used in place of machined metaladapters. Smaller items may be placed in the calorimetercontainer and the void space inside the container may be filledwith metal fill material or shot to provide good thermal contact.7.1.10 Loading ApparatusA hoist or assist may be used toloa
49、d and unload items. Robotic loading systems may be used tohandle the items.8. Heat-Flow Calorimeter Systems8.1 EquilibriumA heat flow calorimeter consists of asample chamber thermally insulated from a constant tempera-ture environment by a thermal resistance. When an item isplaced in the calorimeter the temperature difference across thethermal resistance is disturbed and the difference changes withtime until it converges to a constant value and equilibrium isachieved. The magnitude of the shift in the measured voltage(passive mode) or supplied power (servo m
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