ASTM C1625-19

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it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
Designation: C1625 − 12 C1625 − 19
Standard Test Method for
Uranium and Plutonium Concentrations and Isotopic
Abundances by Thermal Ionization Mass Spectrometry
This standard is issued under the fixed designation C1625; 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 (´) indicates an editorial change since the last revision or reapproval.
1. Scope
1.1 This test method covers the determination of the concentration and isotopic composition of uranium and plutonium in
solutions. The purified uranium or plutonium from samples ranging from nuclear materials to environmental or bioassay matrices
is loaded onto a mass spectrometric filament. The isotopic ratio is determined by thermal ionization mass spectrometry, the
concentration is determined by isotope dilution.
1.2 The values stated in SI units are to be regarded as the standard. Values in parentheses are for information only.
1.3 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 safety safety, health, and healthenvironmental practices and determine the applicability
of regulatory limitations prior to use.
1.4 This international standard was developed in accordance with internationally recognized principles on standardization
established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued
by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
2. Referenced Documents
2.1 ASTM Standards:
C753 Specification for Nuclear-Grade, Sinterable Uranium Dioxide Powder
C757 Specification for Nuclear-Grade Plutonium Dioxide Powder for Light Water Reactors
C776 Specification for Sintered Uranium Dioxide Pellets for Light Water Reactors
C833 Specification for Sintered (Uranium-Plutonium) Dioxide Pellets for Light Water Reactors
C859 Terminology Relating to Nuclear Materials
C1008 Specification for Sintered (Uranium-Plutonium) DioxidePellets—Fast Reactor Fuel (Withdrawn 2014)
C1068 Guide for Qualification of Measurement Methods by a Laboratory Within the Nuclear Industry
C1128 Guide for Preparation of Working Reference Materials for Use in Analysis of Nuclear Fuel Cycle Materials
C1156 Guide for Establishing Calibration for a Measurement Method Used to Analyze Nuclear Fuel Cycle Materials
C1168 Practice for Preparation and Dissolution of Plutonium Materials for Analysis
C1347 Practice for Preparation and Dissolution of Uranium Materials for Analysis
C1411 Practice for The Ion Exchange Separation of Uranium and Plutonium Prior to Isotopic Analysis
C1415 Test Method for Pu Isotopic Abundance By Alpha Spectrometry
237 232 235 238
C1614 Practice for the Determination of Np, Th, U, and U in Urine by Inductively Coupled Plasma-Mass
Spectrometry (ICP-MS) and Gamma Ray Spectrometry (Withdrawn 2015)
D3084 Practice for Alpha-Particle Spectrometry of Water
2.2 Other Documents
International Target Values 2010 for Measurement Uncertainties in Safeguarding Nuclear Materials
This test method is under the jurisdiction of ASTM Committee C26 on Nuclear Fuel Cycle and is the direct responsibility of Subcommittee C26.05 on Methods of Test.
Current edition approved June 1, 2012Sept. 15, 2019. Published July 2012October 2019. Originally approved in 2005. Last previous edition approved in 20052012 as
C1625C1625 – 12.–05. DOI: 10.1520/C1625-12.10.1520/C1625-19.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
The last approved version of this historical standard is referenced on www.astm.org.
K. Zhao et. al., “International Target Values 2010 for Measurement Uncertainties in Safeguarding Nuclear Materials,” International Atomic Energy Agency STR-368,
2010.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
C1625 − 19
3. Terminology
3.1 For definitions of pertinent terms not listed here, see Terminology C859.
3.2 Definitions of Terms Specific to This Standard:
3.2.1 isotope dilution mass spectrometry (IDMS)—isotope ratio measurements, using mass spectrometry, of samples spiked with
accurately known weights of individual low abundance isotopes (adapted from Practice determination of elemental concentration
of a sample, by mass spectrometry, using the addition of a spike material to the sample with significantly different isotopic
composition from the sample and accurately characterized mass of the major spike isotope.C1614).
4. Summary of Test Method
4.1 The uranium and plutonium are separated from each other and purified from other elements by selective extraction, anion
exchange (such as in C1411) or extraction chromatography. The uranium and plutonium fractions are individually mounted on
filaments of rhenium, tungsten, or tantalum, and are analyzed by thermal ionization mass spectrometry to determine the relative
233 242 244
abundance of the isotopes. If a known U or Pu (or Pu) spike is added prior to chemical separation the corresponding
elemental concentration may also be determined by isotope dilution mass spectrometry (IDMS).
5. Significance and Use
5.1 Uranium and plutonium oxides can be used as a nuclear-reactor fuel in the form of pellets. In order to be suitable for use
as a nuclear fuel the starting material must meet certain specifications, such as found in Specifications C757, C833, C753, C776,
C1008, or as specified by the purchaser. The uranium and/or plutonium concentration and concentration, plutonium concentration,
or both, and the isotopic abundances are measured by mass spectrometry following this test method.
5.2 The separated heavy element fractions placed on mass spectrometric filaments must be very pure. The quantity required
depends upon the sensitivity of the instrument detection system. If an electron multiplier detector is to be used, only a few
nanograms are required. If a Faraday cup is used, a few micrograms are needed. Chemical purity of the sample becomes more
important as the sample size decreases, because ion emission of the sample is suppressed by impurities.
6. Interferences
238 241
6.1 Uranium-238 and Pu interfere in the measurement of each other, and Am interferes with the measurement of
Pu, thereby requiring chemical separation. Removal of impurities provides uniform ionization of uranium or plutonium, hence
improved precision, and reduces the interference from molecular species of the same mass number as the uranium or plutonium
isotopes being measured. Isotopic analysis of plutonium should be completed within a reasonable time period (approximately 20
241 241
days) after separation from americium to minimize interference of Am ingrowth from Pu.
6.2 Extreme care must be taken to avoid contamination of the sample by environmental uranium. The level of uranium
contamination should be measured by analyzing an aliquot of 8M nitric acid as a reagent blank and calculating the amount of
uranium it contains.
6.3 When Pu is present in low abundance it may be necessary to measure it by alpha-spectrometry following Test Method
C1415 or Practice D3084.
7. Apparatus
7.1 Mass Spectrometer—The suitability of mass spectrometers for use with this test method of analysis shall be evaluated by
means of performance tests described in this test method. The mass spectrometer used should possess the following characteristics:
7.1.1 A thermal ionization source with single or multiple filaments of rhenium, tungsten or tantalum.
7.1.2 An analyzer radius sufficient to resolve adjacent masses in the mass-to-charge range being studied, that is, m/z = 233 to
+ + 236 235
238 for U or 238 to 244 for Pu . Abundance sensitivity must be great enough to detect one part of U in 400 parts U.
7.1.3 A minimum of one stage of magnetic deflection. Since the resolution is not affected, the angle of deflection may vary with
the instrument design.
7.1.4 A mechanism for changing samples.
7.1.5 A direct-current (Faraday cup) or electron multiplier detector, as a single detector system or, several detectors in a multi
collector design, followed by a current measuring device.
-6
7.1.6 A pumping system to attain a vacuum of less than 400 μPa (3 × 10 torr) in the source, the analyzer, and the detector
-8
regions. The ability to measure minor isotopes is directly related to analyzer pressure. Analyzer pressures below 7 μPa (5 × 10
torr) are preferable.
7.1.7 A mechanism to scan masses by means of varying the magnetic field or the accelerating voltage.
7.1.8 A computer to collect and process data produced by the instrument.
7.2 An Optical Pyrometer should be available to determine the filament temperature.
7.3 Filament preheating and degassing unit for cleaning unloaded filaments.
C1625 − 19
8. Materials and Reagents
8.1 Purity of Reagents—all reagents used in the final purification and filament loading steps should be of the highest purity
available. Other grades may be used if they are determined not to affect the final result.
8.2 Filaments—high purity, the size and configuration are instrument dependent. Filaments should be degassed, and maybe
carbon saturated, prior to use.
NOTE 1—The purity of the filaments should be confirmed with each batch received. Zone refined filaments should be used for low-level analyses.
8.3 Certified Reference Materials (CRM)—of varying isotopic composition, traceable to a national standard body , for use as
calibration and quality control standards.
8.4 Spikes—Materials, preferably CRMs, for use in the determination of elemental concentration by IDMS.IDMS, examples of
233 238 233
spikes used for uranium concentration include NBL CRM 111-A ( U spike), NBL CRM 112-A ( U spike), IRMM 040a ( U
235 242
spike), and IRMM 054 ( U spike). For plutonium commonly used spikes include NBL CRM 130 ( Pu spike), and IRMM
049c/d/e/f series ( Pu spikes).
9. Instrument Calibration
9.1 The measurement method may be qualified following Guide C1068 and calibrated following Guide C1156.
9.2 Mass Calibration—The relationship between the masses to be analyzed and the magnetic field needed to direct the ion beam
for those masses to the detector shall be updated on a periodic basis. The interval between mass calibrations is determined by the
manufacturer. The stability of the mass calibration is affected by laboratory conditions. It is recommended that a mass calibration
check be performed prior to each day’s analysis.
9.3 Peak Centering—The peak centering routine is used as fine adjustment to ensure that the ion beam is centered within the
detector. This routine should be used during the mass calibration check, and at the start of each sample analysis.
9.4 Amplifier Baseline/Background Calibration—The baseline, or background, for the Faraday cup amplifiers is the background
signal that can be measured when there is no ion beam to the detector. This shall be measured on a routine basis and checked for
stability. The amplifier baseline should be performed at the beginning of each analysis day.
9.5 Amplifier Gain Calibration—The amplifier gain calibration is typically performed as a programmed routine on the mass
spectrometer. A constant voltage is applied to each amplifier and the amplifier response is recorded. The output for each amplifier
is normalized to a single amplifier to determine a gain factor for each amplifier. This calibration is not required for single collector
systems. Depending on the stability of the amplifier system, the amplifier gain may be performed on a weekly basis, or as often
as prior to each analysis.
9.6 The measurement and correction for mass discrimination and dead time are critical factors in obtaining precise and accurate
results. Equally critical to the accuracy of the measurement is the linearity of the total measuring circuit including the collector.
Calibration of the mass spectrometer is based on the assumption that these are the only sources of significant (>1 in 10 ) systematic
error in the measurement. Thus, accurate calibration is made by analyzing standards of known isotopic composition under
conditions in which cross-contamination between samples does not occur.
9.6.1 For multi-collector systems, the bias between collectors may also be an important factor in the systematic error and thus
must also be evaluated prior to making measurements.
9.6.2 For very low-level samples, or samples with extreme ratios, other corrections may need to be made, for example, dark
count data/dark current.
9.7 Mass Discrimination—Use a traceable isotopic standard to determine the mass discrimination. The deviation from the
certified value of the 235/238 ratio (for U) or the 239/242 ratio (for Pu) is a measure of the mass discrimination of the mass
spectrometer.
9.7.1 Calculate the elemental mass discrimination bias factor, B, as follows:
B 5 ~1/c!@~aR /R ! 2 1# (1)
i/j s
where:
B = mass discrimination factor,
aR = average measured atom ratio of isotope i to isotope j
i/j
R = certified atom ratio value of the CRM
s
c = Δ mass/mass. The values for c for various ratios and ion species include:
Available from USDOE New Brunswick Laboratory,NBL Program Office, Argonne, IL, or other equivalent source.
C1625 − 19
+ +
ratio U or Pu
235 238
U/ U +3/238
236 235
U/ U -1/235
233 238
U/ U +5/238
234 235
U/ U +1/235
242 239
Pu/ Pu -3/239
240 239
Pu/ Pu -1/239
241 239
Pu/ Pu -2/239
238 239
Pu/ Pu +1/239
9.7.2 Correct every measured ratio, R , for mass discrimination as follows:
i/j
R 5 a R /~11cB! (2)
i/j i/j
where R is the corre
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