ASTM C1165-23

Standard Test Method for Determining Plutonium by Controlled-Potential Coulometry in H<inf>2</inf>SO<inf>4</inf> at a Platinum Working Electrode

SIGNIFICANCE AND USE
5.1 This test method is used to ascertain whether or not materials meet specifications for plutonium concentration or plutonium mass fraction.  
5.1.1 The materials (nuclear grade plutonium nitrate solutions, plutonium metal, plutonium oxide powder, and mixed oxide and carbide powders and pellets) to which this test method applies are subject to nuclear safeguards regulations governing their possession and use. However, adherence to this test method does not automatically guarantee regulatory acceptance of the resulting safeguards measurements. It remains the sole responsibility of the user of this test method to ensure that its application to safeguards has the approval of the proper regulatory authorities.  
5.1.2 When used in conjunction with appropriate certified reference materials (CRMs), this test method can demonstrate traceability to the international measurements system (SI).  
5.2 Fitness for Purpose of Safeguards and Nuclear Safety Application—Methods intended for use in safeguards and nuclear safety applications shall meet the requirements specified by Guide C1068 for use in such applications.  
5.3 A chemical calibration of the coulometer is necessary for accurate results.
FIG. 1 Example of a Cell Design Used at Los Alamos National Laboratory (LANL)
SCOPE
1.1 This test method covers the determination of milligram quantities of plutonium in unirradiated uranium-plutonium mixed oxide having a U/Pu ratio range of 0.1 to 10. This test method is also applicable to plutonium metal, plutonium oxide, uranium-plutonium mixed carbide, various plutonium compounds including fluoride and chloride salts, and plutonium solutions.  
1.2 The recommended amount of plutonium for each aliquant in the coulometric analysis is 5 mg to 10 mg. Precision worsens for lower amounts of plutonium, and elapsed time of electrolysis becomes impractical for higher amounts of plutonium.  
1.3 The quantity values stated in SI units are to be regarded as standard. The quantity values with non-SI units are given in parentheses for information only.  
1.4 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, health, and environmental practices and determine the applicability of regulatory limitations prior to use. Specific precautionary statements are given in Section 9.  
1.5 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.

General Information

• Status: Published
• Publication Date: 31-Dec-2022
• ICS: 27.120.30 - Fissile materials and nuclear fuel technology
• Technical Committee: C26 - Nuclear Fuel Cycle
• Drafting Committee: C26.05 - Methods of Test

Relations

• Refers: ASTM C859-24 - Standard Terminology Relating to Nuclear Materials
• Effective Date: 01-Jan-2024
• Refers: ASTM C1168-23 - Standard Practice for Preparation and Dissolution of Plutonium Materials for Analysis
• Effective Date: 01-Oct-2023
• Refers: ASTM C1156-18 - Standard Guide for Establishing Calibration for a Measurement Method Used to Analyze Nuclear Fuel Cycle Materials
• Effective Date: 01-Sep-2018
• Refers: ASTM C1297-18 - Standard Guide for Qualification of Laboratory Analysts for the Analysis of Nuclear Fuel Cycle Materials
• Effective Date: 01-Jul-2018
• Refers: ASTM C1168-15 - Standard Practice for Preparation and Dissolution of Plutonium Materials for Analysis
• Effective Date: 01-Sep-2015
• Refers: ASTM C1128-15 - Standard Guide for Preparation of Working Reference Materials for Use in Analysis of Nuclear Fuel Cycle Materials
• Effective Date: 01-Feb-2015
• Refers: ASTM C859-14a - Standard Terminology Relating to Nuclear Materials
• Effective Date: 15-Jun-2014
• Refers: ASTM C859-14 - Standard Terminology Relating to Nuclear Materials
• Effective Date: 15-Jan-2014
• Refers: ASTM C859-13a - Standard Terminology Relating to Nuclear Materials
• Effective Date: 01-Jun-2013
• Refers: ASTM C859-13 - Standard Terminology Relating to Nuclear Materials
• Effective Date: 01-May-2013
• Refers: ASTM E691-13 - Standard Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Method
• Effective Date: 01-May-2013
• Refers: ASTM C1009-13 - Standard Guide for Establishing and Maintaining a Quality Assurance Program for Analytical Laboratories Within the Nuclear Industry
• Effective Date: 01-Jan-2013
• Refers: ASTM C1108-12 - Standard Test Method for Plutonium by Controlled-Potential Coulometry
• Effective Date: 01-Jul-2012
• Refers: ASTM C1210-12 - Standard Guide for Establishing a Measurement System Quality Control Program for Analytical Chemistry Laboratories Within the Nuclear Industry
• Effective Date: 01-Jun-2012
• Refers: ASTM E691-11 - Standard Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Method
• Effective Date: 01-Nov-2011

Overview

ASTM C1165-23: Standard Test Method for Determining Plutonium by Controlled-Potential Coulometry in H₂SO₄ at a Platinum Working Electrode establishes a procedure for the accurate determination of milligram quantities of plutonium in various materials, including unirradiated uranium-plutonium mixed oxide (MOX) with a U/Pu ratio from 0.1 to 10, plutonium metal, plutonium oxide, mixed carbide, and solutions. This test method employs controlled-potential coulometry using a platinum working electrode in sulfuric acid electrolyte, enabling highly precise and SI-traceable measurements of plutonium concentration or mass fraction. The procedure is essential in contexts where nuclear material accountability, quality control, and regulatory compliance are paramount.

Key Topics

• Scope of Application

  • Determination of plutonium in MOX, plutonium metal, oxides, carbides, and relevant compounds
  • Measurement range recommended: 5 mg to 10 mg plutonium per analytical aliquant
  • Applicable to both research and industrial laboratory settings

• Method Overview

  • Controlled-potential coulometry: The platinum working electrode is held at specific potentials to selectively reduce and then oxidize plutonium, allowing quantification via Faraday’s law
  • Sulfuric acid as electrolyte: Provides selectivity and repeatable electrochemical conditions, also serving to remove interferences and depolymerize inactive species

• Significance & Use

  • Supports nuclear safeguards, materials control, and nuclear safety applications
  • Offers SI-traceable results when coupled with certified reference materials (CRMs)
  • Requires appropriate regulatory approval for nuclear safeguard measurements

• Quality & Calibration

  • Chemical calibration of the coulometer system is essential for accuracy
  • Incorporates blank and standard measurements, quality control, and correction factors (e.g., iron interference)
  • Must align with laboratory quality assurance programs (referenced in related ASTM documentation)

• Safety and Compliance

  • Involves handling hazardous chemicals (e.g., hydrofluoric acid, sulfuric acid) and nuclear materials
  • Users must establish and observe robust safety, environmental, and regulatory controls

Applications

The test method outlined in ASTM C1165-23 is integral to laboratories, nuclear facilities, and organizations engaged in:

• Nuclear Material Accountability

  • Ensuring MOX fuels, plutonium metal, and oxides meet concentration specifications
  • Generating data for regulatory and safeguard reporting

• Research & Development

  • Conducting analytical support for nuclear fuel cycle studies
  • Quality control in the development of new fuel forms or processes

• Quality Assurance

  • Routine verification of plutonium content in production, processing, or storage
  • Calibration and validation of analytical equipment and techniques

• Regulatory Compliance

  • Satisfying requirements for nuclear material tracking imposed by safeguards regimes and international agreements

Related Standards

ASTM C1165-23 references several related standards and guides to ensure comprehensive analytical quality and regulatory compliance:

• ASTM C859: Terminology Relating to Nuclear Materials
• ASTM C1009: Guide for Establishing a Quality Assurance Program for Analytical Laboratories Within the Nuclear Industry
• ASTM C1068: Guide for Qualification of Measurement Methods by a Laboratory Within the Nuclear Industry
• ASTM C1108: Test Method for Plutonium by Controlled-Potential Coulometry
• ASTM C1128: Guide for Preparation of Working Reference Materials for Use in Analysis of Nuclear Fuel Cycle Materials
• ASTM C1156: Guide for Establishing Calibration for a Measurement Method
• ASTM C1168: Practice for Preparation and Dissolution of Plutonium Materials for Analysis
• ASTM C1210: Guide for Measurement System Quality Control Program for Analytical Chemistry Laboratories
• ASTM C1297: Guide for Qualification of Laboratory Analysts
• ASTM E691: Practice for Conducting Interlaboratory Studies to Determine Precision of a Test Method

Keywords: controlled-potential coulometry, plutonium analysis, MOX fuel, platinum electrode, nuclear safeguards, sulfuric acid electrolyte, analytical chemistry, nuclear materials testing.

Standards Content (Sample)

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.
Designation: C1165 − 23
Standard Test Method for
Determining Plutonium by Controlled-Potential Coulometry
in H SO at a Platinum Working Electrode
2 4
This standard is issued under the fixed designation C1165; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope C1009Guide for Establishing and Maintaining a Quality
AssuranceProgramforAnalyticalLaboratoriesWithinthe
1.1 This test method covers the determination of milligram
Nuclear Industry
quantities of plutonium in unirradiated uranium-plutonium
C1068Guide for Qualification of Measurement Methods by
mixed oxide having a U/Pu ratio range of 0.1 to 10. This test
a Laboratory Within the Nuclear Industry
methodisalsoapplicabletoplutoniummetal,plutoniumoxide,
C1108Test Method for Plutonium by Controlled-Potential
uranium-plutonium mixed carbide, various plutonium com-
Coulometry
pounds including fluoride and chloride salts, and plutonium
C1128Guide for Preparation of Working Reference Materi-
solutions.
als for Use in Analysis of Nuclear Fuel Cycle Materials
1.2 The recommended amount of plutonium for each ali-
C1156Guide for Establishing Calibration for a Measure-
quant in the coulometric analysis is 5mg to 10 mg. Precision
ment Method Used toAnalyze Nuclear Fuel Cycle Mate-
worsens for lower amounts of plutonium, and elapsed time of
rials
electrolysis becomes impractical for higher amounts of pluto-
C1168PracticeforPreparationandDissolutionofPlutonium
nium.
Materials for Analysis
1.3 The quantity values stated in SI units are to be regarded C1210Guide for Establishing a Measurement System Qual-
ity Control Program for Analytical Chemistry Laborato-
as standard.The quantity values with non-SI units are given in
parentheses for information only. ries Within Nuclear Industry
C1297Guide for Qualification of Laboratory Analysts for
1.4 This standard does not purport to address all of the
the Analysis of Nuclear Fuel Cycle Materials
safety concerns, if any, associated with its use. It is the
E691Practice for Conducting an Interlaboratory Study to
responsibility of the user of this standard to establish appro-
Determine the Precision of a Test Method
priate safety, health, and environmental practices and deter-
mine the applicability of regulatory limitations prior to use.
3. Terminology
Specific precautionary statements are given in Section 9.
3.1 Except as otherwise defined herein, definitions of terms
1.5 This international standard was developed in accor-
are as given in Terminology C859.
dance with internationally recognized principles on standard-
ization established in the Decision on Principles for the
4. Summary of Test Method
Development of International Standards, Guides and Recom-
4.1 In controlled-potential coulometry, the analyte reacts at
mendations issued by the World Trade Organization Technical
an electrode having a controlled potential that precludes
Barriers to Trade (TBT) Committee.
reactionsofasmanyimpuritycomponentsasisfeasible.Inthe
2. Referenced Documents
electrolysis, current decreases exponentially as the reaction
proceeds until a selected background current is reached. The
2.1 ASTM Standards:
quantity of analyte reacted is calculable by Faraday’s law.
C859Terminology Relating to Nuclear Materials
Detailed discussions of the theory and applications of this
technique are presented in Refs (1) and (2).
ThistestmethodisunderthejurisdictionofASTMCommitteeC26onNuclear
4.2 Plutonium and many impurity element ions are initially
Fuel Cycle and is the direct responsibility of Subcommittee C26.05 on Methods of
Test.
reducedina0.5mol/L(0.5 M)H SO electrolyteataplatinum
2 4
Current edition approved Jan. 1, 2023. Published January 2023. Originally
working electrode (3) maintained at+0.310V versus a satu-
approved in 1990. Last previous edition approved in 2022 as C1165–22. DOI:
rated calomel electrode (SCE). Plutonium is then oxidized to
10.1520/C1165-23.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
Standards volume information, refer to the standard’s Document Summary page on The boldface numbers in parentheses refer to a list of references at the end of
the ASTM website. the text.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
C1165 − 23
Pu(IV) at a potential of+0.670V. The quantity of plutonium, 5.3 A chemical calibration of the coulometer is necessary
w, is calculated from the number of coulombs, Q, required for for accurate results.
oxidation according to Faraday’s law:
6. Interferences
t
Q 5 idt 5 nwF/M (1)
*
o 6.1 Categories of interferences are diverse metal ions that
oxidize or reduce at the potential of+0.670V used for the
Rearranging to solve for w yields:
oxidation of Pu(III) to Pu(IV), organic matter, anions that
w 5 MQ/nF (2)
complex plutonium, and oxygen.
where:
6.2 The major interfering metallic impurity element, of
w = mass of Pu(III) oxidized to Pu(IV), g,
those usually included in specifications for FBR mixed oxide
M = molar mass of plutonium (adjusted for isotopic
fuel,isiron (4).Inthe0.5mol⁄L(0.5 M)H SO electrolyte,the
2 4
composition), g/mol,
Fe(II)−Fe(III) and Pu(III)−Pu(IV) couples have essentially
o
Q = number of coulombs to oxidize Pu(III) to Pu(IV), C,
the same E value of + 0.490 V. The iron interference,
n = number of electron change to oxidize Pu(III) to
therefore,isquantitativeandiscorrectedbasedonitsmeasured
Pu(IV)=1, and
value that can be determined by a spectrophotometric method
F = Faraday constant, C/mol.
(5). Alternatively, other techniques such as ICP, DCP, or
emission spectrometry can also be used if the iron content is
4.3 An electrolyte of sulfuric acid, that selectively com-
sufficiently low. When the iron result is <20µg⁄g, the lower
plexes Pu(IV), provides very reproducible electrolysis of
limit of quantification for the spectrophotometric method, no
Pu(III)toPu(IV).Ina0.5mol⁄L(0.5 M)H SO electrolyte,the
2 4
correction is necessary. The best available method for iron
reduction potential of+0.310V for conversion of Pu(IV and
determinationisrecommendedsincetheuncertaintyintheiron
VI) to Pu(III) and the oxidation potential of+0.670V for
correction contributes to the uncertainty in the plutonium
conversion of Pu(III) to Pu(IV) accounts for about 99.9% (as
value.
calculated from the Nernst equation) conversion of the total
plutonium in solution. There are few interferences at the
6.3 When iron is present in quantities greater than the
selected potentials of the metallic impurities usually listed in
nuclear-grade specifications for plutonium metal, oxides, and
specifications for fast breeder reactor (FBR) mixed oxide fuel.
nitrate solutions, the iron may be removed or substantially
A chemical calibration of the coulometric system using the
reduced by column purification using resins known to be
selectedpotentialstechniqueisnecessarytocorrectfortheless
quantitative for plutonium recovery. Guidance and instructions
than 100% conversions of Pu(III) and Pu(IV).
for column purification of plutonium test samples, calibration
standards,andqualitycontrol(QC)referencematerialsmaybe
4.4 Sulfuric acid is a convenient electrolyte since it is used
applied as described in C1108.
for preliminary fuming of samples to volatilize interfering
components (see 6.4 and 6.5). The preliminary fuming with
6.4 Organic matter usually is not present in calcined mixed
sulfuric acid also serves to depolymerize any polymeric
oxide fuel pellets nor in mixed oxide powder blends prepared
plutonium species, which tend to be electrolytically inactive
using calcined uranium oxide and calcined plutonium oxide.
(3).
However, it may be introduced as an impurity in reagents.The
sulfuric acid fuming of reference material and of samples that
5. Significance and Use
precedes the coulometric analysis volatilizes most organic
components.
5.1 This test method is used to ascertain whether or not
materials meet specifications for plutonium concentration or
6.5 The sulfuric acid fuming volatilizes nitrate, nitrite,
plutonium mass fraction.
fluoride, and chloride, that are introduced by the use of a
5.1.1 The materials (nuclear grade plutonium nitrate nitric-hydrofluoric acid mixture or acid mixtures containing
solutions, plutonium metal, plutonium oxide powder, and
mixedoxideandcarbidepowdersandpellets)towhichthistest
method applies are subject to nuclear safeguards regulations
governingtheirpossessionanduse.However,adherencetothis
testmethoddoesnotautomaticallyguaranteeregulatoryaccep-
tance of the resulting safeguards measurements. It remains the
sole responsibility of the user of this test method to ensure that
its application to safeguards has the approval of the proper
regulatory authorities.
5.1.2 When used in conjunction with appropriate certified
reference materials (CRMs), this test method can demonstrate
traceability to the international measurements system (SI).
5.2 Fitness for Purpose of Safeguards and Nuclear Safety
Application—Methods intended for use in safeguards and
nuclear safety applications shall meet the requirements speci-
FIG. 1 Example of a Cell Design Used at Los Alamos National
fied by Guide C1068 for use in such applications. Laboratory (LANL)
C1165 − 23
≥99.95%) have been used successfully.
chloride for the dissolution of samples and interfere in the
coulometric determination of plutonium.
7.3 Timer or stopwatch for measuring electrolysis times
6.6 Oxygen interferes and must be purged continuously (capable of measuring in seconds).
from both the solution and atmosphere in the electrolysis cell
with an oxygen-free inert gas before and during the electroly- 8. Reagents
sis.
8.1 Purity of Reagents—ACS ultratrace grade chemicals
NOTE 1—The purge gas tube extends through the cell cover and is
shall be used in all tests. Unless otherwise indicated, it is
positioned approximately 1cm above the sample solution in the cell. The
intended that all reagents conform to the specifications of the
inert gas flow is maintained at a flow rate that causes a dimple to be seen
Committee onAnalytical Reagents of theAmerican Chemical
on the surface of the solution with the stirrer off. The inert gas flow rate
Society where such specifications for ultratrace grade chemi-
should be such that no splashing occurs with the stirrer on.
cals are available.
6.7 Nitricacidandhydrofluoricacidmustbeaddedduring
8.2 Purity of Water—Unless otherwise indicated, references
the preparation of the plutonium metal to ensure oxidation of
to water shall be understood to mean distilled, deionized water
the plutonium to Pu(IV) and to match the acid matrix from
with a conductivity of <0.1µS (resistance >10MΩ).
plutonium oxide dissolution. Plutonium that is dissolved in
only hydrochloric acid and then evaporated to dryness in
8.3 Argon, Oxygen-Free (99.99 %)—Helium, nitrogen, or
sulfuric acid while in the Pu(III) oxidation state will contain
other pure inert gas may be used instead of argon.
tiny blue crystals within the pink plutonium (IV) sulfate
8.4 Hydrochloric Acid (HCl, 10.9 mol/L)—Concentrated
material, and lower recoveries are experienced during the
HCl, ACS ultratrace grade.
coulometricmeasurement.Bluecrystalsarenotobservedwhen
plutoniumoxidematerialsaredissolvedinHNO andHFacids
8.5 Hydrochloric Acid (HCl, 6 mol/L)—Add 550 mL of
and subsequently fumed to dryness in H SO .
2 4
10.9mol⁄L (10.9 M) HCl to less than 400 mL of water and
6.8 Due to a slight overlap between the potential at which dilute to 1L with water.
Np(VI) reduces to Np(V), +0.660V, and the potential used in
8.6 Hydrochloric Acid (HCl, 1.0 mol/L)—Add 92 mL of
the current method to oxidize Pu(III) to Pu(IV), +0.670V, a
10.9mol⁄L (10.9 M) HCl to less than 500 mL of water and
large amount of neptunium will cause the plutonium assay to
dilute to 1L.
bebiasedhighandnotaccuratelyreflecttheplutoniumcontent
of the material being analyzed. Thus, neptunium can only be 8.7 Hydrofluoric Acid (HF, 29 mol ⁄L)—Concentrated HF,
ACS ultratrace grade.
tolerated up to 1% in the sample, above that level the
neptuniummustberemovedpriortothesampleundergoingthe
8.8 Hydrofluoric Acid (HF, 1.3 mol ⁄L)—Add 4.5 mL of
coulometry process.
29mol⁄L(29 M) HF to less than 50 mLof water and dilute to
100 mL.
7. Apparatus
8.9 Nitric Acid (HNO , 15.9 mol ⁄L)—Concentrated HNO ,
7.1 Controlled-Potential Coulometer—A potentiostat hav-
3 3
ACS ultratrace grade.
ing stable potential control at approximately 200mAand 20V
and an integrator capable of 0.05% reproducibility are re-
8.10 Sulfuric Acid (H SO , 18.1 mol/L)—Concentrated
2 4
quired. The linearity of the integrator should be better than
H SO , ACS ultratrace grade.
2 4
0.1% for the selected range.
8.11 Sulfuric Acid (3 mol/L)—Add 166 mL of 18.1mol⁄L
7.2 Cell Assembly—A cell assembly similar to the one
(18.1 M)H SO to less than 500mL of water, while stirring,
2 4
described in Ref (5) has been used satisfactorily. Cell design is
and dilute to 1L with water.
very critical in controlled-potential coulometry. There are
many factors that must be considered in choosing or designing 8.12 Sulfuric Acid (0.5 mol/L)—Add 28mL of 18.1mol⁄L
a cell assembly. It is beyond the scope of this test method to (18.1 M)H SO to less than 500mL of water, while stirring,
2 4
describe all of the factors that should be considered. A and dilute to 1L with water.
thorough detailed discussion of electrolysis cell design is
8.13 Plutonium Reference Solution (with desired Pu mass
presented in Ref (2).
fraction of 5 mg ⁄g)—Dissolve a weighed quantity (balance
NOTE 2—Fig. 1 is an example of a cell design that has been used capableofweighingto 60.01mg)of0.5gto1gofNBL(Note
successfully at the LosAlamos National Laboratory. The electrolysis cell
4) CRM 126-series of plutonium metal (or its replacement)
consists of a 50mL cut off beaker. The working and counter electrode
...

This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Because
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: C1165 − 22 C1165 − 23
Standard Test Method for
Determining Plutonium by Controlled-Potential Coulometry
in H SO at a Platinum Working Electrode
2 4
This standard is issued under the fixed designation C1165; 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 milligram quantities of plutonium in unirradiated uranium-plutonium mixed
oxide having a U/Pu ratio range of 0.1 to 10. This test method is also applicable to plutonium metal, plutonium oxide,
uranium-plutonium mixed carbide, various plutonium compounds including fluoride and chloride salts, and plutonium solutions.
1.2 The recommended amount of plutonium for each aliquant in the coulometric analysis is 5 mg to 10 mg. Precision worsens for
lower amounts of plutonium, and elapsed time of electrolysis becomes impractical for higher amounts of plutonium.
1.3 The quantity values stated in SI units are to be regarded as standard. The quantity values with non-SI units are given in
parentheses for information only.
1.4 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, health, and environmental practices and determine the applicability of
regulatory limitations prior to use. Specific precautionary statements are given in Section 9.
1.5 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:
C859 Terminology Relating to Nuclear Materials
C1009 Guide for Establishing and Maintaining a Quality Assurance Program for Analytical Laboratories Within the Nuclear
Industry
C1068 Guide for Qualification of Measurement Methods by a Laboratory Within the Nuclear Industry
C1108 Test Method for Plutonium by Controlled-Potential Coulometry
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
C1210 Guide for Establishing a Measurement System Quality Control Program for Analytical Chemistry Laboratories Within
Nuclear Industry
C1297 Guide for Qualification of Laboratory Analysts for the Analysis of Nuclear Fuel Cycle 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 July 1, 2022Jan. 1, 2023. Published August 2022January 2023. Originally approved in 1990. Last previous edition approved in 20172022 as
C1165 – 17.C1165 – 22. DOI: 10.1520/C1165-22.10.1520/C1165-23.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
C1165 − 23
E691 Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Method
3. Terminology
3.1 Except as otherwise defined herein, definitions of terms are as given in Terminology C859.
4. Summary of Test Method
4.1 In controlled-potential coulometry, the analyte reacts at an electrode having a controlled potential that precludes reactions of
as many impurity components as is feasible. In the electrolysis, current decreases exponentially as the reaction proceeds until a
selected background current is reached. The quantity of analyte reacted is calculable by Faraday’s law. Detailed discussions of the
theory and applications of this technique are presented in Refs (1) and (2).
4.2 Plutonium and many impurity element ions are initially reduced in a 0.5 mol/L (0.5 M) H SO electrolyte at a platinum
2 4
working electrode (3) maintained at + 0.310 V versus a saturated calomel electrode (SCE). Plutonium is then oxidized to Pu(IV)
at a potential of + 0.670 V. The quantity of plutonium, w, is calculated from the number of coulombs, Q, required for oxidation
according to Faraday’s law:
t
Q 5 i dt 5 nwF/M (1)
*
o
Rearranging to solve for w yields:
w 5 MQ/nF (2)
where:
w = mass of Pu(III) oxidized to Pu(IV), g,
M = molar mass of plutonium (adjusted for isotopic composition), g/mol,
Q = number of coulombs to oxidize Pu(III) to Pu(IV), C,
n = number of electron change to oxidize Pu(III) to Pu(IV) = 1, and
F = Faraday constant, C/mol.
4.3 An electrolyte of sulfuric acid, that selectively complexes Pu(IV), provides very reproducible electrolysis of Pu(III) to Pu(IV).
In a 0.5 mol ⁄L (0.5 M) H SO electrolyte, the reduction potential of + 0.310 V for conversion of Pu(IV and VI) to Pu(III) and the
2 4
oxidation potential of + 0.670 V for conversion of Pu(III) to Pu(IV) accounts for about 99.9 % (as calculated from the Nernst
equation) conversion of the total plutonium in solution. There are few interferences at the selected potentials of the metallic
impurities usually listed in specifications for fast breeder reactor (FBR) mixed oxide fuel. A chemical calibration of the coulometric
system using the selected potentials technique is necessary to correct for the less than 100 % conversions of Pu(III) and Pu(IV).
4.4 Sulfuric acid is a convenient electrolyte since it is used for preliminary fuming of samples to volatilize interfering components
(see 6.4 and 6.5). The preliminary fuming with sulfuric acid also serves to depolymerize any polymeric plutonium species, which
tend to be electrolytically inactive (3).
5. Significance and Use
5.1 This test method is used to ascertain whether or not materials meet specifications for plutonium concentration or plutonium
mass fraction.
5.1.1 The materials (nuclear grade plutonium nitrate solutions, plutonium metal, plutonium oxide powder, and mixed oxide and
carbide powders and pellets) to which this test method applies are subject to nuclear safeguards regulations governing their
possession and use. However, adherence to this test method does not automatically guarantee regulatory acceptance of the resulting
safeguards measurements. It remains the sole responsibility of the user of this test method to ensure that its application to
safeguards has the approval of the proper regulatory authorities.
5.1.2 When used in conjunction with appropriate certified reference materials (CRMs), this test method can demonstrate
traceability to the international measurements system (SI).
The boldface numbers in parentheses refer to a list of references at the end of the text.
C1165 − 23
5.2 Fitness for Purpose of Safeguards and Nuclear Safety Application—Methods intended for use in safeguards and nuclear safety
applications shall meet the requirements specified by Guide C1068 for use in such applications.
5.3 A chemical calibration of the coulometer is necessary for accurate results.
6. Interferences
6.1 Categories of interferences are diverse metal ions that oxidize or reduce at the potential of + 0.670 V used for the oxidation
of Pu(III) to Pu(IV), organic matter, anions that complex plutonium, and oxygen.
6.2 The major interfering metallic impurity element, of those usually included in specifications for FBR mixed oxide fuel, is iron
o
(4). In the 0.50.5 mol ⁄L (0.5 M) H SO electrolyte, the Fe(II) − Fe(III) and Pu(III) − Pu(IV) couples have essentially the same E
2 4
value of + 0.490 V. The iron interference, therefore, is quantitative and is corrected based on its measured value that can be
determined by a spectrophotometric method (5). Alternatively, other techniques such as ICP, DCP, or emission spectrometry can
also be used if the iron content is sufficiently low. When the iron result is <20 μg ⁄g, the lower limit of quantification for the
spectrophotometric method, no correction is necessary. The best available method for iron determination is recommended since
the uncertainty in the iron correction contributes to the uncertainty in the plutonium value.
6.3 When iron is present in quantities greater than the nuclear-grade specifications for plutonium metal, oxides, and nitrate
solutions, the iron may be removed or substantially reduced by column purification using resins known to be quantitative for
plutonium recovery. Guidance and instructions for column purification of plutonium test samples, calibration standards, and quality
control (QC) reference materials may be applied as described in C1108.
6.4 Organic matter usually is not present in calcined mixed oxide fuel pellets nor in mixed oxide powder blends prepared using
calcined uranium oxide and calcined plutonium oxide. However, it may be introduced as an impurity in reagents. The sulfuric acid
fuming of reference material and of samples that precedes the coulometric analysis volatilizes most organic components.
6.5 The sulfuric acid fuming volatilizes nitrate, nitrite, fluoride, and chloride, that are introduced by the use of a nitric-hydrofluoric
acid mixture or acid mixtures containing chloride for the dissolution of samples and interfere in the coulometric determination of
plutonium.
6.6 Oxygen interferes and must be purged continuously from both the solution and atmosphere in the electrolysis cell with an
oxygen-free inert gas before and during the electrolysis.
NOTE 1—The purge gas tube extends through the cell cover and is positioned approximately 1 cm above the sample solution in the cell. The inert gas
flow is maintained at a flow rate that causes a dimple to be seen on the surface of the solution with the stirrer off. The inert gas flow rate should be such
that no splashing occurs with the stirrer on.
6.7 Nitric acid and hydrofluoric acid must be added during the preparation of the plutonium metal to ensure oxidation of the
FIG. 1 Example of a Cell Design Used at Los Alamos National Laboratory (LANL)
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plutonium to Pu(IV) and to match the acid matrix from plutonium oxide dissolution. Plutonium that is dissolved in only
hydrochloric acid and then evaporated to dryness in sulfuric acid while in the Pu(III) oxidation state will contain tiny blue crystals
within the pink plutonium (IV) sulfate material, and lower recoveries are experienced during the coulometric measurement. Blue
crystals are not observed when plutonium oxide materials are dissolved in HNO and HF acids and subsequently fumed to dryness
in H SO .
2 4
6.8 Due to a slight overlap between the potential at which Np(VI) reduces to Np(V), +0.660 V, and the potential used in the
current method to oxidize Pu(III) to Pu(IV), +0.670 V, a large amount of neptunium will cause the plutonium assay to be biased
high and not accurately reflect the plutonium content of the material being analyzed. Thus, neptunium can only be tolerated up to
1 % in the sample, above that level the neptunium must be removed prior to the sample undergoing the coulometry process.
7. Apparatus
7.1 Controlled-Potential Coulometer—A potentiostat having stable potential control at approximately 200 mA and 20 V and an
integrator capable of 0.05 % reproducibility are required. The linearity of the integrator should be better than 0.1 % for the selected
range.
7.2 Cell Assembly—A cell assembly similar to the one described in Ref (5) has been used satisfactorily. Cell design is very critical
in controlled-potential coulometry. There are many factors that must be considered in choosing or designing a cell assembly. It is
beyond the scope of this test method to describe all of the factors that should be considered. A thorough detailed discussion of
electrolysis cell design is presented in Ref (2).
NOTE 2—Fig. 1 is an example of a cell design that has been used successfully at the Los Alamos National Laboratory. The electrolysis cell consists of
a 50 mL cut off beaker. The working and counter electrodes with a platinum mass fraction of ≥999.5 mg ⁄g (that is, Pt purity of ≥99.95 %) have been used
successfully.
7.3 Timer or stopwatch for measuring electrolysis times (capable of measuring in seconds).
8. Reagents
8.1 Purity of Reagents—ACS ultratrace grade chemicals shall be used in all tests. Unless otherwise indicated, it is intended that
all reagents conform to the specifications of the Committee on Analytical Reagents of the American Chemical Society where such
specifications for ultratrace grade chemicals are available.
8.2 Purity of Water—Unless otherwise indicated, references to water shall be understood to mean distilled, deionized water with
a conductivity of <0.1 μS (resistance >10 MΩ).
8.3 Argon, Oxygen-Free (99.99 %)—Helium, nitrogen, or other pure inert gas may be used instead of argon.
8.4 Hydrochloric Acid (HCl, 10.9 mol/L)—Concentrated HCl, ACS ultratrace grade.
8.5 Hydrochloric Acid (HCl, 6 mol/L)—Add 550 mL of 10.9 mol ⁄L (10.9 M) HCl to less than 400 mL of water and dilute to 1 L
with water.
8.6 Hydrochloric Acid (HCl, 1.0 mol/L)—Add 92 mL of 10.9 mol ⁄L (10.9 M) HCl to less than 500 mL of water and dilute to 1 L.
8.7 Hydrofluoric Acid (HF, 29 mol ⁄L)—Concentrated HF, ACS ultratrace grade.
Coulometer suppliers or designers who have reported instrument performances that are consistent with the specification provided in this standard include: the SRNL
Coulometer, Savannah River National Laboratory, Aiken, South Carolina, USA; the Mayak Coulometer PIK-200, Ozersk, Russia; and the coulometer at the LAMM
Laboratory, CEA Centre de Marcoule, Bagnols-sur-CèreCedex, France. If you are aware of alternative suppliers, please provide this information to ASTM International
Headquarters. Your comments will receive careful consideration at a meeting of the responsible technical committee, which you may attend.
ACS Reagent Chemicals, Specifications and Procedures for Reagents and Standard-Grade Reference Materials, American Chemical Society,
...