ASTM C1855-18

Standard Test Method for Determination of Uranium and Plutonium Concentration in Aqueous Solutions Using Hybrid K-Edge Densitometry and X-Ray Fluorescence

SIGNIFICANCE AND USE
5.1 The HKED technique is highly element specific and depends upon a well-known controlled geometry.  
5.2 The HKED technique can provide concentration measurements of actinides in solutions with precision typically better than 0.3 % for uranium concentrations >50 g/L and 1 % for plutonium in typical U-Pu solutions for a typical measurement time of 3 × 1000 s (3 replicates, 1000 s live time each) (1).  
5.3 For pure plutonium only product solutions, the KED technique can achieve measurement precisions better than 0.3 % for plutonium concentrations >50 g/L for a typical measurement time of 3 × 1000 s.  
5.4 For pure uranium only solutions, precisions of better than 0.3 % can be achieved using the KED technique for uranium concentrations >50 g/L, for a typical measurement time of 3 × 3600 s.  
5.5 For uranium only or plutonium only solutions of concentrations approximately 1 g/L, assayed using XRF, a measurement precision of 1.0 % has been achieved (1). For solutions of concentration approximately 50 g/L, assayed using XRF, measurement precisions of 0.2 % or better have been achieved. The typical measurement time for stand-alone XRF assay is 3 × 3000 s.  
5.6 Quality Control (QC) samples are assayed for a typical measurement time of 3 × 3000 s.  
5.7 It is applicable when solutions to be measured are homogeneous with respect to chemical composition.  
5.8 Results are typically used for fuel fabrication, process control, quality control, material control and accountancy, and safeguards in nuclear fuel reprocessing plants. Each application can have its own data quality objectives (Guide C1068).  
5.9 The HKED instrument may use a single cylindrical vial for both the KED and XRF measurements, or separate sample containers for KED and XRF. The typical values for the path length of the rectangular cuvette and the inner diameter of the cylindrical vial are given in 7.8.  
5.10 The transfer of the sample into the HKED system can be accomplished either horizontally b...
SCOPE
1.1 This test method specifies the determination of the volumetric uranium and plutonium concentrations, typically, in nitric acid solutions through the combination of K-Edge absorption Densitometry (KED) and K X-Ray fluorescence (XRF) using an X-Ray generator. It is known as the “Hybrid K-Edge” (HKED) technique whose original implementation is described in Ref (1).2 The method is applicable to dissolver (input) solutions and product solutions. The test method also specifies the determination of low concentrations (  
1.2 This test method is applicable to the following common-use conditions:  
1.2.1 Spent nuclear fuel reprocessing and fuel production.  
1.2.2 Homogeneous aqueous solutions contained in cylindrical vials or cuvettes. HKED systems may use two separate sample containers, namely a rectangular cuvette for KED and a cylindrical vial for XRF. Alternatively, there are HKED systems that use a sample contained in a single cylindrical vial, for both K-Edge and XRF.  
1.2.3 The results produced by the two sample configuration (a rectangular cuvette for K-Edge densitometry and a cylindrical vial for XRF) are compliant with the International Target Values (ITV) (1).  
1.2.4 The precision results produced by the single cylindrical vial configuration are degraded in comparison to the two container system.  
1.2.5 This test method is applicable to facilities that do not adopt the ITVs, but have their own Data Quality Objectives (DQO).  
1.2.6 Solutions which contain uranium and plutonium with uranium concentration of 150 to 250 g/L and a U:Pu ratio of 100:1 typically, in the presence of fission products with β, γ, activity of up to 10 TBq/L.
1.2.6.1 This test method is not applicable to samples where a minor element such as U needs to be quantified in which Pu is the major element.
1.2.6.2 This test method is applicable for common use process control applications for quantifying Pu in the 5 g/L to 30 g/L range ...

General Information

• Status: Published
• Publication Date: 31-May-2018
• ICS: 17.240 - Radiation measurements
• Technical Committee: C26 - Nuclear Fuel Cycle
• Drafting Committee: C26.10 - Non Destructive Assay

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 C1297-18 - Standard Guide for Qualification of Laboratory Analysts for the Analysis of Nuclear Fuel Cycle Materials
• Effective Date: 01-Jul-2018
• Refers: ASTM C1673-10a(2018) - Standard Terminology of C26.10 Nondestructive Assay Methods
• Effective Date: 01-Apr-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 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 C1068-03(2011) - Standard Guide for Qualification of Measurement Methods by a Laboratory Within the Nuclear Industry
• Effective Date: 01-Jun-2011
• Refers: ASTM C1297-03(2011) - Standard Guide for Qualification of Laboratory Analysts for the Analysis of Nuclear Fuel Cycle Materials
• Effective Date: 01-Jun-2011
• Refers: ASTM C1673-10a - Standard Terminology of C26.10 Nondestructive Assay Methods
• Effective Date: 01-Nov-2010
• Refers: ASTM C859-10b - Standard Terminology Relating to Nuclear Materials
• Effective Date: 01-Nov-2010

Overview

ASTM C1855-18 is an international standard developed by ASTM for determining uranium and plutonium concentrations in aqueous solutions using the Hybrid K-Edge Densitometry (HKED) and X-Ray Fluorescence (XRF) techniques. This test method is applicable primarily to nitric acid solutions of nuclear materials, allowing precise, element-specific measurement of actinide concentrations. The standard ensures robust quality control and measurement accuracy for nuclear applications, such as nuclear fuel reprocessing and fuel fabrication facilities.

Key Topics

• Element-Specific Analysis: The HKED method leverages precise, non-destructive measurement of uranium and plutonium, relying on X-ray transmission and emission characteristics controlled under well-known geometry.
• Hybrid Measurement Technique: HKED combines K-Edge absorption (KED) densitometry with K X-Ray fluorescence (XRF), providing optimized analysis for various concentration ranges.
• Precision and Measurement Range:
  • For uranium concentrations above 50 g/L, KED yields precision better than 0.3%.
  • Plutonium in uranium-plutonium mixtures can be measured with 1% precision for typical reprocessing solutions.
  • For pure plutonium solutions above 50 g/L, KED achieves better than 0.3% precision.
  • XRF in stand-alone mode accurately addresses lower U and Pu concentrations (as low as ~0.2 g/L); precision of 0.2-1.0% is achievable for 1-50 g/L.
• Flexible Sample Handling: The method supports both single and dual-container configurations (cylindrical vials and rectangular cuvettes), accommodating diverse nuclear facility setups.
• Quality Control: The standard mandates regular assay of quality control (QC) samples, detailed uncertainty analysis, and compliance with International Target Values (ITV) or facility-specific Data Quality Objectives (DQO).

Applications

ASTM C1855-18 is widely applied in the nuclear industry, where accurate quantification of uranium and plutonium concentrations underpins process safety, regulatory compliance, and material accountability. Key applications include:

• Nuclear Fuel Reprocessing: Supports input (dissolver) and product solution analysis for control, inventory, and compliance.
• Fuel Fabrication: Ensures batch consistency and chemical homogeneity in nuclear fuel production.
• Process and Quality Control: Provides rapid, non-destructive verification of actinide concentration for ongoing operations.
• Safeguards and Material Control: Facilitates robust tracking and accountability of nuclear material, critical for nonproliferation and audit regimes.
• Adaptability to Complex Matrices: Suitable for solutions with high actinide concentrations (up to 400 g/L) and in the presence of significant fission product activities.

Related Standards

ASTM C1855-18 references and aligns with several key standards vital for laboratory operations, quality management, and technical competence in the nuclear sector:

• ASTM C1068: Guide for Qualification of Measurement Methods by Laboratories
• ASTM C1128: Guide for Preparation of Working Reference Materials in Nuclear Analysis
• ASTM C1168: Practice for Preparation and Dissolution of Plutonium Materials
• ASTM C1210: Guide for Establishing a Measurement System Quality Control Program
• ASTM C1297: Guide for Qualification of Laboratory Analysts
• ISO 13464: Simultaneous Determination of Uranium and Plutonium by K-Edge and XRF in Reprocessing Solutions
• ISO/IEC 17025: General Requirements for Competence of Testing and Calibration Laboratories

Practical Value

ASTM C1855-18 offers a proven, efficient, and accurate methodology for assaying uranium and plutonium concentrations, supporting safe nuclear operations, regulatory conformance, and international safeguards. Its hybrid approach maximizes flexibility, reduces hazardous waste, and streamlines the analytical workflow crucial in high-throughput nuclear environments. By complying with this standard, facilities ensure operational excellence and uphold global expectations in nuclear material measurement and control.

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: C1855 − 18
Standard Test Method for
Determination of Uranium and Plutonium Concentration in
Aqueous Solutions Using Hybrid K-Edge Densitometry and
X-Ray Fluorescence
This standard is issued under the fixed designation C1855; 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 1.2.6 Solutions which contain uranium and plutonium with
uranium concentration of 150 to 250 g/L and a U:Pu ratio of
1.1 This test method specifies the determination of the
100:1 typically, in the presence of fission products with β, γ,
volumetricuraniumandplutoniumconcentrations,typically,in
activity of up to 10 TBq/L.
nitric acid solutions through the combination of K-Edge
1.2.6.1 This test method is not applicable to samples where
absorption Densitometry (KED) and K X-Ray fluorescence
a minor element such as U needs to be quantified in which Pu
(XRF) using an X-Ray generator. It is known as the “Hybrid
is the major element.
K-Edge” (HKED) technique whose original implementation is
1.2.6.2 This test method is applicable for common use
described in Ref (1). The method is applicable to dissolver
process control applications for quantifying Pu in the 5 g/L to
(input) solutions and product solutions. The test method also
30 g/L range using XRF only in the presence of up to ~10%
specifies the determination of low concentrations (<50 g/L) of
(~100 000 ppm) of transuranic impurities (predominantly U
U and Pu using XRF measurements alone (the “stand-alone
andAm). In this application, the impurity concentration in the
XRF” mode). Using the XRF measurement in the stand-alone
Pu samples is not quantified.Additional uncertainties must be
mode, solutions in the 0.2 g/L to 50 g/L range of Pu with or
estimated and factored in the Pu concentration results.
withoutUandsolutionsinthe0.2g/Lto50g/LrangeofUwith
1.2.7 Solutions containing 50 g/L to 400 g/L of uranium
or without Pu are commonly measured.
alone.
1.2 Thistestmethodisapplicabletothefollowingcommon-
1.2.8 Solutions containing 50 g/L to 400 g/L of plutonium
use conditions:
alone.
1.2.1 Spent nuclear fuel reprocessing and fuel production.
1.2.9 Solutions with low concentrations of U and Pu,
1.2.2 Homogeneous aqueous solutions contained in cylin-
typically in the 0.2 g/L to 50 g/L range.
drical vials or cuvettes. HKED systems may use two separate
sample containers, namely a rectangular cuvette for KED and 1.2.10 The concentration ranges given in 1.2.6 – 1.2.9 are
application of the HKED technique for Materials Control and
a cylindrical vial for XRF. Alternatively, there are HKED
systemsthatuseasamplecontainedinasinglecylindricalvial, Accountancy (MC&A) purposes. For process control applica-
tions where precision requirements are less stringent, KED
for both K-Edge and XRF.
1.2.3 The results produced by the two sample configuration methodcanbeusedtoassaysampleswithlowerconcentrations
of U or Pu (down to 30 g/L).
(a rectangular cuvette for K-Edge densitometry and a cylindri-
cal vial for XRF) are compliant with the International Target
1.3 Units—The values stated in SI units are to be regarded
Values (ITV) (1).
asstandard.Nootherunitsofmeasurementareincludedinthis
1.2.4 The precision results produced by the single cylindri-
standard.
cal vial configuration are degraded in comparison to the two
1.4 This standard does not purport to address all of the
container system.
safety concerns, if any, associated with its use. It is the
1.2.5 This test method is applicable to facilities that do not
responsibility of the user of this standard to establish appro-
adopt the ITVs, but have their own Data Quality Objectives
priate safety, health, and environmental practices and deter-
(DQO).
mine the applicability of regulatory limitations prior to use.
1.5 This international standard was developed in accor-
ThistestmethodisunderthejurisdictionofASTMCommitteeC26onNuclear
dance with internationally recognized principles on standard-
Fuel Cycle and is the direct responsibility of Subcommittee C26.10 on Non
Destructive Assay.
ization established in the Decision on Principles for the
Current edition approved June 1, 2018. Published August 2018. DOI: 10.1520/
Development of International Standards, Guides and Recom-
C1855-18.
2 mendations issued by the World Trade Organization Technical
The boldface numbers in parentheses refer to a list of references at the end of
this standard. Barriers to Trade (TBT) Committee.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
C1855 − 18
2. Referenced Documents from a blank to zero, in the vicinity of the cut-off, after the
3 pile-up correction has been applied.
2.1 ASTM Standards:
3.2.3 K-Edge Densitometry—technique to determine el-
C859Terminology Relating to Nuclear Materials
emental concentrations in a sample by measuring the ratio of
C1068Guide for Qualification of Measurement Methods by
photon transmission across the energy characteristic of the
a Laboratory Within the Nuclear Industry
actinide K-Edge cross-section of the element present in the
C1128Guide for Preparation of Working Reference Materi-
sample.
als for Use in Analysis of Nuclear Fuel Cycle Materials
C1168PracticeforPreparationandDissolutionofPlutonium
3.2.4 major element, n—actinideelementofhighestconcen-
Materials for Analysis
tration in the solution.
C1210Guide for Establishing a Measurement System Qual-
3.2.5 minor element, n—actinide element with concentra-
ity Control Program for Analytical Chemistry Laborato-
tions typically 50 to 100 times lower than the concentration of
ries Within the Nuclear Industry
the major element. Due to its low relative concentration, the
C1297Guide for Qualification of Laboratory Analysts for
minor element is typically measured using XRF.
the Analysis of Nuclear Fuel Cycle Materials
3.2.6 self-fluorescence, n—X-Ray fluorescence of an ac-
C1490GuidefortheSelection,TrainingandQualificationof
tinide in the specimen due to excitation by the decay of
Nondestructive Assay (NDA) Personnel
radionuclides present in the solution; the interrogating X-Ray
C1592/C1592MGuide for Making Quality Nondestructive
beam is turned off.
Assay Measurements (Withdrawn 2018)
C1673Terminology of C26.10 NondestructiveAssay Meth-
4. Summary of Test Method
ods
4.1 The Hybrid K-Edge method is a highly element specific
2.2 ISO Standards:
method for determining the concentration of uranium and
ISO 13464Simultaneous Determination of Uranium and
transuranic elements. The method was developed for applica-
Plutonium in Dissolver Solutions from Reprocessing
tiontobothfeedandproductaqueoussolutiongeneratedinthe
Plants–Combined Method using K-absorption Edge and
process of spent fuel.
X-Ray Fluorescence Spectrometry
4.2 Compare to destructive analysis (DA), the HKED
ISO/IEC 17025General Requirements for the Competence
method is rapid. HKED method requires minimal sample
of Testing and Calibration Laboratories
preparation and handling, and generates minimal amount of
ISO 7870-2Control Charts – Part 2: Shewhart Control
radioactive waste.
Charts
4.3 TheHKEDinstrumentcanbeoperatedinthreedifferent
3. Terminology
modes:(1)KEDdensitometryonlywhereUorPu,orboth,are
measured in the 50 g/L to 400 g/L concentration range, (2)
3.1 Definitions:
HybridmodewheretheconcentrationofUisdeterminedusing
3.1.1 For definitions of terms used in this test method, refer
KED densitometry and the U:Pu (100:1 typically) ratio is
to Terminology C859 or C1673.
determinedusingXRFmeasurements,(3)Stand-aloneXRFfor
3.2 Definitions of Terms Specific to This Standard:
low U and Pu concentrations (0.2 g/L to 50 g/L).
3.2.1 absorption edge—an absorption edge is the disconti-
nuity in the mass attenuation coefficient of an element at the
4.4 This method relies on a fixed and controlled geometry
characteristic energy corresponding to the electron binding
for the K-Edge and XRF measurements.
energy of the given atomic shell. When the energy of the
4.5 This test method details the apparatus, calibration,
incidentphotonexceedsthebindingenergyofanelectroninits
measurement protocol, calculations, and the demonstrated
shell, a photo-electric interaction becomes energetically pos-
precision and bias of the HKED technique.Also presented are
sible with this electron. This leads to an abrupt increase in the
suggested quality control measurements to track and maintain
mass attenuation coefficient, and hence a discontinuity in the
the performance of the HKED equipment.
variation of the mass attenuation coefficient as a function of
4.6 HKED involves the irradiation of sample solutions by a
photon energy.
continuous-energy X-Ray (Bremsstrahlung) beam. The con-
3.2.2 End-point Energy—the highest energy of the
centrationofthemajorelementisdeterminedbymeasuringthe
bremsstrahlung continuum, corresponding to the maximum
transmission of the incident X-Ray beam across the character-
energyoftheX-Raytube’selectronbeam.Itcanbedetermined
istic K-Edge energy of the element. Simultaneously, the
by extrapolating the KED pulse height distribution measured
intensities of prominent K X-Rays fluoresced by the incident
α
X-Ray beam are used to determine the element ratios of
For referenced ASTM standards, visit the ASTM website, www.astm.org, or actinides present in the sample. The minor element concentra-
contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
tion is calculated from the product of densitometry value for
Standards volume information, refer to the standard’s Document Summary page on
the major element concentration and the elemental ratio of the
the ASTM website.
actinides from the XRF measurement.
The last approved version of this historical standard is referenced on
www.astm.org.
4.7 For the determination of U or Pu concentrations in the
Available from International Organization for Standardization (ISO), ISO
50 g/Lto 400 g/Lrange, the method uses densitometry (KED)
Central Secretariat, BIBC II, Chemin de Blandonnet 8, CP 401, 1214 Vernier,
Geneva, Switzerland, http://www.iso.org. only.
C1855 − 18
4.8 For the determination of U or Pu concentrations in the the precision of such chemical analyses. This is especially
0.2 g/L to 50 g/L, the XRF method is typically used in the useful when high sample throughput is important.
stand-alone mode.
5.12 For the three modes of operation that are possibly,
namely, K-Edge only, Hybrid K-Edge/XRF, and Stand-alone
5. Significance and Use
XRF, the uncertainty levels that can be achieved for U and
5.1 The HKED technique is highly element specific and U/Pu samples have been established for routine safeguards
depends upon a well-known controlled geometry. measurements are described in the ITV (2).
5.2 The HKED technique can provide concentration mea-
6. Interferences
surements of actinides in solutions with precision typically
6.1 K-Edge Measurement—In the energy region of interest,
better than 0.3% for uranium concentrations >50 g/Land 1%
the intensity of the transmitted X-Ray beam for KED is about
for plutonium in typical U-Pu solutions for a typical measure-
three orders of magnitude higher than that obtained from the
ment time of 3 × 1000 s (3 replicates, 1000 s live time each)
self-radiation of typical input solutions. In view of this, the
(1).
KED measurement is insensitive to self-radiation from input
5.3 For pure plutonium only product solutions, the KED
solutions. This is true for fuels with relatively short cooling
technique can achieve measurement precisions better than
times (1).
0.3% for plutonium concentrations >50 g/L for a typical
6.2 Ifthesystemiscalibratedforsamplesinalimitedrange
measurement time of 3 × 1000 s.
of U:Pu ratios, for example 100:1, in a given mass range, (50
5.4 For pure uranium only solutions, precisions of better
g/Lto 400 g/L), but a sample with a much higher U:Pu ratio is
than 0.3% can be achieved using the KED technique for
measured, the attenuation of the bremsstrahlung by the minor
uranium concentrations >50 g/L, for a typical measurement
actinide (Pu) will cause a bias on the KED results from the
time of 3 × 3600 s.
major actinide (U). The hybrid XRF measurement of samples
5.5 For uranium only or plutonium only solutions of con-
with U and Pu may be subject to the following types of
centrations approximately 1 g/L, assayed using XRF, a mea- interferences.
surement precision of 1.0% has been achieved (1). For
6.2.1 The UK and the PuK peaks overlap and interfere
α1 α2
solutionsofconcentrationapproximately50g/L,assayedusing with each other. In the current region of interest (ROI) based
XRF, measurement precisions of 0.2% or better have been approach, a correction is applied for this interference.
achieved. The typical measurement time for stand-alone XRF 6.2.2 The UK and UK peaks overlap, and so do UK
α2 α3 β1
assay is 3 × 3000 s. and UK .An ROI that includes UK and UK , and another
β3 α2 α3
ROI that includes UK and UK are set up and used during
β1 β3
5.6 Quality Control (QC) samples are assayed for a typical
calibrationaswellassampleanalysis.Thereforenobiasresults
measurement time of 3 × 3000 s.
from interferences in these cases.
5.7 It is applicable when solutions to be measured are
6.2.3 TheAmK ROIisusedtoprovideacorrectionforthe
α1
homogeneous with respect to chemical composition.
presence of AmK X-Rays in the PuK background ROI.
α2 α1
6.2.4 Dissolver solutions (or “input” solutions) from spent
5.8 Results are typically used for fuel fabrication, process
control, quality control, material control and accountancy, and nuclear fuels are chemically complex and highly radioactive.
The spectrum from a dissolver solution is dominated by
safeguards in nuclear fuel reprocessing plants. Each applica-
tion can have its own data quality objectives (Guide C1068). gamma rays from a few longer lived fission products such as
137 144 154 155
Cs, Ce, Eu, and Eu. The gamma rays from fission
5.9 The HKED instrument may use a single cylindrical vial
products cause the excitation of uranium and plutonium in the
for both the KED and XRF measurements, or separate sample
sample and result in the emission of their characteristic
containers for KED and XRF. The typical values for the path
X-Rays. This is termed “self-radiation.”
length of the rectangular cuvette and the inner diameter of the
6.2.4.1 To correct for self-radiation effects, a separate pas-
cylindrical vial are given in 7.8.
sive spectrum can be acquired by turning off the X-Rays.
5.10 The transfer of the sample into the HKED system can
Alternatively, an empirical derived correction factor can be
be accomplished either horizontally by means of a suitably
usedbyrelatingtheadditionalcountsduetofissionproductsin
designed sample conveyor system coupled to a shielded
theenergyrange125keVto131keV,tothepassivecountrates
glovebox or hot cell facility or vertically through a pneumatic
intheROIsfortheevaluationofthenetX-Raypeakcounts (1).
sample transfer system.
6.2.5 Besides self-radiation, the downscattering of the fis-
sion product gamma rays increases the continuum levels,
5.11 The U and Pu concentrations measured by HKED are
degrading the precision of the measurements.
dependent on the sample temperature. The analysis software
includes a normalization of the measured concentration at the
7. Apparatus
ambientroomtemperaturetoareferencetemperatureof25°C.
The ambient room temperature is input into the analysis 7.1 Standard equipment for high resolution gamma ray
software. HKED has been employed as a rapid alternative to spectroscopy,includingtwohighresolutionhigh-puritygerma-
destructive chemical analyses, such as Isotope Dilution Mass nium detectors each with electronics for fast pulse processing,
Spectroscopy (IDMS) or titration, because there is minimal a multichannel analyzer and a dedicated software package are
sample preparation, and precision of HKED is comparable to used for spectrum acquisition and evaluation. Electronics
C1855 − 18
should be capable of handling a count rate of at least 50000 vials are spectroscopy cells whose thickness is known to a
counts per second (cps). precision less than 0.01%.
7.10 In HKED systems that use a single cylindrical vial for
7.2 Planar HPGe detectors with an active area of 100 mm
bothKEDandXRF,theuncertaintyintheKEDmeasurements
to 200 mm and a thickness of 10 mm are generally used.
due to uncertainty in the pathlength is ~0.07% typically. The
7.3 The energy resolution is demonstrated using Cd and
pooreruncertaintyisbecauseofthecurvatureofthecylindrical
Co by measurement of the FWHM of the gamma ray peaks
container. The uncertainty in sample positioning is typically
for these two isotopes with the same electronics configuration
<0.1%.
as used under routine measurement conditions. During system
7.11 The vial wall thickness should be as acceptably thin as
installation and set up, the energy resolution (FWHM) of the
possible in order to manage the intensity of scattered radiation
KED and XRF detectors is demonstrated using a Co source
from the X-Ray beam while maintaining structural integrity
and is typically 570 eV or better at 122 keV at a shaping time
and safe containment of the solutions.
of2.0microseconds.Duringoperation,theenergyresolutionis
monitored using the FWHM at the 88 keV gamma ray peak
7.12 If secondary containment is required for the sample
from Cd and is typically 520 eV or better at a count rate of
container (for example, to prevent contamination of the
approximately 50000 cps.
system), it should allow for transmission of the X-Rays from
the generator and the sample with minimal interference. A
7.4 Someinstrumentsuseasamplechanger.Thepositionof
schematic drawing of the HKED system geometry is shown in
thesamplesmustbecontrolledtowithin0.3mmtocontrolthe
Fig. A1.2 in Annex A1. The drawing shows the configuration
misalignment from causing more than 0.1% bias.
with a composite sample container consisting of a quartz
7.5 Cd source is typically affixed near the detectors for
cuvette for the KED measurement and a polyethylene vial for
energy calibration and gain stabilization. The typical count
XRF.
rates from the Cd source are 2000 cps (peak/background
ratio of 2:1).
8. Hazards
7.6 X-Ray equipment consisting of a cooled X-Ray tube,
8.1 Safety Hazards:
high voltage power supply, and operation console. An X-Ray
8.1.1 The high voltage supply for the X-Ray generator has
tube with a window diameter not exceeding 50 mm is
sufficient power to be a lethal hazard.Appropriate precautions
recommended.
shouldbetakenwhenperformingmaintenanceorduringinitial
system set up. The HV generator must be properly grounded.
7.7 The X-Ray tube is nominally run at 150 kV and 5 mA
8.1.2 The X-Ray generator creates a high level of ionizing
to 15 mA. Stability of the high voltage supply should be less
radiation when energized, that can result in a lethal dose in a
than 0.1% with adjustable high-voltage and current controls.
short period of time (on the order of minutes). Appropriate
7.8 Sample Containers:
precautions should be taken when performing maintenance or
7.8.1 Either a single cylindrical vial or a combination of
during initial system set up.
rectangularcuvetteandcylindricalvialaretypical.Inasystem
8.1.3 High resolution gamma-ray detectors operate at volt-
thatusestwosamplecontainers(seeFig.A1.1,AnnexA1),the
ages as high as 5 kV.Appropriate precautions should be taken
typical path length of the X-Rays through the rectangular
when using, assembling, and disassembling these systems.
cuvette is 2.0 cm, and the typical inner diameter of the
8.1.4 Some detectors have beryllium windows which are
cylindrical vial is 0.9 cm. In a system where the sample
fragile and considered hazardous due to oxidation and inhala-
containedinasinglecylindricalvialisusedforKEDandXRF,
tion hazard due to BeO.
the typical inner diameter of the vial is 1.4 cm. These path
8.1.5 Collimators and shielding may use materials (for
lengths are dependent on the areal density of the samples and
example, lead and cadmium) which are considered toxic, and
must be selected appropriately. For example, a measurement
can be physically heavy and difficult to maneuver. Proper care
precision of 0.23% can be achieved in a KED assay of a 150
in their use and disposal are required.
g/L uranium solution contained in a cuvette of path length
8.1.6 Uranium-, plutonium-, and fission-product-bearing
equal to 2.0 cm (1).This corresponds to an areal density of 0.3
materials present both chemical and radiological hazards. The
g/cm . To achieve a similar precision for a 100 g/L uranium
analyst should be aware of these hazards and take appropriate
solution, one will need to use a cuvette of path length equal to
precautions.
3.0 cm (areal density = 0.3 g/cm ). Refer to 13.3 for additional
8.1.7 Thesolutionsaretypicallyhighlyacidic(forexample,
guidelines on areal densities of samples.
nitric or hydrofluoric acid). Proper care must be taken in the
preparation and handling of these solutions.
7.9 The K-Edge measurement depends on the effective path
length of the X-Ray beam through the solution. For meeting 8.1.8 The X-Ray system is connected to a three phase
external power supply of 220/230/240 volts. Proper procedure
the ITVs this geometrical parameter must be carefully
controlled, because its fractional uncertainty propagates di- must be followed in energizing or de-energizing the X-Ray
tube to prevent arcing.
rectly into the fractional uncertainty of the uranium or pluto-
nium concentration measurement. The uncertainty on the path 8.1.9 The operator must be cognizant of the possibility of
length in this case must be small compared to other sources of liquid leaking from the cooler or the generator, leading to a
uncertainty (0.01% typically). The preferred type of sample slippery condition or electrocution.
C1855 − 18
TABLE 1 Summary of Uncertainties for K-Edge Densitometry
8.1.10 Proper maintenance of high voltage cable in the
Measurement for a Two Sample Container System (Rectangular
X-Ray system is necessary to prevent arcing in the X-Ray
Cuvette for KED and Cylindrical Vial for XRF)
system.
Magnitude of Comment
Uncertainty Component
8.1.11 The high voltage generator must be grounded to the
Uncertainty (%)
earth to minimize the potential for arcing of the system.
Counting precision Concentration range:
0.15 %
(3 times 1000 s live time) 150 – 300 g/L
8.1.12 Sealed calibration standards stored for an extended
0.01 % For individual cuvette
period of time pose a hazard due to build-up of pressure which
Variation for a
Cell length
<0.1 % production batch of
could result in the seals cracking, leading to spread of
cuvettes
contamination.
Determined by
Cell positioning <0.1 % dimensional tolerances
8.2 Technical Hazards:
for sample holder
8.2.1 Personnel operating the HKED system must have the
Can be taken into
Sample matrix <0.2 %
account in calibration
appropriate qualifications and training, in accordance with
Uranium isotopic Per % change of U
recommendations found in Guides C1297 and C1490. 0.013 %
composition enrichment
8.2.2 The detector and the signal processing electronics Per degree centigrade
Sample temperature 0.05 %
of sample temperature
must be properly grounded to eliminate ground loops.
Uncertainty in
8.2.3 Electromagneticinterference,vibrations,andcoupling
reference
Calibration 0.2 %
concentration from
to a hot cell (mechanical or electrical, or both) can also
chemical analysis
introduce noise artifacts and must be mitigated.
Concentration range:
Non-linearity <0.2 %
150 – 300 g/L
8.2.4 Inhomogeneityofthesamplesolutionduetoresidues/
Monitored from control
sedimentationorprecipitationwillimpactthecorrelationofthe
Instrument variability <0.3 %
charts
transmissionoftheX-RaystotheconcentrationofUandPuin
Total 0.5 % Summed in quadrature
the solution.
8.2.5 If the sample contained in the vial is not used
immediately after being prepared, and instead stored, evapo-
8.2.13 Sample vials from different batches or vendors may
ration will occur. The evaporation rate could be as much as
have varying dimensions and tolerances, which can introduce
0.2% per hour and will result in an overestimation of the U or
bias in the result if not accounted for.
Pu concentration in the container the sample was drawn from.
The rate of evaporation depends on the temperature, humidity
9. Preparation of Apparatus
and the fill height of the solution in the vial.
9.1 Ensure that the high-purity germanium detectors and
8.2.6 Thefillheightofthesolutioninsidethecontainermust
signal processing modules (for example, Amplifier, Analog to
be high enough in order to envelope the X-Ray beam passing
Digital Converters, Stabilizer) are set up properly according to
through it.
the Operations Manual.
8.2.7 The activity of the Cd source must be high enough
9.2 Optimize the shaping time of the amplifier so that it
toensurethatthe88keVpeakisdetectedabovethecontinuum
provides the highest throughput without degrading spectro-
andcanbereliablyusedforgainstabilizationandsmallenough
scopic quality of the data, for example, the energy resolution.
to avoid random coincidence summing between the 22 keV
The typical shaping time parameter for an analog amplifier is
X-Ray and the 88 keV gamma ray lines.
1µs(Gaussianshape),ordigitalequivalentwithaRise-timeof
8.2.8 The matrix of the reference (blank) solution must be
1.8 µs and Flat-top of 0.6 µs (trapezoidal shape). Adjust the
the same as the matrix of the sample.
amplifier gain and pole-zero. For optimum performance the
8.2.9 The high voltage generator and the X-Ray tube must
system dead time should not exceed 30%. The X-Ray tube
be cooled to a consistent temperature; otherwise the output
current can be adjusted if necessary to reduce the dead time to
could vary.
desired levels. The energy range of the spectra for the HPGe
8.2.10 Solutions with high concentrations of uranium or
detectorsintheK-EdgeandXRFsub-systemsis0toabout170
plutonium can cause radiolysis in the matrix, leading to the
keVandaminimumof2048channels.Whensetupinthisway
formation of bubbles. The rate of radiolysis on the HKED
and in order to achieve near optimal performance, the energy
results depends on the isotopic composition of uranium or
resolution(FWHM)shouldbelessthanabout520eVatthe88
plutonium in the sample. The impact on the results is not
keV gamma line from Cd, when the total count rate is
predictable. Shorter lived isotopes can cause higher radiolysis
50000 cps. If the energy resolution is worse than 520 eV,
241 238 240 239
( Pu, Pu, Pu) than longer lived isotopes such as Pu.
investigate.
8.2.11 Partialwarm-upofGedetectorscanleadtogainshift
9.3 Enable pile-up-rejection.
anddegradationinenergyresolution,andresultinginincorrect
results.
9.4 Sources of Cd are mounted in front of the detectors
8.2.12 Sample temperature is required as an operator input (away from the X-Ray beam path) for performing energy and
for the normalization of the final result. The appropriate shape calibration, and gain stabilization. Gain stabilization is
referencetemperaturemustbeindicatedinthesoftwaresetup. set up around the 88 keVgamma ray peak from Cd.The 22
Entering an incorrect temperature leads to a bias in the result keVX-Ray peak can be used in addition to the 88 keVgamma
(see Table 1). peak.
C1855 − 18
9.5 Monitor that the HVsetting corresponds to the intended both, contained in aqueous solutions. The calibration should
value using the end-point energy of K-Edge spectrum. Set up remain valid as long as the QA/QC permits.
the acquisition and analysis software.
10.2 The calibration in the three operating modes requires
reference materials that are prepared in accordance with Guide
9.6 OfcriticalimportanceareparameterssuchastheX-Ray
voltage and current, source certificates and declarations, Re- C1128andPracticeC1168oranyotherinternationalconsensus
standard (ISO/IEC 17025). These materials must be prepared
gions of Interest (ROI) before (left) and after (right) the U and
shortly(withinafewdays)beforethecalibrationmeasurement
Pu K-Edges for the K-Edge analysis, peak analysis parameters
campaign is begun. This is to avoid any changes in the
fortheUandPuK andK X-RaypeaksfortheXRFanalysis,
α β
concentration values because of evaporation and other degra-
and ROIs for continuum subtraction.
dation mechanisms.
9.7 Typical KED ROIs bounds are shown in Table 2. Figs.
10.3 A blank nitric acid solution not containing U or Pu,
1and2showaspectrumoftheK-EdgespectrumwiththeROI
similar in concentration to that of the sample solutions (typi-
limits.
cally 3 or 4 mol/L).
9.8 XRF ROIs—TypicallytheROIsfortheXRFanalysisare
10.4 A set of three or more synthetic U-Pu solutions
set according to the following rules:
simulating the characteristics of feed solutions with respect to
9.8.1 Bounds of ROIs are set 61.1 FWHM from the peak
uranium concentration (~50 g/L to 400 g/L), U/Pu ratio
centroid.
(typically 100 to 150) spanning the expected measurement
9.8.2 Background windows are centered 1.7 keVbelow and
range, and nitrate concentration (typically 3 or 4 mol/L). The
3.7 keV above the peak centroid.
uncertainty on the calibration standards must be specified to
9.8.3 ExceptionisU doublepeakcomplex;peakROIis
kβ1,3
meet the data quality objectives (DQO).
from U – 1.1 FWHM to U + FWHM.
Kβ3 Kβ1
9.8.4 Three other ROIs are included beyond those for the
10.5 To perform uranium or plutonium only calibration
U ,U ,U , and Pu . These are:
using stand-alone KED measurements, measure a set of three
kα2 kα1 kβ1 Kα1
9.8.4.1 TheAm ROI is available to provide a correction
or more uranium or plutonium only calibration solutions
Ka1
for the presence of Am X-Rays in the Pu background
ideally spanning the range of expected uranium or plutonium
Ka2 Ka1
ROI. The ROI is also used to quantify Am in the solution if
concentrations(forexample,50g/Lto400g/L),andnitricacid
present.
concentration (typically 3 or 4 mol/L). The uncertainty on the
9.8.4.2 Background window between Eu (123.07 keV)
calibrationstandardsmustbespecifiedtomeetthedataquality
and Ce (133.54 keV) to account for passive self-
objectives (DQO).
fluorescence.
10.6 To perform XRF only calibration for measuring low
9.8.4.3 Eu (123.07 keV) for bias correction.
uraniumorplutoniumconcentrations,measureasetofthreeor
9.8.5 Table 3 shows example ROI limits used in XRF
more U or Pu only calibration solutions simulating the char-
analysis. Fig. 3 illustrates the XRF spectrum with the ROI
acteristics of process solutions with respect to uranium or
window limits.
plutonium concentration (0.2 g/L to 50 g/L), and nitric acid
9.9 Other set-ups include count times, number of replicate concentration (typically 3 or 4 mol/L). The uncertainty on the
counts for each assay, sample changer set up (if there is an
calibrationstandardsmustbespecifiedtomeetthedataquality
automated sample changer), counting protocol set up (K-Edge objectives (DQO).
only or XRF only or Hybrid), quality control, and reporting.
10.7 Thehighvoltageisroutinelysetto150kV.Thecurrent
9.10 Perform a warm-up procedure of the X-Ray tube is set to an
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