ISO/FDIS 24459

Determination of uranium content in samples coming from the nuclear fuel cycle by L-absorption edge spectrometry

Détermination de l'uranium dans les solutions du cycle du combustible nucléaire par absorption de rayons X à la discontinuité L

General Information

• Status: Published
• ICS: 27.120.30 - Fissile materials and nuclear fuel technology
• Technical Committee: ISO/TC 85/SC 5 - Nuclear installations, processes and technologies
• Drafting Committee: ISO/TC 85/SC 5/WG 1 - Analytical methodology in the nuclear fuel cycle
• Current Stage: 5020 - FDIS ballot initiated: 2 months. Proof sent to secretariat
• Start Date: 06-Jul-2021
• Completion Date: 06-Jul-2021

Standards Content (sample)

FINAL
INTERNATIONAL ISO/FDIS
DRAFT
STANDARD 24459
ISO/TC 85/SC 5
Determination of uranium content in
Secretariat: BSI
samples coming from the nuclear fuel
Voting begins on:
2021­07­06 cycle by L-absorption edge
spectrometry
Voting terminates on:
2021­08­31
Détermination de l'uranium dans les solutions du cycle du
combustible nucléaire par absorption de rayons X à la discontinuité L
RECIPIENTS OF THIS DRAFT ARE INVITED TO
SUBMIT, WITH THEIR COMMENTS, NOTIFICATION
OF ANY RELEVANT PATENT RIGHTS OF WHICH
THEY ARE AWARE AND TO PROVIDE SUPPOR TING
DOCUMENTATION.
IN ADDITION TO THEIR EVALUATION AS
Reference number
BEING ACCEPTABLE FOR INDUSTRIAL, TECHNO­
ISO/FDIS 24459:2021(E)
LOGICAL, COMMERCIAL AND USER PURPOSES,
DRAFT INTERNATIONAL STANDARDS MAY ON
OCCASION HAVE TO BE CONSIDERED IN THE
LIGHT OF THEIR POTENTIAL TO BECOME STAN­
DARDS TO WHICH REFERENCE MAY BE MADE IN
NATIONAL REGULATIONS. ISO 2021
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ISO/FDIS 24459:2021(E)
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© ISO 2021

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ii © ISO 2021 – All rights reserved
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ISO/FDIS 24459:2021(E)
Contents Page

Foreword ........................................................................................................................................................................................................................................iv

1 Scope ................................................................................................................................................................................................................................. 1

2 Normative references ...................................................................................................................................................................................... 1

3 Terms and definitions ..................................................................................................................................................................................... 1

4 Principle ........................................................................................................................................................................................................................ 1

5 Reagents and materials ................................................................................................................................................................................. 2

6 Apparatus ..................................................................................................................................................................................................................... 2

7 Method ............................................................................................................................................................................................................................ 4

7.1 Pre­checks ................................................................................................................................................................................................... 4

7.2 Reference spectrum ............................................................................................................................................................................ 4

7.3 Calibration .................................................................................................................................................................................................. 4

7.4 Sample measurement ........................................................................................................................................................................ 5

7.5 Spectrum evaluation .......................................................................................................................................................................... 5

7.5.1 Region of interest ............................................................................................................................................................ 5

7.5.2 Smoothing (optional) ................................................................................................................................................. 5

7.5.3 Background subtraction ............................................................................................................................................ 6

7.5.4 Calculation of the X-ray transmission ............................................................................................................ 6

7.6 Calculation of the concentration of uranium ................................................................................................................ 7

7.7 Quality control ......................................................................................................................................................................................... 8

7.8 Uncertainty evaluation ..................................................................................................................................................................... 8

7.8.1 Standard uncertainty of the calibration factor ...................................................................................... 8

7.8.2 Standard uncertainty of the uranium concentration ........................................................................ 9

Annex A (informative) Calculation method for correction factors of atomic mass and

temperature ...........................................................................................................................................................................................................10

Annex B (informative) Preparation of a solid quality control sample............................................................................11

Bibliography .............................................................................................................................................................................................................................13

© ISO 2021 – All rights reserved iii
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ISO/FDIS 24459:2021(E)
Foreword

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bodies (ISO member bodies). The work of preparing International Standards is normally carried out

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ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of

electrotechnical standardization.

The procedures used to develop this document and those intended for its further maintenance are

described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the

different types of ISO documents should be noted. This document was drafted in accordance with the

editorial rules of the ISO/IEC Directives, Part 2 (see www .iso .org/ directives).

Attention is drawn to the possibility that some of the elements of this document may be the subject of

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iso/ foreword .html.

This document was prepared by Technical Committee ISO/TC 85, Nuclear energy, nuclear technologies,

and radio protection, Subcommittee SC 5, Analytical methodology in the nuclear fuel cycle.

Any feedback or questions on this document should be directed to the user’s national standards body. A

complete listing of these bodies can be found at www .iso .org/ members .html.
iv © ISO 2021 – All rights reserved
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FINAL DRAFT INTERNATIONAL STANDARD ISO/FDIS 24459:2021(E)
Determination of uranium content in samples coming from
the nuclear fuel cycle by L-absorption edge spectrometry
1 Scope

This document specifies a method for the determination of uranium concentrations in nitric acid or

TBP-DILUANT (for example TBP-kerosene) solutions coming from the nuclear fuel cycle.

The method is applicable

— for process control to solutions, free of suspension, which contain between 10 g/l to 300 g/l uranium,

and

— for high accuracy purposes (Safeguards) to nitric acid solutions, free of suspension, which contain

between 100 g/l and 220 g/l uranium.
Having

— the content of neptunium and plutonium impurities in the solution less than 1 % of the uranium

content.

— the content of neutron poisons (gadolinium, erbium) less than 1 % of the uranium content to ensure

the absence of significant interferences at the level of required precision, for high accuracy purposes.

The method is applicable to solid samples as well, provided that they can be fully dissolved in nitric

acid.
2 Normative references
There are no normative references in this document.
3 Terms and definitions
No terms and definitions are listed in this document.

ISO and IEC maintain terminological databases for use in standardization at the following addresses:

— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
4 Principle

A highly collimated X-ray beam passes through a uranium solution with well-defined path length.

The transmission spectrum is recorded with a solid-state detector. A sharp jump of the photon

transmission, which is related to the concentration of uranium, occurs at the L-edge energy of uranium

(E = 17,17 keV). Uranium concentration is determined from the size of the jump using calibration and

LIII
spectrum processing algorithms.

The proposed spectrum processing algorithms require the acquisition of reference spectrum to cancel

out the influence of the matrix.

For high accuracy measurement, the isotopic composition of uranium and the temperature shall be

known and corrections may apply.
© ISO 2021 – All rights reserved 1
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ISO/FDIS 24459:2021(E)

The uncertainty of the number of counts in the channels before and after the L-edge is one of the main

contributors to the measurement uncertainty.

The acquisition time needed to reach the necessary number of counts depends of the total count

rate. The total count rate is a function of the intensity of the X-ray generator, of the characteristic of

instrument, and of the concentration of uranium.

It is therefore specific to the laboratory, which shall evaluate beforehand the fit-for-purpose accuracy

that will decide the target total count in the spectrum, the count rate and the acquisition time.

For high accuracy measurements, a minimum total number of counts of 2 000 000 in the fitting window

is required to ensure satisfactory statistics around the L-edge. The count rates and measurement times

given as indication in the document reflect this requirement. The reference, calibration and sample

spectra shall be recorded with the same count rate and the same high voltage (HV) cut­off.

For process control purposes, the necessary total number of counts will depend of the needed accuracy.

The measurement should be performed at the same HV cut­off and current.
5 Reagents and materials
Only analytical grade reagents shall be used.
All aqueous solutions shall be prepared with distilled water or deionized water.

5.1 Nitric acid solutions, c(HNO )≈3 mol/l, prepared from w(HNO ) 65 %, ρ= 1,42 g/cm .

3 3
5.2 Uranium reference solutions.

These solutions are used for calibration and quality control purposes. They should ideally be prepared

from a solid or liquid material with known uranium concentration, and known uranium isotopic

composition for high accuracy purposes. The standard uncertainty of the uranium concentration

should be equal or better than 0,06 %. The use of certified reference material traceable to SI units is

recommended.
6 Apparatus

The L-absorption edge spectrometer consists of an X-ray tube, an X-ray detector, a multichannel

analyser, a temperature sensor and software for data acquisition and processing. A principle diagram

of the instrument components is shown in Figure 1.
2 © ISO 2021 – All rights reserved
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ISO/FDIS 24459:2021(E)
Key
1 HV controller 6 detector
2 X-ray tube 7 MCA
3 collimator 8 sample cell
4 temperature sensor 9 computer
5 collimator
Figure 1 — Schematic of the instrument components
6.1 X-ray tube.

The maximum working voltage of X-ray tube is higher than 25 kV, voltage-controlled, current-controlled.

It shall be stable over time and shall reach an intensity (adjustable, usually lower than 100 μA) high

enough to ensure satisfactory total count rate for fast and accurate measurement (as described in

Clause 4).
6.2 Shielding and collimator.

The shielding body is made of brass or other shield materials. X-ray tube, X-ray detector and sample cell

are directly mounted in the shielding body. The thickness of the shielding is chosen to ensure no X-ray

leakage, and to satisfy the radioprotection requirements.

The collimator is made of tungsten, or other materials, whose fluorescence X-rays do not interfere with

the region of interest.
6.3 Sample cell.

The sample cell can be made of glass or polycarbonate (PC), which can withstand nitric acid and TBP-

DILUANT or in quartz that is resistant to nitric acid.

The optimum path length and the specifications of the cell depend on the characteristic of the apparatus

and the analytical needs.
Examples of cell specifications:
— for process control purposes, disposable 4mm long PC cell;
— for high accuracy purposes, fixed flow-through cell with a path len
...