SIST EN ISO 7097-2:2026

SLOVENSKI STANDARD
01-oktober-2026
Tehnologija jedrskega goriva - Ugotavljanje urana v raztopinah, uranovem
heksafluoridu in trdnih snoveh - 2. del: Titrimetrična metoda z redukcijo železa
(II)/oksidacijo cerija(IV) (ISO 7097-2:2022)
Nuclear fuel technology - Determination of uranium in solutions, uranium hexafluoride
and solids - Part 2: Iron(II) reduction/cerium(IV) oxidation titrimetric method (ISO 7097-
2:2022)
Kernbrennstofftechnologie - Bestimmung von Uran in Lösungen, Uranhexafluorid und
Feststoffen - Teil 2: Reduktion mit Eisen(II)/Oxidation mit Cer(IV)/Titrationsverfahren
(ISO 7097-2:2022)
Technologie du combustible nucléaire - Dosage de l'uranium dans des solutions,
l'hexafluorure d'uranium et des solides - Partie 2: Méthode titrimétrique par réduction au
fer(II) et oxydation au cérium(IV) (ISO 7097-2:2022)
Ta slovenski standard je istoveten z: EN ISO 7097-2:2026
ICS:
27.120.30 Cepljivi materiali in jedrska Fissile materials and nuclear
gorivna tehnologija fuel technology
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EN ISO 7097-2
EUROPEAN STANDARD
NORME EUROPÉENNE
August 2026
EUROPÄISCHE NORM
ICS 27.120.30
English Version
Nuclear fuel technology - Determination of uranium in
solutions, uranium hexafluoride and solids - Part 2:
Iron(II) reduction/cerium(IV) oxidation titrimetric
method (ISO 7097-2:2022)
Technologie du combustible nucléaire - Dosage de Kernbrennstofftechnologie - Bestimmung von Uran in
l'uranium dans des solutions, l'hexafluorure d'uranium Lösungen, Uranhexafluorid und Feststoffen - Teil 2:
et des solides - Partie 2: Méthode titrimétrique par Reduktion mit Eisen(II)/Oxidation mit
réduction au fer(II) et oxydation au cérium(IV) (ISO Cer(IV)/Titrationsverfahren (ISO 7097-2:2022)
7097-2:2022)
This European Standard was approved by CEN on 10 August 2026.

CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this
European Standard the status of a national standard without any alteration. Up-to-date lists and bibliographical references
concerning such national standards may be obtained on application to the CEN-CENELEC Management Centre or to any CEN
member.
This European Standard exists in three official versions (English, French, German). A version in any other language made by
translation under the responsibility of a CEN member into its own language and notified to the CEN-CENELEC Management
Centre has the same status as the official versions.

CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia,
Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway,
Poland, Portugal, Republic of North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Türkiye and
United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION

EUROPÄISCHES KOMITEE FÜR NORMUNG

CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels
© 2026 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 7097-2:2026 E
worldwide for CEN national Members.

Contents Page
European foreword . 3

European foreword
The text of ISO 7097-2:2022 has been prepared by Technical Committee ISO/TC 85 "Nuclear energy,
nuclear technologies, and radiological protection” of the International Organization for Standardization
(ISO) and has been taken over as EN ISO 7097-2:2026 by Technical Committee CEN/TC 430 “Nuclear
energy, nuclear technologies, and radiological protection” the secretariat of which is held by AFNOR.
This European Standard shall be given the status of a national standard, either by publication of an
identical text or by endorsement, at the latest by February 2027, and conflicting national standards
shall be withdrawn at the latest by February 2027.
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CEN shall not be held responsible for identifying any or all such patent rights.
Any feedback and questions on this document should be directed to the users’ national standards body.
A complete listing of these bodies can be found on the CEN website.
According to the CEN-CENELEC Internal Regulations, the national standards organizations of the
following countries are bound to implement this European Standard: Austria, Belgium, Bulgaria,
Croatia, Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland,
Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Republic of
North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Türkiye and the
United Kingdom.
Endorsement notice
The text of ISO 7097-2:2022 has been approved by CEN as EN ISO 7097-2:2026 without any
modification.
INTERNATIONAL ISO
STANDARD 7097-2
Second edition
2022-11
Nuclear fuel technology —
Determination of uranium in
solutions, uranium hexafluoride and
solids —
Part 2:
Iron(II) reduction/cerium(IV)
oxidation titrimetric method
Technologie du combustible nucléaire — Dosage de l'uranium dans
des solutions, l'hexafluorure d'uranium et des solides —
Partie 2: Méthode titrimétrique par réduction au fer(II) et oxydation
au cérium(IV)
Reference number
ISO 7097-2:2022(E)
ISO 7097-2:2022(E)
© ISO 2022
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on
the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below
or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: +41 22 749 01 11
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii
ISO 7097-2:2022(E)
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Principle . 2
5 Reactions and interferences .2
5.1 Reactions . 2
5.2 Interferences . 3
6 Reagents . 3
7 Apparatus . 6
8 Sample preparation .7
8.1 General . 7
8.2 Uranium metal . 8
8.3 Uranium dioxide pellets . 8
8.4 Uranium oxide powder (UO , UO , U O ) . 8
2 3 3 8
8.5 Uranium hexafluoride . 9
8.6 Uranyl nitrate hexahydrate . 9
9 Procedure .9
10 Expression of the results .10
10.1 General . 10
10.2 Method of calculation . 10
10.2.1 Linear interpolation . 10
10.2.2 Calculation for the test solution . 11
10.2.3 Calculations for samples . 11
10.2.4 Average atomic mass . 11
10.3 Repeatability .12
10.4 Bias . 12
11 Test report .12
Annex A (normative) Uranium hexafluoride sampling and preparation of the test solution .13
Annex B (informative) Expression of results for samples .15
Bibliography .17
iii
ISO 7097-2:2022(E)
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out
through ISO technical committees. Each member body interested in a subject for which a technical
committee has been established has the right to be represented on that committee. International
organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.
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
patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www.iso.org/patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and
expressions related to conformity assessment, as well as information about ISO's adherence to
the World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT), see
www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 85, Nuclear energy, nuclear technologies,
and radiological protection, Subcommittee SC 5, Nuclear installations, processes and technologies.
This second edition cancels and replaces the first edition (ISO 7097-2:2004), which has been technically
revised.
The main changes are as follows:
— the Scope was updated (see Clause 1);
— information on interferences was updated (see 5.2);
— requirements for standardisation of ceric titrant were updated (see 6.16);
— Annex A was divided into two annexes (Annex A and Annex B).
A list of all parts in the ISO 7097 series can be found on the ISO website.
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 7097-2:2022(E)
Introduction
This document describes procedures for the determination of uranium in solutions, uranium
hexafluoride, and solids. The procedures described in the two independent parts of this International
Standard are similar: this document uses a titration with cerium(IV) and ISO 7097-1 uses a titration
with potassium dichromate.
v
INTERNATIONAL STANDARD ISO 7097-2:2022(E)
Nuclear fuel technology — Determination of uranium in
solutions, uranium hexafluoride and solids —
Part 2:
Iron(II) reduction/cerium(IV) oxidation titrimetric
method
1 Scope
This document describes an analytical method for the determination of uranium in samples from
pure product materials such as U metal, UO , UO , U O , uranyl nitrate hexahydrate and uranium
2 3 3 8
hexafluoride from the nuclear fuel cycle. This procedure is sufficiently accurate and precise to be used
for nuclear materials accountability. This method can be used directly for the analysis of most uranium
and uranium oxide nuclear reactor fuels, either irradiated or un-irradiated, and of uranium nitrate
product solutions. Fission products equivalent to up to 10 % burn-up of heavy atoms do not interfere,
and other elements which could cause interference are not normally present in sufficient quantity to
affect the result significantly. The method recommends that an aliquot of sample is weighed and that a
mass titration is used, in order to obtain improved precision and accuracy. This does not preclude the
use of alternative techniques which could give equivalent performance. The use of automatic device(s)
in the performance of some critical steps of the method has some advantages, mainly in the case of
routine analysis.
This method does not generate a toxic mixed waste as does the potassium dichromate titration in
ISO 7097-1.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments) applies.
ISO 3696, Water for analytical laboratory use — Specification and test methods
ISO 9894, Subsampling of uranium hexafluoride in the liquid phase
ISO 5725-1, Accuracy (trueness and precision) of measurement methods and results — Part 1: General
principles and definitions
3 Terms and definitions
For purposes of this document, the terms and definitions given in ISO 5725-1 apply.
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/
ISO 7097-2:2022(E)
4 Principle
Uranium(VI) is reduced to uranium(IV) in concentrated phosphoric acid, in the presence of sulfamic
acid, by reaction with iron(II) sulfate. The excess of iron(II) sulfate is subsequently oxidized by nitric
acid in the presence of molybdenum, and the uranium(IV) is determined by mass titration with
standardized cerium sulfate solution to a potentiometric end point; see References [2][3][4][5][6].
An aliquot of the sample containing about 15 mg to 25 mg of uranium is taken for the titration. An
excess of iron(II) sulfate solution is then added to reduce all the uranium to the quadrivalent state.
Sulfamic acid is added to eliminate nitrite ions present at this stage. The excess of iron(II) is oxidized by
nitric acid, catalysed by molybdenum. The uranium is determined by mass titration with standardized
cerium sulfate solution to a potentiometric end point. To improve precision, the titration is performed
in the presence of vanadium in dilute phosphoric acid, which increases the kinetics of the reaction. The
addition of vanadium(IV) solution acts to dilute the sample solution and shift the redox potential so as
to allow the titration to proceed.
The ceric sulfate solution is calibrated with a certified uranium reference material, as described in 6.16;
[1]
see ISO 10980 .
5 Reactions and interferences
5.1 Reactions
Under the given experimental conditions, the principal reactions are as follows:
a) In concentrated phosphoric acid solution:
2+
2+ + 4+ 3+
UO + 2Fe + 4H → U + 2Fe + 2H O
2 2
Mo
−
2+ + 3+
3Fe + NO + 4H → 3Fe + NO + 2H O
3 2
Mo
−
2+ + 3+
Fe + NO + 2H → Fe + NO + H O
3 2 2
Mo
− −
2+ + 3+
2Fe + NO + 2H → 2Fe + NO + H O
3 2 2
b) In diluted phosphoric acid solution:
2+
4+ 3+ 2+ +
U + 2Fe + 2H O → UO + 2Fe + 4H
2 2
2+ 2+ + 3+ 3+
Fe + VO + 2H→ Fe + V + H O
The overall reaction can be represented as follows:
2+
4+ 2+ 3+
U + 2VO → UO + 2V
c) On titration with ceric sulfate solution:
4+ 3+ 3+ 2+ +
Ce + V +H O → Ce + VO + 2H
4+
which is equivalent to the titration of U with cerium:
2+
4+ 4+ 3+ +
2Ce + U +2H O → 2Ce +UO + 4H
2 2
ISO 7097-2:2022(E)
5.2 Interferences
This procedure is less subject to interference from foreign ions than most other methods of determining
[7]
uranium . In usual reprocessing solutions, fluoride, perchlorate, sulfate, Be, Si, Nb, Ti, Cr, Fe, Co, Ni, W,
Cu, Sb(V), Pb, Pu, Am, the rare earths and the alkaline earth metals do not interfere. The extent of Np
interference, if any, has not been verified.
For titrations involving uranium aliquots in the range of 15 mg to 25 mg:
−
a) Al, Zr, and NO do not interfere when present in the range 0 mg to 4 mg in the aliquot.
b) As(V) and Th do not interfere when present in the range 0 mg to 1 mg in the aliquot.
c) Mo and Mn do not interfere when present in the range 0 mg to 0,5 mg in the aliquot; Mo interferes
only if large amounts of nitrate are also present and vice versa.
d) Bromide, oxalate, Au, Sn, and some platinum group elements interfere at 0,1 % when present at
levels of 2 mg in the aliquot.
e) Interference from iodine, iodate, Ag, V (V), and Tc is more severe. Each of these impurity levels shall
be kept below 1 mg in the aliquot (0,1 % interference at 1 mg level).
f) As(III) and Sb(III) yield a bias which is proportional to the amount added. When present at 0,5 mg
levels, As(III) can cause a positive bias of 0,3 % and Sb(III) can cause a bias of ~4 %.
g) Nitrate and peroxide will not interfere unless present in higher than normal concentrations as
described here. Nitrate levels shall be <3 ml of concentrated nitric acid. Excessive amounts of
peroxide are indicated by failure to observe dark coloration during the oxidation step. Thus, it is
likely that the titration results of a sample containing excessive amounts of peroxide would be
biased.
h) A temperature range of 20 °C to 31 °C will have no influence on the titration results. Temperatures
outside of this range can affect reaction rates and times.
The possible effect of intense β and γ radiation and of some radioactive species (for example ruthenium)
on the electrode system remains to be established. Effects on the electrode by intense radiation have
been observed during a single run. Since the types of material to be analysed cover a very wide range,
the user of the method should consider the possibility of interference for each specific case, considering
published information and the results of any additional experiments which might be necessary.
6 Reagents
Use only reagents of recognized analytical grade and water as specified in 6.1.
6.1 Water, meeting the requirements for ISO 3696 grade 2 water (electrical conductivity less than
0,1 mS/m and resistivity greater than 0,01 MΩ⋅m at 25 °C).
It is recommended that the water used be obtained from a water purification system that delivers
ultrapure water having a resistivity greater than 0,18 MΩ⋅m (usually expressed by manufacturers of
water purification systems as 18 MΩ⋅cm).
6.2 Hydrofluoric acid (HF), c ≈ 29 mol/l ≈ mass fraction of 48 % ( d =11,)8 .
WARNING — Hydrofluoric acid is a highly corrosive and toxic acid that can severely burn skin,
eyes, and mucous membranes. The burning sensation is not immediately apparent and might
not be felt for several hours. The fluoride ion readily penetrates the skin, even with dilute
concentrations, causing destruction of deep tissue layers. Unlike other acids that are rapidly
neutralized, hydrofluoric acid reactions with tissue can continue for days if left untreated.
Familiarization and compliance with the Safety Data Sheet is essential.
ISO 7097-2:2022(E)
6.3 Nitric acid (HNO ), c ≈ 16 mol/l ≈ mass fraction of 69 % d =14, 2 .
()
3 4
6.4 Nitric acid (HNO ), c ≈ 8 mol/l.
Dilute the 16 mol/l nitric acid (6.3) 2 to 1 with water (6.1).
6.5 Nitric acid (HNO ), c ≈ 4 mol/l.
Dilute the 16 mol/l nitric acid (6.3) 4 to 1 with water (6.1).
6.6 Orthophosphoric acid (H PO ), c ≈ 15 mol/l ≈ mass fraction of 85 % d =17, 1 .
()
3 4 4
Historically, issues relating to the presence of excessive amounts of reducing agents such as Sb(III)
had been reported for this reagent. The use of analytical grade reagents is, in general, a sufficient
precautionary measure to avoid these issues.
6.7 Phosphoric acid reagent.
Add 1 ml of 0,4 mol/l ceric sulfate solution (6.14) to a 2,5 l reagent bottle of orthophosphoric acid (6.6)
and mix.
A pale straw colour is expected. If the solution turns green, it has been contaminated with reducing
agents and should be discarded.
6.8 Sulfuric acid (H SO ), c ≈ 18 mol/l ≈ mass fraction of 96 % d =18, 4 .
()
2 4 4
6.9 Sulfuric acid (H SO ), c ≈ 1,0 mol/l.
2 4
Add 56 ml of sulfuric acid (6.8) slowly and carefully to 900 ml of water, while stirring. Allow to cool and
adjust the solution to 1 000 ml with water (6.1).
6.10 Iron(II) sulfate (FeSO ·7H O), c ≈ 1 mol/l.
4 2
Add 10 ml of concentrated sulfuric acid (6.8) carefully to 75 ml of water (6.1) in a 500 ml beaker with
constant stirring. Add 28 g ± 1 g of iron(II) sulfate (FeSO ·7H O) and stir until it is dissolved. Dilute to
4 2
100 ml with water (6.1) and mix. This solution is not stable under all conditions for extended periods
of time and its use shall be verified on a regular basis determined by laboratory experience using an
appropriate quality control test or be prepared fresh once a week.
6.11 Sulfamic acid (NH SO H), c ≈ 1,55 mol/l.
2 3
Dissolve 150 g of Sulfamic acid in less than 1 l of water (6.1) at room temperature and dilute final
solution to 1 l. Filter freshly prepared sulfamic acid through a suitable filter paper before storing in glass
or low-density polyethylene (LDPE) bottle. As this solution is almost saturated, heating would tend to
decompose the sulfamic acid. This solution is not stable, and its use shall be verified, as appropriate, on
a regular basis using an appropriate quality control test or be prepared fresh once a week.
6.12 Oxidizing reagent.
Dissolve 10,0 g ± 0,1 g of hexaammonium heptamolybdate [(NH ) Mo O ·4H O] in 250 ml of water
4 6 7 24 2
(6.1).
Add 10 ml of sulfamic acid (6.10) to 50 ml of nitric acid (6.3), mix well, add 10 ml of the hexaammonium
heptamolybdate solution and add 30 ml of water (6.1). This solution can be unstable in some
environments and its use shall be verified, as appropriate, on a regular basis using an appropriate
quality control test or prepared fresh weekly.
ISO 7097-2:2022(E)
–2
6.13 Vanadium (IV) oxide sulfate, c ≈ 10 mol/l.
Weigh approximately 2 g of vanadium(IV) oxide sulfate (VOSO 2H O) and dissolve it in 200 ml of the
4 2
1 mol/l sulfuric acid solution (6.9). Adjust to 2 000 ml with water (6.1) and mix well. This solution is
not stable, and its use shall be verified, as appropriate, on a regular basis using an appropriate quality
control test or prepare fresh weekly.
6.14 Ceric sulfate, Ce(SO ) , c = 0,4 mol/l.
4 2
Dissolve 13,5 g anhydrous Ce(SO ) or 16,5 g Ce(SO ) 4H O or 21,9 g (NH ) Ce(NO ) in about 70 ml of
4 2 4 2 2 4 2 3 6
1,0 mol/l H SO (6.9), and dilute to 100 ml with additional H SO (6.9). (The solution can be boiled to
2 4 2 4
increase its stability, if desired.) Store in the dark. Alternatively, pre-made solutions can be procured
commercially.
6.15 Cerium(IV) titrant solution, 0,027 mol/l.
6.15.1 This procedure will prepare 5 l of 0,027 mol/l Ce(IV) titrant solution. Other volumes can be
prepared as desired. The procedure shall be started at least one month prior to expected use.
6.15.2 Weigh 74 g of ammonium ceric nitrate or 54,6 g of Ce(SO ) 4H O or 45 g of Ce(SO ) into a
4 2 2 4 2
weighing boat, scoop, or paper. Any equivalent source of Ce(IV) is acceptable. Transfer to a 5 l volumetric
flask, and dissolve in about 4 l of 1,0 mol/l H SO (6.9). Dilute to volume with 1,0 mol/l H SO (6.9) and
2 4 2 4
mix well.
6.15.3 Stopper the flask, place the flask in the dark, and allow to sit for at least one month. Carefully
filter the top 4 l of the
...