ISO 12183:2016
(Main)Nuclear fuel technology — Controlled-potential coulometric assay of plutonium
Nuclear fuel technology — Controlled-potential coulometric assay of plutonium
ISO 12183:2016 describes an analytical method for the electrochemical assay of pure plutonium nitrate solutions of nuclear grade, with a total uncertainty not exceeding ±0,2 % at the confidence level of 0,95 for a single determination (coverage factor, K = 2). The method is suitable for aqueous solutions containing more than 0,5 g/L plutonium and test samples containing between 4 mg and 15 mg of plutonium. Application of this technique to solutions containing less than 0,5 g/L and test samples containing less than 4 mg of plutonium requires experimental demonstration by the user that applicable data quality objectives will be met. For some applications, purification of test samples by anion exchange is required before measurement to remove interfering substances when present in significant amounts.
Technologie du combustible nucléaire — Dosage du plutonium par coulométrie à potentiel imposé
L'ISO 12183:2016 décrit une méthode analytique pour le dosage électrochimique de plutonium pur dans des solutions nitriques de qualité nucléaire, avec une incertitude ne dépassant pas ± 0,2 % dans un intervalle de confiance de 0,95 pour une simple détermination (facteur d'élargissement, K = 2). La méthode est adaptée aux solutions aqueuses contenant plus de 0,5 g/L de plutonium et à des échantillons d'essai contenant entre 4 mg et 15 mg de plutonium. L'application de cette technique aux solutions contenant moins de 0,5 g/L et d'échantillons d'essai contenant moins de 4 mg de plutonium exige que l'utilisateur démontre expérimentalement que les objectifs relatifs à la qualité des données applicables soient atteints. Pour certaines applications, une purification des échantillons d'essai par échange anionique est nécessaire avant la mesure pour éliminer les substances interférentes présentes en quantités significatives. Se reporter à l'Article 10 qui traite des interférences et des actions correctives. La purification est aussi nécessaire dans les situations où la pureté de l'échantillon d'essai n'est pas connue ou quand elle peut fluctuer de façon imprévisible dans le procédé de fabrication. L'Article 11 traite des changements dans l'application de la méthode et de la méthodologie qui peuvent être appliquées et des considérations importantes pour sélectionner les paramètres de mesure, tout en restant à l'intérieur du domaine d'application du présent document.
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INTERNATIONAL ISO
STANDARD 12183
Third edition
2016-08-15
Nuclear fuel technology — Controlled-
potential coulometric assay of
plutonium
Technologie du combustible nucléaire — Dosage du plutonium par
coulométrie à potentiel imposé
Reference number
ISO 12183:2016(E)
©
ISO 2016
---------------------- Page: 1 ----------------------
ISO 12183:2016(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2016, Published in Switzerland
All rights reserved. Unless otherwise specified, 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
Ch. de Blandonnet 8 • CP 401
CH-1214 Vernier, Geneva, Switzerland
Tel. +41 22 749 01 11
Fax +41 22 749 09 47
copyright@iso.org
www.iso.org
ii © ISO 2016 – All rights reserved
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ISO 12183:2016(E)
Contents Page
Foreword .iv
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Principle . 1
5 Reagents . 2
6 Apparatus . 2
7 Procedure. 8
7.1 Plutonium determination . 8
7.1.1 Weighing the test sample, with an uncertainty of ±0,01 %, K = 1. . 8
7.1.2 Preparation of the test sample . 9
7.1.3 Electrode pre-treatment. 9
7.1.4 Electrical calibration of the current integration system .10
7.1.5 Formal potential determination .11
7.1.6 Coulometric blank determination.12
7.1.7 Plutonium measurement .13
7.2 Analysis of subsequent test samples .13
8 Expression of results .14
8.1 Calculation of the electrical calibration factor .14
8.2 Calculation of the blank .14
8.3 Fraction of electrolysed plutonium .15
8.4 Plutonium content .16
8.5 Quality control .16
9 Characteristics of the method .16
9.1 Repeatability .16
9.2 Confidence interval .17
9.3 Analysis time .17
10 Interferences .17
11 Procedure variations and optimization .21
11.1 Accountability measurements and reference material preparation .21
11.2 Process control measurements.21
11.3 Measurement cell design .21
11.4 Electrolyte and electrode options .22
11.5 Test sample size .22
11.6 Background current corrections .22
11.7 Correction for iron .23
11.8 Control-potential adjustment .24
11.9 Calibration methodologies .24
Annex A (normative) Purification by anion-exchange separation .25
Annex B (normative) Determination of formal potential, E .27
0
Bibliography .28
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ISO 12183:2016(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 on 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 the following URL: www.iso.org/iso/foreword.html.
The committee responsible for this document is Technical Committee ISO/TC 85, Nuclear energy, nuclear
technologies, and radiological protection, Subcommittee SC 5, Nuclear fuel cycle.
This third edition cancels and replaces the second edition (ISO 12183:2005), which has been technically
revised.
iv © ISO 2016 – All rights reserved
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INTERNATIONAL STANDARD ISO 12183:2016(E)
Nuclear fuel technology — Controlled-potential
coulometric assay of plutonium
1 Scope
This document describes an analytical method for the electrochemical assay of pure plutonium nitrate
solutions of nuclear grade, with a total uncertainty not exceeding ±0,2 % at the confidence level of
0,95 for a single determination (coverage factor, K = 2). The method is suitable for aqueous solutions
containing more than 0,5 g/L plutonium and test samples containing between 4 mg and 15 mg of
plutonium. Application of this technique to solutions containing less than 0,5 g/L and test samples
containing less than 4 mg of plutonium requires experimental demonstration by the user that applicable
data quality objectives will be met.
For some applications, purification of test samples by anion exchange is required before measurement to
remove interfering substances when present in significant amounts. Refer to Clause 10 for a discussion
of interferences and corrective actions. Purification is also appropriate in situations where the purity
of the test sample is unknown or when it may fluctuate unpredictably in a manufacturing process.
Clause 11 discusses the changes in application of the method and methodology that can be applied and
important considerations when selecting measurement parameters, while still remaining within the
intended scope of this document.
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:
— IEC Electropedia: available at http://www.electropedia.org/
— ISO Online browsing platform: available at http://www.iso.org/obp
4 Principle
The key steps and their purposes are outlined below:
— test samples are prepared by weighing and then fuming to dryness with sulphuric acid to achieve a
consistent and stable anhydrous plutonium sulphate salt that is free from chloride, fluoride, nitrate,
nitrite, hydroxylamine, and volatile organic compounds;
— if needed to remove interferences, dissolve test samples and purify by anion exchange, then fume
the eluted plutonium solution in the presence of sulphuric acid to obtain the dry plutonium sulphate
chemical form;
— measure a blank of the nitric acid supporting electrolyte and calculate the background current
correction applicable to the electrolysis of the test sample from charging, faradaic, and residual
[1]
current ;
— dissolve the dried test sample in the previously measured supporting electrolyte (the blank);
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ISO 12183:2016(E)
— reduce the test sample at a controlled potential that electrolyses the plutonium to greater than
3+
99,8 % Pu and measure the equilibrium solution potential at the end of this step by control-
[2]
potential adjustment ;
— oxidize the test sample at a controlled potential that electrolyses the plutonium to greater than
4+
99,8 % Pu and measure the equilibrium solution potential at the end of this electrolysis by control-
potential adjustment;
— correct the result for the background current and the fraction of plutonium not electrolysed;
— calibrate the coulometer using traceable electrical standards and Ohm’s Law;
— use the measured value of the coulometer calibration factor and the Faraday constant to convert the
coulombs of integrated current from the electrolyses to moles of plutonium;
— use traceable quality-control plutonium standards to demonstrate independently the performance
of the measurement system;
— periodically measure the formal potential of the plutonium couple, E which is user-specific based
0,
on the cell design, connections, reference electrode type, and the acid-type and molarity of the
supporting electrolyte.
These steps ensure that representative, reproducible, and stable test samples are prepared for
measurement. The test samples are measured using a protocol that is based upon first principles and is
consistent with a traceable, electrical calibration of the coulometer. Additional details are provided in
Clauses 10 and 11.
5 Reagents
Use only analytical grade reagents.
All aqueous solutions shall be prepared with double-distilled or distilled, demineralized water with a
resistivity greater than 10 MΩ⋅cm, i.e. ISO 3696 Grade 1 purified water.
5.1 Nitric acid solution, c (HNO ) = 0,9 mol/L.
3
NOTE Refer to 11.4 for other electrolyte options.
5.2 Amidosulphuric acid solution, c (NH HSO ) = 1,5 mol/L.
2 3
5.3 Sulphuric acid solution, c (H SO ) = 3 mol/L.
2 4
NOTE Molarity is not a critical parameter for sulphuric acid used to fume plutonium test samples, provided
the concentration of the reagent is well above the level where colloidal plutonium complexes form.
5.4 Pure argon or nitrogen, (O content lower than 10 ppm).
2
5.5 Pure air, free of organic contaminants.
6 Apparatus
Usual laboratory equipment found in a medium-activity radiochemical laboratory suitable for work
with plutonium shall be used.
6.1 Analytical balance, installed in radiological containment unit and must be capable of weighing
1 g mass, with an uncertainty of ±0,1 mg (coverage factor, K = 1). This represents a relative uncertainty
of 0,01 %.
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ISO 12183:2016(E)
— Weighing less than 1 g will increase the relative uncertainty to >0,01 %, in an inversely
proportional manner.
— If the uncertainty of the balance, as installed, does not meet the ±0,01 mg criterion, then
correspondingly larger test samples are required.
6.2 Weighing burette, glass or plastic, the material selection is not critical provided it maintains a
stable mass (tare weight) and static charge is controlled as described in 7.1.1.
6.3 Equipment for test sample evaporation in the coulometric cell, comprising of an overhead
radiant heater or hot-plate with controls to adjust temperature. Design requirements and optional
features for effective evaporation and fuming include:
— providing settings that allow both rapid and well-controlled rate of initial evaporation, followed by
fuming the remaining sulphuric acid solution to dryness at a higher temperature;
— preventing mechanical loss of the test sample solution from boiling and/or spattering;
— preventing contamination by extraneous chemicals, such as those which may be used to neutralize
acid vapours;
— heating of the coulometer cell wall to optimize fuming and minimize refluxing of sulphuric acid by
placing the cell inside an optional aluminium tube with an inner diameter that is 1 mm to 3 mm
larger than the outer diameter of the cell and a height that is 1 mm to 5 mm shorter than the cell may
be placed around the cell during the fuming step to heat the walls of the cell;
NOTE An aluminium block with holes bored to a similar specification for inserting the cell may be used
instead of the aluminium tubes.
— addition of an optional air supply with the delivery tube directed towards the surface of the liquid
to optimize the evaporation rate and disperse the acid fumes;
— addition of an optional vapour capture and local neutralization to control acid fumes, depending
upon facility design and ventilation system requirements.
See Figure 1.
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ISO 12183:2016(E)
Dimensions in centimetres
Figure 1 — Sample evaporation system
6.4 Controlled-potential coulometer.
See Figure 2.
6.4.1 Coulometer cell assembly, comprising the following:
−1
— a stirrer motor with a rotation frequency of at least 1 000 min ;
NOTE 1 Adjustable-speed motors allow optimizing rotation rates for individual cell designs. Stirrer
motors powered by isolated DC power supplies are desirable to prevent electrical noise from being
superimposed on the blank and test sample electrolysis current signals sent to the integrator.
— a cylindrical or tapered glass coulometric cell of capacity 50 mL, or less, with an O-ring seal and a
tight-fitting lid with openings to insert the following internal equipment:
— an inlet tube for humidified, inert gas to displace dissolved and atmospheric oxygen from the
solution and the electrolysis cell, respectively;
— a stirrer with blade and shaft made from chemically inert materials [e.g. polytetrafluoroethylene
(PTFE)], and designed to prevent splashing; the shaft of the stirrer is typically located in the
centre of the cell and connected directly to the stirrer motor;
— a working electrode made of gold (e.g. 99,99 %) and consisting of a gold wire welded or machined
to a cylindrical gold wire frame, nominally 15 mm high and 20 mm in diameter, around which
is welded or machined a very fine gold mesh, which is typically several layers (e.g. four layers);
NOTE 2 Refer to 11.4 for other working electrode options.
— a glass tube plugged at the bottom end with a sintered-glass disc (typical dimensions of 2,5-mm
thick and pore size <0,01 μm), the tube filled with nitric acid (5.1) and the tip of the sintered-glass
end positioned within the ring of the working electrode;
— a reference electrode, saturated calomel electrode (SCE), or other reference electrodes as described
in 11.3, is inserted into the glass tube;
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ISO 12183:2016(E)
— another glass tube, similar to the first one, also filled with nitric acid (5.1), and the tip of the sintered-
glass end positioned within the ring of the working electrode;
— an auxiliary electrode consisting of a platinum wire, 0,5 mm to 3,0 mm in diameter, is inserted into
the second glass tube;
NOTE 3 The platinum wire may be coiled to increase the surface area submerged in the supporting
electrolyte, as illustrated in Figure 2.
— a gas washer bottle, filled with reagent water as described in Clause 5, to humidify the inert gas
before it is introduced into the coulometer cell assembly.
The diameter of the glass tube and sintered-glass disc containing the auxiliary electrode may be larger
than that of the glass tube and sintered-glass disc containing the reference electrode. The flow rate of
the solution through both glass discs shall be less than 0,05 mL/h.
a) A thermocouple or resistance thermometer installed in the coulometer cell assembly for measuring
the temperature of the test sample solution during the measurement process is an optional feature.
The solution temperature should be measured either during the oxidation of the test sample or
immediately following the analysis. An uncertainty goal for the temperature measurement is
±0,2 °C (K = 1).
— If it is not possible to insert a temperature sensor into the electrolysis cell or not desirable
to measure the temperature of the test sample solution immediately after the electrolysis is
completed, then estimate the solution temperature from the ambient air temperature or the
reagent temperature. Note that the purge gas is cooled by expansion causing the solution
temperature to decrease relative to the ambient temperature; the extent of this decrease is a
function of the inert-gas flow rate and the cell design. The measured air or reagent temperature
value must be corrected for this cooling effect. A higher uncertainty of ±1 °C, K = 1, is expected
in the calculated solution temperature.
b) For optimum potential control, position the sintered-glass discs of the reference and auxiliary
electrodes glass tubes to meet the following requirements:
— the closest distance from the reference electrode sintered-glass disc to the working electrode is
2 mm or less;
— the distance between the two sintered-glass discs containing the auxiliary and reference
electrodes is less than the distance between the auxiliary electrode disc and the nearest point
on the working electrode.
c) The hole through which the stirrer shaft is inserted serves as the primary escape vent for the
inert gas. Except for this hole, all other insertions are tight fitting. The inert-gas flow rate must
be sufficiently high to quickly remove oxygen from the supporting electrolyte and the test sample
solution. Furthermore, it must prevent leakage of air into the cell assembly during the electrolysis.
A practical guide for adjusting the flow rate is to direct all or part of the inert gas supply toward
the solution, such that a 2 mm to 4 mm dimple is formed on the surface without causing the
solution to splash.
— Cell assemblies with an optimized design, an adequate inert-gas flow rate, and a tight fit, will
remove oxygen in 5 min or less. The time required to remove oxygen from the solution should
be established by users based on testing of their cell assembly under routine conditions.
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ISO 12183:2016(E)
Key
1 video 8 auxiliary (or counter) electrode in bridge tube filled with
supporting electrolyte
2 printer (optional)
3 control computer 9 reference electrode in bridge tube filled with supporting
electrolyte
4 keyboard 10 inert gas
5 potentiostat and integrator 11 stirrer
6 digital voltmeter (DVM) 12 working electrode
7 AC/DC power for stirring motor 13 cell
Figure 2 — Coulometric cell assembly connections
[3][4]
6.4.2 Instrumentation, comprising the following :
a) Potentiostat with the desired range of electrolysis potentials for plutonium measurement and the
following capabilities:
— a power amplifier with a current output capability of 250 mA, or greater;
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ISO 12183:2016(E)
— a quick-response control-potential circuit, with maximum rise-time of 1 ms from zero volts to
the desired control potential, with voltage overshoot not exceeding 1 mV;
— a control amplifier with a common-mode rejection of 90 dB, or greater;
— automatic control-potential adjustment, with a resolution of 0,001 V, or less;
— a voltage-follower amplifier, to isolate the reference electrode (electrometer), with a minimum
11
input impedance of 10 Ω;
— capability to monitor the electrolysis current, including charging current for zero to 500 mA,
with a detection capability of 0,5 μA.
NOTE This procedure assumes that the coulometer has two accurate potentiometers, one for selecting
the oxidation potential and the other for the reduction potential, although this is not a system requirement.
b) Coulometric integrator capable of integrating blank and test sample electrolysis currents from at
least 150 mA down to 1 μA with a readability of ±10 μC (refer to 7.1.4 for integrator capabilities and
calibration requirements);
— The control-potential system should not drift more than ±1 mV and the current integration
system should not drift more than 0,005 % during routine measurements (between electrical
calibrations), over the range of temperatures to which the control-potential circuitry will be
exposed. If the room temperature varies excessively, the instrumentation should be located
in a cabinet having temperature controls sufficient to limit electronic drift within these
specifications.
— An electronic clock, with an uncertainty of ±0,002 % (K = 1) for determining the duration of
electrical calibrations and electrolyses.
— A system for generating a known constant current, stable to ±0,002 % over the range of
temperatures to which the constant-current circuitry will be exposed. This system will be used
for electrical calibration of the integration circuit of the coulometer, as described in 7.1.4.
— The cable connecting the potentiostat to the cell should be a three-wire conductor, twisted-
shielded cable, preferably with the shield grounded at the potentiostat. Gold-plated connectors
at the cell are recommended as these are not susceptible to corrosion.
— The charging-current peak maximum observed during the first 25 ms to 50 ms of the blank and
test sample oxidations must be within the instrument specification for the integrator circuit.
The surface area of the working electrode can be decreased to reduce the charging current peak
maximum. An oscilloscope or a voltmeter with high-speed data acquisition is required to measure
the amplitude of this peak, which has a typical width at half the maximum of 10 ms to 20 ms.
10
6.5 Digital voltmeter (DVM), with an input impedance of 10 Ω or greater and having an uncertainty
within ±0,001 % (K = 1) for voltages in the range 0,5 V to 10 V, and within ±0,01 % (K = 1) for voltages
in the range 100 mV to 500 mV. These uncertainties are required for electrical calibration of the
instrumentation, as described in 7.1.4.
6.6 Regulated power, instrumentation should be protected with an uninterruptable power supply
that provides a regulated voltage within ±1 % of the standard for that particular country, and provides
appropriate surge protection.
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ISO 12183:2016(E)
7 Procedure
7.1 Plutonium determination
7.1.1 Weighing the test sample, with an uncertainty of ±0,01 %, K = 1.
The test sample may be weighed after delivery into a tared coulometer cell, and the apparent mass
corrected for the air buoyancy effect using either Formula (1) or Formula (2), as described below.
Alternatively, a known mass of the test sample may be delivered into the coulometer cell, as described
in steps a) through f).
For test samples at high plutonium concentrations (e.g. 15 g/L or more), it is recommend that the
solution be diluted to achieve an overall weighing uncertainty of ±0,01 %.
If a weight burette made of polythene, or other material susceptible to static electricity, is used, then
the problem of static electricity may be eliminated by contact between the dropping tube and a copper
plate connected to the ground, or a similar arrangement.
a) Fill a weighing burette with the solution to be analyzed.
b) Weigh the burette to 0,1 mg.
c) Deliver a test sample of at least 1 mL, drop by drop, into a coulometric cell, ensuring that at least
4 mg of plutonium has been delivered.
d) Weigh the burette again to 0,1 mg.
e) The mass difference gives the apparent mass, m , of the test sample in the cell.
a
f) Correct the apparent mass of the test sample for the air buoyancy effect using Formula (1):
−1
M = M (1 − D /D ) (1 − D /D ) (1)
Real a a b a s
where
D is the density of air, which is a function of temperature, pressure, and humidity, but typical-
a
3 3
ly is between 0,001 16 g/cm and 0,001 20 g/cm ;
3
D is the density of the stainless steel weights used in modern analytical balan
...
DRAFT INTERNATIONAL STANDARD
ISO/DIS 12183
ISO/TC 85/SC 5 Secretariat: BSI
Voting begins on: Voting terminates on:
2015-09-01 2015-12-01
Nuclear fuel technology — Controlled-potential
coulometric assay of plutonium
Technologie du combustible nucléaire — Dosage du plutonium par coulométrie à potentiel imposé
ICS: 27.120.30
THIS DOCUMENT IS A DRAFT CIRCULATED
FOR COMMENT AND APPROVAL. IT IS
THEREFORE SUBJECT TO CHANGE AND MAY
NOT BE REFERRED TO AS AN INTERNATIONAL
STANDARD UNTIL PUBLISHED AS SUCH.
IN ADDITION TO THEIR EVALUATION AS
BEING ACCEPTABLE FOR INDUSTRIAL,
TECHNOLOGICAL, COMMERCIAL AND
USER PURPOSES, DRAFT INTERNATIONAL
STANDARDS MAY ON OCCASION HAVE TO
BE CONSIDERED IN THE LIGHT OF THEIR
POTENTIAL TO BECOME STANDARDS TO
WHICH REFERENCE MAY BE MADE IN
Reference number
NATIONAL REGULATIONS.
ISO/DIS 12183:2015(E)
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 SUPPORTING DOCUMENTATION. ISO 2015
---------------------- Page: 1 ----------------------
ISO/DIS 12183:2015(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2015, Published in Switzerland
All rights reserved. Unless otherwise specified, 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
Ch. de Blandonnet 8 • CP 401
CH-1214 Vernier, Geneva, Switzerland
Tel. +41 22 749 01 11
Fax +41 22 749 09 47
copyright@iso.org
www.iso.org
ii © ISO 2015 – All rights reserved
---------------------- Page: 2 ----------------------
ISO/DIS 12183
Contents Page
Foreword iv
1 Scope 1
2 Normative References 1
3 Principle 1
4 Reagents 2
5 Apparatus 2
6 Procedure 7
6.1 Plutonium determination 7
6.2 Analysis of subsequent test samples 13
7 Expression of results 14
7.1 Calculation of the electrical calibration factor 14
7.2 Calculation of the blank 14
7.3 Fraction of electrolysed plutonium 15
7.4 Plutonium content 15
7.5 Quality control 16
8 Characteristics of the method 16
8.1 Repeatability 16
8.2 Confidence interval 16
8.3 Analysis time 16
9 Interferences 17
10 Procedure variations and optimisation 20
10.1 Accountability measurements and reference material preparation 20
10.2 Process control measurements 20
10.3 Measurement cell design 21
10.4 Electrolyte and electrode options 21
10.5 Test sample size 22
10.6 Background current corrections 22
10.7 Correction for iron 23
10.8 Control-potential adjustment 23
10.9 Calibration Methodologies 23
Annex A (normative) Purification by anion-exchange separation 25
Annex B (normative) Determination of formal potential, E 27
0
Bibliography 28
© ISO 2015 – All rights reserved iii
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ISO/DIS 12183
Foreword
ISO (the International Organisation for Standardisation) 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 organisations, 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 standardisation.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 3.
The main task of the technical committee is to prepare International Standards. Draft International Standards
adopted by the technical committees are circulated to the member bodies for voting. Publication as an International
Standard requires approval by at least 75 % of the member bodies casting a vote.
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.
ISO 12813 was prepared by Technical Committee ISO/TC 85, Nuclear energy, nuclear technologies, and
radiological protection, Subcommittee SC 5, Nuclear fuel cycle.
This third edition cancels and replaces the second edition (ISO 12183:2005), which has been technically revised.
© ISO 2015 – All rights reserved iv
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ISO/DIS 12183
Nuclear Energy — Fuel Technology — Controlled-potential
coulometric assay of plutonium
1 Scope
This International Standard describes an analytical method for the electrochemical assay of pure
plutonium nitrate solutions of nuclear grade, with a total uncertainty not exceeding ± 0,2 % at the
confidence level of 0,95 for a single determination (coverage factor, K = 2). The method is suitable for
aqueous solutions containing more than 0,5 g/L plutonium and test samples containing between 4 mg
and 15 mg of plutonium. Application of this technique to solutions containing less than 0,5 g/L and test
samples containing less than 4 mg of plutonium requires experimental demonstration by the user that
applicable data quality objectives will be met.
For some applications, purification of test samples by anion exchange is required before
measurement to remove interfering substances when present in significant amounts. Refer to Clause
9 for a discussion of interferences and corrective actions. Purification is also appropriate in situations
where the purity of the test sample is unknown or when it may fluctuate unpredictably in a
manufacturing process.
Clause 10 discusses the changes in application of the method and methodology that can be applied
and important considerations when selecting measurement parameters, whilst still remaining within
the intended scope of this standard.
2 Normative references
The following document is an indispensable reference for the application of the analysis procedure
described in this document.
ISO 10980, “Validation of the strength of reference solutions used for measuring concentrations.”
Note that for dated references, only the edition cited applies. For undated references, the latest
edition is the appropriate reference.
3 Principle
The key steps and their purposes are outlined below:
— test samples are prepared by weighing and then fuming to dryness with sulphuric acid to achieve
a consistent and stable anhydrous plutonium sulphate salt that is free from chloride, fluoride,
nitrate, nitrite, hydroxylamine, and volatile organic compounds;
— if needed to remove interferences, dissolve test samples and purify by anion exchange, then fume
the eluted plutonium solution in the presence of sulphuric acid to obtain the dry plutonium
sulphate chemical form;
— measure a blank of the nitric acid supporting electrolyte and calculate the background current
correction applicable to the electrolysis of the test sample from charging, faradaic, and residual
[1]
current;
— dissolve the dried test sample in the previously measured supporting electrolyte (the blank);
— reduce the test sample at a controlled potential that electrolyses the plutonium to greater than
3+
99,8 % Pu and measure the equilibrium solution potential at the end of this step by control-
[2]
potential adjustment;
1
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ISO/DIS 12183
— oxidise the test sample at a controlled potential that electrolyses the plutonium to greater than
4+
99,8 % Pu and measure the equilibrium solution potential at the end of this electrolysis by
control-potential adjustment;
— correct the result for the background current and the fraction of plutonium not electrolysed;
— calibrate the coulometer using traceable electrical standards and Ohm’s Law;
— use the measured value of the coulometer calibration factor and the Faraday constant to convert
the coulombs of integrated current from the electrolyses to moles of plutonium;
— use traceable quality-control plutonium standards to demonstrate independently the performance
of the measurement system;
— periodically measure the formal potential of the plutonium couple, E which is user-specific based
0,
on the cell design, connections, reference electrode type, and the acid-type and molarity of the
supporting electrolyte.
These steps ensure that representative, reproducible, and stable test samples are prepared for
measurement. The test samples are measured using a protocol that is based upon first principles and
is consistent with a traceable, electrical calibration of the coulometer. Additional details are provided
in Clauses 9 and 10.
4 Reagents
Use only analytical grade reagents.
All aqueous solutions shall be prepared with double-distilled or distilled, demineralised water with a
resistivity greater than 10 MΩ⋅cm, i.e., ISO 3696 Grade 1 purified water.
4.1 Nitric acid solution, c (HNO ) = 0,9 mol/L.
3
NOTE Refer to 10.4 for other electrolyte options.
4.2 Amidosulphuric acid solution, c (NH HSO ) = 1,5 mol/L.
2 3
4.3 Sulphuric acid solution, c (H SO ) = 3 mol/L.
2 4
NOTE Molarity is not a critical parameter for sulphuric acid used to fume plutonium test samples, provided the
concentration of the reagent is well above the level where colloidal plutonium complexes form.
4.4 Pure argon or nitrogen, (O content lower than 10 parts per million).
2
4.5 Pure air, (free of organic contaminants).
5 Apparatus
Usual laboratory equipment found in a medium-activity radiochemical laboratory suitable for work with
plutonium.
5.1 Analytical balance, installed in radiological containment unit must be capable of
weighing 1 g mass with an uncertainty of ± 0,1 mg (coverage factor, K = 1). This
represents a relative uncertainty of 0,01 %.
— weighing less than 1 g will increase the relative uncertainty to >0,01 %, in an inversely
proportional manner;
2
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ISO/DIS 12183
— If the uncertainty of the balance, as installed, does not meet the ± 0,01 mg criterion, then
correspondingly larger test samples are required.
5.2 Weighing burette, glass or plastic, the material selection is not critical provided it
maintains a stable mass (tare weight) and static charge is controlled as described in
6.1.1.
5.3 Equipment for test sample evaporation in the coulometric cell, comprising of
an overhead radiant heater or hot-plate with controls to adjust temperature. Design
requirements and optional features for effective evaporation and fuming include:
— provide settings that allow both rapid and well-controlled rate of initial evaporation, followed by
fuming the remaining sulphuric acid solution to dryness at a higher temperature.
— prevent mechanical loss of the test sample solution from boiling and/or spattering.
— prevent contamination by extraneous chemicals, such as those which may be used to neutralise
acid vapours.
— the coulometer cell wall may be heated to optimise fuming and minimise refluxing of sulphuric
acid by placing the cell inside an aluminium tube with an inner diameter that is 1 mm to 3 mm
larger than the outer diameter of the cell and a height that is 1 mm to 5 mm shorter than the cell
may be placed around the cell during the fuming step to heat the walls of the cell. An aluminium
block with holes bored to a similar specification for inserting the cell may be used instead of the
aluminium tubes.
— an air supply with the delivery tube directed towards the surface of the liquid may be added to the
apparatus to optimum the evaporation rate and disperse the acid fumes.
— vapour capture and local neutralisation may be appropriate to control acid fumes depending upon
facility design and ventilation system requirements.
The equipment in figure 1 is suitable. Dimensions in centimetres
Figure 1 Sample evaporation system
3
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ISO/DIS 12183
5.4 Controlled-potential coulometer
The following equipment is suitable (see figure 2).
5.4.1 Coulometer cell assembly, comprising the following:
-1
— a stirrer motor with a rotation frequency of at least 1000 min ;
NOTE Adjustable-speed motors allow optimising rotation rates for individual cell designs. Stirrer motors
powered by isolated direct-current supplies are desirable to prevent electrical noise from being
superimposed on the blank and test sample electrolysis current signals sent to the integrator.
— a cylindrical or tapered glass coulometric cell of capacity 50 mL, or less, with an O-ring seal and a
tight-fitting lid with openings to insert the following internal equipment:
— an inlet tube for humidified, inert gas to displace dissolved and atmospheric oxygen from the
solution and the electrolysis cell, respectively;
— a stirrer with blade and shaft made from chemically inert materials (e.g., Teflon™), and designed
to prevent splashing; the shaft of the stirrer is typically located in the centre of the cell and
connected directly to the stirrer motor;
— a working electrode made of gold (e.g., 99,99 %) and consisting of a gold wire welded or
machined to a cylindrical gold wire frame, nominally 15 mm high and 20 mm in diameter, around
which is welded or machined a very fine gold mesh. The gold mesh is typically several layers
(e.g., four layers);
NOTE Refer to 10.4 for other working electrode options.
— a glass tube plugged at the bottom end with a sintered-glass disc (typical dimensions of 2,5-mm
thick and pore size <0,01 µm), the tube filled with nitric acid (4.1) and the tip of the sintered-glass
end positioned within the ring of the working electrode;
— a reference electrode, saturated calomel electrode (SCE), or other reference electrodes as
described in 10.3, is inserted into the glass tube;
— another glass tube, similar to the first one, also filled with nitric acid (4.1), and the tip of the
sintered-glass end positioned within the ring of the working electrode;
— an auxiliary electrode consisting of a platinum wire, 0,5 mm to 3,0 mm in diameter, is inserted into
the second glass tube. The platinum wire may be coiled to increase the surface area submerged
in the supporting electrolyte, as illustrated in Figure 2;
— a gas washer bottle, filled with reagent water as described in section 4.0, to humidify the inert gas
before it is introduced into the coulometer cell assembly.
The diameter of the glass tube and sintered-glass disc containing the auxiliary electrode may be larger than that
of the glass tube and sintered-glass disc containing the reference electrode. The flow rate of the solution through
both glass discs shall be less than 0,05 mL/h.
a. A thermocouple or resistance thermometer installed in the coulometer cell assembly for
measuring the temperature of the test sample solution during the measurement process is an
optional feature. The solution temperature should be measured either during the oxidation of
the test sample or immediately following the analysis. An uncertainty goal for the temperature
measurement is ± 0,2 °C (K = 1).
— If it is not possible to insert a temperature sensor into the electrolysis cell or not desirable to
measure the temperature of the test sample solution immediately after the electrolysis is
completed, then estimate the solution temperature from the ambient air temperature or the
reagent temperature. Note that the purge gas is cooled by expansion causing the solution
4
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ISO/DIS 12183
temperature to decrease relative to the ambient temperature; the extent of this decrease is a
function of the inert-gas flow rate and the cell design. The measured air or reagent
temperature value must be corrected for this cooling effect. A higher uncertainty of ± 1 °C, K =
1, is expected in the calculated solution temperature.
b. For optimum potential control, position the sintered-glass discs of the reference and auxiliary
electrodes glass tubes to meet the following requirements:
— the closest distance from the reference electrode sintered-glass disc to the working electrode
is 2 mm or less.
— the distance between the two sintered-glass discs containing the auxiliary and reference
electrodes is less than the distance between the auxiliary electrode disc and the nearest point
on the working electrode.
c. The hole through which the stirrer shaft is inserted serves as the primary escape vent for the inert
gas. Except for this hole, all other insertions are tight fitting. The inert-gas flow rate must be
sufficiently high to quickly remove oxygen from the supporting electrolyte and the test sample
solution. Furthermore, it must prevent leakage of air into the cell assembly during the electrolysis.
A practical guide for adjusting the flow rate is to direct all or part of the inert gas supply toward the
solution, such that a 2 mm to 4 mm dimple is formed on the surface without causing the solution
to splash.
— Cell assemblies with an optimised design, an adequate inert-gas flow rate, and a tight fit, will
remove oxygen in 5 min or less. The time required to remove oxygen from the solution should
be established by users based on testing of their cell assembly under routine conditions.
Figure 2 – Coulometric cell assembly connections
5
---------------------- Page: 9 ----------------------
ISO/DIS 12183
Printer (optional)
Video
Control Computer Keyboard
Potentiostat and
Digital Voltmeter
Integrator
AC or DC Power for
Stirring Motor
Inert Gas Key Connections
1) Stirrer
2) Working Electrode
3) Auxiliary (or counter) Electrode in
bridge tube filled with supporting
electrolyte
4) Cell
5) Reference Electrode in bridge tube
filled with supporting electrolyte
Glove box, Air Hood or equivalent
[3,4]
5.4.2 Instrumentation, comprising the following:
a) Potentiostat with the desired range of electrolysis potentials for plutonium measurement and the
following capabilities:
— a power amplifier with a current output capability of 250 mA, or greater;
— a quick-response control-potential circuit, with maximum rise-time of 1 ms from zero volts to
the desired control potential, with voltage overshoot not exceeding 1 mV;
— a control amplifier with a common-mode rejection of 90 dB, or greater;
— automatic control-potential adjustment, with a resolution of 0,001 V, or less;
— a voltage-follower amplifier, to isolate the reference electrode (electrometer), with a minimum
11
input impedance of 10 Ω;
— Capability to monitor the electrolysis current, including charging current for zero to 500 mA,
with a detection capability of 0,5 µA.
6
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ISO/DIS 12183
NOTE This procedure assumes that the coulometer has two accurate potentiometers one for selecting the
oxidation potential and the other for the reduction potential, although this is not a system requirement.
b) Coulometric integrator capable of integrating blank and test sample electrolysis currents from at
least 150 mA down to 1 µA with a readability of ±10 μC; (Refer to 6.1.4 for integrator capabilities
and calibration requirements.)
— The control-potential system should not drift more than ±1 mV and the current integration
system should not drift more than 0,005 % during routine measurements (between electrical
calibrations), over the range of temperatures to which the control-potential circuitry will be
exposed. If the room temperature varies excessively, the instrumentation should be located in
a cabinet having temperature controls sufficient to limit electronic drift within these
specifications.
— An electronic clock, with an uncertainty of ± 0,002 % (K = 1) for determining the duration of
electrical calibrations and electrolyses.
— A system for generating a known constant current, stable to ± 0,002 % over the range of
temperatures to which the constant-current circuitry will be exposed. This system will be used
for electrical calibration of the integration circuit of the coulometer, as described in 6.1.4.
— The cable connecting the potentiostat to the cell should be a three-wire conductor, twisted-
shielded cable, preferably with the shield grounded at the potentiostat. Gold-plated
connectors at the cell are recommended as these are not susceptible to corrosion.
— The charging-current peak maximum observed during the first 25 ms to 50 ms of the blank
and test sample oxidations must be within the instrument specification for the integrator
circuit. The surface area of the working electrode can be decreased to reduce the charging
current peak maximum. An oscilloscope or a voltmeter with high-speed data acquisition is
required to measure the amplitude of this peak, which has a typical width at half the maximum
of 10-ms to 20-ms.
10
5.5 Digital voltmeter (DVM), with an input impedance of 10 Ω or greater and having
an uncertainty within ± 0,001 % (K = 1) for voltages in the range 0,5 V to 10 V, and
within ± 0,01 % (K = 1) for voltages in the range 100 mV to 500 mV. These
uncertainties are required for electrical calibration of the instrumentation, as described
in 6.1.4.
5.6 Regulated power, instrumentation should be protected with an uninterruptable power
supply that provides a regulated voltage within ± 1 % of the standard for the nation, and
provides appropriate surge protection.
6 Procedure
6.1 Plutonium determination
6.1.1 Weighing the test sample, with an uncertainty of ± 0,01 %, K = 1.
The test sample may be weighed after delivery into a tared coulometer cell, and the apparent mass
corrected for the air buoyancy effect using either Equation (1) or (2), as described below.
Alternatively, a known mass of the test sample may be delivered into the coulometer cell, as
described in steps a) through f).
For test samples at high plutonium concentrations (e.g., 15 g/L or more), it is recommend that the solution be
diluted to achieve an overall weighing uncertainty of ± 0,01 %.
7
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ISO/DIS 12183
NOTE If a weight burette made of polythene, or other material susceptible to static electricity, is used then the
problem of static electricity may be eliminated by contact between the dropping tube and a copper plate
connected to the ground, or a similar arrangement.
a) Fill a weighing burette with the solution to be analysed.
b) Weigh the burette to 0,1 mg.
c) Deliver a test sample of at least 1 mL, drop by drop, into a coulometric cell, ensuring that at
least 4 mg of plutonium has been delivered.
d) Weigh the burette again to 0,1 mg.
e) The mass difference gives the apparent mass, m , of the test sample in the cell.
a
f) Correct the apparent mass of the test sample for the air buoyancy effect using Equation (1):
-1
M = M (1 - D /D ) (1 - D /D ) (1)
Real a a b a s
where:
D is the density of air, which is a function of temperature, pressure, and humidity, but typically is
a
3 3
between 0,00116 g/cm and 0,00120 g/cm .
3
D is the density of the stainless steel weights used in modern analytical balances, 8,0 g/cm .
b
D is the density of the test sample.
s
In addition to applying an air buoyancy correction to the mass of the test sample, air buoyancy corrections should
be applied to all mass measurements (including any bulk material mass measurements). This correction is
required to eliminate systematic errors that can exceed 0,1 % for solutions. The correction is less for solids, but
can still be significant.
For plutonium metal and alloy test samples, an additional buoyancy correction term for self-heating
[5]
from radioactive decay, as detailed in Equation (2) is also appropriate.
-1 -2/3 -1
M = M (1 - D /D ) (1 - D /D ) (1 - Δm' x M x Pu ) (2)
Real a a b a s a heat
where:
M is the apparent mass in grams.
a
5/3 -1
Δm' is the mass coefficient for the heat buoyancy term, with a value of 0,00003 g mW ± 0,00001
5/3 -1
g mW (1σ) for test samples ranging from 1 g to 15 g.
-1
Pu is the specific-heat of the plutonium, mW g , calculated from the plutonium isotopic abundance
heat
241 -1 -1
and Am content. This value is nominally 2 mW g to 3 mW g for plutonium with a burn up ranging
-1 -1
from 2 MWDKg to 8 MWDKg (or GW-days per metric ton). The specific heat increases with higher
238
reactor burn up and increased Pu content.
6.1.2 Preparation of the test sample
a) Add 1 mL of sulphuric acid solution (4.3) to the coulometric cell containing the test sample.
b) Place the cell containing the test sample into the sample evaporation system and carefully
evaporate the liquid in the test sample so as to avoid splashing.
c) Evaporate the remaining liquid in the test sample at a temperature sufficient to evolve fumes of
SO , and continue until SO fumes are no longer observed and a residue of plutonium sulphate
3 3
(pink/orange-coloured precipitate) is formed. Do not allow the solution to boil or splash as this will
cause mechanical loss.
8
---------------------- Page: 12 ----------------------
ISO/DIS 12183
The colour of the plutonium sulphate is dependent on the type of lighting used in the laboratory. Under
fluorescent lighting the dried sulphate is coral pink. Degradation of plutonium sulphate to plutonium oxide should
not be expected even after baking the residue unless subjected to extremely high temperatures. Failure to use (i)
high purity reagents, (ii) anion-exchange resins washed free of resin fines, and (iii) heating equipment that is well
maintained and clean will impact the fuming operation adversely. Any or all of these failures can produce a visible
black residue in combination with the dried sulphate powder. These residues could be mistaken for plutonium
oxide, and depending on their composition might interfere in the coulometric measurement.
d) Allow the test sample to cool to room temperature.
6+ 2+ 3+ 4+
e) If Pu (PuO ) is present, it shall be reduced to lower oxidation states (Pu and Pu ) prior to
2
coulometric measurement by the addition of either hydrogen peroxide or nitrite ion or ferrous ion.
The excess reducing agent shall be removed by purification or destroyed prior to coulometric
measurement. Refer to Clause 9 for details.
f) If the presence of significant amounts of impurities is suspected, dissolve and purify the dried test
sample to eliminate the interfering elements. Repeat the sulphuric acid fuming step as detailed in
6.1.2. Anion-exchange is an effective purification process; it is outlined in Annex A.
6.1.3 Electrode pre-treatment
Electrode conditioning is critical to ensuring reproducibility. The following storage and treatment
techniques may be used individually or in combination to condition the working and auxiliary
electrodes:
— storing in 8 mol/L nitric acid when the electrodes are not in use (this storage technique is
recommended as the general practice);
— soaking in concentrated nitric acid;
— soaking in concentrated sulphuric acid containing 10 % hydrofluoric acid, followed by 8 mol/L
nitric acid;
— soaking in aqua regia (limited to several minutes to prevent damage to the working electrode);
— boiling in nitric acid;
— flaming the platinum auxiliary electrode to white or red heat.
Electrode treatment may be performed on a preventative basis, at the beginning and/or at the end of
the day of electrode use. Alternatively, treatment may be on an ‘as needed’ basis, particularly needed
in case of failure to obtain optimum electrode performance in either the blank or the test sample
measurements. The background current values (total mC, charging current mA maximum, and
residual current μA) should be reproducible for a given installation and are normally used as
indicators of satisfactory performance.
Each day, or more often as desired, before performing the actual blank determination, further
conditioning of the electrodes is achieved by performing the following sequence of electrolyses:
a) Assemble the cell lid, complete with the electrodes and other internal equipment (see 5.4.1).
b) Take a clean dry coulometric cell and add sufficient nitric acid solution (4.1) to immerse the
working electrode, and the sintered-glass discs of the reference and auxiliary electrode tubes.
c) Add one drop of amidosulphuric acid solution (4.2).
d) Firmly fit the cell under the lid.
9
---------------------- Page: 13 ----------------------
ISO/DIS 12183
e) Start the stirrer at the desired speed. (This speed should be selected to maximize the stirring rate,
whilst avoiding splashing or forming any excessive vortex that would interrupt electrical
connections.)
f) Open the gas inlet and maintain a sufficient flow of inert gas throughout the electrolysis period.
(Inadequate purging to remove oxygen can be mistaken for an electrode-conditioning problem.)
g) Preselect the oxidation potential at E +0,32 V and the reduction potential at E –0,36 V.
0 0
h) After degassing for 5 min., start the oxidation and oxidise at E +0,32 V until a residual current of
0
10 µA is obtained.
i) Start the reduction and reduce at E –0,36 V until a residual current lower than 10 µA is obtained.
0
j) Oxidise at E +0,32 V.
0
k) Stop the electrolysis when the current is lower than 10 µA.
l) Rinse the electrolysis cell and the outside wall of the fritted-glass tubes with fresh supporting
electrolyte.
m) Based upon electrode performance:
— Perform further electrode conditioning, 6.1.3, until the desired performance is observed; or
— Measure the supporting electrode blank determination, 6.1.6, in preparation for the
subsequent measurement of plutonium test samples.
—
6.1.4 Electrical calibration of the
...
NORME ISO
INTERNATIONALE 12183
Troisième édition
2016-08-15
Technologie du combustible
nucléaire — Dosage du plutonium par
coulométrie à potentiel imposé
Nuclear fuel technology — Controlled-potential coulometric assay of
plutonium
Numéro de référence
ISO 12183:2016(F)
©
ISO 2016
---------------------- Page: 1 ----------------------
ISO 12183:2016(F)
DOCUMENT PROTÉGÉ PAR COPYRIGHT
© ISO 2016, Publié en Suisse
Droits de reproduction réservés. Sauf indication contraire, aucune partie de cette publication ne peut être reproduite ni utilisée
sous quelque forme que ce soit et par aucun procédé, électronique ou mécanique, y compris la photocopie, l’affichage sur
l’internet ou sur un Intranet, sans autorisation écrite préalable. Les demandes d’autorisation peuvent être adressées à l’ISO à
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ISO copyright office
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Tel. +41 22 749 01 11
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copyright@iso.org
www.iso.org
ii © ISO 2016 – Tous droits réservés
---------------------- Page: 2 ----------------------
ISO 12183:2016(F)
Sommaire Page
Avant-propos .iv
1 Domaine d’application . 1
2 Références normatives . 1
3 Termes et définitions . 1
4 Principe . 1
5 Réactifs . 2
6 Appareillage . 2
7 Mise en œuvre . 8
7.1 Mesure du plutonium . 8
7.1.1 Pesée de l’échantillon d’essai, avec une incertitude de ± 0,01 %, K = 1. . 8
7.1.2 Préparation de l’échantillon d’essai . 9
7.1.3 Traitement préliminaire de l’électrode . 9
7.1.4 Étalonnage électrique du système d’intégration de courant .11
7.1.5 Détermination du potentiel formel .11
7.1.6 Détermination du blanc coulométrique .12
7.1.7 Mesure du plutonium .13
7.2 Analyse d’échantillons d’essai successifs .14
8 Expression des résultats.14
8.1 Calcul du facteur d’étalonnage électrique .14
8.2 Calcul du blanc .15
8.3 Fraction de plutonium électrolysé .16
8.4 Teneur en plutonium .16
8.5 Contrôle qualité .17
9 Caractéristiques de la méthode .17
9.1 Répétabilité .17
9.2 Intervalle de confiance .17
9.3 Temps d’analyse .17
10 Interférences .17
11 Variantes et optimisation de la procédure .21
11.1 Mesures de comptabilité et préparation des matériaux de référence .21
11.2 Mesures de contrôle de procédé .21
11.3 Conception de la cellule de mesure .22
11.4 Options pour les électrolytes et électrodes .22
11.5 Taille de l’échantillon d’essai .23
11.6 Corrections de courant de fond .23
11.7 Correction du fer .24
11.8 Ajustement du potentiel de contrôle .24
11.9 Méthodes d’étalonnage .25
Annexe A (normative) Purification par séparation par échange anionique .26
Annexe B (normative) Détermination du potentiel formel, E .28
0
Bibliographie .29
© ISO 2016 – Tous droits réservés iii
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ISO 12183:2016(F)
Avant-propos
L’ISO (Organisation internationale de normalisation) est une fédération mondiale d’organismes
nationaux de normalisation (comités membres de l’ISO). L’élaboration des Normes internationales est
en général confiée aux comités techniques de l’ISO. Chaque comité membre intéressé par une étude
a le droit de faire partie du comité technique créé à cet effet. Les organisations internationales,
gouvernementales et non gouvernementales, en liaison avec l’ISO participent également aux travaux.
L’ISO collabore étroitement avec la Commission électrotechnique internationale (IEC) en ce qui
concerne la normalisation électrotechnique.
Les procédures utilisées pour élaborer le présent document et celles destinées à sa mise à jour sont
décrites dans les Directives ISO/IEC, Partie 1. Il convient, en particulier de prendre note des différents
critères d’approbation requis pour les différents types de documents ISO. Le présent document a été
rédigé conformément aux règles de rédaction données dans les Directives ISO/IEC, Partie 2 (voir www.
iso.org/directives).
L’attention est appelée sur le fait que certains des éléments du présent document peuvent faire l’objet de
droits de propriété intellectuelle ou de droits analogues. L’ISO ne saurait être tenue pour responsable
de ne pas avoir identifié de tels droits de propriété et averti de leur existence. Les détails concernant
les références aux droits de propriété intellectuelle ou autres droits analogues identifiés lors de
l’élaboration du document sont indiqués dans l’Introduction et/ou dans la liste des déclarations de
brevets reçues par l’ISO (voir www.iso.org/brevets).
Les appellations commerciales éventuellement mentionnées dans le présent document sont données
pour information, par souci de commodité, à l’intention des utilisateurs et ne sauraient constituer un
engagement.
Pour une explication de la signification des termes et expressions spécifiques de l’ISO liés à l’évaluation
de la conformité, ou pour toute information au sujet de l’adhésion de l’ISO aux principes de l’Organisation
mondiale du commerce (OMC) concernant les obstacles techniques au commerce (OTC), voir le lien
suivant: www.iso.org/iso/fr/avant-propos.html
Le comité chargé de l’élaboration du présent document est l’ISO/TC 85, Énergie nucléaire, technologies
nucléaires, et radioprotection, sous-comité SC 5, Installations nucléaires, procédés et technologies.
Cette troisième édition annule et remplace la deuxième édition (ISO 12183:2005) qui a fait l’objet d’une
révision technique.
iv © ISO 2016 – Tous droits réservés
---------------------- Page: 4 ----------------------
NORME INTERNATIONALE ISO 12183:2016(F)
Technologie du combustible nucléaire — Dosage du
plutonium par coulométrie à potentiel imposé
1 Domaine d’application
Le présent document décrit une méthode analytique pour le dosage électrochimique de plutonium
pur dans des solutions nitriques de qualité nucléaire, avec une incertitude ne dépassant pas ± 0,2 %
dans un intervalle de confiance de 0,95 pour une simple détermination (facteur d’élargissement,
K = 2). La méthode est adaptée aux solutions aqueuses contenant plus de 0,5 g/L de plutonium et à des
échantillons d’essai contenant entre 4 mg et 15 mg de plutonium. L’application de cette technique aux
solutions contenant moins de 0,5 g/L et d’échantillons d’essai contenant moins de 4 mg de plutonium
exige que l’utilisateur démontre expérimentalement que les objectifs relatifs à la qualité des données
applicables soient atteints.
Pour certaines applications, une purification des échantillons d’essai par échange anionique est
nécessaire avant la mesure pour éliminer les substances interférentes présentes en quantités
significatives. Se reporter à l’Article 10 qui traite des interférences et des actions correctives. La
purification est aussi nécessaire dans les situations où la pureté de l’échantillon d’essai n’est pas connue
ou quand elle peut fluctuer de façon imprévisible dans le procédé de fabrication.
L’Article 11 traite des changements dans l’application de la méthode et de la méthodologie qui peuvent
être appliquées et des considérations importantes pour sélectionner les paramètres de mesure, tout en
restant à l’intérieur du domaine d’application du présent document.
2 Références normatives
Le présent document ne contient aucune référence normative
3 Termes et définitions
Aucun terme n’est défini dans le présent document.
L’ISO et l’IEC tiennent à jour des bases de données terminologiques destinées à être utilisées en
normalisation, consultables aux adresses suivantes:
— IEC Electropedia: disponible à l’adresse http://www.electropedia.org/
— ISO Online browsing platform: disponible à l’adresse http://www.iso.org/obp
4 Principe
Les étapes essentielles et leurs objectifs sont décrits ci-après:
— les échantillons d’essai sont préparés par pesée et portés à sec en présence d’acide sulfurique pour
obtenir un sel de sulfate anhydre de plutonium solide et stable chimiquement, exempt de chlorure,
fluorure, nitrate, nitrite, hydroxylamine et de composés organiques volatils;
— si cela est nécessaire pour éliminer les interférences, dissoudre les échantillons d’essai et les
purifier par échange anionique, puis mettre à sec la solution de plutonium élué en présence d’acide
sulfurique pour obtenir la forme chimique sèche de sulfate de plutonium;
— mesurer un blanc de l’électrolyte à base d’acide nitrique et calculer la correction de courant de fond
[1]
à appliquer à l’électrolyse de l’échantillon d’essai due au courant de charge, faradique et résiduel ;
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— dissoudre l’échantillon d’essai sec dans l’électrolyte préalablement mesuré (le blanc);
— réduire l’échantillon d’essai à un potentiel contrôlé qui électrolyse le plutonium à plus de 99,8 %
3+
en Pu et mesurer le potentiel de la solution à l’équilibre à la fin de cette étape par ajustement du
[2]
potentiel de contrôle ;
— oxyder l’échantillon d’essai à un potentiel contrôlé qui électrolyse le plutonium à plus de 99,8 % en
4+
Pu et mesurer le potentiel de la solution à l’équilibre à la fin de cette électrolyse par ajustement du
potentiel de contrôle;
— corriger le résultat du courant de fond et de la fraction du plutonium qui n’est pas électrolysé;
— étalonner le coulomètre en utilisant des étalons électriques traçables et la loi d’Ohm;
— utiliser la valeur mesurée du facteur d’étalonnage du coulomètre et la constante de Faraday pour
convertir les coulombs du courant intégré de l’électrolyse en moles de plutonium;
— utiliser des étalons plutonium de contrôle qualité traçables pour démontrer de façon indépendante
la performance du système de mesure;
— mesurer périodiquement le potentiel formel du couple plutonium, E , qui est propre à l’utilisateur
0
selon la conception de la cellule, les connexions, le type d’électrode de référence, ainsi que du type
d’acide et de la molarité de l’électrolyte.
Ces étapes permettent de s’assurer que les échantillons d’essai préparés pour la mesure sont
représentatifs, reproductibles et stables. Les échantillons d’essai sont mesurés selon un protocole basé
sur les principes fondamentaux et compatible avec un étalonnage électrique traçable du coulomètre.
Des informations détaillées supplémentaires sont fournies dans les Articles 10 et 11.
5 Réactifs
Utiliser uniquement des réactifs de qualité analytique reconnue.
Toutes les solutions aqueuses doivent être préparées avec de l’eau déminéralisée, bidistillée ou distillée
ayant une résistivité supérieure à 10 MΩ·cm, c’est-à-dire de l’eau purifiée de qualité 1 selon l’ISO 3696.
5.1 Solution d’acide nitrique, c (HNO ) = 0,9 mol/L.
3
NOTE Se reporter au 11.4 pour d’autres options concernant les électrolytes.
5.2 Solution d’acide amidosulfurique, c (NH HSO ) = 1,5 mol/L.
2 3
5.3 Solution d’acide sulfurique, c (H SO ) = 3 mol/L.
2 4
NOTE La molarité n’est pas un paramètre critique pour l’acide sulfurique utilisé pour mettre à sec les
échantillons d’essai de plutonium, sous réserve que la concentration du réactif se situe bien au-dessus du niveau
auquel se forment des complexes de plutonium colloïdal.
5.4 Argon ou azote pur, (teneur en oxygène inférieure à 10 ppm).
5.5 Air pur, (exempt de contaminants organiques).
6 Appareillage
Équipement courant de laboratoire de radiochimie de moyenne activité, adapté au travail avec du
plutonium.
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6.1 Balance analytique, installée en milieu confiné et capable de peser une masse de 1 g avec une
incertitude de ± 0,1 mg (facteur d’élargissement, K = 1). Cela représente une incertitude relative de 0,01 %.
— Le fait de peser une masse inférieure à 1 g augmente l’incertitude relative à une valeur supérieure à
0,01 %, de manière inversement proportionnelle.
— Si l’incertitude de la balance installée ne répond pas au critère de ± 0,01 mg, des échantillons d’essai
plus grands sont requis en conséquence.
6.2 Burette à peser, en verre ou en matière plastique, le choix du matériau n’est pas critique à
condition qu’il assure une masse stable (tare) et que la charge électrostatique soit contrôlée comme
décrit en 7.1.1.
6.3 Équipement pour évaporation de l’échantillon d’essai dans la cellule coulométrique,
comprenant un chauffage radiant par-dessus ou une plaque chauffante avec réglage de température. Les
exigences de conception et les caractéristiques optionnelles pour l’évaporation et la mise à sec efficaces
comprennent les actions suivantes:
— fournir des réglages permettant à la fois une évaporation rapide et bien contrôlée, suivie d’une mise
à sec de la solution restante d’acide sulfurique à une température plus élevée;
— empêcher la perte mécanique de la solution de l’échantillon d’essai, par ébullition et/ou éclaboussures;
— empêcher la contamination par des produits chimiques extérieurs tels que ceux pouvant être
utilisés pour neutraliser les vapeurs acides;
— chauffer la paroi de la cellule coulométrique pour optimiser la mise à sec et pour réduire autant
que possible le reflux d’acide sulfurique en plaçant la cellule à l’intérieur d’un tube optionnel en
aluminium d’un diamètre intérieur supérieur de 1 mm à 3 mm au diamètre extérieur de la cellule et
d’une hauteur inférieure de 1 mm à 5 mm à celle de la cellule; la paroi du tube entourant la cellule
permet de chauffer la paroi de celle-ci lors de l’étape de mise à sec;
NOTE À la place des tubes d’aluminium, il est possible d’utiliser un bloc en aluminium muni de trous
percés selon une spécification similaire pour l’insertion de la cellule.
— ajouter une alimentation d’air facultative avec un tube d’alimentation dirigé vers la surface du
liquide afin d’obtenir une vitesse d’évaporation optimale et disperser les vapeurs acides;
— ajouter un piégeage optionnel des vapeurs et leur neutralisation localement pour contrôler les
vapeurs acides en fonction de la conception de l’installation et des exigences relatives au système de
ventilation.
Voir la Figure 1.
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Dimensions en centimètres
Figure 1 — Système d’évaporation d’échantillon
6.4 Coulomètre à potentiel imposé.
Voir la Figure 2.
6.4.1 Cellule de coulométrie, comprenant les éléments suivants:
−1
— un agitateur motorisé avec une fréquence de rotation supérieure à 1 000 min ;
NOTE 1 Des moteurs à vitesse ajustable permettent une optimisation des vitesses de rotation des cellules
individuelles. Il convient d’utiliser des agitateurs motorisés alimentés par des courants continus isolés
afin d’empêcher le bruit électrique de se superposer au blanc et aux signaux du courant d’électrolyse de
l’échantillon d’essai envoyés à l’intégrateur.
— une cellule coulométrique en verre cylindrique ou conique d’une capacité de 50 mL ou moins, munie
d’un joint torique et d’un couvercle adapté pour les équipements internes suivants:
— un tube d’injection de gaz inerte humidifié pour éliminer l’oxygène atmosphérique dissous de la
solution et de la cellule d’électrolyse, respectivement;
— un agitateur muni d’une pale et d’un axe réalisés en matériaux chimiquement inertes [par
exemple, polytétrafluoroéthylène (PTFE)] et conçu pour empêcher les éclaboussures; en
général, l’axe de l’agitateur est situé au centre de la cellule et est relié directement au moteur de
l’agitateur;
— une électrode de travail en or (par exemple, 99,99 %) et comprenant un fil d’or usiné ou soudé à
un cadre cylindrique en fil d’or, d’une hauteur nominale de 15 mm et d’un diamètre nominal de
20 mm, autour duquel est soudée ou usinée une très fine toile d’or généralement composée de
plusieurs couches (par exemple, 4 couches);
NOTE 2 Se reporter au 11.4 pour d’autres options concernant les électrodes de travail.
— un tube en verre fermé à l’extrémité inférieure par un disque en verre fritté (dimensions habituelles:
2,5 mm d’épaisseur et taille de pore < 0,01 μm); le tube est rempli d’acide nitrique (5.1) et l’extrémité
en verre fritté est placée dans l’anneau de l’électrode de travail;
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— une électrode de référence, électrode au calomel saturé (ECS) ou autres électrodes de référence,
comme décrit en 11.3, est placée à l’intérieur du tube en verre;
— un autre tube en verre, similaire au premier, est également rempli d’acide nitrique (5.1) et l’extrémité
en verre fritté est placée dans l’anneau de l’électrode de travail;
— une électrode auxiliaire comprenant un fil en platine, de 0,5 mm à 3,0 mm de diamètre, est placée à
l’intérieur du second tube en verre.
NOTE 3 Le fil en platine peut être spiralé afin d’augmenter la superficie immergée dans l’électrolyte,
comme illustré à la Figure 2;
— un barboteur à gaz, rempli d’eau comme décrit à l’Article 5, pour humidifier le gaz inerte avant de
l’introduire dans la cellule de coulométrie assemblée.
Les diamètres du tube en verre et du disque en verre fritté contenant l’électrode auxiliaire peuvent
être plus grands que les diamètres du tube en verre et du disque en verre fritté contenant l’électrode
de référence. Le débit de la solution à travers les deux disques en verre fritté doit être inférieur à
0,05 mL/h.
a) Il existe une option qui consiste à installer un thermomètre à thermocouple ou à résistance dans
la cellule de coulométrie assemblée pour mesurer la température de la solution de l’échantillon
d’essai lors du processus de mesurage. Il convient que la température de la solution soit mesurée
durant l’oxydation de l’échantillon d’essai ou immédiatement après l’analyse. Pour la mesure de la
température, l’incertitude visée est ± 0,2 °C (K = 1).
— S’il n’est pas possible d’insérer une sonde de température dans la cellule d’électrolyse ou s’il n’est
pas souhaitable de mesurer la température de la solution de l’échantillon d’essai immédiatement
après l’électrolyse, il faut alors estimer la température de la solution à partir de la température
de l’air ambiant ou de la température du réactif. Il convient de noter que le gaz de purge est
refroidi par dilatation, ce qui a pour effet de réduire la température de la solution par rapport
à la température ambiante; l’importance de cette baisse dépend du débit du gaz inerte et de
la conception de la cellule. La valeur mesurée de la température de l’air ou du réactif doit être
corrigée pour tenir compte de cet effet de refroidissement. On s’attend à avoir une incertitude
plus importante de ± 1 °C, K = 1 dans la température calculée de la solution.
b) Pour un contrôle optimal du potentiel, placer les disques en verre fritté des électrodes de référence
et auxiliaire de manière à respecter les exigences suivantes:
— la distance la plus courte entre le disque en verre fritté de l’électrode de référence et l’électrode
de travail est inférieure ou égale à 2 mm;
— la distance entre les deux disques en verre fritté contenant les électrodes de référence et
auxiliaire est inférieure à la distance entre le disque de l’électrode auxiliaire et le point le plus
proche sur l’électrode de travail.
c) L’orifice à travers lequel est inséré l’axe de l’agitateur sert d’évent primaire d’échappement du
gaz inerte. À l’exception de cet orifice, toutes les autres insertions sont effectuées par ajustement
serré. Le débit du gaz inerte doit être suffisamment élevé pour éliminer rapidement l’oxygène de
l’électrolyte et de la solution de l’échantillon d’essai. Par ailleurs, il doit empêcher l’air de pénétrer
dans la cellule lors de l’électrolyse. Il existe un moyen pratique pour ajuster le débit qui consiste
à diriger tout ou partie du gaz inerte vers la solution de l’échantillon, de telle façon qu’une ride de
2 mm à 4 mm soit produite sur la solution d’échantillon sans provoquer d’éclaboussure.
— Les cellules de conception optimisée, avec un débit de gaz inerte adéquat et un ajustement serré,
élimineront l’oxygène dans un délai inférieur ou égal à 5 min. Il convient que le temps nécessaire
pour éliminer l’oxygène de la solution soit déterminé par les utilisateurs sur la base d’essais de
l’ensemble cellule dans des conditions normales.
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Légende
1 vidéo 8 électrode auxiliaire (ou contre-électrode) en tube du pont
électrique rempli d’électrolyte
2 imprimante (facultative)
3 ordinateur de contrôle 9 électrode de référence en tube du pont électrique rempli
d’électrolyte
4 clavier 10 gaz inerte
5 potentiostat et intégrateur 11 agitateur
6 voltmètre numérique 12 électrode de travail
7 alimentation continue ou alternative 13 cellule
pour le moteur de l’agitateur
Figure 2 — Raccordements de la cellule de coulométrie
[3][4]
6.4.2 Instrumentation, comprenant les éléments suivants :
a) Potentiostat avec une étendue de potentiels adaptée pour les mesures du plutonium et avec les
possibilités suivantes:
— un amplificateur de puissance avec un courant de sortie possible de 250 mA ou plus;
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— un circuit de contrôle de potentiel à réponse rapide, avec un temps de montée de 1 ms à partir de
zéro volt au potentiel de contrôle requis, et avec une tension de dépassement n’excédant pas 1 mV;
— un amplificateur de contrôle avec une réjection de mode commun de 90 dB ou plus;
— un ajustement automatique de potentiel contrôlé, avec une résolution de 0,001 V, ou moins;
— un amplificateur suiveur de tension, pour isoler l’électrode de référence (électromètre), avec
11
une impédance d’entrée minimale de 10 Ω;
— une fonction de contrôle du courant d’électrolyse, y compris un courant de charge de zéro à
500 mA, avec une capacité de détection de 0,5 μA.
NOTE Ce mode opératoire suppose que le coulomètre a deux potentiomètres précis: un potentiomètre
pour sélectionner le potentiel d’oxydation et l’autre pour sélectionner le potentiel de réduction, bien que cela
ne soit pas impératif.
b) Intégrateur coulométrique, capable d’intégrer les courants d’électrolyse du blanc et de
l’échantillon d’essai, depuis au moins 150 mA jusqu’à 1 μA, et pouvant être lu à ± 10 μC (voir 7.1.4
pour les capacités de l’intégrateur et les exigences relatives à l’étalonnage);
— Il convient que la dérive du système de contrôle du potentiel ne dépasse pas 1 mV et que la dérive
du système d’intégration ne dépasse pas 0,005 % pendant les mesures courantes (entre les
étalonnages électriques), sur toute la gamme de température à laquelle les circuits de contrôle
de potentiel seront exposés. Si la température ambiante varie fortement, il convient de placer
les instruments dans une armoire munie de dispositifs de contrôle de température suffisants
pour maintenir la dérive électronique dans les limites spécifiées.
— Une horloge électronique, avec une incertitude de ± 0,002 % (K = 1) pour déterminer la durée
des étalonnages électriques et des électrolyses.
— Un système de génération de courant constant, stable à ± 0,002 % dans la gamme de température
à laquelle le circuit sera exposé. Ce système sera utilisé pour l’étalonnage électrique du circuit
d’intégration du coulomètre, comme décrit en 7.1.4.
— Il convient que le câble reliant le potentiostat à la cellule soit un câble torsadé et blindé à trois
conducteurs, de préférence avec un blindage relié à la masse du potentiostat. Il est recommandé
d’utiliser des connecteurs plaqués au niveau de la cellule car de tels connecteurs sont protégés
contre la corrosion.
— La valeur de crête maximale du courant de charge, observée au cours des premières 25 ms à
50 ms des oxydations du blanc et de l’échantillon d’essai, doit se situer dans les limites spécifiées
pour le circuit de l’intégrateur. La superficie de l’électrode de travail peut être diminuée pour
réduire la valeur de crê
...
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