EN ISO 12183:2019

SLOVENSKI STANDARD
01-september-2019
Tehnologija jedrskih goriv - Kulometrična analiza plutonija z nadzorovanim
potencialom (ISO 12183:2016)
Nuclear fuel technology - Controlled-potential coulometric assay of plutonium (ISO
12183:2016)
Kernbrennstofftechnologie - Coulometrische Bestimmung von Plutonium mit
kontrolliertem Potential (ISO 12183:2016)
Technologie du combustible nucléaire - Dosage du plutonium par coulométrie à potentiel
imposé (ISO 12183:2016)
Ta slovenski standard je istoveten z: EN ISO 12183:2019
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 12183
EUROPEAN STANDARD
NORME EUROPÉENNE
June 2019
EUROPÄISCHE NORM
ICS 27.120.30
English Version
Nuclear fuel technology - Controlled-potential coulometric
assay of plutonium (ISO 12183:2016)
Technologie du combustible nucléaire - Dosage du Kernbrennstofftechnologie - Coulometrische
plutonium par coulométrie à potentiel imposé (ISO Bestimmung von Plutonium mit kontrolliertem
12183:2016) Potential (ISO 12183:2016)
This European Standard was approved by CEN on 8 March 2019.

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, Former Yugoslav Republic of Macedonia, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania,
Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland,
Turkey 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
© 2019 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 12183:2019 E
worldwide for CEN national Members.

Contents Page
European foreword . 3

European foreword
The text of ISO 12183:2016 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 12183:2019 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 December 2019, and conflicting national standards
shall be withdrawn at the latest by December 2019.
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.
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, Former Yugoslav Republic of Macedonia,
France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta,
Netherlands, Norway, Poland, Portugal, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland,
Turkey and the United Kingdom.
Endorsement notice
The text of ISO 12183:2016 has been approved by CEN as EN ISO 12183:2019 without any modification.

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
ISO 12183:2016(E)
© 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

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
Bibliography .28
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

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);
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.
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).
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 %.
2 © ISO 2016 – All rights reserved

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.
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;
4 © ISO 2016 – All rights reserved

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.
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;
6 © ISO 2016 – All rights reserved

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
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.
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.
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 ;
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 Formula (2) is also appropriate.

8 © ISO 2016 – All rights reserved

ISO 12183:2016(E)
−1 -2/3 −1
M = M (1 − D /D ) (1 − D /D ) (1 − Δm’ x M × Pu ) (2)
Real a a b a s a heat
where
M is the apparent mass, g;
a
5/3 −1
Δm’ is the mass coefficient for the heat buoyancy term, with a value of 0,000 03 g mW
5/3 −1
±0,000 01 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
heat
241 −1 −1
abundance and Am content. This value is nominally 2 mW g to 3 mW g for plutonium
−1 −1
with a burn up ranging from 2 MWDKg to 8 MWDKg (or GW-days per metric ton). The
specific heat increases with higher reactor burn up and increased Pu content.
7.1.2 Preparation of the test sample
a) Add 1 mL of sulphuric acid solution (5.3) 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.
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
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 10 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
7.1.2. Anion-exchange is an effective purification process; it is outlined in Annex A.
7.1.3 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;
ISO 12183:2016(E)
— 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 (6.4.1).
b) Take a clean dry coulometric cell and add sufficient nitric acid solution (5.1) 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 (5.2).
d) Firmly fit the cell under the lid.
e) Start the stirrer at the desired speed. This speed should be selected to maximize the stirring
rate, while 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 oxidize at E +0,32 V until a residual current of
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.
j) Oxidize at E +0,32 V.
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 (see 7.1.3) until the desired performance is observed, or
— measure the supporting electrode blank determination (see 7.1.6) in preparation for the
subsequent measurement of plutonium test samples.
7.1.4 Electrical calibration of the current integration system
The electrical calibration factor of the coulometer is measured by using a high accuracy, highly stable
constant current in place of the electrolysis cell. Detailed instructions for the calibration of a current
integration system are highly dependent upon the design of the specific integration circuit. However,
10 © ISO 2016 – All rights reserved

ISO 12183:2016(E)
the following general principles and specifications apply toward determining the calibration factor
within an uncertainty envelope not exceeding ±0,01 % (K = 1).
— Generate a constant current (stable and known to within ±0,002 %, K = 1) in a manner that is
electronically equivalent to the process by which the electrolysis current from the test sample and
the blank are integrated.
NOTE Typically, the potentiostat is converted into a constant current source with the current flowing
through a standard resistor, instead of the cell assembly. The voltage drop across the standard resistor
is measured to determine accurately the actual calibration current. Alternatively, if a constant current
source is used instead of the potentiostat, then this external source requires periodic calibration to ensure
consistency and traceability.
— Determine the duration of calibration (i.e. current flow) within ~0,002 %, K = 1.
The linearity of the integrator response shall be demonstrated for the range of currents observed during
plutonium measurement (~50 μA to 100 mA). Ensure that the impact of the integrator nonlinearity on
the plutonium measurement is 0,005 %, K = 1, or less.
A typical sequence for performing an electrical calibration is:
a) configure the instrumentation for electrical calibration and set to the desired constant current, for
example 10,000 mA;
b) set the integration time to an appropriate duration, for example 300 s;
c) reset the integrator;
d) allow time for the electronics to stabilize;
e) initiate the calibration and record the constant current used, I , mA;
c,
f) at the completion of the calibration, record the output signal from the integrator, Q (in the units
C
appropriate for the specific measurement system) and the actual calibration time, t , in seconds;
C
Electrical calibration should be performed at least daily and in the same laboratory where the plutonium
measurements are performed. An automated coulometer should perform the electrical calibration
without the user needing to reconfigure the instrumentation. Refer to 8.1.
7.1.5 Formal potential determination
4+ 3+
The formal potential, E , of the Pu /Pu couple should be measured at regular intervals (as described
in Annex B), especially when electrodes have been replaced or if the electrodes have been out of use
for a considerable time. Before performing this measurement, ensure that the working and auxiliary
electrodes have been properly pre-treated and conditioned. Also ensure that the SCE is filled with
saturated potassium chloride solut
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