© ISO 2005 – All rights reserved
ISO TC 85/SC 5
Date: 2008-02-09
ISO/CD 12799
ISO TC 85/SC 5/WG 1
Secretariat: BNFL for BSI
Nuclear energy — Determination of nitrogen content in UO2 ,
(U,Gd)O2 and (U,Pu)O2 sintered pellets — Inert gas extraction
and conductivity detection method.
Energie nucléaire — Détermination de la teneur en azote dans les pastilles frittées d’UO 2, (U,Gd)O2 et
(U,Pu)O2 – Méthode par extraction sous gaz inerte et mesure par conductivité.
Warning
This document is not an ISO International Standard. It is distributed for review and comment. It is subject to
change without notice and may not be referred to as an International Standard.
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.
Document type: International Standard
Document subtype:
Document stage: (30) Committee
Document language: E
D:\81920583.doc STD Version 2.1c
ISO/CD 12799
© ISO
Copyright notice
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© ISO 2005 – All rights reserved
ISO/ CD12799
Contents
© ISO
Page
1
Scope ...................................................................................................................................................... 1
2
Principle.................................................................................................................................................. 1
3
Reactions................................................................................................................................................ 1
4
4.1
4.2
4.3
4.4
4.5
4.6
4.7
Reagents and materials ........................................................................................................................ 1
Helium ..................................................................................................................................................... 1
Nitrogen .................................................................................................................................................. 1
Reference material ................................................................................................................................ 2
Copper(II)oxide ...................................................................................................................................... 2
Oxidation reagent for CO ...................................................................................................................... 2
Absorption media for CO2 .................................................................................................................... 2
Absorption media for H2O .................................................................................................................... 2
5
5.1
5.2
5.3
5.4
Apparatus ............................................................................................................................................... 2
Nitrogen analyser .................................................................................................................................. 2
Graphite crucibles ................................................................................................................................. 2
Balance ................................................................................................................................................... 2
Gas supply ............................................................................................................................................. 2
6
6.1
6.2
Sampling................................................................................................................................................. 2
Sampling procedure .............................................................................................................................. 2
Sample preparation ............................................................................................................................... 2
7
7.1
7.2
Procedure ............................................................................................................................................... 3
Calibration .............................................................................................................................................. 3
Determination ........................................................................................................................................ 3
8
Calculation ............................................................................................................................................. 4
9
Precision................................................................................................................................................. 4
10
Test report .............................................................................................................................................. 4
© ISO 2005 – All rights reserved
iii
ISO/CD 12799
© ISO
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.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.
Attention is drawn to the possibility that some of the elements of ISO 12799 may be the subject of patent
rights. ISO shall not be held responsible for identifying any or all such patent rights.
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.
International Standard ISO 12799 was prepared by Technical Committee ISO/TC 85, Nuclear Energy,
Subcommittee SC 5, Fuel Technology.
iv
© ISO 2005 – All rights reserved
© ISO
ISO/ CD12799
Nuclear energy — Determination of nitrogen content in UO2 ,
(U,Gd)O2 and (U,Pu)O2 sintered pellets — Inert gas extraction
and conductivity detection method.
1
Scope
This standard describes a procedure for measuring the nitrogen content of UO2, (U,Gd)O2 and (U,Pu)O2
pellets. Nitrogen may be present in the nuclear fuel either in an elemental form or within a chemical compound.
The technique described herein serves to determine the total content of nitrogen excluding those compounds
whose decomposition temperature is above 2 200 °C (most notably Pu and U nitrides).
2
Principle
For determining the nitrogen content, an analyser is employed which operates according to the carrier gas
principle, using helium as the carrier gas.
The weighed samples to be analysed are heated in a degassed 100 % pure graphite crucible at a temperature
of more than 1770°C in a helium atmosphere. This high temperature destroys the majority of the nitrogen
bearing compounds and causes nitrogen to be released along with other gaseous components. The released
gases are then swept by the carrier gas through oxidation and absorption columns to effect removal of
interfering species. The nitrogen passes through without being retained, and its quantity is subsequently
measured in a thermal conductivity cell.
3
Reactions
The samples must not be heated to temperatures above 2 200 °C since this would cause a reaction to take
place between the UO2 and the graphite, resulting in large quantities of CO2 gas being released. This gas
would lead to errors in conductivity measurement.
The carrier gas must be as free of impurities as possible.
4
Reagents and materials
Use reagents of recognized analytical grade. The reagents and materials below serve as examples to be used
according to manufacturer’s recommendation.
4.1 Helium
Use helium as carrier gas with a purity of a volume fraction > 99,995 %.
4.2 Nitrogen
Use nitrogen as calibration gas with a purity of a volume fraction > 99,998 %.
© ISO 2005 – All rights reserved
1
ISO/CD 12799
4.3
© ISO
Reference material
with certified nitrogen content (e.g. metal standards).
4.4 Copper(II)oxide
CuO purifies He/N2; converting H2 to H2O.
4.5 Oxidation reagent for CO
Schutze reagent (iodine pentoxide over silica gel) eventually preceded by Hopcalite (manganese oxide/
copper(II) oxide) oxidizes CO to CO2.
4.6 Absorption media for CO2
Ascarite (sodium hydroxide over asbestos) or equivalent absorbs the CO2.
4.7 Absorption media for H2O
Anhydrone (Mg(ClO4)2) traps any H2O formed. A molecular sieve can also be used.
5
Apparatus
5.1 Nitrogen analyser
Fitted with an appropriate furnace with controllable temperature and suitably adapted for handling plutonium
bearing samples where relevant.
5.2 Graphite crucibles
Suitable for the appropriate sample types.
5.3 Balance
With an accuracy of < 1 mg.
5.4 Gas supply
6
Sampling
6.1 Sampling procedure
When sampling the fuel pellets, special care must be taken to ensure that the pellets are only handled using
pincers.
6.2 Sample preparation
The fuel pellets are crushed in a percussion mortar. The fragments used for the analysis should be larger than
1 mm it could be obtain by passing the crushed pellet through an appropriate sieve.
2
© ISO 2005 – All rights reserved
ISO/ CD12799
7
© ISO
Procedure
Prior to use, the analyser must be checked visually for the condition of key components such as furnace Orings and reagent tubes. The analyser should be designed to enable leak test and system check to be
performed.
7.1 Calibration
7.1.1
Blank test
To verify the functional capability of the analyser, blanket values are determined to obtain information on the
condition of the upstream gas purification columns and on the leak tightness of the analyser. If the range of
scatter of the blanket values is greater than the analyser detection limit, appropriate corrective actions must be
taken.
7.1.2
Calibration of the analyzer
Nitrogen analyser shall be calibrated before sample measurement. There are two possibilities of calibration:
. Calibration with gas
. Calibration with certified standards
In case of calibration with gas, depending of the type of analyser, it can be performed by the analyser
manufacturer or/and the final user. A well defined volume of the calibration gas (4.2), which is corrected on
standard conditions, is injected and analyzed. This calibration is performed three times.
In the case of calibration with steel certified standards, they are weighed to the nearest 1mg accuracy.
7.1.3
Calibration check using metal standard
To check the calibration of the equipment, steel standard (4.3) having certified nitrogen content is weighed to
the nearest 1 mg and analysed. The quantity of he released nitrogen is measured. The result may differ from
the certified values by not more than the total uncertainty of the analysis process.
If not the calibration is repeated.
7.2 Determination
Prior to loading of the sample in the graphite crucible, the later is first heated to around 2 200 °C for degassing.
Weigh the sample to the nearest 1 mg.
Insert sample into the analyzer.
Purge with carrier gas.
The sample is filled into the crucible and heated up to > 1 770 °C.
The nitrogen content is measured.
© ISO 2005 – All rights reserved
3
ISO/CD 12799
8
Calculation
Calculate the nitrogen mass fraction
9
© ISO
wN2 (µg / g sample) from the following equation:
wN2 
mN2
m
w N2
is the nitrogen mass fraction in µg /g sample;
mN2
m
is the nitrogen mass in µg;
is the mass of sample in g;
Precision
The repeatability standard deviation at around 10 µg /g level and a sample mass of 1 or 2 g can reach:
sr = 20 % relative.
The relative standard deviation based on the analysis of steel standards can reach 15 % at the 10 µg /g level
and 66 % at the 2 µg /g level.
10 Test report
The test report shall include the following information:
a) identification of sample;
b) the method used by reference to this International Standard;
c) the results and the form in which they are expressed;
d) any deviations from the procedure;
e) any unusual features observed;
f) location and date of the test.
4
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