Nuclear Energy Determination of Nitrogen Content in UO2, (U,Gd)O2and (U,Pu)O2sintered

ISOISOTC8585/SC55

Date:2008-02-09

ISO/CD 12799

ISOISOTC8585/SC55/WG11

Secretariat: BNFL forBSIBSI

Nuclear energy — Determination of nitrogen content in UO2, (U,Gd)O2and (U,Pu)O2sintered pellets — Inert gasextraction and conductivity detection method.

Energie nucléaire— Détermination de la teneur en azote dans les pastilles frittées d’UO2, (U,Gd)O2 et (U,Pu)O2 – Méthode par extraction sous gaz inerte et mesure par conductivité.

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ISO/CD12799©ISO

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ContentsPage

1Scope

2Principle

3Reactions

4Reagents and materials

4.1Helium

4.2Nitrogen

4.3Reference material

4.4Copper(II)oxide

4.5Oxidation reagent for CO

4.6Absorption media for CO2

4.7Absorption media for H2O

5Apparatus

5.1Nitrogen analyser

5.2Graphite crucibles

5.3Balance

5.4Gas supply

6Sampling

6.1Sampling procedure

6.2Sample preparation

7Procedure

7.1Calibration

7.2Determination

8Calculation

9Precision

10Test report

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, Part2.

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.

ISO/CD12799©ISO

Nuclear energy — Determination of nitrogen content in UO2, (U,Gd)O2 and (U,Pu)O2sintered pellets — Inert gas extraction and conductivity detection method.

1Scope

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 2200 °C (most notably Pu and U nitrides).

2Principle

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.

3Reactions

The samples must not be heated to temperaturesabove 2 200 °C since this would cause a reaction to take place between the UO2and the graphite, resulting in large quantities of CO2gas being released. This gas would lead to errors in conductivity measurement.

The carrier gas must be as free of impurities as possible.

4Reagents and materials

Use reagents of recognized analytical grade.The reagents and materials below serve as examplesto be used according tomanufacturer’s recommendation.

4.1Helium

Use helium as carrier gas with a purity of a volume fraction 99,995 %.

4.2Nitrogen

Use nitrogen as calibration gas with a purity of a volume fraction 99,998 %.

4.3 Reference material

with certified nitrogen content (e.g. metal standards).

4.4Copper(II)oxide

CuO purifies He/N2; converting H2 to H2O.

4.5Oxidation reagent for CO

Schutze reagent (iodine pentoxide over silica gel)eventually preceded byHopcalite (manganese oxide/ copper(II) oxide)oxidizes CO to CO2.

4.6Absorption media for CO2

Ascarite (sodium hydroxide over asbestos) or equivalent absorbs the CO2.

4.7Absorption media for H2O

Anhydrone (Mg(ClO4)2) traps any H2O formed. A molecular sieve can also be used.

5Apparatus

5.1Nitrogen analyser

Fitted with an appropriate furnace with controllable temperature and suitably adapted for handling plutonium bearing samples where relevant.

5.2Graphite crucibles

Suitable for the appropriate sample types.

5.3Balance

With an accuracy of 1 mg.

5.4Gas supply

6Sampling

6.1Sampling procedure

When sampling the fuel pellets, special care must be taken to ensure that the pellets are only handled using pincers.

6.2Sample 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 obtainby passing the crushed pellet through an appropriate sieve.

7Procedure

Prior to use, the analyser must be checked visually for the condition of key components such as furnace O-rings and reagent tubes. The analyser should be designed to enable leak testand system check to be performed.

7.1Calibration

7.1.1Blank 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.

7.1.2Calibrationof 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 injectedand analyzed. This calibration is performed three times.

In the caseof calibration with steel certified standards, they are weighed to the nearest 1mg accuracy.

7.1.3Calibration 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.

7.2Determination

Prior to loading of the sample in the graphite crucible, the later is first heated to around 2200 °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.

8Calculation

Calculate the nitrogen mass fraction (µg / g sample) from the following equation:

is the nitrogen mass fractionin µg /g sample;
is the nitrogen mass in µg;
is the mass of sample in g;

9Precision

The repeatability standard deviation at around10 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.

10Test 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.