BS ISO 21484:2017 pdf download.Nuclear Energy — Fuel technology — Determination of the O/M ratio in MOX pellets by the gravimetric method.
7 Apparatus
7.1 Furnace, one of the following furnaces can be used.
7.1.1? Muffle? furnace, controlled up to 950 °C, having a device for measuring the temperature and having sweeping possibility with various gases.
7.1.2 Other furnaces, other furnaces, with same performance can also be used such as Infrared gold image furnace (IR lamp heating).
7.2 Crucibles, use platinum or quartz crucibles.
7.3 Analytical balance, use an analytical balance with an accuracy of at least ±0,1 mg when muffle furnace is used or at least ±0,01 mg if samples are smaller.
8 Sampling
A representative sample shall be taken from the pellet batch for analysis. If necessary, crush pellets to make smaller samples according to the furnace type or the crucible size.
If necessary, care shall be taken to avoid sample oxidation during the sampling procedure and the sample preparation. Typical precautions include performing the sampling operation under argon atmosphere, placing the sample in an argon-filled bottle, etc. The laboratory performing the analyses shall establish the procedure.
9 Procedure
9.1 Preliminary test
The balance shall be checked at regular intervals using a standard mass.
9.2 Preparing the crucibles
The crucibles shall be clean and weighed before use. An example of a cleaning procedure that could be used is as follows.
a) Clean the crucibles by heating them in nitric acid (6.1) near the boiling point.
b) Rinse thoroughly with deionized water.
c) Dry the crucibles in the furnace for 30 min at 150 °C under inert atmosphere.
d) Allow the crucibles to cool to 35 °C in the furnace under inert atmosphere.
e) Remove each crucible from the furnace and weigh it to within ±0,1 mg or better.
f) Record the crucible mass, m 0 , in grams.
9.3 Weighing the sample
9.3.1 Place the sample, sampled as indicated in Clause 8, in an empty crucible.
9.3.2 Weigh the crucible containing the pellets to within ±0,1 mg or better.
9.3.3 Record the mass, m 1 , in grams of the crucible containing the pellets.
9.4 Heat treatment cycles
9.4.1 General
The sample shall be heat treated in such a way that the O/M ratio is changed to exactly 2,000. The duration of the oxidation-reduction cycles and the gas flow rates in the furnace shall be optimized according to the nature of the furnace used, the number of sample pellets measured, the pellet composition, etc.
Load the furnace with the crucible containing the sample pellets. Apply the desired heat treatment cycle.
9.4.2 Example 1
9.4.2.1 Under argon sweeping, raise the temperature to 900 °C ± 30 °C and hold for 5 min.
9.4.2.2 Under air sweeping, maintain the furnace temperature for 1 min to 7 min at 900 °C ± 30 °C.
9.4.2.3 Under argon sweeping, maintain the furnace temperature for 5 min at 900 °C ± 30°C.
9.4.2.4 Under argon +5 % to 7 % H 2 sweeping, maintain the furnace temperature for 8 h to 13 h at 900 °C ± 30 °C.
9.4.2.5 Under argon +5 % to 7 % H 2 sweeping, shut off the furnace heating and allow the temperature to drop to 35 °C.
9.4.3 Example 2
9.4.3.1 Heat the samples for 16 h at 800 °C, in an atmosphere comprising a volume fraction of 4 % H 2 in argon saturated with water at room temperature.
9.4.3.2 Cool under dry argon containing a volume fraction of 4 % H 2 .
9.5 Final weighing
9.5.1 Remove the crucible from the furnace.
9.5.2 Weigh the crucible to within 0,1 mg or better.
9.5.3 Record the mass, m 2 , in grams of the crucible after oxidation-reduction heat treatment.
10 Calculation
10.1 Mean atomic mass of oxide after heat treatment
Calculate the mean atomic mass of the oxide after treatment, when O/M = 2,000 exactly, by using Formula (1):
where
m a is the mean atomic mass of the oxide of heavy metals;
m(Pu) is the mean atomic mass of plutonium in the oxide;
m(U) is the mean atomic mass of uranium in the oxide;
m(Am) is the mean atomic mass of americium in the oxide;
x Pu is the mole fraction in percent of plutonium in the oxide;
x U is the mole fraction in percent of uranium in the oxide;
x Am is the mole fraction in percent of americium in the oxide;
m(O) is the atomic mass of oxygen (15,999 4);
x Pu + x U + x Am = 100 %.BS ISO 21484 pdf download.BS ISO 21484:2017 pdf free download
