ISO 12795:2004 specifies a method of determining the mass fraction of uranium and the oxygen-to-uranium atomic ratio in hyperstoichiometric uranium dioxide (UO_2+X) powders and pellets.

ISO 12795:2004 is used for the determination of the U mass fraction and the O/U-ratio of nuclear grade uranium dioxide.

An impurity correction in the U mass fraction and the O/U-ratio determination should be performed, if the amount of total impurities in oxide form exceeds 1 500 micrograms per gram of sample. Lower impurity levels influence the O/U-ratio by less than 0,000 5 and can be neglected. The non-volatile impurities shall be determined by an appropriate technique, and the correction applied. If the total content of the non-volatile impurities in oxide form is greater than 1 500 micrograms per gram of sample, the overall precision of the method depends on the accuracy of these impurity measurements.