ASTM C698-10

Mixed oxide, a mixture of uranium and plutonium oxides, is used as a nuclear-reactor fuel in the form of pellets. The plutonium content may be up to 10 weight %, and the diluent uranium may be of any ²³⁵U enrichment. In order to be suitable for use as a nuclear fuel, the material must meet certain criteria for combined uranium and plutonium content, effective fissile content, and impurity content as described in Specification C833.

The material is assayed for uranium and plutonium to determine whether the plutonium content is as specified by the purchaser, and whether the material contains the minimum combined uranium and plutonium contents specified on a dry weight basis.

Determination of the isotopic content of the plutonium and uranium in the mixed oxide is made to establish whether the effective fissile content is in compliance with the purchaser's specifications.

Impurity content is determined to ensure that the maximum concentration limit of certain impurity elements is not exceeded. Determination of impurities is also required for calculation of the equivalent boron content (EBC).

1.1 These test methods cover procedures for the chemical, mass spectrometric, and spectrochemical analysis of nuclear-grade mixed oxides, (U, Pu)O₂, powders and pellets to determine compliance with specifications.

1.2 The analytical procedures appear in the following order:

1.3 The values stated in SI units are to be regarded as standard. The values given in parentheses are for information only.

1.4 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use. (For specific safeguard and safety precaution statements, see Sections 11, 20, 64, and 112 and 102.6.1.)

7.1 This test method covers the determination of 5 to 100 μg/g of nitride nitrogen in mixtures of plutonium and uranium oxides in either pellet or powder form.

15.1 This test method covers the determination of 10 to 200 μg of residual carbon in nuclear grade mixed oxides, (U,Pu)O₂.

27.1 This test method is applicable to the determination of 5 to 100μ g/g of chlorine and 1 to 100 μg/g of fluorine in 1-g samples of nuclear-grade mixed oxides, (U, Pu)O₂.

35.1 This test method covers the determination of sulfur in the concentration range from 10 to 600 μg/g for samples of nuclear-grade uranium and plutonium mixed oxides, (U, Pu)O₂.

44.1 This test method covers the determination of moisture in nuclear-grade mixed oxides of uranium and plutonium (U,Pu)O₂. Detection limits are as low as 10 μg.

52.1 This test method covers the determination of rare earths in uranium-plutonium dioxide over the range from 10 to 200 μg/g.

60.1 This test method covers the analysis of uranium-plutonium dioxide [(U, Pu)O₂] for the 25 elements in the ranges indicated in Table 1, using gallium oxides or sodium fluoride as the carrier. (See also Table 2.)

70.1 This test method covers the spark source spectrographic analysis of uranium and plutonium dioxide for impurity elements. Because of its extreme sensitivity, it may be the most practical test method for the determination of certain impurities whose concentration is below the detectable limits of other spectrographic methods.

77.1 This test method covers the measurement of volatiles other than water in reactor-grade mixed dioxide pellets. The lower limit of the test method using the described equipment and a sample of approximately 1 g is 0.01 cm³ per gram of sample at STP conditions (23).

85.1 This test method covers the determination of 5 to 150 μg of tungsten in 1-g samples of nuclear-grade uranium and plutonium mixed oxides (U, Pu)O₂ (24).

94.1 This test method covers the determination of dysprosium, europium, gadolinium, and samarium in mixed oxides of uranium and plutonium over the concentration range from 0.1 to 10 μg/g of mixed oxide.

98.1 This test method covers the determination of the isotopic composition of uranium and plutonium in nuclear-grade mixed oxides ((U, Pu)O₂).

107.1 This test method covers the determination of the oxygen-to-metal atom ratio (O/M) in sintered mixed oxide pellets and powders.