ASTM E692-08

1.1 This test method covers the determination of the number of atoms of ¹³⁷Cs in aqueous solutions of irradiated uranium and plutonium nuclear fuel. When combined with a method for determining the initial number of fissile atoms in the fuel, the results of this analysis allows atom percent fission (burn-up) to be calculated (1). The determination of atom percent fission, uranium and plutonium concentrations, and isotopic abundances are covered in Test Methods E 267 and E 321.

1.2 ¹³⁷Cs is not suitable as a fission monitor for samples that may have lost cesium during reactor operation. For example, a large temperature gradient enhances ¹³⁷Cs migration from the fuel region to cooler regions such as the radial fuel-clad gap, or, to a lesser extent, towards the axial fuel end.

1.3 A nonuniform ¹³⁷Cs distribution should alert the analyst to the potential loss of the fission product nuclide. The ¹³⁷Cs distribution may be ascertained by an axial gamma-ray scan of the fuel element to be assayed. In a mixed-oxide fuel, comparison of the ¹³⁷Cs distribution with the distribution of nonmigrating fission-product nuclides such as ⁹⁵Zr or ¹⁴⁴Ce would indicate the relative degree of ¹³⁷Cs migration.

1.4 The values stated in SI units are to be regarded as standard. No other unites of measurement are included in this standard.

1.5 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.