Determination of135Cs in sodium from an in-pile loop by activation analysis

Several months after shut-down,¹³⁷Cs and¹³⁴Cs were the main activities in coolant residues from an in-pile sodium loop where a fuel pin had failed at 40000 MWd/t burn-up, FR2-reirradiation of coolant residues increased¹³⁴Cs and generated¹³⁶Cs, thus indicating the presence of stable¹³³Cs and of long-lived¹³⁵Cs in the samples. The amount of¹³⁵Cs calculated from¹³⁶Cs activities was of the same quantity as the number of¹³⁷Cs atoms.