Radiochemical Neutron Activation Analysis for Trace Chlorine in Steels and Alloys

Chlorine is usually present at low concentrations in reactor materials and thermal neutron activation of 35Cl produces 36Cl, which has a long half-life and is a radionuclide of significance in nuclear waste disposal. This paper describes a radiochemical method that has been developed to measure low concentrations of Cl in reactor stainless steels, so that the amount of 36Cl in radioactive wastes can be estimated. The method is based on the irradiation of a 1 g sample in a thermal neutron flux of 1016 n m-2 s-1, followed by dissolution in HNO3 with the addition of stable KCl carrier/tracer. The Cl is precipitated as AgCl, and the recovery is measured gravimetrically. The 38Cl, which has a half-life of 37 min, is measured with γ-ray spectrometry. The entire process, from irradiation to the end of counting, takes ∼1.5 h. The recovery is near-quantitative, and the detection limit for Cl in most stainless steels is below 1 mg/kg.