Measurement of 36 Cl in nuclear wastes and effluents: Validation of a radiochemical protocol with an in-house reference sample

TLDR: In this article, the original radiochemistry developed to extract 36Cl from solid samples and purify it before a liquid scintillation counting is explained, and the replication of the measurements on the constituted reference materials gives a repeatability around 8% at a confidence level of 95% that is very close to the calculated combined uncertainty value.

Abstract: 36Cl is a beta-emitter with a very low specific activity. It is produced during the irradiation of nuclear fuel, in the reactor core of power plants, from neutron capture by stable 35Cl that may be present at trace level in any part of the irradiated material. Due to its long half-life (T1/2 = 3.01 . 105 y), 36Cl may be significant in impact assessment studies of disposal sites of nuclear wastes. Considering these different elements, the National Radioactive Waste Management Agency (Andra-France) requests information on the 36Cl content of the waste packages destined to be stored at Andra sites. As for other halogens, the measurement of 36Cl is a difficult analytical task in view of its potential losses during the different chemical steps and also because of the lack of international certified reference material needed to validate the chemical and measurement procedures. This paper describes the methodology processed to constitute an in-house solid reference sample with a known content of stable and radioactive chlorine. The original radiochemistry developed to extract 36Cl from solid samples and purify it before a liquid scintillation counting is explained. The comparison of the results given by this radiochemical protocol and other methods allow its validation. The replication of the measurements on the constituted reference materials gives a repeatability around 8% at a confidence level of 95% that is very close to the calculated combined uncertainty value.