Analysis of Non-Metals in Sodium: Experience at The Reactor Research Centre, Kalpakkam

Abstract

Measurement and control of non-metallic impurities like oxygen, hydrogen and carbon in sodium is of considerable importance in the successful long-term operation of the high temperature sodium systems of the fast reactors. In order to minimise corrosion of the structural materials, oxygen is to be maintained below 10 ppm level. Hydrogen estimation is important especially for the secondary sodium system of the reactor in order to monitor water to sodium leak in the steam generator. Control of carbon level is necessary to control carburisation/decarburisation of the structural materials. Considerable development has taken place during the last three decades in order to evolve suitable procedures for the estimation of these impurities in sodium. As a result, the laboratory methods developed in various laboratories have undergone various modifications to extend the sensitivities down to 1 ppm level. Foil equilibration methods such as vanadium wire equilibration, steel foil equilibration, and scandium foil equilibration have been developed in various laboratories to estimate oxygen, carbon and hydrogen respectively to ppb level. More recent development has been the electrochemical and diffusion type meters for on-line monitoring of these impurities in sodium. The analytical development work was started in our laboratory few years back. Several methods have been tried in keeping with the developments in this field. The evolution of the present methods have gone through several stages of modifications in order to evolve accurate, simple and fast procedures for the estimation of these impurities in sodium. This paper describes our experience in this field leading to the presently standardised procedures which are used routinely in our laboratory for the analysis of commercial sodium as well as reactor grade sodium.