Laboratory studies on the adsorption kinetics of 137Cs in sediment

During the operation of a nuclear reactor, extreme care is taken to minimize the release of radionuclides to the environment. Low level radioactive liquid waste generated is treated and released to the nearest water body after monitoring to ensure that the activity levels are well within the regulatory limits. Environmental Survey Laboratories (ESL) attached to power plants carry out a systematic environmental monitoring and impact assessment to ensure that the dose to the member of public is well within the limits. This paper presents the results of a systematic laboratory study carried out at ESL, Kakrapar Atomic Power Station (KAPS) on the adsorption kinetics of 137Cs in sediment. The study is to evaluate the sorption kinetics of 137Cs+ onto site specific sediment. Sets of adsorption experiments were conducted at specific time intervals for two different 137Cs+ concentrations, keeping other experimental conditions same. The kinetics of 137Cs+ adsorption on sediment is analyzed using pseudo first order, pseudo second order, and intra-particle diffusion kinetic models. The pseudo-second order kinetic model is better correlated with the kinetics data compared with the pseudo first-order model. This indicates 137Cs+ ions can be involved in chemical bonding during the adsorption process to the analysed sediment. This chemi-sorption processes show a good compliance with the pseudo-second order kinetic model. It is also evident that lower concentration exhibits greater adsorption rate (k2 value is 1.85 x 10-5 Bq g-1 min-1 for 1245 Bq sets and 1.05 x 10-5 Bq g-1 min-1 for 2456 Bq sets) from the pseudo second order model. Intra-particle diffusion rate constants (Kid) were also obtained by two different models for both the concentrations and found to be higher for higher concentration. (author)