The aim of the study is the activity concentration measurements of organic and inorganic 14C in the discharges of JSC “Institute of Nuclear Materials” (INM). In INM the research water-water reactor “IVV-2M” is operating. Collecting of 14C species was performed using a 14C sampler with a chromium oxide and platinum catalysts at different temperatures: 400, 550 and 700 °C. The measurements of 14C activity were performed using a liquid scintillation counter. The share of organic 14C in emissions ranged from 0.30 to 0.84 and depends on the temperature of the catalyst, core structure and reactor operating mode. © 2023 Korean Nuclear Society.