A survey of Canadian CANDU-PHWR (CANadian Deuterium Uranium - Pressurized Heavy Water Reactor) revealed that the natural organic matter found in the raw water used for cooling condensers is mainly in the acidic portion of fulvic acid, whereas in makeup water the neutral portion predominates. So far, few thermolysis experiments have been performed at 260°C and 300°C on the organic matter concentrated from the makeup water of one of these plants. High-performance ion chromatography analysis of the liquid phase revealed the formation of a high level of acetate and propionate, with smaller amounts of formate and glycolate. Chloride was also produced with an estimated contribution in the steam generator of 2-6 ppb at 260°C and up to 9 ppb at 300°C. Gaschromatography mass-spectrometry analysis indicated the presence of numerous volatile aromatic organics, different phenolic compounds, cyclic and aliphatic ketones, along with other unidentified compounds. Analysis of the gas phase showed the production of a high level of carbon dioxide and hydrogen, along with lower amounts of methane, propane, ethylene, ethane and carbon monoxide.