Behaviour of two products containing film forming amines (FFA) in the secondary circuit physico-chemical conditions of the pressurized water reactor (PWR)

Summary

Using filming amines (FA) is believed to be an effective way to protect the main parts of the water/steam circuit against corrosion during the shutdown periods. FA is a versatile solution to form an oxygen tight film efficient during the numerous start/stop operations and hard to plan downtime periods. By injecting a FA before the shutdown, most of the internal surfaces would be covered with a hydrophobic protective layer. However, organic substances such as FA are susceptible to thermal decomposition at high temperatures. The present study assesses the thermal stability of two commercial formulations of FA in the physico-chemical conditions of the secondary circuit of PWR. Main decomposition products were identified as well.These formulations are a mixture of FA without other alkalizing amine compounds, reducing agents or dispersants. The first one contains mostly octadecylamine while the second one contains primarily oleyl propylenediamine. Each of them was tested at 280 DC for short and long residence times, i.e. 20 min and one week. The stability of the FA mixtures was evaluated using UV-visible spectroscopy. Different mass spectrometry analysis and Fourier transform infrared spectroscopy by attenuated total reflection (ATR-FTIR) were carried out to identify the organic products formed at high temperature. The choice of analysis methods will be critically argued and decomposition mechanism will be proposed. In light of the results, the impact of the various decomposition products on the physico-chemical parameters of the secondary circuit will be discussed.