Decomposition products of oxygen scavengers and their effect on corrosion of steam generator materials – I. Diethyl-hydroxylamine and carbohydrazide

Hydrazine used as oxygen scavenger in the secondary circuit of pressurized water reactors is hazardous to the environment and potentially carcinogenic, thus, suitable replacement chemicals for it are actively sought. In the present paper, decomposition products of two potential replacements – carbohydrazide and diethyl-hydroxylamine – are analyzed, and their effect on secondary water chemistry and corrosion of the main steam generator materials – carbon steel 22 K, stainless steel 0X18H10T and Alloy 690 – is studied by in-situ electrochemical techniques complemented by ex-situ analyses of the formed oxides by spectroscopic and microscopic methods. Quantitative interpretation of the electrochemical impedance data with the Mixed-Conduction Model allowed for the estimation of oxidation and corrosion release rates depending on scavenger formulation, alloy type and temperature. Conclusions on the extent of interaction of decomposition products with construction materials are drawn based on the experimental and calculational results.<br/

Ionic and electronic conductivity of the surface film on titanium during pulse electrolysis of water

The processes of corrosion and degradation of electrode materials are crucial for the efficiency of pulse electrolysis and are expected to depend on the electrical characteristics of the pulse (current/voltage, frequency, duty cycle). The aim of the present paper is to investigate the effect of these characteristics on the electrochemical properties of Ti electrodes. Pulse electrolysis was carried out in 6 M KOH for 24 and 72 h with current amplitude of 65 mA, frequencies of the signal of 0.5-10 kHz and pulse duty cycle between 1 and 99%. The electrochemical properties of the titanium anode and cathode surfaces after operation were characterized by electrochemical impedance spectroscopy in a borate buffer solution (pH 7.4) at the open circuit potential, as well as by linear sweep voltammetry in a similar solution containing an equimolar mixture of K4Fe(CN)6 and K3Fe(CN)6 as a redox couple to probe the electronic conductivity of the surface films