Sensors to Control Dissolved Oxygen Concentration in Heavy Liquid Metal Coolants

Oxygen impurities control is of a paramount importance for providing structural steel corrosion resistance; and the current lead-based heavy liquid metal coolant (HLMC) technology rests to a large extent on it. In the early period of HLMC development, in particular, Pb-Bi, a method of coolant sampling was used with the aim to control oxygen impurities in it, with the follow-up remote analysis of these samples. Later on, more effective and prompt methods of control were developed and used; they were based on electro-chemical sensors with solid oxygen-conducting electrolyte. Based on the vast JSC ^SSC RF - IPPE experience in developing various control devices for the nuclear power industry, an active development is currently under way of solid electrolyte sensors to control oxygen in lead and lead-bismuth coolants. One of the sensors developed was conventionally called a ^capsule-type sensor due to a typical shape of its ceramic sensitive element (CSE). The CSE is the main component of the sensors designed to control thermo-dynamic activity (TDA) or contents of oxygen and hydrogen in melts that are based on lead and cover (inert) gas. As a result of studies performed by the SSC RF - IPPE specialists, it was determined that CSEs based on solid electrolytes made of oxide ceramics were capable of being in operation for a long time under the conditions of high temperatures and thermal shock in metal melts (in gas), they demonstrate stability of their conducting and mechanical properties, high thermal resistance and low gas permeability. The conducted R&D work resulted in development of the optimal chemical and phase composition to give the CSE the above-mentioned properties. Justifying calculations and experiments were performed to substantiate the geometrical shape of the sensor ceramic sensitive element in terms of its best strength, thermal resistance and hydrodynamics in the melt flow.