To keep optimal conditions in the primary cooling circuit of nuclear power plants, various chemical species are dosed in. Among the species the concentration of which is monitored in primary coolant, belong Oxygen and Hydrogen. While a plenty of companies offer oxygen sensors suitable for the measurement in primary coolant, the hydrogen sensor, really selective to H2 concentration, is offered by only one company. It is worth, therefore, accomplishing the development of hydrogen sensor, which was started at UCT Prague and, after several successfull measurements in nuclear powerplant, interrupted due to fateful events in the research team. We introduce here the results of the first part of contemporary work of the Mass transfer laboratory based on new technologies but using the experiences from 1990's.