**1. Introduction**

Since first AC current high‐power hydropower plant was put in operation, built by Nikola Tesla and George Westinghouse in 1895 on Niagara Falls, electrification of the world is dramatically changed. The growing power demand and energy consumption in the last decades require fun‐ damental changes in the process, power production and services. These requirements tend to use both conventional and nonconventional energy generation in order to have power plants useful both economically and environmental friendly to the society. Although new trends in this field focus on producing clean energy from renewable sources, the world's most used fuel in power plants is still coal with 41% of produced global electricity [1]. Coal, oil, nuclear and gas power plants are still dominant for supplying base load in all power grids. Also, energy consumed at power plants for generating electricity is still high. Based on OECD data [2], the amount of elec‐ tricity supplied to the final consumers was 33% of the total energy consumed at power plants.

In Europe, the largest share of budget spent on research, development and demonstration (RD&D) on energy technology was in energy efficiency and renewable sources [3]. On the other side, in Japan, 39% share of total energy RD&D in 2015 remains in the field of nuclear energy [3]. Regarding nuclear power plant (NPP), more attention is spent on improving safety, especially after accident in Fukushima NPP in March 2011.
