Ural federal university: Microscopic Water Droplets Can Help Cool Nuclear Reactors

Scientists at Ural Federal University have created a technology that increases the efficiency of nuclear reactor cooling systems. It makes power generation more productive and safer and is suitable for nuclear power plants in hot and arid countries of the Middle East and North Africa. The authors of the invention are Akram Hamzah Abed (Iraq), postgraduate student at the Department of Nuclear Power Plants and Renewable Energy Sources of UrFU, Sergey Shcheklein, head of the Department, and Valeriy Pakhaluev, professor at the Department.

The essence of the development is in the flow of cooling air, which goes to the heat exchanger (removes heat from the reactor), by means of fine ultrasonic atomizing water aerosol (droplet size 2-10 microns). Ultrasonic aerosol generator, which was used by scientists of UrFU, differs from analogues by economical power consumption and quiet mode of operation.

When in contact with the heat exchanger, the aerosol absorbs heat from the heated surface, evaporates and, together with the air, escapes into the atmosphere. Another part of the vapor destroys the thermal boundary layer of the air flow in the vicinity of the heat exchanger tubes and reduces the heat transfer resistance. Evaporation of one kilogram of water leads to absorption and removal of 2.5 thousand kJ of heat energy. Such a result is not possible with traditional technologies.

“Standard systems such as cooling towers and SPOT heat exchangers are designed for heat removal at NPPs under normal conditions. They are used both in normal mode, when operating at nominal power, and during a planned reactor shutdown, as well as in emergency situations. However, in the climate of African and Middle Eastern countries, such systems are not very productive. We offer a system that ensures high performance and reliability of nuclear power plants in any temperature environment,” explains Sergey Shcheklein.

Scientists tested the technology on an experimental unit. They fed air with different concentrations of air-water “fog” of aerosol, at different speeds and temperatures. They found that as the mass and velocity of the air-water flow increased, the surface temperature of the heat exchanger decreased and, therefore, the intensity of heat transfer increased.

“In the experiment and with the help of the formula we compiled, we calculated the parameters of humidity and velocity of air-water flow, which provide the greatest efficiency of heat transfer. For normative heat dissipation the amount of moisture equal to 0,05-0,1% of the total volume of cooling medium and relatively low speed – 15-20 m/sec is enough. That is, the water consumption and, therefore, the necessary water reserves at the NPP are insignificant,” describes Sergey Shcheklein.

The heat dissipation systems can become more compact and lighter. When the maximum amount of liquid is supplied, the surface temperature of the heat exchanger drops by half, and the heat output and, accordingly, the intensity of heat removal increases threefold.

“Before us, no one has received such a result, humidification of air flows led to an increase in performance only by 30-40%. The secret is in the size of the droplets: large droplets, the size of 1 mm or more, do not evaporate completely, and droplets the size of a few microns evaporate instantly,” explains Akram Hamzah Abed.

Scientists have also developed an option for emergency situations. If there is no electricity the air will circulate in the system thanks to the difference in temperature and the special design of the traction section.

According to Project Manager Sergey Shcheklein, Egypt, Turkey, Syria, Iraq, Iran and other countries in the region express their readiness to develop nuclear power in cooperation with specialists from the Russian state corporation Rosatom.

“Given the uniqueness and high efficiency of the created technology, the scientific team headed by Sergey Shcheklein received a patent for the invention of the NPP reactor emergency cooldown system. Nuclear industry specialists are showing increased interest in the work. We expect that the technology will be widely used both in Russia and in the partner countries of Rosatom Corporation,” comments Alexander Cherepanov, Deputy Director of the UrFU Center for Work with Enterprises.