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        There are four hundred and forty eight operating commercial nuclear power reactors in the world today. Fifty more reactors are under construction. Most of these reactors are water-cooled and water-moderated. The fuel elements in these reactors are mostly zirconium alloys. These alloys are stable and effective up to a temperature of six hundred and sixty-two degrees Fahrenheit. If the heat-removal systems in the reactors are shut down, the temperatures of the fuel containers can reach as high as one thousand six hundred and fifty two degrees Fahrenheit. At these high temperatures, a chemical reaction between zirconium and water vapor can generate explosive hydrogen gas.
      The generation of hydrogen gas from the interaction of zirconium in fuel tubes with water vapor at very high temperatures in nuclear power reactors has led to destructive explosions at nuclear power plants in the past.
       Boris Kalin is the head of the Moscow Engineering Physics Institute’s (MEPI) Faculty of Physical Problems in Material Science. He leads a team of researchers at the National Research Nuclear University (NRNU) at the MEPI. He recently said “To prevent zirconium-vapor interaction, the researchers propose coating the surface of heat elements with materials (including chromium) that will prevent contact between zirconium and water vapors. We have achieved the science and technological goal of selecting the required compound and coating sections of fuel-element tubes up to 500 mm long with a protective chromium-content substance. This slows the zirconium-oxidization process in water vapors at up to twenty two hundred degrees Fahrenheit.”
      The NRNU team says that their ion-beam method requires that the surface of the tubes containing the fuel pellets be polished with argon ions. This insures a very smooth surface. Then alloys acting as electrodes are sprayed onto the surface of the tubes inside the vacuum chamber. This continues until a layer of alloy up to ten micrometers thick is deposited on the surface of the tubes.
       After treating the fuel tubes with their process, the NRNU technicians examined the composition, structure and thickness of the alloy coatings with electron and ion microscopes. The wear resistance of the coatings were tested by rubbing them against zirconium components. They also tested the water-oxidation at six hundred and sixty-two degrees Fahrenheit for seventy two hours and then repeated the test at twenty two hundred degrees Fahrenheit.
       Kalin said, “We repeated the experiment several times, adjusted the composition of magnetron electrodes and treatment modes, and analyzed each result. This allowed us to choose the optimal composition of coatings and prevent the oxidization of the external surface of zirconium tubes at plus 1,200 degrees Celsius for 400 seconds.”
       The results of the work at NRNU are going to be presented at the Sixteenth International school conference: New Materials: Tolerant Nuclear Fuels which was held at the NRNU. The event was initiated by the research school and the Laboratory for the Ion-Beam Treatment of Materials at the Faculty of Physical Problems of Materials Science.
       Improving the safety of the fuel assemblies under extreme conditions is a high priority research subject in the nuclear industry.