Russian scientists study molybdenum fuel element casing

18 January 2018

Researchers at Russia’s National Research Nuclear University (MEPhI) have conducted a study on the use of isotopically modified molybdenum as an alternative to zirconium alloys currently used for fuel-element casings containing uranium oxide pellets. The study was published in the peer-reviewed scientific journal Chemical Engineering Research & Design.  

Zirconium has advantages in that it is highly resistant to erosion and corrosion in water and has a low thermal neutron capture cross-section (which characterises the probability of chemical interaction between neutron particles and the atom nucleus). However, adverse factors include the generation of heat in water and the production of hydrogen, which accelerates the degradation of the fuel-element casings. Hydrogen production occurs during zirconium-steam reactions at temperatures reach more than 700 degrees Celsius, which poses a risk in emergency situations at water-cooled nuclear plants. A zirconium-steam reaction is believed to have caused hydrogen explosions which occurred during the Fukushima Daiichi nuclear disaster in 2011.

A refractory molybdenum alloy casing, like zirconium, has high corrosion resistance, but also higher thermal conductivity, which is a problem. This increases costs, as it requires higher enrichment of the uranium fuel, which makes the technological process much more expensive. MEPhi scientists believe isotopically modified molybdenum, created using centrifugal isotope separation technology, would make possible an alloy with thermal neutron capture cross-section figures similar to or even smaller than that of zirconium.

Valentin Borisevich, a professor at MEPHI's department of molecular physics, told RIA Novosti that the university's study had provided researchers with the information necessary for the design of a separation system for the large-scale production of isotopically modified molybdenum. The technology could lead to substantial increases in nuclear power plant safety. The research was supported by the Russian Foundation for Basic Research in cooperation with the department of engineering physics at Tsinghua University in Beijing.

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