Researchers from the National Research Nuclear University MEPhI (Moscow, Russia) recently conducted a study1 on the use of isotopically modified molybdenum as an alternative to zirconium alloys from which nuclear fuel-element casings are created.
The researchers say their study shows that using isotopically modified molybdenum can enhance the safety of nuclear reactors.
Zirconium alloys are the main material used in casings containing uranium oxide (UO2) pellets, the researchers explain. The material features high erosion and corrosion resistance in water, along with a low thermal neutron capture cross-section.
Zirconium alloys are also known to have several drawbacks, however, including the generation of heat in water and the production of hydrogen—which accelerates the degradation of fuel-element casings. This occurs during zirconium-steam reactions, which take place when temperatures reach above 1,292 °F (700 °C).
These reactions can be very dangerous in emergency situations at water-cooled nuclear power stations, the researchers explain, noting that a zirconium-steam reaction is believed to have been one of the causes of the Fukushima nuclear disaster in 2011.
Nuclear physicists have long discussed the possibility of replacing zirconium alloys with a refractory molybdenum alloy casing. Like zirconium, the molybdenum alloy offers high corrosion resistance, but also higher thermal conductivity. The main drawback to the material has traditionally been its expense, which requires an increase in the degree of the uranium’s enrichment. In turn, this makes the technological process more expensive.
However, Russian scientists believe they may have found a solution by changing the natural composition of molybdenum isotopes through the use of centrifugal separation technology. This allows the creation of an alloy with thermal neutron capture cross-section figures similar to or even smaller than that of zirconium, the researchers say.
The university study has provided researchers with “all the information necessary to design a separation system for the large-scale production of isotopically modified molybdenum on the basis of existing Russian technology for the separation of non-uranium isotopes in gas centrifuges,” says Valentin Borisevich, professor at MEPHI’s department of molecular physics.
If introduced, researchers believe the technology could lead to substantial increases in nuclear power plant safety. The study was made possible with support from the Russian Foundation for Basic Research (Moscow, Russia) and in cooperation with the department of engineering physics at the Tsinghua University (Beijing, China).
Reference
1 “Russian Scientists Create New Breakthrough Material for Nuclear Reactors,” What’s Happening, Jan. 29, 2018,
https://eng.mephi.ru/news/119920 (Feb. 16, 2018).