A way to reduce to the damage caused to metal alloys used in cladding of the fuel in nuclear reactor from exposure to hydrogen has been found by a team of researchers at the Massachusetts Institute of Technology (MIT).
The researchers have conducted a study on the impact of hydrogen on zirconium alloys which are widely used in nuclear industry.
Hydrogen, which is released when water molecules from a reactor’s coolant break apart, can reduce the metal’s ductility by entering it and reacting with it. The reaction could lead to premature cracking and failure of the metal.
MIT Associate Professor Bilge Yildiz said that finding solutions to enhance the metal’s longevity is of high importance in nuclear power plants.
The entry of hydrogen atoms into the metal mainly depends on the characteristics of the outside layer of the metal.
A careful engineering of a coating of zirconium oxide that naturally forms on the surface of the zirconium in high-temperature water can prevent the hydrogen from entering the crystal layer of the metal, according to the researchers.
Yildiz said: "If we know how it enters or how it can be discharged or ejected from the surface, that gives us the ability to predict surface modifications that can reduce the rate of entry,".
The team has found a way to stop hydrogen from damaging the metal. To prevent hydrogen from penetrating into the bulk of the metal, it has to be dissolved in the oxide layer.
The hydrogen s dissolution can be checked by introducing atoms of another element or elements into the layer.
"There is a certain type of doping element that minimizes hydrogen’s ability to penetrate, whereas other doping elements can introduce a maximum amount of electrons in the oxide, and facilitate the ejection of hydrogen gas right at the surface of the oxide," said Mostafa Youssef, who was also involved in the study.
The doping could be achieved by introducing a small amount of the dopant metal into the initial zirconium alloy matrix, so that this in turn gets incorporated into the oxidation layer that naturally forms on the metal, the team said.
A professor of sustainable energy, environmental, and earth systems engineering at the University of Michigan Gary Was said: "The behavior of hydrogen has been cited by the commercial nuclear power community as perhaps the greatest challenge in nuclear reactor fuel performance under normal operating conditions, and more recently, as a safety issue under accident conditions."