At Rosatom’s Mining & Chemical Combine (GKhK – Gorno-Khimicheskom Kombinate) materials are being tested for a planned molten salt research reactor, which is expected to begin operation in 2030. The reactor will burn nuclear fuel and minor dissolved in molten salts. GKhK in Zheleznogorsk, Krasnoyarsk Territory, is currently selecting structural materials for the reactor and its systems. Since April, the plant’s laboratories have been testing several samples of corrosion-resistant alloys. The samples spend 4,000 hours in molten salts, heated to almost 700 °C, which contain the most radiotoxic elements resulting from the reprocessing of used fuel.
“The most representative way to test the corrosion resistance of a material is to test it in a contact medium,” explained Igor Efremov, head of the materials science laboratory at GKhK’s central plant laboratory. “Research takes a long time due to the relatively low corrosion rate. We determine the kinetics of corrosion, changes in the properties of the molten fuel salt due to the accumulation of corrosion products and the possibility of their removal.”
For the experiment, specialists from the plant and scientists from the Ural Federal University developed and manufactured equipment with automatic maintenance of an inert atmosphere and melt temperature, which measures the redox potential. “Maintaining the basic properties of fuel salt is ensured by the inertness of the atmosphere with which it comes into contact. The inert atmosphere normalises the content of oxygen and other impurities that affect the corrosive activity of the salt in relation to the structural material,” the plant noted.
During the tests, salt samples are taken and changes in its impurity composition as a result of corrosion are monitored. Laboratory staff also plan to test a method for purifying fuel salt while the reactor is operating at power.
In November, samples will be removed from the fuel salt and the surface will be cleaned. Then detailed investigations will begin identifying corrosion defects and determining mechanical properties. “The generalised result of studying the samples will allow us to draw conclusions about the corrosion properties of the alloy and the possibility of its use in molten salt reactor technology,” said Efremov.
Minor actinides are formed in fuel during operation of any reactor. Isotopes of neptunium, americium and curium cause the greatest problems during used fuel reprocessing and radioactive waste management. By burning minor actinides it will be possible to achieve radiation equivalence of the initial uranium raw material and the nuclear waste to be isolated in just 300 years. That 2,300 times faster than in an open nuclear fuel cycle.
Rosatom is developing several technologies that make it possible to utilise minor actinides. They can also be burned in fast neutron reactors. In particular, this year at the Beloyarsk NPP, fuel assemblies with mixed oxide fuel (MOX) were loaded into the BN-800 reactor for the first time. Three of them contain minor actinides – americium-241 and neptunium-237. These assemblies were manufactured at GKhK.
Vasily Tinin, Rosatom’s Director for State Policy in the Field of Radioactive Waste, Used Nuclear Fuel & Decommissioning of Radiation Hazardous Facilities, said: “Energy without radioactive waste is the dream of nuclear scientists around the world. Russia is the furthest along in realising this dream.” He added: “The research reactor, which is to be constructed at the Mining & Chemical Combine in Zheleznogorsk, is an important project from an environmental point of view. It is designed to test technologies for the utilisation of minor actinides – long-lived, highly radiotoxic isotopes that remain after reprocessing used fuel from thermal reactors. Just a few molten salt reactors will be capable of neutralising the entire volume of the most dangerous elements in used fuel from thermal reactors in our country.”
Vladimir Matselya, head of the GKhK central plant laboratory noted that everything developed for the research molten salt reactor is new. “Therefore, GKhK, as the operating organisation, must study all the processes in detail: from the preparation of fuel salt to the choice of structural materials. The main thing that remains to be done is to compare the results obtained with the goals and objectives of the project.”
Researched and written by Judith Perera
