Zoltán Hózer is the head of the Fuel and Reactor Materials Department at the HUN-REN Centre for Energy Research. His primary scientific interest lies in the behaviour and failure of nuclear fuel under normal operating conditions and high-temperature accident scenarios. He has initiated several series of separate effect tests involving various zirconium alloys and accident-tolerant fuel designs. He supervises the CODEX experimental program, which investigates reactor accident scenarios by simulating high-temperature conditions with electrically heated fuel bundles. He has participated in numerous international projects focusing on fuel behaviour and severe reactor accidents, including coordinating the OECD-IAEA Paks Fuel Project. From 2018 to 2023, he served as the chairman of the OECD Working Group on Fuel Safety.
Title of presentation: Development of Accident Tolerant Fuel for Nuclear Power plants
Abstract:
The analyses of the Fukushima accident highlighted that the scenario and the extent of damage to the units were heavily influenced by the materials used in the reactor core. The production of hydrogen primarily occurred due to the chemical interaction between steam and zirconium components of the fuel assemblies. The release of radioactive fission products into the environment was facilitated by the hydrogen explosions, which compromised the containment integrity.
To prevent Fukushima-like accident scenarios, several measures were implemented in nuclear power plants (e.g., additional diesel generators, hydrogen re-combinators, spent fuel pool cooling make-up, etc). One significant action was the proposed replacement of traditional nuclear fuel with so-called Accident Tolerant Fuel (ATF). The primary objective of ATF is to prevent or mitigate the release of radionuclides from the reactor in the event of an accident.
The development of ATF currently focuses on several technical solutions. The zirconium cladding used in today’s fuel rods is being replaced by alternatives such as chromium-coated zirconium tubes, FeCrAl alloys, or SiC tubes. New pellet designs include additives to UO₂ fuel to increase grain size. Silicide-type fuels, with their high thermal conductivity, can achieve lower temperatures and store less energy at the onset of an accident. In micro-cell fuel designs, additional barriers within the pellets help prevent the transport of radionuclides.
ATF must demonstrate reliable performance not only during accidents but also under normal operating conditions. The requirements applied to the traditional nuclear fuel may not be fully applicable to ATF, and some new operational limits might be necessary. Before the routine loading of ATF into nuclear power plants, extensive testing must be conducted in out-of-pile and in-pile facilities. Lead test assemblies must be loaded first into selected nuclear power plants for further evaluation.
Several international projects have been launched to support the development, testing, and qualification of ATF. Selected research activities will be illustrated using results from projects involving the Lithuanian Energy Institute (LEI) and HUN-REN EK.
