Fission product diffusion in ig-110 graphite

Abstract

The threat of global climate change and resultant disasters has never been higher. The promises made by many countries of carbon neutrality by 2050 will be impossible to achieve without nuclear technology. Global public support for nuclear energy is at its highest level in modern history but is still severely hampered by perceptions of safety and issues involving nuclear waste and proliferation. The Fukushima disaster of 2011 and the attack on Ukraine by the Russian Federation in 2022 only served to highlight the dangers of older reactor technology and the potential for large releases of radioactivity either by accident or intentional sabotage. For these reasons most countries have a keen interest in improved reactor technologies, particularly in regards to safety, as they plan to build, or continue building, their nuclear fleets. Generation-IV reactors are characterized by improved safety, economics, and proliferation resistance compared to current light water reactor designs. The hightemperature gas-cooled reactor (HTGR) exemplifies these characteristics with the additional benefit of process heat production capabilities. Past and current demonstration reactors have proved the technical feasibility of the design and several future reactors are set to enter demonstration phases as early as the late 2020s. Despite strong performance in past and present reactors, there remains several unknown variables, particularly in regards to fission product behavior and transport under differing reactor conditions. Due to the robust nature of the tristructural isotropic fuel particles used in HTGRs, as well as the large amount of graphite comprising the core, there is little risk of a reactor meltdown. Instead, the primary safety consideration of HTGRs is the release of radioactive materials from the core, either during normal operation or an off-normal event. Most fission and activation products will be completely retained in either the fuel particle or the surrounding matrix graphite; a few, however, have a demonstrated ability to migrate through all core structures and deposit onto cooling system components. This poses a danger to reactor workers and, if the closed coolant circuit were to be compromised, the public. With that in mind, it is essential to fully understand the transport parameters of these select radionuclides in every component of the reactor core, including the core structural graphite. This work has measured effective diffusion coefficients of Sr, Ag, Pd, Eu, and Cs in IG-110 structural graphite. A time-release method was utilized to measure these diffusion coefficients at temperatures up to 1973 K using an inductively-coupled plasma mass spectrometer. The effective diffusion coefficients here reported can be used to aid predictive fission product transport programs.