In the relentless pursuit of harnessing fusion power, scientists have uncovered a significant challenge that could reshape how we approach the design and operation of future fusion reactors. A groundbreaking study led by M.A. Lively from the Theoretical and Computational Physics Divisions at Los Alamos National Laboratory has revealed that the radiation back-flux generated from neutron-material interactions in fusion reactors is far more substantial than previously thought. This discovery, published in the journal Nuclear Fusion, could have profound implications for the commercial viability and safety of fusion power.
Fusion reactors, which aim to replicate the sun’s energy-producing process, will inevitably generate intense neutron fluxes that bombard the plasma-facing and structural materials. These interactions, it turns out, produce a considerable back-flux of radiation, including neutrons, gamma rays, and electrons. According to Lively’s research, the magnitude of these back-fluxes is astonishingly large. “The neutron and gamma radiation back-fluxes are on the same order of magnitude as the incident fusion neutron flux,” Lively explained. This means that the radiation bouncing back into the plasma could be just as intense as the radiation initially produced by the fusion reactions.
The implications of this finding are vast. For one, the back-flux of radiation can significantly impact plasma dynamics, potentially seeding runaway electrons during disruptions. This phenomenon occurs when background electrons are scattered by wall-emitted gamma radiation, a process known as Compton scattering. The presence of these runaway electrons can lead to further disruptions, making the plasma more difficult to control and potentially damaging the reactor’s components.
Moreover, the study highlights that the configuration of materials plays a crucial role in determining the magnitude of these back-fluxes. The structural material primarily dictates the neutron back-flux, while the thickness of the first wall— the innermost layer of the reactor—attenuates the gamma ray and electron back-fluxes. This insight could guide the selection of materials and the design of future fusion reactors, optimizing them for better performance and safety.
One of the most intriguing aspects of the research is the identification of delayed back-fluxes. These are gamma rays and electrons that are emitted not immediately after the fusion neutrons impact the surface, but rather from nuclear decay processes in the activated materials. These delayed back-fluxes, though smaller in magnitude, can persist even during transients when fusion no longer occurs. During disruptions, the build-up of delayed gamma radiation back-flux could represent a potential mechanism for seeding runaway electrons, adding another layer of complexity to disruption mitigation in a power reactor.
The study underscores the importance of considering back-flux generation in the materials selection process for fusion power reactors. As the energy sector continues to explore fusion as a viable and sustainable power source, understanding and mitigating these radiation back-fluxes will be crucial. This research, published in the journal Nuclear Fusion, which translates to English as Nuclear Fusion, provides a critical step forward in that direction.
For the energy sector, this means that the path to commercial fusion power is not just about achieving sustained fusion reactions, but also about managing the complex interplay of materials and radiation within the reactor. The insights from Lively’s work could influence the design of future reactors, making them safer and more efficient. As we stand on the cusp of a potential fusion revolution, this research serves as a reminder that the journey is fraught with challenges that require innovative solutions. The future of fusion power may well depend on our ability to navigate these complexities and harness the full potential of this transformative technology.
