UC Berkeley

Radiative heat transfer (radHT) is the reason we exist. For life, we need energy, and for that energy, we turn to the sun. Thermal radiation, another term for radHT, simply provides the means to transfer the sun's energy to us. On Earth, we interact with radHT as well --- we bask in the heat of a fire from across the room, we see metals glow red hot, we feel the evening warmth from buildings heated by the day as we walk past, and we see sunbeams through water turn blue and eventually peter out. All of these examples, both earthly and stellar, are driven by the transfer of energy via photons.

The amount of thermal radiation emitted by an object scales rapidly (to the fourth power) with temperature --- the reason why the fire across the room feels hotter than the building we pass by, loosely speaking. The proportion of radiation a body interacts with or absorbs varies as well --- the reason why sunlight travels mostly unabated through the atmosphere but attenuates noticeably in water. These two factors, temperature dependence and proportional interaction of various media, are important to consider when analyzing radHT in any system.

Of particular interest to this dissertation, is the consideration of these two factors within heat transfer analysis for nuclear reactors. The system temperatures and participating media interaction of conventional light water reactors are too low to render thermal radiation a significant heat transfer mechanism, less extraordinary circumstances. However, advanced reactors utilize significantly higher temperatures and non-water coolants that have the potential for increased radiative interaction. The fluoride-salt-cooled high-temperature reactor (FHR) is one such advanced reactor concept.

This dissertation addresses the impacts of radHT in FHRs through two means, introduced and contextualized by Chapter 1. On one hand, FHR development requires scaled-down experiments, in which low temperatures and surrogate fluids render radHT insignificant. The proportional impact of thermal radiation will be distorted compared to the prototypical reactor. Chapter 2 presents a scaling methodology to scale the system-level thermal-hydraulic behavior of FHR systems, with particular emphasis on quantifying radHT distortions. On the other hand, thermal radiation will serve as an important heat transfer mechanism in some full-scale FHR scenarios. Thus, radHT modeling must be included in FHR safety analyses to determine if thermal radiation plays a significant heat transfer role, and requires further consideration, or is low enough to be neglected. Chapter 3 details the development process of radHT simulation capabilities for System Analysis Module (SAM), a system-level thermal hydraulics code being developed for advanced reactor modeling. Chapter 4 then ties together the work conducted in Chapters 2 and 3 by laying out a proposed demonstration of the FHR scaling methodology and utilizing system-level modeling for radHT distortion quantification. The FHR scaling methodology and SAM radHT simulation tools presented in this dissertation can be used to address the impact of radHT in FHR systems. It is my hope this work will be utilized to facilitate FHR development and help realize the dream of building FHRs for clean energy production.