Charles Whitmer

A Once-Through Fuel Cycle for Fast Reactors

A paradigm shift has recently altered the design targets for advanced nuclear energy systems that use a fast neutron spectrum. A previous emphasis on extending fissile fuel reserves has been supplanted by a desire for reactor technologies that are “cleaner, more efficient, less waste-intensive, and more proliferation-resistant.” [1] This shift, along with recent advances in fast-reactor designs that enable high fuel burn-up even with fuels that have been minimally enriched, creates an opportunity to employ fast reactors in an open nuclear fuel cycle. These goals now appear feasible as a result of recent design work exploiting a phenomenon, known as a traveling wave, that can attain high burn-ups without reprocessing. A traveling-wave reactor (TWR) breeds and uses its own fuel in place as it operates. Fueled almost entirely by depleted or natural uranium, such reactors would also require little initial enrichment. We have performed calculations demonstrating that TWRs can achieve burn-ups of ≥20%, which is four to five times that realized in current LWRs. Burn-ups of up to 50% appear feasible. The factors that contribute to these high burn-ups and the implications for materials design will be discussed.© 2009 ASME

Computational Tools for the Integrated Design of Advanced Nuclear Reactors

Abstract Advanced nuclear reactors offer safe, clean, and reliable energy at the global scale. The development of such devices relies heavily upon computational models, from the pre-conceptual stages through detailed design, licensing, and operation. An integrated reactor modeling framework that enables seamless communication, coupling, automation, and continuous development brings significant new capabilities and efficiencies to the practice of reactor design. In such a system, key performance metrics (e.g., optimal fuel management, peak cladding temperature in design-basis accidents, levelized cost of electricity) can be explicitly linked to design inputs (e.g., assembly duct thickness, tolerances), enabling an exceptional level of design consistency. Coupled with high-performance computing, thousands of integrated cases can be executed simultaneously to analyze the full system, perform complete sensitivity studies, and efficiently and robustly evaluate various design tradeoffs. TerraPower has developed such a tool—the Advanced Reactor Modeling Interface (ARMI) code system—and has deployed it to support the TerraPower Traveling Wave Reactor design and other innovative energy products currently under development. The ARMI code system employs pre-existing tools with strong pedigrees alongside many new physics and data management modules necessary for innovative design. Verification and validation against previous and new physical measurements, which remain an essential element of any sound design, are being carried out. This paper summarizes the integrated core engineering tools and practices in production at TerraPower.