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NRC unveils Part 53 final rule
The Nuclear Regulatory Commission has finalized its new regulatory framework for advanced reactors that officials believe will accelerate, simplify, and reduce burdens in the new reactor licensing process.
The final rule arrives more than a year ahead of an end-of-2027 deadline set in the Nuclear Energy Innovation and Modernization Act (NEIMA), the 2019 law that formally directed the NRC to develop a new, technology-inclusive regulatory approach. The resulting rule—10 CFR Part 53, “Risk-Informed, Technology-Inclusive Regulatory Framework for Advanced Reactors”—is commonly referred to as Part 53.
Zachary K. Hardy, Jim E. Morel, Jan I. C. Vermaak
Nuclear Science and Engineering | Volume 199 | Number 4 | April 2025 | Pages 599-612
Research Article | doi.org/10.1080/00295639.2024.2384223
Articles are hosted by Taylor and Francis Online.
The second moment method is a linear acceleration technique that couples the transport equation to a diffusion equation with transport-dependent additive closures. The resulting low-order diffusion equation can be discretized independent of the transport discretization, unlike diffusion synthetic acceleration, and is symmetric positive definite, unlike quasidiffusion. While this method has been shown to be comparable to quasidiffusion in iterative performance for fixed source and time-dependent problems, it is largely unexplored as an eigenvalue problem acceleration scheme due to the belief that the resulting inhomogeneous source makes the problem ill posed. Recently, a preliminary feasibility study was performed on the second moment method for eigenvalue problems. The results suggested comparable performance to quasidiffusion and more robust performance than diffusion synthetic acceleration. This work extends the initial study to more realistic reactor problems using state-of-the-art discretization techniques. The results in this paper show that the second moment method is more computationally efficient than its alternatives on complex reactor problems with unstructured meshes.