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The deadline arrives: Checking in on the Reactor Pilot Program
On May 23, 2025, President Trump signed Executive Order 14301, “Reforming Nuclear Reactor Testing at the DOE,” which instructed the Department of Energy to create a Reactor Pilot Program (RPP)—a new system in which companies could pursue DOE authorization to build and test their first-of-a-kind nuclear technologies. EO 14301 set an ambitious goal for that program: three reactors achieving criticality by July 4, 2026.
Kirk A. Mathews
Nuclear Science and Engineering | Volume 132 | Number 2 | June 1999 | Pages 155-180
Technical Paper | doi.org/10.13182/NSE99-A2057
Articles are hosted by Taylor and Francis Online.
Discrete ordinates calculations are presumed to translate particles from cell to cell in the directions specified in the angular set. This should result in uncollided particles from a small source propagating through the spatial mesh in narrow beams in these directions. Accurate high-order angular quadratures presume accurately attenuated propagation in the intended directions. This work examines the ability of various spatial quadratures to propagate rays correctly. Some widely used methods are shown to fail at this fundamental task. Diamond-difference approximations introduce undamped lateral oscillations, resulting in severely unphysical flux representations. Nonlinear fixups can prevent negativity but do not correct the underlying failure to properly propagate rays. First-moment conserving schemes tend to be successful but can be degraded in performance by simplifying approximations that are often used. Characteristic schemes are shown to have significant advantages. New characteristic methods are developed here that are exact (in a certain sense) in propagating rays and that uncouple the calculation of adjacent spatial cells in the mesh sweep. This enables DO loops to be converted to DO INDEPENDENT loops, with obvious implications for vector and/or parallel implementations.