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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.
J. E. Morel, K. D. Lathrop
Nuclear Science and Engineering | Volume 147 | Number 2 | June 2004 | Pages 158-166
Technical Paper | doi.org/10.13182/NSE04-A2425
Articles are hosted by Taylor and Francis Online.
The integral transport equation clearly indicates that the angular flux in a void is constant along each characteristic. Yet, simple arguments can be used to demonstrate that there exist angular flux solutions in voids that have a delta-function angular dependence and a nonconstant spatial dependence. Such solutions can appear to be nonconstant along a characteristic. Using a simple example problem, we demonstrate that such solutions represent the limit of a continuous sequence of nonsingular solutions, each of which is constant along every characteristic. We also show that care must be taken in applying the integral transport equation to singular problems of this type because erroneous solutions are easily obtained. Two reliable approaches for obtaining proper solutions are presented. We also show that the differential form of the transport equation in one-dimensional spherical geometry requires less care than the integral form of the transport equation for problems of this type. Finally, we discuss the applicability of the Sn method to problems in curvilinear geometries with singular solutions of this type.