Applicability of Shift-generated Albedos for Reactor Analysis with MPACT

Typical simulation of reactor neutronics focuses solely on the internals of the reactor itself, that is to say, the portion of the reactor within the containment vessel.However, reactors with significant leakage relative to total flux may have neutronically important containment and exterior geometries which can be represented implicitly by an albedo.This work introduces a methodology to generate one group, group-wise, and group-to-group albedos on any surface using the Shift Monte Carlo code.The new capability by the MPACT deterministic neutron transport code to use such albedos is then described.Three distinct problems are then run to analyze the effectiveness of the a lbedos.The 1D slab problem shows that albedos can improve a solution compared to a vacuum approximation.However, if the containment is important to the subgroup calculation in MPACT, the error can still be 1000 pcm or more.Additionally, this problem shows that group-wise and group-to-group albedos match well, with differences of only 52 p cm.The 2D BEAVRS problem shows that in a system where the containment does not affect the subgroup calculation so substantially, group-wise albedos can match an explicit MPACT radial MOC calculation within 70 pcm.Finally, the 3D MSRR problem shows that albedos can be generated for a set configuration and still be effective for other configurations of the same m odel.Specifically, albedos generated for 110 cm of control rod withdrawal are just as effective w hen s olving f ull c ontrol r od i nsertion a nd f ull c ontrol rod withdrawal, with eigenvalue errors being between -292 and -375 pcm for all three configurations when using the albedo.