  We report simulation studies of six low-energy electron-antineutrino detector
designs, with the goal of determining their ability to resolve the direction to
an antineutrino source. Such detectors with target masses on the one-ton scale
are well-suited to reactor monitoring at distances of 5--25 meters from the
core. They can provide accurate measurements of reactor operating power, fuel
mix, and burnup, as well as unsurpassed nuclear non-proliferation information
in a non-contact cooperating reactor scenario such as those used by IAEA. A
number of groups around the world are working on programs to develop detectors
similar to some of those in this study. Here, we examine and compare several
approaches to detector geometry for their ability not only to detect the
inverse beta decay (IBD) reaction, but also to determine the source direction
of incident antineutrinos. The information from these detectors provides
insight into reactor power and burning profile, which is especially useful in
constraining the clandestine production of weapons material. In a live
deployment, a non-proliferation detector must be able to isolate the subject
reactor, possibly from a field of much-larger power reactors; directional
sensitivity can help greatly with this task. We also discuss implications for
using such detectors in longer-distance observation of reactors, from a few km
to hundreds of km. We have modeled six abstracted detector designs, including
two for which we have operational data for validating our computer modeling and
analytical processes. We have found that the most promising options, regardless
of scale and range, have angular resolutions on the order of a few degrees,
which is better than any yet achieved in practice by a factor of at least two.
