  Numerous experimental efforts have shown that antineutrino-based monitoring
provides a non-intrusive means to estimate the fissile content and relative
thermal power of nuclear reactors for nonproliferation. Until now, there have
been no experimental demonstrations dedicated to exploring the nonproliferation
potential of large detectors required for long-range monitoring. The goal of
the Advanced Instrumentation Testbed (AIT) program is to test novel methods for
the discovery of reactor cores, specifically in the mid-field to far-field,
beyond 200 meters and out to tens or hundreds of kilometers, using
kiloton-scale to megaton-scale detectors. The main physical infrastructure of
the AIT consists of an underground laboratory in the Boulby mine in Northern
England. The site is located at a 26-km standoff from the Hartlepool Reactor
Complex, which houses two 1.5-GWth advanced gas-cooled reactors. The first
detector to be deployed at the AIT is the WATer CHerenkov Monitor of
ANtineutrinos (WATCHMAN). WATCHMAN will use ~6,000 tons of gadolinium-doped
water in order to detect a few reactor antineutrinos per week from the
Hartlepool reactor complex. WATCHMAN will focus on understanding the signal
efficiency, radiological backgrounds, and the reactor operational status. Here,
the nonproliferation goals are to understand the sensitivity for discovery of
one reactor in the presence of another, the discovery of any reactor operations
above a well-understood background, and the sensitivity to confirm the declared
operational cycles of both reactors. Uniquely, AIT-WATCHMAN also offers a
flexible platform at which nascent technologies such as water-based
scintillator and fast photomultiplier tubes can be tested in real-world
conditions. We present the AIT-WATCHMAN program and status.
