Title: Nuclear Monitoring with a Gigaton Array of Antineutrino Detectors

Abstract: The nuclear fuel used in fission bombs is highly enriched in plutonium-239, which is produced in fission reactors via the capture of a neutron by uranium-238. Reactors that produce weapons grade plutonium have a very different fuel cycle compared to commercial nuclear reactors used to produce electricity. Thus, fission reactors that are registered in the IAEA are difficult to use to produce weapons grade plutonium. Any reactor that produces serious amounts of weapons grade plutonium is likely to be unregistered -- a rogue reactor. In this study, we considered the ability of a global array of antineutrino detectors to detect such rogue reactors. The array consists of 1596 10-megaton modules, each module using water doped with 0.2% gadolinium as the target material. Antineutrinos are detected via the inverse beta decay process. The modules are deployed in major bodies of water where at least 2 km of shielding from cosmic rays is available. We find that a rogue reactor deployed near large bodies of water is easily detected with the array after an exposure time of several months. A rogue reactor that is placed hundreds of miles inland can be detected after a year's exposure if its power is about 1-2 GWth. The position of such a reactor can be determined to within several hundred miles.