A consortium of American and British science institutions, led by the Lawrence Livermore National Laboratory (LLNL), is working on a way to use antineutrinos to remotely monitor nuclear reactors. Sponsored by the US Department of Energy's National Nuclear Security Administration, the Advanced Instrumentation Testbed (AIT) program is installing the 3,500-ton WATer CHerenkov Monitor of ANtineutrinos (WATCHMAN) detector in a 1,100-meter-deep (3,600 ft) mine located on the northeast coast of England as part of international nuclear weapon non-proliferation efforts.

Controlling the spread of nuclear weapons is a major international concern, and a key aspect of this is being able to remotely monitor nuclear fission reactors to ensure that they aren't being used for the production of weapons-grade plutonium. This remote sensing is needed at both short range to examine reactors without having to remove their fuel rod assemblies, and at long distances to assess reactors in the hands of unfriendly powers.

One promising method for doing this uses antineutrinos. Discovered in 1950, the antineutrino is the antimatter version of the neutrino and is produced in nuclear reactions when a neutron decays into an electron, a proton, and a neutrino. Like the neutrino, antineutrinos are the tiniest of elementary particles, with a mass a million times smaller than an electron and no electric charge.