Antineutrinos and nonproliferation

A simple, compact detector may help international inspectors peer inside a working nuclear reactor by directly measuring the flux of antineutrinos emerging from the core. Typical nuclear reactors consume uranium-235 and both produce and consume plutonium-239, which could be diverted and fashioned into bomb material. Determining how best to monitor a working civil reactor is a large part of nuclear nonproliferation efforts. The cubic-meter-scale detector proposed by Adam Bernstein of Lawrence Livermore National Laboratory and built by a team from Livermore and Sandia National Laboratories is well attuned to the number of antineutrinos produced over hourly, daily, and weekly intervals. Because fissile material can only be acquired while the reactor is shut down, those time scales are well suited to the needs of the International Atomic Energy Agency. In tests done at the San Onofre Nuclear Generating Station in southern California, a prompt shutdown that occurred over about an hour could be reliably detected with five hours of antineutrino data, collected remotely in real time. The figure shows the hourly antineutrino events before and during an outage. The detector operates unattended for long periods, is self-calibrating, does not affect plant operations, and can be made tamper-proof. Further, the antineutrino signature (the arrival of a positron followed 30 microseconds later by a neutron) is hard to mimic with surrogate neutron or gamma sources. (A. Bernstein et al., J. Appl. Phys., in press.)