Anti-Neutrinos and Nonproliferation

A new compact detector may help international inspectors peer inside a working nuclear reactor in a non-intrusive way by directly measuring the flux of anti-neutrinos coming out. Since their first use, nuclear reactors have, at least in principle, been closely related with nuclear weapons. For example, reactors produce plutonium which can later be fashioned into bomb material. The question of how to monitor the actual operation of a particular reactor and compare the changing plutonium inventory to what is expected from normal operations (producing electric power, say) is a large component of nuclear non-proliferation efforts.

The cubic-meter-scale detector, proposed by Adam Bernstein, leader of the Advanced Detectors Group at Lawrence Livermore National Laboratory (925-422-5918, bernstein3@llnl.gov) and built by a team from Livermore and Sandia National Laboratories California branch, would not attempt to monitor the reactor’s performance on a moment by moment basis. Instead its sensitivity is more attuned to the number of antineutrinos produced over hourly, daily and weeklong intervals. These time scales, Bernstein says, are well suited to the kind of monitoring performed by the International Atomic Energy Agency (IAEA).

The detector built by the LLNL/SNL collaboration operates unattended for long periods without significant maintenance, is self-calibrating, and does not affect plant operations in any way (see illustration of a detector at work, http://www.aip.org/png/2008/295.htm). Data from the detector is acquired remotely in real time. The detector module can be made tamper-proof using standard techniques, and the anti-neutrino signature seen by the detector (the arrival of a positron followed 30 microseconds later by a neutron) is hard to mimic with surrogate neutron or gamma sources. In conjunction with knowledge of the input fuel load and core design, the observed anti-neutrino flux provides a direct measure of the reactor’s power and isotopic content. (Bernstein et al.,upcoming article in the Journal of Applied Physics.)