The Water Cherenkov Monitor for Antineutrinos, or WATCHMAN, brainchild of the energy department and the National Nuclear Security Administration, should be able to spot a suspicious nuclear reactor up to 1,000km away. A network of such devices, set up within range of someone who might be producing plutonium, should indeed verify whether he can be trusted.
The WATCHMAN is a neutrino detector—or, to be precise, an antineutrino detector....No amount of shielding can stop them [neutrinos] escaping from a nuclear reactor. If it were possible to tell both where the particles were coming from, and whether that source was natural or artificial, then it would be impossible to hide a nuclear reactor. The WATCHMAN’s designers think they can do that...
A prototype WATCHMAN is under construction in an old salt mine (to shield it from cosmic rays and other sources of interference) in Painesville, Ohio. This is 13km from a nuclear power station at North Perry, on Lake Erie. Though the Perry reactor is built for electricity generation rather than plutonium production, all reactors create some plutonium as a by-product, so its proximity will be a good test for the WATCHMAN system.
If that system works, and the decision is taken to deploy it, then there will still be the question of where and how. The predicted 1,000km range means quite a bit of diplomatic arm-wrestling may be involved, for the detectors would be of little use if built on American soil. But if, say, a country like Turkey could be persuaded to house one, the nuclear activities of a neighbour such as Iran might thus be monitored without inspectors having to set foot on the soil of the country in question. If that can be done, the WATCHMAN may help make the world a safer place.
Nuclear proliferation:The watcher in the water, Economist, May 16, 2015, at 73