Antineutrino Detectors May Offer a Foolproof Way of Monitoring Iran's Reactors

Also: cheaper, less invasive, and more reliable.

Jul 19 2015, 11:00am

Highly enriched uranium. Image: Wiki

Monitoring a nuclear reactor isn't an especially straight-forward task, but it's a cornerstone of the 159 page agreement reached last week between the US-led P5+1 nations and the Iranian republic. The broad sketch of the deal is a compromise (of sorts), allowing Iran to continue enriching uranium in a limited and verifiable fashion while being incrementally relieved of the onerous economic sanctions it's been subject to for over a decade. And so the International Atomic Energy Agency has a whole lot more work on its hands with Iran's suite of nuclear reactors, enrichment sites, uranium mines, and assorted military facilities all requiring inspection.

Of particular interest will be Iran's in-development Arak heavy-water nuclear facility. As designed, the facility would be capable of producing weapons-grade plutonium—the project is currently paused—but under the agreement Iran will need to redesign the plant such that it no longer has this ability. Moreover, all spent fuel from the reactor is to be shipped out of the country for disposal and Iran will forgo the right to build new heavy-water nuclear facilities for 15 years.

There's no easy, passive way to monitor nuclear facilities.

There's no easy, passive way to monitor nuclear facilities. Currently, monitoring consists of a suite of different things including cameras, seals, and radiation detectors—an imperfect and expensive arrangement. But, for the past several years, Patrick Huber, a physics professor at the Center of Neutrino Physics at Virginia Tech, has been at work perfecting a technology that could make all of the difference: aboveground, lightweight antineutrino detection.

Huber's part of a (currently) Belgium-based international group working on a form of antineutrino detection technology that could be ready within two years. Which isn't too bad given that aboveground antineutrino detection is itself a very new capability—it was demonstrated only last September by a group of Japanese researchers.

You're maybe be wondering at this point just what in the hell an antineutrino is. Fair enough.

So, it's possible for a proton, the positively charged particle within an atomic nucleus, to become a neutron (the other, neutral particle in the nucleus) thanks to the weak force, which is one of the fundamental forces of nature and it governs the process of radioactive decay. The general idea is that a neutron or proton emits or absorbs either a W or Z boson, superheavy particles that pretty much only serve as mediators of the weak interaction, and the neutron becomes a proton or the proton becomes a neutron. In the process of beta decay, the prior conversion occurs and as part of the deal both an electron and an electron antineutrino are released.

In a nuclear fission reaction, we wind up stuck with unstable reaction byproducts, like certain isotopes of plutonium. This instability is because the fission process leaves the remaining atoms with extra bonus neutrons, which decay and this is where we find our antineutrinos. So, if there's a bunch of plutonium sitting around somewhere it will have an antineutrino signature. Or, if the levels of antineutrino emission were to change for a given reactor, it might indicate that plutonium had been removed, perhaps in violation of the agreement.

The buzz about antineutrino detection actually started up last year thanks to a study Huber published describing an earlier version of the detection technology. Here's how Physics World explained it at the time:

But the energy spectrum of the antineutrinos depends on whether they are produced via fission in uranium or plutonium—those from plutonium have a lower average energy. This means that antineutrinos carry with them signature information about the amount and type of fissile material in the reactor core. So, by observing the spectrum, it is possible to determine the relative fraction of fissions that arise from plutonium, and this in turn can be used to work out the amount of plutonium that are in the core.

Not having to actually go into the Iranian nuclear facility in question—or to be able to just confirm other monitoring methods—could make the whole affair a lot more reasonable.

In any case, the Iranian agreement is still subject to congressional approval in the United States. It's unlikely that hard-line legislators will wind up with enough of a majority to derail it, but American politics is also a complete crimescene at the moment, so we'll see.