Neutrino detectors could keep discreet tabs on nuclear reactors

Osiris is only a modest research reactor – the next step will be to try the detector out on the real thing (Image: PF Grosjean/CEA)

Researchers have managed to peer into a nuclear reactor to track the amount of plutonium inside – without needing access to data from the control room. Although the technology is still at an early stage, it could open up new ways of keeping tabs on whether reactors are being used to make material for nuclear weapons.

Earlier this year, Iran agreed to a deal with major world powers to limit its nuclear activities. Iran has promised it will allow monitors from the International Atomic Energy Agency to inspect its plants and ensure they are being used strictly for peaceful purposes.

The deal is built on fragile trust – Iran doesn’t want to reveal any more of its nuclear secrets than it has to. A magic box that could monitor reactors from a distance, without the need for foreign inspectors to visit, would smooth the way such deals are implemented.

As it turns out, we have a way to build one. Specialised detectors can pick up particles called antineutrinos, produced by nuclear reactions. They barely interact with ordinary matter, so stream away from reactors and can be picked up far away with a suitable instrument.

Flashing liquid

For the past year, researchers in France have used one such detector, dubbed Nucifer, to monitor a reactor next door. Nucifer is full of a liquid scintillator, one which flashes on the rare occasions that a neutrino interacts with it. The rate at which this happens reveals the activity level inside the reactor.

The detector was only 7 metres away from the reactor, meaning it was within reach of other energetic particles streaming out, like gamma rays. But the team was able to build shielding for Nucifer and get useful readings.


Over the course of 145 days, the team could detect whether the reactor was switched on or off – and more importantly, track the amount of plutonium-239 inside. This isotope is especially useful for producing nuclear weapons, so any sudden change in its level suggests armaments may be the actual goal.

Researchers have previously run detectors on the same principle in Russia and the US, but they were one-off creations and required maintenance, which wouldn’t be possible in a real-world monitoring situation. “With Nucifer, we wanted to improve the performance and use off-the-shelf parts,” says team member David Lhuillier of the Saclay Nuclear Research Centre near Paris.

Nucifer kept tabs on the small Osiris research reactor at Saclay. A larger reactor would produce more antineutrinos and so could be monitored from a discreet distance and with greater accuracy, since the distance would reduce unwanted background radiation.

Fifteen years off

The team are trying to find such a reactor for further tests, says Lhuillier. “In a commercial reactor we could put the detector in place, close the door and leave it like that for one year, in conditions very close to what the IAEA inspectors would like to see.” But it would probably be at least 15 years before the technology is ready for use somewhere like Iran, he says.

“The IAEA is aware of the development of this technology as one of a number… that seek to contribute to the same verification goals,” an IAEA spokesperson told New Scientist. “The Agency already has a variety of technologies to hand and has no current plans to deploy this particular idea.”

Patrick Huber of Virginia Tech in Blacksburg works on similar detectors and says Nucifer is a great step forward. “We’re not quite there yet, but it goes a very long way from where we were 10 years ago.”

Production costs will need to come down further before the IAEA can afford them, he says, but the results should get people on board. “If you explain to people you have a technology that can look into a nuclear reactor while it’s running, you get everyone’s attention.”


By Jacob Aron

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