The incredible Nucifer

May 12 2011
VERTIC Blog >> Arms Control and Disarmament

Kristiane Roe Hammer, London

A French team has developed a radiation detector that detects five times as many antineutrinos as earlier detectors developed. The detector, called Nucifer, is part of a new generation of detectors that could potentially revolutionize nuclear reactor monitoring. The IAEA has taken renewed interested in the technology and the detectors, that for years had been considered too large and unreliable.

Nucifer has been developed by a collaboration of French institutes. It is a heavy machine, the Gadolinium-doped liquid scintillator detector weighs about one metric tonne, but only takes up three by three meters of floor space. It is soon undergoing field trials. The sensor may be used at the French Osiris reactor and the ILL research reactor in Grenoble by the end of 2012, after which it will be tested at a commercial reactor sometime in 2013. The International Atomic Energy Agency (IAEA) is keenly watching progress. Indeed, the organization has already set up a working group made up of specialists on the technology. Their first meeting will be held in September this year.

Detecting the antiparticle
Neutrinos are the most plentiful particles in the universe. But they are also very discreet. They are tiny particles that are released from different types of nuclear decay, like for example the nuclear reactions we have in the sun. The particles are extremely small. Travelling close to the speed of light they are also unbelievably fast. They have no electrical charge, so they almost never interact with other particles. In fact, most neutrinos produced by the sun pass right through our planet without interacting with a single atom of it.

Nuclear fission reactors do not produce neutrinos, but they produce the twin and antiparticle of the neutrino called antineutrino by the billions. Because of the antineutrinos ability to pass through matter unaffected, it is almost impossible to catch or measure it, or hinder it for that matter. But sometimes an antineutrino reacts with a proton to produce a neutron and a positron. The positron created will quickly go on to wipe out electrons creating gamma rays. It is possible to measure the rays from the collision of the antineutrino and the gamma ray. And it is this that the detector registers.

As the antineutrino quickly passes through all matter—including shielding—it is impossible to try to prevent them from escaping the reactor. This means the detector, according to the IEEE Spectrum magazine, can be placed as far as 100 meters away from the plant. This is not necessary, however. As the Nucifer detector is small, it can be placed inside nuclear plants without plant interference or interruptions.

Une nouvelle idée?
The French, despite their pioneering spirit, cannot be credited with the idea of using neutrino sensors for nuclear safeguards. A team of Soviet researchers proposed the idea almost 35 years ago, in 1977. Nothing much happened after that, mostly since it has been difficult to detect the elusive particle, but also since detectors have been too crude to filter out the constant bombardment of particles from space.

And the French also have competitors. A joint venture by Lawrence Livermore National Laboratory and Sandia National Laboratories, with researchers from Atomic Energy of Canada Limited’s Chalk River Laboratories is testing a detector for capturing reactor-born antineutrinos. This detector is scheduled to be installed at the Point Lepreau Generating Station, a CANDU reactor in New Brunswick, Canada. Since 2003 they have tested earlier versions of the detector at the San Onofre Nuclear Generating Station in San Clemente, California.

Based in an underground room 25 meters from the reactor, the sensor could within 5 hours detect a shut down. This enables the monitor to get a heads-up on any fuel unloading operation. But this is not all the detector can do. While the nuclear plant is running uranium-235 is burned while plutonium-239 is produced. Since the fission of plutonium-239 gives off less antineutrinos than uranium-235, the detector will at any time be measuring the amounts of plutonium and uranium in the core. With this information it is possible to tell if any fuel has been removed or if the plant is producing more plutonium than normal.

So far the results from LLNL and SNL have shown the ability to detect a 73 kg removal of plutonium from a nuclear plant. This is, of course, far more material than is needed to make one nuclear pit. But it proved the principle. Nucifer has significantly lowered the detection threshold. According to the collaborating institutes, it can detect a removal of about 14 kilogrammes of plutonium. It is still more fissile material than what’s necessary to build one bomb, but a stunning achievement nevertheless.

The way forward
According to the IEEE Spectrum the detectors have the potential of becoming inexpensive enough for commercial use. Their cost could go down to US$100k when produced at a greater scale.

The IAEA seems keen to put in the money. It has highlighted that the detectors are less prone to tampering as they measure the fission process in the reactor core. The organization has also noted that the technology can be especially useful on the new PBMR reactor that will be refuelled continuously and which could present a safeguards challenge to the IAEA.

At this point there are several continuing projects on antineutrino detectors around the world, several waiting to present their project. The Nucifer project appears to be ahead of its competitors.

There are still some challenges to overcome. The liquid scintillator material used in some detectors is toxic and flammable, making it unwanted in a nuclear plant, and the future cost of the commercialized detectors is still only based on estimates.

However, there should be reason to be optimistic. Some experts prophesise the detectors could be installed at commercial reactors within the end of the decade. With the potential for monitoring a plant in a non-intrusive and tamper-proof way, the future looks promising.

Last changed: May 26 2011 at 12:56 PM