Researchers at the Virginia Tech College of Science are carrying out a research project at Dominion Power’s North Anna Nuclear Generating Station in Virginia that could lead to a new turning point in how the United Nations tracks rogue nations that seek nuclear power.
The years-long project centers on a high-tech box full of luminescent plastic cubes stacked atop one another that can be placed just outside a nuclear reactor operated by, say, Iran. The box would detect subatomic particles known as neutrinos produced by the reactor, which can be used to track the amount of plutonium produced in the reactor core.
It is plutonium — the key ingredient in nuclear weapons — that U.N. regulators seek to track in all nations that are party to the Nuclear Non-proliferation Treaty, but particularly in nations seen as volatile. The Virginia Tech team calls the box “tamper proof” and says if successful, can all but eliminate instances of falsified paperwork or uneasy inspection visits.
“If they want a nuclear reactor, we can let them build it and detect its activity with a minimal impact on its operations,” said Jonathan Link, a professor in the Department of Physics, part of the College of Science. Link views nuclear energy as an important part of a new worldwide low-carbon future that nevertheless requires careful oversight from all participating nations to ensure its safety.
Link believes rogue nations that balk at having to submit to inspections would have no reason to refuse such a small, unobtrusive device. The cube is an early prototype — roughly a two-foot cube, with an active volume weighing 175 pounds — but Link and his team say with enough data collected during several months of testing at North Anna, it could soon justify to larger detectors operated by the International Atomic Energy Agency at facilities around the world.
Dubbed CHANDLER, this project is part of Virginia Tech’s Center for Neutrino Physics, of which Link is director. Together with fellow physics faculty and center members Patrick Huber and Camillo Mariani, he predicts the current detector, a prototype known as MiniCHANDLER, will demonstrate the potential for a future larger detector weighing in at a few tons. The cube now sits just at the base of the concrete containment building of North Anna’s reactor 2, inside a small trailer dubbed the Mobile Neutrino Lab that contains a rack full of processors, all cooled by two air-conditioning units. The trailer will stay at North Anna for several months. On a recent trip, Link set the trailer up, starting data collection, with the ability to beam data wirelessly to Virginia Tech's Blacksburg campus.
The North Anna Nuclear Generating Station is located near Mineral, Virginia, roughly 100 miles southwest of Washington, D.C.
Created in large amounts during plant operation, the cast-off neutrinos that escape the reactor cannot be shielded or disguised, thus creating a foolproof tracking system for regulators, Link said. There is a challenge in separating neutrinos created by the reactor from everyday radioactive “noise” from the ground or raining down from energetic cosmic particles slamming into the Earth's atmosphere, but Link and his team are confident they can extract a signal solely from the reactor neutrino output.
Up until now, neutrinos produced during nuclear fission could not be detected except with a massive machine the size of a house or built very close to the reactor, near impossible to deploy in a rogue nation.
How does the box work? If your career is nuclear physics, it’s easy. If not, well, it’s complicated. Roughly: The light-tight, high-tech box is packed with hundreds of small wavelength-shifting plastic scintillator cubes — they appear green in natural light — that carry the chore of detecting neutrinos emitting from a nearby reactor. When a neutrino interacts in the cube, it creates a small flash of light that can be recorded and tracked. The detection of light can then be sent remotely to researchers either nearby or hundreds of miles away, according to initial research plans by Link and his team.
“The whole problem with nuclear inspections is you have to know what is happening at all times to make this calculation,” Huber said. “You need continuity of knowledge to make conclusions. But the stream of data from a reactor can be interrupted because of technical malfunction or diplomatic reasons. With antineutrino detection, you don’t have to know all that. It’s based simply on the detection of neutrinos.”
Anna Erickson is an assistant professor of the Nuclear and Radiological Engineering Program at Georgia Tech, where she researches nuclear reactor design and nuclear detection with a focus on the needs for proliferation-resistant nuclear power. She is not involved with the CHANDLER project, but said the neutrino project by Virginia Tech could set a new standard for antineutrino detectors, a field stalled by tricky technology, including the sizes of previous devices too large for easy assembly, transport, and setup. Previous detectors used liquid scintillators, rather than solid plastic as does CHANDLER.
“This could open a new path for antineutrino-based reactor monitoring technology,” she said.
The challenge of working detectors around the globe are many. In addition to perfecting the technology itself, getting rogue nations to agree to placement "can be as much of a challenge as advancing the technology itself," Erickson said.
The box has a scientific mission, too: searching for a possible fourth type of neutrino, known as a sterile neutrino. The sterile neutrino is the focus of a long-running scientific mystery story. Several experiments have identified weak hints for a sterile neutrino while other experiments were inconclusive, Link said.
“If a sterile neutrino exists and were to be discovered by us, that would be a paradigm-shifting discovery in particle physics whose impact cannot be overstated,” Link said, adding that several small-scale experiments are now taking data or preparing to take data in the near future to address the mystery of sterile neutrinos. “The CHANDLER detector represents a significant improvement in the state-of-the-art, and if the funding comes through we may still have a chance to compete for a discovery.”
Funding for the CHANDLER project has come from the National Science Foundation and Virginia Tech, including the Institute for Critical Technology and Applied Science and the Institute for Society, Culture, and Environment.