Neutrinos could ensure a submarine’s nuclear fuel isn’t weaponized

Nuclear submarines could provide rogue nations with a pathway to nuclear weapons. But neutrinos could help reveal attempts to jump from boats to bombs.

Neutrinos, light subatomic particles that are released from the reactors that power nuclear submarines, could expose the alteration or disposal of nuclear fuel for nefarious purposes, physicists report in an accepted paper. Physical examination letters. Above all, this monitoring could be carried out remotely, while a submarine is in a port with its reactor shut down.

To ensure that countries without nuclear weapons do not develop them, international inspectors monitor the use of many types of nuclear technology around the world. Nuclear submarines are particularly worrisome. Many use highly enriched uranium, a powerful type of fuel that can be weaponized relatively easily. But the submarines are protected from surveillance by a loophole. Unlike nuclear power plants, nuclear submarines are used for covert military purposes, so physical inspections could undermine a country’s national security.

“Neutrino-based methods can significantly reduce intrusion by making measurements remotely, without having to physically access the ship,” says nuclear scientist Igor Jovanovic of the University of Michigan at Ann Arbor, who has no participated in the research.

These particles – especially their variety of antimatter, antineutrinos – are pouring in en masse from operating nuclear reactors. The particles interact weakly with other matter, allowing them to pass through solid materials, including a submarine hull. So a neutrino detector placed near a submarine could reveal what’s going on inside, say neutrino physicists Bernadette Cogswell and Patrick Huber of Virginia Tech’s Center for Neutrino Physics in Blacksburg.

Scientists have previously suggested using neutrinos to detect other nuclear misdeeds, such as nuclear weapons testing (SN: 08/20/18).

But submarines, often in motion, are difficult to monitor with fixed instruments. When ships are in port, their nuclear reactors can be turned off. So the researchers came up with a solution: they would examine the neutrinos produced by the decay of varieties of chemical elements, or isotopes, that remain after a reactor has shut down. A detector located in the water about 5 meters below the submarine’s reactor could measure the neutrinos produced during the decay of certain isotopes of cerium and ruthenium. These measurements would reveal whether nuclear material had been removed or exchanged.

This method of monitoring a shut down reactor is “very clever”, says physicist Ferenc Dalnoki-Veress of the Middlebury Institute for International Studies in Monterey, California.

But the idea would still require the buy-in of every country to accept detectors in underwater berths. “Something like this would be so much better if it didn’t require cooperation,” says physicist Giorgio Gratta of Stanford University.

Submarine surveillance may become more pressing in the near future. Until now, all the countries that have nuclear submarines already have nuclear weapons, so the question was hypothetical. But that is changing. The United States and the United Kingdom, two nuclear-weapon states, announced last September that they were signing a security cooperation agreement with Australia and would help the country, a non-nuclear-weapon state, acquire nuclear submarines.

There is little suspicion that Australia would use these submarines as cover for a nuclear weapons program. But “you still have to worry about the precedent it sets,” says Cogswell. So, she says, monitoring nuclear submarines is of new importance. “The question was how the hell do that.”