spallation neutron source

The Department of Energy plans to send 6 tons of heavy water from Iran to the Spallation Neutron Source at the Oak Ridge National Laboratory.

Oak Ridge National Laboratory

U.S. goes shopping in Iran’s nuclear bazaar, will buy heavy water for science

Mere months ago, Iran’s nuclear program was an international pariah. Now, it’s supplying the U.S. Department of Energy (DOE) with a strategic substance that the United States itself can’t produce. DOE has struck a deal to purchase 32 tons of heavy water—water containing the hydrogen isotope deuterium—from the Atomic Energy Organization of Iran.

The $8.6 million sale, expected to be completed Friday morning in Vienna, helps Iran meet a commitment under last July’s nuclear deal to shed heavy water—and it will have a swords-to-ploughshares payoff. “We’re securing material that will allow us to do great science,” says Thom Mason, director of Oak Ridge National Laboratory in Tennessee. DOE will resell a portion to industry for uses such as nuclear magnetic resonance imaging and protecting optical fibers and semiconductors against deterioration by blasting them with deuterium gas. DOE will also send 6 tons to Oak Ridge for an upgrade of the Spallation Neutron Source (SNS), the world’s most powerful accelerator-driven machine for generating neutrons for research.

Deuterium—hydrogen with an added neutron—accounts for just one in every 6420 hydrogen atoms. That neutron makes heavy water (D2O) more efficient than regular water at slowing neutrons and initiating fission. As a result, a handful of countries use it as a moderator in nuclear power reactors. But deuterium has a dark side. Heavy water reactors can transmute uranium into plutonium, for use in weapons.

In 2002, an Iranian opposition group revealed that Iran was building a secret facility at Arak later identified as a heavy water production plant, along with a reactor that could breed enough plutonium for one or two bombs a year. That and other revelations led to years of crippling sanctions and finally the agreement with world powers that sharply constrains Iran’s nuclear program. Iran is now working with the United States and China to reconfigure the Arak Heavy Water Reactor to largely eliminate plutonium production. And it has reduced its heavy water stockpile to less than 130 tons, as the deal mandates, by shipping excess stock out of the country for storage.

After the deal was concluded, the DOE realized that buying some of the heavy water also makes sense, says U.S. Energy Secretary Ernest Moniz. The United States relinquished its own production capacity in 1981, when DOE shuttered a heavy water plant at Savannah River National Laboratory in Georgia to save money. These days, Canada and India satisfy most of the global demand for nonnuclear uses, about 100 tons a year, by distilling heavy water from feed water, like brandy from wine. A single pound of reactor-grade heavy water, which is 99.75% D2O, requires a staggering 340,000 pounds of purified feed water. U.S. buyers snap up about 75%, and appetite is increasing. “Heavy water has been on our radar screen for some time,” says a DOE official.

Savannah River has already tested samples of Iran’s heavy water, confirming it is top-shelf. The shipment to arrive in the coming weeks should allow SNS to raise its game. “Heavy water is by far the most cost-effective way to increase neutron intensity that I can imagine,” says Mason, a condensed matter physicist. Next spring, Oak Ridge will replace an inner reflector plug filled with regular water with one filled with heavy water. The plug has a slot for the target that produces neutrons. It reflects the neutrons toward moderators that slow them to energies required for experiments. Heavy water cools the reflector assembly, improving the efficiency of the reflection process and increasing neutron flux by up to 22%. “We can measure smaller effects,” Mason says. Hundreds of research teams stand to benefit, he says. More neutrons means faster experiments, which would free up beam time at a facility that now receives four to five times more proposals than it can accommodate.

The heavy water purchase could open the floodgates to other collaborations with Iran. According to the nuclear agreement, Iran’s Fordow uranium enrichment facility is slated to become an international science and technology center. There, Russia is reconfiguring uranium-enrichment centrifuges to produce iridium-191; adding a neutron at the reconfigured Arak reactor would yield iridium-192, which is used in gamma cameras to check for structural flaws in metal. With the D2O deal done and dusted, Moniz says he has asked DOE rank-and-file “to begin thinking about other areas of collaboration.”