DOE begins rationing helium-3

Drained by years of high demand for Department of Homeland Security (DHS) and DOE radiation-detection applications, the US inventory of ³He has plunged from a peak of well over 200 000 liters in 2001 to somewhere between 43 000 and 48 000 liters (see chart). Worse, DOE anticipates that it will have fewer than 8000 liters per year of ³He to sell for years to come.

Agency documents provided to the investigations and oversight subcommittee of the House Committee on Science and Technology contain inconsistent data on DOE’s total releases of ³He. According to a recent DOE memorandum, 313 000 liters were distributed from 1991 through January of this year. But William Brinkman, director of DOE’s Office of Science, testified that 200 000 liters have been distributed since 2003, and another 58 000 liters have been dispensed since 2001 for the Spallation Neutron Source (SNS) at Oak Ridge National Laboratory.

In the US, ³He is generated as a byproduct of tritium, which is used in nuclear weapons. With a 12.3-year half-life, tritium in warheads must be replenished every five years or so. The ³He that is generated when tritium decays is extracted during replenishment. As thousands of warheads were dismantled over the past two decades, enough tritium was freed up for recycling into remaining warheads and no new tritium was needed. Production at DOE’s Savannah River Site was halted in 1988. It resumed in 2007, at a far lower level, in a commercial reactor operated by the Tennessee Valley Authority.

Although more tritium could be produced in commercial reactors to help meet ³He demand, the cost would be prohibitive—more than $20 000 per liter, by one estimate—and the process could take 20 years or more to yield significant quantities of ³He. A more immediate source could be the processing of tritium from heavy-water reactors, and the isotope could also be separated from natural-gas fields that have a high concentration of helium. There, ³He occurs at a ratio of 0.2 parts per million of ⁴He and, according to David O’Connor, a nuclear engineer at General Electric (GE) Co, can easily be separated from ⁴He by gaseous diffusion. O’Connor estimates that a “fair-sized” extraction plant would provide 5000-10 000 liters per year. Industry cost estimates provided to DOE last year for such a plant were in the “tens of millions,” he says.

For more than a year, US and Canadian officials have been discussing the use of ³He stored at an Ontario nuclear power plant. Ontario Power Generation (OPG) has been filtering tritium from heavy-water reactors at a complex near Toronto since 1990 and now filters it from 16 CANDU (Canada deuterium uranium) reactors in Ontario. Steve Fetter, assistant director of the White House Office of Science and Technology Policy, estimated that 20 000 liters of ³He could be separated annually from OPG’s tritium storage beds for three years, and 10 000 liters per year could be extracted for the following seven years. At a 22 April US House subcommittee hearing, Brinkman said feasibility and cost studies will be completed in the fall.

Canada offers the greatest near-term potential for more ³He, since it has 22 heavy-water reactors, half the global total. But OPG operates the world’s only heavy-water tritium separation plant. The recovery of ³He alone is unlikely to justify the expense of tritium removal, Fetter says, although other nations, including South Korea, Argentina, and China, may well decide, as OPG did, to remove tritium for environmental reasons.

In recent years, scientific users of ³He were increasingly elbowed out by the burgeoning needs of DHS and DOE for neutron detectors. The two departments have equipped US and foreign ports, border crossings, and airports with hundreds of radiation portal monitors to detect surreptitious shipments of weapons-usable nuclear materials in cargo and baggage. The resulting spike in demand occurred as the US stockpile of tritium shrank in response to the steep decline in the numbers of nuclear weapons. At one 2009 interagency meeting, a DOE official noted that two-thirds of the ³He that had accumulated over 40 years was dispensed in only six years.

The price of ³He skyrocketed as the full extent of the shortage became apparent. As recently as a year ago, a liter cost less than $100. But Giorgio Frossati, president of the Dutch dilution refrigerator manufacturer Leiden Cryogenics, says he recently paid $2150 per liter for 50 liters. The material’s origin wasn’t disclosed to him, he said, but it “could very well be from Russia.” US customers fortunate enough to have DOE accept their application can still get the material at $450 per liter, he says, a situation that is “unfair towards the non-US scientists.” But some US customers have been unable to get the gas they need, and others have been told to wait until next year. “You can imagine that a young scientist with starting money who must show results on a short term will be in a very difficult situation,” Frossati laments.

Brinkman told lawmakers that customers are currently paying $350-$400 per liter. He admitted there were reports of higher prices, but none, he said, came close to $1000 per liter. Brinkman blamed the sudden shortage on Russia’s abrupt withdrawal from the ³He market, which he said had occurred late in 2008. Russia, the only supplier other than the US, had sold an average of 25 000 liters annually in the US from 2004 to 2008, but it has provided none since. No one seems to know why, though there have been suggestions that Russia may be using the gas in portal monitors to equip its ports and nuclear facilities.

Representative Brad Miller (D-NC), chair of the House subcommittee, upbraided DOE and DHS for failing to see the shortage coming. He said the two agencies should have recognized years ago that “it would be a disaster to base radiation-detecting equipment on helium-3 technology.”

Even research related to national security has been caught up in the crunch. In a 16 April letter to Miller, Lawrence Livermore National Laboratory scientist Darin Kinion said he’s been waiting for seven months for a response to his request for 23 liters of ³He required to operate the dilution refrigerator needed for his quantum computing project. Sponsored by the Intelligence Advanced Research Projects Activity, the project involves experiments at a temperature of just a few millikelvin. “Working on an intelligence-backed activity at a National Laboratory, I am a bit surprised at the trouble I am facing from the Department of Energy,” Kinion wrote. Janis Research Co, which built his dilution refrigerator, has loaned him some ³He as a stopgap. But he said Janis doesn’t have enough to loan it to every customer.

Northwestern University physics professor William Halperin told the House hearing that his continued inability to get 20 liters for his dilution refrigerator imperils his NSF grant. “Should Janis and other companies stop providing refrigerators, low-temperature science will end,” Halperin warned. Brinkman, however, said the interagency task force had approved the full 1000 liters that cryogenics users had requested in fiscal year 2010. He added that it may be several months before the supply and demand situation stabilizes.

A total of 60 000 liters of ³He has been used to date for neutron tubes that equip about 1300 portal monitors for detecting radioactive materials at US ports, border crossings, and airports, according to Richard Kouzes, a fellow at Pacific Northwest National Laboratory. Another 1000 portal monitors are in use elsewhere around the world, many of them installed through DOE’s “second line of defense” program to find illicit nuclear materials prior to shipment to the US. In addition, multiple agencies have been stocking up on handheld and backpack radiation detectors for battlefield and civilian use. All are equipped with ³He-filled tubes. Overall, security-related neutron detection has accounted for about one-third of demand in recent years.

Radiation portal monitors are the biggest user of ³He, since a single one contains anywhere from 8 to 100 liters, says Thomas Anderson, a product line manager with GE Energy. GE manufactures both the tubes containing ³He and portal monitors and other radiation-detection devices.

Thousands more neutron detectors were proposed to be deployed in a second-generation portal monitor known as the advanced spectroscopic portal (ASP) system. Aimed at curtailing the high rate of nuisance alarms that occur when everyday slightly radioactive materials like ceramics and cat litter pass through today’s portals, the ASP system would require an estimated 200 000 liters of ³He, Miller stated. At that level, portal monitors alone would have constituted 80% of future demand, according to Brinkman. Miller voiced his astonishment that the Domestic Nuclear Detection Office (DNDO) hadn’t verified the availability of adequate ³He supplies.

Procurement of ASP monitors has been pushed back by several years due to performance problems unrelated to ³He, and William Hagan, acting director of the DNDO, assured lawmakers that the agency has enough ³He to meet its needs through at least September 2011. Officials from DOE’s nonproliferation program also have informed the interagency task force that the program can make do with its existing supply until then.

Demand for neutron detectors in scientific applications also has taken off, nowhere more so than in neutron scattering. As many as 1000 neutron detectors are required for some of the neutron scattering experiments planned for the $1.4 billion SNS, said GE’s Anderson. Although DOE has already set aside 58 000 liters of ³He for the SNS, the facility wants another 26 000 liters by 2015. The interagency task force has said that the numerous other large neutron scattering sources that are under construction or in development will need to fend for themselves: “The US can no longer be the major supplier satisfying these needs,” Brinkman said.

Ronald Cooper, detector team leader at the SNS, said his own survey of large neutron scattering facilities around the world yielded a projected demand totaling 125 000 liters of ³He through 2015. Some of the biggest wish-list items were 21 000 liters for the China SNS, 16 000 liters for the neutron source at the Japan Proton Accelerator Research Complex, and 14 556 liters for the Los Alamos Neutron Science Center. But Cooper said the neutron science community is well aware that such volumes won’t be available. Alternatives to ³He for large detector arrays are being “actively pursued” by 10 research groups around the globe, he said, with boron-10-lined detection tubes and scintillator arrays being the “two main thrusts.”

The two approaches offer the greatest opportunity for alternatives in security applications as well. GE expects to begin selling portal monitors that use ¹⁰B neutron-detection tubes later this year, says Anderson. Gaseous boron trifluoride is both corrosive and caustic, so GE opted to coat the insides of the tubes with boron metal and fill them with an inert gas. Although ¹⁰B has a lower sensitivity to neutrons than ³He does, GE will still be able to fit the new tubes within the relatively large housings of its current line of portal monitors. But Anderson says alternatives will be far more difficult for such applications as pager-sized or handheld neutron detectors, which use as little as 0.1 liter of ³He. For those uses, he says, “We’re going to have to do a lot more work and redesign [with] boron-10 in order to achieve [³He] kind of sensitivity.”

Less-developed alternative technologies are lithium-6-loaded glass fibers and ⁶Li-coated plastic fibers. Since a neutron lacks charge, GE’s O’Connor notes, detecting one requires a reaction that produces a charged particle. And only a handful of isotopes will do that: ³He, ⁶Li, ¹⁰B, gadolinium-157, uranium-233, uranium-235, and plutonium-239. DOE has also been urging users to recycle the ³He that may be sitting around in outmoded instruments.