Inventing the Future
ITER is bringing the reality of fusion power closer than ever before
Fusion energy—clean, plentiful power from readily available resources—has long seemed just out of reach. Now, increased interest in several fusion-related research projects is bringing the reality of fusion power closer than ever before.
Illustration of ITER's plasma vessel.
The most prominent of these efforts is the ITER project, an international collaboration of scientists and engineers assembled to build an experimental fusion reactor. ORNL's experience in shepherding the mammoth Spallation Neutron Source project to completion, combined with its decades of experience in fusion research, uniquely qualify ORNL for a leading role in the ITER partnership. The laboratory is playing a key role in ITER's construction and in meeting the ever-evolving research and development needs of this project that defines the leading edge of twenty-first-century technology.
Stan Milora, head of ORNL's Fusion Energy Division, notes that much of the work his organization has performed over the last few years involved anticipating technologies and materials needed to build and operate not only ITER, but also its near-term successors. Scheduled to be completed in the fall of 2019, ITER will produce a superheated fusion plasma, as well as 500 MW of thermal power. However, ITER's heat will not be used to demonstrate power production. The task of proving the viability of fusion power for commercial use will be left to one of ITER's successors, known as DEMO, a demonstration fusion power reactor that is expected to churn out several hundred megawatts of electricity.
Extreme materials challenge
Many of the challenges faced by ORNL's fusion researchers involve developing exceptionally durable materials for use in ITER and in other proposed fusion research facilities. Milora says these materials must be able to withstand the unforgiving environment inside a fusion reactor (constant neutron bombardment and contact with 150 million degree plasma); convert heat of the fusion reaction into electricity; and use neutrons created by the fusion reaction to breed more tritium, which, along with deuterium, fuels the ongoing reaction.
Scientists find themselves in a bit of a quandary, however, when it comes to testing these materials. "The best place to test materials designed to withstand a fusion environment is in the fusion environment itself," Milora says. Unfortunately, no such test facility currently exists. Two proposed facilities are expected to enable researchers to test materials under reactor conditions.
The first of these facilities, the Plasma Nuclear Materials Test Station, would simulate the conditions at the outer reaches of the fusion plasma. Unlike the circulating, self-sustaining plasma of a fusion reactor, the PMTS would continuously generate a column of plasma using radio waves. However, the effect of the plasma on materials would be very similar to that of a fusion reactor.
The second facility, the Fusion Nuclear Sciences Facility, would be a true, small-scale fusion research reactor. The primary purpose of the FNSF would be to test the performance of lithium-containing components, called "blankets," embedded in the walls of the reactor. The blankets will be bombarded by neutrons produced by the fusion reaction. This shower of neutrons will gradually transform the lithium into tritium, which will be recovered and used, along with deuterium, to fuel the reactor. The blankets will also be used to convert the energy of the neutron bombardment into heat, which will then be used to generate electricity. The production of blankets that can tolerate a fusion environment for long periods of time will require new, highly durable, radiation-resistant materials. "That's another aspect that will be investigated at this facility," Milora says.
At ORNL, this materials development work is managed by Roger Stoller of the laboratory's Materials Science and Technology Division. "Research focused on developing tough, radiation-resistant structural materials has been a mainstay of the U.S. fusion materials effort for many years," Stoller says. "New steels and ceramic composites that are being considered for use in DEMO have been developed in collaboration with Japanese scientists." Much of this research has been conducted at ORNL's High Flux Isotope Reactor—a small nuclear fission reactor where materials can be exposed to intense neutron bombardment. This ongoing research will be used to identify materials for use in the design phase of DEMO, although additional studies of these materials using higher energy neutrons may be required to approximate the conditions inside a fusion reactor.
Milora explains that one of the primary drivers for building the FNSF is to expose materials and associated components to neutron bombardment and fusion plasma at the same time. "We could pretreat samples with neutrons in the HFIR and then expose those samples to plasma in the PMTS," he says. "In fact we will do this to guide the selection of the plasma-facing components in the FNSF. However, once the FNSF is completed, we will be able to do both simultaneously under conditions that closely resemble those in DEMO."
A practical option
Despite the magnitude of the materials challenge and the need to develop two world-class research facilities along the way, Milora is positive about the prospects for both ITER and for fusion energy in general. "Fusion power has many advantages over traditional means of generating power," he says. "It's clean; it produces no greenhouse gases; the technology will be shared with all of ITER's international partners; and its primary fuel, deuterium, comes from seawater, which we have in abundance."
"Once ITER and DEMO demonstrate the practicality of fusion reactors as well as that of fusion power production," Milora says, "generating power with a fusion reactor will be a viable option for utility companies around the world—on a par with nuclear, coal or natural gas power production—and with fewer drawbacks."—Jim Pearce