Phoenix Rising

I attended David LeBlanc's lecture at ORNL yesterday (May 18, 2010).

Jess Gehin, our host, took the opportunity to do a set of show-and-tell presentations about molten-salt-related programs at ORNL. It is safe to say, from what I saw yesterday, that the phoenix is rising at ORNL.

David's talk was exciting. David has been in contact with retired ORNL MSR researcher Dick Engel. Dick participated in the ORNL 1980 fling at getting backing for Molten Salt Reactor development, the DMSR. (For documentation of the DMSR concept, see here, here, here and here.) David notes in his Mechanical Engineering article,

The “D” stands for “denatured”—the uranium in the reactor contains too much U-238 to be useful in weapons. The concept also dispenses with processing the salt to remove fission products; the same salt is used throughout the 30-year life of the reactor with small amounts of low enriched uranium added each year to keep the fissile material constant. The amount of uranium fuel needed—about 35 metric tons per GWe year—is only one-sixth of what is used by a pressurized water reactor. . . .

The amount of fissile material needed to start new reactors is also very important, especially in terms of a rapid fleet expansion. The 1 GWe DMSR was designed for 3.5 metric tons of U-235 (in easy-to-obtain low-enriched uranium) which can be lowered if uranium costs go up. A new PWR, by contrast, needs about 5 metric tons, whereas a sodium-cooled fast breeder such as the PRISM design requires as much as 18 tons of either U-235 or spent fuel plutonium. Any liquid fluoride reactor can be started on plutonium as well, but this turns out to be an expensive option, since removing plutonium from spent fuel costs around $100,000 per kilogram.

Reviewing the DMSR from a 2010 perspective, LeBlanc finds many advantages.

The DMSR features a larger, lower power density graphite core than other MSR breeder concepts. So while the graphite would last a full 30 years, the DMSR would still be only a fraction of the size of gas-cooled graphite reactors and would not require a pressure vessel. In fact, the simple thin-walled DMSR containment vessel would be wider but much shorter than those of PWRs and BWRs. The construction of the reactor containment building offers savings as it does not need the huge volume and ability to deal with steam pressure buildup needed for LWRs or CANDU reactors.

The overall thermal efficiency of the plant would be quite high. With a salt outlet of 700 °C and using the latest ultra-supercritical steam cycles or gas Brayton cycles, efficiencies close to 50 percent would be possible.

While up-to-date cost estimates for a molten salt reactor are not available, it is quite simple to see the potential overall advantages. The DMSR needs no capital and O&M costs for fuel processing, and the superior nature of the salts as coolants results in far smaller heat exchangers and pumps. Building and fabrication costs should be lower than conventional nuclear plants, since the design doesn’t put the same sort of stresses on the system.

Among the advantages LeBlanc points out, the potential to lower nuclear costs is the most conspicuous.

It is not unreasonable, then, to assume that capital costs could be 25 to 50 percent less for a simple DMSR converter design than for modern light water reactors. Compared to fast breeders such as the integral fast reactor, which rarely try to claim low capital costs, the DMSR should be even better.

In his ORNL talk, LeBlanc noted the possibility of simply eliminating a Thorium blanket for the DMSR entirely, and running the DMSR as a pure uranium-fuel cycle reactor. While the Uranium fuel cycle DMSR would offer less sustainable technology than the LFTR, it would be a very strong competitor for the current generation of Light Water Reactors. It would offer a very high level of safety, proliferation resistance and nuclear waste control, at a lower cost that current light-water reactor technology. Actinides, the big problem in nuclear waste, could be separated from reactors salts, either periodically or when the reactor is decommissioned. The recovered actinides can be returned to the core of a DMSR where they will be burned as nuclear fuel. Other fission products will essentially disappear after 300 years, if reactor managers chose to treat them as waste, but this is unlikely. Fission products present in "spent nuclear fuel" represent a potential source of valuable materials and noble gases, and the DMSR concept opens the door for the recovery of these minerals.

LeBlanc concluded his Mechanical Engineering essay by declaring,

Molten salt or liquid fluoride reactors will also take a large effort, but every indication points to a power reactor that will excel in cost, safety, long-term waste reduction, resource utilization, and proliferation resistance. As we move deeper into a century that portends financial instability, political uncertainty, environmental catastrophe, and resource depletion, this technology is too valuable to once again place back on the shelf.

Nuclear Green concurs with this view. The DMSR represents a technology that is doable in the year 2010. The technology required to build it exists now, thus developers would not be saddled with huge R&D costs, and and the technological uncertainties that would confront LFTR development. The DMSR would represent a transition, between the traditional solid fuel reactors, and the sustainable LFTR technology. The Phoenix is beginning to rise from its ashes.