1 - Navy Nuclear Design
Bret Kugelmass: Tell me about your experiences in the Navy designing reactors.
Ed Pheil: In 1984, Ed Pheil started at the Knolls Atomic Power Lab training Navy students at the Kesselring Site prototypes. He then moved into design, spending the remainder of his career designing nuclear submarines, aircraft carriers, and for a time, spacecraft to go to Jupiter. Pheil supported all Navy reactors at the time and multiple new designs, such as Virginia-class and Ohio-class. The Navy utilizes pressurized water reactors (PWR), but has always been looking for something that would be more of an advanced reactor to provide better performance. However, changing to different fluids and different temperatures also requires fuel redesign, which was outside the Navy budget. Submarine reactors are much smaller than commercial reactors. They propel the ship and provide support for about 100 people. The commercial sector is interested in Navy nuclear personnel because they are used to startup, shutdown, and casualty drills on a regular basis, providing much more experience in variants. The Navy has two Naval nuclear laboratories: Bettis Atomic Power Lab and Knolls Atomic Power Lab. Teams at the labs work together on new design, maintenance of existing fleet, and decommissioning. Electric Boat, part of General Dynamics, and Huntington Ingalls run the shipyards where submarine building takes place. The Newport News Shipyard is involved in the AP-1000 construction. Electric Boat has the biggest experience in modular construction. Both companies have civilian arms that do work in the nuclear sector. Pheil spent a total of 32 years in the Navy.
2 - Reimagining the Nuclear Fuel Cycle
Bret Kugelmass: How many different types of reactors did you look at during your 32 years in the Navy?
Ed Pheil: During Ed Pheil’s 32 years in the Navy, he looked at about 20 different types of reactors, such as lead reactors, lithium reactors, molten salt reactors, and more. The future of energy is the uranium-plutonium cycle. All the spent fuel has 96% of uranium left in it; in reality, only 0.5% of the uranium extracted from the ground is being burned. All the depleted uranium is fuel too, in the right reactor. This requires a low cost fast reactor to close the fuel cycle. Elysium’s reactor is a molten salt fast reactor using chloride salt. The uranium is dissolved into the salt. Weapons-grade plutonium is diluted into spent nuclear fuel to make it non-weapons grade. This reduces the weapons risk while creating new fuel and eliminating spent nuclear fuel. This can be done with other fast reactors, but solid fuel is needed, which requires very clean uranium and plutonium. A liquid fuel doesn’t need to be cleaned up because there is only one step to convert it. While in the Navy, Pheil got bored of operating, starting, and maintaining water reactors. He knew the commercial industry had lost experience in building reactors and wanted to do something for the commercial industry to save nuclear power, leaving the Navy before he was eligible for retirement. Pheil’s undergraduate degree was in fusion and he reviewed that technology for practicality as well, but determined the molten salt reactor was the best technology. The biggest issues in the commercial industry were economics and nuclear waste.
3 - Molten Salt Reactor Design
Bret Kugelmass: How much impact does the anti-nuclear community have on the public, which has limited knowledge about nuclear?
Ed Pheil: Anti-nuclear communities typically drag out the reactor licensing and construction process. One of the reasons the AP-1000 died is because the process was drug out so long and the financing for construction was so large that the interest doubled the cost of the plant. A similar strategy is used in gas pipelines. One problem the nuclear industry has is that they don’t communicate their position very well. Publicity and media can be used to the benefit of the industry to explain to the public why the people that have the soapbox, the anti-nuclear community, are not correct. The number one priority of Elysium is to reduce cost, but other priorities include solve some of the political issues, spent fuel, reprocessing, and safety issues. Elysium’s design is a molten chloride salt fast reactor. Most salt reactors are starting up with high assay, low enriched uranium between 5-20% enrichment. Since there is currently none of that available in the U.S., Elysium went for plutonium and spent fuel because the U.S. has 61 tons of what the government considers weapons-grade waste plutonium. Fission products aren’t removed intentionally in the Elysium design, even though some fall out naturally, such as gases that bubble off when melted. The spent fuel will be split long ways, chopped into pieces, and poured into a molten salt vat. One of the components of the molten salt will react and grab all the oxides and precipitate out.
4 - Elysium’s Fuel Design
Bret Kugelmass: Is new plutonium added to the spent fuel dissolved in the molten salt to up the enrichment?
Ed Pheil: For the reactor startup fuel, raw plutonium, which is in excess in the U.S., is added to the molten salt after spent fuel is dissolved in it. After startup, plutonium doesn’t need to be added. It is not considered reprocessing because there are no separations of the fuel. The fission products don’t absorb all the neutrons since it is not a fast reactor. The Elysium reactor is a giant cylinder filled up with molten salt, without rods or moderators. A thermal reactor has a moderator in the core. The neutrons are born around 2 meV and are slowed down by the moderator to thermal where the cross-section is much higher and less fuel is needed to go critical. A fast reactor doesn’t slow the neutrons down as much and the reactor operates around 1 meV. Plutonium releases 3 neutrons per fission, compared to uranium-235 which releases 2.4 neutrons per fission. Plutonium-239 is fissile and will fission when introduced to a neutron. Plutonium-240 is fertile and has a high spontaneous fission probability, which inhibits the use of reactor-grade plutonium in weapons. Uranium fuel is not very expensive and there is excess supply. Nuclear fuel is one-third of the cost of operations. However, Elysium is using weapons-grade waste and storage is expensive.
5 - Strategy for Extending Reactor Lifetimes
Bret Kugelmass: What percentage of the fuel is used at the end of its lifetime?
Ed Pheil: The lifetime of the fuel is infinite. The liquid salt repairs itself five to six orders of magnitude faster than the radiation damages it. Every 40-100 years, fission products need to be removed and put back in the reactor. At the end of life of the reactor and there is too much radiation damage, the fuel could be disposed or put in another version of the reactor. The Elysium reactor is designed to continuously replace all the components. If the fuel is continued to be used, 99% of the fuel can be used. In a fast reactor, the cross-section is a lot lower and all the neutrons stay at high energy, so the flux must stay higher to keep the same fission rate. The neutrons go into the materials, hit the iron or nickel atoms, and knock them out of their lattice structure. Nickel creates helium and at high temperatures, helium migrates to the grain boundaries and allows cracking if there is build-up. Over a long period of time, materials creep. The reactor pressure vessel is expected to last 40 years. Leaving fuel in for 40-100 years assumes iso-breeding. Enough fuel is made to replace the fuel being consumed plus fission products. The Elysium reactor could also operate with high assay, low enriched uranium, but the cost of enrichment is very high.
6 - Commercialization Process for Elysium Reactor
Bret Kugelmass: What’s the total power output of the plant you envision?
Ed Pheil: The maximum megawatts electric for Elysium’s system is primarily set by grid size. A 10 MW thermal initial test reactors is planned for startup. A bill was just introduced in Congress that makes low assay, high enriched uranium available for advanced reactors, but Pheil also needs access to plutonium. The Nuclear Regulatory Commission (NRC) has said they can review a license for a molten salt reactor in one year. The reactor vessel has the same volume whether it is at 10 MW thermal or 3,000 MW thermal because the fissile content to be critical is the same. The other half of the fuel volume changes with power. Savannah River or Yucca Mountain would be potential sites, but Yucca Mountain won’t be ready in time. Savannah River has the weapons-grade plutonium and spent fuel can be shipped in. The heat exchanger and pump will probably be built for 500 MW and operated at 10 MW for the initial license. As soon as it is operating at 10 MW, Ed Pheil and Elysium would apply for a uprate license to something like 125 MW thermal. The Elysium molten salt reactor can also operate as a fast test reactor and an isotope production reactor. The core doesn’t need to be designed around the test cells; the test cells can be put anywhere in the core and more fissile is added to compensate for the absorptions. Elysium’s goal is to drive down cost with low pressure, low cost vessels. If the system gets a leak, it chemically bonds and freezes and gases are constantly released. The system operates at very high temperature and can operate at high or low efficiency. Instead of a four-and-a-half year fuel cycle, the fuel cycle is only limited by reactor vessel component replacement.