Plutonium-239 (Pu-239) is a nuclear fuel source that should play an important role in a sustainable, rapidly growing nuclear power enterprise. It is a natural byproduct that is created inside every fission reactor using uranium fuel. It is fissile with characteristics that are similar to U-235, the fissile material that provides most of today’s nuclear power.
During the 1960s and into the 1970s, energy visionaries spoke and wrote about a coming Plutonium Economy that would gradually replace the existing Hydrocarbon Economy and give human society an inexhaustible fuel source.
Thirty years from now this same man-made element can be expected to be a predominant energy source in our lives.
… On earth we expect that plutonium will be the fuel for over 50% of our total electrical energy needs.
…Plutonium will become the basis for our electric power generation and therefore be a prime factor in our total economy which is dependent on electrical energy.Remarks by Glenn T. Seaborg, Chairman of the U.S. Atomic Energy Commission. “The Plutonium Economy of the Future” Oct 5, 1970
It’s easy to imagine that people whose wealth and power came from the Hydrocarbon Economy weren’t thrilled about the near-term prospect of having their comfortable lives disrupted by a powerful new competitor.
A sustained campaign aimed at demonizing plutonium began sometime in the early 1970s. Plutonium has been called the most toxic substance known to man. Some people opposed to its use have also claimed that it was named after Pluto, “the god of the underworld” due to its hellish nature.
Aside: Plutonium was named after Pluto, the dwarf planet that is near the edge of our solar system. The selection continued the pattern established by the names chosen for uranium (Uranus) and neptunium (Neptune). End Aside.
The Pu demonization campaign has been largely successful, though there are several countries that ignored the US-based effort to discourage the beneficial use of plutonium.
Most of the organized and open opposition to using plutonium is concerned about using the material in routine trade because they believe that carefully locking up the raw material needed for nuclear weapons is the best way to halt the proliferation of those weapons.
Discouraging the use of plutonium as fuel in civilian nuclear power reactors has long been stated policy of the US nuclear non-proliferation community. France, China and Russia haven’t paid much attention to the discouragement while other nations, including South Korea, India and Japan have expressed their desire to move forward with used fuel recycling programs that recover plutonium and use it for reactor fuel.
Those countries recognize an important truth – using plutonium in nuclear power reactors helps to prevent nuclear weapons proliferation. Every gram of plutonium that is stored inside a nuclear reactor will not be available to use in a nuclear weapon. Any remaining risks associated with the additional handling and transportation of plutonium and fabricated fuels containing plutonium can be addressed in modern systems that include safeguards mechanisms as part of the design.
Substitute for U-235 in advanced reactor fuel (HALEU alternative)
Smaller and advanced reactors work best when using fuels containing higher fissile material concentrations. They have a smaller critical mass, achieve longer fuel cycles and produce less highly activated waste material. Internet word searches for the acronym HALEU (high assay low enriched uranium) show a dramatically increasing frequency.
Aside: HALEU is a uranium fuel with a concentration of between 10% and 20% fissile material (U-235). Fuel material with a U-235 concentration between 5% and 10% is called LEU+ while conventional commercial fuel material is simply called LEU. End Aside.
Reactor developers, advocates, and politicians often discuss the importance of improved fuels with a focus on HALEU. They worry about the lack of sufficient capacity to produce the required material outside of a few unfriendly nations. (Russia, China and Iran all produce HALEU.) They are planning to spend billions of dollars creating the industrial capacity to produce, store, transport HALEU as well as the capacity needed to manufacture finished fuel products. Opponents have seized on the HALEU supply challenge as another talking point in their effort to minimize the use of nuclear energy.
While HALEU-related investments are important and should not be delayed, even an unlimited budget cannot overcome certain physical delays. There is little wiggle room between projected completion dates for demonstration reactors that need substantial quantities of HALEU and the operational dates for the industrial capacity to produce as much HALEU as needed. In Dec 2022, TerraPower announced that limited supplies of HALEU will delay their Natrium project by 2 years.
From a technological point of view, it’s not difficult to use Pu-239 as a substitute for U-235 as the fissile isotope in metal alloy fuels. As of June 2018 there were at least 7 fast reactors that planned to use metal alloy fuels under development in the US. The Experimental Breeder Reactor program and the continuing research conducted at the Fast Flux Test Facility conducted extensive testing of ternary fuel, a three-component metal alloy consisting of U-238, Pu-239 and Zr (U-Pu-Zr).
The US has an inventory of several dozen tons of Pu-239 that has been declared to be surplus from the nuclear weapons program. While the supply is limited, that material could be readily alloyed with either natural or depleted uranium to provide a fuel supply that would be sufficient for several fast reactors during the time that HALEU capacity is being developed and constructed.
Several US allies, notably the UK and France have even larger inventories of separated Pu that could be securely stored inside newly constructed operating nuclear power plants.
Plutonium doesn’t have to be limited to metal alloy fuels for fast reactors. It can be the fissile isotope in molten salt reactors and may be suitable for use in the tiny kernels of actinides that are the particles in coated particle fuels (TRISO). Pu-239 would work well in Lightbridge’s alloy fuel for light water reactors.
Changing the philosophical and political treatment of plutonium will require a significant political effort. Several of the reactor designers that could most immediately benefit from using plutonium as an integral part of their future fuel cycle plans believe that the lift is too hard or too politically risky for them to undertake.
As a nuclear energy advocate and investor, I believe it’s a worthwhile endeavor with reasonable chances of success. It’s easier to change minds than to change physics.
Disclosure: Lightbridge is in my personal portfolio. Nucleation Capital is an investor in several advanced reactor companies whose products can beneficially use Pu-239 as fissile material.