More than 85,000 metric tons of spent nuclear fuel (SNF) has accumulated in America. Approximately one percent of that is composed of isotopes heavier than uranium (called transuranics), mostly various isotopes of plutonium. When struck by "fast" neutrons (kinetic energy greater than 0.1 MeV), the relative probability of the neutron causing fission as opposed to simply being absorbed goes up. Moreover, a fast neutron causing fission releases more neutrons in the reaction than a "slow" neutron causing fission. The 850 or so metric tons of transuranics accumulated in American SNF alone represents energy equivalent to 1% of the global natural gas reserves, without taking into account the enormous potential of breeding.


Plutonium is universally dreaded because it is a weapons-usable material that is generated whenever naturally-occurring isotopes of uranium are used in a reactor. Extracted plutonium from SNF is not an efficient weapons material, but when extracted from SNF, it still represents a real threat in the hands of a dedicated antagonist. Furthermore, several tons of weapons-grade plutonium from dismantled weapons are stranded in the U.S. after the failed attempt to build a mixed-oxide fuel fabrication facility in South Carolina. The only way to permanently rid of this plutonium is with the neutrons in a reactor, from whence the plutonium came.



Loading plutonium into a reactor with uranium restarts the cycle of creating plutonium and the proliferation risks that come with it. Uranium-233, on the other hand, created in a reactor from thorium is also fissile and a possible weapons material. But unlike plutonium, it is self-protecting since it is invariably contaminated with isotopes that decay by producing powerful gamma rays. Even if some suicidal bomb maker were to expose him/herself to U-233, the presence of the gamma rays means that its diversion can be easily detected anywhere in the world. Simultaneously consuming plutonium and producing uranium-233 should be the goal.


To alleviate the burden posed by weapons-grade plutonium and to prevent a new stewardship problem from SNF-retrieved plutonium, Curio is developing an integral, mass-manufacturable, fast reactor of fully modular construction that is walk-away safe. The mission is to make nuclear reactors affordable, consume the plutonium stockpiles of America to produce clean and affordable energy, and to once and for all, close the current LWR fuel cycle and lead a transition to next-gen thorium reactors that can be globally deployed.