1911
Ruff and Heinzelmann create the first uranium hexafluoride sample
Otto Ruff and Alfred Heinzelmann successfully synthesized uranium hexafluoride (UF6), the first stable
gaseous uranium compound. This discovery paved the way for large-scale enriched uranium production through processes like gaseous
diffusion and is the primary long-term nuclear fuel for the ACE Engine.
1938
Hahn and Strassmann discover nuclear fission
Otto Hahn and Fritz Strassmann discovered nuclear fission by bombarding uranium with slow neutrons and observing
the production of barium among the reaction products. Unlike previous neutron bombardment experiments, which resulted in only small
changes in the nuclei for most elements, uranium split into two nearly equal parts – revealing the enormous energy potential of
nuclear fission.
1942
Chicago Pile-1 achieves criticality and is the first nuclear reactor
On 2 December 1942, a team led by Enrico Fermi at the University of Chicago successfully achieved the world's
first self-sustained nuclear fission chain reaction. The Chicago Pile-1 reactor used natural uranium in both solid metal and oxide
form as fuel, with graphite bricks as the neutron moderator. This milestone demonstrated that nuclear fission could be harnessed in
a controlled manner, laying the foundation for nuclear power and future advanced reactor concepts like the ACE Engine.
1945
Los Alamos Dragon reactor produces the first nuclear pulse
In 1944, Otto Frisch, now regarded as the father of pulsed reactors, conceived of a reactor capable of sustaining
a prompt neutron supercritical chain reaction lasting only 1/100 of a second. During a design review, Richard Feynman likened the
concept to, “tickling the tail of a sleeping dragon.” The Dragon reactor operated by dropping a cylindrical slug of enriched uranium
hydride through a slightly subcritical annulus of the same material to produce a nuclear pulse. This experiment provided vital insight
into the dynamic behavior of nuclear chain reactions and generated essential experimental data for multiphysics simulations of
criticality excursions.
1945
Oak Ridge K-25 goes online and is the first gaseous diffusion plant
The massive four-story, U-shaped K-25 building at Oak Ridge – half a mile long and 1,000 feet wide –
was the largest in the world at the time of construction. K-25 pioneered industrial-scale uranium enrichment by forcing gaseous
uranium hexafluoride (UF6) through a porous barrier. This achievement not only enabled the sustained production of
enriched uranium for decades but also demonstrated safe and effective handling of UF6, establishing the engineering foundation
for its role as the long-term fuel for the ACE Engine.
1953
Kerner publishes the first paper on, “the possible use of gaseous fissionable materials in an engine of the internal
combustion engine type”
In 1953, Edward Kerner submitted the first known paper proposing the use of gaseous nuclear fuel in an internal
engine configuration. He emphasized key advantages of the concept, including the relatively small size, high thermal efficiency, and
the elimination of heat transfer limitations inherent in solid-fuel reactors. Kerner's vision provided an early scientific basis for
nuclear internal engine concepts, ultimately inspiring advanced gaseous-fuel reactor designs such as the ACE Engine.
1957
USSR experimental reactor achieves the first critical assembly using continuously circulating gaseous nuclear fuel
On 9 August 1957, a Soviet experimental reactor achieved the world's first critical assembly using continuously
circulating gaseous uranium hexafluoride (UF6). This milestone demonstrated the feasibility of sustaining a controlled
chain reaction with gaseous UF6. The experiment underscored potential economic benefits across the fuel cycle, numerous
inherent nuclear safety advantages, and broad energy applications. The Soviet team concluded that, “there are no insurmountable
obstacles for developing nuclear power plants with circulating UF6."
1957
Shippingport Atomic Power Station begins commercial operation and is the first atomic electric power plant
On 2 December 1957, exactly 15 years after Chicago Pile-1 achieved criticality, the Shippingport Atomic Power
Station in Pennsylvania began operation and is the world’s first full-scale commercial nuclear power plant. It supplied
approximately 60 MW of electricity to the Pittsburgh area, marking the transition of nuclear fission from experimental science to
practical energy production.
1966
Western New York Nuclear Service Center goes online and is the first US commercial reprocessing facility
In 1966, the Western New York Nuclear Service Center in Ashford, New York began operation and is the first
US commercial spent nuclear fuel reprocessing facility. The plant was supported by New York State, which had embraced the Atomic
Energy Commission's privatization initiatives of the 1950's and established the Office of Atomic Development in 1956. Under
10 CFR Part 50, Nuclear Fuel Services was licensed as the operator and the New York State Atomic Research and Development
Authority was licensed as the owner. These regulations remain in effect today.
1967
Idaho Cavity Reactor Critical Experiment achieves criticality using gaseous nuclear fuel in a cylindrical cavity
On 17 May 1967, the Idaho Falls Cavity Reactor Critical Experiment (CRCE) achieved criticality using gaseous
uranium hexafluoride (UF6) in a cylindrical cavity surrounded by a heavy water reflector region. Sponsored by NASA, the
CRCE explored the possibility of developing high specific impulse nuclear rockets. The experiments successfully validated reactor
design calculations and demonstrated the feasibility of controlled chain reactors using gaseous nuclear fuel.
1969
Idaho Spherical Gas Core Reactor achieves criticality using gaseous nuclear fuel in a spherical cavity
In 1969, the Idaho Falls Spherical Gas Core Reactor performed criticality experiments using gaseous uranium
hexafluoride (UF6) in multiple spherical configurations. Sponsored by NASA, the experiments provided benchmark results
for a nuclear rocket concept. The reactor produced valuable experimental data for validating one-dimensional reactor codes and
further advanced the study of gaseous-fuel reactor systems.
1976
Los Alamos Plasma Core Assembly achieves critically using continuously circulating gaseous nuclear fuel
In 1976, the Los Alamos Plasma Core Assembly (PCA) achieved criticality using static and circulating flow
configurations of gaseous uranium hexafluoride (UF6). Following the abrupt cancellation of NASA’s Rover Program in
1972, research beginning in 1974 shifted toward applying high-thrust, high-specific-impulse space nuclear propulsion concepts to
meeting terrestrial energy needs. The PCA experiments were successful, demonstrating many of the components later incorporated
into the ACE Engine nuclear power supply system.
1980
US Department of Energy publishes its first report and praises the gaseous reactor uranium utilization and
nonproliferation attributes
In 1980, the newly formed US Department of Energy released its first major report, Nuclear Proliferation
and Civilian Nuclear Power: Report of the Nonproliferation Alternative Systems Assessment Program (DOE/NE-0001). Among the reactor
concepts evaluated, the gaseous core reactor scored the highest for uranium utilization and was recognized for numerous proliferation
resistant features. Interesting, the authors appeared unaware of earlier gaseous reactor research conducted by both the USSR and
NASA.
1991
Lawrence Livermore initiates research on internal nuclear engines as an economic clean energy solution
In 1991, the Lawrence Livermore National Laboratory published several articles exploring a family of
nuclear-powered internal engines designed to dramatically reduce the cost of electricity. Conducted at the end of the Cold War,
this research highlighted the US strengths in multiphysics simulations and advanced engineering experiments, positioning gaseous
nuclear internal engines as a safe and economical clean energy solution.
1995
Science-Based Stockpile Stewardship program begins a new era of nuclear engineering in the United States
In 1995, the US Department of Energy initiated the Science-Based Stockpile Stewardship program,
“to ensure the preservation of the core intellectual and technical competencies of the United State in nuclear weapons.”
The program set a new standard for developing and applying multiphysics predictive simulation capabilities, validated through
a wide range of experimental facilities. This effort has since paved the way for the rapid design and advancement of modern
nuclear technologies, including the ACE Engine.
