Chicago Pile-3 (CP-3) was the world's first

heavy water reactor A pressurized heavy-water reactor (PHWR) is a nuclear reactor that uses heavy water ( deuterium oxide D2O) as its coolant and neutron moderator. PHWRs frequently use natural uranium as fuel, but sometimes also use very low enriched uranium. The ...

. One of the first

research reactors Research reactors are nuclear fission-based nuclear reactors that serve primarily as a neutron source. They are also called non-power reactors, in contrast to power reactors that are used for electricity production, heat generation, or mari ...

, it was built in 1943 near Palos Hills, Illinois, original site of

Argonne National Laboratory Argonne National Laboratory is a science and engineering research national laboratory operated by UChicago Argonne LLC for the United States Department of Energy. The facility is located in Lemont, Illinois, outside of Chicago, and is the l ...

. Joining CP-1/CP-2, it first went critical on 15 May 1944, and was at first used in the experimental physics work of the

Metallurgical Laboratory The Metallurgical Laboratory (or Met Lab) was a scientific laboratory at the University of Chicago that was established in February 1942 to study and use the newly discovered chemical element plutonium. It researched plutonium's chemistry and m ...

for the

Manhattan Project The Manhattan Project was a research and development undertaking during World War II that produced the first nuclear weapons. It was led by the United States with the support of the United Kingdom and Canada. From 1942 to 1946, the project w ...

. After its useful research-life ended, it was deactivated in 1954. CP-3 was initially fueled with

natural uranium Natural uranium (NU or Unat) refers to uranium with the same isotopic ratio as found in nature. It contains 0.711% uranium-235, 99.284% uranium-238, and a trace of uranium-234 by weight (0.0055%). Approximately 2.2% of its radioactivity comes ...

and used heavy water as a neutron moderator. In January 1950, the reactor was dismantled due to suspicion of corrosion of the aluminum cladding that surrounded the control rods. The reactor was rebuilt and redesignated CP-3′ (CP-3 prime). It was restarted in May 1950 and operated until 1954. The reactor was authorized to operate up to 300 kilowatts. The two versions of the reactor were used to study physics, separate fission products, recover tritium from irradiated lithium, and study radionuclide metabolism in laboratory animals. After the reactor was decommissioned, the fuel and heavy water were shipped to the

Oak Ridge National Laboratory Oak Ridge National Laboratory (ORNL) is a U.S. multiprogram science and technology national laboratory sponsored by the U.S. Department of Energy (DOE) and administered, managed, and operated by UT–Battelle as a federally funded research an ...

. Pipes, valves, and building debris were placed in the reactor's containment shell, which was then filled with concrete. The shell was buried on the site in a deep pit. The site, now known as the

Site A/Plot M Disposal Site The Site A/Plot M Disposal Site is located within Red Gate Woods and situated on the former grounds of Argonne National Laboratory and its predecessor, the University of Chicago Metallurgical Laboratory in Cook County, Illinois and is part of the ...

, sits within Red Gate Woods, part of the Cook County Forest Preserve system. A historical marker commemorates the site of CP-3 and its sister reactor CP-1/CP-2.

See also