# Clarence Larson
**Clarence Edward Larson** (1909–1999), also written Clarence E. Larson, was an American chemist and nuclear administrator who devised uranium-recovery methods at the [Manhattan Project](https://www.edgepedia.org/manhattan-project)'s Y-12 Plant, directed [Oak Ridge National Laboratory](https://www.edgepedia.org/oak-ridge-national-laboratory) from 1950 to 1955, and served on the U.S. Atomic Energy Commission from 1969 to 1974.[1](https://nap.nationalacademies.org/read/10094/chapter/35) • [2](https://ahf.nuclearmuseum.org/ahf/profile/clarence-larson/) • [3](https://www.ornl.gov/content/ornl-directors) • [4](https://www.energy.gov/management/articles/history-atomic-energy-commission)
| Fact | Detail |
|---|---|
| Born | 1909, Minnesota[2](https://ahf.nuclearmuseum.org/ahf/profile/clarence-larson/) • [5](https://aspace.gmu.edu/resources/c0079) • [6](http://smithdray1.net/historicallyspeaking/2016/9-19-16%20Clarence%20Larson.pdf) |
| Died | February 15, 1999, aged 89[1](https://nap.nationalacademies.org/read/10094/chapter/35) • [7](https://www.nae.edu/29031/dr-clarence-e-larson) |
| Education | Chemistry degree, University of Minnesota; Ph.D., University of California, Berkeley, 1937[2](https://ahf.nuclearmuseum.org/ahf/profile/clarence-larson/) • [5](https://aspace.gmu.edu/resources/c0079) • [6](http://smithdray1.net/historicallyspeaking/2016/9-19-16%20Clarence%20Larson.pdf) |
| Known for | Direct peroxide precipitation process for recovering uranium at Y-12[2](https://ahf.nuclearmuseum.org/ahf/profile/clarence-larson/) • [8](https://ahf.nuclearmuseum.org/voices/oral-histories/clarence-larsons-interview/) |
| ORNL director | 1950–1955[2](https://ahf.nuclearmuseum.org/ahf/profile/clarence-larson/) • [3](https://www.ornl.gov/content/ornl-directors) |
| AEC commissioner | 1969–1974[1](https://nap.nationalacademies.org/read/10094/chapter/35) • [4](https://www.energy.gov/management/articles/history-atomic-energy-commission) |
| National Academy of Engineering | Elected 1973[6](http://smithdray1.net/historicallyspeaking/2016/9-19-16%20Clarence%20Larson.pdf) • [7](https://www.nae.edu/29031/dr-clarence-e-larson) |
## Early life and education
The Atomic Heritage Foundation gives his date of birth as September 20, 1909.[2](https://ahf.nuclearmuseum.org/ahf/profile/clarence-larson/) [George Mason University](https://www.edgepedia.org/george-mason-university) records his birthplace as Cloquet, Minnesota.[5](https://aspace.gmu.edu/resources/c0079) He earned a chemistry degree at the [University of Minnesota](https://www.edgepedia.org/university-of-minnesota) and completed a Ph.D. at the [University of California](https://www.edgepedia.org/university-of-california), Berkeley, in 1937.[2](https://ahf.nuclearmuseum.org/ahf/profile/clarence-larson/) • [5](https://aspace.gmu.edu/resources/c0079) • [6](http://smithdray1.net/historicallyspeaking/2016/9-19-16%20Clarence%20Larson.pdf) As a graduate student in biochemistry he studied the clotting of blood.[1](https://nap.nationalacademies.org/read/10094/chapter/35) • [6](http://smithdray1.net/historicallyspeaking/2016/9-19-16%20Clarence%20Larson.pdf) He devised a glass electrode for measuring the pH of flowing solutions.[1](https://nap.nationalacademies.org/read/10094/chapter/35)
He began experimenting with isotopes from Ernest O. Lawrence's Berkeley cyclotron as a graduate student and continued that research on the faculty of the College of the Pacific in [Stockton, California](https://www.edgepedia.org/stockton-california), where he became chairman of the chemistry department.[1](https://nap.nationalacademies.org/read/10094/chapter/35) • [6](http://smithdray1.net/historicallyspeaking/2016/9-19-16%20Clarence%20Larson.pdf) • [8](https://ahf.nuclearmuseum.org/voices/oral-histories/clarence-larsons-interview/)
## Manhattan Project
Larson joined Lawrence's team at Berkeley in July 1942.[2](https://ahf.nuclearmuseum.org/ahf/profile/clarence-larson/) • [8](https://ahf.nuclearmuseum.org/voices/oral-histories/clarence-larsons-interview/) In 1943 he moved to [Oak Ridge, Tennessee](https://www.edgepedia.org/oak-ridge-tennessee), as director of the technical staff of the Tennessee Eastman Corporation, which ran the Y-12 Plant until 1946.[1](https://nap.nationalacademies.org/read/10094/chapter/35) • [2](https://ahf.nuclearmuseum.org/ahf/profile/clarence-larson/) Y-12's calutrons separated uranium-235 electromagnetically from the more abundant uranium-238, and almost all of the uranium in the core of the [Hiroshima](https://www.edgepedia.org/hiroshima) bomb was separated there.[1](https://nap.nationalacademies.org/read/10094/chapter/35) • [6](http://smithdray1.net/historicallyspeaking/2016/9-19-16%20Clarence%20Larson.pdf)
His task was to recover the uranium that ended up on the walls and in the receivers of the calutrons.[2](https://ahf.nuclearmuseum.org/ahf/profile/clarence-larson/) • [8](https://ahf.nuclearmuseum.org/voices/oral-histories/clarence-larsons-interview/) In his own account, only about a tenth of the uranium vapor in a calutron was ionized, and the rest collected on the inside of the machine.[8](https://ahf.nuclearmuseum.org/voices/oral-histories/clarence-larsons-interview/) Uranium also buried itself in the stainless steel receivers, and the yield stayed low until Larson proposed copper surfaces from which it could be recovered.[1](https://nap.nationalacademies.org/read/10094/chapter/35) • [6](http://smithdray1.net/historicallyspeaking/2016/9-19-16%20Clarence%20Larson.pdf) Lawrence wanted the change made within a day, and Larson's team finished it in twenty-four hours.[1](https://nap.nationalacademies.org/read/10094/chapter/35) • [6](http://smithdray1.net/historicallyspeaking/2016/9-19-16%20Clarence%20Larson.pdf) • [8](https://ahf.nuclearmuseum.org/voices/oral-histories/clarence-larsons-interview/)
For uranium scattered through the machines, he developed a direct precipitation of uranium peroxide, carried out in double-walled vessels chilled with circulating brine to keep an otherwise unstable reaction under control.[6](http://smithdray1.net/historicallyspeaking/2016/9-19-16%20Clarence%20Larson.pdf) • [8](https://ahf.nuclearmuseum.org/voices/oral-histories/clarence-larsons-interview/) The method recovered the uranium in pure form in a single step.[2](https://ahf.nuclearmuseum.org/ahf/profile/clarence-larson/) • [8](https://ahf.nuclearmuseum.org/voices/oral-histories/clarence-larsons-interview/)
## Y-12 and Oak Ridge National Laboratory
After [Union Carbide](https://www.edgepedia.org/union-carbide) replaced Tennessee Eastman as Y-12's operator in 1946, Larson served as the plant's director of research and development and then as its superintendent, a post he held from 1948.[1](https://nap.nationalacademies.org/read/10094/chapter/35) • [2](https://ahf.nuclearmuseum.org/ahf/profile/clarence-larson/) • [6](http://smithdray1.net/historicallyspeaking/2016/9-19-16%20Clarence%20Larson.pdf) Under his supervision the plant produced hafnium-free zirconium for naval and commercial power reactors and separated lithium-6 for the hydrogen bomb.[1](https://nap.nationalacademies.org/read/10094/chapter/35)
In 1950 Union Carbide appointed him director of Oak Ridge National Laboratory, succeeding Nelson Rucker, with Alvin Weinberg as his research director.[1](https://nap.nationalacademies.org/read/10094/chapter/35) • [3](https://www.ornl.gov/content/ornl-directors) • [6](http://smithdray1.net/historicallyspeaking/2016/9-19-16%20Clarence%20Larson.pdf) He oversaw a $20-million program of new buildings.[3](https://www.ornl.gov/content/ornl-directors) • [6](http://smithdray1.net/historicallyspeaking/2016/9-19-16%20Clarence%20Larson.pdf) The Bulk Shielding Reactor, the Homogeneous Reactor Experiment, and the Aircraft Reactor Experiment began operating during his tenure, and in 1954 the laboratory gained ORACLE, its first large computer.[6](http://smithdray1.net/historicallyspeaking/2016/9-19-16%20Clarence%20Larson.pdf) • [9](https://www.ornl.gov/timeline) The laboratory also developed methods for extracting plutonium from irradiated fuel and designed the core of the Materials Testing Reactor.[1](https://nap.nationalacademies.org/read/10094/chapter/35) According to The Oak Ridger's Historically Speaking column, he was the only ORNL director or employee to become an Atomic Energy Commission commissioner.[6](http://smithdray1.net/historicallyspeaking/2016/9-19-16%20Clarence%20Larson.pdf) Weinberg succeeded him as director in 1955.[3](https://www.ornl.gov/content/ornl-directors) • [6](http://smithdray1.net/historicallyspeaking/2016/9-19-16%20Clarence%20Larson.pdf)
## Union Carbide
In 1955 Larson left the laboratory to become a vice president in Union Carbide's carbon products business.[1](https://nap.nationalacademies.org/read/10094/chapter/35) • [2](https://ahf.nuclearmuseum.org/ahf/profile/clarence-larson/) • [6](http://smithdray1.net/historicallyspeaking/2016/9-19-16%20Clarence%20Larson.pdf) In 1961 he returned to Oak Ridge to lead Union Carbide's nuclear division, which operated the laboratory, the Y-12 Plant, and the K-25 gaseous diffusion plant, and he held that post until 1969.[1](https://nap.nationalacademies.org/read/10094/chapter/35) • [6](http://smithdray1.net/historicallyspeaking/2016/9-19-16%20Clarence%20Larson.pdf)
## Atomic Energy Commission
Larson became a commissioner of the Atomic Energy Commission in September 1969 and served until June 1974.[1](https://nap.nationalacademies.org/read/10094/chapter/35) • [4](https://www.energy.gov/management/articles/history-atomic-energy-commission) He served under three chairmen: Glenn Seaborg, James Schlesinger, and Dixy Lee Ray.[4](https://www.energy.gov/management/articles/history-atomic-energy-commission) • [6](http://smithdray1.net/historicallyspeaking/2016/9-19-16%20Clarence%20Larson.pdf) His term spanned the commission's two-year public rulemaking hearing on emergency core cooling systems, which ended with new requirements in December 1973.[4](https://www.energy.gov/management/articles/history-atomic-energy-commission) • [6](http://smithdray1.net/historicallyspeaking/2016/9-19-16%20Clarence%20Larson.pdf)
## Honors
In 1973 Larson was elected to the National Academy of Engineering for the "development of processes for recovery and purification of uranium and leadership in nuclear plant design."[6](http://smithdray1.net/historicallyspeaking/2016/9-19-16%20Clarence%20Larson.pdf) • [7](https://www.nae.edu/29031/dr-clarence-e-larson)
## Later life
With his second wife, Jane Warren, Larson produced a videotaped history of scientists from the Manhattan Project and other wartime programs, now held at George Mason University.[1](https://nap.nationalacademies.org/read/10094/chapter/35) • [2](https://ahf.nuclearmuseum.org/ahf/profile/clarence-larson/) • [5](https://aspace.gmu.edu/resources/c0079) In 1985 he published "Personal Reminiscences" in *Nuclear Science and Engineering*.[10](https://wx1.ans.org/pubs/journals/nse/a_18483) He also made colored glazes for his wife's ceramic tiles, became expert in computers, and built early television sets and an electric car.[1](https://nap.nationalacademies.org/read/10094/chapter/35)
Larson died of pneumonia on February 15, 1999, at the age of 89.[1](https://nap.nationalacademies.org/read/10094/chapter/35) • [7](https://www.nae.edu/29031/dr-clarence-e-larson) He was survived by his wife and two of his three sons.[1](https://nap.nationalacademies.org/read/10094/chapter/35)
## References
1. Alvin M. Weinberg, "Clarence Edward Larson," Memorial Tributes: Volume 9, National Academy of Engineering, 2001. https://nap.nationalacademies.org/read/10094/chapter/35
2. Clarence Larson, Atomic Heritage Foundation, Nuclear Museum. https://ahf.nuclearmuseum.org/ahf/profile/clarence-larson/
3. ORNL Directors, Oak Ridge National Laboratory. https://www.ornl.gov/content/ornl-directors
4. Alice Buck, "The Atomic Energy Commission," U.S. Department of Energy, 1983. https://www.energy.gov/management/articles/history-atomic-energy-commission
5. Clarence E. Larson Science and Technology oral history collection, George Mason University Special Collections Research Center. https://aspace.gmu.edu/resources/c0079
6. Carolyn Krause, "Clarence Larson: only ORNL director to be AEC commissioner," The Oak Ridger, Historically Speaking, September 19, 2016. http://smithdray1.net/historicallyspeaking/2016/9-19-16%20Clarence%20Larson.pdf
7. Dr. Clarence E. Larson, National Academy of Engineering member profile. https://www.nae.edu/29031/dr-clarence-e-larson
8. Clarence Larson's Interview (1965), Voices of the Manhattan Project, Atomic Heritage Foundation. https://ahf.nuclearmuseum.org/voices/oral-histories/clarence-larsons-interview/
9. Oak Ridge National Laboratory 80 Years of Great Science: 1943–2023, timeline. https://www.ornl.gov/timeline
10. Clarence E. Larson, "Personal Reminiscences," Nuclear Science and Engineering, Vol. 90, No. 4, August 1985, p. 373. https://wx1.ans.org/pubs/journals/nse/a_18483
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*Topic: Encyclopedia › Physical world and mathematics › Physical and mathematical scientists › Chemists › Nuclear and radiochemists*
*Initially written Sep 21, 2026 · Reviewed: Sep 25, 2026 · Edited: Sep 25, 2026 · Last review: Sep 25, 2026*
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