ORNL physicist Libby Johnson, one of the world’s first nuclear reactor operators, standardized the field of criticality safety with peers from ORNL and Los Alamos National Laboratory.
Johnson worked for more than a decade as a senior experimenter in the lab’s Critical Experiments Facility. As evidence of the facility’s successes developing criticality standards, there hasn’t been a criticality accident — that is, an accident involving a sustained nuclear chain reaction — on U.S. soil since 1978.
“The experiments that you and your colleagues conducted over these years were crucial to the whole business of nuclear energy,” former ORNL Director Alvin Weinberg told facility director Dixon Callihan, Johnson’s colleague and mentor, in 1996 during a historic group interview.
“All of us owe you a great debt for your having pioneered in this ever-so-important enterprise and shown the way.”
The Oak Ridge Critical Experiments Facility was established in 1950. This isolated facility, now slated for demolition, is nestled in the hills between ORNL and the neighboring Y-12 National Security Complex. The facility had been constructed for uranium storage and was remodeled to support studies underpinning safety standards. Years later, Callihan would recall his unsuccessful efforts to get a women’s restroom included in the remodeling plans — a request that was later granted. His advocacy for this amenity contrasted sharply with the overall scientific environment of that time, which was organized by and optimized for men.
“Johnson trod the silent path of women’s history in the nuclear industry,” said Nuclear Regulatory Commission historian Thomas Wellock. The NRC appointed Johnson to the Atomic Safety Licensing Board in 1975 as its first full-time female technical expert.
Johnson was a graduate student in physics at Vanderbilt University in 1944, when at age 23 she was recruited to work on the Manhattan Project at Columbia University. She came to Oak Ridge in 1948 to work as a research assistant at the K-25 uranium enrichment plant in Oak Ridge. From 1950 to 1961, she worked as a supervisor and senior reactor operator at ORNL’s Bulk Shielding Facility, where she oversaw fuel loadings and reactor maintenance, trained reactor operators and coordinated experimental programs. She also taught students from ORNL’s pioneering Oak Ridge School of Reactor Technology how to assemble reactor fuel safely.
In 1954, Johnson became a charter member of the American Nuclear Society, where she served in numerous leadership roles, chairing the society’s Nuclear Criticality Safety Division, speaking at national standards meetings, forming standards subcommittees, contributing immeasurably to standards writing groups as both member and secretary and mentoring incoming professionals.
Johnson also helped found ORNL’s ANS chapter. The society made her a fellow in 1982, recognized her with an achievement award in 1985 for her work in nuclear criticality safety and posthumously awarded her with its Standards Service Award in 2013. Upon her appointment in 1975 to the Atomic Safety Licensing Board, Johnson contributed to open hearings that included legal and technical experts to answer questions from the public and discuss concerns before construction licenses were issued. When Johnson retired in 1994 as the longest-serving female in the board’s history, she remained its sole female technical expert.
Johnson also helped open doors for women in nuclear science — including for her granddaughter, Autumn Higgins, who joined the Nuclear Navy in 1995, a year before Johnson’s death. In 2022, Higgins earned her senior reactor operator license for the Tennessee Valley Authority’s Sequoyah Nuclear Plant.
“If I could talk to her today, I would want her to know her struggle meant something for me and other women,” Higgins said. “Not only her scientific contributions, but also her personal contributions. They meant something.”