Idaho National Laboratory Cultural Resource Management Plan

gas-driven turbo-generator. It reached full-power operation on February 28, 1963. 174 During ML-1 tests,
the operators trucked the reactor into a weather-sheltering metal building in the center of the ARA-IV
area. The reactor control building was 500 ft away from the reactor just outside the perimeter fence.
Evaluation, repair, and studies of the ML-1 took place within the GCRE buildings at ARA-III. 175
The ML-1 proved to be disappointing, typically operating only a few days or hours before shutting
down because of leaks, failed welds, or other problems. Only four days after it reached full power, a leak
shut it down. It was out of action until spring 1964. After that, operations continued, but still with
breakdowns. Radioactive releases were typical of ML-1; the experimenters realized that if it were to
operate in the field, it would place its operators in danger. ML-1 tests ended in 1965. 176
Meanwhile, in Washington, D.C., the Army Reactor Group had placed several prototype reactors on
line in Greenland, Alaska, Wyoming, and Antarctica. Even though these had acquitted themselves well,
the Group was having trouble persuading any of the services, including the Army, to order any of the
plants. It appeared that the “life time” cost of a nuclear plant was lower than that of a conventional one,
but the initial cost was far higher. When it came time actually to set a budget, the services opted for low
first-cost alternatives. Economists suggested that this was false economy, but “balance the budget”
pressures were more powerful. 177
The SL-1 Accident. On January 3, 1961, the SL-1 had been shut down for maintenance since
December 23, 1960. Three military crew members on an evening shift were preparing the reactor for
another run. A violent explosion occurred in the reactor vessel, killing all three men. This was the first—
and is still the only—fatal accident in the history of American reactor operations.
The AEC immediately appointed an investigating committee to discover what had caused the
accident. After interviewing hundreds of people, the committee never could say conclusively what had
caused it. High levels of radioactivity in the building prohibited a detailed examination of its contents,
although the technicians did manage to photograph parts of it remotely.
It seemed plausible that one of the crew had moved a control rod farther out of the reactor than was
specified in the maintenance procedures. In four milliseconds, the reactor went critical, heated rapidly,
and caused water in the core to flash to steam. The column of steam slammed into the lid of the pressure
vessel, causing the entire vessel to jump from its foundation, shearing all of its piping connections and
blowing shield plugs and shielding material from the top of the vessel. The men died from the impacts of
the explosion rather than from the effects of nuclear radiation (although radiation in the reactor building
was at lethal levels after the accident). Most of the radiation released from the reactor vessel by the
explosion remained inside the building. 178
The investigating committee identified many problems with the management of the SL-1 reactor. One
of the worst, and possibly a contributing cause of the accident, was that the fuel elements had been
174. Suid, p. 91.
175. See Photos from ARA HAER report: Nos. ID-33-D-96 through ID-33-D-102. These views show the ML-1 being moved from
ARA-IV to ARA-III and set up for examination at in the GCRE pool.
176. Suid, p. 92-93.
177. “Economic Military Power Arrives, But Pentagon Hesitates,” Nucleonics (April 1960), p. 27.
178. Many sources describe and discuss the SL-1 accident, among them “SL-1 Explosion Kills 3; Cause and Significance Still
Unclear,” Nucleonics (February 1961), p. 17-23; a series of press releases in Dworshak Papers, Box 122B, File “AEC-Idaho Press
Releases;” “Summary of the SL-1 Reactor Incident at the National Reactor Testing Station in Idaho on January 3, 1961,”
prepared by the Staff of the JCAE, January 10, 1961, also in Dworshak Papers, Box 122B, File “AEC-Idaho Press Releases;”
“SL-1 Accident, Findings of the Board of Investigation,” published verbatim in Nuclear News (July 1961), p. 13-16. A videotape
The SL-1 Accident produced by the NRTS Idaho Operations Office shows film of the recovery effort and the disposition of the
reactor building. See also William McKeown, Idaho Falls, The Untold Story of America's First Nuclear Accident (Toronto: ECW
Press, 2003).
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