Idaho National Laboratory Cultural Resource Management Plan

isk of releasing catastrophic amounts of radioactivity to the environment. The semiscale tests thus
became part of the national debate over the safety of commercial nuclear power plants. 235
Each LOFT experiment required time to construct and set up. The reactor vessel was installed on the
MTA on November 6, 1972; the steam generator was set in place in December. In November 1973, the
MTA moved into the LOFT containment vessel. During 1975, workers conducted functional testing of
the LOFT systems. Non-nuclear large-break loss-of-coolant accidents (known as the L-1 series) took
place from 1976 to 1978. At last, first LOFT nuclear experiment began at the end of 1978 and continued
into 1979 and 1982 as the L-2 series of nuclear large-break loss-of-coolant accidents. 236
The containment building was a new domed building. Its substantial 200-ton doors were ready to
withstand the force arising from a flash to steam when coolant was withdrawn from the reactor core. To
begin the first simulation in December 1978 scientists opened a valve to imitate a “large break” in the
cooling pipe. It was over in thirty minutes. The scientists learned that water flowed into the reactor vessel
faster than it was expelled in the crucial first seconds after the “break,” which kept the core cooler than
they had expected.
Before a second test could be arranged the following May, an accident at a commercial nuclear power
plant at Three-Mile Island (TMI) in Pennsylvania caused a partial meltdown of the reactor core. LOFT
scientists altered their work schedule and used their models (Semiscale) and computer programs to help
determine how a potentially dangerous hydrogen bubble inside the TMI reactor could be dissipated.
When the crisis was over, LOFT returned to its own test program, but as a result of TMI accelerated its
study of “small breaks.” The TMI experience had demonstrated that these, combined with the
inappropriate intervention of human operators, potentially could be as dangerous as larger coolant-flow
breaks. 237
In 1982 federal financing for the LOFT experiment ran out after thirty tests. An international
consortium arranged to fund several more tests, including the last one in 1985, when scientists tried to
simulate the TMI accident and melt the core. The test (numbered LP-FP-2) was performed with a
specially insulated center fuel module that was the subject of the test. The main core was set up as a
driver core, which created the desired experimental environment in a central fuel module. The center fuel
module was the only portion of the core that simulated the “small-break” loss-of-coolant accident that
occurred at TMI. The driver core of LOFT did not melt, nor did it experience conditions much different
than normal operating conditions. The temperature rose to 4,000F, but the core did not melt. The safety
system operated to flood the core and cool it off. After the analysis of this last experiment, the LOFT
program ended in 1986. 238
Significance of LOFT. The significance of the LOFT tests can hardly be overstated in the history of
the nuclear power industry. A coincidence of historical timing linked the long-planned tests of reactor
safety with the real-world accident at the TMI plant. The final LOFT tests validated the effectiveness of
the safety systems that had been built into the TMI and other nuclear power plants.
The buildings associated most importantly with LOFT are the containment building (TAN-650) and
the aluminum building (originally made to protect the ANP reactors from the weather) recycled as an
entry into the containment building (TAN-624). The LOFT building should be preserved in place as an
exceptionally significant part of American nuclear history.
235. U.S. Department of Energy, Human Radiation Experiments: The Department of Energy Roadmap to the Story and the Records
(Washington, D.C.: Assistant Secretary to Environment, Safety and Health, February 1995), p. 96.
236. LOFT Historical Brief.
237. Bob Passaro, “TAN has Colorful, Secretive Past, to be mothballed by 2000,” Post Register, May 15, 1994, p. H-12. The damaged
core and tons of other contaminated waste from TMI was sent to the Site for analysis and study.
238. Stacy, Hangar HAER, p. 62.
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