At the end of World War II, the U. S. government upgraded the existing, hastily constructed nuclear laboratories at Los Alamos, New Mexico, and Oak Ridge, Tennessee, and built several more across the country. Major labs were built in Brookhaven, New York, Livermore, California, Idaho Falls, Idaho, Aiken, South Carolina, and at Simi Hills, California.

At Simi Hills, overlooking the Simi Valley 30 miles (48 km) north of Los Angeles, the Santa Susana Field Laboratory (SSFL) was constructed on 2,668 acres (10.8 km2) of land. Its purpose was to test rocket engines, guided missiles, munitions, and nuclear reactors in what was then a sparsely populated area. As seemed usually the case in the 1950s, nuclear engineers were interested in exotic reactor designs using high-perfor­mance coolants, such as liquid sodium. A commercial nuclear power plant was developed at the SSFL. It was named the Sodium Reactor Experiment.

Sodium has some good properties as a reactor coolant, but it also has a few disadvantages. It does not absorb neutrons parasitically, nor does it boil away at anything but the highest temperatures, and it has excellent heat conduction. However, at low temperature it is a solid, locking every­thing immersed in it in a metallic block. It is opaque. You cannot simply look and see what is going on in a sodium-cooled reactor core. It also reacts vigorously with air or water vapor, and this means that it cannot be allowed to leak out into a room. Its compound with water is extremely corrosive and will quickly dissolve aluminum.

The sodium reactor experiment was brought to power operation in April 1957, and on July 12, 1957, its electrical output was switched into the California power grid, making it the first commercial nuclear power pro­duction reactor in the United States. For a short period of time, just long enough to prove the point, it supplied power to 1,100 homes in the Moor­park area of California. On July 13, 1959, the Sodium Reactor Experiment made another first. It became the first power-producing nuclear reactor in the United States to experience a core overheating.

The reactor was operating normally when it experienced a sudden power excursion, with the power level and temperature rising rapidly. With considerable effort, the reactor was brought under control and shut down. The cause of the excursion was baffling and was not determined, but the decision was made to ignore the problem as an unexplained anomaly and continue operating as if nothing had happened, so a few hours later the reactor was restarted and taken to operating power.

Subsequent reactor behavior seemed strange, and radiation alarms kept going off, so after 13 more days of wrestling with the controls the reactor was shut down for analysis. The operating crew discovered that almost one-third of the reactor core had melted, releasing radioactive fis­sion products into the liquid metal coolant. Radioactive gases from the wrecked core were collected in holding tanks and then bled into the atmo­sphere over a period of several weeks. The problem had been caused by leaking seals in coolant pumps. When the seals failed, the coolant for the pump bearings leaked into the sodium coolant. The coolant was an exotic organic fluid, Tetralin, and it carbonized when it hit the sodium, blocking coolant passages. The blockage kept coolant from the fuel, and the clad­ding melted in the increased temperature. The reactivity of the graphite­moderated core improved without coolant, causing the power level to rise out of normal control.

There was a weakness in the reactor design, and a simple, predictable problem led to a major breakdown. Pump-seal coolant will eventually leak, as the moving parts experience wear. Any flow disruption of the molten sodium in the core would lead to a runaway, instead of an auto­matic, shutdown. A stronger design would allow anything that is capable of failure to fail without causing a larger problem, and a disturbance of the coolant should cause the reactor to revert to a safer condition and not a less safe condition. In retrospect, the operating procedures for the reactor were fundamentally wrong. When a problem with unknown char­acteristics arises, the reactor should not be restarted until the cause is known. These were the lessons learned from the Sodium Reactor Experi­ment meltdown. These lessons would require further reinforcement, but it was a beginning of the nuclear power learning process.

In parallel to the sodium reactor development at the SSFL, Admi­ral Hyman Rickover oversaw the naval reactors program for the AEC. His development of the power plant for the nuclear submarine Nautilus proved remarkably successful. Based on his pressurized water design,

using ordinary water for both the reactor coolant and the neutron mod­erator, the naval reactors amassed a perfect safety record. No reactor in the U. S. Navy has ever experienced an accidental release of radioac­tive material. In Rickovers nuclear navy there has never been a reac­tor meltdown. Never has a sailor or the environment surrounding a nuclear-powered navy vessel been subjected to abnormal radiation due to a malfunction.

The navy, greatly pleased with the nuclear submarine program, ordered more submarines and nuclear-powered surface ships. The 10-megawatt Westinghouse reactor used in the Nautilus was upgraded into a 60-megawatt design for use in an ambitious Navy plan to build a nuclear-powered aircraft carrier. Under the auspices of Hyman Rickover in his role inside the AEC, the aircraft carrier engine design was modified

for use in a stationary, full-scale electric power plant, in a project pro­posed by the Duquesne Light Company.

On the Ohio River in Beaver County, Pennsylvania, about 25 miles (40 km) from Pittsburgh, the Shippingport Atomic Power Station was built, beginning on September 6,1954. It was the cornerstone of President

Eisenhowers Atoms for Peace concept, and he turned the first shovelful of dirt at the groundbreaking ceremony. It cost only $72.5 million to build, because all the expensive up-front engineering had been paid for by the U. S. Navy.

It took 32 months to build the plant, and the reactor first started up at 4:30 a. m. on December 12, 1957. The plant was brought to full power 21 days later, after the correct operation of all systems had been checked and confirmed. After May 26, 1958, Shippingport was online and officially generating power. It was the worlds first full-scale atomic power plant devoted exclusively to peacetime uses. It generated electric­ity without a problem for 25 years, and it seemed to prove that nuclear power could be used safely and that it was more economical than a con­ventional plant. There was no need to constantly move train-cars of coal on and off site, and there was no smokestack pouring soot and carbon