Next, they attached a contact microphone to a control-rod extension and listened as the liquid sodium was pumped around the primary loop. They heard a clapping sound. They slowed the pumps. The clapping sound slowed. Was there something loose in the core? It was impossible to see.
They had to feel around using the fuel-loading devices to determine the state of the core. Proceeding slowly and cautiously, it would take four months, into January 1967, to confirm that fuel had melted. First they raised the hold-down column on top of the core, and they found that it was not welded to the reactor. This was good. Next, they swung the refueling arm over the core and tried to lift the fuel assemblies, one at a time. The strain gauge on the arm would weigh each assembly. Two seemed light. Fuel had dropped out the bottom, apparently. Two were stuck together and could not be moved without breaking something. It took five months, until May 1967, to remove the fuel using the automatic equipment. Finally, seeing the fuel assemblies in the light of day, it was clear that two had melted and one had warped. There was still no explanation as to why.
The sodium was drained out of the reactor tank, although there was no provision in the design for doing so. A periscope, 40 feet long with a quartz light attached, was specially built to be lowered into the darkness from the top of the reactor vessel. Finally, the engineers could see the bottom of the reactor tank. It looked clean and neat. There was no melted uranium dripped onto the spreader cone. No loose fuel slugs were scattered around. All of the damaged fuel had collected on the support plate for the bottom of the reactor core. There was, however, something out of place. It looked like … a stepped-on beer can, lying on the floor of the reactor tank? That could explain the core melt and the clapping noise. Caught in the maelstrom of coolant forcing its way through the bottom of the reactor core, this piece of metal had slapped up against an inlet nozzle and blocked sodium from flowing past a couple of red-hot fuel assemblies. But what was it, and how did it get in the reactor?
To answer that question, the metal thing would have to be removed from the reactor, and that was not easy. Cisler stood firm under a hail of abuse from anti-nuclear factions as the Fermi 1 engineers accomplished the impossible. They built a special remote-manipulating tool and lowered it down into the floor of the reactor tank through the sodium inlet pipe. It had to make two 90-degree turns to get there. With the new tool in place, they were able to move the metal thing closer to the periscope, flip it over, and take pictures.
Still, the experts could not tell what it was. They all agreed on one thing: it was not a component for the reactor as shown on the design prints. It would have to be removed. With enormous effort and a great deal of money, another special remote operator was built and inserted through the sodium inlet. One worker swung the quartz light on the end of the periscope to bat the object into the grabber at the end of the new tool. Another man, working 30 feet away, manipulated the grabber tool blindly from instructions over an intercom. Finally, a year and a half after the accident, on a Friday night at 6:10 P.M., the mystery object fell into the grip of the tool. Slowly, taking 90 minutes, they snaked it up through the pipe and into the hands of the awaiting engineers.
They looked at it, turned it over, looked again, and finally truth dawned. It was a piece of the zirconium cover that they had attached to the stainless steel spreader cone, nine years ago. They had not bothered to have it approved and put on the final prints. It had cost an additional $12 million to figure this out.
By May 1970, all repairs had been made and Fermi 1 was ready for a restart. AEC inspectors were on hand, making the operators nervous at the close monitoring of their every action. Things were tense as 200 pounds of sodium suddenly broke loose in the primary transfer tank room, tearing out a water-pipe run and causing a loud thud as the mixture of water, air, and sodium exploded. This embarrassing incident cost another two months of down-time to repair the damage, but in October the plant finally reached its designed power level, making 200 megawatts of heat. For the next year of operation, the plant was able to remain online for only 3.4 % of the time.[151] Denied an extension to its operating license in August 1972, its operation ended on September 22, 1972. The plant was officially decommissioned on December 31, 1975, the fuel and the sodium were removed, and it still sits quietly at Lagoona Beach, next to Fermi 2, a General Electric boiling-water reactor that is currently making power for DTE Energy. All things considered, Fermi 1 failed at its mission, to spearhead the age of commercial plutonium breeding in the United States. Admiral Rickover had summed it up clearly back in ’57 in one sentence, saying that sodium-cooled reactors were “expensive to build, complex to operate, susceptible to prolonged shutdown as a result of even minor malfunctions, and difficult and time-consuming to repair.”
Did we almost lose Detroit? No. There was no water in the reactor vessel to destructively explode into steam with a suddenly overheated reactor core. No steam meant that there was no source of force to break open the containment dome and spread fission products from the core.[152] The water and steam were out in another building, and the worst that could happen was to mix them with the secondary sodium loop and not with the primary loop containing radioactive sodium. The results of a massive breakdown in the secondary loop could dissolve every aluminum drink can within five miles with vaporized sodium hydroxide, but it would spread no radioactivity. The reactor was too feeble to build up enough fission product to justify the thousands of casualties predicted if the core were to somehow explode. In a maximum accident, the entire core would overheat and melt into the bottom of the reactor vessel, but it would melt the controls and the non-fissile core structure along with it, making it unable to maintain a critical mass. The dire predictions and warnings had been dramatic, but hardly realistic.
The school of business at Northern Michigan University was renamed the Walker L. Cisler College of Business. He died in 1994 at the age of 97.
Not even slightly discouraged, the AEC proceeded to secure funding for yet another stab at a commercial sodium-cooled contraption in 1970, the Clinch River Breeder Reactor Project, to be built inside the city limits of Oak Ridge, Tennessee. This would be a full-sized power reactor, making a billion watts of heat, turning out 350 megawatts of electricity, and producing more plutonium than it burned. Lessons learned from Fermi 1 were applied to the design, including multiple coolant intake passages per fuel assembly to make inlet blockages “impossible.”
Estimated cost of the plant was $400 million, with $256 million to be paid by private industry. Being built right in the middle of the Great Atomic Downturn in the mid-seventies, the project spun out of budgetary control and was plagued with contracting abuse charges, including bribery and fraud. By the time the Senate drove a stake through its heart in 1983, $8 billion had washed away, and plans for a commercial breeder economy in the United States went with it.[153]
The U.S. was not alone in an early quest for a sodium-cooled plutonium breeder. In 1964, the Soviet Union under Minister of Atomic Energy Yefim P. Slavsky began construction of what would become the world’s first and only nuclear-heated desalination unit making more fuel than it used, the BN-350 power station. The site was two miles in from the shore of the Caspian Sea on the Mangyshlak Peninsula. The reactor was designed to run at 750 megawatts, driving five sodium loops at the same time with one spare. It was first started up in 1972, and although it was not able to make its designed power level, it ran for 26 years. For 22 of those years, it actually had an operating license, and the fact that it kept going for so long speaks well of the operating staff. They were an exceptionally tough bunch, eventually developing an immunity to frequent sodium fires and explosions.
151
This number, 3.4 %, is the
152
No steam not only meant that there could be no steam explosion, it also meant that there could be no explosive hydrogen buildup. Hydrogen gas can be made from steam in a reactor accident by heat-induced corrosion of metals or radiolysis. More on this topic in the Fukushima chapter.
153
Meanwhile, in 1975 the Shippingport Atomic Power Station in Pennsylvania, a pressurized water reactor based on a Westinghouse aircraft carrier engine, was converted into a thermal breeder using a thorium-uranium-233 fuel cycle. The Shippingport reactor had been running since May 26, 1958, and was the first commercial reactor making significant electrical power in the U.S. The reactor ran smooth and quiet for 25 years, and it never gave any trouble.