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Just how well the NRC is handling its responsibility to ensure the safety of nuclear power will be probed by the special commission set up by President Carter. But on the basis of the NRC's findings about what happened at Three Mile Island, the public had good reason to believe that safety standards had been ignored.
The sequence of human errors and mechanical failures began two weeks before the mishap. As part of a test, valves in three auxiliary pumps in the plant's secondary loop, which carries superheated water to the turbines that drive the electrical generators, were shut down. Incredibly—and in violation of NRC regulations—they were not reopened before the plant was put back into operation.
What triggered the accident was the failure of a pump in the secondary loop that transports hot water from the reactor. When this happened, the auxiliary pumps switched on as they were supposed to do. But, with their valves shut, they could not pump water. Their failure backed up water in the secondary loop and sent pressure inside the reactor soaring. This pressure rise, in turn, caused a relief valve to pop open. It stuck. Pressure then dropped so rapidly that the emergency core cooling system, designed to keep the core from overheating, was automatically activated. That started a reactor "scram" or shutdown. Tons of water flowed into the reactor and out through the open relief valve. At the same time, malfunctioning instruments gave reactor operators misleading readings of reactor pressure, which made them believe that the core of enriched uranium was covered with coolant when it was not. The operators switched off the system on the assumption that it was no longer needed. The premature shutdown and temporary loss of coolant caused the reactor's fuel rods to overheat. They reached a temperature of around 2,500° F., which could have led to a meltdown. Water pouring into the reactor overflowed to form a 250,000-gal. lake on the floor of the reactor building. Some of this water, laden with highly radioactive products, was pumped into the plant's auxiliary building, a structure not designed to handle high-level radioactivity. Gases given off by this water were picked up by the plant's ventilation system and spewed into the atmosphere.
The sequence that stopped just short of disaster exposed a number of weaknesses in the safeguard system, including the obvious flaw of not having a remote-control method of adjusting a stuck valve. But human fallibility apparently was the more alarming shortcoming of what happened at Three Mile Island. Once the original on-site mistakes had been made, the blame spread to the NRC itself. Commission officials privately admit that they were slow to get an emergency crew with the necessary skill and authority to the scene of the disaster. Had the right men been there at the right time, three days before they finally did show up, they might have limited the damage and certainly would have reduced the meltdown risk. Astonishingly, in the age of the atom and travel to the moon, the NRC engineers who first went to Three Mile Island had trouble keeping in communication with their home office. Says one NRC official in Washington: "We had a hell of a time trying to find out what was going on. The whole commercial phone system was jammed. We couldn't get through."