Newspaper: The Patriot
Date: April 4, 1979
Title: Accident Traced to Error
Author: Casey Burko and Bill Neikirk, Chicago Tribune Press Service
The nuclear accident at the Three Mile Island Nuclear Generating station was triggered because a manual valve in a key backup cooling system was inadvertently left closed after a test several days before the incident, the Chicago Tribune has learned.
As a result, the nuclear reactor was denied critical cooling water for 12 minutes, causing it to overheat dangerously, sources said. Even a 30-second loss of coolant is considered dangerous, they said.
Officials in the industry and in the Nuclear Regulatory Commission attempting to piece together the cause of the accident said the backup cooling system failed to kick in when the main cooling system malfunctioned last Wednesday.
When cooling water from an emergency core cooling system finally was rushed into the reactor 12 minutes later, it crashed against the overheated core of nuclear fuel, causing a thermal shock of intense proportions. More than 25 percent of the fuel was damaged.
When that happened, a dangerous bubble of hydrogen gas apparently was formed, rising to the top of the reactor threatening further efforts to cool down the system.
The disclosures, pieced together from several sources, apparently were among the reasons the NRC ordered on-site federal inspectors sent to the five other nuclear power sites in the country with similar designs.
Industry sources said the test in the cooling system is believed to have taken place two days before the accident. As part of that test, the manual valve in the auxiliary cooling system was closed, rendering the entire backup system inoperative. The valve apparently was never reopened.
Many newer plants are designed so the backup cooling system cannot be manually shut off, sources said.
Although there has been no official word from the NRC on the cause of the accident, Roger Mattson, director of the NRC’s office of technical review, appeared to confirm the reported causes when he said the backup cooling system failed to come on after the primary system malfunctioned last Wednesday morning.
“There were failures of equipment and there were operator actions on the initiation of safety equipment,” Mattson said.
Shortly after the accident, John Herbein, vice president of Metropolitan Edison, operator of the plant, said that “two pumps were lost.”
“We lost these pumps,” he said, without further explanation.
As information on the sequence of events leading to the accident began seeping out, nuclear technicians at the plant continued their efforts to reduce further the size of the hydrogen bubble, which has dissipated dramatically.
But a new concern arose. Radiation inside the huge, silo-like containment building surrounding the troubled reactor reached such levels that officials feared instruments might fail.
The interval radiation buildup totaled 30,000 rems-a lethal dose for living things-and raised speculation that the gigantic power plant that rests on an island in the Susquehanna River may never be used again.
“The contamination inside the containment building is unprecedented in the history of nuclear power,” said Rep. Morris K. Udall, D-Ariz., chairman of the House subcommittee on energy and the environment.