Reactor Defects Traced to Builder : ‘Unorthodox’ Assembly May Have Caused Cracks in Pipes
The Du Pont Corp. appears to have used unacceptable and potentially hazardous methods of installing coolant pipes on the nuclear weapons reactors it runs for the government at Savannah River in South Carolina and this may have caused cracks found in a segment of pipe, Energy Department officials said Friday.
The officials said Du Pont’s “unorthodox” installation practices--which included the heating of pipes to bend them into proper alignment--may have induced stresses that could account for cracking found in a pipe removed from the L-reactor, one of three tritium-production units currently shut down for extensive safety improvements.
A senior Du Pont official at Savannah River, Dr. Joseph D. Spencer, acknowledged that the installation techniques had been used in the 1950s to build the three reactors and upgrade their power, but he said the techniques were no longer a common practice. Energy Department officials said these techniques are prohibited in commercial nuclear power plants.
Heating the pipes to make them more pliable also tended to discolor them, Spencer noted in a telephone conversation, and he said Du Pont over the years has tried to intensify its inspection of the discolored areas. Spencer, the nuclear technology program manager at Savannah River, said the most recent cracking was found only on Wednesday morning and appears to have been caused by excessive heating.
The crack was nearly a quarter-inch wide, more than 6 inches long and penetrated almost through the wall of the pipe, Spencer said.
Officials in Washington and Savannah River said the discovery of the cracking is a setback to intense efforts to revive the aging reactors, which are the government’s only source of perishable tritium gas for nuclear weapons. But they said the safety significance of the cracks and their impact on plans to restart the similar K-reactor by this summer are still unclear.
“It’s really premature to guess what this does to the schedule,” Richard W. Starostecki, the Energy Department’s chief safety official, said. “It’s a source of concern we have to deal with. . . . First, we have to understand the mechanism that has caused these (cracks) to occur.”
Starostecki said the discovery of two separate and apparently unrelated cracking problems in the L-reactor pipe mean the cooling systems of all three reactors will have to be surveyed now, in addition to the steel walls of the reactor vessels. Previously, the department had planned to concentrate on inspecting the integrity of welded joints.
The three Savannah River reactors, all built in the early 1950s, were shut down between April and August for extensive safety improvements, after a study by the National Academy of Sciences concluded in late 1987 that they were nearing the end of their useful life and required “extraordinary maintenance efforts.”
Degree of Crisis Debated
Some officials have said the shutdown threatens a critical shortage of tritium, but others--along with a variety of independent arms control analysts--contend that available supplies of the radioactive gas can be stretched into 1990 without impairing the U.S. nuclear weapons stockpile.
Du Pont has run the reactors under contract to the government since 1956, but it is turning the operation over to the Westinghouse Corp. in April.
In October 1987--one month before a National Academy of Sciences report described the Savannah River reactors as “poorly maintained and modernized"--Du Pont announced that it would not seek to renew its operating contract. The same month, apparently by coincidence, technicians cut out a segment of primary coolant pipe on the L-reactor after discovering a defective weld connecting it to a brace.
The company waited until last March, however, to inspect the inside of the stainless steel pipe, and only last week told the Energy Department of a crack inside, near a wrap-around or circumferential weld joining the pipe to a brace.
This has raised concern that Du Pont used improper welding methods or materials to attach roughly 100 similar braces to reactor pipes in recent years in a modernization program designed to strengthen the reactor’s earthquake resistance. Energy Department officials said they have asked whether the same welding techniques have been used to attach bracing to the steel reactor vessel itself, and Du Pont has replied that it is “still looking.”
This week, Du Pont told the government of a new, lengthwise crack in the same pipe segment from the L-reactor that appears unrelated to any stress caused by welding.
“This should not be happening,” Starostecki said, noting that he had never heard of similar signs of lengthwise cracking in the coolant piping of commercial reactors. A former chief of commercial reactor inspection for the Nuclear Regulatory Commission, he is the energy Department’s deputy assistant secretary for safety, health and quality assurance.
The most likely explanations for the lengthwise cracking, he said, are either a manufacturing defect “or the way it was installed in the first place.”
In building commercial nuclear power plants, engineers are prohibited from forcing pipes into position, as this could bring on stresses that could later lead to a catastrophic failure, a loss of cooling water and possible meltdown.
“You can’t force pipes to line up. You can’t manhandle them. It appears Du Pont has been using unorthodox methods of making things line up,” Starostecki said.
He and other officials said Du Pont’s installation practices include “flame-washing” reactor pipes--heating the stainless steel pipes to make them bend--then forcing them into place. Poor record keeping, Starostecki said, has made it hard to determine the full extent of this practice, which also is considered unacceptable in commercial nuclear plants.
The officials noted, however, that the Savannah River reactors operate at much lower pressure than most nuclear power plants--about 100 pounds per square inch, compared to 2,000 pounds in commercial reactors--making it less likely that stress-induced cracks would lead to a catastrophic failure during normal operation. But they said significant cracking would affect the Savannah River reactors’ ability to withstand shaking in an earthquake.