Federal inspectors, plant operators discuss nuke plant leak

By Michael Graczyk
Associated Press Writer
The Associated Press


Federal regulators told operators of the South Texas Project nuclear plant on Monday they would notify them by the end of the week whether a generating unit idled by a pair of leaks in a reactor can be restarted now that the repairs have been completed.

"I think you can tell from our presentation we're very satisfied with the actions you have taken," Dwight Chamberlain, acting deputy regional administrator for the Arlington-based Region IV Nuclear Regulatory Commission, said after hearing an explanation of the inspections, repairs and future monitoring by operators of the power plant near Bay City.

"We believe we have developed a very strong safety culture at South Texas Project," said Joe Sheppard, president and CEO of the STNP Nuclear Operating Co. "We believe we have done it right and we believe we are ready to restart Unit 1 to service in a safe and reliable manner."

Unit of the twin reactor South Texas Project about 90 miles southwest of Houston already was shut in March for routine refueling and maintenance when an inspection April 12 detected a tiny deposit containing boric acid described as about half the size of an aspirin on the bottom of the containment area of the reactor vessel.

Small vertical cracks known as "axial" cracks, were found in two of the 58 instrumentation tubes inside the reactor vessel, a 6-inch-thick steel container 46 feet high and more than 14 feet wide. Instruments within the tubes measure the operations of the reactor.

"We believe the cause of this condition was a fabrication flaw in the original construction that created and overstressed condition that caused the initiation of the cracks," Sheppard said.

"This theory has merit," Russ Bywater, a senior reactor analyst and head of the NRC inspection team, said. "The repair is acceptable no matter what the cause of the cracks in the weld."

Experts from as far away as France and Japan were brought in to help devise a repair plan that involved cutting out the cracked part of the vessel and replacing it by welding in a more corrosion-resistant alloy for the tubes, which were described as having the circumference of a person's little finger.

Sheppard noted that since the specific problem had never occurred before, "We deployed technology in May that did not exist in April."

"We have properly addressed the ...condition in a safe and comprehensive manner," plant manager Ed Halpin said. "The engineering analysis supporting the repair has been very thorough. We understand the cause and actions for future monitoring have been put into place.

"We have confidence in the repair and the quality of the work that has been done. Unit 1 is ready for a safe reliable startup and return to power operations."

"We're confident the repair is fine." Bywater agreed.

He also said inspectors were confident of the commitment of the plant managers to monitor the reactor and its twin Unit 2.

Another possible cause of the leak was a phenomenon known as primary water stress corrosion cracking, a slow corrosion for certain alloys that can occur at high temperatures and stress levels.

That problem has been found at other nuclear plants but in tubes at the top of the reactor and not the bottom, like at South Texas.

Bywater said samples of the metal taken from the cracked area of the vessel were being tested but results would not be known until later in the year.

All 58 of the instrumentation tubes on Unit 1 were examined and no other cracks were found. The repairs were completed earlier this month.

The plant's second reactor, which remains up and running, is set for maintenance in 2005, when it will undergo similar inspection.

"We just have to wait and see," Halpin said about prospects for a green light from the NRC to restart Unit 1. "We're ready. We want to do it safely. We're not in a rush."

The two reactors produce 2,500 megawatts of electricity and serve more than 1 million homes in south central Texas. Unit 1 went into service on August 1988. Unit 2 joined it 10 months later.

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