South Texas Project (STP) nuclear power plant officials revealed Thursday that ultrasonic testing has confirmed small vertical cracks in the two instrumentation tubes inside the Unit 1 reactor vessel. The tubes had exhibited seepage in late April during a scheduled refueling and maintenance outage.

STP launched the investigation after the company’s inspectors discovered trace amounts of boric acid on the bottom of the reactor vessel. The company noted that the Unit 1 reactor — which remains shutdown — is housed inside a reinforced concrete and steel-lined containment building.

STP said the inspection procedure was expected to be completed over this past weekend. An engineering team is continuing to develop a corrective action plan to address the affected tubes prior to safely restoring the unit to service by late summer.

“We remain absolutely committed to ensuring the safety and integrity of our facilities,” said Ed Halpin, plant general manager. “I believe our rigorous and disciplined approach to understanding and resolving this condition on Unit 1 is evidence of our commitment to doing what is right. The good news is we know how to safely address the problem.”

An inspection team of specialists from the Nuclear Regulatory Commission (NRC) has been on site since May 13 monitoring the investigation and evaluating the corrective action plan being developed. STP said it expects the NRC to conduct a public meeting in the near future on the results of the examination and STP’s proposed corrective actions.

Framatome ANP, which was tapped as the non-destructive examination (NDE) vendor last month, will also implement the repair plan as well. The NDE process involved ultrasonic tests using three different types of probes to detect potential cracks on each of the instrumentation tubes. Additional inspection techniques will be used to further examine the two affected instrumentation tubes.

After evaluating several alternative repair options, officials at STP selected a procedure that involves replacing a portion of each affected instrumentation tube with an upgraded alloy material. Framatome said it will test the repair procedure beforehand on a full-scale mockup of the reactor bottom at its headquarters in Virginia. Another full-scale mock up at the STP plant will be used to further refine the repair procedures. STP assured that it will review the repair method with the NRC prior to restarting the unit.

STP’s twin reactors produce 2,500 MW of electricity. The facility supplies power to customers in an area stretching from Houston to Austin and San Antonio to Corpus Christi. The plant is managed by the STP Nuclear Operating Co. and owned by AEP Texas Central Co., Austin Energy, City Public Service of San Antonio and Texas Genco L.P.

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