NRC team to investigate tube failure at San Onofre nuclear station

Source: U.S. Nuclear Regulatory Commission 

San Onofre Nuclear Generating Station The Nuclear Regulatory Commission will send an Augmented Inspection Team (AIT) to the San Onofre Nuclear Generating Station to review the circumstances that led to three tubes failing a pressure test at Unit 3.

Operators of the nuclear power plant, located near San Clemente, Calif., shutdown Unit 3 on Jan. 31, after a tube leak in one steam generator was identified. Resident inspectors responded to the control room to monitor site activities during the incident. The unit has remained safely shutdown and NRC has had a steam generator expert and additional inspectors at the site inspecting the licensee’s activities and tests of the steam generator tubes. 

On Wednesday, March 14, three tubes in Unit 3 failed a pressure test indicating they would be more likely to rupture during certain plant events that affect the pressure inside the steam generator. The test involves pumping water inside a tube and increasing the pressure while monitoring a pressure gauge to evaluate the integrity of the tube. The integrity of steam generator tubes is important because the tubes provide an additional barrier inside the containment building to prevent a radioactive steam release. Steam generators do experience some wear during the first year of operation but the level of tube wear at Unit 3 is unusual. 

AITs are used by the NRC to review more significant issues such as a tube failure at NRC-licensed facilities. The team has assumed responsibility from the resident inspectors for gathering information about the current condition and will travel to the site in the coming days. The team will include inspectors from the NRC’s Region IVoffice and NRC Headquarters in Rockville, Md. The team will be led by NRC Region IV Branch Chief Greg Werner of the Division of Reactor Safety. 

“An AIT is used when the NRC wants to promptly review the circumstances surrounding a significant issue,” said NRC Region IV Administrator Elmo E. Collins. “We want to make sure we understand the cause of the degraded steam generator tubes and take appropriate actions based on our inspection results.” 

The team will review information associated with the design, construction, shipping, operation, and testing of the Unit 3 steam generators. The team’s report will not contain inspection findings, but will identify areas for further inspection follow-up. 

The NRC will hold a public exit meeting with the licensee upon completion of the inspection to discuss preliminary findings. The meeting will be open to interested members of the public and the news media, and team members will be available to answer questions after the results are presented. The AIT will also issue a written report within 30 days of completion of the inspection.

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