Taiwan Power Co (Taipower), the operator of the nation’s nuclear power plants, said yesterday it has finished replacing and repairing six anchor bolts after local media reported that seven anchor bolts of the first reactor at the Guosheng Nuclear Power Plant in Wanli District (萬里), New Taipei City (新北市), were found to be fractured or cracked during annual maintenance last month.
Because the seventh anchor bolt interferes with other devices on site, it will be necessary to use alternative means to repair it, and its replacement has been scheduled for inclusion in the next major rehabilitation project, Taipower said.
The first reactor, which began commercial operation in 1981, was temporarily shut down on March 16 for routine maintenance. Earlier this month local media revealed that one of the anchor bolts was broken, two fractured, and four cracked. The report was later confirmed by Taipower
Taipower said there are 120 anchor bolts in the first reactor that secure the bottom part of the reactor to the steel-reinforced concrete substrate, and that the weight of all the components in the reactor is supported by the substrate.
It said that according to reactor designer General Electric Co’s (GE) ultrasonic examination, the other 113 anchor bolts were good enough to ensure the reactor’s safe operation. GE said the reactor would be able to resume operation once repairs had been completed, Taipower added.
The fracturing of the anchor bolts could have been caused by defective materials, the manufacturing process, environmental influences or metal fatigue, Taipower said, adding that it was difficult to determine what caused the cracks. However, initial evaluation of the fractured surface appeared to show they were caused by long-term stress instead of sudden shearing.
Taipower said it would consult other related agencies to analyze and fix the problem and add vibration sensors near the supporting base of the reactor for continuous monitoring.
However, at a coordination meeting at the Legislative Yuan on Friday, an official from the Atomic Energy Council said this was the only case of fractured anchor bolts in GE BWR-6 boiling water reactors that had ever been recorded anywhere in the world.
The Chinese-language Liberty Times (the Taipei Times’ sister paper) yesterday quoted a Taipower official named Lin Te-fu (林德福) as saying GE charged US$3 million for the six newly replaced anchor bolts. The rehabilitation price was questioned by civil engineer Wang Wei-min (王偉民), who said the bolts were massively over-priced, and that as the fractures resulted from metal fatigue, all 120 anchor bolts should have been replaced to ensure safe operation.
In response to the media report, Taipower said the rehabilitation work was contracted to GE and included emergency treatment by its specialists, the bolt material, monitoring personnel, structural safety analysis and engineering design, so the price could not be compared with ordinary mechanical components.
The Green Citizens’ Action Alliance, a civic group, said it was concerned that ultrasonic examinations might not detect possible metal fatigue in the remaining 113 original anchor bolts until they cracked.