Lawmakers in Taiwan accused Taipower of not being serious in explaining why seven anchor bolts for a reactor at Guosheng Nuclear Power Plant were found to be damaged. In December 1981, the reactor became the first at the plant to enter commercial operations, according to the state-owned utilities website.
Eight ward chiefs and two district council members of Jinshan District, which neighbors Wanli District, site of Taiwan’s No. 2 Nuclear Power Plant, held a protest in front of the plant, demanding the replacement of all of the anchor bolts in question.
Many experts have warned of what they describe as the AEC’s passive attitude to monitoring Taipower’s nuclear safety, and slow reactions to abnormal phenomena at the power plants.
March shutdown reveals anchor bolt damage
During a temporary shutdown on March 16th for routine maintenance of the reactor, workers discovered problems with at least seven of the anchor bolts used to secure the bottom of the reactor to the steel-reinforced concrete substrate.
One bolt was broken, two were fractured and four were cracked.
The utility was later embarrassingly forced to confirm the damage only after local media had revealed the extent of the damage in public reports weeks after the findings.
Taipower said there are 120 anchor bolts in the first reactor — of which 60 are on the inner rim and 60 on the outer —, used to 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.
Taiwan Environmental Protection Union secretary-general Lee Cho-han said the Union questioned Taipower’s credibility when the utility said that after having reactor designer General Electric replace six bolts and conduct ultrasonic tests on the other 113 anchor bolts, the reactor was safe to resume operations.
Green Consumers’ Foundation chairman Jay Fang, said the broken bolts might reflect metal fatigue of components in the reactor that has operated for more than 30 years, and a resumption of operations could shorten the lifespan of the reactor from overwork.
Taipower president Lee Han-shen admitted that the cause of the fractured anchor bolts had yet to be determined, and added that the company has replaced six of the seven bolts which were found to be damaged.
The seventh anchor bolt interferes with other devices on site, as such, it will be necessary to use alternative means to repair it. The utility has tentatively schedule the work to be carried out during the next major rehabilitation project.
Atomic Energy Minister Tsai Chuen-horng said the council has instructed Taipower to submit a report analyzing the safety of the reactor once it re-enters service with the six replaced bolts, but did state that because there was no precedent for such defects, he could not say how long it would take to fix the problem.
The AEC said, metallographic analysis has initially ruled out the possibility of corrosion, but further tests are required to determine the cause of the damage.
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.
Democratic Progressive Party (DPP) Legislator Tien Chiu-chin, said Taipower’s explanation that the fractured anchor bolts resulted from long-term stress was unreasonable, because none of the anchor bolts were found to be fractured in the previous maintenance checks.
“Taipower said one of the anchor bolts had not been replaced because it was at a sensitive location in the reactor, but this is like telling us that all but one broken screw bolt in a tire frame was fixed and that it’s safe to drive the car,” Tien said, adding that nuclear safety was a matter of safety for everyone in Taiwan.
Tien said an administrative hearing on the case should be held so that the cause can be clarified and the information made public. However, the Atomic Energy Council refused requests that the specialists’ case review meetings be made public, adding that the council would not allow Taipower to resume operations without its review and permission.
The Green Citizens’ Action Alliance, a civic group, said it was concerned that ultrasonic examinations might not detect possible metal fatigue in the remaining original anchor bolts until after they cracked.
Green Citizens’ Action Alliance secretary-general Tsui Shu-hsin, said “Taipower’s rehabilitation plan isn’t complete” because the anchor bolts are fundamental components and are designed to have the same life expectancy as the reactor, so the cause of the broken bolts should be examined in case the same problem occurs on the other 113 anchor bolts.
An official from the Atomic Energy Council said on Friday, 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.
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.
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