State-run Taiwan Power Co (Taipower, 台電) yesterday sought to reassure the public that the nuclear power plant in Ma-anshan (馬鞍山), Pingtung County, was operating safely after its first reactor went into an emergency halt during scheduled maintenance on Wednesday.
Taipower said the stoppage was due to low water levels in the steam generator caused by the tripping of one of the water coolant pumps.
However, nuclear engineering professor Ho Li-wei (賀利維) said the incident was reminiscent of the Chernobyl disaster and that Taiwan was only spared a nuclear security incident because Taipower personnel at the plant had made the appropriate response.
According to Taipower spokesman Tsai Feng-fu (蔡豐富), the plant has been undergoing routine maintenance since the middle of October and has maintained parallel power generation since Nov. 28.
He added that Wednesday was the scheduled date for the first reactor’s maintenance.
During the maintenance, the plant lowered power generation to 80 percent, but as one of the pumps had been undergoing maintenance and the other had tripped, water levels in the steam generator dropped too low, causing the system to trip, Tsai said.
Hsu Ming-te (徐明德), head of the Atomic Energy Council’s nuclear engineering division, said that normally, one pump is able to maintain the reactor at 50 percent capacity, meaning that as long as two out of the three pumps are in working condition, the reactor would still be running at 100 percent capacity.
Once the system initiates an emergency shutdown for whatever reason — which in this case was due to low water levels in the steam generator — the control rods would be re-inserted into the reactor, introducing nuclear poison to slow down fission and bring the reactor to an emergency stop, Hsu said.
He added that if the system fails, workers may insert the rods manually.
If both methods fail, the plant still has a backup plan of pumping boric acid, also used as a “neutron poison,” directly into the reactor core to avoid fission reaction.
Commenting on the incident, Ho said the system trip in the first reactor was very similar to what happened at Chernobyl in 1986.
He added that the only difference was that during the re-insertion of the control rods at Chernobyl, one of the rods broke and jammed the conduit, whereas the rods at the Ma-anshan plant were inserted correctly.
Ho said the Chernobyl plant had also been testing its safety emergency core cooling, but ran into problems when the reactor produced an excessive amount of xenon-135, a fission product of uranium and the most powerful known neutron-absorbing “nuclear poison.” This caused a power spike in the reactor.
Workers at the plant had attempted to compensate by initiating emergency measures and reinserting the rods, which led to the disaster, Ho said.
In response to Ho’s comments, Hsu said it was not possible to compare the two incidents because the Chernobyl technicians had initiated the tests after disabling or bypassing the built-in safety mechanism system to allow manual operation.
They had violated safety precautions to carry out the tests, which would never happen in Taiwan, Hsu said.
The council has said that it would ask Taipower to provide an explanation on why the water pumps had tripped and why the first reactor was undergoing maintenance again.