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Partial shutdown at 3rd Nuclear Power Plant after water pump failure
Taiwan News, Staff Writer
2013-12-05 12:05 PM
Reactor Number One at Taipower’s Third Nuclear Power Plant at Kenting shut down suddenly at 1:01PM Thursday afternoon during a routine maintenance procedure on the system’s steam generator. Officials from Taipower quickly explained that the reactor shutdown was an automatic safety response and there was at no time any danger of a leak or other mishap with the reactor.

Following a quick inspection and review of the system, Taipower confirmed that the plant safety system reacted normally and there was no release of radiation, and neither the environment nor personnel were affected. The incident did not disrupt system-wide power supply in the electric grid, and Taipower is working to identify the precise cause of the incident and confirm the integrity of the safety system before the reactor is started up again.

Taipower spokesman Tsai Fu-feng said the nuclear plant underwent an overhaul that started in October and was completed November 28. At that time the plant was restored to full capacity. During a routine maintenance procedure Wednesday, the reactor was operating at 80% of capacity when one of three water pumps in the steam generator shut down suddenly after a second pump had been shut down due to vibration during balance testing. This led to a sudden buildup of steam and a drop in the water level, which in turn triggered a shutdown of the reactor.

Wu Tsu-hua, Manager of the Third Nuclear Plant’s Maintenance Division, explained that the steam generator uses heat from the nuclear reactor to produce steam that drives turbines to produce electricity. The steam generator is independent from the reactor and thus there is no danger of radioactivity.

Each of the three water pumps in the steam generator is capable of supplying 50% of the water needed to keep the system running and prevent the reactor from overheating. If two of the three pumps are functioning the plant can produce power normally, but if a second pump goes out as happened Wednesday, the water supply drops to 50% of what is needed. With the reactor operating at 80% of capacity Wednesday there was not enough water circulating to keep the temperature of the reactor core down and the reactor shut down automatically.

If the water level in the steam generator falls too low, control rods are quickly lowered into the reactor to slow the nuclear reaction. If this does not happen automatically the rods can be inserted manually, and should that still be insufficient, there is a second backup system which injects neutron-absorbing boric acid into the reactor core to prevent chain reaction.

Atomic Energy Commission (AEC) Vice chairman Chou Yuan-ching said the commission has asked Taipower to explain why one of the three water pumps failed less than a week after an overhaul of the facility.

There have been four incidents at nuclear power plants in Taiwan this year in which the reactor tripped off line. The first two events took place at the First Nuclear Power Plant during the first part of major overhaul and resulted from improper calibration of a system as well as poor coordination between members of the operating team. The third incident was at the Third Nuclear Power Plant and resulted from is loosened fan blades from a cooling fan which hit a high voltage power line and caused the reactor to shut down temporarily.

AEC spokesman Hsu Ming-teh said the activation of the safety system shows that the Third Nuclear Power Plant is well designed and safe. He added, however, that while the plant can quickly be returned to normal operation it is not good to have shutdowns too often in order to avoid changes in temperature that can lead to metal fatigue and cracking.

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