The No.2 nuclear power plant in New Taipei City (photo courtesy of Ellery). The No.2 nuclear power plant in New Taipei City (photo courtesy of Ellery). (Wikimedia Commons photo)

Taipei, March 28 (CNA) The No. 2 reactor at the Second Nuclear Power Plant in New Taipei automatically shut down Wednesday because of a possible pressure problem, a day after resuming operations, state-run utility Taiwan Power Co. (Taipower) said.

The incident occurred at 1:25 p.m., with an initial check suggesting that the reactor tripped when too much steam was discharged from side valves as steam was being released, creating a pressure overload, Taipower said.

The glitch triggered the reactor's protection mechanism, and the facility remains safe and able to function normally, Taipower said.

For the reactor to be restarted, however, the exact cause of the glitch will have to be tracked down so that Taipower can write a report on what happened and what improvements can be made to the Atomic Energy Council (AEC) for review, the utility said.

The reactor can not be restarted until the AEC gives the green light to do so, Taipower said, estimating it would take at least one or two days to complete the report.

Before being restarted on Tuesday, the reactor had been shut down since May 16, 2016, when some of its surge arresters burned down because of an excessive voltage level, and Taipower decided to overhaul the reactor.

On Feb. 5, Taipower applied for AEC approval to restart the reactor after completing the overhaul, but it was not until March 5 that the AEC determined the reactor could run again without safety concerns.

The AEC issued a formal document on March 20 giving Taipower the green light to restart the reactor.

A fully operational second reactor will give Taipower more flexibility in supplying power as the weather turns warmer.

As summer approaches, the state-owned utility wants to keep its operating reserve margin -- the percentage of total generating capacity available above peak demand conditions -- at 6 percent or more to accommodate an expected increase in electricity use.

The operating reserve margin fell below 2 percent at times last August, leaving Taiwan vulnerable to plant breakdowns and power shortages.

According to Taipower data, the electricity the No. 2 nuclear power plant generated accounted for 7.84 percent of the total in 2014. (By Huang Ya-chun and Elizabeth Hsu)