World’s largest nuclear plant restarts 1,356MW reactor after Fukushima shutdown

The reactor is scheduled to return to commercial operation in mid-March.

Japan has taken a major step in its nuclear recovery after restarting unit 6 at the world’s largest nuclear power station by installed capacity, following an almost 14-year shutdown after the Fukushima disaster.

The reactor is located at the Kashiwazaki-Kariwa Nuclear Power Plant, in Japan’s Niigata Prefecture. It is the world’s first nuclear power plant to use an advanced boiling water reactor. The site is operated by the Tokyo Electric Power Company (Tepco).

Brought back to life on February 9, the reactor had been shut down for more than a decade. Its closure followed the 2011 Fukushima disaster when a 49-foot-long (15-metre) tsunami disabled critical power and cooling systems.

“We will continue to conduct integrity checks of the plant equipment under actual steam operating conditions, while fully and sincerely responding to inspections by the Nuclear Regulation Authority,” Tepco officials stated.

Reactor returns online

The 1,356-megawatt (MW) advanced boiling water reactor (ABWR) was restarted at 2pm local time with criticality confirmed just over an hour later at 3:20pm. For clarity, criticality refers to the condition when a nuclear reactor is maintaining a self-sustaining nuclear chain reaction.

“We will continue to demonstrate through our actions and results that we are making safety our top priority at the Kashiwazaki-Kariwa Nuclear Power Plant,” Tepco representatives pointed out.

The reactor was first restarted in the evening of January 21. However, according to the company, shortly after midnight on January 22, an alarm in the control rod monitoring system halted the withdrawal of one control rod.

As a result, the unit’s restart was suspended while an investigation into the cause of the alarm was carried out. Tepco said it intends to gradually raise the pressure inside the reactor once operations resume. It will resume power generation and transmission on February 16.

The company will then temporarily shut the reactor on February 20, or later, to check for any abnormalities before undergoing a final inspection by the Nuclear Regulation Authority. Commercial operation is scheduled to begin on March 18.

Japan’s nuclear comeback

The restart marks Tepco’s first reactor to re-enter operation since the Fukushima Daiichi accident, a disaster that led to the shutdown of Japan’s entire nuclear fleet and triggered sweeping regulatory reforms.

While the Kashiwazaki-Kariwa facility was not damaged by the Tōhoku earthquake and tsunami, all seven of its reactors have remained offline since the accident amid tightened safety requirements and public scrutiny.

Kashiwazaki-Kariwa units 6 and 7, both ABWRs that entered commercial service in the mid-1990s, were the first Tepco reactors approved for restart by the NRA in 2017.

Still, local consent remained a critical hurdle. Approval from Niigata Prefecture Governor Hideyo Hanazumi was granted late last year, with backing from the prefectural assembly shortly afterward.

Restarting the two units would increase the company’s earnings by an estimated USD 633 million (JPY 100 billion) a year. Meanwhile, a full restart of unit 6 would strengthen the firm’s power supply. Before Fukushima, nuclear energy provided around 30 percent of Japan’s electricity.

“As this is the first operation in nearly 14 years, we are carefully and methodically verifying the integrity of each piece of plant equipment,” Tepco officials said in a press release.

“We will continue to provide clear and timely information on the status of each startup phase.”