Onagawa N-Plant’s Safety Measures Show Lessons Learned From 2011 Meltdown; Back-Up Power Source Kept High and Dry

The Yomiuri Shimbun

20:00 JST, October 30, 2024

To protect Tohoku Electric Power Co.’s Onagawa nuclear power plant’s No. 2 reactor, safety measures have been put in place based on the new regulatory standards created after the 2011 meltdown of Tokyo Electric Power Company Holdings, Inc.’s disaster-hit Fukushima No. 1 nuclear power plant.

An 800-meter-long seawall, reaching 29 meters above sea level, has been built at the Onagawa plant. In addition, a gas turbine generator has been installed 60 meters above sea level to ensure a power supply even in the case of an accident. In the reactor building, a device has been installed to prevent hydrogen explosions by recombining any hydrogen that leaks from the containment vessel with oxygen.

Akio Yamamoto, a professor of nuclear engineering at Nagoya University, said, “[The standards are] more stringent than those of other countries, based on the idea of ‘taking all possible measures for safety,’ and took domestic and international disasters and research into consideration.”

The No. 2 reactor at Onagawa is a boiling water reactor, the same type that was used at the Fukushima No. 1 plant.

About 50 minutes after the 2011 Great East Japan Earthquake, a massive tsunami approximately 13 meters high – more than twice the maximum height assumed at the time – hit TEPCO’s Fukushima No. 1 plant, flooding almost the entire site. The power supply facilities, including emergency generators, were rendered inoperable, and critical functions such as reactor cooling and water circulation were lost, leading to a core meltdown.