Measures against Recriticality and Future Earthquakes and Tsunamis

< Recriticality >

When criticality occurs (a status where chain fission reaction occurs and continues), Xe-135 and other noble gases increase in an unexpected fashion. At Tokyo Electric Power Company (TEPCO)'s Fukushima Daiichi NPS, generation of noble gases is being monitored at all hours. At present, the amount of noble gases generated has been stable, which suggests that recriticality has not occurred. However, in preparation for any risks of recriticality, a boric acid water system to suppress nuclear fission in the event of criticality has been installed.

< Measures against earthquakes and tsunamis >

■ Measures against earthquakes

It has been confirmed that important buildings in the premises are sound enough not to fall down even in the event of an earthquake of the same level as the Great East Japan Earthquake. For securing a seismic safety margin, the demolition of the upper part (approximately 60 m) of the common exhausted stack for Units 1 and 2 was implemented in May 2020.

■ Measures against tsunamis

As measures against earthquakes and tsunamis, a tide embankment against Chishima Trench Tsunami was installed in September 2020. Measures against Japan Trench Tsunami, which is expected to be larger, have also been deliberated. While the work to block openings of the buildings has been underway to prevent inflow of seawater in the event of a tsunami, backup power sources such as emergency power supply vehicles and water injection means such as fire engines are placed at a higher area where tsunamis are unlikely to reach.

• Included in this reference material on February 28, 2018
• Updated on March 31, 2021