Investigation findings regarding burn marks on posted notice in Hamaoka Nuclear Power Station Units 1 and 2 worker break room (outside the radiation controlled area) (Fire)

Press Release

Investigation findings regarding burn marks on posted notice in Hamaoka Nuclear Power Station Units 1 and 2 worker break room (outside the radiation controlled area) (Fire)

August 28, 2025
Chubu Electric Power Co., Inc.

The following is our internal investigation report regarding the fire that occurred on August 7, 2025, in the restroom of the workers' break room (outside the radiation controlled area) at Units 1 and 2 of the Hamaoka Nuclear Power Station(Press release issued on August 7, 2025)
We deeply apologize for any inconvenience or concern this may have caused to the local community and many others.

1. Investigation Results

After investigating the factors related to equipment, environment, and management, it was determined that the possibility of these factors causing the fire was extremely low, and the cause could not be identified. The details of the findings are as follows.

• Equipment factors
• At the fire site, we confirmed that there were no electrical or mechanical equipment that could have caused the fire, and that the building structure did not present any unique conditions conducive to the convergence phenomenon (Note).
  
• Environmental factors
• At the fire site, we confirmed that no items capable of spontaneous combustion under the estimated ignition time period's temperature and humidity (August 6, 3:30 pm to August 7, 1:25 pm) were stored.
  
• • Management factors
• At the fire site, we confirmed that no work involving open flames was being performed. Furthermore, combustible materials (cleaning tools) were stored appropriately in accordance with company rules, and we confirmed that the cleaning detergents stored posed no risk of ignition due to oxidation reactions or similar causes.
  Additionally, we confirmed that fire safety inspections and patrols are conducted at the frequency stipulated by company rules for the break room in question.
  

2. Future Actions Based on Investigation Results

Although the cause could not be identified, we have reminded our employees and contractor workers to "refrain from bringing unnecessary open flames onto the premises" and to "exercise extreme caution when using open flames." We will continue to rigorously enforce fire prevention management. Furthermore, since human factors cannot be ruled out, we will strengthen our management and surveillance systems to prevent suspicious behavior before it occurs.
We have filed a police report regarding this incident and will continue to cooperate fully with the police investigation.

(Note)　Convergence phenomenon refers to the phenomenon where sunlight is concentrated at a single point by a reflective object acting as a convex lens or concave mirror.