A quantum science and technology research and development institution in Chiba City, Chiba Prefecture, Japan, revealed on August 17 that the area experienced record-breaking heavy rain on August 13. This caused water to enter some areas of the basement within the institution. Radioactive waste liquid was "potentially leaked outside," but the exact composition of the radioactive material was not disclosed.
Starting in the evening of August 13th, areas such as Chiba Prefecture experienced a historic extreme rainfall event known as "Chiba Heavy Rain in August 2025". The 24-hour rainfall in Chiba City reached 367 millimeters, which is about three times the amount of rainfall in August in previous years. The local area was once issued a severe rain warning.
According to the agency, the heavy rain caused the drainage capacity of the dry area located in front of the underground radiation management area of the positron building to exceed its limit. Under the pressure of water, the gate was opened, allowing rainwater to flow into the storage room behind.
As of the evening of August 14th, the area was completely flooded, and it is not possible to determine the condition inside. Authorities estimate that the storage tanks for radioactive materials in the storage room have been submerged by water. Therefore, “radioactive waste may have leaked outside the facility” and may have been discharged into the drainage system along with the rainwater.
However, the agency stated that based on usage records, this incident caused “no impact” on the environment. Additionally, after analyzing the water accumulated in the dry areas on August 14th, the agency confirmed that there is “no risk of further expansion in the future.”
According to a report by Japanese NHK television station on the same day, statistics from Chiba Prefecture show that this heavy rain has caused 10 deaths in Chiba City, and 2 people are missing in Meguro City.
In addition, floods damaged 1,834 buildings and caused over 2,500 vehicles to break down on the roads. As of now, approximately 500 affected vehicles have been moved to roadside areas for safe passage.
Four days have passed since the heavy rain in Chiba Prefecture. The reconstruction work in the disaster area remains slow, with tasks such as cleaning up houses and removing flooded vehicles still ongoing.
Flooded Chiba Prefecture. From the internet.
