I found this article on Japan. And so the overheating came to be because of power failure.

If the reactor’s fuel rods aren’t cooled, the reaction can burn out of control. That’s what happened at the two Japanese plants after the quake and tsunami caused a power failure and the cooling systems malfunctioned. This overheating could cause radiation to escape and sicken many people.

Very good.

thank you. After yesterday i tried looking everywhere for the information.

The article you found explains that the overheating in the reactors in Japan happened due to a power failure and malfunctioning cooling systems caused by a severe earthquake and tsunami. When a nuclear reactor's fuel rods are not properly cooled, the reaction inside the reactor can escalate and result in an uncontrolled increase in temperature. This overheating poses a serious risk as it can lead to the release of radiation into the environment, potentially affecting the health of many people.

To get a more detailed understanding of the incident, you can research further by looking for reliable sources that cover the Fukushima nuclear disaster. Investigating news articles, scientific reports, and official investigations can help you gather more information on the specific causes, consequences, and the subsequent actions taken to mitigate the disaster. Government documents and reports from organizations such as the International Atomic Energy Agency (IAEA) and the World Health Organization (WHO) can provide valuable insights into the incident's impact and aftermath.