Monday marks 20 years since a deadly nuclear criticality accident at a fuel processing plant in Ibaraki Prefecture, northeast of Tokyo.
At the time, it was Japan's worst-ever nuclear accident, leaving two workers dead.
It took place at a plant of the JCO nuclear fuel processing company at Tokai Village on September 30, 1999.
The company had engaged in illegal procedures, including the use of stainless buckets to mix uranium with nitric acid. This led to a state of criticality, a self-sustaining nuclear chain reaction. Three workers were exposed to a large amount of radiation and two died. More than 600 nearby residents were also exposed to radiation.
JCO's license to process nuclear fuel was revoked. Six company officials, including the then-head of the plant, were found guilty of negligence resulting in death and given suspended prison terms.
The accident also revealed flaws in Japan's nuclear disaster management system.
The central and local governments and the company failed to work together effectively and it took a whole day to stop the nuclear chain reaction. There was also confusion over who should issue evacuation orders.
The central government introduced new legislation allowing it to take the initiative in responding to a nuclear disaster. It also set up offsite emergency response centers across Japan.
Two decades on, the country faces a problem as to how to pass on the experience and lessons from the accident to future generations.
Fewer than 30 percent of village officials now serving experienced the accident and the number of residents with direct knowledge of the accident has also declined.
Village mayor Osamu Yamada says there have been recent cases of errors and accidents. He said it is the village's mission to keep the memory of the accident alive.