|Circumstances of the Tokaimura accident|
This diagram shows the circumstances of the criticality accident in Tokai-mura. The buckets, unloaded by the two Japanese technicians contained uranium highly enriched in fissile U-235 isotope. By exceeding more than seven times the amount permitted by safety standards, they caused an early chain reaction that cost them their lives. The large container in which they poured the uranyl nitrate to save time had a form unsuitable. If he had been flat, for example, the accident could have been avoided.