Nuclear criticality accident safety, near misses and classification

• Overview of historical criticality accidents.
• Analysis of near misses.
• Review of accidents where criticality was narrowly avoided.
• Nuclear Criticality Safety trends.

The majority of known nuclear criticality accidents occurred during the 1950s and 1960s, this during a time when nuclear science was young and safety measures to deal with this new science were not fully understood. As the progression in the development of technology occurred, a new understanding for a focus on establishing a safety culture within the nuclear industry developed, this in turn has led over the decades post ceding the early years of nuclear, a decrease in the number of nuclear criticality incidents.The purpose of this paper is to provide a brief summary of historical (pre 2000) criticality accident statistics and conclusions, while focusing on nuclear criticality incidents occurring after 2000. In preparing the historical overview statistics, it was found that there were several Russian submarine nuclear criticality accidents occurring before 2000 that were not previously widely presented in the public domain. Furthermore, noted were instances of Japanese power companies covering up rod withdrawal accidents, leading to unintended nuclear criticalities. To add in this other information to previously understood practices, a new method of characterizing criticality accident near misses is to be presented, followed by data analysis showing that the safety culture that has evolved since the emergence of nuclear energy on the world stage has provided the platform for the development of a strong and relevant nuclear criticality safety stance.