A criticality excursion (also referred to as a criticality accident) is the accidental production of a self-sustaining or divergent chain reaction of fissionable material.
Simulation codes for transient nuclear reaction are needed for evaluation of criticality accidents in fissile solutions. The codes can estimate power history, release energy, temperature and pressure of the fissile media during criticality excursions, and have been developed in several countries.
Expert Group on Criticality Excursion Analysis (EGCEA) was established in 2006 within the Working Party on Nuclear Criticality Safety to ensure the accuracy of the predictions of such codes based on experimental data. Sub-group 4 was established in 2018 to succeed to the former EGCEA activity.
The Working Party on Nuclear Criticality Safety (WPNCS) deals with technical and scientific issues relevant to criticality safety. Specific areas of interest include (but are not limited to) investigations of static and transient configurations encountered in the nuclear fuel cycle. These include fuel fabrication, transport and storage.