Criticality is the state of a nuclear reactor when there is a self-sustaining chain reaction of fissionable material. Used or spent fuel criticality is associated with the scientific issues around assessing criticality safety for systems and operations involving spent nuclear fuel.
The NEA Expert Group on Used Nuclear Fuel criticality (EGUNF) was formed in 2015-2017 as a follow-up activity of the NEA Expert Group on Burn-up Credit Criticality Safety (EGBUC), to assess the accuracy and validity of burn-up credit methodologies of used nuclear fuel (UNF). EGUNF mainly covered storage and transport of UNF and many NEA member countries were interested in the direct disposal of UNF.
EGUNF performed the two benchmarks as below;
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.