Water/sand flooded and immersed critical experiment and analysis performed in support of the TOPAZ‐II safety program

Presented is a brief description of the Narciss‐M2 critical assemblies, which simulate accidental water/wet‐sand immersion of the TOPAZ‐II reactor as well as water‐flooding of core cavities. Experimental results obtained from these critical assemblies, including experiments with several fuel elements removed from the core, are shown. These configurations with several extracted fuel elements simulate a proposed fuel‐out anticriticality‐device modification to the TOPAZ‐II reactor. Preliminary computational analysis of these experiments using the Monte Carlo neutron‐transport method is outlined. Nuclear criticality safety of the TOPAZ‐II reactor with an incorporated anticriticality unit is demonstrated.