CRITICALITY SAFETY ANALYSIS OF A CALCINER EXIT CHUTE

Calcination of uranyl nitrate into uranium oxide is part of normal ope rations of some enrichment plants. Typically, a calciner discharges ur anium oxide powder (U3O8) into an exit chute that directs the powder i nto a receiving can located in a glove box. One possible scenario for a criticality accident is the exit chute becoming blocked with powder near its discharge. The blockage restricts the flow of powder causing the exit chute to become filled with the powder. If blockage does occu r, the height of the powder could reach a level that would not be safe from a criticality point of view. In this analysis, the subcritical h eight limit is examined for 98% enriched U3O8 in the exit chute with f ull water reflection and optimal water moderation. The height limit fo r ensuring criticality safety during such an accumulation is 28.2 cm a bove the top of the discharge pipe at the bottom of the chute. Chute d esign variations are also evaluated with full water reflection and opt imal water moderation. Subcritical configurations for the exit chute v ariation are developed, but the configurations are not safe when combi ned with the calciner. To ensure criticality safety, modifications mus t be made to the calciner tube or safety measures must be implemented if these designs are to be utilized with 98% enriched material. A geom etrically safe configuration for the exit chute is developed for a blo ckage of 20% enriched powder with full wafer reflection and optimal wa ter moderation, and this configuration is safe when combined with the existing calciner.