Prevention of Criticality in Reprocessing Plants

A nuclear fission chain reaction in a reprocessing plant is an accident that must be carefully guarded against. Although such a critical reaction is not likely to generate sufficient energy to be mechanically destructive, it emits intense neutron and gamma radiation that can kill nearby plant personnel and may release radioactive fission products outside the plant. 

The principal factors that must be taken into account in assessing criticality safety are as follows  

Proportion of fertile nuclide ( U, Th, or Pu) diluting fissile nuclide 

Geometry (shape and dimensions) of region holding fissile material 

Nature and thickness of reflectors surrounding fissile material 

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