CRITICALITY SAFETY STUDIES RELATED TO ADVISORY MATERIAL FOR THE IAEA REGULATIONS

Criticality safety studies are reviewed related to Advisory Material for 1996 Edition of the IAEA Regulation for the Safe Transport of Radioactive Material. Criticality calculations based on the perturbation theory are given with and without small variations in fuel concentration for UOr H20 and Pu~-H . They show that variations in fuel concentrations of 5% can give at most a 0.4%6klk increase in the neutron multiplication factor. Heterogeneity effect of fuel is examined for arrays of low-enriched U~ fuel particles immersed in water. In case of fuel particles having a diameter of 50 J.Un, the relative increase in the neutron multiplication factor is shown to be less than 0.1 %∇klk. Isolation thickness of water is discussed in term of the Reflector Factor, which is defmed as a relative increase in the neutron multiplication factor of fuel with finite thick isolator to that with infinite thick isolator. Thirty em is regarded as a practical value for isolation thickness of water.