MAXIMUM MASS RULES FOR CALCULATING TRANSPORT INDEX FOR SAFE SHIPMENT OF FISSILE MATERIAL PACKAGES

According to the U.S. Code of Federal Regulations (10 CFR 71), any fissile material package must be controlled by either the shipper or the carrier to ensure that an array of such packages remains subcritical during both normal conditions of transport (NCT) and hypothetical accident conditions (HAC). To enable this control, the criticality safety analyst of a fissile material package shall derive a dimensionless number, called the transport index (TI), which must be placed on the label of a package to designate the degree of criticality control required. A rigorous procedure has been developed to calculate the TI for safe shipment of fissile material packages containing lowenrichment uranium (LEU) ingots in steel-banded wooden shipping containers [1,2]. A practical yet conservatively safe procedure based on previously established maximum subcritical masses for certain types of ingots may be used to derive expeditiously the TI for other similar types of ingots. These empirical maximum mass rules are based on extensive explicit modeling results obtained by the rigorous procedure. This paper confirms the validity of these rules and demonstrates how these rules may be used to derive the TI for safe shipment of packages containing LEU ingots in steelbanded wooden shipping containers.