Development of a Brittle Fracture Acceptance Criterion for the International Atomic Energy Agency (IAEA)*

Radioactive material (RAM) shipments are increasing in importance because of heightened level of awareness by the general public. Public scrutiny of RAM shipments demands that meticulous attention be given to compliance to all rules and regulations that may apply to a specific payload and shipment. The appearance of any impropriety, or incompleteness in meeting both the letter and the spirit of the rules and regulations must be avoided if public acceptance is to be gained. Regulators that certify transport casks also require exacting verification of compliance with all pertinent rules and regulations. At times, a particular regulator may require demonstration of package integrity above and beyond the regulatory requirements to assure that the transport package is safe. Given the volume of shipments crossing international boundaries, the plethora of rules and regulations that a transport package must comply with, and the certification philosophy of individual regulators, it is imperative that uniform, consensus regulations be developed and adopted to assure that RAM transport operations can continue in an efficient and safe manner. This philosophy is embodied in the International Atomic Energy Agency (IAEA) regulations in the form of the Type B(U) certification. The \"U\" stands for unilateral certification. This certification is given by the competent authority in the country of origin. Separate transport certification from each country that a particular cask may enter is not required since the Type B(U) certification is a verification that the cask has met all IAEA rules and regulations. This process obviates the need for redundant (and expensive) certification from each country that a cask is transported through during a RAM shipment. Although the Type B(U) certification is designed to allow transport of RAM materials in certified casks across international boundaries of IAEA signatory countries, individual competent authorities may still deny entry due to misgivings about the integrity of a particular cask. Such misgivings may arise from gaps in the IAEA regulations, or may be due to differences in the level of risk accepted by separate competent authorities. The methods by which competent authorities evaluate cask designs for susceptibility to brittle fracture of the containment boundary provides a relevant example in which Type B(U) certification is not uniformly applied or accepted. The existing guidance in the IAEA, as provided for in Appendix IX of Safety Series #37, is limited and dated. Several nations involved in the transport of RAM have individually developed criteria to meet specific needs. However, the lack of an international consensus criterion limits the applicability of these criteria. An effort is underway to develop a consensus brittle fracture evaluation criterion that would have international technical consensus and that would be adopted into the IAEA Safety Series. This criterion would provide a clear and consistent approach to evaluating the potential for brittle fracture of a wide range of structural materials for cask construction.