Impact of “transport security threshold” on the practical transport operation

IAEA security implementing guides, “Security in the Transport of Radioactive Material”, was published as NSS No.9 in 2008, and it is currently under revision as NST044. In this document, “transport security threshold” was defined as “ten times of D value for specific 25 radionuclides, and 3000 times of A2 value for the other nuclides”, and it was introduced into UNOB Rev.17 in 2011, then IMDG code and ICAO TI. However it has not been introduced into Japanese transport regulations at present, since IMDG code and ICAO TI maintains these provision recommendatory. And the following questions could still be raised about 10 D transport security threshold in practical operation.1) NSS No.9 says the 25 radionuclides are chosen as those included in the “Code of Conduct on the Safety and Security of Radioactive Sources (2004)”. In the same time, the code says “the 25 radionuclides are listed for illustrative purpose only, and D values for the other nuclides may be found in TECDOC-1344”. And now D values for 373 nuclides may be found in “Dangerous quantities of radioactive material (D-values)”, EPR-D-VALUES 2006, published in 2006. So, why 25 nuclides and why two different definitions are needed?2) The transport security threshold is not restricted to sources. Should 10 D thresholds be applied to all kind of radioactive material, such as nuclear fuels or radioactive waste, other than sources?3) Eleven nuclides of the 25 radionuclides have the lower transport security thresholds than their A1 values, and 3 nuclides have the lower thresholds than their A2 values. Does it mean some radioactive materials, even in type A package, could be categorized as high consequence dangerous goods and required the additional security measures?Regarding 3), we carried out a survey on the transport of radioactive sources to examine an impact, supposing that the 10 D threshold is introduced into the transport regulations in Japan. As a result, we found that there were at least 4 transports of Co-60 sources as type A package with greater radioactivity than10 D in past 4 years. We also reviewed the past discussion on the introduction of the security provision into UNOB rev.13 (2003) and IMDG code Amdt. 32-4, and looked at the background the security provision remains as a recommendatory in the modal regulations.