Safety of the Package of Natural UF6 Under Fire Conditions·

In the IAEA's Transport Regulations of 1996, it is planned that a thermal test requirement is imposed on packages shipping natural uranium hexafluoride (UF6) taking account of chemical hazard in addition to the radiological hazard. However, it is very difficult to evaluate the safety of the packages under fire conditions because the thermal behavior of UF6 is very complicated. Several studies have been performed on the thermal behavior of UF6 in the packaging(Yamakawa et al. 1988), most of which have been analytical studies because UF6 is difficult to use in tests. Compared with their results, it is impossible to say that thermal behavior of UF6 in the packaging has been already made clear. The main characteristic of the thermal behavior of UF6 is its low temperature triple point, phase change, and volume expansion, and it is difficult to get an accurate solution for a calculation taking account of all of them. To provide an accurate solution, it is necessary to assess the thermal phenomena of UF6 in the packaging by experimental studies, yet there are few existing experimental studies with UF6. Although interesting results have been obtained, they are not enough to make a calculation model. To assess the thermal behavior of UF6 in the packaging of natural UF6, an experimental study called a TENERIFE project has been in progress. In the study, tests are carried out using a container with full scale diameter but shorter length containing real UF6. To evaluate the safety of the package of natural UF6 under fire conditions, mechanical analysis of the package and measurement of UF6 leakage from the valve are needed.