APPLICATION OF THE REVISED REQUIREMENTS OF IAEA ST-1 TO THE TRANSPORT OF NATURAL URANIUM HEXAFLUORIDE.

The 1996 issue of IAEA STl (formerly SS6) will, from January 2001, call for transport cylinders containing natural uranium hexafluoride ('hex') to be considered against the requirements of the lAEA thermal test. In the~ of the 48inch diameter cylinders normally used for commercial transport of natural hex, a package design will require - • from January 2001, Multilateral Approval if compliance with the thermal test has not been proven. - or • from January 2004, Unilateral Approval if it has been shown to satisfy the requirements of the thermal test. In parallel with the revision of SS6, the IAEA established a Coordinated Research Programme (CRP) to consider the behaviour of hex cylinders in fires. BNFL has contributed to that CRP principally in the areas of computer modelling ofthe thennophysical processes occurring within the cylinder and of the mechanical behaviour of the cylinder itself. Further details of the early work are includ~ in References [Bailey, 1995; Clayton, 1991; Lomas, 1992]. Validation of these models, and those of other contributors to the CRP, has been provided by reference to past experimentation, and to the extensive 'Tenerife' test programme carried out as a French/Japanese/EEC joint contribution to the CRP. Confidence in the various computer simulations has grown steadily as the CRP progressed. Despite this, the predicted survival time remained uncertain to the extent that it could still be either a little longer or a little shorter than the 30 minutes specified by the IAEA standard. With the benefit of results emerging from the Tenerife test programme, our calculations now predict that an unprotected, fully loaded, 48Y hex cylinder would be expected to survive the thermal test. However, the limited experimental data. and the small predicted margin of safety, mean that survival cannot be guaranteed.