Proof-of-principle leakage testing on the model FL containment vessel. Part 2 - O-ring leakage tests

The model FL packaging was designed to ship payloads of various sizes, weights and shapes between US DOE facilities while meeting the strict requirements of 10 CFR 71. As part of a recent re-certification effort, it was decided that the model FL containment vessels should meet the ANSI N14.5-1987 definition of 'leak-tight'. Proof-of-principle leakage testing was performed at the Lawrence National Laboratory (LLNL) on three model FL containment vessels. The purpose of the testing was twofold 1)to develop a set of leakage test procedures that could be used to redefine the allowable leakage rate criteria for the model FL containment vessel from 10-4 cm3/sec to 107 cm3/sec, i.e., the ANSI N14.5-1987 definition of 'leak-tight' 2)and to develop a set of leakage test methods that could be used to prove that the model FL containment vessel can meet the redefined allowable leakage rate criteria. The first part of this paper also published in this proceedings describes the data obtained from the leakage testing on the model FL containment vessel bodies. These data show that a set of leakage test procedures can be developed to redefine the allowable leakage rate criteria for the model FL containment vessel bodies to meet the ANSI N14.5 definition of 'leak-tight'. The data obtained from the tests on the O-ring sealing surfaces and the O-rings themselves showed that the silicone O-rings used for the model FL containment vessels are too porous to be used for leakage testing at, or below, the 10-7 cm3/sec region, using conventional helium leakage testing techniques. Although variations in the test methods were attempted, none of the variations altered the original conclusion, which suggested two options: 1)a new type of helium leakage detector should be developed to accommodate the continued use of silicone O-rings, or 2)the O-rings themselves should be changed from silicone to an entirely different elastomer. (authors)