LEAKAGE TESTING OF PACKAGINGS WITH THREE-0-RING CLOSURE SEALS

Both the American National Standard for Radioactive Materials - Leakage Tests on Packages for Shipment (ANSI Nl4.5) - and the ISO 12807:1996 Safe Transport of Radioactive MaterialsLeakage Testing on Packages - provide guidance for leakage rate testing to show that a particular packaging complies with regulatory requirements; both also provide guidance for determining appropriate acceptance criteria. Recent radioactive packaging designs have incorporated three- 0-ring closure seals, the middle 0-ring being the containment seal. These designs have the potential for false positive results in leakage rate tests. The volume between the containment 0-ring and the inner 0-ring is used for the helium gas required for the leakage rate tests, in order to reduce both the amount of helium used and the time required to conduct the tests. A leak detector samples the evacuated volume between the outer 0-ring and the containment 0-ring. False positive results can have two causes: a large leakage in the containment seal or leakage in the inner seal. This paper describes the problem, together with possible solutions and areas that should be addressed in a Safety Analysis Report for Packaging (SARP) before a particular packaging design can be certified for transport. Ultimately, the SARP should provide justification that the requirements for leakage rate testing procedures, including the length of time needed to conduct the tests, will ensure that the containment closure seal is properly tested.