Degradation and Failure of Stored Radiological Material Containers and Packages, Idaho National Engineering and Environmental Laboratory, United States of America

On 3 December 2003, at the Naval Reactors Facility, Idaho National Engineering and Environmental Laboratory, in the United States of America, a canister containing an irradiated non-fuel test specimen failed catastrophically while stored in a water pool. The failure made a large noise, dislodged the stainless steel canister made from 10 cm diameter schedule 40 pipe 45 cm long, ruptured its brass cap, and projected part of the cap 3 m away underwater. No injuries or other damage occurred and there was no measurable release of radioactivity to the environment. The brass cap screwed onto the canister, with two nitrile rubber O-rings providing a watertight seal. Investigators found evidence of water leakage inside the canister. Their preliminary conclusion is that during the 14 years the canister was stored in the water pool, the nitrile rubber seals degraded from exposure to high flux gamma radiation emitted from the test specimen. Water leaked into the canister and the canister subsequently resealed tightly as a result of the brass cap's corrosion. Radiolysis caused the captured water to break down into hydrogen and oxygen gas, pressurizing the canister. (Decomposition of the nitrile rubber could also generate flammable gases.) The investigators concluded that the hydrogen detonated and caused the failure. Although the ignition source is still not clear, it could have been thermal energy from the specimen, reactions from radicals produced by the radiolysis, sparking from interaction of metallic components, or static electricity discharge