Fast Burst Reactor Burst Rod Adaptor Failure Analysis

Failure of a 440C stainless steel burst rod adaptor from the White Sands Missile Range Fast Burst Reactor is analyzed. The operational history of the adaptor, including nature of loading, radiation accumulation, and thermal environment, was examined. Problems associated with handling radioactive materials were overcome through careful monitoring and disposal. The chemical composition of the adaptor material was checked by x-ray and electron probe spectroscopy. The failure surface was examined and photographed at various magnifications, using optical and scanning electron microscopes. Areas of crack origin, rapid fracture, final breakoff, and abrasion from rebound are identified. Metallographic specimens were prepared, the grain structure examined, and hardness profiles obtained. The grain structure indicated the presence of microvoids and carbide segregation, and slight hardening was noted. Failure occurred at the base of a male thread in a region showing significant tool markings. Examination of the failure surface indicated crack initiation due to Stage I fatigue followed by rupture from shock overload. Recommendations to avoid similar occurrences are given.