As HANARO has been recently required to support new R&D relevant to future nuclear systems requiring much higher neutron\nfluence, two types of bottom rod tip of the capsule were preliminarily prepared. The first one is a conventional design made of\nSTS304 and welded using a tungsten inert gas (TIG) weldingmethod. The other is a new designmade of STS316L and welded using\nelectron beam (EB) welding to strengthen the fatigue property of the rod tip. During the out-pile testing, they failed after 40 and\n203 days, respectively. The fracture surfaces were examined using microscopes and the maximal applied stresses were estimated.\nThe combination of these stresses was proved to be sufficient to cause a fatigue failure of the rod tip of the capsule. Based on the\nfailure analysis, an optimized design of the rod tip of the capsule was made for long-term irradiation testing. It was designed to\nimprove the welding and fatigue properties, to decrease the applied stress on the rod tip, and to fundamentally eliminate the effect\nof residual stress due to welding. The newly designed capsule was safely out-pile-tested up to 450 days and will be utilized for\nHANARO irradiation testing.
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