Experimental creep life assessment of tubular structures with geometrical imperfections in welds with reference to fast reactor plant life

Abstract

Creep damage is a major life limiting factor for components operating at high temperature. For the fast breeder reactor (FBR), the hot sodium pool components and the steam generator are critical in determining the operating temperatures from structural mechanics considerations. Therefore, creep fatigue damage at various critical locations is estimated based on viscoplastic analyses, in compliance with the high temperature design rules of RCC-MR. In addition, welded joints of steam generator tubes with spigots made of modified 9Cr-1Mo and the welds of fuel pins made of 20% cold worked stainless steel to annealed end plugs, which have certain geometrical imperfections in the welds are also critical and the applicability of existing design rules to these components needs to be investigated carefully. Towards assessing the life of such tubular components realistically, accelerated tests were conducted simulating the creep damage to rupture. The generated test data were investigated by applying the existing creep damage assessment procedure recommended in the design code RCC-MR and the results demonstrated that with the recommended multiaxial creep damage assessment rule, the creep crack initiation lives have been predicted accurately. Further, the extrapolated life predicted by applying an appropriate Larson-Miller parameter indicates that the circumferential welds in the steam generator tubes and fuel pins are not life limiting factors in the design.