Study Of Mechanical Fatigue Under Various Load Spectra On The Zr-2.5%Nb Pressure Tube Specimens

The paper presents the results of the mechanical fatigue tests under various load spectra performed in RATEN ICN on the pressure tube specimens made from Zr-2.5%Nb. The tests have been done on the C-shape type specimens at room temperature and having the hydrogen concentrations exceeding terminal solid solubility. In the paper is described the experimental procedure with the following main steps: the hydride formation and the mechanical fatigue tests. Hydride formation involves the hydrogen migration under stress gradient, hydrides precipitation and reorientation in the region of the stress spots. The mechanical fatigue tests consist of spectra loading with two cycling sequences having different mechanical loadingamplitudes. It is measured the number of cycles for every sequent (mechanical stress amplitude). For each test is defined the "cycling sequences fraction"as ratio of cycles number for every cycling sequences. An analytical relationship that correlates the cycling sequence fraction with the mechanical stress amplitude applied for every cycling sequence and the hydrogen concentration is obtained. The results can be used for the structural integrity analyses of pressure tubes in CANDU fuel channels subject to periodic inspections at Cernavodă NPP. (author).