Youn Ho Jung

Effect of Contacting Shapes on the Worn Area Properties of a Nuclear Fuel Rod in Room Temperature Air and Water

Fretting wear experiments were conducted to evaluate the effects of the contacting shapes of spacer grid springs on the wear behavior of a nuclear fuel rod in room temperature air and water. The main objective was to quantitatively compare the wear behavior of the nuclear fuel rod with the variation of the contacting spring shapes. The variation of the real worn area in the wear scar, the change in the wear volume and the maximum wear depth with the slip amplitude were calculated and measured through an optical micrometer and surface profilometry. The results of the wear tests showed that the wear volume and the maximum wear depth were sensitively affected by each spring shape with increasing slip amplitude and with a change of the test environment. From the analysis of the wear scar, it is possible to separate the size of the wear scar from the real worn area and the transferred one. In addition, we found that the wear volume has a linear relation with the real worn area rather than the size of the wear scar and this was only determined by using each spring shape even though the wear tests were carried out with different conditions. From the above results, it is possible to evaluate a wear resistant spring by using the correlation between the variation of the real worn area and the wear behavior at each spring shape.

A New Approach for a Wear Depth Prediction Using Contact Tractions

The shear energy density dissipation is considered to develop a wear model representing the depth increase behaviour. Contact mechanics is used to evaluate the shear traction and slip displacement on the contact surface. Both the partial and gross slip conditions are considered and the irreversibility of the shear traction and the behaviour of the dissipated energy density during a shear cycle are investigated. The profile of the wear depth is simulated by that of the dissipated shear energy density and compared with the actual wear results. The energy density dissipation during a shear force cycle is also evaluated to propose a wear model for a depth prediction. The validity of the model is discussed. Introduction Wear is the damage of a surface caused by an interaction of contacting surfaces. Wear damage is widely found in mechanical components, however it is difficult to eliminate it since there are many different types and mechanisms of wear. A lot of factors affect it, e.g. mechanical force and displacement, materials, existence and the properties of lubricants, environments etc. Another feature of wear damage is that it usually evolves very slowly when compared with other mechanical failures. Therefore, it is very useful to obtain a model that can predict the wear evolution. So, many researchers have made efforts to develop a better model. An interesting statistic on the wear model can be found in [1]. They investigated more than 300 models from 5466 papers published in the Wear journal and Wear of Materials conference during 1957 ~ 1992. A wear model (sometimes called “wear equation”) represents a relationship between the influence variables of the wear and the wear amount. Even in the case of a sliding wear, 100 variables and constants were found to be used [1]. Among the variables, contacting force and sliding distance are widely used since the multiplication of these yields an energy dissipation, which can be interpreted as a source of wear from a mechanical viewpoint. On the other hand, wear volume or weight loss is usually used as a wear amount. A linear relationship between the wear volume, V (or weight loss) and the multiplication of the contact force, F and slip distance, S has been generally proposed in the case of an adhesive and an abrasive wear [2] such that

Prediction of Slip Displacement in Nuclear Fuel Fretting Wear

Slipping characteristic on the contacts between the tubes and the supports is investigated to study the fretting wear of a vibratory tube. Tests were carried out to simulate the vibration of the fuel rods supported by the springs and dimples. A tube was forced to vibrate with 30Hz. The supporting condition was varied artificially: positive contact force or gap existence. During the tube vibration, amplitudes were measured continuously in the vicinity of the supports. Simple equations were derived to evaluate the slip displacement on the contacts. As a result, it was found that the supporting condition affected the vibration characteristic near the contacts. In the positive contact condition, the phase difference of the vibration signals at both sides of the contact was 180 degrees. It is altered in the gap condition and the higher frequency components than 30Hz appeared. The severer wear in the case of the gap existence is discussed with the evaluated slip distance per cycle.

Experimental Study on the Wear Behavior of Nuclear Fuel Rod in High Temperature Water Environment

In this study, the variation of spring characteristics with increasing temperature was examined and the effect of their variations on the wear behavior of a nuclear fuel rod in both room and high temperature (300°C) water conditions was evaluated. From the results of the load-displacement tests, the spring stiffness was remarkably varied with increasing temperature. The results of the wear tests indicated that the wear damages are decreased at high temperature water when compared with the room temperature result. These results indicated that the removal mechanisms of wear debris at high temperature water are dependent on not only the formation of the wear particle layer but also on the changed contact conditions such as the contact length or area due to the stiffness drops.