Vibration tests of a commercial gas cooled reactor core

In the seismic design of a nuclear power plant, the structures and equipments of the plant including foundation soil are represented by an equivalent mathematical model, and the deflections and stresses during earthquake are analyzed. In the analysis, the dynamic properties of various elements that influence on the dynamic behavior of the plant are examined. The damping constant assumed in the analysis plays an important role to determine the response amplitude of core. The effect of damping may even be more important than the effects of stiffness, mass, and other factors for the determination of the amplitude of core response. The damping has been generally assumed to take a value within a range from 1 to 5% of the critical from our empirical judgment for ordinary structures. However, these two extreme values lead to two or three times difference between the peak amplitudes of the response. Because the damping is not accurately known, it has been common practice to take a conservative value, generally less than 2% for the dynamic analyses of core. This is undesirable from the economical point of view if the damping is estimated too little. Under those circumstances, much attention of the persons concerned had been directed toward obtaining a right knowledge of the damping characteristics of core. That became a direct motive to scheme and practice the full scale model test for the commercial gas cooled reactor core that was under construction at Hunterston in Scotland. This experiment was carried out August 1972 in cooperation with the Nuclear Power Group Ltd. in United Kingdom, Fuji Electric Co. Ltd. and Shimizu Construction Co. Ltd. in Japan