Proving test of earthquake-resistant pipings, equipment and active components

Abstract

In Japan we initiated the project of a shaking table to prove the earthquake-resistant properties of key items in nuclear power stations. This two-axial shaking table will be able to shake a 1000 ton object on a table of 15 × 15 m by 2600 tonG in horizontal force and by 1300 tonG in vertical force. In this paper, the philosophy of such projects as well as various experiences on such proven tests done in Japan will be described. The main purposes of the proven tests are to understand: 1. (1)The behavior of nuclear structures and equipment under strong earthquakes both from the viewpoint of structural dynamics and process dynamics. 2. (2)The endurance limits of structures and equipment to destructive earthquakes both from the viewpoint of structural integrity and function. 3. (3)The behavior and availability of active components under deformations and accelerations induced by destructive earthquakes. 4. (4)The margin of safety of structures and equipment under assumed destructive earthquake conditions both for society at large and related engineers. Although we have almost eleven centuries of historical data on earthquake damage, we still learn new facts from each new destructive earthquake. We have almost no experience of earthquake damage to nuclear structures and equipment. We have endeavoured to estimate the ‘modes of failure’ of various structures and items in nuclear power stations. Therefore, we should be afraid of lack of knowledge on that, because earthquakes are natural phenomena and have a somewhat unpredictable nature. However, we can understand the behavior of structures and equipment in their ultimate condition through the shaking test. One of our uncertainties on earthquake effects is the effect of vertical ground motions. The three-dimensional response seems to cause no particular problems; however, overturning and unstable moving of a solid structure are highly non-linear problems. The behavior of free-surface water in a containment under three-dimensional excitation is not known completely also. These things can be clarified only through shaking experiments using a two- or three-dimensional shaking table, including vertical component motions. The availability of active components, such as control rod driving mechanisms, valves and pumps can be checked only through shaking and/or forced deformation tests, because troubles in such active components may be induced by mechanical friction or contact of moving parts. The malfunction of electrical components is also complicated, for example chattering of the contact of relays. To evaluate the behavior of such active components and electrical components, the so-called mathematical model is inadequate. It is almost impossible to establish an adequate model of those components including all elemental factors related to its function. In Japan, we have many experiences of shaking tests of various size models and for various purposes, not only for nuclear power stations, but also for other areas. Their philosophy, methodologies, results and remarks will be briefly described.