Seismic capability evaluation of the prestressed/reinforced concrete containment, Yonggwang nuclear power plant Units 5 and 6

Abstract

There are two methodologies to evaluate the seismic safety for a given structure; one is a seismic fragility method of analysis (SFA), and the other is a conservative deterministic failure margin method of analysis (CDFM). The former is a probabilistic approach, whereas the latter is a deterministic approach. In this paper, the containment structure of the Yonggwang Nuclear Power Plant Units 5 and 6 (YGN 5 and 6) is evaluated, using the two methods described above, to find the upper-shelf seismic capacity of the containment structure under the severe seismic loading exceeding the design basis earthquake. The YGN 5 and 6 containment structure is subjected to a design peak ground acceleration (PGA) of 0.2 g and a design pressure of 57 psig. The most critical failure mode is a diagonal shear failure of the cylindrical shell near the wall/base slab junction; the shear capacity of which was computed using a truss analogy theory. The two seismic capacities obtained from the SFA and CDFM approach are expressed as high capacity and low probability of failure (HCLPF) numbers and the evaluated final HCLPF numbers for YGN 5 and 6 are 1.20 and 1.34 g, in terms of PGA, respectively. A comparison of the two final numbers is then performed to obtain some insight over the two approaches, the ratio of which resulted in approximately 1.12. The ratio of 1.12 is judged to be reasonable based on similar studies in the U.S.