Experimental study on post-buckling behavior of fast reactor vessel under excessive earthquakes

Abstract

The Fukushima Daiichi nuclear accident has raised the nuclear industry’s interest in the countermeasures for Beyond Design Basis Events (BDBEs) such as excessive earthquake. Sable failure modes are acceptable in BDBEs with the safety goal being to prevent unstable failure modes. The Fast Reactor Vessel (FRV) is vulnerable to seismic buckling due to thin-walled structure. Under excessive earthquakes, the safety goal of FRV is to achieve a stable post-buckling state. This paper presents an experimental study on post-buckling behavior of short and medium cylinders under horizontal vibration, simulating the phenomena in pool and loop type FRV. Independent of buckling configuration, a global response stability is confirmed after buckling. This stability is achieved by the phase-shift phenomenon, where buckling initiation increases the frequency ratio and enables the displacement-controlled characteristic of the dynamic load. Such phenomenon is independent of input conditions. In addition, longer cylinders show a higher post-buckling frequency ratio with significant response reduction compared to short cylinders. Next, the post-buckling failure development process is investigated and can be summarized into three stages. The ultimate rupture boundary can be measured by the critical cumulative input energy, which shows clear dependency on the buckling configuration. A preliminary criterion against ultimate rupture and the energy-based failure mode map are proposed to assess the safety margin of FRV. It demonstrates a considerable margin from buckling initiation to ultimate rupture during an excessive earthquake. This paper largely extends the database and contributes to a more comprehensive understanding in the post-buckling domain of FRV under BDBEs.