Abstract
In a postulated severe accident, the thermo-mechanical loads from the corium debris that has relocated to the lower head of the reactor pressure vessel (RPV) can pose a credible threat to the RPV’s structural integrity. In case of a vessel breach, it is vital to predict the mode and timing of the vessel failure. This affects the ex-vessel accident progression and plays a critical role in the development of mitigation strategies. We propose a methodology to assess RPV failure based on MELCOR and ANSYS Mechanical APDL simulations. A Nordic-type boiling water reactor (BWR) is considered with two severe accident scenarios: i) SBO (Station Blackout) and ii) SBO + LOCA (Loss of Coolant Accident). In addition, the approach considers the dynamic ablation of the vessel wall due to a high-temperature debris bed with the use of the element kill function in ANSYS. The results indicate that the stress failure mechanism is the major cause of the RPV failure, compared to the strain failure mechanism. Moreover, the axial normal stress and circumferential normal stress make the dominant contributions to the equivalent stress σ at the lower head of RPVs. As expected, the region with high ablation is most likely the failure location in both SBO and SBO + LOCA. In addition, comparisons of the failure mode and timing between SBO and SBO + LOCA are described in detail. A short discussion on RPV failure between ANSYS and MELCOR is also presented.
Highlights
The Fukushima nuclear accident occurred in 2011, stemming from a strong earthquake and a subsequent tsunami that induced a station blackout (SBO) scenario (Naitoh et al, 2013a; Kaneko et al, 2015; Pellegrini et al, 2016)
A framework involving the ANSYS and MELCOR platforms is established to study the behavior of a Nordic reactor pressure vessel (RPV) lower head under SBO and SBO + station blackout with loss of coolant accident (LOCA)
It is found that RPV failure initially occurs at 6.8 h in the SBO case and 7.1 h in the SBO + LOCA case, both attributed to a stress failure mechanism
Summary
The Fukushima nuclear accident occurred in 2011, stemming from a strong earthquake and a subsequent tsunami that induced a station blackout (SBO) scenario (Naitoh et al, 2013a; Kaneko et al, 2015; Pellegrini et al, 2016). In this scenario, the nuclear power plants (NPPs) experienced serious damage due to the loss of off-site power, resulting in the leakage of large amount of radioactive material to the environment. Analyses of RPV failure are warranted to provide insights into the reactor’s accident progression and develop effective mitigation strategies
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Disclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.