22-05-2025 | Posted by Joaquín Martí
In the context of our seismology-related activities within the nuclear industry, Principia has participated in the SMATCH international benchmark, collaborating in the same team with Esteyco and Fusion for Energy (F4E). This benchmark focuses on a seismic base-isolated nuclear power plant (NPP) subjected to a real earthquake. Organized by IRSN (Institut de Radioprotection et de Sûreté Nucléaire) and EDF (Électricité de France) under the auspices of OECD-NEA (Nuclear Energy Agency), the benchmark aims to enhance our understanding of earthquake effects on seismically isolated facilities.
On November 11, 2019, a 4.9 magnitude (Mw) earthquake, known as the Le Teil earthquake, occurred approximately 15 km from the Cruas-Meysse NPP. This plant is unique among French NPPs for its seismic base isolation, a design implemented there to adapt the standard design of the French 900 MW NPP series to the seismic hazards identified at the site in the late 1970s. When the waves from the Le Teil earthquake reached the plant, ground and in-structure responses were recorded as per operational procedures. Post-earthquake inspections and walkdowns were also conducted to gather in-situ data on the various structures, systems, and components.
The SMATCH benchmark leverages the data recorded during the Le Teil earthquake to improve our understanding of earthquake effects on seismically isolated facilities. Specifically, the benchmark aims to assess the effectiveness of current engineering practices in calculating seismic ground motion at the Cruas site and evaluating the seismic response of the base-isolated Cruas NPP.
Phase 2 of the benchmark involved characterising the seismic ground motion at the Cruas site. It began with a blind assessment, where participants were invited to simulate the seismic motion at the site during the Le Teil earthquake, based on the size, location, and fault geometry of the triggering event. This was followed by a calibration and best estimate exercise, where participants were provided with the free field recordings and asked to address discrepancies with the previous blind results to improve the estimation of seismic ground motions.
Principia used a combination of empirical methodologies and numerical calculations, including stochastic simulations. In the empirical approach a Ground Motion Prediction Model (GMPM) was used, but strong motion databases were also searched for time histories matching the characteristics of the Le Teil earthquake; the spectra from real accelerograms tended to show higher accelerations than those from the GMPM. It was found that, although the results were reasonably consistent given the uncertainties involved in the GMPMs, some of the observed differences could be critical in seismic design.
It also became evident that empirical methods by themselves did not fully utilize all the information provided, whereas a complete stochastic simulation to generate time histories required additional input data. Principia offered a combination of methodologies that made effective use of all the available information through relatively simple and established procedures.
Incidentally, it is worth noting that standardising nuclear reactors is a way to reduce their capital cost and achieve parity with other power sources, such as fossil fuels and renewables. The seismic load case has thwarted standardisation because of its site-specific demands. Seismic isolation has the potential to address this issue, thereby reducing costs, delays, and uncertainties for future installations.
Principia’s successful participation in the SMATCH benchmark underscores our dedication to the seismological field and our commitment to enhancing the seismic safety of NPPs. We are eager to continue our work in these areas and to share our progress with the wider community.
