Sensitivity analysis of the probabilistic seismic hazard assessment on the Hanhikivi site

• Main Author: Tang, Janika
• Other Authors: Helander, Juho, Perustieteiden korkeakoulu, Tuomisto, Filip, Aalto-yliopisto, Aalto University
• Format: Master Thesis
• Language: English
• Published: 2019
• Subjects: probabilistic seismic hazard assessment; ground motion predictio; magnitude; nuclear safety; seismology; Dahle; New Ground; Fennoscandia; Fennoscandian
• Online Access: https://aaltodoc.aalto.fi/handle/123456789/40948

Nuclear energy company Fennovoima is planning to construct a nuclear power plant (NPP) on the Hanhikivi peninsula in Pyhäjoki. Prior to construction, the Hanhikivi 1 NPP shall be designed to withstand seismic hazards. In the Finnish nuclear industry, the assessment of seismic risks begins with a probabilistic seismic hazard assessment (PSHA). The aim of this work is to review the most significant parameters in the logic tree of Hanhikivi 1 PSHA. The scope of the thesis includes examining approaches to evaluate the maximum magnitude mmax and involving two new ground motion prediction equations (GMPEs) in the PSHA. We corrected the weights calculated by applying the Kijko approach in the current PSHA and demonstrated the shortcomings of the weight assessment method. We also attempted to derive the mmax directly from the Kijko approach, but the calculated value was deemed unreasonably low. The first included GMPE was the modified G16 GMPE recently developed to the Fennoscandian conditions. The second GMPE was derived from the Dahle function by the author. The modified Dahle GMPE was calibrated to Fennoscandia in the applicability range of Rhyp <= 200 km and M_w <= 6,5. A comparison to the measured data and the other GMPEs suggests that the modified Dahle GMPE underestimates ground motion for M_w < 5,0 in near distance (Rhyp <= 10 km). Therefore, we included the modified Dahle GMPE in the logic tree with a relatively small weight factor. We ran the seismic hazard analyses on EZ-FRISK and compiled the ground response spectra (GRS) following the logic tree. The GRS were compiled for a range of annual frequencies of exceedance (AFE = 10-4 a-1 - 10-8 a-1), but the thesis only discusses the results at AFE = 10-5 a-1 due to its significance in nuclear safety. We compared the computed GRS with the current GRS of the Hanhikivi 1 site. Including the new GMPEs alleviated the unphysical features in the current Hanhikivi 1 GRS caused by the drastically different ranges of the Pezeshk and Fennoscandian GMPEs. In ...