Mühleberg, Switzerland

Mühleberg Nuclear Power Plant


The 1,097 MW power plant went into commercial operation in 1971 and consists of a single-unit boiling water reactor. The owner/operator of the Mühleberg Nuclear Power Plant (KKM) needed to submit an updated Level 1 probabilistic safety assessment (PSA) to the Swiss nuclear regulator. SGH developed seismic fragilities of essential structures, systems, and components (SSCs).

Essential safety systems are contained in several buildings. Within the reactor building, the reactor vessel is enclosed by a light bulb-shaped steel drywell connected to a torus-shaped primary suppression chamber supplemented by a secondary suppression chamber. SGH developed seismic fragilities for SSCs, an essential element of the updated seismic PSA. Earthquake ground motion was based on the most recent site-specific seismic hazard. For this project, SGH:

  • Carried out a seismic walkdown of SSCs per EPRI NP-6041-SL
  • Developed a database to document the seismic walkdown
  • Performed probabilistic seismic response analysis of the structures to obtain probability distributions of seismic forces and in-structure response spectra
  • Analyzed soil-structure interaction effects for the KKM structures using CLASSI and SASSI software
  • Developed the seismic fragilities of numerous SSCs per EPRI TR-103959 and EPRI TR-1002988 recommendations
  • Used nonlinear analysis in combination with Latin Hypercube Sampling to develop the seismic fragility evaluation of structures
  • Developed seismic fragilities of essential underground piping systems for displacements due to soil liquefaction
  • Extended the seismic fragility evaluation to address the plant seismic risk during an outage
  • Performed seismic walkdowns to identify seismic-fire and seismic-flood interactions

Project Summary



Completion Date
Repair & Rehabilitation
Structures | Advanced Analysis
BKW FMB Energie AG
Specialized Capabilities
Seismic Engineering | Nuclear | Buried Infrastructure | Computational Mechanics

Key team members

Philip Hashimoto
Philip Hashimoto
Senior Principal