Mühleberg Nuclear Power Plant
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).

Scope | Solutions

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

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