Light Water Reactor Sustainability Program Advanced Seismic Soil Structure Modeling

Light Water Reactor Sustainability Program Advanced Seismic Soil Structure Modeling

Risk calculations should focus on providing best estimate results, and associated insights, for evaluation and decision-making. Specifically, seismic probabilistic risk assessments (SPRAs) are intended to provide best estimates of the various combinations of structural and equipment failures that can lead to a seismic induced core damage event. However, in some instances the current SPRA approach has large uncertainties, and potentially masks other important events (for instance, it was not the seismic motions that caused the Fukushima core melt events, but the tsunami ingress into the facility). SPRA's are performed by convolving the seismic hazard (this is the estimate of all likely damaging earthquakes at the site of interest) with the seismic fragility (the conditional probability of failure of a structure, system, or component given the occurrence of earthquake ground motion). In this calculation, there are three main pieces to seismic risk quantification, 1) seismic hazard and nuclear power plants (NPPs) response to the hazard, 2) fragility or capacity of structures, systems and components (SSC), and 3) systems analysis. Two areas where NLSSI effects may be important in SPRA calculations are, 1) when calculating in-structure response at the area of interest, and 2) calculation of seismic fragilities (current fragility calculations assume a lognormal distribution for probability of failure of components). Some important effects when using NLSSI in the SPRA calculation process include, 1) gapping and sliding, 2) inclined seismic waves coupled with gapping and sliding of foundations atop soil, 3) inclined seismic waves coupled with gapping and sliding of deeply embedded structures, 4) soil dilatancy, 5) soil liquefaction, 6) surface waves, 7) buoyancy, 8) concrete cracking and 9) seismic isolation The focus of the research task presented here-in is on implementation of NLSSI into the SPRA calculation process when calculating in-structure response at the area of interest. The specific nonlinear soil behavior included in the NLSSI calculation presented in this report is gapping and sliding. Other NLSSI effects are not included in the calculation. The results presented in this report document initial model runs in the linear and nonlinear analysis process. Final comparisons between traditional and advanced SPRA will be presented in the September 30th deliverable.

Energy Research Abstracts

Light-water Reactor Research and Development

The Energy Research Advisory Board (ERAB) was requested to under take an examination of safety research and development (R and D) on light water reactors (LWRs) in order to advise the Department of Energy (DOE) on the adequacy of those efforts for making effective use of nuclear power. In carrying out this examination, DOE asked that ERAB: (1) review the adequacy of DOE's LWR safety R and D management plan prepared pursuant to Public Law 96-567, (2) examine the safety-related R and D conducted by the various government and nongovernment groups, and (3) identify R and D that could result in major design improvements to LWRs. To carry out this examination, ERAB appointed an expert panel. This report contains the results of ERAB's examination of the first two of the above subjects. The Board has yet to consider the subject of nonsafety-related long-term LWR R and D, as also requested by DOE. Furthermore, in keeping with the Department's guidance, this report does not include an examination of the R and D on related activities such as reprocessing, waste management, and the breeder.