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Title: Reducing Uncertainty in the Seismic Design Basis for the Waste Treatment Plant, Hanford, Washington

Abstract

The seismic design basis for the Waste Treatment Plant (WTP) at the Department of Energy’s (DOE) Hanford Site near Richland was re-evaluated in 2005, resulting in an increase by up to 40% in the seismic design basis. The original seismic design basis for the WTP was established in 1999 based on a probabilistic seismic hazard analysis completed in 1996. The 2005 analysis was performed to address questions raised by the Defense Nuclear Facilities Safety Board (DNFSB) about the assumptions used in developing the original seismic criteria and adequacy of the site geotechnical surveys. The updated seismic response analysis used existing and newly acquired seismic velocity data, statistical analysis, expert elicitation, and ground motion simulation to develop interim design ground motion response spectra which enveloped the remaining uncertainties. The uncertainties in these response spectra were enveloped at approximately the 84th percentile to produce conservative design spectra, which contributed significantly to the increase in the seismic design basis.

Authors:
; ; ;
Publication Date:
Research Org.:
Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
960319
Report Number(s):
PNNL-SA-53948
830403000; TRN: US0904371
DOE Contract Number:
AC05-76RL01830
Resource Type:
Conference
Resource Relation:
Conference: Waste Management 2007: Proceedings of the Symposium on Waste Management
Country of Publication:
United States
Language:
English
Subject:
11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS; DESIGN; GROUND MOTION; NUCLEAR FACILITIES; SAFETY; SIMULATION; SPECTRA; VELOCITY; WASTE MANAGEMENT; WASTE PROCESSING

Citation Formats

Brouns, Thomas M., Rohay, Alan C., Reidel, Steve, and Gardner, Martin G. Reducing Uncertainty in the Seismic Design Basis for the Waste Treatment Plant, Hanford, Washington. United States: N. p., 2007. Web.
Brouns, Thomas M., Rohay, Alan C., Reidel, Steve, & Gardner, Martin G. Reducing Uncertainty in the Seismic Design Basis for the Waste Treatment Plant, Hanford, Washington. United States.
Brouns, Thomas M., Rohay, Alan C., Reidel, Steve, and Gardner, Martin G. Tue . "Reducing Uncertainty in the Seismic Design Basis for the Waste Treatment Plant, Hanford, Washington". United States. doi:.
@article{osti_960319,
title = {Reducing Uncertainty in the Seismic Design Basis for the Waste Treatment Plant, Hanford, Washington},
author = {Brouns, Thomas M. and Rohay, Alan C. and Reidel, Steve and Gardner, Martin G.},
abstractNote = {The seismic design basis for the Waste Treatment Plant (WTP) at the Department of Energy’s (DOE) Hanford Site near Richland was re-evaluated in 2005, resulting in an increase by up to 40% in the seismic design basis. The original seismic design basis for the WTP was established in 1999 based on a probabilistic seismic hazard analysis completed in 1996. The 2005 analysis was performed to address questions raised by the Defense Nuclear Facilities Safety Board (DNFSB) about the assumptions used in developing the original seismic criteria and adequacy of the site geotechnical surveys. The updated seismic response analysis used existing and newly acquired seismic velocity data, statistical analysis, expert elicitation, and ground motion simulation to develop interim design ground motion response spectra which enveloped the remaining uncertainties. The uncertainties in these response spectra were enveloped at approximately the 84th percentile to produce conservative design spectra, which contributed significantly to the increase in the seismic design basis.},
doi = {},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Tue Feb 27 00:00:00 EST 2007},
month = {Tue Feb 27 00:00:00 EST 2007}
}

Conference:
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  • The seismic design basis for the Waste Treatment Plant (WTP) at the Department of Energy's (DOE) Hanford Site near Richland was re-evaluated in 2005, resulting in an increase by up to 40% in the seismic design basis. The original seismic design basis for the WTP was established in 1999 based on a probabilistic seismic hazard analysis completed in 1996. The 2005 analysis was performed to address questions raised by the Defense Nuclear Facilities Safety Board (DNFSB) about the assumptions used in developing the original seismic criteria and adequacy of the site geotechnical surveys. The updated seismic response analysis used existingmore » and newly acquired seismic velocity data, statistical analysis, expert elicitation, and ground motion simulation to develop interim design ground motion response spectra which enveloped the remaining uncertainties. The uncertainties in these response spectra were enveloped at approximately the 84. percentile to produce conservative design spectra, which contributed significantly to the increase in the seismic design basis. A key uncertainty identified in the 2005 analysis was the velocity contrasts between the basalt flows and sedimentary interbeds below the WTP. The velocity structure of the upper four basalt flows (Saddle Mountains Basalt) and the inter-layered sedimentary interbeds (Ellensburg Formation) produces strong reductions in modeled earthquake ground motions propagating through them. Uncertainty in the strength of velocity contrasts between these basalts and interbeds primarily resulted from an absence of measured shear wave velocities (Vs) in the interbeds. For this study, Vs in the interbeds was estimated from older, limited compressional wave velocity (Vp) data using estimated ranges for the ratio of the two velocities (Vp/Vs) based on analogues in similar materials. A range of possible Vs for the interbeds and basalts was used and produced additional uncertainty in the resulting response spectra. Because of the sensitivity of the calculated response spectra to the velocity contrasts between the basalts and interbedded sediments, DOE initiated an effort to emplace additional boreholes at the WTP site and obtain direct Vs measurements and other physical property measurements in these layers. One core-hole and three boreholes have been installed at the WTP site to a maximum depth of 1468 ft (447 m) below ground surface. The three boreholes are within 500 ft (152 m) of and surrounding the high level waste vitrification and pretreatment facilities of the WTP, which were the Performance Category 3 (PC-3) structures affected by the interim design spectra. The core-hole is co-located with the borehole closest to the two PC-3 structures. These new measurements are expected to reduce the uncertainty in the modeled site response that is caused by the lack of direct knowledge of the Vs contrasts within these layers. (authors)« less
  • In August 2007, Secretary of Energy Samuel W. Bodman approved the final seismic and ground motion criteria for the Waste Treatment and Immobilization Plant (WTP) at the Department of Energy’s (DOE) Hanford Site. Construction of the WTP began in 2002 based on seismic design criteria established in 1999 and a probabilistic seismic hazard analysis completed in 1996. The design criteria were re-evaluated in 2005 to address questions from the Defense Nuclear Facilities Safety Board (DNFSB), resulting in an increase by up to 40% in the seismic design basis. DOE announced in 2006 the suspension of construction on the pretreatment andmore » high-level waste vitrification facilities within the WTP to validate the design with more stringent seismic criteria. In 2007, the U.S. Congress mandated that the Secretary of Energy certify the final seismic and ground motion criteria prior to expenditure of funds on construction of these two facilities. With the Secretary’s approval of the final seismic criteria this past summer, DOE authorized restart of construction of the pretreatment and high-level waste vitrification facilities.« less
  • In August 2007, Secretary of Energy Samuel W. Bodman approved the final seismic and ground motion criteria for the Waste Treatment and Immobilization Plant (WTP) at the Department of Energy's (DOE) Hanford Site. Construction of the WTP began in 2002 based on seismic design criteria established in 1999 and a probabilistic seismic hazard analysis completed in 1996. The design criteria were reevaluated in 2005 to address questions from the Defense Nuclear Facilities Safety Board (DNFSB), resulting in an increase by up to 40% in the seismic design basis. DOE announced in 2006 the suspension of construction on the pretreatment andmore » high-level waste vitrification facilities within the WTP to validate the design with more stringent seismic criteria. In 2007, the U.S. Congress mandated that the Secretary of Energy certify the final seismic and ground motion criteria prior to expenditure of funds on construction of these two facilities. With the Secretary's approval of the final seismic criteria in the summer of 2007, DOE authorized restart of construction of the pretreatment and high-level waste vitrification facilities. The technical basis for the certification of seismic design criteria resulted from a two-year Seismic Boreholes Project that planned, collected, and analyzed geological data from four new boreholes drilled to depths of approximately 1400 feet below ground surface on the WTP site. A key uncertainty identified in the 2005 analyses was the velocity contrasts between the basalt flows and sedimentary interbeds below the WTP. The absence of directly-measured seismic shear wave velocities in the sedimentary interbeds resulted in the use of a wider and more conservative range of velocities in the 2005 analyses. The Seismic Boreholes Project was designed to directly measure the velocities and velocity contrasts in the basalts and sediments below the WTP, reanalyze the ground motion response, and assess the level of conservatism in the 2005 seismic design criteria. The characterization and analysis effort included 1) downhole measurements of the velocity properties (including uncertainties) of the basalt/interbed sequences, 2) confirmation of the geometry of the contact between the various basalt and interbedded sediments through examination of retrieved core from the core-hole and data collected through geophysical logging of each borehole, and 3) prediction of ground motion response to an earthquake using newly acquired and historic data. The data and analyses reflect a significant reduction in the uncertainty in shear wave velocities below the WTP and result in a significantly lower spectral acceleration (i.e., ground motion). The updated ground motion response analyses and corresponding design response spectra reflect a 25% lower peak horizontal acceleration than reflected in the 2005 design criteria. These results provide confidence that the WTP seismic design criteria are conservative. (authors)« less
  • The seismic design basis for the Waste Treatment Plant (WTP) at the Department of Energy's Hanford Site near Richland, Washington, was established in 1999 based on an extensive probabilistic seismic hazard analysis completed in 1996 by Geomatrix Consultants, Inc. In subsequent years, the Defense Nuclear Facilities Safety Board (DNFSB) staff questioned the some of the assumptions used in developing the seismic design basis, particularly the adequacy of the site geotechnical surveys. Existing site-specific shear wave velocity data were considered insufficient to reliably use California earthquake response data to directly predict ground motions at the Hanford Site. To address this concern,more » the Department of Energy's Office of River Protection (ORP) and Pacific Northwest National Laboratory (PNNL) developed and executed a plan for acquiring site-specific soil data down to approximately 500 feet, and for reanalyzing the effects of deeper layers of sediments interbedded with basalt. New geophysical data were acquired, analyzed, and interpreted with respect to existing geologic information gathered from other Hanford-related projects in the WTP area. Existing data from deep boreholes were assembled and interpreted to produce a model of the deeper rock layers consisting of inter-layered basalts and sedimentary interbeds. These data were analyzed statistically to determine the variability of seismic velocities. The earthquake ground motion response was simulated on a large number of models resulting from a weighted logic tree approach that addressed the geologic and geophysical uncertainties. Weights in the logic tree were chosen by a working group based on the strength or weakness of the available data for each combination of logic tree parameters. Finally, interim design ground motion spectra were developed to envelope the remaining uncertainties. The results of this study demonstrate that the site-specific soil structure (Hanford and Ringold formations) beneath the WTP is thinner than was assumed in the 1996 Hanford Site-wide model. This thinness produces peaks in the response spectra (relative to those in 1996) near 2 Hz and 5 Hz. The soil geophysical properties, shear wave velocity, and nonlinear response to the earthquake ground motions are known sufficiently, and alternative interpretations consistent with this data did not have a strong influence on the results. The structure of the upper four basalt flows (Saddle Mountains Basalt), which are inter-layered with sedimentary interbeds (Ellensburg Formation), produces strong reductions in the earthquake ground motions that propagate through them to reach the surface. Uncertainty in the strength of velocity contrasts between these basalts and interbeds resulted from an absence of measured shear wave velocities (Vs) in the interbeds. For this study, Vs in the interbeds was estimated from older, limited compressional wave (Vp) data using estimated ranges for the ratio of the two velocities (Vp/Vs) based on analogues in similar materials. The Vs for the basalts, where Vp/Vs is well defined, still is limited by the quality and quantity of the Vp data. A range of possible Vs for the interbeds and basalts was included in the logic trees that produced additional uncertainty in the resulting response spectra. The uncertainties in these response spectra were enveloped at approximately the 84. percentile (based on the logic tree) to produce conservative design spectra. This conservatism increased the seismic design basis by up to 40% compared to the 1999 values. Because of the sensitivity of the calculated response spectra to the velocity contrasts between the basalts and interbedded sediments, additional boreholes and direct Vs measurements through these layers are now being planned. The new measurements are expected to reduce the uncertainty in the site response that is caused by the lack of direct knowledge of the Vs contrasts within these layers. (authors)« less
  • This interim report documents the collection of site-specific geologic and geophysical data characterizing the Waste Treatment Plant site and the modeling of the site-specific structure response to earthquake ground motions.