Reducing Uncertainty in the Seismic Design Basis for the Waste Treatment Plant, Hanford, Washington
- Pacific Northwest National Laboratory, Richland, WA (United States)
- EnergySolutions, Richland, WA (United States)
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 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)
- Research Organization:
- WM Symposia, 1628 E. Southern Avenue, Suite 9 - 332, Tempe, AZ 85282 (United States)
- OSTI ID:
- 21294760
- Report Number(s):
- INIS-US-09-WM-07434; TRN: US10V0294040950
- Resource Relation:
- Conference: WM'07: 2007 Waste Management Symposium - Global Accomplishments in Environmental and Radioactive Waste Management: Education and Opportunity for the Next Generation of Waste Management Professionals, Tucson, AZ (United States), 25 Feb - 1 Mar 2007; Other Information: Country of input: France; 7 refs
- Country of Publication:
- United States
- Language:
- English
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