ML021070151
| ML021070151 | |
| Person / Time | |
|---|---|
| Site: | Diablo Canyon  |
| Issue date: | 04/11/2002 |
| From: | Page W Pacific Gas & Electric Co |
| To: | Office of Nuclear Material Safety and Safeguards, Office of Nuclear Reactor Regulation |
| References | |
| +sispmjr200505, -RFPFR | |
| Download: ML021070151 (18) | |
Text
Response to NRC question William D. Page William D. Page Senior Engineering Geologist Senior Engineering Geologist PG&E Geosciences Department PG&E Geosciences Department NRC/PG&E Open Meeting, San Francisco, CA Diablo Canyon Independent Spent Fuel Storage Installation April 11, 2002
Question:
Explain Degree of Confidence in Results
Input parameters used for modeling Input parameters used for modeling potential large-scale rock mass movements potential large-scale rock mass movements are realistic and conservative are realistic and conservative
Confidence in predicted foundation Confidence in predicted foundation conditions at CTF, ISFSI Pads and ISFSI conditions at CTF, ISFSI Pads and ISFSI cutslopes cutslopes
Input Parameters for Modeling
Geometry of clay beds well understood Geometry of clay beds well understood
Groundwater conditions known, clay beds Groundwater conditions known, clay beds assumed saturated assumed saturated
Change in dip direction Dip Direction
Temporary perched water on clay beds after storms Main water table
Large-scale Mass Movements
Geologic interpretations of extent of clay Geologic interpretations of extent of clay beds is conservative, but not extreme beds is conservative, but not extreme
Potential slide planes are chosen to follow Potential slide planes are chosen to follow the full extent of more extensive clay beds the full extent of more extensive clay beds and step between clay beds, this assumes and step between clay beds, this assumes minimum rupture of rock minimum rupture of rock
Rock to rock contact along potential slide Rock to rock contact along potential slide plane along clay beds not factored into plane along clay beds not factored into model, this would increase the clay strength model, this would increase the clay strength from that used from that used
Clay Beds Not Continuous
Clay Bed Extent Based on Thickness
Potential Slide Plane Breaks through Rock along Clay Bed Shears offset clay bed Thin areas where rock contact occurs across clay bed Thick areas of clay bed Potential slide plane smoothes undulations of clay bed by breaking through rock
Evidence of No Landslides at ISFSI
No evidence on pre-1971 air photos No evidence on pre-1971 air photos
No evidence in studies for and excavation No evidence in studies for and excavation of borrow site of borrow site
No evidence of any fissures or fissure fills No evidence of any fissures or fissure fills in trenches for ISFSI in trenches for ISFSI
Assumed Displacement of Large Scale Slide Mass
Fractures in the slope larger than 3 to 4 inches Fractures in the slope larger than 3 to 4 inches would have left a record on the slope would have left a record on the slope
No vegetation lineaments (similar to the zones No vegetation lineaments (similar to the zones of intense growth in filled trenches) of intense growth in filled trenches)
No open fractures or soil-filled fractures in No open fractures or soil-filled fractures in trenches on slope trenches on slope
Hillslope is 430,000 years old Hillslope is 430,000 years old
Subjected to many large earthquakes Subjected to many large earthquakes
Assumed 4 inches would occur in one slide Assumed 4 inches would occur in one slide event event
Marine Terraces Q1 Q2 Q3 Q4 Marine Terrace deposits
Hill Slope is 430,000 Years Old, but degraded a Few Tens of Feet Q4 Q5 Marine wave-cut platform (430,000 years old)
Slope 430,000 years ago 1971 slope Marine wave-cut platform older than 430,000 years
Clay beds at base of modeled large-scale movements extrapolated to pre-1971 slope
Results of Sensitivity Study Clay Bed Strengths 0
50 100 150 200 0
50 100 150 200 250 Normal Stress (psi)
Shear stress (psi) 800 psf / 15 deg 3000 psf / 22 deg 800 psf / 36 deg 0 psf / 40 deg 2500 psf / 23 deg 800 psf / 26 deg 0 psf / 37 deg Shallow Model stress range Median Model stress range Deep Model stress range Strength used in study
Confidence in Predicted Foundation Conditions at CTF, ISFSI Pads and Cutslopes
High confidence in rock types predicted High confidence in rock types predicted
Sandstone Sandstone
Dolomite Dolomite
Friable Sandstone Friable Sandstone
Friable Dolomite Friable Dolomite
Clay beds Clay beds
Interpretations with Less Certainty
Locations and percentage of rock types not Locations and percentage of rock types not known with certainty known with certainty
Friable Friable diabase diabase may be encountered and is may be encountered and is expected to have the same properties as expected to have the same properties as friable sandstone friable sandstone
Attitude of clay beds uncertain, more clay Attitude of clay beds uncertain, more clay beds may be exposed beds may be exposed
Precise location of faults uncertain, other Precise location of faults uncertain, other shear zones are expected shear zones are expected
High degree of confidence that there High degree of confidence that there will be no significant surprises will be no significant surprises
Features will be mapped during Features will be mapped during construction construction
Planned mitigation measures will be Planned mitigation measures will be applied as appropriate applied as appropriate Conclusion