ML14190A185
| ML14190A185 | |
| Person / Time | |
|---|---|
| Site: | Cook  |
| Issue date: | 07/09/2014 |
| From: | Indiana Michigan Power Co |
| To: | Office of Nuclear Reactor Regulation |
| Balazik M, NRR/JLD, 415-2856 | |
| References | |
| Download: ML14190A185 (20) | |
Text
Donald C. Cook Nuclear Plant Site Seismic Hazard Screening Information Exchange July 9, 2014 1
CNP Site Seismic Hazard Screening Results Donald C. Cook Nuclear Plant (CNP) screens in for performance of:
Seismic Risk Evaluation Spent Fuel Pool Evaluation High Frequency Evaluation Expedited Seismic Evaluation Process (ESEP) is in progress 2
CNP Site Seismic Hazard Screening Results 3
Seismic Hazard Reevaluation
Background
The NRC identified areas where the NRC preliminary seismic hazard evaluation differed from the CNP submitted report.
- CNP used six base case velocity profiles in the evaluation, whereas the NRC used three base case profiles in its preliminary evaluation.
- Minor differences in the near surface profile granularity assumed by the NRC vs. the CNP submittal values.
The NRC also indicated that they were unable to replicate licensees GMRS perhaps due to differences in standard deviation of log normally distributed Amp Factor as a function of input rock motion.
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Seismic Hazard Reevaluation
Background
CNP used available site specific information and indirect data to develop the site response (SPID Section 2.4.1)
- Site geological licensing information from late 1960s is available (Preliminary Safety Analysis Report, Appendix A, Site Environmental Studies, 1967)
- Detailed, measured soil and soft-rock dynamic parameters to extensive depths are not available 5
Seismic Hazard Reevaluation
Background
Summary of Geological Conclusions (UFSAR Section 2.3.3)
- Geology of site and surrounding area is basically simple. A thick sequence of sand dunes, beach sands and glacial lake and till deposits conceals the underlying shale bedrock
- Bedrock characteristics and geological features at the site conform to the regional conditions
- No fault or other adverse geologic phenomenon is known or suspected in the vicinity of the site Subsurface geology was investigated by means of 19 test borings, 2 seismic refraction surveys, an uphole velocity survey, and laboratory testing prior to initial licensing. The report of site geology is included in Appendix A to the Preliminary Safety Analysis Report, Site Environmental Studies.
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Seismic Hazard Reevaluation Source Data Geological Column information from Preliminary Safety Analysis Report Appendix A, Site Environmental Studies dated 1967 7
Seismic Hazard Reevaluation Source Data UFSAR Figure 2.3-2 8
Seismic Hazard Reevaluation CNP used a site-specific geological profile consistent with results of available previous geological investigations and evaluations (UFSAR Section 2.3, Geology) 9
Seismic Hazard Reevaluation CNP used 6 velocity profiles in the evaluation using available site-specific data.
- These 6 profiles address uncertainty resulting from limited availability of measured soil and soft-rock parameters, including shear-wave velocity (Vs) data.
- The 6 alternative profiles consist of 3 profiles with shallow depths and 3 profiles with deep depths.
- The relative weights on the 6 profiles are 0.2, 0.15, 0.15, 0.2, 0.15 and 0.15.
- This representation is consistent with SPID Section 2.4.1 and Appendix B.
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Seismic Hazard Reevaluation CNP low strain damping values (kappa) used for CNP GMRS development Effective Kappa estimates were determined using SPID Appendix B when no site-specific nonlinear dynamic material properties were available for CNP soils or firm rock
- Total Effective Kappa estimated based on small strain damping contributed by the profile with the addition of the hard basement rock value of 0.006s.
- Base case profiles P1, P2 & P3, with 127 of soil overlying hard rock, kappa contributed by soil low strain damping was about 0.002s resulting in total kappa (total effective kappa) values of 0.008s.
- Base case profiles P4, P5 & P6, with 127 soil and 3,387 firm rock, contribution from low strain damping in soil and rock curves to 500 then 1.25% below (0.018s, 0.028s, 0.010s) with 0.006s for hard rock for total effective kappa 0.024s, 0.034s & 0.016s.
- Epistemic uncertainty in profile damping (kappa) ranges from 0.007s to 0.034s.
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Seismic Hazard Reevaluation Questions & Responses What are the bases for velocities as well as lack of velocity gradients for both soil and rock layers?
Response
PSAR Appendix A is the source of data for the sub-surface seismic parameters at the CNP site. This Appendix is based on a test program that included 19 test borings, 2 seismic refraction surveys, an up-hole velocity survey and laboratory tests. PSAR Appendix A summarized recommended values of compressional wave velocity, Poissons ratio and shear wave velocity within a Geological Column Table (Plate II C-1). Each of these values includes the method of derivation, i.e. measured/calculated/estimated.
This same Geological Column Table is provided in the CNP GMRS report as Table 2.3.1-1 (Slide 7).
Average values are provided in this table in part due to the obscure layering 12
Seismic Hazard Reevaluation Questions & Responses What is the basis for the high P-wave velocities (17,000 fps) for the sedimentary rocks as shown in Table 2.3.1-1?
Response
The compressional wave velocity for the sedimentary rock was estimated during the development of PSAR Appendix A.
The 17,000 fps value was reviewed and found to be in a reasonable range for sedimentary rock.
Other site-specific subsurface geology velocity data including the recently completed Independent Spent Fuel Storage Installation did not extend to the sedimentary rock layer.
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Seismic Hazard Reevaluation Questions & Responses What is the basis for assumed Poisson ratio of 0.2 for sedimentary rock?
Response
The Poissons ratio for the sedimentary rock was estimated during the development of PSAR Appendix A.
The 0.2 Poissions ratio value was reviewed and found to be in a reasonable range for sedimentary rock.
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Seismic Hazard Reevaluation Questions & Responses What is the basis for considering sedimentary rock to have reference rock velocity for 3 of the 6 profiles rather than just 1 of 3?
Response
The PSAR Appendix A profile indicated a shear-wave velocity in the sedimentary rock units of 10,000 fps, so it was considered appropriate to give credibility to this model. 3 of the 6 profiles, comprising 50% of the weight given to alternative profiles, represented this model, with the other 3 profiles (50%
weights) modeling a deeper depth to reference rock.
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Seismic Hazard Reevaluation Questions & Responses What is the basis for control point such that beach sands are not included in velocity profiles?
Response
A constant velocity profile for the soil column was selected by judgment.
Upon review, it appears that a 25 ft thick layer of beach sand with a Vs of about 800 ft/sec should have been included in the Control Point profile.
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Seismic Hazard Reevaluation Questions & Responses What is basis for second sentence in Section 2.3.2.1 as soil layers total about 128 ft?
The firm soil material over the upper 500 ft was assumed to have behavior
Response
The upper 500 ft of the profile is analyzed with non-linear properties. Of that, the top 127 ft is modeled as soil, the remaining 373 ft is modeled as sedimentary rock.
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Seismic Hazard Reevaluation Questions & Responses Total site kappa values for P4, P5, P6 are similar to staffs values; however basis for statement in Section 2.3.2.2 is unclear
- a. As documented in Reference 14 for shallow, less than about 3000 ft soil/firm rock sites, kappa may be estimated based on the small strain damping contributed by the profile
- b. To what depth were EPRI rock curves used?
- c. Does above statement refer to kappa estimate for P1 P2 & P3 only
Response
The kappa estimates for all six profiles were described in response to NRC Primary Issue presented on Slide 11 18
Seismic Hazard Reevaluation Questions & Responses Range for total standard deviations (sT or slnAFlx) of ln AF given rock motions are much lower than staffs values shown in NRC Slides
- a. Affects hazard integral probability calculations P(AF>z/xlx)
- b. Consistent with standard deviations in Table A2-B2 for specific models, profiles, and PGA levels?
Response
We believe the difference may be due to comparing a total standard deviation to a standard deviation from one curve.
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Seismic Hazard Reevaluation Summary
- The CNP GMRS has been developed in accordance with site-specific data, the NRC endorsed SPID guidance and reasonable technical judgment
- CNP will continue implementation of ESEP to meet requirement for completion and ESEP report submittal by December 31, 2014
- CNP will perform seismic risk evaluation for report submittal by June 30, 2017
- CNP will continue to work with NRC to achieve understanding and agreement on appropriate hazard profiles for use in station seismic risk assessment 20