ML18249A130
| ML18249A130 | |
| Person / Time | |
|---|---|
| Site: | Brunswick  |
| Issue date: | 08/13/2018 |
| From: | Duke Energy Progress |
| To: | Office of Nuclear Reactor Regulation |
| Shared Package | |
| ML18249A165 | List:
|
| References | |
| RA-18-0131 | |
| Download: ML18249A130 (4) | |
Text
UPDATED FSAR ADDITIONAL GEOPHYSICAL INFORMATION APPENDIX 2B Revision:
26 Appendix:
2B Page:
i of i TABLE OF CONTENTS 2B ADDITIONAL GEOPHYSICAL IINFORMATION [HISTORICAL]................................................................ 1 fa DUKE
~ ENERGY
UPDATED FSAR ADDITIONAL GEOPHYSICAL INFORMATION APPENDIX 2B Revision:
26 Appendix:
2B Page:
1 of 3 2B ADDITIONAL GEOPHYSICAL IINFORMATION [HISTORICAL] is a copy of a letter from Mr. R. L. Whitaker, the geophysicist in charge of the seismic portion of the work done for North Carolina Oil and Gas Company, which documents that the only seismic line running south of Wilmington is the one along Highway 211.
Figure 2B-1 is a map showing the wells from which seismic data was obtained in Brunswick County. is a discussion of the geophysical interpretation of the data.
UPDATED FSAR ADDITIONAL GEOPHYSICAL INFORMATION APPENDIX 2B Revision:
26 Appendix:
2B Page:
2 of 3 ATTACHMENT 1 June 26, 1975 Mr. Gary Forrest CAROLINA POWER AND LIGHT P.O. Box 1551 Raliegh, North Carolina 27602 Re: Seismic Survey NORTH CAROLINA OIL AND GAS COMPANY
Dear Sir:
To the best of my remembrance the only seismic traverse run from North Carolina Oil and Gas Company in the area southwest of Wilmington, North Carolina during the winter of 1965-1966 by a Seismograph Service Corporation field crew under my direction was a line running along Highway 211 between Supply and Southport.
Sincerely,
// Original Signed //
R. L. Whitaker Interpretation Supervisor RLW:ac
UPDATED FSAR ADDITIONAL GEOPHYSICAL INFORMATION APPENDIX 2B Revision:
26 Appendix:
2B Page:
3 of 3 ATTACHMENT 2 Upon examining the seismic cross-section along Highway 211, it is apparent that the reflecting horizons are continuous, flat, and parallel along a gentle eastward dip. Despite the fact that this line runs almost perpendicular to the accepted regional trend, there is virtually no indication of structural features. The two dominant reflections, a horizon within the Cretaceous section and the top of basement (highlighted in yellow and orange, respectively, in Figure 2B-2, Figure 2B-3, and Figure 2B-4) show only three exceptions to a continuous "railroad track" effect:
- a. Graben - Between shotpoints 59 and 61, there is evidence of a downdropped block along the top of basement reflection (Figure 1). There are two reasons for picking faults here, the abrupt truncations in the continuity of the basement reflection and a reversed dip segment lying below the linear extension of the basement reflection. There are no obvious diffractions and no shadow zones. Since these faults only break the basement reflections, it is difficult to assess their precise position and dip. However, the primary interpretational points remain; this is a small tensional feature, and it is older than the overlying Cretaceous sediments since they are not broken by the faults.
- b. Diffractions - The sediments which lie over the basement rock contain lime stringers and calcareous sand lenses. The abrupt truncations of these intermittent layers can generate diffractions. The most prominent examples of these diffractions with stratigraphic origins are shown in Figure 2B-2, highlighted by a dark line. They conform to the proper curvature for a 0.75 to 1.0 compression ratio. They are not believed to have any structural significance and are pointed out because they interrupt the continuity of the basement reflection.
- c. Low velocity layer - In Figure 2B-3 between shotpoints 27 and 28, there is a static delay pattern displayed. It is probably caused by a weathering trough (a generalized term which in this case may refer to a buried stream channel filled with unconsolidated material) at the surface. The interpretative signs that indicate that this anomaly is produced by a low velocity layer are:
- 1. The parallel tracking of reflections at different times due to static time delays
- 2. The lower amplitudes and broader peaks and troughs within the pattern due to energy losses, with the higher frequencies being the most attenuated The gravity and magnetic maps in the vicinity of BSEP show irregular contour surfaces. As was pointed out in our letter of June 4, 1975, from J. A. Jones to B. C. Rusche, the initial response to these maps might be to suspect significant changes in depth to bedrock to be responsible for the contoured undulations. However, the seismic data clearly show that the depth to basement is relatively constant along anomalous slopes that might otherwise be identified as possible faults. Compare Figure 2B-4, Figure 2B-5, and Figure 2B-6 between shotpoints 50 and 60. The radical slopes and undulations of the gravity and magnetic data along this seismic line appear to be in response to lithologic changes in the basement rock rather than changes in its depth.
In summary, the only faults identified are bounding a tensile feature and are older than Cretaceous. The anomalous slopes shown on the gravity and magnetic maps are apparently not due to faulting. The basement appears to be relatively flat and undisturbed since it was peneplained and covered. There are no features identified by this new information which would impose a threat to the safety of the Brunswick Plant.
END-OF-APPENDIX