ML18003A283
| ML18003A283 | |
| Person / Time | |
|---|---|
| Site: | Harris  |
| Issue date: | 10/17/1978 |
| From: | Mcduffie M CAROLINA POWER & LIGHT CO. |
| To: | Harold Denton Office of Nuclear Reactor Regulation |
| References | |
| NUDOCS 7810270123 | |
| Download: ML18003A283 (25) | |
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RECIPIENT:
ORIGINATOR:
REGULATOR NFORMATION DISTRI BUTION TEM DOC DATE:
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/4 COPIES RECEIVED:
COMPANY NAME<AROLINA PWR i LI T
SUBJECT:
LTR SIZE:
10 ENCL o 'de eo o ic eval a io f schistose zone in west wall of main dam diversion aonduit as well as colo ic ma of u stream west wall of diversion conduit in res onse to 781004 NRC re uest.
Ma available in Central File.
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4 UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D. C. 20566 l~ORAÃ)Usaf FOR:
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US hhRC/TIDC/Distribution Services Branch Special Document Handling Requirements 0 1.
Please use the following special distribution list for the attached document.
2.
The attached document requires the following special considerations:
Q Do not sand oversize enclosnre to the i'DR.
V Only one oversize enclosure was received please return for his~ m +8c~~ Pg Q Proprietary inforaat"on send affidavit only to the NRC PDR Q Other: (specify) cc:
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+I'~s Carolina power a Ught Compang ~1//gr October 17, 1978
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Mr. Harold R. Denton, Director Office of Nuclear Reactor Regulation United States Nuclear Regulatory Commission Washington, D. C.
20555 SHEARON HARRIS NUCLEAR POWER PLANT, UNIT NOS ~ 1, 2, 3, AND 4 DOCKET NOS. 50-400, 50-401, 50-402, AND 50-403 GEOLOGICAL FEATURE AT THE WEST WALL OF MAIN DAM DIUERSION CONDUIT
Dear Mr. Denton:
On May 10, 1978, representatives of Carolina Power
& Light Company (CP&L) met with your staff to discuss various aspects of the construction schedule for the main and auxiliary dams at the Shearon Harris Nuclear Power Plant (SHNPP) site.
During this meeting, CP&L described the sequential type construction activities which were to be implemented during the construction of the SHNPP's dams.
Also during the meeting, your staff identified construc-tion milestones which were of interest to them and requested that site visits be arranged to view those activities.
On May 30, 1978, CP&L formally trans-mitted the construction schedules for both dams and committed to provide ample notification prior to reaching the milestones identified in the May 10, 1978,
- meeting, as well as any additional milestones subsequently identified so that NRC site visits could be arranged without delaying construction.
On September 19, 1978, representatives from CP&L conducted members of your staff on an initial site visit during the construction of the main and auxiliary dams.
Areas viewed by your staff included exposed portions of the auxiliary dam foundation, the main dam spillway area at the railroad
- bridge, the west main dam core trench walls and west conduit wall, a portion of the channel at the main dam core trench which had gust been cleaned, and the impervious borrow area.
Several schistose zones which pass through the granitic rock mass at the upstream west wall of the diversion conduit excava-tion were identified to the site visiting team.
A geologic map of the wall, which was near completion, was shown to the staff during the inspection.
Mr. Tom Cardone, NRC staff geologist, requested that a copy of the geological map be forwarded when completed.
Accordingly, the geological map of the upstream west wall of the diversion conduit is provided as Attachment A.
On October 4, 1978, CP&L was requested by a telephone call from your staff to provide a geologic evaluation of a particular schistose zone in the west conduit wall as well as the geological maps.
Carolina Power
& Light Company is hereby providing the requested evaluation of the schistose zone as Attachment B.
As described in this attachment, the schistose zones resulted from deformation which occurred over 225 million years ago and thus does not constitute a capable fault as defined by Appendix A of 10CFR100.
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October 17, 1978 Geologic conditions along the main dam conduit are similar to those at the railroad bridge/spillway, an area only 1,000 feet to the southwest, where a small geologic anomaly was reported on December 8,
1977.
Carolina Power Light Company provided the results of the evaluation of that feature on December 15, 1977, indicating that the feature was typical of the local geology and that a number of these relic structural features might be found as excavation proceeded.
On December 14, Mr. Robert Jackson, an NRC staff geologist, visited the site and concluded that the feature was not a capable fault within the meaning of Appendix A to 10CFR100, and that the staff would anticipate discovery of similar features of this type elsewhere in the area as the excavation proceeded.
Mr. M.
Cutchin, counsel for the NRC staff, concluded in his letter of December 19, 1977, to the ASLB, that the presence of such faults was not significant to the decision on issuance of construction permits for SHNPP.
During the May 10, 1978, meeting with your staff, documented by letter of May 30, 1978, CP&L committed to provide an interim report containing the mapping of the cutoff trench for each dam prior to the submittal of the Final Safety Analysis Report (FSAR) and to provide a final mapping report in the FSAR. It was CP&L's understanding that unquestionably ancient geological features, such as those located at the main dam spillway and west main dam conduit wall, need not be reported at the time of discovery, but should be identified and discussed with the submittal of geological maps, as indicated above.
Since we anticipate routinely discovering numerous additional features such as these, in the future we plan to follow the actions as outlined below:
1, Any feature or fault identified by the site geologist which can be readily associated with geologic structural features which are geologically old (at least Pre-Quarternary) will be documented in the interim report for each dam cutoff trench and/or the FSAR.
This type of feature is defined to be "not capable" by 10CFR100, Appendix A.III.(g) and, therefore, is not required to be reported immediately.
2.
Any feature or fault identified by the site geologist which cannot be readily associated with geologic structural features which are geologically old (at least Pre-Quarternary) will result in the initiation of a more detailed investigation.
If this investigation fails to resolve the age of a feature in a timely manner, CP&L will contact the NRC and provide as much detailed information concerning the feature as available at that time.
Carolina Power
& Light Company believes that the above actions satisfy your staff's concern and the requirements of 10CFR100, Appendix A for reporting of geological features.
If it is not your understanding that these actions satisfy your requirements, please let us know immediately so that we can reevaluate the need. to notify the staff and the Atomic Safety and Licensing Board of geological features discovered at the SHNPP site.
Yours very truly, M. A. McDuffie Senior Vice President Engineering
& Construction MAM/mf Attachments cc:
Mr. J.
P. O'Reilly NRC I&E Region II
I FIGURE 2B
, KEY FOR GEOLOGIC SECTION WEST WALLOF DIVERSION CONDUIT STATIONS 1+70 TO 4+05 1.
Foliation strike and dip: 000,40 W.
2.
Contact of mica schist andhomblende mica gneiss dip and strike: 048, 50 NW.
3.
Foliation strike and dip: 030, 35 NW.
4.
Foliation strike and dip: 030,35 NW.
5.
Small fold of foliation: Axial Plane 048,45 NW; Axis dips48 to the 300.
6.
Foliation: 007,44 NW.
7.
Closely spaced, tight fractures and joints; no movement apparent.
8.
Weathered schist present in joint/fracture.
9.
Small fold of foliation inmicaceous layer: Axial Plane: 020,35 NW; Axis dips30 to the 265 10.
Tight fold of foliation inmicaceous layers Axial Plane: 038,46 NW; Axis dips 2'-25 to the 265 11.
Crack is open 5-6 inches; may have been caused by an infillingmica schist unit destroyed by blasting.
12.
Zone of abundant fracturing and quartz stringers; no movement apparent.
13.
Clear to white quartz; blocky; very fractured.
14.
Clear to white quartz; blocky; very fractured.
15.
Highly foliated granite; remainder of these zones consist of highly deformed icompressed and folded) mica schist.
16.
Thick mica schist layer in joint.
17.
Hornblende-mica. gneiss unit in mica schist.
18.
Areas of highly deformed quartz veins.
These veins may have been injectedinto the rock or "sweated" out of the granite from a reasonably close distance.
Whatever the emplacement mechanism of the quartz, it was before the final deformation.
19.
Areas of highly deformed quartz veins.
These veins may have been injected into the rock or "sweated" out of the granite from a reasonably close distance.
Whatever the emplacement mechanism of the quartz, it was before the final deformation.
20.
Zones of ductile deformation in the granites related to tectonic deformation; these are old bands of deformation.
21.
The smaller kink bands do not pass from the granite through to the mica schist zones.
The larger kink bands do appear to pass through from the granite into the mica schist zone.
Oiscrepancies between the foliation in the granite and the mica schist are probably functions of more intense deformation in the mica schist and a type of refraction of the foliation.
22.
Zone of highly weathered rock near the top of wall. The mica schist weathers much more. readily than the surrounding rock.
23.
Foliation: 033,55 NW; kink bands: 040,40 SE.
24.
Foliation: 000,30 W.
25.
Orientation of mica schist zone:
020, 60 NW; the foliation in the mica schist and felsic volcanics is much better developed and more steeply dipping than in the surrounding granites.
26.
Zone of highly weathered rock.
27.
Joint crosses schist zone without any offset.
28.
Foliation: 355,25 SW.
29.
Bottom of wedge of more highly weathered rock.
30.
Zone of ductile shear strain; a joint has developed along the zone
- 31. Joint filledwith quartz, small shear zones present.
Several joints intersect here, forming blocks of granite rock.
32.
Weathered and fractured rock.
33.
Soine weathered mica schist in an open joint.
34.
Zone of jointed/fractured and weathered rock.
35.
Some jointed/fractured granite rock alon~ the edge of mica schist zone; more highly weathered than surrounding granite.
36.
Attitude of mica schist zone:
042o, 44 NW; the foliation in the granite becomes more intense with proximity to the mica schist zone and also dips more steeply than the foliation further away from the mica schist zone.
Foliation ot granite several inches from mica schist:
005, 50 NW; foliation of granite three feet from mica schist: 005, 28 NW. The granite in this area contains pieces of baked country rock. There are several ductile shear zones present in the granite.
In places it appears that the more steeply dipping foliation in the granite is overprinted on the less steep foliation.
37.
Joint orientation: strike 067, dip varies from 80 NW to 80 SE.
38.
Offset of a ductile shear zone in granite by two small fractures which die out in several feet. Offset is 2 inches along one fracture and 1 inch along the other. These fractures do not offset any major joints. /See detail sketch ar end o/Keyj.
39.
Foliation of the granite within the mica schist zone is quite variable in orientation: 050, 55 NW; 028,60 NW; 050, 58 NW; 020,50 NW. Orientation of foliation inmicaschist: 048,60 NW.
40.
Joint orientation: 058, 75 SE'oliation: 020, 38 NW; major joint orientation: 065, 35 NW.
41.
a) Joint orientation: 005, 60 NW; b) joint orientation: 068, 70 SE; granite foliation: 005, 45 NW; orientation of mica schist zone:
015,66 NW; foliation of mica schist: 005, 58 NW.
42.
Jointorientation: 070,80 SE; foliation: 008,40 NW.
43.
Mica schist zone: 352, 70 SW (local dip near quartz).
44.
Joint orientation(varies):
042 60 NW; 041,52 NW; 338,30 SW. Foliation: 025 44 NW.
45.
Granite boudins enclosed in mica schist.
46.
A major area of mica schist with many highly deformed granitic pods and boudins included within. Generally, the foliation of the schist is concordant with the boundaries of the boudins.
Discordance was probably caused by some late rotational movement of the boudin, or possibly because the boudins were originally part of granite units folded in with the mica schist.
There is a good deal of flattened/sheared granitic material enclosed within the mica schist.
47.
Zones of mica schist with interfoided and boudinaged granitic rock.
There are many tight and isoclinal folds present in this mica schist.
These zones are more highly weathered than the surrounding granitic rocks.
48.
Foliation: 015,38 NW.
49.
Joint face Iface of slope)i 318, 45 NE.
50.
Orientation of joint with weathered granite present in it: 080,43 SE; foliation: 022, 30 NW.
51.
Orientation of mica schist zone: 024,46 NW.
Folds in mica schist:
Axial Plane: 050o,42 SE; Axis: 30 to 194, Axial Plane: 042,37 SE; Axis: 24 to 192 Micaceous schistosityt 045, 40 NW.
52.
Many fine, steeply dipping joints in this area.
Joint orientations:
Some of these terminate at the mica schist unit and some cut through the mica schist.
53.
Jointorientation: 065,72 SE; 085,45 NW; 010,60 NW; foliation:018,42 NW.
54.
Joint orientation: 048,65 SE; foliation: 002,40 NW.
DETAILSKETCH OF NUMBER 38 Joint This joint does not offset any other joints.
Dies out in 6 feet.
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ocrrle Sheer Zone get gV Dies out In 33 ln.
Joint does not offset any joint below. 59 in. long. There are no slickensides on exposed face This joint does not offset next joint up {32 In.), nor any other feature it crosses.
Dies out in 5 to 6 feet.
f34 r'n.J Docr/le Sheer Zo Joint O37 JOINT DETAIL Appears to very slight drag folding of shear zone at joint Scale:
1" ~ 10"
ATTACHMENT B An Evaluation of the Geology Observed in the Excavation for the Conduit Beneath the Main Dam, SHNPP The main dam and spillway are to be constructed in gneisses and schists of the North Carolina Piedmont.
These rocks are considerably older than the Triassic sedimentary rocks which underlie the power plant (i.e.,
possibly 600,000,000 as opposed to about 200,000,000 years old).
Prior to the deposition of the Triassic sedimentary units, the lithologies constituting the Piedmont were deeply buried and sub)ected to several periods of deformation.
The burial and deformation changed the original rock units to the gneisses and schists now exposed.
Zn addition, the rocks were pointed, folded, and faulted, which permitted the intrusion of many granitic dikes and quartz veins.
During the Triassic period and somewhat earlier, Piedmont rocks were unearthed by
- erosion, and the erosional debris was deposited in basins created during the Triassic by tensional stresses.
Since the Triassic, the area has been under no major, tightly deforming regional tectonic compressive stress.
- Hence, most deformational features in the Peidmont rocks, such as faults and folds, must be older than the beginning of the Triassic period (i.e., greater than 225,000,000 years old).
Samples of core drilled from the gneiss at the main dam site and two nearby locations have been radiometrically dated, as reported to the Nuclear Regulatory Commission by Carolina Power
& Light Company in "Shearon Harris Nuclear Power Plant, Fault Investigation:
Responses to Mr. U. R. Butler' letter of May 16, 1975, Question 9."
The dates prove that the gneiss was heated most recently more than 250 million years ago.
This heating was due to the intrusion of granitic plutons throughout the Peidmont about 300 million years
- ago, and marks the end of the last period of regional meta-morphism.
At most places within the Piedmont, regional compressional stresses associated with this metamorphism resulted in folding and pointing of the rocks, in)ection of quartz veins, and minor faulting of the veins (See "Final Geologic Report on Brecciated
- Zones, Catawba Nuclear Units 1 and 2, Duke Power
- Company, March 1, 1976, and January 31, 1977").
The following is a description of the rock at the conduit wall which was mapped to determine whether there had been any movement along the zones since the last deformation/metamorphism to affect these Piedmont rocks.
The west wall of the diversion conduit is composed of foliated granite hornblende mica gneiss, and mica schist.
Quartz is present in small amounts as pods and veins in all lithologies.
The quartz is predominantly blocky, white to light grey, with pyrite present in many locations.
The granites contain numerous small inclusions of baked country rock, usually not more than several inches in longest dimension.
Weathered granitic pods and layers are included within the mica schist units.
The boundary between the granite and the hornblende mica gneiss is gradational, with stringers of baked hornblende mica schist included in the granite at the contact.
The rock is predominantly fresh, with some areas of slightly to moderately weathered rock in joints.
The mica schist tends to be moderately weathered, especially when occurring in wide zones as at stations 3+40, 3+30, 3+20, 2+50, 2+25, etc.
As shown on the map, some highly weathered to com-pletely weathered rock occurs near the top of the wall.
The granite lenses included in the mica schist are slightly to moderately weathered, probably because the mica schist transmits water more easily than massive granite, especially once the schist weathers slightly.
Joints are generally tight, with relatively smooth, clean surfaces which are generally free of slickensides, clay, or other mineralization.
Slight to moderate weathering has occurred on joints in several places, especially where mica is present along the joint face.
The major points dip steeply to the north-west and southeast, with an average strike of 065 One large sub-horizontal joint, located between stations 3+50 and 3+60 at elevations of 185 feet to 190 feet, is open several
- inches, apparently from blast destruction of a mica schist zone.
Minor joints, usually less than 10 feet long, are present.
These have variable strikes and sub-vertical orientations.
All of the above units have been affected by several regional folding and metamorphic events of Paleozoic age; therefore, these events are much older than the deformation which formed the Triassic Basin Faults.
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From the amount of exposure presently available, it appears that deformation produced folds, which are now seen as intrafolial and rootless intrafolial folds, having the pervasive foliation as their axial planes.
This foliation, generally oriented 020'5' 50'W in this wall, is best developed in the mica schist zones and the adjacent granite and most poorly developed near the centers of the massive granites.
These early folds are only seen in the mica schist.
Later folding has distorted this foliation and the lithologic contacts.
One set of later folds trends to the northwest, plunging at roughly 35'.
There are at least two other sets of folds which fold all previous planar and linear
- features, the final folding producing kink bands.
The kink bands are pre-dominantly in the granite, the larger ones passing into the mica schist.
Deformation in the granites is also expressed by the presence of numerous ductile shear zones that are restricted to the granites and are a product of the regional Paleozoic tectonic deformation.
The zones are two to three inches across and often outlined by epidote.
Folds are abundant in the mica schist.
Folds are present in the granites and the hornblende mica gneiss, but are not well developed in this wall because of its orientation.
In places, a poorly developed second foliation is present in all lithologies, but is best developed in the mica schist and in the ad)acent granite.
The exact time of granite intrusion has not yet, been determined, but must have preceeded=deformation or occurred during the early stages of folding because of the foliation in the granite.
These granites would have behaved essentially as rigid bodies during deformation.
The bulk of the folding was taken up by the mica schist and the edges of the granite bodies.'he foliation in the granite is more intensely developed adjacent to the mica schist areas.
In some areas (stations 2+50 and 2+20), granite which has been intruded into and folded with the mica schist has been boudinaged.
The granite boudins signify extensive flattening across the mica schist zones.
Since the boudins have not been rotated out of the foliation plane, it is unlikely that there has been much simple shear across the mica schist zones.
Local minor discordances between the foliation of the mica schist and the edges of the granite boudins may indicate that the granite was initially
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infolded with the mica schist and then boudinaged as can be seen in the core trench.
Later folding deformed both the mica schist and the boudinaged granite.
In conclusion, it can be stated that defoxmational features seen in these rocks at the Main Dam are typical of this type of structural/metamorphic terrain.
Any movements which may have occurred in the geologic past in the mica schist
- zones, occurred during the Late Paleozoic regional tectonic events which affected these rocks.
There are several lines of evidence indicating that there has been no movement along these mica schist zones since the last regional tectonic deforma-tion:
(1) There is no fault gouge or breccia present in or near the mica schist zones.,
Some highly deformed rocks, with textures approaching that of a mylonite, are present near the mica schist zones, but these were formed by compxession across these rocks during the folding events; (2) Numerous folds are present in the mica schist
- zones, and the folds have not been disrupted by shearing.
Orienta-tions of folds present in the mica schist are the same as similar age folds in the hornblende mica schist and granite; (3) The smaller mica schist zones are crossed by )oints in the surrounding rocks.
None of these )oints are offset.
Very few joints are seen to cross the larger mica schist zones, but this is most likely a function of the different material properties of the schist and the granite; (4) There are no areas of metamorphism from frictional heating by faulting; (5) Larger kink bands are seen to pass from the granite into the mica schist; and (6) The granite boudins have not been rotated since they were formed.
Mapping in the main dam core trench shows that these mica schist zones are very irregular in form and that they pinch out in the granite and hornblende mica gneiss.
These mica schist units are crossed by numerous points which are not offset.
The mica schist has been int'ensely folded and several phases of this folding are visible.
In many cases, the mica schist and adjacent granite axe folded together'n small 6 inch to 18 inch amplitude) parasitic folds; good evidence that no younger faulting movement has occurred across these zones.
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We have concluded from the evidence as described above that the schistose zones resulted from deformation which occurred over 225 million years ago; therefore, these zones cannot be described as "capable faults" as that term is defined in Appendix A to 10CFR100.
Therefore, these features pose no problems for the integrity or safety of the Shearon Harris Nuclear Power Plant main dam.
PHOTO 1
View south of core trench at Station 3+10.
Fault A offsets vein (behind hat of geologist with board) and offsets dikelet at center of photo near en echelon faults B.
Note NW fracture between vein and dikelet, which is not offset.
No. SHNPP Main Dam 11/78 1 11/10/78
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PHOTO 2 Invert of conduit trench Stations 2&0 to 2+80. Note three schistose zones No. SHNPP Main Dam 11/78 3 11/10/78
PHOTO 3 Invert of conduit trench Stations 2+45 to 2+60. Note boudins enclosed in mica schist left of pump No. SHNPP Main Dam 11/78-4 11/10/78
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PHOTO 1
West Wall of Conduit Trench from Stations 3+50 to 1+70 No. SHNPP Main Dam 11/78-2