ML13317A722
| ML13317A722 | |
| Person / Time | |
|---|---|
| Site: | San Onofre  |
| Issue date: | 11/02/1981 |
| From: | Moody W Southern California Edison Co |
| To: | Crutchfield D Office of Nuclear Reactor Regulation |
| References | |
| TASK-02-04.D, TASK-02-04.F, TASK-2-4.D, TASK-2-4.F, TASK-RR NUDOCS 8111100532 | |
| Download: ML13317A722 (11) | |
Text
Southern California Edison Company P. 0.
BOX 800 2244 WALNUT GROVE AVENUE ROSEMEAD. CALIFORNIA 91770 W. C. MOODY TELEPHONES MANAGER, NUCLEAR LICENSING NOvember 2 1981 (213) 572-1817 (213) 572-1806 Director, Office of Nuclear Reactor Regulation Attention: D. M. Crutchfield, Chief Operating Reactors Branch No. 5 Division of Licensing U. S. Nuclear Regulatory Commission Washington, D.C.
20555 Gentlemen:
Subject:
Docket No. 50-206 SEP Topics II-4.D and II-4.F San Onofre Nuclear Generating Station Unit 1 Enclosed are the draft assessments for SEP Topics II-4.D, Stability of Slopes; and II-4.F, Settlement of Foundations and Buried Equipment. These assessments are based on the lead topic assessments prepared by the NRC for the Palisades Plant dated April 17, 1981.
Subsequent to preparation of the initial draft of these assessments, we received your letter dated August 5, 1981 which provides additional guidance for the preparation of assessments for these topics.
We have reviewed this guidance relative to the enclosed assessments.
Based on this review, it is concluded that, although the guidance requests a significant amount of additional details regarding these topics, the conclusions of these assessments are not affected. If you require additional information regarding these SEP topics, please let me know.
Very truly yours, Enclosure 8111100532 8111 0 PDR ADOCK 05000206 PDR
SAN ONOFRE NUCLEAR GENERATING STATION, UNIT 1 SYSTEMATIC EVALUATION PROGRAM (SEP)
TOPIC II-4.F -
SETTLEMENT OF FOUNDATION AND BURIED EQUIPMENT INTRODUCTION In order to assure that safety related structures, systems and components are adequately protected against excessive settlement of the foundations, an assessment has been made of the actual movements and performance of the foundations to date.
The scope of this evaluation includes a review of existing geotechnical studies at the site, settlement data during and after construction, performance of equipment and structures, and anticipated settle ments during the design life of the facility.
Using current review criteria, the effect of settlement on safety related structures has been evaluated.
REVIEW CRITERIA The current review criteria for this specific safety topic are:
- 1. SRP 2.5.4
- 2. Appendix A to 10 CFR Part 100
- 3.
NAVFAC DM-7, Design Manual for Soil Mechanics, Foundations, and Earth Structures RELATED SAFETY TOPICS AND INTERFACES None.
(
-2 DISCUSSION Prior to construction the San Onofre site consisted of terrace deposits approximately 55 feet thick, overlying the San Mateo Formation which is about 1000 feet thick at the site. The terrace deposits are comprised of very stiff silty clays overlying dense cemented silty sand with layers of gravels and cobbles. The San Mateo Formation is a yellow-brown very dense, cemented, well graded fine to coarse sand with occasional lenses of thin bedded siltstone.
Prior to construction of the plant, the original site elevation at the top of the bluff ranged from +80 to +115 feet MLLW, with the ground water level at approximately elevation +5 MLLW. The site was developed by excavating a notch in the coastal bluff. The excavation was extended to elevation +19 MLLW with all safety related structures founded on the San Mateo sand materials in their native state or recompacted to 95% of maximum dry density in accordance with ASTM D-1557 standards.
A total of 10 borings were placed at the Unit 1 site ranging in depth from 40 to 295 feet.
Representative samples were taken of the various materials, which are homogeneous in gradation and density across the site.
Field and laboratory testing indicated that the San Mateo sand exhibits extremely high bearing capacity for the shallow spread and mat foundations.
Allowable bearing capacities of 15 to 20 ksf were recommended for static loading with a 50 percent increase during dynamic conditions (Ref. 1&2).
Actual static foundation bearing values ranged from 1 to 11 ksf.
The existing foundations are embedded to depths ranging from elevation +18 to -5 MLLW.
-3 Structural backfill was specified to be compacted to a minimum of 95% of maximum dry density.
In connection with a recent plant modification, a few isolated areas north of the fuel storage building were excavated for placement of new pipe supports.
The footings were small in size and located near the surface.
It was observed that the soil at a few of these locations was not compacted to 95%.
In light, of this, the pipe supports were relocated.
An investigation into this item concluded that this was a localized, near surface condition, due to the presence of congested buried piping in an area which has probably been subjected to repeated rework. Based on the lack of any evidence of settlement in other areas of the plant, it is concluded that this was an isolated condition.
Settlement measurements were made during construction of Unit 1 (Ref.
3).
Actual foundation settlments were less than anticipated during construction.
In addition, there have been no settlement associated problems with the operation of the Unit 1 equipment since construction was completed in 1966.
As part of this evaluation, structures including the turbine pedestal, north and south extensions of the pedestal, east and west heater platforms, reactor auxiliary building, control building, diesel generator building, fuel storage
- building, sphere enclosure building and other safety related component and equipment foundations were inspected for any structural distress caused by settlement or vibration of operating equipment.
There was no evidence of any significant cracking or distress in any of the structures.
This good perform ance is attributed to the original overburden, which preloaded the soil prior to construction, and quality control of foundation installation on both native and recompacted materials.
CONCLUSIONS The recommended allowable bearing capacities utilized in design of the Unit 1 facilities are conservative and provide adequate support for the anticipated loading conditions.
A review of settlements which occurred during and after construction has indicated actual movements less than predicted with no impact on operation of equipment or associated structures. Unit 1 has been in opera tion since 1968 and has experienced no settlement related problems to date.
Based on past records and our recent site inspection of the facilities, it is concluded that the settlement of foundations and buried equipment will not be a safety problem of concern for the Unit 1 facilities.
REFERENCES
- 1.
Southern California Edison Company, October 22,
- 1963, "Report on Foundation Investigation at the San Onofre Nuclear Generating Station Site," Report No. 176.
- 2.
Woodward-McNeill and Associates, SONGS 2 and 3 FSAR, Vol.
3, Section 2.5.4.
- 3.
Southern California Edison Company, Drawing Numbers 567856-3 and 5102275-4, April, 1975.
SAN ONOFRE NUCLEAR GENERATING STATION, UNIT 1 SYSTEMATIC EVALUATION PROGRAM (SEP)
TOPIC II-4.D -
STABILITY OF SLOPES INTRODUCTION This evaluation reviews the static and dynamic stability of all slopes which, if they fail, could potentially adversely affect plant safety during anticipated loading conditions.
In order to assure that all safety related structures, systems and components are adequately protected against the failure of natural
- slopes, the possibility of movement of these slopes is evaluted by comparing forces resisting movements to the driving forces.
To perform this evaluation, the condition of existing slopes was inspected, the slope stability studies previously conducted for San Onofre Units 1,
2&3 were reviewed and the pertinent slopes were analyzed using current design criteria to evaluate their stability under static and dynamic conditions.
REVIEW CRITERIA The current review criteria for this specific safety topic are:
- 1.
SRP 2.5.5
- 2. Appendix A to 10 CFR Part 100
- 3.
NAVFAC DM-7, Design Manual for Soil, Mechanics, Foundations, and Earth Structures
-2 RELATED SAFETY TOPICS AND INTERFACES None.
DISCUSSION The only permanent slope which is close enough to San Onofre Unit 1 structures to require evaluation is located north of the plant.
At its nearest point, the toe of the slope is approximately 105 feet from the sphere enclosure building. The bottom of the slope is at elevation +19 MLLW, and the top is at elevation +93 MLLW.
The slope is graded at 1/2 horizontal to 1 vertical with a bench 15 feet wide, at elevation +48 MLLW. The total slope is protected by a layer of gunite to control erosion and facilitate efficient drainage of surface runoff. The service water reservoir is located on top of this bluff.
The soils at the site consist of an upper formation of terrace deposits comprised of very stiff silty clay overlying dense, cemented silty sand with layers of gravel and cobbles.
These terrace deposits are underlain by the San Mateo Formation, which is a yellow-brown, very dense, cemented, well graded fine to coarse sand with gravel and occasional lenses of thin bedded siltstone.
The upper limit of the ground water table at the site is at elevation +5 MLLW.
-3 Soil strength parameters used in the analysis of the subject slope are:
Terrace Deposits Clay, 0 = 170 C
= 2600 psf Sand, 9 = 380C
= 200 psf San Mateo Formation -
Sand, 0 = 41.50C =
750 psf Where 0 = angle of internal friction and C = cohesion.
These values were obtained from triaxial compression tests on undisturbed and remolded samples (Ref. 1) and represent the lower bound strength of each material.
Based on the results of a static stability analysis in accordance with Reference 2,
the slope has a
factor of safety of 2.3.
Under dynamic conditions, associated with a 0.67g Housner earthquake, this slope is calculated to have a factor of safety of 1.2 against a deep seated slide in accordance,with Reference 3.
During such extreme ground shaking there is a
possibility of only minor sloughing of surface materials occurring.
Although minor movements of the slope may occur, it is concluded that they will not jeopardize the integrity of any safety related structure or adversely affect the operation of the plant due to the distance separating the slope from the nearest structure.
Furthermore, the service water reservoir will not be affected.
CONCLUSION Based upon previous evaluations and our recent analysis using 0.67g Housner loading conditions, it is concluded that the slope at San Onofre Unit 1 is statically stable and is safe during extreme ground shaking with only minor sloughing of surface materials expected.
Any minor movements of slope materials will not affect the operation or performance of safety related structures and equipment.
The existing gunite lining on the entire slope will prevent surface erosion and maintain the long term stability of the slope.
REFERENCES
3, Section 2.5.5.
- 2. Bishop, A. W.,
"The Use of the Slip Circle in the Stability Analysis of Slopes," Geotechnique, Vol. 5, 1955, pp. 7-17.
- 3. N.
M.
- Newmark, "Effects of Earthquakes on Dams and Embanknents," Geotechnique, Vol. 15, 1969, pp. 140-141, 156.