ML20040H126
| ML20040H126 | |
| Person / Time | |
|---|---|
| Site: | Summer  |
| Issue date: | 02/08/1982 |
| From: | Nichols T SOUTH CAROLINA ELECTRIC & GAS CO. |
| To: | Harold Denton Office of Nuclear Reactor Regulation |
| References | |
| RTR-NUREG-0717, RTR-NUREG-717 NUDOCS 8202170235 | |
| Download: ML20040H126 (6) | |
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Ebbruary 8, 1982 d,
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Mr. Harold R. Denton, Director g
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U. S. Nuclear Regulatory Comission Washington, D. C.
20555
Subject:
Virgil C. Suntner Nuclear Station Docket No. 50/395 Service Water Pond Structures SER Itms 1.8.20
Dear Mr. Denton:
South Carolina Electric and Gas anpany has reviewed Supplement 3 of the Safety Evaluation Reprt for the Virgil C. Stmmer Nuclear Station (NUREG 0717) item 1.8.20 and section 2.5.4.
Based on this review we provide the following conments in the order addressed in the SER.
FACIORS CONTRIBITTING 'IO THE STRUCTURAL SETTLEMENT
'Ihe SER states that the select fill beneath the foundation level was campacted with more noisture than allowed by the specifications.
However, as shown in Table 1 of Report No. 2 (dated June 28, 1978),
all of the 24 in-place density tests below the foundation level in the vicinity of the Pumphouse and Intake Structure show that the moisture specifications were met, i.e.,
that the empaction noisture content ranged from 1 permntage point below to 4 percentage pints above the optimum noistura content, except for one test which was slightly drier.
It is also pointed out in the SER that three of the four block samples frcm the West Embanknes* below the Pumphouse foundation level had average moistnre contenu above the specification limit. However, the noisture content of the fill frequently changed between the time the fill was cmpactM and the block samples were obtained, due to ambient humidity cr precipitation. This is documental for West Embankment Block Sample UDS-3, for example, which had an average moisture content 5.9 3 00I percentage points above optimum. The inspection report of September 3
4,1973, by the Resident Geotechnical Engineer indicates that no filling was possible on the day that the sample was obtained because
/ f of rain over the Irevious weekend and the high humidity that day.
It should also be noted that the properties of a cmpacted material are determined by its moisture content at the time of cmpaction. It was naturally recognized that the select fill would became saturated after filling of the Service Water Pond and, therefore, engineering property tests for design and verification were conducted on samples which were saturated following campction at the specified moisture content.
8202170235 820208 PDR ADDCK 05000395 E
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Mr. Harold R. Denton Pbbruary 8,1982 Page_2 i
i The SER refers to the moisture content of samples obtained from Borings WE-6 and WE-7 in September,1977. It is suggested that since the misture content at-elevation 360 varies frcan 22 to 27 percent.
(about 5 to 10 percentage points above the optimum moisture content) the fill was too wet when placed. As reported in FSAR Question 362.19, however, even though the Service Water Ibnd hai not yet been filled the groundwater level in the fill was rising. At the time of the borings, the groundwater level was elevation 365 and thus the samples at elevation 360 were saturated and had recisely the I
moisture content which would be anticipated under those conditions.
Therefore, in no way could this data be construed to indicate that the fill was placed with too much water.
FACIORS C0fffRIBUfING TO THE CRACKING OF THE INTAKE STRUCWR_E_
The SER states that the recent investigation report shows that the thickness of fill and saprolite beneath the eastern half of the i
Intake Structure is different than used in the settlement analyses.
This statement is Irobably tased on the subsurface trofile shown on Figure 5 of our report dated March 6,1981. However, as noted on.the figure, the two recent borings, WE-14 and WE-15, are located 10 feet north of the Intake Structure. These borings show a different condition than that shown in older Boring WE-5, located about 30 feet north of the Intake Structuro, and are also different than the actual conditions beneath the Intake Structure, due to the steeply sloped original ground contours in the area before construction. The conditions at the eastern end of the Intake Structure used for the settlement analysis were based upon the foundation contours shown in FSAR Figure 2.5-109 as well as Boring WE-5. 'It should be noted that the results of Borings WE-14 and WE-15 were consistent with the foundation contours. Therefore, it is concluded that the trofile used in the settlement analysis was sufficiently accurate for the purpose. Very little settlement occurred at the eastern end of the Intake Structure, due to the lack of significant load; thus, the exact stratigraphy at that location is not critical.
The SER also states that the "more heavily loaded Pumphouse would be expected to settle nore than the nore lightly loaded Intake Structure." In fact, the weights of the structures have relatively little l influence on the settlenent. The weight of the surrounding embankment fill is the primary load on the subsoils, and the Pumphouse and Intake Structure merely settled along with the entire embankment. Essentially the same settlement profile along the Intake Structure would have occurred even if the Pumphouse were not Iresent and that area was filled with soil, a
Mr. Harold R. Denton.
February 8, 1982
'Page 3 The. statement that the variable foundation loadings of these contiguous structures were not considered in the original design is not correct. The correct values were used in the analysis. As has been clearly demonstrated by the laboratory testing and the actual performance of the embankments and structures, it was the overestimation of the 14cunc:,clidation pressure of the saIrolite that caused the underestimation of settlement. Additionally, the..
pumphouce and the intake structure are not contiguous, and the settlement of the Immphouse did not cause the cracking of the tunnel. The Intake Structure cracked because of the non-uniform settlement experienced by the intake structure.
PtFf0RE SETTLEMENTS The SER states that "for a backpressure of 60 feet of water....
the compressibility of the saprolite appears to increase". This contention ic clearly not supported by the test data. Wo tests were conducted at a backpressure of 60 feet (26 psi), one on select fill and one on saprolite. The saprolite test showed an increase in cmpressibility and the select fill test showed a decrease. Each of these tests was part of a series of three tests, with backpressures of 0, 13 and 26 psi. Since these were uncontrolled field samples, as W to controlled samples reconstituted in the laboratory, it is normal that there would be variations in material properties between each test speiman in both series. In the select fill series, the moisture content and void ratio of the-26 psi test specimen was lower than those of the others, and thus a lower canpressibility would be ea g ued.
In the saprolite series, the moisture content and void ratio of the 26 psi speiman was larger than the other specimens and
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thus a greater ccepressibility would be expected.
In both cases,-
this is exactly what happened and we believe that the backpressure has no influence on the conpressibility.
3 The SER suggests that additional settlement may be anticipated -
due to creep and because of structural change in the saIrolite due to high water tressures. It is also pertinent to note that the fourdation soils have been subjected to pore pressures for almost 4 years which are equal to the full long-term pcessures and, to date, I
there-is no field evidence to support the position as stated by the staff in the SER. To the. contrary, the structures have continued to rebound very slightly as predicted. However, should any settlement occur in the' future, it would be detected by the existing monitoring program.
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- The' movements of the structures for the 12 months of 1981 were as follows:
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Mr. Harold R. Denton Ebbruary 8, 1982 Page 4 Pumphouse 0.01 Inch Downward Intake Structure West End 0.04 Inch Upward Intake Structure Middle 0.05 Inch Upward Intake Structure East End 0.01 Inch Ibwnward Wese measurments are very small, and p obably less than the accuracy of the monitority systs. Thus, it is concluded that the structures have essentially stabilized. In addition, the average grouMwater level in the seven west embankment piezameters has been stable at about elevation 420.9 for the period from August to December, 1981.
PERMANENT ENBANKMENT MOVEMENT UNDER SEISMIC CONDITIONS Using "very conservative" soil properties, the SER
" conservatively" estimates that the displacement of the West Embankment under SSE conditions would be in the range of 2 inches.
Our analysis, presented in FSAR Question 362.46, concludes that the deformation would be not more than 1.5 inches and probably significantly less. Ibwever, we concur that the Intake Structure should be inspected following the measurement in the plant of a seismic event of severity greater than or equal to the CBE.
SE. TLEMENT OF THE SERVICE WATER PIPELINES T
Based on the settlement of the Service Water pipelines aM the surveyed profile of the induced bending stress the SER concludes that the pipe has adequate strength to accmodate this additional stress.
This conclusion is supported by our subnittal of March 6,1981, entitled " Supplemental Investigations Service Water Pond West j
Embankment."
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MONI'K) RING REQUIREMENTS The SER lists four requirements for future monitoring, which are discussed below.
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1.
Ebur settlement points are required near the Pumphouse to monitor both horizontal and vertical movements of the West anbankment. Wree settlement monuments are already in place (as reported in SCE&G submittal dated Oct.1979 entitled "Pinal Report Service Water Intake Structure Settlement Effects and Related Work")
near to the Pumphouse and adjacent to West Embankment piezameters WE-8, WE-12 and WE-12A. We nonuments are located about 19 to 33
O Mr. Harold R. Denton February 8, 1982 Page 5 feet from the edge of the abankment. Since their installation in Septanber,1978, these monuments have shown the following total movements:
WE-8 0.43 Inch Upward WE-12 1.13 Inch Upward WE-12A 1.43 Inch Upward However, Monuments WE-8 initially underwent a " seating" adjustment, settling 0.43. inches during the first six months. Also, 1
Monument WE-12 was disturbed by earthworks in November,1979. If these early disturbances are neglected, the total movements for the most recent 2-year period fran December,1979 through December,1981 were:
WE-8 0.43 Inch Upward WE-12 0.49 Inch Upward WE-12A 0.56 Inch Upward mese movements are quite uniform and do not show any indication of instability. Unfortunately, the nonuments were not set up to read horizontal movements, like the ones on the North and South Dams.
In order to set up a horizontal nonument Irogram the coordinate
'Tations of the existing monuments will be established to an
> racy of 0.01 feet, using the permanent plant site base lines and Je.,rence points. Because WE-12 and WE-12A are only about 16 feet apart, two additional nonitoring monuments will be installed. %e locations of the."new" monuments will be provided at a later date.
2.
SCE&G commits to perform periodic surveys of the subnerged West anbankment slope to detect unusual movement as outlined in item 4.
3.
SCE6G commits to perform periodic underwater inspection of the Intake Structure as described in ita>n 4.
The SER required remedial action for any cracks found to be. larger than 0.015 inches. mis number seems to be very small, in light of the fact that only those cracks which exceeded a width of 0.012 inches were grouted.
Therefore, cracks discovered to be greater than 0.015 inches will be reported to the staff and an engineering evaluation made of the significance of these cracks. Additional inspections will be conducted following the measurement in the plant of a seismic event greater than or equal to the OBE.
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Mr. Harold R. Denton Ebbruary 8, 1982 Page 6 4.
'Ihe schedule for itms 1-3 above is required to be in accordance with Regulatory Guide 1.127. This doc ment requires annual inspections for the first 4 years following water impoundment, 2-year intervals for the next 4 years, and 5-year intervals thereafter, if warranted by the results of revious inspections. Since the water I
was impoundel in Ebbruary, 1978, it is our interpretation that inspections would be required early in 1982,1984,1986,1991, and at 5-year intervals thereafter.
If you have any questions, please let us know.
Very truly yours, T. C. Nichols, Jr.
NEC:lkb cc:
V. C. Summer T. C. Nichols, Jr.
G. H. Fischer H. N. Cyrus H. T. Babb D. A. Naman M. B. Whitaker, Jr.
W. A. Williams, Jr.
O. S. Bradham R. B. Clary M. N. Browne A. R. Koon G. J. Braddick-J. L. Skolds J. B. Knotts, Jr.
B. A. Bursey C. L. Ligon (NSRC)
J. C. Ruoff J. P. O'Reilly NPCF File
.