ML19098B305

5/13/1975 Summary of Meeting with NRC Staff, VEPCO, & Stone & Webster Corp to Discuss Possibility of Differential Settlement for Major Safety Related Structures

ML19098B305
Person / Time
Site:	Surry
Issue date:	07/23/1975
From:	Ragone S, Stallings C Virginia Electric & Power Co (VEPCO)
To:	Goller K Office of Nuclear Reactor Regulation
References
Serial No. 541
Download: ML19098B305 (5)

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VIRGINIA ELECTRIC AND POWER COMPANY RICHMOND,VIROINIA 23261 July 23, 1975 Mr. K. R. Goller, Assistant Director Serial No. 541 for Operating Reactors PO&M/JTB:clw Division of Reactor Licensing Office of Nuclear Reactor Regulation Docket Nos. 50-280 U.S. Nuclear Regulatory Commission 50-281 Washington, D. C. 20555 License Nos. DPR-32 DPR-37

Dear Mr. Goller:

On May 13, *197 5-, representatives of Vepco and our architect-engineers, Stone & Webster Engineering Corporation, met with members of the Regulatory Staff in Bethesda, Maryland to discuss the possibility of differential settle-ment having occurred.between various major safety related structures at the Surry Power Station, Unit Nos *. 1 and 2. The purpose of this letter is to for-mally document information presented at the meeting substantiating the fact that significant differential settlement has not occurred between structures and that there are no safety implications associated therewith.

The major items discussed at the meeting were:

.1. The presentation of survey data taken during the period May 1()-,13,' 1975-

2. The.comparison of the current data with prior data

3. The results of the visual inspection of structures

.4. The future surveillance which will be performed to provide additional information regarding potential settlement

5. The significance of our findings.

Each of these items is briefly discussed below.

Table 1, attached hereto, presents the data which was recorded during the May 15, 1975 survey. As indicated on the table, the elevations at the various locations are based on the U.S. Coast and Geodetic Survey (USC&GS) horizontal control marker "Vain" as the datum. As part of the investigation,

, e VIRGINIA E:r,ECTRIC AND POWER COMPANY TO Mr. K. R. Goller Page 2 a first order survey was run from USC&GS marker "Bacon 1932" located at Bacons Castle, approximately six (6) miles from the Surry Power Station, to "Vain 1938", a horizontal USC&GS marker located in close proximity to the station. The "Bacon" to "Vain" survey accuracies and level loop closures are within the definition specified by the .U.S. Department. of Commerce, National Oceanic and Atmospheric Administration, National Ocean Survey as First Order.

Based on the elevation of "Bacon 1932"; L953 adjustment, the elevation of l'Vain 1938 11 was measured to be 25.521. This value is 0.{)71 feet higher than the elevation of 25.45 used as the datum for the May 1975 station survey. The elevation of 11Vain 11 was surveyed in 1966 and found to be 25.45 at that time.

Table 1 also presents the data available for February 1971 and April 1972.

These data were obtained from original field survey*. books used during con-struction and were not meant to be used for the determination of long term settlement. Since they are the only historical data available, they are being used for comparison purposes. Several comments should be made in regard to*

the February 1971 and April 1972 data. Based on the field survey books, the February 1971 survey used "Vain" (25 *.45) as the original reference elevation, with "Manhole A.T. No. l" (27.43} as a temporary.benchmark. In April *1972, a survey loop was run from "Manhole A. T. No.* 111 (assumed at elevation 27. 43) to "Vain" which resulted in "Vain" having a measured elevation of 25.-54. Because "Vain" was a USC&GS marker, it was assumed.that it had not moved in the time between the two surveys, and therefore; the.elevation of "Manhole A.T. No. 1" was adjusted down by an amount equal t0 the difference between the measured elevation of "Vain" (25.54) and the original ,1966 value of (25.45), i.e .. 0.09 ft.

The corrected survey data is presented in Table 2. The original February 1971 data, as presented in Table 1, have been corrected by subtracting 0.09 foot from each of the.reported elevations. As can be seen, when this correction is made, the February 1971 data compare very favorably with the April 1972 and May

• 1975 data. The only significant difference indicated is the.elevation.of the auxiliary building sump; .i.e. the February *1971 data indicate a higher value than the other two surveys. The approximate 0.03 or.0.04 foot difference can be accounted for by.the thickness of the cover plate over the sump. Based on the review of the survey book, it is only indicated that the lip of the sump was shot, with no specification as to whether the c0ver plate was in position. Based on the physical arrangement, the type of survey which was being performed, and the other-wise_ good agreement of . all other data' it can reasonably be assumed that the February 1971 data include the thickness of the cover plate for the auxiliary building containment.sump. If this value is corrected for the approximate one-half inch thickness of the cover plate it agrees favorably with the other data.

As can be seen from a perusal of the attached tables., when the. corrections discussed above are considered, all data are in good _agreement and.are well within the accuracies of the survey. The corrections noted are based on

e e VIRGINIA EWCTRIC AND POWER COMPANY TO Mr. K. R. Goller Page 3 historical data and appear to be valid based on the review which has been conducted. When correlated with the results of the visual inspection described below, the evidence that no significant differentialsettlement has.occurred appears to.be incontrovertible.

Visual inspections of major interconnecting structures housing safety related equipment, systems, and components were made by individuals possessing expertise in station operations, structures, piping and geotechnical engineering.

Some of the inspectors were the*original designers of .the buildings and piping systems involved. The inspections revealed no indication of differential settlement between interconnecting structures or abnormal piping conditions.

The results of the inspections c0nfirmed that there has been no significant differential settlement of structures of the Surry Power Station, Unit Nos. 1 and 2.

Although there are no signs af differential settlement, a surveillance program has been initiated to reconfirm that differential settlement is not occurring. The surveillance program will consist of establishing a number of survey points which are accessible.duringnormal station operation and an appropriate vertical control benchmark which will.be surveyed on.a periodic basis. The planned frequency for these surveys, in addition to the baseline survey which has already been performed, is as follows:

1. 6 manths after initial survey

.2. 1 year after initial survey

3. 2 years after initial survey The surveys will be terminated after two (2) .years, unless there are s.ignificant indications of differential settlement.

The investigations conducted at the Surry Power Station, Unit Nos *. 1 and 2, indicate that signif.icant differential settlement has net. occurred and that piping systems have not been displaced as a result of differential settlement.

Therefore, there have.been no safety implications identified as a result of our investigations *

.We trust that the information contained herein will satisfy your needs.

v/

~ce v~~d Attachments cc: Mr. Norman . C. Moseley

TABLE 1 SURVEY DATA SURRY POWER STATION UNIT NOS. 1 AND 2 ELEVATION (FEET)

LOCATION FEB '71 3 APRIL '72 MAY '75 No. 1 Turbine Pedestal 5.814 5.733 5.73 5.797 5. 722 5. 72 No *. 2 Turbine Pedestal Auxiliary Building Sump 1. 784 1.652 1. 66 e

Containment No. l Column 16 21. 783 21.689 21.70 Column 18 21. 782 21. 682 21.69 Containment No. 2 Column 17 22.754 No Point Located No Point Located Manhole A.T. No. l 27.43 27.34 27.35 Vain 25.45 3 25.45 2 25.45 1 1 The elevation of 11 Vain 11 was assumed to be at elevation of 25.45 feet since it is a Coast and Geodetic Survey marker. Other recorded elevations for the May 1975 are based on "Vain" as the datum.

2 The elevation of 11 Vain 11 was checked following the measurement of the elevation of Manhole A.T.

No. 1. The check indicated that the elevation of 11 VainH was 25.54 feet. Since 11 Vain 11 is a USC&GS marker it was assumed to*be at its established elevation of 25.45 feet and "Manhole A.T. No. l" was adjusted downward by 0.09 foot.

3 February 1971 survey as*sumes a *datum of 25.45 feet at "Vain" based on the earlier (1966) survey from Bacons Castle.

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TABLE 2*

'.

CORRECTED SURVEY DATA

. SURRY POWER STATION UNIT NOS. 1 AND 2 ELEVATION (FEET)

LOCATION FEB '71** APRIL '72 MAY '75 No. l Turbine Pedestal 5. 72 5.733 5,73 a No. 2 Turbine Pedestal 5. 71 5. 722 5. 72 Auxiliary Building Sump* 1.69 1.652 1.66 Containment No. l Column 16 21.69 21.689 21.70 Column 18 21.69 21. 682 21.69 Containment No. 2 Column 17 22.66 No Point Located No Point Located Manhole A.T. No. l 27.34 27.34 27.35 Vain 25.45 25.45 25.45

• In 1971 it is believed the top of the cover plate was shot rather than the lip of the sump which was shot in 1972 and 1975 (thickness of cover plate approximately 0.04- ft).

• • February 1971 data cori;ected to Manhol~ A.T. No. 1" which is assumed at 27.34 ft.

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