ML20212N244
| ML20212N244 | |
| Person / Time | |
|---|---|
| Site: | Beaver Valley |
| Issue date: | 03/09/1987 |
| From: | Carey J DUQUESNE LIGHT CO. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| 2NRC-7-045, 2NRC-7-45, TAC-62885, NUDOCS 8703120413 | |
| Download: ML20212N244 (9) | |
Text
.
'Af 2'IRC-7-045 Bewer Vall
- o. 2 Unit Project Organization
, copy 4 64 52 Ext.160 P.o. Box 328
.4 arch 9, 1987 Shippingport, PA 15077 United States Nuclear Regulatory Commission ATTN:
Document Control Desk Washington, DC 20555
SUBJECT:
Beaver Valley Power Station - Unit No. 2 Docket No. 50-412 Response to SER Confirmatory item 2
REFERENCE:
DLC Letter 2NRC-6-lll, dated October 23, 1986, Mr. J. J. Carey to Mr. Harold R. Denton Gentlemen:
The above-noted reference provided a partial response to SER Confirmatory item 2 (Differential Settlements of Buried Pipes).
Attached to this letter is the remainder of the response to this item.
DLC believes that the attached r esponse provides the additional information necessary for the NRC to close SER Confirmatory item 2.
DUQUESNE LIGHT COMPANY
/
By J.
W.' Carey Sr. Vice President JD0/ijr NR/JD0/CFRM/ITM Attachment AR/NAR cc:
Mr. P. Tam, Project Manager
- w/ attachment Mr. J. Beall, NRC Sr. Resident Inspector
- w/ attachment Ms. A. Asars, NRC Resident inspector
- w/ attachment Dr. T. E. Mur ley, NRC Region 1 Ad;ninistrator
- w/ attachment INPO Recor ds Center
- w/ attachment Bool
'I G703120413 B70309 PDR ADUCK 05000412 E
United States Nucle r Regulatory Commission
. Response to SER Confirmatory iten 2 Page 2 COMMONWEALTH OF PENNSYLVANIA )
SS:
COUNTY OF BEAVER On this day
/fd/[)
, /k[, before me, a Notary Public in and for said Commonwealth and County, personally appeared J. J. Carey, who being duly sworn, deposed and said that (I) he is Senior Vice President of Duquesne Light, (2) he is duly authorized to execute and file the foregoing Submi ttal on behalf of said Company, and (3) the statements set forth in the Submittal are true and correct to the best of his knowledge.
(
N sunus c. FATIC2E. BOTARY PuWgry Pub li Not sinPPINCPoti 8080. BEARE M sy commssect!EIrtBE10CT.23. M sem. PennerWais assesimie d 88#r#8
SER Confirmatory item 2 (Differential Settlements of Buried Pipes)
From SER Section 2.5.4.3.3, Page 2-51:
Longitudinal sections of pipelines (shown in FSAR Figures 2.5.4-52 and 2.5.4-54 and discussed in response to Question 241.2) indicate a considerable thickness of sitty clay directly below compacted granular backfill.
Also, as seen in FSAR Figure 2.5.4-54, a steep gr adient exists in the enbankment slope that contains the 30-inch-diameter-pipelines from the present floodplain to the main plant area.
These conditions can cause differential settlements of the overly-ing pipelines.
The applicant has been asked to evaluate this differential settlenent and include the results in an FSAR amendment; the staff regards this as a confirmatory item.
Response
The pipelines referred to above are the service water system (SWS) pipelines shown in plan on Figure 1.
Stresses in the pipes induced by estimated differ-ential settlenents have been computed as descr ibed in FSAR Section 3.78.3.12.3.
The computed stresses compare f avor ably with allowable limits.
The response is provided in two parts.
The first deals with the SWS piping from the intake structure to the valve pit northwest of the r eactor containment.
The second discusses the SWS piping in the vicinity of the safeguards area valve pit.
SWS Piping From The intake Str ucture to the Valve Pit g The SWS pipelines from the intake structure to the valve pit are 30-inch diame-ter steel pipe.
They were intalled in 1973 from the intake str ucture up to the concrete encasement for the BVPS-1 circulating water lines and blocked-off.
Installation resumed in 1976 and was completed to the valve pit by early 1977.
Soil profiles along the centerline of each pipe at e shown on Figure 2.
The pipe alignment traverses the old floodplain of the Ohio River, and the top sur f ace of the clay in the profile corresponds to the original ground surf ace in 1954 prior to any construction at the site.
AlI of the soil overlying the clay is fill material placed later.
From a detailed study of construction drawings, construction phct.ographs, and periodic site topographic mapping, it was determined that the ground surf ace was largely brought to the grades shown on Figure 2 by 1974.
Estimated site topography in 1974 is shown on Figure 3.
In the area of concern, namely the steeply inclined portion of the pipelines, the clay is normally ccnsolidated under the weight of the fill, but it becomes stiffer and over consolidated with distance from the Ohio River.
Settienent of the pipelines is the result of consolidation of the clay caused by the fill.
Tne clay layer was completely renoved within the limits of the Vibt oflotation Densification of the under lying sands and gravels (Figure 1).
Primary consolidation of the clay due to fill placement to the 1974 levels occurred pr ior to pipe installation, so that settlement is due primarily to secondary compression of the clay.
Settlement profiles along the center line of each pipe are shown on Figure 2.
The settlements shown i epresent the consoli-dation of the clay from the year the pipes were installed to the end of Page 1 of 2
F a 40-year plant life that starts in 1987.
They were determined using one-dimensional consolidation theory, taking into consideration the stress increases and resulting consolidation of the clay that occurred before install-ing the pipe.
Settlement at the valve pit is based on measured settlement data.
Soil properties and the stress history of the clay were evaluated from laboratory test data on undisturbed samples that are presented in Appendix 2.5D of the BVPS-2 FSAR.
The rate of secondary compression was estimated from the measured settlements of the alternate access facility.
SWS Piping in the Vicinity of the Safeguards Area Valve Pit Tne SWS pipelines in the vicinity of the safeguards area valve pit are 24-inch otameter steel pipe.
Settlement of buried safety-related piping in the main plant area is of concern mainly in the vicinty of penetrations into structures.
The modeling procedure described in FSAR Section 2.5.4.10.2 is used to estimate a profile of settlement along buried piping that extends from structures out into the yard ar ea.
Stresses induced in the piping system due to the settle-ments at e evaluated by the procedures described in FSAR Section 3.7B.3.12.3 and are compared to allowable values.
Stresses are below allowable limits; the presence of the clay is not detrimental to the buried piping.
Soil conditions in the vicinity of the safeguards area valve pit are shown on FSAR Figure 2.5.4-52.
Under lying the select granular fill is a layer of very stiff silty clay approximately 25 feet thick.
The top of the clay layer is roughly coincident with the original ground sur f ace in 1954, prior to any con-struction activity at the site.
Consolidation tests performed on undisturbed block samples recovered from the reactor containment excavation (FSAR Appendix 2.50) indicate that the clay is heavily overconsolidated, even under the pre-sent overburden.
The maximum past pr essure ranges ft om 9.5 ksf to 18 ksf, and dverages about 15 ksf.
The present in-situ vertical effective stress at the elevation of the test specimens is about 7.4 ksf, indicating an overconsoli-dation ratio of 2.0.
The clay was deposited by the Ohio River and overconsol-idation was probably caused by dessication as a result of fluctuating Ohio River levels.
The present normal water level is about El. 665 f t.,
roughly the bottom elevation of the clay.
The ground surf ace was raised in stages and by 1972 was at the final grade of El. 735 f t.
From construction photographs, in March 1977, during the soil densification pr ogr am, the fill placed nor theast of the reactor containment in the area of the future SWS piping was excavated to El. 690 ft.
as shown on FSAR Figure 2.5.4-19.
At the time of the excavation, the clay layer was fully consolidated under the weight of the fill material placed between 1954 ano 1972.
Additional consolidation settlement in the clay caused by repIatement of the original backfilI with compacted structural fili to El. 735 ft. is not expected.
Tne model used to compute settlements of the pipe and the adjacent valve pit consider s only the stress increase caused by the plant structures.
Computed settlements at selected points near the safe-guards at ea valve pit are shown on Figure 4.
Stresses induced in the piping systems due to these settlements ar e within allowable limits.
Page 2 of 2
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