ML20071P234

Forwards Rept on Confirmatory Geotechnical Investigations, Essential Svc Water Pipeline Corridor,Byron Station Units 1 & 2, Per NRC 820601 Request.Rept Reconfirms Previous Conclusion.Ser Outstanding Item 1 Closed.Addl Response Encl

ML20071P234
Person / Time
Site:	Byron
Issue date:	10/27/1982
From:	Tramm T COMMONWEALTH EDISON CO.
To:	Harold Denton Office of Nuclear Reactor Regulation
Shared Package
ML20071P237	List: ML20071P234 ML20071P243
References
5306N, NUDOCS 8211020399
Download: ML20071P234 (7)

Text

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/ -~'N Commonwealth Edison

• 7 ) one First National Ptsza. Chicatjo, lihnois

• O Address Arply to: Post Ofhce Box 767 Chicago, Illinois 60690 l October 27, 1982 i

Mr. Harold R . Denton, Director Office of Nuclear Reactor Regulation U.S. Nuclear Regulatory Commission Washington, DC 20555

Subject:

Byron Station Units 1 and 2 Essential Service Water Pipelin e 5 VS7 NRC Docket Nos. 50 a nd 50 --37^ -

Re ferences (a): June 1,1982 letter from B. J. Youngblood t o L. O . DelGeo rge .

(b): July 20, 1982 letter from T. R. Tramm to H. R . Denton.

(c): July 29, 1982 letter from B. J. Youngblood t o L . O . De l Ge o rg e .

Dear Mr. Denton:

'b?.; is to provide additional information regarding the support of Byron Station's buried essential service water pipeline.

This information was requested by the NRC in reference (a) and should enable closure of Outstanding Item 1 in the Byron SER.

Attachment A to this letter addresses the six requests contained in reference (a). It summarizes the recent confirmatory geotechnical investigations which are documented in the enclosed report. Acceptance criteria for this work were established in references (a), (b), and (c).

The findings of the recent investigations can be summarized as follows:

1. Soil samples were collected from four borings in Area 11 during the installation of groundwater monitoring piezo-O g)() 'I meters. The results o f laboratory testing and evaluation o f D the soil samples from these four borings indicate that all anticipated pipeline settlement for both the static and dynamic cases are less than predicted.

2.

The results o f the consolidation tests show that the soil profile encountered is preconsolidated to loads well in excess o f the existing overburden. This is in agreement with previous investigations as documented in the FSAR.

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qg. 4 H. R. Denton October 27, 1982

3. The results of drilling four vertical and four angle borings to document the conditions of the foundation soils and rock below the ESW pipeline confirmed the adequacy and stability of the bedrock below the ESW pipeline and satisfies the acceptance criteria given by the NRC.

4. In view o f the current subsurf ace investigations, no unexpected subsurface soil conditions were encountered and our interpretation of the general subsurf ace profile and soil properties remains unchanged.

In general, this e ffort has confirmed our previous conclusion regarding the adequacy of the essential service water pipeline. Pleas e direct further questions regarding this matter to this office.

One signed original and fifteen copies of this letter and the enclosures are provided for your review.

Very truly yours, jlj)Lfcvw~

T.R. Tramm Nuclear Licensing Administrator 1m Attachment

Enclosure:

" Report , Confirmatory Geotechnical Investigations, ESW Pipeline Corridor, Byron Station Units 1 and 2, Commonwealth Edison Company," September 30, 1982.

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ATTACHMENT A Additional Subsurface Information Byron Station Essential Service Water Pipeline Staff Requirements (1) At least four slanted borings should be drilled at the site, two borings at area 9 and two borings at area 11. These borings should be drilled at an angle about 450 from the vertical with a penetration of about 80 f t into rock. The advancement o f the borings should be in a direction that will directly cross the two major joint trends in area 9 and 11. A double-tube core barrel with bottom discharge bit should be used for core recovery. All information pertinent to core recovery (bit rotation speed, drilling rod pressure, rate of advancement and bit condition) should be recorded. If, during the drilling operation, dropping of rods in excess of 1 f t in 5 f t of penetration and coincident loss of significant drilling fluid occur, in situ observations methods or additional slanted borings should be used to determine the nature, geometry , and spacing o f these anomalies. When joints are encountered, the infill materials should be sampled, and their source identified.

(3) If the above slanted borings in area 9 and 11 find that the joint conditions might adversely af fect the support o f the pipe- line, as determined in accordance to staf f's acceptance criteria (Enclosure 2), additional slanted borings should be drilled at area 12 to determine the rock and the joint conditions there.

Response

The field investigation was performed between Aug Jst 9, 1982, and Augus t 20, 1982. An NRC representative, Dr. J.T. Chen, was onsite August 16, 17, and 18 to observe the drilling and sampling. A complete description o f the methods and results o f the investigation is presented in the September 30, 1982, report titled, " Confirmatory Geotechnical Investigations , ESW Pipeline Co r rido r" , to be included in the FSAR as Attachment 2.5J. A summary o f the report conclusions are:

a. Areas of Concern 9 and 11 are located at intersections of the ESW pipeline corridor with northwest trending joint sets.

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b. The joints encountered in the four angle borings are tight (closed) and no voids (open joints) were encountered within the upper 50 feet (vertical) of the bedrock.

c. Some joint sets contained highly fractured zones, but there was no noticeable increase in bedrock solution activity and no voids encountered.

d. The investigation confirmed that solution features were i developed by differential solutioning along joints and that collapse of the bedrock. due to solution phenomena is not possible. (See FSAR attachment 2.5 I for a complete discussion o f solution features along the pipeline) .

The results of the investigation confirmed the adequacy and stability of the bedrock below the ESW pipeline.

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Staff Requirements (2) The applicant should establish the maximum unsupported span for the as-built pipeline and its limiting differential settlement values.

Response

4 The supported pipeline has been designed for a limiting differen-tial settlement of 10 inches over 100 lineal feet. This considers both the encased and unencased portions of the pipeline. The maximum differential settlement expected is 0.2 inches over 100 lineal feet.

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Staf f Requirements (4) At Area 11, two soil borings, about 50' apart, should be drilled in the vicinity of Sta. 48 + 20N, where differential settlement is of concern, to secure undisturbed soil samples from the organic clayey silt layer and the underlying silty clay layer. These undisturbed samples should be subjected to laboratory testing to determine their compression and consolidation properties.

(5) At Area 12, between Sta. 40 + SON and Sta. 45 + 20N, where settle-ments are of concern, soil borings should be drilled at about 50 foot spacing. Two o f these borings should use continuous sampling technique to verify the subsurface profile. All other borings (about 6) should use the Standard Penetration Test Procedure ( ASTM 0-1586). Undisturbed samples should be obtained from the organic silt and silty clay layers for laboratory consolidation tests.

The compacted fill above the pipeline needs no sampling.

(6) The differential settlements along the uncased pipeline should be determined and their ef fects on the pipeline should be evaluated from the information obtained form the exploration and testing program outlined in (3) through (5).

Response

During March and April 1982 additional soil samples were collected from 4 borings in Area 11 during the installation o f groundwater monitoring piezameters. The results o f laboratory testing and evaluation of the soil samples from these 4 borings indicate all anticipated pipeline settlements for both the static and dynamic cases are less than predicted in response to FSAR Question 241.6.

It is our interpretation that the soil profile encountered in Area 11 is representative of the soil profile in Area 12. The re fo re ,

the results o f the sampling and testing program are applicable to area 12. Details o f the investigation are presented in the Dames and Moore report dated September 30, 1982.

The boring logs are presented on Figures A-2.1 through A-2.4. Th e samples were tested for classification purposes, and consolidation tests were performed on undisturbed clay, silt, and clayey and silty sand samples. The results of the laboratory tests are presented in the boring logs and Figures A-3.1 through A-3.4 and A-4 and summarized in Table 1. All 4 piezameters when measured have been dry from time o f installation to the most recent measurement on September 21, 1982. This indicates the groundwater level is below elevation 810 feet (MSL) in Area 11 for this period.

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The results o f the. consolidation tests show that the soil profile encountered is preconsolidated to loads well in excess o f the existing overburden.. This is in agreement with consolidation tests on similar soils- from the plant site area presented in FSAR Figures 2.5-53 through 2.5-55.

The results of the pipeline settlement evaluation are presented in Table 2. The analyses show a maximum total settlement of.0.5 inches and a maximum dif ferential settlement of 0.2 inches over a distance of 100 feet in Area 11. In Area 12, the maximum total settlement was calculated to be C.4 inches, and the maximum differential settlement was calculated to be 0.2 inches over a distance of 100 feet. These settlements are in agreement with those previously estimated in response to FSAR questions (see .FSAR Question and Response 241.6).

In view of the o"rrent subsurface investigations along the pipeline which included continuous sampling, no unexpected subsurface soil conditions have been encountered, and our interpretation of the general subsurf ace profile and soil properties along the pipeline remains unchanged.

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