ML20133E845

Surveillance Guidelines for San Onofre Nuclear Generating Station Unit 1 Intake Structure

ML20133E845
Person / Time
Site:	San Onofre
Issue date:	09/30/1985
From:	BECHTEL GROUP, INC.
To:
Shared Package
ML20133E833	List: ML20133E831 ML20133E845
References
PROC-850930, TAC-55928, NUDOCS 8510100040
Download: ML20133E845 (17)

Text

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ENCLOSURE 1 SURVEILLANCE GUIDELINES For SONGS UNIT 1 INTAKE STRUCTURE Prepared For

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Southern California Edison i

By Bechtel Power Corporation September 1985 h

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TABLE OF CONTENTS P_ age

1. Introduction 1

1.1 Background

1.2 Purpose 1.3 Scope

2. Collection of Data 2 2.1 Visual 2.1.1 Areas to be Examined 2.1.2 Signs of Corrosion to be Recorded 2.1 3 Mapping of Areas of Inspection 2.2 Half-Cell Potential Measurements 2.2.1 Silver-Silver Chloride (ASTM C876) 2.2.2 Areas to be Examined 2.2.3 Recording of Data 2.3 Core Drilling 2 3.1 Number and Location 2.3.2 Visual Examination 2.3.3 Chloride Content Measurement (AASHTO T-260) 3 Surveillance Interval 5

4. Evaluation of Data ,

6 4.1 Data Evaluation Basis 4.2 Correlation of Results from Different Surveillance Methods 4.3 Comparison with Base Data 4.4 Comparison of Results from Different Areas

• 5. Assessment of Surveillance Program 6

6. References 6

7. Surveillance Program Data Form _ 7 4

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1. .. Introduction

1.1 Background

'Ihe San Onofre Unit 1 Intake Structure was constructed in the nn.d 60's. This reinforced concrete structure provides the structural transition for the conduits used to collect and discharge sea water for condenser cooling and for safety related salt water cooling. Gates have been provided to dewater segments of the structure and control the flow. Bar screens are used for trash removal upstream of the pump wells.

In June of 1984 an attempt was made to dewater the north pump well and screen well. Because excessive leakage was observed during dewatering, divers visually examined the north pump gate slot. During this examination the divers noted spalled -

areas and corrosion of the exposed reinforcing steel.

Subsequent to the visual examination, an engineering investigation was conducted which included concrete coring and chipping. This investigation led to the conclusion that reinforcing steel corrosion and concrete delaminations were present in the areas of the pump and screen wells. The in-vestigation of areas between the screen wells and the Tsunami gates revealed sound concrete with reinforcing steel in excellent condition, except for areas at the gate slots and areas with no structural significance. The reinforcing steel corrosion was less significant in the screen wells than within the pump wells.

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. The engineering investigation concluded that a repair program was required. The repair program consisted of bolting a

, series of strap plates onto the inside concrete surface to replace the positive moment load carrying capability of the deteriorated interior reinforcing steel. The plates were attached to designated areas of the screen and pump wells. ,

These pla.tes were designed assuming that the inside reinforc- 1 ing steel is nonexistent in the repaired areas. The strap plates are protected with a coal tar epoxy coating in addi-  !

tion to zinc anodes for corrosion protection. The bolting j material is monel. Finally, remedial work was done on the ,

. gate slots as appropriate for operational considerations. l 2

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l 1.2 Purpose '

The purpose of this doc ment 1-s to establish the guidelines l for surveillance of the San Onofre Unit 1 Intake Structure.

Fra this docment specific surveillance procedures will be developed. By the use of these guidelines and procedures a surveillance baseline will be established. Subsequent surveillances will nunitor the structure's condition and allow a c mparison to the established baseline.

13 Scope These guidelines are to be used to assess the overall condi-tion of the reinforced concrete in the intake structure. A continuing monitoring program will be established by these guidelines. .

The areas not repaired during the 1984 work effort are of specific interest. These areas include the intake structure from the tsunami gates to the screen well, the upper portions of the screen wells and the internal concrete beams in the screen well and surrounding the pump openings. As a basis for correlation one area in the pump well will be selected for examination. Surveillance of any nonstructural element is excluded from this program. Surveillance guidelines for

-the zine anodes on the strap plates are provided in the document titled " Maintenance Guidelines, Sacrificial Cathodic Protection System, Intake Structure Reinforcing Plates, SONGS Unit 1."

2. Collection of Data i

2.1 Visual 9

Divers will be used to visually examine the intake structure.

They will video tape and photograph areas of concern. The intake will not be dewatered for this purpose. Maps of these areas will be made fra the video tapes and photographs. Shells-and other marine growth will be reoved frm the concrete surfaces by hydro-laser and scraping as needed. Care must be tak e in r eoving growth fr a the strap plates located in examinatim areas to avoid damage to the coal tar epoxy coating.

2.1.1 Areas to be Examined Extensive visual examination of the following areas will be made:

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i A) The walls, ceiling and floor of the intake structure from the tsunami gates to the screen wells.

B) The unrepaired portions of the screen  !

well walls from Elevation -10'0" to l

+6'0".

C) The internal concrete beams in the screen well and surrounding the pump oper.ings in the pump bay.

D) The north pump bay's north wall (this wall has been completely repaired using strap plates).

E) The gate slots for the various gates separating the intake, screen well and pump bay structures.

Changes in the areas to be examined may be made after an engineering review of the first surveillance results. Areas to be visually examined are shown in Figures 1 and 2.

2.1.2 Signs of Corrosion to be Recorded The following specific signs of corrosion or concrete deterioration shall be recorded on the Surveillance Program Data Form:

A) Areas exhibiting cracks.

B) Spalled or displaced concrete (or grout behind the strap plates).

C) Areas where the r'einforcing steel has been exposed.

D)

Areas that show any deposits (excluding typical marine growth), especially red or black deposits on the concrete surface.

Any areas that might be characterized as dark rusty deposits exuding from point locations or those characterized by a moderate lump of rust congealed on the surface.

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i E) Obvious loss of pretension of anchoring bolts for strap plates (indicated by the 1 nut being loose or a gap between the washer and the nut).

2.1 3 Mapping of Areas of Inspection The locations and dimension of the areas of concern noted in paragraph 2.1.2 above shall be mapped on intake structure floor, ceiling and wall elevation drawings.

2.2 Half-Cell Potential Measurements 2.2.1 Silver-Silver Chloride (ASTM C876)

Half-Cell potential measurements shall be made in accordance with ASTM Standard C876 titled " Standard Test Method for Half-Cell Potentials for Reinforcing Steel in Concrete" except that a silver-silver chloride half cell shall be used and therefore Section 7 of ASTM C876 shall not apply. A four foot maximum grid pattern over the areas specified

.in paragraph 2.2.2 shall be established for testing. However, the spacing between measurements should generally be reduced ,

where adjacent readings exhibit algebraic reading differences exceeding 150 mV (areas ,

of high corrosion activity). Minimum spacing generally should provide at least a 100 mV difference between readings.

, , 2.2.2 Areas to be Examined l

The areas to be tested shall be:,

. A) The north and south walls of the intake structure from the tsunami gates to the recirculation gates.

B) The unrepaired portions of the screen

. well walls from Elevation -10'0" to '

+6'0".

C) The north pump bay's north wall from just opposite the centerline of the saltwater cooling pump progressing east to the centerline of the circulating water pump.

The areas for half-cell potential measure-ments are shown in Figures 3 and 4.

2.2 3 Recording of Data The half-cell potential reading shall be recorded to the nearest 10 mV. By convention a negative (-) sign is to be used for all readings. Report all half-cell potential values in volts and correct for temperature as requested by paragraph 5.1 of ASTM C876.

The equipotential readings shall be presented as an equipotential contour map. To obtain the contour map the locations of the half-cell potential values shall be plotted on a scaled plan view of the wall and ceiling and a line shall be drawn to connect the points of equal or interpolated equal values. The maximum contour interval shall be 100 mV.

Data from the half-cell potential measure-ments shall be recorded on a Surveillance Program Data Form.

2.3 core Drilling 2.3.1 Number and Location A minimum of three core drilled samples will be taken during the forth, eighth, twelfth, etc., surveillance cycles. One each will be taken from unrepaired portions of the north screen well, the south screen well and intake structure. The core drill locations will be selected from areas , exhibiting the highest half-cell potential readings during the pre-

, vious surveillances. The need for additional samples will be based on the evaluation of these samples.

2.3.2 visual Examination The samples will be visually examined. Any indication of delamination shall be noted.

Should reinforcing bar be encountered, the extend of corrosion shall also be noted.

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77 2 3.3 Chloride Content Measurement (AASHTO T-260) i

! #i The samples shall be subjected to testing for

, chloride content in accordance with AASHTO T-260.

3 ,surveillan'ce Interval Surveillance of the intake structure shall be performed at

, each refueling outage (at approximately 18 months intervals).

Core drilling will be performed at approximately 5 year intervals or every forth refueling outage. The interval may be revised,as a result of evaluation of the first two

, ' surveillance findings.

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, . Evaluation of Data n  ;

4.1 Data Evaluation Basis The data resulting from the initial visual-examina-i tion and half-cell potential measurements will be the basis for evaluation of the data obtained from all subsequent surveillances.

4.2 Correlation of Results from Different Surveillance Methods The data from the visual examination will be compared to the equipotential half-cell measurements to assess

the degree of correlation that can be established between the two surveillance methods.

, ,. 4.3 Comparison with Base Data i

l The results of subsequent surveillance will be l kg ,<f. compared with those of the base line survey.

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( Compari$on of Results from Different Areas 4.4 The results from the north pump wel-1 wall will be i

compared to the results from other areas in order to

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, establish a degree of relative corrosion activity.

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5. Assessment of Surveillance Program An assessment of the surveillance program will be made upon the completion of each surveillance. The accuracy and valid-ity of a surveillance method in determining the condition of the structure is of major concern. Consideration will be given to either lengthening or shortening the surveillance interval depending on the results of past surveillances. In addition, the need for actual core drilling during every fourth surveillance will be evaluated considering the result '

of previous surveillances. Finally the adoption of any new or innovative surveillances methods that could give a better indication of the structure's condition will be considered.

6. References 6.1 ASTM C876-80 Standard Test Method for Half-Cell Potentials of Reinforcing Steel in Concrete.

6.2 AASHTO T-260 Standard Method of Sampling and Testing for Total Chloride Ion in Concrete and Concrete Raw Materials 6.3 Drawings FGD-C-1386 FGD-C-1389 FGD-C-1390 6.4 Maintenance Guidelines for Sacrificial Cathodic Protection System Intake Structure Reinforcing Plates, SONGS Unit 1; Doc. ID No. M-82101, e Rev. O, dated 10/1/84 e

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SONGS' Unit 1 Intake Structure Surveillance  :

Proposed Surveillance Program Data Form l I. VISUAL EXAMINATION A. Area Examined 4

B. Concrete Examination Results 1t& E9.

1. Any Cracks

2. Spalled Concrete If yes, indicate approximate size X X

3. Reinforcing Steel Exposed

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4. Any Surface Deposits If yes:

a) Color b) Hardness c) Size ,

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5. Area Video-Tape Recorded I

C. Comments

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III. HALF-CELL POTENTIAL SURVEY A. Area Surveyed

B. Readings GRID GRID GRID LOCATION READING LOCATION READING LOCATION READING C. Comments i

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