ML20080T527

Forwards Summary of Midcycle Steam Generator Insp Results & Safety Assessment.Util Will Proceed W/Unit Startup

ML20080T527
Person / Time
Site:	Braidwood
Issue date:	03/08/1995
From:	Saccomando D COMMONWEALTH EDISON CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
NUDOCS 9503130369
Download: ML20080T527 (8)

Text

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- 7 T Commonwealth Edison e

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. March 8',

1995.

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-Nuclear Regulatory Commission L

Document Control Desk

. Washington, D.C. 20555

< Attn:.

Document. Control' Desk ~

Subject:

. Safety Assessment for Braidwood Unit 1 Mid-Cycle Outage A1M05.

NRC Docket Number 50-456

Reference:

1.

R. Assa letter to D. Farrar dated August 18',

1994, transmitting the Safety Evaluation for Amendment 54 2.

D.

Saccomando letter-to-NRC dated March 1, 1995, transmitting information pertaining to Braidwood Unit 1 Mid-Cycle Inspection-Reference 1 transmitted the Nuclear Regulatory Commission (NRC)'s Safety Evaluation Report (SER) for the use of Interim Plugging Criteria (IPC) for Commonwealth Edison Company: (Comed)'s Braidwood Unit 1. The SER requested that the inspection data and

. repair results of the mid-cycle inspection along with the licensee's safety assessment prior ~to start up. Braiwood' Station will provide a more detail summary of the A1M05 inspection results in the forth coming 90 day Inspection Report.

Attached you will find the summary of the midcycle steam generator inspection results and the safety assessment.

As stated in Reference 2, after transmittal of this safety assessment to the Staff, Braidwood Unit 1 will proceed with unit startup.

If you have any questions concerning this, please contact this office.

Si sarely,

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enise M.

Sa mando Nuclear Licensing Administrator Attachment ec:

D. Lynch, Senior Project Manager-NRR R. Assa, Braidwood Project Manager-NRR S. Dupont, Senior Resident Inspector-Braidwood J. Martin, Regional Administrator-RIII Office of Nuclear Safety-IDNS Kinla\\bwd\\stupl\\1

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4 ATTACHMENT L

Summarv of Braidwood Cycle 5 Mid-Cycle Steam Generator InsoectiQn Results During the Braidwood Unit 1 Cycle 5 Mid-Cycle Steam Generator Inspection Outage (AlMOS), bobbin coil eddy current inspections were performed on 100% of the inservice Unit 1 Steam Generator (SG) tubes.

All tubes were inspected through their full length.

A 0.610 inch bobbin coil eddy current probe was used to inspect all SG Tube Support Plate (TSP) intersections where the Interim Plugging Criteria (IPC)was applied.

All inspections were performed in accordance with the Braidwood/ Byron eddy current inspection guidelines.

A total of 3935 indications were found at the TSP by bobbin coil examination.

All of these indications were verified to be-at the outer diameter of the tube and were confined'within the TSP.

834 of these indications were further examined by RPC and were verified to be consistent with axial oriented Outside Diameter Stress Corrosion Cracking (ODSCC).

Tables 1, 2, 3 and 4 provide a summary of the inspection results.

A total of 840 tubes were plugged, 815 due to ODSCC and 25 for other reasons.

Table 2 provides a summary of the repair results for this inspection.

Database for Leak and Burst Correlations The database used to perform the leak and burst assessments to support operation of Braidwood Unit 1 for the remainder of Cycle 5 is described in the Braidwood August 18, 1994, Safety Evaluation Report (SER), with the inclusion of Byron Cycle 6 and Braidwood Cycle 4 tube pull examination results.

This database is consistent with the database described in WCAP 14046, "Braidwood Unit 1 Technical Support for Cycle 5 Steam Generator Interim Plugging Criteria," Revision 1, Augurt 1994 with the following differences:

Inclusion of the Braidwood Cycle 4 and Byron Cycle 6 tu 2 pull examination results into the leak and burst correlations, Model boiler specimen 598-1 is excluded from all correlations, Inclusion of model boiler specimen 598-3 into the leak i

rate correlation database, and Plant S tube R28C41 data point assigned a leakage value of 2496 liters per hour.

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Leak ahd Burst Assessment Methodoloav and Results Main Steam Line Break (MSLB) leak rate and burst probabilities were calculated using methods described in WCAP'14277, "SLB Leak Rate and Tube Burst Probability Analysis Methods for ODSCC at TSP Intersections," January 1995, using the as found mid cycle voltage distribution.

Table 5 provides a summary of the leak and burst analysis results.

Control Room Dose Assessment As discussed in Braidwood Station's November 23, 1994, D.

Saccomando letter to Office of Nuclear Reactor Regulation (NRR) transmitting Braidwood Unit 1 Mid-Cycle Inspection Plans, Braidwood Station committed to perform an assessment of control room dose in accordance with Draft Generic letter 94-XX, " Voltage Based Repair Criteria for the Repair of Westinghouse Steam Generators Affected by Outside Diameter Stress Corrosion Cracking," August 1994 (Draft Generic Letter).

This assessment has been performed and determined that the Braidwood Station post accident control room dose during a MSLB with IPC applied is bounded by the current design basis-Loss of Coolant Accident (LOCA) control room dose.

Safety Assessment As shown in Table 5, the MSLB leak rates and tube burst probabilities calculated using as-found Mid-Cycle data are significantly less than the allowable limits of 9.1 gallons per minute (gpm) and 1. 0 x 10-2 respectively.

Additionally, Braidwood Station has performed a qualitative comparison of predicted versus actual voltage distributions and in all cases no unexpected results were observed.

This is reflected in the comparison of predicted versus actual MSLB leak rates and burst probabilities in Table 5.

These results provide confidence that the IPC model used by Comed and the industry is a very conservative predictor of SG tube degradation by ODSCC.

Table 4 indicates that the average voltage growth rate per EFPY has increased. Braidwood will assess this increase in growth rate and provide aeditional information in the forthcoming 90 day.

report.

Table 5 shows that tube leakage is acceptably low and tube burst is a highly improbable event during a MSLB.

Tube burst is precluded during normal operation by the presence of the tube support plate.

Thus, for the remainder of Cycle 5, Braidwood Unit 1 SGs will cor.tinue to satisfy the requirements of Regulatory Guide 1.121.

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W in the' #argin.of safety to protect the public health and safety.

In' conclusion, based on the arguments presented above, Braidwood has~ determined that operation of Unit 1 for the remainder of Cycle 5 presents no significant risks.

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Table ~1:

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ODSCC. Indications'Found'By Bobbin Coil i

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-t Voltage-SG:A-SG'B' SG1CJ SG:D TOTAL ~

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Range j

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769' 335-1095-690 2889 l

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1.0-2.70 v 288'

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422 236 1023-

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2.70-4.54 v.

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0 Total 1065-413 1526-931.

3935

.l Table 2-ODSCC Indications Confirmed by RPC

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. Voltage SG A~

SG B SG C SG D TOTAL j

Range 1.0-2.70 v 248 42-330 191 811 J

2.70-4'.54 v-8 1-8 5

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-> 4.54 v 0-0 1-0 1

1. Tubes 252 43-327 193 815

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Repaired *

'1

• Note:-

Tubes repaired due to. application'of IPC only.

.Some

~ tubes contained multiple indications at various locations.

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f Table 3 c<.

' Summary of Indications >-2.70' Volts

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SG A SG B.

SG C SG D 4.03-3.11 5.13 3-81 3.36 3.65' 3.17 3.35 3.22 3.16 7

3.3 3.17 3.03 1

3.26 2.83 2.86 3.07-2.77 2.9 2.72-j, 2.8 2.71 2.71 t

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'LTable 4-Cycle 5. Growth Rate Summary SG A SG B SG C SG D ALL f

SGs Ave. Voltage 0.32 0.19' O.28-0.30 0.29 Growth for Cycle

-(0.714 EFPY)

Ave. Voltage 0.45 0.27 0.39 0.42-0.40 Growth per EFPY Max.. Voltage 3.02 2.16 4.12 2.28 4.12 Growth for Cycle (0.714 EFPY).

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a Table 5 Braidwood Unit 1 Mid-Cycle Leakrate and Burst Probabilities

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Steam MSLB Leak Rate (gpm)

MSLB Tube Burst Probability.

Generator Deterministic Monte Carlo Deterministic Monte Carlo Predicted Actual Predicted Actual Predicted Actual.

Predicted' Actu'al POD =0.6 A

4.20' O.77 2.40 0.57 2.38E-02 5.45E-03 1.90E-02 3.22E-03' B

0.86 0.21 0.41 0.08 3.72E-03 9.56E-04 2.72E-03 6.20E C 1.36 1.15 0.93 0.78 1.09E-02 7-53E-03 5.63E 4.71E-03 D

7.74-0.51~

3.11 0.35 3.34E-02 3.51E-03 2.78E-02 1.97E-03 l

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