ML12121A638

Response to Nuclear Regulatory Commission Standard Steam Generator Questions for Oconee Unit 3

ML12121A638
Person / Time
Site:	Oconee
Issue date:	04/30/2012
From:	Andrea Johnson Steam Generator Tube Integrity and Chemical Engineering Branch
To:
Johnson A
References
Download: ML12121A638 (4)

Text

Response to NRC Standard Steam Generator Questions For Oconee Unit 3 EOC26 April 2012

1. Discuss any trends in the amount of primary-to-secondary leakage observed during the recently completed cycle.

Duke Response:

No leakage has been observed

2. Discuss whether any secondary side pressure tests were performed during the outage and the associated results.

Duke Response:

No secondary side pressure tests were performed.

3. Discuss any exceptions taken to the industry guidelines.

Duke Response:

An exception has been taken to the examination guidelines to use single pass analysis versus dual pass analysis.

4. For each steam generator, provide a description of the inspections performed including the areas examined and the probes used (e.g., dents/dings, sleeves, expansion-transition, U-bends with a rotating probe), the scope of the inspection (e.g., 100% of dents/dings greater than 5 volts and a 20% sample between 2 and 5 volts), and the expansion criteria.

Duke Response The scope of the inspection is as follows:

1. 100 % bobbin full length

2. Special Interest with array probe

a. All bobbin indications 35% TW

b. All bobbin indications at the 7th TSP down to the LTE 20% TW

c. All indications regardless of size at the drilled holes at the 14th TSP

d. All ADI, DSI, DWI, NQI, PLP and HIS codes other than wear

3. Five tubes deep around the periphery with the array first TSP to LTS

4. Plus Point on ADIs

5. For each area examined (e.g., tube supports, dent/dings, sleeves, etc), provide a summary of the number of indications identified to-date for each degradation mode (e.g., number of circumferential primary water stress corrosion cracking indications at the expansion transition). For the most significant indications in each area, provide an estimate of the severity of the indication (e.g., provide the voltage, depth, and length of the indication). In particular, address whether tube integrity (structural and accident induced leakage integrity) was maintained during the previous operating cycle. In addition, discuss whether any location exhibited a degradation mode that had not previously been observed at this location at this unit (e.g., observed ENCLOSURE

circumferential primary water stress corrosion cracking at the expansion transition for the first time at this unit).

Duke Response:

Tube to Tube Wear SG 3A SG 3B Indication 58(86) 32(43)

Location 7th to 8th span 58 32 Length Max (inches) 9.0 8.3 Length Min (inches) 1.0 3.2 Length Avg (inches) 5 6.1 Max Depth (%TW) 20 17 Average Depth 11 11 Number of Wear Indications 50% TW 0 0 Number of Wear Indications 40% TW < 50% TW 0 0 Number of Wear Indications 30% TW < 40% TW 0 0 Number of Wear Indications 20% TW < 30% TW 12(1) 1 Number of Wear Indications 10% TW < 20% TW 46(85) 31(43)

Average Growth Rate per EFPY 0.3 -0.9 95th Percentile Growth Rate per EFPY 2.3 0 Maximum Growth Rate per EFPY 4.3 2.9 The indications are generally located in the center of the bundle.

( ) = Array data Tube support plate wear SG 3A SG 3B Number of Tubes Inspected with Bobbin 15621 15648

% of Tubes Inspected with Bobbin 100% 100%

Number of Wear Indications 14824 6821 Number of Tubes with Wear Indications 8248 4724

% of Tubes Inspected with Wear Indications 53% 30%

Average Wear Depth 8% 8%

Maximum Wear Depth 39% 46%

Number of Wear Indications 50% TW 0 0 Number of Wear Indications 40% TW < 50% TW 0 2 Number of Wear Indications 30% TW < 40% TW 49 24 Number of Wear Indications 20% TW < 30% TW 398 163 EFPY 1.39 1.39 Average Growth Rate per EFPY 0.3% 0.8%

95th Percentile Growth Rate per EFPY 2.9% 3.6%

Maximum Growth Rate per EFPY 12.9% 21.6%

6. Describe repair/plugging plans.

Duke Response:

There are no tubes requiring plugging in A ROTSG. Two tubes are to be plugged and stabilized in B ROTSG for wear at tube support plate locations 40% TW.

7. Describe in-situ pressure tests and tube pull plans and results (as applicable and if available).

Duke Response:

No in-situ pressure tests were performed and no tube pulls are planned

8. Discuss the following regarding loose parts:

1. what inspections are performed to detect loose parts

2. a description of any loose parts detected and their location within the SG (including

3. the source or nature of the loose part, if known)

4. if the loose parts were removed from the SG

5. indications of tube damage associated with the loose parts Duke Response:

Two loose parts were detected visually. Bounding with the array was performed. PLPs were identified at the top of tubesheet. No degradation was detected. They are located interior to the bundle in a low flow area.

9. Discuss the scope and results of any secondary side inspection and maintenance activities (e.g., in-bundle visual inspections, feedring inspections, sludge lancing, assessing deposit loading, etc).

Duke Response:

The scope of the secondary side inspection is as follow (contingent up on getting to the locations):

1. Top of tubesheet - Annulus, five tubes deep and interior of the bundle (selected rows only), bottom and top of orifice plate in both ROTSGs

2. General tube conditions (deposit loading, deposit characteristics and blockage) and Structural assessment of the various features at the 9th TSP, 10th TSP, and 11th TSP and in A ROTSG.

Small amounts of sludge coupled with corrosion product flakes were noted at the TTS in A ROTSG. Two foreign objects were found, one being on the 11th support plate and a second on the top of tube sheet, but well within the bundle in A ROTSG. No other issues have been noted. B ROTSG lower tubesheet inspection is pending.

10. Discuss any unexpected or unusual results.

Duke Response:

There were no unexpected or unusual results.

11. Provide the schedule for steam generator-related activities during the remainder of the current outage.

Duke Response:

1) Complete secondary side visual inspections

2) Perform retrieval of foreign objects

3) Perform tube plugging and stabilization