05000275/LER-2005-001, Steam Generator Tube Plugging Due to Stress Corrosion Cracking
| ML053410394 | |
| Person / Time | |
|---|---|
| Site: | Diablo Canyon  |
| Issue date: | 11/25/2005 |
| From: | Oatley D Pacific Gas & Electric Co |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| DCL-05-138 LER 05-001-00 | |
| Download: ML053410394 (7) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(ii) 10 CFR 50.73(a)(2)(ii)(A), Seriously Degraded |
| 2752005001R00 - NRC Website | |
text
-i Pacific Gas and Electric Company" David H. Catley Diablo Canyon Power Plant Vice President and General Manager P. 0. Box 56 Avila Beach, CA 93424 November 25, 2005 805.545.4350 PG&E Letter DCL-05-138 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555-0001 Docket No. 50-275, OL-DPR-80 Diablo Canyon Unit 1 Licensee Event Report 1-2005-001-00 Steam Generator Tube Plug-ging Due to Stress Corrosion Cracking
Dear Commissioners and Staff:
In accordance with Technical Specification (TS) 5.6.10.a, TS 5.6.10.c, and 10 CFR 50.73(a)(2)(ii), Pacific Gas & Electric Company is submitting the enclosed licensee event report regarding steam generator (SG) tube plugging due to stress corrosion cracking identified during the Unit 1 thirteenth refueling outage. TS 5.6.10.c requires a special report since more than one percent of the tubes inspected in SG 1-1 and SG 1-2 were identified as defective, and TS 5.6.10.a requires reporting of the number of tubes plugged in each SG.
This event did not adversely affect the health and safety of the public.
Sincerely, David H. Oatley ddm/2246/A0650656 Enclosure cc:
Bruce S. Mallett, NRC Region IV Terry W. Jackson, NRC Senior Resident Inspector Alan B. Wang, NRR Project Manager Diablo Distribution INPO State of California, Pressure Vessel Unit A member of the STARS (Strategic Teaming and Resource Sharing) Alliance Callaway
- Comanche Peak
- Diablo Canyon
- Palo Verde
- South Texas Project
- WolfCreek
LICENSEE EVENT REPORT (LER)
FACILITY NAME (1)
DOCKET NUMBER (2)
PAGE (3)
Diablo Canyon Unit 1 10151010101217151 l OF l 6 TITLE (4)
Steam Generator Tube Plugging Due to Stress Corrosion Cracking EVENT LER NUMBER (6)
REPORT OTHER FACILITIES INVOLVED (8)
DATE (5)
DATE (7)
MO DAY I YEAR YEAR SEQUENTIAL NUMBER REVISION MO DAY YEAR FACILITY NAME DOCKET NUMBER NUMBER 11 11 2005 2005 -l 0 I0 1 - 0 11 25 2005 OPERATING THIS REPORT IS SUBMITTED PURSUANT TO THE REQUIREMENTS OF 10 CFR: (11)
MODE (9) 6 X
POWER LEVEL 10 X
OTHER Special Report per TS 5.6.10.a and c 0
Ol(SPECIFY IN ABSTRACT BELOW AND IN TEXT, NRC FORM 366A)
LICENSEE CONTACT FOR THIS LER (12)
TELEPHONE NUMBER AREA CODE I Lawrence M. Parker - Senior Regulatory Services Engineer 805 545-3386 COMPLETE ONE UNE FOR EACH COMPONENT FAILURE DESCRIBED IN THIS REPORT (13)
CAUSE
SYSTEM COMPONENT MANUFACTURER REPORTABLE
CAUSE
SYSTEM COMPONENT MANUFACTURER REPORTABLE TO EPIX TO EPIX B
A 3 SIGl I
W11 1210 N j l l l I
l I I iI I I I I I I I I I I i I I i SUPPLEMENTAL REPORT EXPECTED (14)
EXPECTED MON DAY YR YES (If yes, complete EXPECTED SUBMISSION DATE) pX] NO SUBMISSION DATE (15)
ABSTRACT (Umit to 1400 spaces. i.e.. approxdmately 15 single-spaced typewnitten lines.) (16)
On November 11, 2005, at 1200 PST, with Unit 1 in Mode 6 (refueling, with the reactor defueled), analysis of eddy current testing on Steam Generator (SG) 1-1 and SG 1-2 indicated that greater than one percent of the tubes were defective.
Pacific Gas & Electric Company (PG&E) made a non-emergency report to the NRC as required by Technical Specification (TS) Table 5.5.9-2, "Steam Generator (SG) Tube Inspection," at 1230 PST, via NRC Event 42136.
On November 9, 2005, PG&E discussed the preliminary results of the SG eddy current inspection during a phone conference with the Office of Nuclear Reactor Regulation (NRR). The primary cause of the SG tube cracking was circumferential outside diameter stress corrosion cracking at the hot leg tube support plates and at the hot leg top of tubesheet.
In accordance with TS 5.5.9, "Steam Generator (SG) Tube Surveillance Program," PG&E has plugged all defective Unit 1 tubes identified during the current refueling outage. All defective tubes met condition-monitoring requirements at the end of Cycle 13. PG&E maintains a comprehensive program to minimize SG tube degradation, and plans to replace the SGs at the end of Cycle 15.
A LICENSEE EVENT REPORT (LER) TEXT CONTINUATION WCILITY NAME (1)
DOCKET NUMBER (2)
LER NUMBER (6)
PA(
SEQUENTIAL NUMBER REVISION
)iabloCanyonUnit1 0 5 0 0 0 2 7 5 2005 0 1 0 1 l-00 2
T I.
Plant Conditions
Unit 1 was in Mode 6 (refueling, with the reactor defueled) in its thirteenth refueling outage (1R13).
II.
Description of Problem A.
Background
Technical Specification (TS) 5.5.9, "Steam Generator (SG) Tube Surveillance Program," requires that the results of each SG tube inspection be classified as Category C-3 if more than one percent of the total tubes inspected are defective. Defective tubes have service induced degradation in excess of TS tube repair limits. Defective tubes must be removed from service by plugging.
TS 5.6.10, "Steam Generator (SG) Tube Inspection Report," paragraph a, requires the number of tubes plugged in each SG [AB][TBG] to be reported within 15 days following the completion of each inservice inspection. TS 5.6.10, paragraph c, requires the results of SG tube inspections, which fall into Category C-3, to be reported in a special report to the Commission within 30 days and prior to resumption of plant operation.
If the results of the SG tube inspections are classified as Category C-3, then NRC notification is required in accordance with TS Table 5.5.9-2, "Steam Generator (SG) Tube Inspection," and submittal of a special report is required in accordance with TS 5.6.10.c.
B.
Event Description
On November 9, 2005, PG&E discussed the preliminary results of the inspection during a scheduled phone conference with the NRR.
On November 11, 2005, at 1200 PST, final analysis of eddy current testing on SG 1-1 and SG 1-2 indicated that greater than one percent of the tubes inspected were defective, therefore classifying the SGs as Category C-3, per TS 5.5.9. SG 1-1 had 37 defective tubes and SG 1-2 had 41 defective tubes that were removed from service by tube plugging during 1 R1 3.
Additional degraded tubes were also preventively plugged.
On November 11, 2005, a non-emergency report was made in accordance with TS Table 5.5.9-2 and 10 CFR 50.72(b)(3)(ii)(A), at 1230 PST.
LICENSEE EVENT REPORT (LER) TEXT CONTINUATION FACILITY NAME (1)
DOCKET NUMBER (2)
LER NUMBER (6 PAGE (3)
SEQUENTIAL NUMBER REVISION NUMBR Diablo Canyon Unit 0
15 0
0 2 1 7 1 5 2005
- - I 0 l 0 1 l -
0 0 3 1 OF 6 TEXT C.
Status of Inoperable Structures, Systems, or Components that Contributed to the Event None.
D.
Other Systems or Secondary Functions Affected
None.
E.
Method of Discovery
The defective tubes were found during routine scheduled eddy current testing of Unit 1 SG tubing performed during 1 R1 3.
F.
Operator Actions
None.
G.
Safety System Responses None.
Ill.
Cause of the Problem A.
The number of defective tubes in SG 1-1 and SG 1-2 identified during 1 R1 3 exceeded one percent of the total tubes inspected, placing the SGs in Category C-3, per TS 5.5.9.
B.
Root Cause The majority of the tube defects are attributed to axial outside diameter stress corrosion cracking (ODSCC) at the hot leg tube support plate, and circumferential ODSCC at hot leg tube support plate and at the hot leg top of tubesheet. In addition, axial ODSCC at the hot leg top of tubesheet was identified at Diablo Canyon Power Plant (DCPP) for the first time.
C.
Contributory Cause None.
LICENSEE EVENT REPORT (LER) TEXT CONTINUATION 1-.lIT K I.,C1 f =Tb2IA= o IV.
Assessment of Safety Consequences
The licensing-basis, large-break, loss-of-coolant accident analysis assumes a tube-plugging limit of 15 percent per SG. Including the tubes plugged during 1 R1 3, the following table presents the number of tubes (out of a total of 3,388 tubes for each SG) that are currently plugged in each of the four Unit 1 SGs.
SG Tubes Plugged in Total Tubes Total Percentage of NO.
1 R13 Plugged to Date Tubes Plugged 1-1 38 232 6.8 1-2 43 315 9.3 1-3 16 92 2.7 1-4 19 186 5.5 The plugging percentage for each Unit 1 SG remains within the current allowable limit of 15 percent.
There were no actual safety consequences involved in this event since all defective tubes met the performance criteria of the Nuclear Energy Institute (NEI) 97-06, Revision 2, "Steam Generator Program Guidelines."
Also, the condition is not considered a Safety System Functional Failure.
Therefore, the event is not considered risk significant and it did not adversely affect the health and safety of the public.
V.
Corrective Actions
A.
Immediate Corrective Actions
The Unit 1 SG tubes classified as defective during 1 R1 3 have been plugged in accordance with DCPP TS 5.5.9.
B.
Corrective Actions to Prevent Recurrence PG&E has initiated several programs to minimize SG tube degradation and implemented alternate repair criteria to leave certain indications in service, thus extending the SG service life. Circumferential ODSCC indications are not subject to alternate repair criteria (ARC), and must be plugged upon detection.
PG&E maintains a comprehensive program to minimize SG tube degradation, and plans to replace the SGs at the end of Cycle 15.
LICENSEE EVENT REPORT (LER) TEXT CONTINUATION FACILITY NAME (1)
DOCKET NUMBER (2)
LER NUMBER (6)
PAGE (3)
YEAR SEQUENTIAL NUMBER REVISION INUMBER Diablo Canyon Unit 1 0 50 0 0 0 2 71 5 2005 0 0 1
0 0 5 1OF 6
TEXT Secondary side initiatives to minimize tube degradation:
- 1.
EPRI secondary chemistry recommendations were implemented to minimize ODSCC at tube support plates (TSPs) (e.g., hydrazine levels were increased in 1992, the secondary side pH treatment was converted from ammonia to ethanol amine, and a molar ratio control program was implemented in 1993/1994).
- 2.
Tube sheets have been sludge lanced during each refueling outage to minimize ODSCC at the tube sheet.
- 3.
DCPP has an upgraded plant makeup water system to minimize SG contaminate levels.
- 4.
SG blowdown is maintained at approximately one percent of the main steaming rate to minimize SG contaminate levels.
- 5.
A boric acid addition program is in effect, including boric acid soaks at startup to mitigate denting and ODSCC at TSPs.
- 6.
DCPP has condensate polishers and emergency (plant curtailment) procedures to protect against seawater condenser tube leaks.
- 7.
The Unit 1 SGs were chemically cleaned in 2004.
Primary side initiatives to minimize tube degradation:
- 1.
Rows 1 and 2 U-bends were heat treated in 1987/1988 to prevent primary water stress corrosion cracking (PWSCC).
- 2.
The tubes in the hot leg tube sheet region were shot peened in 1992/1993 to minimize PWSCC.
- 3.
Reactor coolant system (RCS) contaminants are maintained at low levels-in accordance with EPRI guidelines.
- 4.
Lithium and boron concentrations are coordinated to minimize pH swings in the RCS.
- 5.
Zinc addition to the RCS was implemented in Units 1 and 2 starting in Cycle 9 to inhibit PWSCC in SG tubes.
~
Z LICENSEE EVENT REPORT (LER) TEXT CONTINUATION FACILFIY NAME (1)
DOCKET NUMBER (2)
LER NUMBER (6)
I P/
YEAR SEQUENTLAL NUMBER REVISION NUMBER Diablo Canyon Unit1 0 _
0 0 ° 0 2 7 5 2005 0
0 1 -
0 0
6 _
TEXT Alternate repair criteria (ARC):
I.
Voltage-based ARC for axial ODSCC at TSPs was implemented starting in the Unit 2 eighth refueling outage and the Unit 1 ninth refueling outage (1R9).
- 2.
W* ARC for axial PWSCC contained in the WEXTEX tube sheet was implemented starting in 1 R9 and the Unit 2 ninth refueling outage.
- 3.
PWSCC ARC for axial PWSCC at dented TSPs was implemented starting in the Unit 1 eleventh refueling outage (1 R1 I) and the Unit 2 eleventh refueling outage.
VI.
Additional Information
A.
Failed Components Component:
Manufacturer:
Westinghouse B.
Previous Similar Events
LER 1-97-007 reported that greater than one percent of the tubes inspected in SG 1-1 and 1-2, during the Unit 1 eighth refueling outage, were defective.
LER 1-2000-010-00 reported that greater than one percent of the tubes inspected in SG 1-2, during the Unit 1 tenth refueling outage, were defective.
LER 1-2002-002-00 reported that greater than one percent of the tubes inspected in SG 1-2, during 1 R11, were defective.
LER 1-2004-001-00 reported that greater than one percent of the tubes inspected in SG 1-1 and SG 1-4, during Unit 1 twelfth refueling outage, were defective.