05000275/LER-2004-001, Regarding Steam Generator Tube Plugging Due to Stress Corrosion Cracking
| ML041400030 | |
| Person / Time | |
|---|---|
| Site: | Diablo Canyon  |
| Issue date: | 05/10/2004 |
| From: | Oatley D Pacific Gas & Electric Co |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| DCL-04-056, OL-DPR-80 LER 04-001-00 | |
| Download: ML041400030 (8) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(ii) 10 CFR 50.73(a)(2)(ii)(B), Unanalyzed Condition |
| 2752004001R00 - NRC Website | |
text
51 Pacific Gas and
.1 Electric Company David H. Oatley Diablo Canyon Power Plant Vice President and PO. Box 56 General Manager Avila Beach CA 93424 May 10, 2004 B05.545.4350 Fax: 805.545.4234 PG&E Letter DCL-04-056 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 1-2004-001-00 Steam Generator Tube Plugging Due to Stress Corrosion Cracking
Dear Commissioners and Staff:
In accordance with Technical Specification (TS) 5.6.10.c and 10 CFR 50.73(a)(2)(ii), PG&E is submitting the enclosed licensee event report regarding steam generator (SG) tube plugging due to stress corrosion cracking identified during the Unit 1 twelfth 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 1-4 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/A0605274 Enclosure cc:
Bruce S. Mallett David L. Prouix Girija S. Shukla 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 0 15 0 10 10 2 17 15 1 1OF 7
TITLE (4)
Steam Generator Tube Plugging Due to Stress Corrosion Cracking EVENT LER NUMBER (6)
REPORT OTHER FACILITIES INVOLVED (B)
DATE (5 DAT7E MO DAY I YEAR YEAR SEQUENTIAL NUMBER REVISION MO DAY YEAR FACILITY NAME DOCKET NUMBER NUMBER 04 08 2 004 2004 -l0o0 1-05 10 2004 TT OPERATING THIS REPORT IS SUBMITTED PURSUANTTOTHE REQUIREMENTSOF 10 CFR: (I)
MODE (9) 6 X
POWER LEVELIt0)X OTHER Special Report perTS 5.6.10.a and c 0 0 0 (SPECIFY IN ABSTRACT BELOWAND IN TEXT. NRC FORM 366A)
LICENSEE CONTACT FOR THIS LER (12)
TELEPHONE NUMBER AREA CODE Lawrence M. Parker - Senior Regulatory Services Engineer 805 545-3386 COMPLETE ONE LINE 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 lBSIGI I W111210 N
I
=
II I
I SUPPLEMENTAL REPORT EXPECTED (14)
EXPECTED DAY YR
]YES (if yes, complete EXPECTED SUBMISSION DATE)
[XJ NO SUBMISSION DATE(15)
ABSTRACT (Limit to 1400 spaces. I., approximately 15 sr"lespaced typewnen Ans.) (16)
On April 8, 2004, with Unit 1 in no Mode (Defueled), analysis of eddy current testing on Steam Generator (SG) 1-4 indicated that greater than one percent of the tubes were defective. PG&E made a nonemergency report to the NRC as required by Technical Specification (TS) Table 5.5.9-2, "Steam Generator (SG) Tube Inspection," at 1402 PDT.
On April 14, 2004, PG&E discussed the preliminary results of the SG eddy current inspection during a phone conference with the NRC. PG&E notified the NRC that primary water stress corrosion cracking (PWSCC) and circumferential indications were detected at tube support plate intersections, per TS 5.6.10 paragraph d.
On April 20, 2004, analysis of eddy current testing on SG 1-1 also indicated that greater than one percent of the tubes were defective. PG&E made a nonemergency report required by TS Table 5.5.9-2, at 2026 PDT.
The majority of the tube defects in SG 1-4 were attributed to circumferential PWSCC in the U-bend region. The majority of the tube defects in SG 1-1 were attributed to axial outside diameter stress corrosion cracking at tube support plate intersections.
PG&E has plugged all defective Unit 1 tubes identified during the current refueling outage in accordance with TS 5.5.9. All defective tubes met condition-monitoring requirements at the end of Cycle 12. PG&E maintains a comprehensive program to minimize SG tube degradation.
LICENSEE EVENT REPORT (LER) TEXT CONTINUATION FACILITY NAME (1)
DOCKET NUMBER (2)
LER NUMBER (6)
PAGE (3)
YEAR SEQUENTIAL NUMBER l
VIUSION DiabloCanyonUnit1 0
0 l 0 l 2 1 7 0
5 2004 -'
0 1 -0 2
OF 7 TEXT
- 1.
Plant Conditions
Unit 1 was in no Mode (Defueled) in its twelfth refueling outage (1 R12).
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 must be repaired or 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. TS 5.6.10, paragraph d, requires NRC notification prior to returning the SG to service if circumferential crack-like indications are detected at tube support plate (TSP) intersections, or if indications are identified at TSP intersections that are attributable to primary water stress corrosion cracking (PWSCC).
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, uSteam Generator (SG) Tube Inspection," 10 CFR 50.72(b)(3)(ii), and submittal of a special report is required in accordance with TS 5.6.10.c.
B.
Event Description
On April 8, 2004, final analysis of eddy current testing on SG 1-4 indicated that greater than one percent of the active tubes inspected were defective, therefore classifying SG 1-4 as Category C-3, per TS 5.5.9. Defects in 92 active tubes in SG 1-4 were removed from service by tube plugging during 1R12.
On April 8, 2004, at 1402 PDT, a nonemergency report was made in accordance with TS Table 5.5.9-2 and 10 CFR 50.72(b)(3)(ii)(B).
LICENSEE EVENT REPORT (LER) TEXT CONTINUATION FACILITY NAME (1)
DOCKET NUMBER (2)
LER NUMBER (6)
PAGE (3)
YEAR SEQUENTIAL NUMBER REVISION
.NUMBER DiabloCanyon Unit 1 0 51 0 0 2 17 15 20041 I
l ° 1 1 -
0 3 1 OF 1 7 TEXT On April 14, 2004, PG&E discussed the preliminary results of the inspection during a scheduled phone conference with the NRC. During this phone conference, PG&E also notified the NRC that PWSCC and circumferential indications were detected at TSP intersections, satisfying TS 5.6.10 paragraph d.
On April 20, 2004, final analysis of eddy current testing on SG 1-1 indicated that greater than one percent of the active tubes inspected were defective, therefore classifying SG 1-1 as Category C-3, per TS 5.5.9.
Defects in 40 active tubes in SG 1-1 were removed from service by tube plugging in 1R12 On April 20, 2004, at 2026 PDT, a nonemergency report was made in accordance with TS Table 5.5.9-2 and 10 CFR 50.72(b)(3)(ii)(B).
In SGs 1-2 and 1-3, the number of defective tubes plugged in 1 R12 was 28 and 27, respectively, thus classifying these SG, inspection results as Category C-2, per TS 5.5.9. Six tubes in SG 1-2 were also preventively plugged (permeability variation) so a total of 34 tubes were plugged in SG 1-2. Preventively plugged tubes do not apply to categories.
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 1R12.
F.
Operator Actions
None.
G.
Safety System Responses None.
LICENSEE EVENT REPORT (LER) TEXT CONTINUATION FACILITY NAME (1)
DOCKET NUMBER (2)
LER NUMBER (6)
PAGE (3)
YEAR SEQUENTIA. NUMBER EVISION DiabloCanyon Unit10 1 l 0
01 4 1OF l7 TEXT Ill.
Cause of the Problem A.
The number of defective tubes in SG 1-1 and SG 1-4 identified during 1R12 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 hot leg TSP intersections (SG 1-1) and circumferential PWSCC in the U-bend region (SG 1-4).
C.
Contributory Cause None.
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 2, 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 Active Tubes Total Tubes Total Percentage of NO.
Plugged in 1R12 Plugged to Date Tubes Plugged 1-1 40 194 5.7 1-2 34 272 8.0 1-3 27 76 2.2 1-4 92 167 4.9 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 criteria of Regulatory Guide 1.121, 'Bases for Plugging Degraded PWR Steam Generator Tubes," for structural integrity at the end of Cycle 12.
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.
LICENSEE EVENT REPORT (LER) TEXT CONTINUATION FACILITY NAME (1)
DOCKET NUMBER (2)
LER NUMBER (6 PAGE (3)
YEAR SEQUENTIAL. NUMBER REVISION NUMBER DiabloCanyonUnit1 0151 0!10l0l2l7l5 2004 -1 00 1 1 -
0 5 1 OF 7
TEXT V.
Corrective Actions
A.
Immediate Corrective Actions
All Unit 1 SG tubes classified as defective during 1R12 have been plugged in accordance with Diablo Canyon Power Plant (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 extend the SG service life.
Secondary side initiatives to minimize tube degradation:
- 1.
Electric Power Research Institute secondary chemistry recommendations were implemented to minimize ODSCC at TSPs (e.g., hydrazine levels were increased in 1992, the secondary side pH treatment was converted from ammonia to ethanol amine in 1993/1994, and a molar ratio control program was implemented in 1993).
- 2.
Tube sheets are 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 (1 R12).
S ICENSEE EVENT REPORT (LER) TEXT CONTINUATION FACILITY NAME (1)
DOCKET NUMBER (2)
LER NUMBER (6)
PAGE (3)
YR7 SEQUENTIAL NUMBER REVISION NUMBER DiabloCanyon Unit 1 50 0 l0 2 17 5 2004
- - I 0 0 1
0 0
6 1 OF l 7 TEXT Primary side initiatives to minimize tube degradation:
- 1.
Rows 1 and 2 U-bends were heat treated in 1987/1988 to prevent 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.
Alternate repair criteria (ARC):
- 1.
Voltage-based ARC for axial ODSCC at TSPs was implemented starting in Unit 2 eighth refueling outage and 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 Unit 2 ninth refueling outage.
- 3.
PWSCC ARC for axial PWSCC at dented TSPs was implemented starting in Unit 1 eleventh refueling outage (1 R11) and Unit 2 eleventh refueling outage.
- 4.
License Amendment Request (LAR) 03-16, submitted in PG&E letter DCL-03-174, dated December 19, 2003, requests a revision to the SG wedge region exclusion zones for SG tube ARC.
- 5.
LAR 03-18, submitted in PG&E letter DCL-03-183, dated January 7, 2004, requests a revision to TS 5.5.9, and TS 5.6.10, to use the 4-volt ARC for SG tube repair.
- 6.
LAR 04-01, submitted in PG&E letter DCL-04-028, dated March 18, 2004, requests the use of a bobbin probability of prior cycle detection (PODCD) methodology for both Units 1 and 2, as was previously approved in the NRC License Amendment No. 164 for use in DCPP Unit 2 Cycle 12.
LICENSEE EVENT REPORT (LER) TEXT CONTINUATION FACILITY NAME (1)
DOCKET NUMBER (2)
LER NUMBER (6)
PAGE (3)
YEAR SEQUENTIAL NUMBER REVISION I
I I
INUMBER DiabloCanyonUnit1 05l0 0
l02 17 5 2004
- - l 0 0 I l0 0 I
7 o
7 TEXT Tube repair techniques:
LAR 03-15, submitted in PG&E Letter DCL-03-132, dated October 22, 2003, requested a revision to TS 5.5.9, Table 5.5.9-2, for the use of Alloy 800 tube sleeves for SG tube repair.
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.