05000445/LER-2001-004
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(ii)(A), Seriously Degraded |
| Initial Reporting | |
| 4452001004R00 - NRC Website | |
I. pESCRIPTION OF REPORTABLE EVENT
A. REPORTABLE EVENT CLASSIFICATION
The subject event is reportable pursuant to the requirements of TS 5.6.10, specifically 10CFR50.73(a)(2)(ii)(A).
B. PLANT OPERATING CONDITIONS PRIOR TO THE EVENT
Comanche Peak Steam Electric Station (CPSES) Unit 1 was in its eighth refueling outage (1RF08).
C. STATUS OF STRUCTURES, SYSTEMS, OR COMPONENTS THAT WERE
INOPERABLE AT THE START OF THE EVENT AND THAT CONTRIBUTED TO
THE EVENT
Not Applicable — There were no structures, systems, or components that were inoperable at the start of the event which contributed to this event.
D. NARRATIVE SUMMARY OF THE EVENT, INCLUDING DATES AND
APPROXIMATE TIMES
CPSES 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 1 percent of the total tubes inspected are defective.
Additionally, if the results of the SG tube sample inspections are classified as Category C-3, then prompt NRC notification is required in accordance with TS 5.5.9 Table 5.5-2 and TS 5.6.10c. During this eighth refueling outage, results of 3 steam generator inspections went into Category C-3 at separate times. Each of these events is listed below.
Event 1 On April 2, 2001, at approximately 4:02 a.m., CPSES Unit 1 was in its eighth refueling outage. Analysis of eddy current testing data on Steam Generator (SG) (EIIS: (AB)(SG)) 1-3 indicated that greater than I percent of the total tubes inspected in SG 1-3 were defective.
On April 2, 2001 at approximately 6:53 a.m., CPSES made notification of the event via the emergency notification system (ENS) pursuant to the requirements of 10CFR50.72(b)(3)(ii)(A) and TS 5.5.9. (Refer to NRC event number 37880) Facility Namc ( I) COMANCHE PEAK STEAM ELECTRIC STATION UNIT 1 LER Number (6) Year � Sequential Revision Number Number 01 004 19 00 Docket Page(3) Enclosure to TXX-01067 Event 2 On April 3, 2001, at approximately 5:00 a.m., CPSES Unit 1 was in its eighth refueling outage. Analysis of eddy current testing data on Steam Generator (SG) (EIIS: (AB)(SG)) 1-4 indicated that greater than 1 percent of the total tubes inspected in SG 1-4 were defective.
On April 2, 2001 at approximately 6:00 a.m., CPSES made notification of the event via the emergency notification system (ENS) pursuant to the requirements of 10CFR50.72(b)(3)(ii)(A) and TS 5.5.9. (Refer to NRC event number 37880) Event 3 On April 3, 2001, at approximately 10:37 p.m., CPSES Unit 1 was in its eighth refueling outage. Analysis of eddy current testing data on Steam Generator (SG) (EIIS: (AB)(SG)) 1-2 indicated that greater than 1 percent of the total tubes inspected in SG 1-2 were defective.
On April 2, 2001 at approximately 11:15 a.m., CPSES made notification of the event via the emergency notification system (ENS) pursuant to the requirements of 10CFR50.72(b)(3)(ii)(A) and TS 5.5.9. (Refer to NRC event number 37880)
E. THE METHOD OF DISCOVERY OF EACH COMPONENT OR SYSTEM FAILURE,
OR PROCEDURAL OR PERSONNEL ERROR
The defective tubes were found during scheduled eddy current testing of CPSES Unit 1 SG tubing.
II. COMPONENT OR SYSTEM FAILURES
A. FAILURE MODE, MECHANISM, AND EFFECTS OF EACH FAILED COMPONENT
TXU Electric believes that top of tube support (TTS) outside diameter stress corrosion cracking (ODSCC) was caused by the temperature, chemistry and residual stress effects on the tubing material (Inconel 600 MA).
B. DURATION OF SAFETY SYSTEM TRAIN INOPERABILITY
Not Applicable — No safety system train was rendered inoperable.
Facility Name (I)
COMANCHE PEAK STEAM ELECTRIC STATION UNIT I
LER Number (6) Year � Sequential � Revision Number � Number 01 � 004 1 1 00 Docket Page(3) Enclosure to TXX-01067
C. SAFETY CONSEQUENCES AND IMPLICATIONS
The outside diameter stress corrosion cracking (ODSCC) associated with the hot leg rolled transition was found to be the predominant degradation mechanism seen during the CPSES 1RFO8 inspection. A total of 179 tubes were taken out of service (plugged) for this mode of degradation. SG 1-1 had 2 tubes plugged, SG 1-2 had 47 tubes plugged SG 1-3 had 79 tubes plugged, and SG 1-4 had 51 tubes plugged as a result of hot leg top of tubesheet ODSCC. An additional 30 tubes were plugged due to loose parts, preheater wear, ODSCC at a freespan ding, Primary Water Stress Corrosion Cracking at the hot leg top of tubesheet roll transition, and data quality issues. The total plugs installed to-date remain well below the 10 percent tube plugging allowance provided by the accident analysis. There were no instances of ODSCC tube degradation identified in the cold leg hard rolled transition based upon 20 percent eddy current (MRPC/Plus Point) inspection performed for SGs 2, 3, and 4. One of the indications reported met the nondestructive examination (NDE) screening criteria for insitu pressure testing. Additionally, the largest voltage indication was tested. These tubes were insitu pressure tested with no leakage or burst. Growth rates based on consecutive inspection data associated with tubes exhibiting baffle plate and anti-vibrations bar (AVB) wear were within expected progression. The condition of the tubes at the end of Cycle 8 meets all NRC accepted integrity levels. The planned operating length for Cycle 9 is 498 effective full power days (EFPD) compared to 506 EFPD (actual) for Cycle 8. This represents a decrease in operating length. There are no planned changes of significance neither in operating temperatures and steam pressure nor in the operating secondary side chemistry. Therefore, the structural and leakage integrity condition of the CPSES Unit 1 SGs is bounded by the acceptable Cycle 8 performance. Based on the aforementioned, it was concluded that the event had no impact on the health and safety of the public
III. CAUSE OF THE EVENT
TXU Electric believes that the top of tube sheet (TTS) outside diameter stress corrosion cracking (ODSCC) was caused by the temperature, chemistry and residual stress effects on the tubing material (Inconel 600 MA).
IV. CORRECTIVE ACTIONS
Chemical cleaning was performed during the CPSES Unit 1 fifth refueling outage (1RF05) to remove the chemical contaminants at the TTS and tube supports (TSPs). Prior to commercial operation, 124 tubes in each steam generator were expanded at the B and D baffle plate to reduce wear.
Facility Name (1) COMANCHE PEAK STEAM ELECTRIC STATION UNIT 1 LER Number (6) Year Sequential � Revision Number � Number � 01 M 004 � 00 Docket Page(3)
- , Enclosure to TXX-01067 A total of 179 tubes were plugged for ODSCC at TTS. SG 1-1 had 2 tubes plugged, SG 1-2 had 47 tubes plugged, SG 1-3 had 79 tubes plugged, and SG 1-4 had 51 tubes plugged as a result of hot leg top of tubesheet ODSCC. An additional 30 tubes were plugged due to loose parts, preheater wear, ODSCC at a freespan ding, primary water stress corrosion cracking (PWSCC) at the hot leg top of tubesheet roll transition, and data quality issues. TXU Electric believes that it has removed all known defective tubes from service as required by CPSES Technical Specification
V. PREVIOUS SIMILAR EVENTS
There has been two other previous similar event of this type at CPSES, which occurred during the 1RFO6 and IRFO7 SG tube inspection. Corrective actions taken for the previous event would not have prevented this event.
VI. ADDITIONAL INFORMATION
The following information meets the requirements of Special Report as specified in CPSES Technical Specification 5.6.10.a. Total tubes plugged during this outage:
CPSES UNIT 1 STEAM GENERATOR 1 11 tubes were plugged in this generator 0 tubes were designated as an F* tube.
CPSES UNIT 1 STEAM GENERATOR 2 58 tubes were plugged in this generator 0 tubes were designated as an F* tube.
CPSES UNIT 1 STEAM GENERATOR 3 85 tubes were plugged in the generator 0 tubes were designated as an F* tube.
CPSES UNIT 1 STEAM GENERATOR 4 55 tubes were plugged in this generator 0 tubes were designated as an F* tube.