05000499/LER-2005-001, Regarding Shutdown of STP Unit 2 Due to Reactor Coolant System Pressure Boundary Leak
| ML050980111 | |
| Person / Time | |
|---|---|
| Site: | South Texas  |
| Issue date: | 04/05/2005 |
| From: | Parkey G South Texas |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| NOC-AE-05001865, STI: 31861096 LER 05-01-00 | |
| Download: ML050980111 (6) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(A), Completion of TS Shutdown 10 CFR 50.73(a)(2)(ii)(A), Seriously Degraded 10 CFR 50.73(a)(2)(i) 10 CFR 50.73(a)(2)(vii), Common Cause Inoperability 10 CFR 50.73(a)(2)(viii)(A) 10 CFR 50.73(a)(2)(ii)(B), Unanalyzed Condition 10 CFR 50.73(a)(2) 10 CFR 50.73(a)(2)(iii) 10 CFR 50.73(a)(2)(ix)(A) 10 CFR 50.73(a)(2)(iv)(A), System Actuation 10 CFR 50.73(a)(2)(x) 10 CFR 50.73(a)(2)(v)(A), Loss of Safety Function - Shutdown the Reactor 10 CFR 50.73(a)(2)(v)(B), Loss of Safety Function - Remove Residual Heat 10 CFR 50.73(a)(2)(v), Loss of Safety Function 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications |
| 4992005001R00 - NRC Website | |
text
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April 5, 2005 NOC-AE-05001865 1 OCFR50.73 U. S. Nuclear Regulatory Commission Attention: Document Control Desk One White Flint North 11555 Rockville Pike Rockville, MD 20852 South Texas Project Unit 2 Docket No. STN 50-499 Licensee Event Report 2005-01 Unit 2 Shutdown Due to Reactor Coolant System Pressure Boundary Leak Pursuant to 10CFR50.73(a)(2)(i)(A) and 10CFR50.73(a)(2)(ii)(A), the South Texas Project submits the attached Licensee Event Report 2005-01 regarding a shutdown of STP Unit 2 due to a Reactor Coolant System Pressure Boundary Leak.
This event did not have an adverse effect on the health and safety of the public.
There are no commitments contained in this event report.
Corrective actions will be handled in accordance with the STP Corrective Action Program.
If there are any questions on this submittal, please contact S. M. Head at (361) 972-7136 or me at (361) 972-7800.
A Gary Parkey Vice President, Generation and Plant General Manager awh/
Attachment: LER 2005-01 LER 2-05-001 (U2 shutdown due to RCPB leak).doc STI: 31861096
NOC-AE-05001 865 Page 2 of 2 cc:
(paper copy)
(electronic copy)
Bruce S. Mallett Regional Administrator, Region IV U. S. Nuclear Regulatory Commission 611 Ryan Plaza Drive, Suite 400 Arlington, Texas 76011-8064 U. S. Nuclear Regulatory Commission Attention: Document Control Desk One White Flint North 11555 Rockville Pike Rockville, MD 20852 Richard A. Ratliff Bureau of Radiation Control Texas Department of State Health Services 1100 West 49th Street Austin, TX 78756-3189 Jeffrey Cruz U. S. Nuclear Regulatory Commission P. 0. Box 289, Mail Code: MN1 16 Wadsworth, TX 77483 A. H. Gutterman, Esquire Morgan, Lewis & Bockius LLP David H. Jaffe U. S. Nuclear Regulatory Commission R. L. Balcom Texas Genco, LP C. A. Johnson AEP Texas Central Company C. Kirksey City of Austin Jon C. Wood Cox Smith Matthews J. J. Nesrsta
- - R. K. Temple E. Alarcon City Public Service C. M. Canady City of Austin Electric Utility Department 721 Barton Springs Road Austin, TX 78704
NRC FORM 366 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB: NO. 3150-0104 EXPIRES: 06/30/2007 (6-2004)
, the NRC may digits/characters for each block) notrconduct or sponsor, and a person Is not required to respond to, the
- 3. PAGE South Texas Project Unit 2 05000 499 1 OF 4
- 4. TITLE: Shutdown of STP Unit 2 due to Reactor Coolant System Pressure Boundary Leak
- 5. EVENT DATE
- 6. LER NUMBER
- 7. REPORT DATE
- 8. OTHER FACILITIES INVOLVED SQ A RFACILITY NAME DOCKET NUMBER MONTH DAY YEAR YEAR SEQUENIAL RENV MONTH DAY YEAR 05000 EFACIRTY NAME DOCKET NUMBER 02 09 2005 2005 -
01 00 04 2005 05000
- 9. OPERATING MODE
- 11. THIS REPORT IS SUBMITTED PURSUANT TO THE REQUIREMENTS OF I0 CFR§: (Checka/l that apply)
O 20.2201(b) 0 20.2203(a)(3)(i) 0 50.73(a)(2)(i)(C) 0 50.73(a)(2)(vii) 1 0 20.2201(d) 0 20.2203(a)(3)(ii) 0 50.73(a)(2)(ii)(A) 0 50.73(a)(2)(viii)(A) o 20.2203(a)(1) 0 20.2203(a)(4) 0 50.73(a)(2)(ii)(B) 0 50.73(a)(2)(viiD(B)
El 20.2203(a)(2)(i) 0 50.36(c)(1)(i)(A) 0 50.73(a)(2)(iii) 0 50.73(a)(2)(ix)(A)
- 10. POWER LEVEL 0 20.2203(a)(2)(ii) 0 50.36(c)(1)(ii)(A) 0 50.73(a)(2)(iv)(A) 0 50.73(a)(2)(x) o 20.2203(a)(2)(iii) 0 50.36(c)(2) 0 50.73(a)(2)(v)(A) 0 73.71 (a)(4) ol 20.2203(a)(2)(iv) 0 50.46(a)(3)(ii) 0 50.73(a)(2)(v)(B) 0 73.71 (a)(5) 100%
0 20.2203(a)(2)(v) 0 50.73(a)(2)(i)(A) 0 50.73(a)(2)(v)(C) 0 OTHER o 20.2203(a)(2)(vi) 0I 50.73(a)(2)(i)(B) 0 50.73(a)(2)(v)(D)
Specify In Abstract below or In SUMMARY OF THE EVENT, INCLUDING DATES AND APPROXIMATE TIMES On 1/28/05 Unit 2 Radiation Transmitter (RT) 8011 particulate channel indicated an increase in activity from 1.1 E-9 to a final value of approximately 1.6 E-9 microcuries per milliliter. On 2/2/05 a second step increase.was noted on the RT-801 1 particulate channel to a final value of approximately 2.2 E-9. A Condition Report was written and an inspection plan was developed to find the source of the increasing trend on the RT-8011 particulate channel. A robotic camera inspection inside the bioshield revealed a small steam plume near Steam Generator (SG) 2A on 2/8/05. This area contained a 3/4" vent line attached to a 12" Safety Injection (SI) line that connects to the Reactor Coolant System (RCS) Loop 2A cold leg. On 2/9/05 it was determined that the steam plume was coming from the inlet side of RC-0127 which is the first vent valve off of the SI line. Due to the fact that this was an unisolable RCS pressure boundary leak, Unit 2 was shutdown to Mode 5 on 2/9/05 to comply with Technical Specification 3.4.6.2.
A root cause team was assembled to determine the preliminary cause of the RCS pressure boundary leak and to determine the extent of condition. It was determined that the crack initiated on the inside of the RC-0127 fillet weld at a weld flaw (lack of fusion) and propagated to the surface of the weld due to High Cycle Fatigue (HCF).
E. THE METHOD OF DISCOVERY OF EACH COMPONENT OR SYSTEM FAILURE, OR PROCEDURAL OR PERSONNEL ERROR Following investigation into an increasing containment atmosphere particulate radiation monitor trend, primary leakage (steam plume) was discovered coming from a 3/4 inch vent line off of the "AW Cold Leg Safety Injection line. The leak was determined to be unisolable Reactor Coolant System Pressure Boundary leakage.
Destructive testing performed on the weld showed the through-wall leak was from a crack that originated from the interior of the weld at the weld root.
II.
COMPONENT OR SYSTEM FAILURES A. FAILURE MODE, MECHANISM, AND EFFECTS OF EACH FAILED COMPONENT The failure mode was a through-wall leak at the socket weld to 3/4 vent valve RC-01 27.(1-2001)
LICENSEE EVENT REPORT (LER)
- 1. FACILITY NAME
- 2. DOCKET 6..LER NUMBER
- 3. PAGE I
ER~
SEQUEN-nAL REuv, sISION 3
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South Texas Project Unit 2 05000 499 NUMBER I NUMBER I O
OF 4
2005 01 00 B. CAUSE OF EACH COMPONENT OR SYSTEM FAILURE The crack initiated at the root of the RC-0127 inlet weld due to lack of fusion which was found on about 120 degrees of the weld root. High Cycle Fatigue (HCF) propagated the crack through the weld.
C. SYSTEMS OR SECONDARY FUNCTIONS THAT WERE AFFECTED BY FAILURE OF COMPONENTS WITH MULTIPLE FUNCTIONS N/A
D. FAILED COMPONENT INFORMATION
The fillet weld with the crack at the inlet of RC-0127 is a stainless steel (ER308L weld material) ASME Class 2 socket weld joint.
Ill. ANALYSIS OF THE EVENT A. SAFETY SYSTEM RESPONSES THAT OCCURRED N/A B. DURATION OF SAFETY SYSTEM TRAIN INOPERABILITY The RC-0127 leak did not result in any safety system not being capable of performing its design basis function.
C. SAFETY CONSEQUENCES AND IMPLICATIONS
This event did not adversely affect the safety of the public or station personnel. There was no release of radiation as a result of this incident.
The RC-0127 leak did not initiate a plant transient condition and would not have prevented the mitigation of an initiating event. Therefore, the RC-0127 socket weld leak did not change the core damage frequency or large early release frequency.
IV. CAUSE OF THE EVENT
The cause of the pressure boundary leak was a crack that initiated on the inside of the RC-0127 fillet weld at a weld flaw and propagated to the surface of the weld due to High Cycle Fatigue (HCF).
V. CORRECTIVE ACTIONS
- 1. The Unit 2 vent line containing RC-01 27 and RC-01 45 was removed and replaced with a welded plug.
- 2. Vibration measurements were taken on the Loop 'B' vent line (line most similar to the leaking line that was removed) prior to the Unit 2 restart to ensure that they meet acceptance criteria.
- 3. Vibration measurements of susceptible lines will be taken at the start of the Unit 2 Fall 2005 refueling outage to identify any further extent of condition.
- 4. Vibration measurements of susceptible lines were taken at the start of the Unit 1 Spring 2005 refueling outage.
Two vent lines are scheduled to be removed during the outage, including the Unit 1 RC-0127/0145 vent.
II(1.2001)
LICENSEE EVENT REPORT (LER) 1
VI. PREVIOUS SIMILAR EVENTS
There have been no similar events at STP within the last 3 years.
VII. ADDITIONAL INFORMATION
STPNOC also plans to establish a fatigue monitoring program for small bore piping that is capable of identifying the specific components and locations that are susceptible to fatigue cracking and implementing measures for monitoring and correcting fatigue cracks.