NOC-AE-05001865, LER 05-01-00 South Texas Project Unit 2 Regarding Shutdown of STP Unit 2 Due to Reactor Coolant System Pressure Boundary Leak

LER 05-01-00 South Texas Project Unit 2 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)

Text

a Nuclear Operating Company Swffi TbasPfcerfcGcncrabinmStWaon PO. S 289 W 7Ths 77483 thdsm A April 5, 2005 NOC-AE-05001865 10CFR50.73 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 A. H. Gutterman, Esquire Regional Administrator, Region IV Morgan, Lewis & Bockius LLP U. S. Nuclear Regulatory Commission 611 Ryan Plaza Drive, Suite 400 David H. Jaffe Arlington, Texas 76011-8064 U. S. Nuclear Regulatory Commission U. S. Nuclear Regulatory Commission R. L. Balcom Attention: Document Control Desk Texas Genco, LP One White Flint North 11555 Rockville Pike C. A. Johnson Rockville, MD 20852 AEP Texas Central Company Richard A. Ratliff C. Kirksey Bureau of Radiation Control City of Austin Texas Department of State Health Services 1100 West 49th Street Jon C. Wood Austin, TX 78756-3189 Cox Smith Matthews Jeffrey Cruz J. J. Nesrsta U. S. Nuclear Regulatory Commission - R. K. Temple P. 0. Box 289, Mail Code: MN1 16 E. Alarcon Wadsworth, TX 77483 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) Estimated burden per response to comply with this mandatory collection request 50 hours5.787037e-4 days <br />0.0139 hours <br />8.267196e-5 weeks <br />1.9025e-5 months <br />. Reported lessons learned are Incorporated into the licensing process and fed back to Industry. Send comments regarding burden estimate to the Records and FOIA/Privacy Service Branch (T-5 F52), U.S.

LICENSEE EVENT REPORT (LER) Nuclear Regulatory Commission, Washington, DC 20555-0001, or by Internet e-mail to lnfocollects~nrc.gov, and to the Desk Officer, Office of Information and Regulatory Affairs NEOB-10202, (3150-0104), Office of Management and fo Budget, Washington, DC 20503. If a means used to Impose anInformation (See reverse for required number of collection does not display acurrentlyvalid OMB control number, the NRC may digits/characters for each block) notrconduct or sponsor, and a person Is not required to respond to, the

1. FACILITY NAME 2. DOCKET NUMBER 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 InAbstract below or InNRC Form 366A

12. LICENSEE CONTACT FOR THIS LER FACILITY NAME ITELEPHONE NUMBER (Include Area Code) 1361-972-7298 0 YES (If yes, complete 15. EXPECTED SUBMISSION DATE)

ABSTRACT (Limit to 1400 spaces, i.e., approximately 15 single-spaced typewitten lines)

On February 9, 2005 at 1222 hours0.0141 days <br />0.339 hours <br />0.00202 weeks <br />4.64971e-4 months <br />, South Texas Project (STP) Unit 2 commenced a reactor shutdown required by Technical Specification (TS) 3.4.6.2, "Reactor Coolant System - Operational Leakage".

Following investigation into an increasing containment atmosphere particulate radiation monitor trend, primary leakage (steam plume) was discovered coming from a 33/4 inch vent line off of the UAW Cold Leg Safety Injection line. The leak was determined to be unisolable Reactor Coolant System Pressure Boundary leakage and Unit 2 was shutdown to MODE 5 in accordance with TS 3.4.6.2. At the time of discovery, the total unidentified reactor coolant system leak rate was determined to be 0.13 gallons per minute.

This event is reportable in accordance with 10CFR50.73(a)(2)(i)(A) as completion of a shutdown required by the Technical Specifications and in accordance with 10CFR50.73(a)(2)(ii)(A) as serious degradation of a principal safety barrier.

The root cause of the pressure boundary leak was a crack propagating from a flaw in a socket weld to due to high cyclE fatigue.

This condition resulted in no personnel injuries, no offsite radiological releases, and no damage to safety-related equipment other than the leaking weld joint. There were no challenges to plant safety.

The leak was repaired by cutting off the leaking vent line and plugging the connection. Vibration measurement for susceptible lines has been performed for STP Unit 1 and is planned for Unit 2 to identify any further extent of condition.

m.4TEDO#4RECYCtEPAp..

NNF FCPMNE II-2WA)

O ,3 m. P"TED N WECD PAp.

NRC FORM 366A U.S. NUCLEAR REGULATORY COMMISSION (1-2001)

LICENSEE EVENT REPORT (LER)

1. FACILITY NAME 2. DOCKET 6. LER NUMBER 3. PAGE South Texas Project Unit 2 05000 499 SUERNBYEAR EULVISIOE2 OF 4 2005 01 00 I. DESCRIPTION OF REPORTABLE EVENT A. REPORTABLE EVENT CLASSIFICATION This event is reportable in accordance with 100FR50.73(a)(2)(i)(A) as completion of a shutdown required by the Technical Specifications and in accordance with 10CFR50.73(a)(2)(ii)(A) as serious degradation of a principal safety barrier .

B. PLANT OPERATING CONDITIONS PRIOR TO THE EVENT South Texas Project Unit 2 was in Mode 1 operating at 100% power.

C. STATUS OF STRUCTURES, SYSTEMS, OR COMPONENTS THAT WERE INOPERABLE AT THE START OF THE EVENT AND THAT CONTRIBUTED TO THE EVENT N/A D. NARRATIVE

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 isthe 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.

NRC FORM 366A U.S. NUCLEAR REGULATORY COMMISSION (1-2001)

LICENSEE EVENT REPORT (LER)

1. FACILITY NAME 2. DOCKET 6..LER NUMBER 3. PAGE South Texas Project Unit 2 05000I 499 ER~ SEQUEN-nAL NUMBER I REuv, sISION NUMBER I O3 O OF 44 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.

1 NRC FORM 366A U.S. NUCLEAR REGULATORY COMMISSION (1.2001)

LICENSEE EVENT REPORT (LER)

II 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.