05000499/LER-2011-003, Regarding Unit 2 Plant Mode Change with Turbine Trip Disabled

Regarding Unit 2 Plant Mode Change with Turbine Trip Disabled

ML15211A027
Person / Time
Site:	South Texas
Issue date:	01/30/2012
From:	Gerry Powell South Texas
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
NOC-AE-12002793 LER 11-003-00
Download: ML15211A027 (7)

LER-2011-003, Regarding Unit 2 Plant Mode Change with Turbine Trip Disabled

Event date:
Report date:
Reporting criterion:	10 CFR 50.73(a)(2)(i) 10 CFR 50.73(a)(2)(vii), Common Cause Inoperability 10 CFR 50.73(a)(2)(ii)(A), Seriously Degraded 10 CFR 50.73(a)(2)(viii)(A) 10 CFR 50.73(a)(2)(ii)(B), Unanalyzed Condition 10 CFR 50.73(a)(2)(viii)(B) 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)(i)(A), Completion of TS Shutdown 10 CFR 50.73(a)(2)(v), Loss of Safety Function 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications 10 CFR 50.73(e)(2)(v)
4992011003R00 - NRC Website

text

Nuclear Operating Company South Thxas Proje-E1ctric GenenrLIng Stat'on PO. Box 289 Wadsworth Teas 77483

/

January 30, 2012 NOC-AE-12002793 File No.: G25 10 CFR 50.73 STI: 33282416 U. S. Nuclear Regulatory Commission Attention: Document Control Desk One White Flint North 11555 Rockville Pike Rockville, MD 20852-2738 South Texas Project Unit 2 Docket No. STN 50-499 Licensee Event Report 2-2011-003 Unit 2 Plant Mode change with Turbine Trip disabled Pursuant to 10 CFR 50.73, STP Nuclear Operating Company (STPNOC) submits the attached Unit 2 Licensee Event Report (LER) 2-2011-003 regarding a condition when both Solid State Protection System (SSPS) channels of the turbine trip signals were defeated while transitioning into Mode 3.

This event did not have an adverse effect on the health and safety of the public.

There are no commitments contained in this LER. Corrective actions will be implemented in accordance with the STP Corrective Action Program.

If there are any questions on this submittal, please contact either Joe Loya at (361) 972-8005 or me at (361) 972-7566.

G. T. Powell Vice President, Generation JAL Attachment: LER 2-2011-003 07/,z7 2-0/6

NOC-AE-1 1002793 Page 2 of 2 cc:

(paper copy)

(electronic copy)

Regional Administrator, Region IV U. S. Nuclear Regulatory Commission 1600 East Lamar Boulevard Arlington, Texas 76011-4511 Balwant K. Singal Senior Project Manager U.S. Nuclear Regulatory Commission One White Flint North (MS 8B1) 11555 Rockville Pike Rockville, MD 20852 Senior Resident Inspector U. S. Nuclear Regulatory Commission P. 0. Box 289, Mail Code: MN116 Wadsworth, TX 77483 C. M. Canady City of Austin Electric Utility Department 721 Barton Springs Road Austin, TX 78704 A. H. Gutterman, Esquire Morgan, Lewis & Bockius, LLP John Ragan Chris O'Hara Jim von Suskil NRG South Texas LP Kevin Polio Richard Pena City Public Service Peter Nemeth Crain Caton & James, P.C.

C. Mele City of Austin Richard A. Ratliff Alice Rogers Texas Department of State Health Services Balwant K. Singal U. S. Nuclear Regulatory Commission

NRC FORM 366 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB: NO, 3150.0104 EXPIRES: 10/31/2013 (10-2010)

, the NRC may digits/characters for each block) not conduct or sponsor, and a person is not required to respond to the information collection.

3. PAGE South Texas Unit 2 0

05000499 L

0F 5

4. TITLE Unit 2 Plant Mode change with Turbine Trip Disabled S. EVENT DATE

.6 LER NUMBER 1 7. REPORT DATE

8. OTHER FACILITIES INVOLVED MONTH DAY i YEAR YEAR SEQUENTIAL REV 1 MONTH DAY YEAR I FACILITY NAME DOCKET NUMBER NUMBER NO.

DO IN/A N/A 11 30 12011 2011 003 0

01 30 2012 I N/A 9tOPERATING MODE

11. THIS REPORT IS SUBMITTED PURSUANT TO THE REQUIREMENTS OF I0CFR§: (Check all that apply) 3l 20.2201(b)

El 20.2203(a)(3)(i)

El 50.73(a)(2)(i)(C)

E 50.73(a)(2)(vii)

[] 20.2201(d)"

l 20.2203(a)(3)(ii)

E] 50.73(a)(2)(ii)(A)

[: 50.73(a)(2)(viii)(A)

E] 20.2203(a)(1)

El 20.2203(a)(4)

El 50.73(a)(2)(ii)(B)

El 50.73(a)(2)(viii)(B)

10. POWER LEVEL El 20.2203(a)(2)(i)

El 50.36(c)(1)(i)(A)

[]

50.73(a)(2)(iii)

[]

50.73(a)(2)(ix)(A) 0%

El 20.2203(a)(2)(ii)

El 50.36(c)(1)(ii)(A)

[: 50.73(a)(2)(iv)(A)

El 50.73(a)(2)(x)

E-20.2203(a)(2)(1i1)

[I 50.36(c)(2)

El 50.73(a)(2)(v)(A)

In 73.71(a)(4)

E] 20.2203(a)(2)(iv)

El 50.46(a)(3)(ii)

El 50.73(a)(2)(v)(B)

ED 73.71(a)(5)

El 20.2203(a)(2)(v)

El 50.73(a)(2)(i)(A)

Z 50.73(a)(2)(v)(C) 0l OTHER [3 20.2203(a)(2)(vi) 0 50.73(a)(2)(i)(B) 0 50.73(e)(2)(v)(D)

Specify In Abstract below or in NRC Form 366A

12. LICENSEE CONTACT FOR THIS LER FACILITY NAME TELEPHONE NUMBER (Include Area Code)

Joe Loya, Licensing Engineer 361-972-8005CAUSE S YSTEM COMPONENT MANU-REPORTABLE TO

CAUSE

SYSTEM COMPONENT MANU-REPORTABLE TO EPIX FACTURER EPIX FACTURER

14. SUPPLEMENTAL RESPONSE EXPECTED 15, EXPECTED MONTH I DAY l

YEAR YES (If yes, complete 1S. EXPECTED SUBMISSION DATE)

• NO SUBMISSION DATE ABSTRACT (Limit to 1400 spaces, Lae., approximately 15 single-spaced typewritten lines)

On November 20, 2011 at 0546 hours0.00632 days <br />0.152 hours <br />9.027778e-4 weeks <br />2.07753e-4 months <br /> [CS'], STP Unit 2 transitioned modes from Mode 4 to Mode 3. Prior to the mode change, the Solid State Protection System (SSPS) generated turbine trip signals were defeated by a maintenance work activity that installed a jumper in both channels (Train R and S) of non-class relays to the turbine trip circuit. The SSPS signals to the non-class relays that were defeated by the jumpers included the turbine trip from reactor trip breakers open (P-4), turbine trip from a reactor trip signal (P-16), and the turbine trip from Steam Generator HI-HI (P-14). In accordance with Technical Specification (TS) 3.3.2 Item 5a and 5b, P-4 and P-14 are required in Modes 1, 2, and 3. The jumpers were removed around 0930 on November 20, 2011 with U2 still in Mode 3. Since Unit 2 had changed Modes from 4 to 3 with TS 3.3.2 Item 5a and 5b and the associated Limiting Conditions of Operation (LCO) Actions not met, this is a condition prohibited by Technical Specification 3.0.4. A review of the performance of this activity in previous outages was conducted. It was identified that a similar event had occurred during 2RE14 in April of 2010. This event, including the one in April 2010, was reported as required by 10 CFR 50.72(b)(3)(v) parts (C) and (D).

The Cause of the event was determined to involve the revision of the associated maintenance work activity's Preventive Maintenance Instruction (PMI). Specifically, the MODE requirement prerequisites in the PMI were revised without full consideration of the Operational restrictions associated with changing plant conditions during procedure performance. The corrective action to prevent reoccurrence includes removing the mode restrictive steps of the associated PMI while adding them to the 7300 Protection System Channel Trip Function Bypass procedure.

There were no personnel injuries, no offsite radiological releases, and no damage to safety-related equipment associated with this condition. This condition did not have an adverse effect on the health and safety of the public.

NRC FORM 366 (10-2010)

I I

SUMMARY OF THE EVENT On 11/09/2011 with the Unit 2 core offloaded to the Spent Fuel Pool (DEFUELED MODE), all SSPS generated turbine trip signals were defeated by a maintenance work activity that installed a jumper in both channels (Train R and S) of non-class relays to the turbine trip circuit. Specifically, a total of four relays K947R & S and K948R & S were defeated by the jumpers. The functions affected included the turbine trip from reactor trip breakers open (P-4), turbine trip from a reactor trip signal (P-16), and the turbine trip from Steam Generator HI-HI (P-14). With the reactor trip breakers open, a P-4 signal is generated that locks in a turbine trip signal, which closes the throttle valves (TV) and governor valves (GV). These signals are addressed in TS 3.3.2 Item 5a and 5b and are required in Modes 1, 2, and 3.

This maintenance work activity is normally done during Modes 5, 6, or defueled. The jumpers were installed per Electro Hydraulic Control System Calibration Preventive Maintenance Instruction (PMI) to support maintenance activities which included stroking the turbine throttle and governor valves.

The PMI allows some sections to be performed in Modes other than 5, 6, and defueled as long as the Main Steam Header is not pressurized. However, Section 5.4 of the PMI, which installs the jumpers, was not included in this exception. Closure of this work package and removal of the jumper were not identified as a Mode 3 restraint.

On November 20, 2011 at 0546 hours0.00632 days <br />0.152 hours <br />9.027778e-4 weeks <br />2.07753e-4 months <br />, Unit 2 transitioned from Mode 4 to Mode 3.

11 FORM 366 (10-2010)LICENSEE EVENT REPORT (LER)

U.S. NUCLEAR REGULATORY COMMISSION CONTINUATION SHEET

1. FACILITY NAME

2. DOCKET

6. LER NUMBER

3. PAGE YEAR SEQUENTIAL REV. NO I NUMBER I3O South Texas Unit 2 05000499 3OF5 2011 003 00 On 11/20/2011 0808, the Control Room Operators were questioned regarding the fact that the Reactor Trip breaker indication on Control Panel 4 indicated open and the Main Turbine Electro Hydraulic Control Console on Control Panel 6 indicated the Main Turbine latched. An investigation began to determine if this condition was appropriate for the current plant conditions. Subsequently, the Shift Manager directed maintenance to remove the electrical jumpers. The Main Turbine was manually tripped and the electrical jumpers were removed at approximately 0930 AM on 11/20/2011.

During further review of the condition by Control Room Staff, it was recognized that the plant Mode change that occurred earlier in the day with the electrical jumpers installed.was likely a violation of Technical Specifications.

After an investigation of the facts surrounding this event, this condition was declared reportable on 11/30/2011 pursuant to:

a 10CFR 50.73(a)(2Mi)(B'):

Unit 2 changed Modes from 4 to 3 with TS 3.3.2 Item 5a and 5b and the associated LCO Actions 20 and 25 for not met for Mode 3. This is a condition prohibited by TS 3.0.4.

a 1 OCFR 50.73(a)(2)(v)(C) and (D): Since both channels of the turbine trip were defeated, and this function is assumed in the safety analysis, this condition Could have prevented the fulfillment of the safety functions to mitigate the consequences of an accident and control the release of radiation.

On 11/30/2011 at 1513, a notification pursuant to IOCFR 50.72(b)(3)(v)(C) and 10CFR50.72(b)(3)(v)(D) was made to the NRC Operations Center.

0 10CFR 50.73(a)(2)(vii)(D): The single cause or condition of having defeated both channels of turbine trip signals due to performance of the associated work activity defeated both channels of the turbine trip which are required to mitigate the consequences of an accident.

A review of the performance of this activity in previous outages was conducted. It was identified that during 2RE14 in April of 2010, a work package for this activity was not closed until after Mode 3 and that that a similar event had occurred.

E.

METHOD OF DISCOVERY

The Technical Specification non-compliance was discovered during the observation of Control Room outage activities by a Quality Inspector.

I1. EVENT-DRIVEN INFORMATION A.

SAFETY SYSTEMS THAT RESPONDED N/A FORM 366 (10-2010)LICENSEE EVENT REPORT (LER)

U.S. NUCLEAR REGULATORY COMMISSION CONTINUATION SHEET

1. FACILITY NAME

2. DOCKET

6. LER NUMBER

3. PAGE YEAR SEQUENTIALI REV. NO South Texas Unit 2 0500N499 40F5 2011 003 00 B.

DURATION OF SAFETY SYSTEM INOPERABILITY

On 11/20/2011 at 0546, Unit 2 met the plant~conditions and entered MODE 3 Hot Standby with the electrical jumpers in place preventing automatic tripping the Main Turbine. The Main Turbine was manually tripped and the electrical jumpers were removed at approximately 0930 AM on 11/20/2011. Therefore, the duration of safety system inoperability was approximately 3 hrs and 45 minutes.

C.

SAFETY CONSEQUENCES AND IMPLICATIONS OF THE EVENT The purpose of the turbine trip on rector trip is to prevent overcooling the RCS after a reactor trip.

Without the turbine trip on a reactor trip, the turbine would continue to draw steam from the steam generators until the main steam isolation valves close due to a compensated steam line pressure signal. This could result in a significant decrease in RCS coolant temperature which could result in a return to criticality and the fuel experiencing Departure from Nucleate Boiling (DNB). However, this event is bounded by the double-ended steam line break analysis which shows that DNB does not occur. A failure of the turbine trip on reactor trip also could result in the uncovery of the steam generator tubes, which could in an increase in calculated dose due to a reduction in the partition factor assumed in the safety analysis. However, the radionuclides in the steam would steam would plate out in the condenser which would more than offset the decrease in partition factor assumed in the safety analysis. Therefore, the failure of the turbine to trip on a reactor trip does not significantly degrade plant safety.

Although Unit 2 was in Mode 3, with the reactor trip breakers open, and turbine throttle valves closed while the jumpers were installed, this condition is conservatively considered to be a safety system functional failure. There was no work process prevention to assure the jumpers would be properly removed; consequently, this condition COULD have prevented the fulfillment of the control of the release radioactive materials or mitigating the consequences of an event.

A risk analysis was performed to determine the risk significance of having P-16 bypassed or defeated while changing plant Mode for Mode 4 to Mode 3. Since a P-1 6 actuation would result in a signal to close the main turbine governor and throttle valves and it has been shown that the throttle valves were in the closed position for the entire time period P-16 was bypassed, the evaluation concluded that there was no increase in the risk of core damage or large early release.

Consequently, there is no adverse effect on the health and safety of the public.

Ill. CAUSE OF THE EVENT The MODE requirement prerequisites in the Preventive Maintenance Instruction were revised without full consideration of the Operational restrictions associated with changing plant conditions during procedure performance.

FORM 366 (10-2010)LICENSEE EVENT REPORT (LER)

U.S. NUCLEAR REGULATORY COMMISSION CONTINUATION SHEET

1. FACILITY NAME

2. DOCKET

6. LER NUMBER

3. PAGE YEAR SEQUENTIAL 1 REV. NO South Texas Unit 2 05000499 2011 MBER 5 OF 5 201 1003 I 00

IV. CORRECTIVE ACTIONS

A. To ensure the jumpers are carried in the procedure that is easily tracked for mode restraints:

a. Remove mode restrictive steps of PMI-IC-EH-0003 (section for turbine trip defeat jumper installation) and, b. Add mode restrictive steps in the 7300 Protection System Channel Trip Function Bypass procedure (PMP08-BS-0002).

B. Revise procedure 0PAP01-ZA-0102 (Plant Procedures) to include process for revision of PMI's.

C. Develop and distribute lessons learned to all procedure writer certified personnel on the importance of close evaluation of re-performing License Compliance Reviews when Review and Comments cycle result in intent change to a procedure step.

V. PREVIOUS SIMILAR EVENTS

A review of work history for the last 3 years indicated the associated maintenance activity had been performed five times. There was only one other instance when this work package was not closed out until after Mode 3. This condition occurred during Unit 2 Refueling Outage in April 2010.

VI. ADDITIONAL INFORMATION

N/A r

FORM 366 (10-2010)