05000277/LER-2003-001, Regarding Outboard Main Steam Isolation Valve Instrument All Line Failure Results in Scram on Reactor High Pressure

Regarding Outboard Main Steam Isolation Valve Instrument All Line Failure Results in Scram on Reactor High Pressure

ML031490372
Person / Time
Site:	Peach Bottom
Issue date:	05/23/2003
From:	Stone J Exelon Nuclear
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
LER 03-001-00
Download: ML031490372 (6)

LER-2003-001, Regarding Outboard Main Steam Isolation Valve Instrument All Line Failure Results in Scram on Reactor High Pressure

Event date:
Report date:
Reporting criterion:	10 CFR 50.73(a)(2)(ii)(B), Unanalyzed Condition 10 CFR 50.73(a)(2)(ix)(A) 10 CFR 50.73(a)(2)(iii) 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)(iv)(A), System Actuation
2772003001R00 - NRC Website

text

Exekn..

Exelon Nuclear Telephone 717.456.7014 Nuclear Peach Bottom Atomic Power Station www.exeloncorp.com 1848 Lay Road Delta, PA 17314-9032 1 OCFR 50.73 May 23, 2003 U. S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555-0001 Peach Bottom Atomic Power Station, Unit 2 Facility Operating License No. DPR-44 NRC Docket No. 50-277

Subject:

Licensee Event Report (LER) 2-03-01 This LER reports an automatic scram of Unit 2 and associated Primary Containment Isolations as a result of a Main Steam Isolation Valve going closed due to a failed instrument air line. In accordance with NEI 99-04, the regulatory commitment contained in this correspondence is to restore compliance with the regulations. The specific methods that are planned to restore and maintain compliance are discussed in the LER.

If you have any questions or require additional information, please do not hesitate to contact us.

Sincerely, J hn A. Stone P ant Manager each Bottom Atomic Power Station JAS/djf/CR1 53675 Attachment cc:

PSE&G, Financial Controls and Co-owner Affairs R. R. Janati, Commonwealth of Pennsylvania INPO Records Center H. J. Miller, US NRC, Administrator, Region I R.. McLean, State of Maryland A. C. McMurtray, US NRC, Senior Resident Inspector CCN 03-14041

SUMMARY OF EXELON NUCLEAR COMMITMENTS The following table identifies commitments made in this document by Exelon Nuclear.

(Any other actions discussed in the submittal represent intended or planned actions by Exelon Nuclear. They are described to the NRC for the NRC's information and are not regulatory commitments.)

Commitment

Committed Date or "Outage" In accordance with NEI 99-04, the In accordance with the Corrective Action regulatory commitment contained in this Program correspondence is to restore compliance with the regulations. The specific methods that are planned to restore and maintain compliance are discussed in the LER.

NRC FORM 366 U.S. NUCLEAR REGULATORY APPROVED BY OMB NO. 3150-0104 EXPIRES 6-30-2001 (1-2001)

COMMISSION Estimated burden per response to complywith this mandatory information collection request:

50 hours5.787037e-4 days <br />0.0139 hours <br />8.267196e-5 weeks <br />1.9025e-5 months <br />. Reported lessons leamed are incorporated into the licensing process and fed back to industry. Send comments regarding burden estimate to the Records Management Branch (T-6E6) U..

Nclea ReulaoryComission. Washington. DC 20555-0001

• or by internet LICENSEE EVENT REPORT (LE-milRo Isinr.go,adtoheesOficer, Cffice of Information and Regulator Affairs, LICENSE E EVENT REPORT (L ER) e-atobs r9vadOthffornm<<ien wfhnlonco500 rynee NEOB-10202 v9150 0104 Ollice of Management and Budget, Washington, DC 20503. If a (See reverse for required number of means used to impose information colletion does not display a currenty valid OMB control digits/characters for each block) number the NRC may not conduct or sponsor and a person is not required to respond to,the FACILITY NAME (1)

DOCKET NUMBER (2)

PAGE 3)

Peach Bottom Atomic Power Station, Unit 2 05000 277 1 OF 4

TITLE (4)

Outboard Main Steam isolation Valve Instrument Al Line Failure Results in Scram on Reactor High Pressure EVENT DATE (5)

LER NUMBER (6)

REPORT DATE (7)

OTHER FACILITIES INVOLVED (8)

FACILITY NAME DOCKET NUMBER tv10 DAY YEAR YEAR NUMBER NO' MO DAY YEAR FACILITY NAME DOCKET NUMBER 4

12 03 03 0 0 1 00 05 23 03 OPERATING THISREPORTISSUBMITTED PURSUANTTOTHEREFUIREMENTS OF1CFR: (jdeckallthat appl)

(11)

MODE (9) 1 20.2201(b) 20.2203(a)(3)(ii) 50.73(a)(2)(ii)(B) 50.73(a)(2)(ix)(A)

POWER 20.2201 (d) 20.2203(a)(4) 50.73(a)(2)(iii)

L 50.73(a)(2)(x)

LEVEL(10) 100 20.2203(a)(1) 50.36(c)(1)(I(A)

X 50.73(a)(2)(v)(A)

_ 73.71 (a)(4) 20.2203(a)(2)(i) 50.36(c)(1 (ii)(A) 50.73(a)(2)(v)(A)

__73.71 (a)(5) 20 2203(a)(2)(ii) 50.36(c)(2) 50.73(a)(2)(v)(B)

OTHER Asrc eo ri 20.2203(a)(2)(iii) 50.46(a)(3)(ii) 50.73(a)(2)(v)(C)

(If more space is required, use addifional copies of NRC Forn 366A) (17)

Unit Conditions Prior to the Event Unit 2 was in Mode 1 and operating at approximately 100% rated thermal power when the event occurred. At the time of the event, there were no activities in progress related to Main Steam Isolation Valves (MSIVs)

(EIIS:

ISV). There were no structures, systems or components out of service that contributed to this event.

Description of the Event At 1847 hours0.0214 days <br />0.513 hours <br />0.00305 weeks <br />7.027835e-4 months <br /> on 4/12/03, Unit 2 scrammed as a result of a high reactor pressure condition. The high pressure condition resulted from the closure of the 'D' Outboard Main Steam Isolation Valve (MSIV). The MSIV closed as a result of a failed instrument air line (EIIS: TBG) that provides a pneumatic supply to the valve control manifold EIIS: PSX).

As a result of the high pressure condition, the Recirculation Pumps tripped and the Alternate Rod Insertion (ARI) system actuated. The mode switch was promptly moved to the 'Shutdown' position and plant cool down was commenced using the normal heat sink (Bypass valves to the condenser). As expected, PCIS Group II and III isolations were received, as a result of reaching the Level 3 reactor water level set point subsequent to the scram. All isolation valves operated as designed.

The PCIS Group II /

III isolations were reset by approximately 1900 hours0.022 days <br />0.528 hours <br />0.00314 weeks <br />7.2295e-4 months <br />. NRC prompt notifications were completed at approximately 2055 hours0.0238 days <br />0.571 hours <br />0.0034 weeks <br />7.819275e-4 months <br />.

A half scram ('A' Channel) signal was generated on 4/13/03 at 0039 hours4.513889e-4 days <br />0.0108 hours <br />6.448413e-5 weeks <br />1.48395e-5 months <br /> due to erratic oscillations in the '2A' Wide Range Neutron Monitor (EIIS: MON). The monitor was bypassed and the half-scram signal was reset.

The plant was maintained in the hot shutdown condition (Mode 3) until the mode switch was placed in the Startup position (Mode 2) on 4/13/03 at 1545 hours0.0179 days <br />0.429 hours <br />0.00255 weeks <br />5.878725e-4 months <br />.

This report is being submitted pursuant to 10CFR50.73 (a)(2)(iv)(A) due to valid actuations of the Reactor Protection System and the Primary Containment Isolation System.

NRC FORM 368A (1-201)

(If more space is required, use additional copies of NRC Forn 366A) (17)

Analysis of the Event

There were no actual safety consequences as a result of this event. All control rods inserted on the reactor scram signal. The Group II / III PCIS isolations resulted in the primary containment isolation safety function being met. ARI and the Recirculation Pump Trip functions operated due to a high reactor pressure condition. This is a conservative plant action that provides backup actions for the Reactor Protection System.

Although the 'D' Outboard MSIV closed due to the failed instrument air line, there were not any actual plant conditions that required the MSIVs to close.

Post-scram cooling was accomplished using the Main Steam Bypass Valves to the Condenser.

A Conditional Core Damage Probability (CCDP) study was performed. This analysis determined that core damage could occur once in approximately every one million events. Therefore, this event did not have any risk significance. This event is bounded by the design basis event entitled, 'Isolation of One Main Steam Line'.

During this event, the plant safety systems responded as necessary. This event did not involve operations that exceeded the design basis. The single MSIV closure did cause a rise in neutron flux, however, the flux rise did not reach the bounding Hi Flux Scram set point as described in the Updated Final safety Analysis Report (UFSAR). The SCRAM on high reactor pressure (which reached approximately 1080 psig) rather than on high neutron flux was evaluated and is considered appropriate for the given transient conditions. This was based on lower void coefficients in the currently licensed fuel and a slower pressure transient than the bounding MSIV failure analyses in the UFSAR.

The MSIV accumulator pneumatic supply is safety related for both the inboard and outboard MSIVs. The MSIV solenoid valve control manifold pneumatic supply to the inboard MSIVs is required to be safety related since they are not isolated from the safety related pneumatic supply to the accumulator. The outboard MSIV pneumatic supply to the control manifolds are not fed from within the safety related pneumatic supply boundary and therefore, are not considered as safety related.

Cause of the Event

The cause of the Unit 2 scram was due to a failed instrument air line that supplies the solenoid valve control manifold for the 'D' Outboard MSIV. It was observed that the instrument line failed at the ferrule area of the tubing fitting at the solenoid valve control manifold. The failed 'D' Outboard MSIV instrument air line was sent to a failure analysis laboratory to determine the exact cause of the failure. It was determined that high cycle, vibration induced fatigue was the cause of the instrument air line failure.

Further engineering review determined that the 'D' Outboard MSIV instrument tubing was vulnerable to fatigue failures due to the method of supporting the instrument air lines. The instrument line that failed is a 3/8" diameter Type 304 stainless steel tubing utilizing a tubing fitting for connection to the solenoid valve control manifold. The instrument air lines that supply the solenoid valve control manifold are not safety related and non-seismic. The tubing that failed contained an expansion loop and the unsupported tubing length was approximately 100".

(If more space is required, use additional copies of NRC Form 366A) (17)The spurious half-scram generated by the '2A' Wide Range Neutron Monitor (General Electric, Model 304A3712G005) is believed to be due to electromagnetic interference and is being further evaluated through the corrective action program.

Corrective Actions

The 'DI Outboard MSIV instrument air tubing was replaced. Similar tubing on the other three Outboard MSIVs was also replaced. An engineering evaluation was performed on the Outboard MSIV instrument tubing supports. This resulted in several additional tubing supports being added to the four Outboard MSIV instrument air lines. Similar upgrades are planned for the Unit 3 Outboard MSIVs when plant conditions permit maintenance.

A walk down of Unit 2 was performed to assess the adequacy of pneumatic control lines. Appropriate minor repairs were made to some pneumatic lines. Additional unit 3 walk downs will be performed when plant conditions permit to assess other instrument air lines for degradation and tubing support adequacy.

Engineering performed a review of the Unit 2 and Unit 3 Inboard MSIV instrument nitrogen supply lines. It was concluded that these lines are more robust than the Outboard lines and do not require additional supports. The Inboard MSIV nitrogen supply lines are safety related.

Appropriate additional grounding of the 2A' Wide Range Neutron Monitor is being considered in accordance with the corrective action program.

Previous Similar Occurrences There were no previous events identified involving a scram due to MSIV closure caused by a failed instrument air line.