05000370/LER-1917-001, Regarding Technical Specification Required Shutdown Due to Reactor Coolant System Leakage

Regarding Technical Specification Required Shutdown Due to Reactor Coolant System Leakage

ML17121A376
Person / Time
Site:	Mcguire
Issue date:	04/24/2017
From:	Capps S Duke Energy Carolinas
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
MNS-17-018 LER 17-001-00
Download: ML17121A376 (7)

LER-1917-001, Regarding Technical Specification Required Shutdown Due to Reactor Coolant System Leakage

Event date:
Report date:
Reporting criterion:	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)(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)(A), Completion of TS Shutdown 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications 10 CFR 50.73(a)(2)(vii), Common Cause Inoperability 10 CFR 50.73(a)(2)(i)
3701917001R00 - NRC Website

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~~ENERGY April 24, 2017 Serial No. MNS-17-018 U.S. Nuclear Regulatory Commission ATTENTION: Document Control Desk Washington, D.C. 20555

Subject:

Duke Energy Carolinas, LLC McGuire Nuclear Station, Unit 2 *,

Docket No. 50-370 Licensee Event Report 370/2017-01, Revision 0 Nuclear Condition Report Numbers 2102868 and 2102990

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Steven D. Capps Vice President McGuire Nuclear Station Duke Energy MGOlVP I 12700 Hagers Ferry Road Huntersville, NC 28078 O: 980.875.4805 f: 980.875.4809 Steven.Capps@duke-energy.com.

10 CFR 50.73 Pursuant to 10 CFR 50. 73 Sections (a) (1) and (d), attached is Licensee Event Report (LER) 370/2017-01, Revision 0, reg.arding Unit 2 plant shutdown due to Reactor Coolant System pressure boundary leakage. There are two pressure boundary leaks associated with this LER.

This report is being submitted in accordance with 10 CFR 50. 73 (a) (2) (i) (A), the completion of any nuclear plant shutdown required by the plant's Technical Specifications, and 10 CFR 50.73 (a) (2) (ii) (A), any event or condition that resulted in the condition of the nuclear power plant, including its principle safety barriers, being seriously degraded.

This LER is preliminary and will be supplemented upon completion of the cause analysis for one of the failures, which is awaiting metallurgical laboratory testing.

This event is considered to be of no significance with respect to the health and safety of the public.

There are no regulatory commitments contained in this LER other than the commitment to submit a supplement to the LER. Duke Energy plans to provide that supplement within 60 days, but does not consider that time frame to be a commitment.

If questions arise regarding this LER, contact P. T. Vu of Regulatory Affairs at 980-875-4302.

Sincerely, Attachment

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U.S. Nuclear Regulatory Commission April 24, 2017 Page2 cc:

Catherine Haney Administrator, Region II U.S. Nuclear Regulatory Commission Marquis One Tower 245 Peachtree Center Ave.

NE Suite 1200, 30303-1257 Mike Mahoney Project Manager (McGuire)

U.S. Nuclear Regulatory Commission 11555 Rockville Pike Rockville, MD 20852-2738 Mail Stop 0-8 G9A Andy Hutto NRC Senior Resident Inspector McGuire Nuclear Station

NRC FORM 366 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB: NO. 3150-0104 EXPIRES: 03/31/2020 (04-2017) htto://www.nrc.gov/reading-rm/doc-collections/nur§9s/staff/sr1022/r3/)

the NRC may not conduct or sponsor, and a person is not required \\o respond to, the information collection.

.PAGE I

McGuire Nuclear Station, Unit 2 05000-0370 1 OF5

4. TITLE Technical Specification Required Shutdown Due to Reactor Coolant System Leakage

5. EVENT DATE

6. LER NUMBER i

7. REPORT DATE

8. OTHER FACILITIES INVOLVED SEQUENTIAL FACILITY NAME DOCKET NUMBER MONTH DAY YEAR YEAR REV MONTH DAY YEAR None NUMBER NO.

05000 02 23 2017 2017

- 01

- 00 04 24 2017 FACILITY NAME DOCKET NUMBER None 05000

9. OPERATING MODE

11. THIS REPORT IS SUBMITTED PURSUANT TO THE REQUIREMENTS OF 10 CFR §: Check all that apply) 1 D 20.2201(b)

D 20.2203(a)(3)(i)

~ 50.73(a)(2)(ii)(A) 0 50.73(a)(2)(viii)(A)

D 20.2201(d)

D 20.2203(a)(3)(ii)

D 50.73(a)(2)(ii)(B) 0 50.73(a)(2)(viii)(B)

D 20.2203(a)(1)

D 20.2203(a)(4)

D so.73(a)(2)(iii) 0 50.73(a)(2)(ix)(A)

D 20.2203(a)(2)(i)

D 50.36(c)(1)(i)(A)

D 50.73(a)(2)(iv)(A)

D 50.73(a)(2)(x)

10. POWER LEVEL D 20.2203(a)(2)(ii)

D 50.36(c)(1)(ii)(A)

D 50.73(a)(2)(v)(A)

D 73.71(a)(4)

D 20.2203(a)(2)(iii)

D so.36(c)(2)

D 50.73(a)(2)(v)(B)

D 73.71(a)(5) 100 D 20.2203(a)(2)(iv)

D 50.46(a)(3)(ii)

D 50.73(a)(2)(v)(C)

D 73.77(a)(1) 0 20.2203(a)(2)(v)

~ 50.73(a)(2)(i)(A) 0 50.73(a)(2)(v)(D)

D 73.77(a)(2)(i) 0 20.2203(a)(2)(vi) 0 50.73(a)(2)(i)(B)

D 50.73(a)(2)(vii)

D 73.77(a)(2)(ii) 0 50.73(a)(2)(i)(C) 0 OTHER Specify in Abstract below or in NRC Form 366A

12. LICENSEE CONTACT FOR THIS LER LICENSEE CONTACT rELEPHONE NUMBER {Include Area Code)

IP.T. Vu Reaulatorv Affairs SB0-875-4302 CAUSE SYSTEM COMPONENT MANU-REPORTABLE

CAUSE

SYSTEM COMPONENT MANU-REPORTABLE FACTURER TO EPIX FACTURER TOEPIX 0

BQ PSX Sumitomo y

B AB v

Flowserve y

14. SUPPLEMENTAL REPORT EXPECTED

15. EXPECTED MONTH DAY YEAR

~ YES (If yes, complete 15. EXPECTED SUBMISSION DATE)

D NO SUBMISSION 06 22 2017 DATE ABSTRACT (Limit to 1400 spaces, i.e., approximately 15 single-spaced typewritten lines)

On February 23, 2017, at 19:22 hours, with Unit 1 and Unit 2 operating at approximately 100 percent power, operators commenced a Unit 2 shutdown upon discovery of pressure boundary leakage on Unit 2 Safety Injection (NI) pipe upstream of the connection to "D" Reactor Coolant System (NC) Cold Leg. During a containment walk down inspection in Mode 3 on the next day, a pinhole pressure boundary leak was observed in the body of 2NC-30, Pressurizer Spray Bypass Valve.

The preliminary cause of the NI pipe leak is thermal fatigue due to cross-flow between the NC loops through the NI lines. The cause of the 2NC-30 valve leak is a casting flaw attributed to a combination of defects during the manufacturing process that resulted in a through wall pinhole leak in the valve body. The NI pipe with the flaw and the valve with the pinhole leak could have structurally performed their design function. Therefore, the health and safety of the public were not affected by these events.

During the Unit 2 shutdown, the NI pipe was repaired by weld overlay and valve 2NC-30 was replaced. During the subsequent Unit 2 spring 2017 refueling outage, the affected NI pipe was replaced, temperature monitoring devices were installed on susceptible pipes, modification for a bleed line off the common NI header was implemented, and leaking check valves in the 28 NI line were replaced. This LER will be supplemented when the cause evaluation of the NI pipe is finalized.

NRl,; Fur<1v1 3ti6 (06-2016) (04-2017)

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CONTINUATION SHEET (See NUREG-1022, R.3 for instruction and guidance for completing this form htto://www.nrc.gov/readinq-rm/doc-collections/nureas/staff/sr1022/r3[)

, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.

3. LERNUMBER YEAR McGuire Nuclear Station, Unit 2 05000-0370 2017 BACKGROUND SEQUENTIAL NUMBER

- 01 REV NO.

- 00 Applicable Energy Industry Identification [EllS] system and component codes are enclosed within brackets.

McGuire-specific system and component identifiers are contained within parentheses.

Safety Injection System [BQ](NI):

The NI system is designed to provide Emergency Core Cooling for the Reactor Coolant System [AB](NC) in order to prevent fuel clad melting to assure that the core remains in place and substantially intact in case of an accident. Each unit's NI system contains an "A" and "B" train pump that both actuate automatically upon a safety injection signal following low pressurizer pressure or high containment pressure. A common NI header in containment splits into four 1.5 inch nominal diameter lines each going into 2A, 2B, 2C and 20 NC Cold Legs. Each of these NI lines has two check valves and one normally opened upstream isolation valve in series.

Chemical and Volume Control System [CB](NV):

The NV system is designed to maintain required water inventory in the NC system; maintain seal-water injection flow to the reactor coolant pumps; control water chemistry conditions; and provide emergency core cooling (part of the system shares piping with the NI system).

The event was reported per 10 CFR 50.72(b)(2)(i) for "The initiation of any nuclear plant shutdown required by the plant's Technical Specifications" and 10 CFR 50. 72(b )(3)(ii)(A) for "Any event or condition that results in the condition of the nuclear power plant, including its principle safety barriers, being seriously degraded." An Emergency Notification System report was made to the Nuclear Regulatory Commission (NRC) on February 23, 2017, at 22:01 hours. A Licensee Event Report (LER) is also required due to the completion of a nuclear plant shutdown required by Technical Specifications (10 CFR 50. 73 (a)(2)(i)(A)) and due to the condition of a nuclear plant, including its principle safety barriers, being seriously degraded (10 CFR 50.73 (a)(2)(ii)(A)).

The.2D NI pipe was replaced during the spring 2014 Unit 2 refueling outage following discovery of a rejectable indication at the pipe to NC nozzle weld. LER 370/2014-01 was submitted and details this event. Corrective actions included the removal of a valve deemed susceptible to leak-by which can introduce cold water to the NI pipe in question. This pipe receives an inspection each refueling outage per Electric Power Research lnstitute's Materials Reliability Program MRP-146, "Management of Thermal Fatigue in Normally Stagnant Non-lsolable Reactor Coolant System Branch Lines." This same pipe was inspected during the fall 2015 Unit 2 refueling outage and no reportable indications were identified.

2NC-30 is a three quarter inch manually operated, Flowserve, Y-Globe, bellows seal design Pressurizer Spray Bypass Valve. Boron was identified at 2NC-30 while conducting a Mode 3 walk down at full temperature and pressure during the spring 2014 Unit 2 refueling outage. The valve was cleaned and the boron was determined to be from an inactive leak. The valve was examined again during the fall 2015 Unit 2 refueling outage and no leaks were identified.

No significant structures, systems, or components were out of service at the time of discovery that contributed to the event. Page 2 of 5 (04-2017)

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U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB: NO. 3150-0104 LICENSEE EVENT REPORT (LER)

CONTINUATION SHEET EXPIRES: 3/31/2020 (See NUREG-1022, R.3 for instruction and guidance for completing this form htto://www.nrc.gov/reading-rm/doc-collections/nureas/staff/sr1022/r3fj

, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.

1. FACILITY NAME

2. 'DOCKET NUMBER YEAR McGuire Nuclear Station, Unit 2 05000-0370 2017

EVENT DESCRIPTION

3. LER NUllllBER I SEQUENTIAL NUMBER

- 01 REV NO.

- 00 On February 23, 2017, at 19:22 hours, with Unit 1 and Unit 2 at approximately 100 percent power, operators commenced a Unit 2 shutdown upon discovery of pressure boundary leakage on Unit 2 NI pipe upstream of the connection to "D" NC Cold Leg. Subsequent investigation revealed the source of the leak to be a through wall crack on the inside of a bend in the pipe just upstream of the nozzle to the Cold Leg. The leak was approximately 5. 75 inches from the nozzle. The indication was* open to the surface for a dimension of approximately 0.6 inch of length.

During a containment walk down inspection in Mode 3 on the next day, a pinhole pressure boundary leak was observed in the body of valve 2NC-30.

The relevant sequence of events, with dates and approximate times of occurrence, is as follows:

2/23/17 2/23/17 2/24/17 2/24/17 2/24/17 3/2/17 3/3/17 3/5/17 3/8/17 19:22 Commenced Unit 2 shutdown from 100% upon identification of pressure boundary leakage 22:00 Reported to the NRC (Event Number 52573) 00:41 Unit 2 entered Mode 3 16:11 Identified 2NC-30 leak 17:21 Unit 2 entered Mode 5 15:56 Completed replacement of 2NC-30 10:30 Received NRC's verbal approval for alternative repair of NI pipe (Relief Request 17-MN-001) 11 :01 Completed NI pipe repair by weld overlay 16:46 Unit 2 entered Mode 1 CAUSAL FACTORS:

The cause evaluation of the NI pipe leak is ongoing. The preliminary cause of the NI pipe leak is thermal fatigue due to cross-flow between the NC loops through the NI lines. Cross-flow was detected between the 28 NC loop and the 2D NC loop through the shared NI line. This is an unanticipated mode of thermal cycling that is not addressed by MRP-146 and is different from the cause documented in LER 370/2014-01.

The cause evaluation of the 2NC-30 leak identified the cause as a casting flaw attributed to a combination of defects during the manufacturing process that resulted in a through wall pinhole leak in the valve body. At the leak site, substantial amounts of interdendritic porosity were concentrated near the ID and OD surfaces. In addition, elemental segregation (silicon in particular) was identified, and numerous, short, oxide-filled, intermittent, circumferential cracks were present within, and extending from, the regions of clustered porosity.

All of the cracks exhibited features consistent with casting flaws (i.e., they were not service-related). The interdendritic porosity in addition to the random silicon presence allowed the crack to form, creating this unique and isolated casting flaw. The Metallurgical Laboratory analysis and results showed that the valve did not have any erosion damage present. Due to the random nature of the casting flaw, there is no implication on extent of condition. (04-2017)

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CONTINUATION SHEET (See NUREG-1022, R.3 for instruction and guidance for completing this form http://www.nrc.gov/readinq-rm/doc-collections/nureas/staff/sr1022/r3l)

, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.

3. LER NUMBER McGuire Nuclear Station, Unit 2 05000-0370

CORRECTIVE ACTIONS

Immediate:

1. Replaced valve 2NC-30.

2. Repaired 20 NI pipe using weld overlay.

Subsequent:

YEAR 2017 SEQUENTIAL NUMBER

- 01 REV NO.

- 00

1. Installed strap-on thermocouples/accelerometer on 20 NI piping to monitor temperature and vibration.

2. Replaced 20 NI pipe.

3. Installed a bleed line off of the common NI header to preclude cross-leakage between the NI pipe connections to the NC loops.

4. Installed temperature monitoring devices on susceptible lines.

5. Replaced 28 NI line check valves.

SAFETY ANALYSIS

The NI line to 20 NC Cold Leg is dedicated for emergency injection only, and it is generally stagnant during normal plant operation. The leak in this line remained small, and an orderly shutdown was performed. The leak was much less than what is considered in the Probabilistic Risk Analysis (PRA) Loss Of Coolant Accident (LOCA) analysis. However, an un-isolable leak in the NC pressure boundary constitutes degradation of a principal safety barrier and is reportable to the NRC.

The finite element analysis results support that if the 1.5 inch NI pipe was subjected to any and all applicable primary design loads - including gravity, LOCA, Safe Shutdown Earthquake inertia and Seismic Anchor Motions - during the time in which it contained the through-wall defect up until the point where it was repaired with weld overlay, the remaining cross-section of the pipe would have remained intact and would not have experienced significant plastic deformation. Additionally, had the leak location failed catastrophically, the pipe break would have constituted a LOCA. Breaks* at this location are bounded by analyses in the McGuire Updated Final Safety Analysis Report which concludes that they can be handled without core damage.

The pinhole leak in 2NC-30 was a minor pressure boundary leak, it did not impact unit operation, and was a negligible contribution to the NC leakage calculation during unit operation. Page 4 of 5 (04-2017)

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CONTINUATION SHEET (See NUREG-1022, R.3 for instruction and guidance for completing Uiis form htto:l/www.nrc.gov/readinq-rm/doc-collections/nureqs/staff/sr1022/r3/)

, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.

3. LERNUMBER YEAR McGuire Nuclear Station, Unit 2 05000-0370 2017

ADDITIONAL INFORMATION

SEQUENTIAL NUMBER

- 01 REV NO.

- 00 A review of the McGuire corrective action program was conducted to determine whether this was a recurring

. event (i.e., similar event with the same cause code). No reactor coolant system pressure boundary through-body valve leaks due to casting flaws have been documented within the past five years. Therefore this event is not considered a recurring event. The cause of the 2014 LER was a legacy issue with leakage through valve 2Nl-3 (Unit 2 NC Cold Leg Isolation) which created the thermal stratification condition in the 2D NI line.

Since the cause of the NI leak is ongoing, this event's recurring event determination will be provided in the supplement to this LER.. Page 5 of 5