05000318/LER-2013-005, Regarding Manufacturing Defect Results in Shutdown Due to Dropped Control Assembly

Regarding Manufacturing Defect Results in Shutdown Due to Dropped Control Assembly

ML13302C069
Person / Time
Site:	Calvert Cliffs
Issue date:	10/25/2013
From:	Flaherty M Calvert Cliffs, Constellation Energy Group, EDF Group
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
LER 13-005-00
Download: ML13302C069 (7)

LER-2013-005, Regarding Manufacturing Defect Results in Shutdown Due to Dropped Control Assembly

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
3182013005R00 - NRC Website

text

Calvert Cliffs Nuclear Power Plant CENG a joint venture of Constellation ng"'jWeDFj CALVERT CLIFFS NUCLEAR POWER PLANT 1650 Calvert Cliffs Parkway Lusby, Maryland 20657 October 25, 2013 U.S. Nuclear Regulatory Commission Washington, DC 20555 ATTENTION:

SUBJECT:

Document Control Desk Calvert Cliffs Nuclear Power Plant Unit No. 2; Docket No. 50-318; License No. DPR 69 Licensee Event Report 2013-005, Revision 00 Manufacturing Defect Results in Shutdown Due to Dropped Control Element Assemblv The attached report is being sent to you as required by 10 CFR 50.73.

There are no regulatory commitments contained in this correspondence.

Should you have questions regarding this report, please contact Mr. Douglas E. Lauver at (410) 495-5219.

Very truly yours, Mark D. Flaherty Plant General Manager MDF/KLG/bjd

Attachment:

As stated cc:

N. S. Morgan, NRC W. M. Dean, NRC Resident Inspector, NRC S. Gray, DNR

NRC FORM 366 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB: NO. 3150-0104 EXPIRES: 10/31/2013 (10-2010)

Estimated burden per response to comply with this mandatory collection request: 80 hours9.259259e-4 days <br />0.0222 hours <br />1.322751e-4 weeks <br />3.044e-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 Section (T-5 F53), U.S. Nuclear LICENSEE EVENT REPORT (LER)

Regulatory Commission, Washington, DC 20555-0001, or by internet e-mail to infocollects.resource@nrc.gov, and to the Desk Officer, Office of Information and Regulatory Affairs, NEOB-10202, (3150-0104), Office of (See reverse for required number of Management and Budget, Washington, DC 20503. If a means used to impose an information collection does not display a currently 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 information collection.

l3. PAGE Calvert Cliffs Nuclear Power Plant, Unit 2 05000 318J 1 OF 06

4. TITLE Manufacturing Defect Results in Shutdown Due to DrooDed Control Element Assemblv

5. EVENT DATE

6. LER NUMBER _

7. REPORT DATE

8. OTHER FACILITIES INVOLVED MOTIA YERiiDOCKET NUMBER MONTH DAY YEAR YEAR SEQUENTIAL REV MONTH DAY YEAR 05000

__________________I N U M BER NO.0 5

0 I

I I

FACILITY NAME DOCKET NUMBER 09 05 2013 2013 - 005 -

00 10 25 2013 05000

9. OPERATING MODE

11. THIS REPORT IS SUBMITTED PURSUANT TO THE REQUIREMENTS OF 10 CFR§: (Check all that apply) 0l 20.2201(b) 0l 20.2203(a)(3)(i) 0l 50.73(a)(2)(i)(C)

[I 50.73(a)(2)(vii)

[ E1 20.2201(d)

[E 20.2203(a)(3)(ii)

[I 50.73(a)(2)(ii)(A)

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

E0 20.2203(a)(1)

El 20.2203(a)(4)

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

[I 50.73(a)(2)(viii)(B) 0l 20.2203(a)(2)(i) 0l 50.36(c)(1)(i)(A)

El 50.73(a)(2)(iii)

[I 50.73(a)(2)(ix)(A)

10. POWER LEVEL 0

20.2203(a)(2)(ii)

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

El 50.73(a)(2)(iv)(A)

[I 50.73(a)(2)(x)

[I 20.2203(a)(2)(iii)

El 50.36(c)(2)

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

[1 73.71(a)(4)

[I 20.2203(a)(2)(iv)

[I 50.46(a)(3)(ii) 0l 50.73(a)(2)(v)(B)

[1 73.71(a)(5) 99.5 0l 20.2203(a)(2)(v) 0 50.73(a)(2)(i)(A) 0l 50.73(a)(2)(v)(C) 0l OTHER [I 20.2203(a)(2)(vi) 0l 50.73(a)(2)(i)(B) 0l 50.73(a)(2)(v)(D)

Specify in Abstract below or in NRC Form 366A

12. LICENSEE CONTACT FOR THIS LER FACILITY NAME ITELEPHONE NUMBER (include Area Code)

Kenneth L. Greene, Licensing Engineer 410-495-4385CAUSE SYSTEM COMPONENT MANU-REPORTABLE

CAUSE

COMPONENT MANU-REPORTABLE FACTURER TO EPIX FACTURER TO EPIX B

CL W120 Y

S

14. SUPPLEMENTAL REPORT EXPECTED

15. EXPECTED MONTH DAY YEAR SUBMISSION [I YES (If yes, complete 15. EXPECTED SUBMISSION DATE) 0 NO DATE ABSTRACT (Limit to 1400 spaces, i.e., approximately 15 single-spaced typewritten lines)

On September 5, 2013, Unit 2's Control Element Assembly (CEA) #27 dropped to the fully inserted position while the CEA was being operated as part of a surveillance test. Operators entered applicable Technical Specifications for the dropped CEA. When operators were unable to restore the CEA to its proper alignment within the required Completion Time, operators commenced a reactor shutdown in accordance with Technical Specification Required Action 3.1.4.F.1. The unit was shutdown at 1735 on September 5, 2013. Troubleshooting identified Control Element Drive Mechanism (CEDM) #27 lift coil lead wire was grounded internally to the coil housing due to a chafed wire. The root cause for the dropped CEA was determined to be a manufacturing defect that resulted in circumferential displacement of the coil within the coil housing and the misalignment of the lift coil lead wire within the coil housing nipple. Corrective actions included replacement of the CEDM coil stack with one that includes a change in design featuring a protective heat shrink wrap at the point where the lead wire penetrates the coil housing nipple. All other Unit 2 CEDMs were meggered with satisfactory results. A detailed plan to replace the remaining Unit 2 CEDM coil stacks is being developed.

Replacement of the Unit 2 coil stacks is expected to begin during the 2015 refueling outage.

NRC FORM 366 (10-2013)U.S. NUCLEAR REGULATORY COMMISSION (10-2010)

LICENSEE EVENT REPORT (LER)

CONTINUATION SHEET

1. FACILITY NAME

2. DOCKET

6. LER NUMBER

3. PAGE SEQUENTIAL I REV YEAR NUMBER NO.

Calvert Cliffs Nuclear Power Plant, Unit 2 05000 318 2013

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of 06

1.

DESCRIPTION OF EVENT

A.

PRE-EVENT PLANT CONDITIONS:

On September 5, 2013 Unit 2 was operating at 99.5 percent power. There were no inoperable systems, structures, or components that would have impacted this event.

B.

EVENT:

At 1016 on September 5, 2013, Unit 2 Control Element Assembly (CEA) #27 dropped to the bottom of the reactor core due to its 240 Volt circuit breaker tripping open while the CEA was being operated during quarterly CEA surveillance testing. Following the dropped CEA, reactor power stabilized at 91 percent. Operators entered Technical Specification 3.1.4, Action B for CEA #27 being misaligned from its group by greater than 15 inches. When CEA #27 could not be realigned within the required Completion Time, operators entered Technical Specification 3.1.4, Action C, and reduced power to 70 percent. When CEA #27 was not able to be realigned within the required Completion Time of Action C operators entered Technical Specification 3.1.4, Action F and commenced a required unit shutdown to Mode 3. Operators commenced the shutdown of Unit 2 at 1404 on September 5, 2013. Unit 2 entered Mode 3, Hot Standby, at 1735 on September 5, 2013.

Initial investigation into the cause of CEA #27 dropped rod identified its Control Element Drive Mechanism (CEDM) lift coil wire was grounded internally to the coil housing due to a chafed wire. During the resulting forced outage, CEDM #27 coil stack was replaced. Unit 2's forced outage ended at 0808 on September 10, 2013 and the unit returned to full power at 2130 on September 10, 2013.

C.

INOPERABLE STRUCTURES, COMPONENTS, OR SYSTEMS THAT CONTRIBUTED TO THE EVENT:

The ground on CEDM #27 lift coil resulted in CEA #27 dropping to the bottom of the reactor core. When this issue could not be corrected within the Required Action Completion Times for Technical Specification Actions 3.1.4.B and 3.1.4.C, operators began a unit shutdown of Unit 2 as required by Technical Specification Required Action 3.1.4.F.1.

D.

DATES AND APPROXIMATE TIMES OF MAJOR OCCURRENCES

September 5, 2013 1016 - CEA #27 dropped to its fully inserted position while CEA #27 was undergoing rod motion during a quarterly surveillance testing. Operators implemented Abnormal Operating Procedure-I B, CEA Malfunction. Reactor power stabilized at 91 percent.

1207 - Commenced reducing reactor power to 70 percent in accordance with Technical Specification Required Action 3.1.4.C.1.U.S. NUCLEAR REGULATORY COMMISSION (10-2010)

LICENSEE EVENT REPORT (LER)

CONTINUATION SHEET

1. FACILITY NAME

2. DOCKET

6. LER NUMBER

3. PAGE SEQUENTIAL I

REV YEAR NUMBER NO.

Calvert Cliffs Nuclear Power Plant, Unit 2 05000 318 2013

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of 06 1404 - Commenced Unit 2 shutdown in accordance with Technical Specification Required Action 3.1.4.F. 1.

1735 - Unit was placed into Mode 3. Exited applicable Technical Specification Actions for CEA #27 due to exiting from modes of applicability.

September 6, 2013 0752 - Entered Mode 5, Cold Shutdown, to facilitate repairs to CEDM #27.

September 8, 2013 1730 - Following replacement of CEDM #27 coil stack, commenced unit heatup.

September 10, 2013 0808 - Paralleled unit to the grid.

2130 - Unit restored to full power.

E.

OTHER SYSTEMS OR SECONDARY FUNCTIONS AFFECTED

No other systems or secondary functions were affected by this event.

F.

METHOD OF DISCOVERY

The event was self-revealing in that the ground on CEDM #27 occurred while operators were conducting CEA surveillance testing.

G.

MAJOR OPERATOR ACTION:

After CEA #27 dropped, when it was determined that the CEA could not be realigned within the Completion Times required by the Technical Specifications, operators placed the unit in Mode 3.

Operators subsequently placed the unit in Mode 5 to facilitate troubleshooting and repairs.

Following replacement of CEDM #27 coil stack, operators began unit startup and returned the unit to full power on September 10, 2013.

H.

SAFETY SYSTEM RESPONSES:

There were no demands for safety system actuations during this event.U.S. NUCLEAR REGULATORY COMMISSION (10-2010)

LICENSEE EVENT REPORT (LER)

CONTINUATION SHEET

1. FACILITY NAME

2. DOCKET

6. LER NUMBER

3. PAGE SEQUENTIAL I

REV YEAR NUMBER NO.

Calvert Cliffs Nuclear Power Plant, Unit 2 05000 318 2013

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of 06 I1.

CAUSE OF EVENT

This event is documented in the site's Corrective Action Program under CR-2013-007020. The root cause for the dropped CEA was determined to be a manufacturing defect that resulted in circumferential displacement of the coil within the coil housing and the misalignment of the lift coil lead wire within the coil housing nipple. A contributing cause was a design flaw that left the coil stack lead wires susceptible to grounding within the coil housing due to; a) rubbing/chafing of the wire insulation due to service stress, and b) hardening of the coil lead wire insulation over time due to thermal and radiation effects. The root cause in combination with the contributing cause allowed the lift coil lead wire insulation to degrade which resulted over time in the lead wire contacting the coil housing nipple thus causing an arc to ground at the contact point.

Ill.

ANALYSIS OF EVENT

This event is reportable 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;"

Operators completed the Technical Specification required shutdown on September 5, 2013 when efforts to realign the CEA to its proper position were not able to be completed within the required Technical Specification Completion Time. This means the event is reportable under 10 CFR 50.73(a)(2)(i)(A).

This event did not result in any actual nuclear safety consequences. While the failure of CEDM #27 lift coil prevented the CEA from being positioned, it did not prevent the safety function of the CEDM (when a reactor trip signal is initiated the CEDM grippers disengage, allowing the CEA to fall to the bottom of the reactor core due to gravitational forces) from occurring as designed. Additionally the dropped CEA event is analyzed in Section 14.11 of the Calvert Cliffs' Updated Final Safety Analysis Report. The most limiting drop event is an uncontrolled CEA insertion at hot full power. This current event is therefore bounded by the Section 14.11 safety analysis.

The risk associated with the CEA drop event is considered to have a relatively low impact.

While the probabilistic risk assessment does not model the failure likelihood of a single dropped CEA, the failure could be a precursor to a plant trip. A plant trip has a Conditional Core Damage Probability of less than 1 E-06 and a Conditional Large Release Probability of less than 1 E-07. A dropped CEA is considered to be within the bounds of a plant trip. As a result, the risk associated with this event is considered small and is not significant from a probabilistic risk assessment perspective.

The event has limited impact on the Nuclear Regulatory Commission's Reactor Oversight Process Performance Indicators for Unit 2. The performance indicator for Unplanned Power Change per 7000 Critical hours rose to 0.9 which remains within the green band.U.S. NUCLEAR REGULATORY COMMISSION (10-2010)

LICENSEE EVENT REPORT (LER)

CONTINUATION SHEET

1. FACILITY NAME

2. DOCKET

6. LER NUMBER

3. PAGE SEQUENTIAL I REV YEAR NUMBER NO.

Calvert Cliffs Nuclear Power Plant, Unit 2 05000 318 2013

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of 06 IV.

CORRECTIVE ACTIONS

A.

ACTION TO RETURN AFFECTED SYSTEMS TO PRE-EVENT NORMAL STATUS:

1.

Replaced CEDM #27 coil stack. The new coil stack includes a change in design that installed protective heat shrink wrap along the length of the lead wire where it penetrates the coil housing nipple.

2.

Conducted insulation resistance testing (meggering) on the remaining 56 Unit 2 CEDM coil stacks during the forced outage while the unit was at 300 degrees Fahrenheit and then again with unit at normal operating temperature. All meggering results were satisfactory.

B.

ACTION TAKEN OR PLANNED TO PREVENT RECURRENCE:

1.

Develop strategy and a detailed plan to replace the remaining 56 Unit 2 coil stacks. Replacement of the coil stacks is expected to begin in the 2015 refueling outage.

2.

Develop procurement requirements for new purchases of CEA coil stacks. The requirements will require installation of the wire sleeve and verification that the lead wires are centered in the coil housing nipple by the vendor.

3.

Add a note in the Westinghouse Vendor Technical Manual that will instruct technicians to ensure coil stack lead wires are centered in the coil housing nipple when reassembling a coil into its coil housing on site.

V. ADDITIONAL INFORMATION

A.

FAILED COMPONENTS:

The CEDM lift coil was supplied by Westinghouse Electric Corporation, model STS80.

B.

PREVIOUS OCCURRENCES

LER 2012-003 On August 12, 2012, Unit l's CEA #9 dropped to the fully inserted position.

The CEA dropped due to failure of its CEDM upper gripper coil. The upper gripper coil failed due to an internal short circuit caused by overheating due to degradation in the CEDM cooling system. This event is not similar to the Unit 2 CEA #27 failure because it involved a short circuit internal to the coil and did not involve a ground of the coil lead wire. Additionally, all Unit 1 CEDM coil stacks were replaced in 2006 with the design change that installed protective heat shrink wrap along the length of where the coil stack lead wires penetrate the coil housing nipple.

Condition Report IRE-021-712 - During the Unit 2 2007 refueling outage, technicians, while reconnecting CEDMs, identified that CEDM #63 lift coil indicated a grounded condition. TheU.S. NUCLEAR REGULATORY COMMISSION (10-2010)

LICENSEE EVENT REPORT (LER)

CONTINUATION SHEET

1. FACILITY NAME

2. DOCKET

6. LER NUMBER

3. PAGE SEQUENTIAL I REV YEAR NUMBER NO.

Calvert Cliffs Nuclear Power Plant, Unit 2 05000 318 2013

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of 06 ground occurred where the leads from the lift coil protruded from the coil itself. The most likely cause of the ground was the physical repositioning of the coil to the new reactor vessel head which caused the insulation to be cut and resulted in the grounded condition.

C.

THE ENERGY INDUSTRY IDENTIFICATION SYSTEM (EIIS) COMPONENT FUNCTION IDENTIFIER AND SYSTEM NAME OF EACH COMPONENT OR SYSTEM REFERRED TO IN THIS LER:

COMPONENT IEEE 803 IEEE 805 FUNCTION ID SYSTEM ID CEDM Lift Coil CL AA D.

SPECIAL COMMENTS:

None.