05000457/LER-2010-003, Regarding Reactor Trip Caused by Phase to Ground Fault of a Failed Crossover Damper/Deionizer Assembly Due to an Inadequate Inspection Acceptance Criteria and Preventive Maintenance Inspection Frequency

Regarding Reactor Trip Caused by Phase to Ground Fault of a Failed Crossover Damper/Deionizer Assembly Due to an Inadequate Inspection Acceptance Criteria and Preventive Maintenance Inspection Frequency

ML102880320
Person / Time
Site:	Braidwood
Issue date:	10/15/2010
From:	Shahkarami A Exelon Generation Co, Exelon Nuclear
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
BW100109 LER 10-003-00
Download: ML102880320 (5)

LER-2010-003, Regarding Reactor Trip Caused by Phase to Ground Fault of a Failed Crossover Damper/Deionizer Assembly Due to an Inadequate Inspection Acceptance Criteria and Preventive Maintenance Inspection Frequency

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
4572010003R00 - NRC Website

text

10 CFR 50.73 October 15, 2010 BW100109 U. S. Nuclear Regulatory Commission ATIN: Document Control Desk Washington, DC 20555-0001 Braidwood Station, Unit 2 Facility Operating License No. NPF-77 NRC Docket No. STN 50-457

Subject:

Licensee Event Report 2010-003 Unit 2 Reactor Trip Caused by Phase to Ground Fault of a Failed Crossover Damper/Deionizer Assembly Due to an Inadequate Inspection Acceptance Criteria and Preventive Maintenance Inspection Frequency The enclosed Licensee Event Report (LER) is being submitted in accordance with 10 CFR 50.73, "Licensee event report system", paragraph (a)(2)(iv)(A), as an event that resulted in a valid actuation of the reactor protection system and auxiliary feedwater system. On August 16, 2010, Braidwood Station Unit 2 received an actuation of the reactor protection system (reactor trip) and the auxiliary feedwater system due to a phase to ground fault of a failed crossover damperl deionizer assembly. 10 CFR 50.73(a) requires an LER to be submitted within 60 days following discovery of the event. Therefore, this report is being submitted by October 15, 2010.

There are no regulatory commitments contained in this letter. Should you have any questions concerning this submittal, please contact Mr. Ronald Gaston, Regulatory Assurance Manager, at (815) 417-2800.

Respectfully, Amir Shahkarami Site Vice President Braidwood Station

Enclosure:

LER 2010-003-00 cc: NRR Project Manager - Braidwood Station Illinois Emergency Management Agency - Division of Nuclear Safety US NRC Regional Administrator, Region III US NRC Senior Resident Inspector (Braidwood Station)

NRC FORM 366 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB: NO. 3150-0104 EXPIRES: 08/31/2010 (9-2007)

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

13. PAGE Braidwood Station, Unit 2 05000457 1 of 4

4. TITLE Reactor Trip Caused by Phase to Ground Fault of a Failed Crossover Damper/Deionizer Assembly Due to an Inadequate Inspection Acceptance Criteria and Preventive Maintenance Inspection Frequency

5. EVENT DATE

6. LER NUMBER

7. REPORT DATE

8. OTHER FACILITIES INVOLVED YEAR ISEQUENTIALIREV FACILITY NAME DOCKET NUMBER MONTH DAY YEAR NUMBER NO.

MONTH DAY YEAR N/A N/A FACILITY NAME DOCKET NUMBER 08 16 2010 2010. 003.

00 10 15 2010 N/A N/A

9. OPERATING MODE

11. THIS REPORT IS SUBMITTED PURSUANT TO THE REQUIREMENTS OF 10 CFR §: (Check al/ that apply) 1 o 20.2201(b) o 20.2203(a)(3)(i) o 50.73(a)(2)(i)(C) o 50.73(a)(2)(vii) o 20.2201(d) o 20.2203(a)(3)(ii) o 50.73(a)(2)(ii)(A) o 50.73(a)(2)(viii)(A) o 20.2203(a)(1) o 20.2203(a)(4) o 50.73(a)(2)(ii)(B) o 50.73(a)(2)(viii)(B) o 20.2203(a)(2)(i) o 50.36(c)(1 )(i)(A) o 50.73(a)(2)(iii) o 50.73(a)(2)(ix)(A)

10. POWER LEVEL o 20.2203(a)(2)(ii) o 50.36(c)(1 )(ii)(A)

[gJ 50.73(a)(2)(iv)(A) o 50.73(a)(2)(x) o 20.2203(a)(2)(iii) o 50.36(c)(2) o 50.73(a)(2)(v)(A) o 73.71(a)(4) 100%

o 20.2203(a)(2)(iv) o 50.46(a)(3)(ii) o 50.73(a)(2)(v)(B) o 73.71 (a)(5) o 20.2203(a)(2)(v) o 50.73(a)(2)(i)(A) o 50.73(a)(2)(v)(C) o OTHER o 20.2203(a)(2)(vi) o 50.73(a)(2)(i)(B) o 50.73(a)(2)(v)(D)

Specify in Abstract below or in the dampers are subjected to. The rate of normal degradation for the crossover damper assemblies is accelerated when compared to the similar model bypass damper assemblies. The analysis noted that the inspection acceptance criteria for the damper assemblies was not detailed enough to account for this turbulent condition on the sub-components of the assembly. Therefore, the root cause for this event was determined to be an inadequate damper assembly inspection acceptance criteria and preventive maintenance frequency that did not account for the more turbulent flow characteristics that the crossover damper assemblies are subjected to.

A contributing cause for this event is that historic changes in operating conditions (Le., two bus duct fan operation) have also increased the rate of degradation for the crossover damper assemblies. The station had not adequately evaluated the air flow characteristics for this change to understand how these factors affected the degradation.

D.

Safety Consequences

There were no actual or potential safety consequences impacting plant or public safety as a result of this event.

Flow control valve 2AF005H to the 20 steam generator failed open, and isolation valve to 2AF013H was throttled to control flow.

All other safety related systems, structures, and components operated normally during this event.

This event did not result in a safety system functional failure.

E.

Corrective Actions

The corrective actions to prevent recurrence include:

Revise the preventive maintenance schedule to ensure the crossover damper assemblies are inspected and/or replaced prior to failure, with the periodicity to be set through engineering analysis. The engineering analysis will determine the air flow characteristics for bus duct fan configurations and the impact of these configurations on internal isolated phase bus components and degradation rates.

Revise the maintenance procedure for isophase bus duct preventive maintenance to include inspection criteria for the crossover damper assembly, including the requirement to remove the assemblies for inspection (to preclude over-reliance on robotic inspections), a detailed inspection of sub-components, dimensional tolerances for the sub-components (where possible), and a hold point for As Found inspection.

Other corrective actions include:

Replacement of Unit 1 and Unit 2 crossover damper assemblies with a more robust design.

Identify systems where the station has changed operating conditions that could increase degradation of internal components and determine if the evaluations were performed adequately (addressed the degradation rate of the components).

Complete a case study for this event with all Engineering personnel, to focus on the organizational weaknesses associated with the oversight and monitoring for the isophase components.

Previous Occurrences

There have been no previous, similar events identified at the Braidwood Station in the past three years.

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Component Failure Data

2010 003 00 Manufacturer H. K. Porter Company, Inc.Nomenclature Crossover Damper/Deionizer Grid Assembly Model L-98021X11 Rev. A with 52412X5 deionizer grid Mfg. Part Number L-98021X11 Rev. A with 52412X5 deionizer grid PRINTED ON RECYCLED PAPER