05000461/LER-2011-002, Regarding Main Control Room HVAC Return Fan B High Vibrations

Regarding Main Control Room HVAC Return Fan B High Vibrations

ML11216A131
Person / Time
Site:	Clinton  (NPF-062)
Issue date:	07/22/2011
From:	Noll W Exelon Nuclear
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
U-604026 LER 11-002-00
Download: ML11216A131 (5)

LER-2011-002, Regarding Main Control Room HVAC Return Fan B High Vibrations

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
4612011002R00 - NRC Website

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Nuclear Clinton Power Station 8401 Power Road Clinton, IL 61727-9351 U-604026 10 CFR 50.73 July 22, 2011 SRRS 5A.108 U. S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, D. C. 20555-0001 Clinton Power Station, Unit 1 Facility Operating License No. NPF-62 NRC Docket No. 50-461

Subject:

Licensee Event Report 2011-002-00 Enclosed is Licensee Event Report (LER) No. 2011-002-00: Main Control Room HVAC Fan High Vibrations. This report is being submitted in accordance with the requirements of 10 CFR 50.73.

There are no regulatory commitments contained in this letter.

Should you have any questions concerning this report, please contact A. Khanifar, at (217)-

937-3800.

Respectfully, William G. Noll Site Vice President Clinton Power Station EET/blf

Enclosure:

Licensee Event Report 2011-002-00 cc:

Regional Administrator - NRC Region III NRC Senior Resident Inspector - Clinton Power Station Office of Nuclear Facility Safety - IEMA Division of Nuclear Safety

4IRC FORM 366 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB: NO. 3150-0104 EXPIRES: 10/31/2013 110-2010)

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

3. PAGE Clinton Power Station, Unit 1 05000461 1 OF 4

,. TITLE Main Control Room HVAC Return Fan B High Vibrations

5. EVENT DATE

6. LER NUMBER

7. REPORT DATE

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

MONTH DAY YEAR N/A N/A FACILITY NAME DOCKET NUMBER 05 23 2011 2011 002 00 07 22 2011 N/A N/A

3. OPERATING MODE

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

(3 20.2201(b)

[l 20.2203(a)(3)(i)

[I 50.73(a)(2)(i)(C)

[l 50.73(a)(2)(vii) 1 [j 20.2201(d)

El 20.2203(a)(3)(ii) 0l 50.73(a)(2)(ii)(A)

El 50.73(a)(2)(viii)(A)

El 20.2203(a)(1)

El 20.2203(a)(4)

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

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

__ 20.2203(a)(2)(i)

[I 50.36(c)(1)(i)(A)

El 50.73(a)(2)(iii)

El 50.73(a)(2)(ix)(A)

10. POWER LEVEL El 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)

[E 20.2203(a)(2)(iii)

El 50.36(c)(2)

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

El 73.71 (a)(4) 97.0 El 20.2203(a)(2)(iv)

[I 50.46(a)(3)(ii)

El 50.73(a)(2)(v)(B) 0l 73.71 (a)(5)

El 20.2203(a)(2)(v)

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

El 50.73(a)(2)(v)(C)

[E OTHER El 20.2203(a)(2)(vi) 0 50.73(a)(2)(i)(B)

El 50.73(a)(2)(v)(D)

Specify in Abstract below or in During the time from 5/23/11 to 6/10/11 the VC A system was always operable. Therefore at all times during this event, the MCR was supported by an operable train of VC, and thus no loss of safety function occurred.

C.

CAUSE OF EVENT

An equipment apparent cause analysis was conducted under Issue Report (IR) 1225739. The equipment apparent cause determined that the hub crack was the result of end-of-life fatigue, caused by low stress, high cycle loading.

OVC04CB had approximately 115,000 hours0 days <br />0 hours <br />0 weeks <br />0 months <br /> of service before the hub crack propagated enough to cause a step change in vibration levels, which stabilized as the crack reached the edge of the hub. The as-found data described a crack from the outside of the fan hub to one fan mounting hole (approximately 4 inches long). The crack penetrated the entire thickness of the hub. The crack length and extent were confirmed after fan removal.

D.

SAFETY CONSEQUENCES

This event is reportable under 10 CFR 50.73(a)(2)(i)(B) as an operation or condition which was prohibited by the plant's Technical Specifications due to exceeding Limiting Condition of Operation (LCO) 3.7.3 of Technical Specification (TS) 3.7.3, Control Room Ventilation System, Required Action A.1, to restore an inoperable Control Room Ventilation subsystem to an operable status within 7 days.

As stated previously, the VC B fan hub cracking was identified and confirmed on 6/7/11 and the VC B fan was replaced and restored to an operable status on 6/10/11. Existing analysis is not sufficient to provide the high degree of confidence necessary to support past operability from the time of the increase in vibrations on 5/23/11, until the fan was replaced, or approximately 18 days.

There were no actual safety consequences impacting plant or public safety as a result of this event. The opposite division train was operable during the time of inoperability; therefore there was no loss of safety function.

E.

CORRECTIVE ACTIONS

The VC B return air fan was replaced.

The VC A return air fan will be replaced in 2012 based on a lower number of operating hours compared to VC B.

The applicable Performance Centered Maintenance (PCM) templates were reviewed for similar high duty cycle fans (extent of condition) and the replacement strategy was changed from performance monitoring to time directed replacement.

F.

PREVIOUS OCCURRENCES

A review of CPS Licensee Event Reports (LERs) for the last three years did not identify any LERs associated with ventilation fan failures; however, one similar previous event was identified.

On 10/26/06, the MCR Supply Fan for VC B, OVC03CB, failed suddenly and broke apart. A root cause investigation noted that the fan failure was due to cracking of the material in the hub. The failure analysis determined that the cracks propagated by fatigue until a hub section failed in a relatively brittle manner due to mechanical overloading.

The difference between this event and the OVC04CB event on 5/23/11, is the physical difference between the hub diameters, 54 inches for the supply fan compared to 48 inches for the return fan. The supply fan runs closer to the stall region on the fan performance curve and the failure was caused by unbalanced loading on the fan (caused by the design of the system). The supply fan was determined to be too large for the application such that normal system transients put the fan in the stall region. There were multiple cracks found in the supply fan hub, whereas the VC B return fan had one crack that had no further growth possible and no indications of additional fatigue cracks. Finally, the return fan air flow has a straight path to the suction and the VC B supply fan operates above the stall region.

G. COMPONENT FAILURE DATA

Component Description: 48 inch vane-axial fan, 120 horsepower (HP)

Manufacturer Nomenclature Model Buffalo Forge N/A W120 5 ARR No. 4 Mfg. Part Number N/A