NRC-98-0114, Submits Relief Requests PR-8,R2 & PR-12 for Approval,Based on Data Taken on Upper Thrust Bearings on Four RHR Pumps

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Submits Relief Requests PR-8,R2 & PR-12 for Approval,Based on Data Taken on Upper Thrust Bearings on Four RHR Pumps
ML20236X971
Person / Time
Site: Fermi DTE Energy icon.png
Issue date: 08/04/1998
From: Gipson D
DETROIT EDISON CO.
To:
NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
CON-NRC-98-0114, CON-NRC-98-114 NUDOCS 9808110060
Download: ML20236X971 (10)


Text

  • l Douglas R. Gipson 4

Senior Vice President, Nuclear Generation Fermi 2 6400 North Dixie Huy, Newport, Michi;;an 4h106 Tel: 813M6.5201 Fax: 313.586.4172 Detroit Edison August 4,1998 NRC-98-01:4 ,

i U S Nuclear Regulatory Commission Attention: Document Control Desk Washington D C 20555-0001 L

References 1) Fermi 2 NRC Docket No. 50-341 NRC License No. NPF-43 1

2) NRC Letter to Detroit Edison, Fermi 2 - Safety Evaluation of Pump and Valve Relief Requests i for the Pump and Valve Inservice Testing Program, dated May 2,1996

Subject:

Relief Requests PR-8 and PR-12 Detroit Edison is submitting two Relief Requests for approval. Revision 2 of Pump Relief Request PR-8, Vibration Limits for Residual Heat Removal (RHR) Pumps A, B and D; and new Pump Relief Request PR-12, Vibration Limits for RHR Pump C.

PR-8, Revision 1, was originally approved by the NRC by Reference 2 and was applicable to all four RHR Pumps.

As data was taken on the upper thrust bearings on the four RHR pumps, it was observed that the C pump upper thrust bearing running speed peak and resonance frequency periodically combine to exceed the overall vibration amplitude and exceed the 0.325 in/sec Alen Level. Based upon our evaluation of the data, the most likely cause of the difference in vibration levels for RHR Pump C is the difference in syst em piping (and piping suppon) configuration from the other RHR pumps. Running speed vibration levels have remained essentially unchanged since the original data analysis in 1984. Therefore, vioration data is indicating no degradation. Based on the continued satisfactory performance of the pump, a new Alen Level value of 0.400

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NRC-98-0114 Page 2 in/sec was developed. This new value will prevent the C RHR pump from being unnecessarily placed on an increased testing frequency. PR-12 was written to separate the vibration limits for the C RHR pump from the other three. The only difference m the vibration limits for the C Pump and the other three is that the C Pump upper thrust bearing Alert Level is being increased from 0.325 in/sec to 0.400 in/sec. PR-8 has also been revised to remove the C pump.

The C RHR pump has been on an increased testing frequency of 45 days; however, while waiting for NRC approval of these relief requests, C RHR pump vibration monitoring will be returned to its normal test frequency of 92 days. At this point there is no additional information to be gained by increased testing.

Ifyou should have any questions concerning this request, please contact Mr. Norman K. Peterson, Director Nuclear Licensing at (734) 586-4258 Sincerely,

's & , D. C 'C ~ -

Enclosures cc: B. L. Burgess G. A. Harris A. J. Kugler Regional Administrator, Region 111 Supervisor, Electric Operators, Michigan Public Service Commission l

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- < Enclosure to NRC-98-0114 1

l RELIEF REQUEST PR-8-R2 VIBRATION LIMITS RHR PUMPS A, B, AND D 2 PAGES 1 4

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ISI-IST Program Rev.4 4 Change 3 I PageA-16 of 33 RELIEF REQUEST PR-8-R2 SYSTEM: Residual Heat Removal System PUMPS:

Pump Code Class ISI Drawing E1102C002A 2 6M721-5813-2 El102C002B 2 6M721-5813-1 E1102C002D 2 6M721-5813-1 FUNCTION: The LPCI mode of operation of the RHR System pumps water into the RPV in time to cool the core, in case of low water level in the reactor or high pressure in the containment drywell.

SECTION XI CODE REQUIREMENTS FOR WHICH RELIEF IS REOUESTED:

Vibration amplitude displacement shall be measured quarterly during inservice testing (Table IWP-3100-1 and IWP-3400(a)).

BASIS FOR RELIEF: During preoperational testing, the vibration velocity measurements for the RHR pumps were high (.19 to .27 ips) relative to the vibration velocity ranges given in Relief Request PR-1. Three of the four pumps fell into the alert range.

The preoperational vibration velocity measurements were part of a series of vibration tests which included vibration amplitude. The results of the tests are summarized in Detroit Edison Research Report 84D98-2 which concludes:

"The vibration measurements which were taken during the preoperational test indicate that the pumps are operating in a satisfactory condition."

i Given that the pumps are operating acceptably at the higher vibration velocities, a new set of vibration velocity ranges were developed with the assistance of the vendor as described in Detroit Edison Engineering Research Report 85D15-5, Revision 1.

i Report 85D15-5 recommends the measurement of overall velocity (filter out), overall amplitude (filter out) and running speed amplitude (filter in). All three quantities will be measured at the pump bearing and compared to the ranges given in alternate testing.

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1 ISI-IST Program Rev.4 Change 3 PageA-16 of 33 RELIEF REQUFST PR 8-R2 (Continued)

Testing data over 10 years using this criteria has revealed that the values for overall velocity have remained constant and that the action levels recommended in Report L 85D15-5 are not conservative. Therefore, the vibration limits contained in ASM/ ANSI OMa-1988, Part 6, Table 3 (ranges for test parameters) are being adopted as the vibration limits for overall velocity for the RHR pumps A, B, and D.

l The methodology of ASME/ ANSI Operations and Maintenance Code, Part 6 (OM-6), is to be utilized for RHR pump vibration monitoring. The provisions ofISTB 4.6.1,4.6.4, 5.2, and 6.1 will be met. The RHR pumps are vertical centrifugal pumps. Since all provisions of OM-6 are being met, no additional approval from the NRC is required per i NUREG-1482, paragraph 5.4.

ALTERNATE TESTING: Pump vibration over all velocity will be measured for each l RHR pump accessible bearing in accordance with OM-6, paragraph 4.6.4(a). The j acceptance criteria for RHR Pumps El102C002A, El102C002B, and El102C002D will

be that of OM-6, Table 3a

l Overall Velocity I

Acceptable Range: s 0.325 in/sec Alert Range: 0.326 in/see to 0.700 irlsec Required Action Range: > 0.700 in/sec Overall Amplitude and Runreing Speed Amplitude will continue to be measured with the ranges given in Table IWP-3100-2 applied as

! acceptance criteria.

l Note: Pump Relief request 1% 12 addresses RHR Pump El102C002C l vibration limits l

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Enclosure to NRC-98-0114 l t

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! RELIEF REQUEST PR-12 l

VIBRATION LIMIT RHR PUMP C 4 PAGES 4 1

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ISI-IST Program Rev.4 Change 3 l Page A- 27 of 33 RELIEF REQUEST PR-12 l SYSTEM: Residual Heat Removal PUMP: Residual Heat Removal Pump C PUMP NO.: El102C002C l

CLASS: 2 l

ISI DRAWING: 6M721-5813-2 FUNCTIONS: The LPCI mode of operation of the RHR System pumps water into the RPV in time to cool the core, in case oflow water level in the reactor or high pressure in the containment drywell. 1 l SECTION XI CODE REQUIREMENTS FOR WHICH RELIEF IS REOUESTED:

Vibration amplitude displacement shall be measured during inservice testing (Table IWP-3100-1 l and IWP-3400 (a)). (Velocity readings are taken in lieu of mils displacement readings per Relief

Request PR-8). IST evaluation 96-029 committed to taking the upper motor bearing vibration l since it carries the pump thrust. This was in response to an NRC open item during NRC Inspection 95002. This IST evaluation used OM-6 absolute limits (0.325 indseci- ALERT &

- 0.7 inisec. - REQUIRED ACTION) as the acceptance criteria.

1 BASIS FOR RELIEF: Pursuant to 10 CFR 50.55a(a)(3)(i) Detroit Edison is requesting relief i from ASME Section XI requirements to run the pump on an increased periodicity due to vibration level exceeding the OM-6 Alert limit. This is based on analysis of the vibration data indicating that no pump degradation is taking place. Detroit Edison is proposing to use alternative vibration Alert Limits based on historical vibration data and analysis of that data. This provides an ,

I alternative method that still meets the intended hmetion of monitoring the pump for degradation over time while keeping the required action level unchanged.

Since the initial IST data was taken at the upper motor bearing on the RHR C pump, the overall vibration limits have periodically exceeded the 0.325 inisec. ALERT limit. Vibration analysis has shown that the RHR C pump has the highest running speed peak (.2 .25 inisec.) of the 4 RHR pumps but this is well below any alen limit. The vibration data also indicates a resonant frequency between 9 - 14 Hz. Both these items were identified in the initial vibration Engineering Research Report 85D15-5, Rev 1 dated 1984. What was not identified when IST evaluation 96-029 and the Engineering Research Report was written was that the resonance frequency is cyclic, and/or changes from run to run, depending on small changes in flow. The combination of the running speed peak and the resonance frequency periodically make the overall vibration amplitude exceed the ALERT limit of 0.325 inisec. The running speed peak is the best vibration indicator i l

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ISI-IST Program Rev.4 Change 3 Page A- 27 of 33 for actual pump condition and this peak has remained unchanged. No bearing peaks have been identified in the vibration spectrum and all other indicators
flow, oil analysis and pressures, indicate that the RHR C pump is operating in a satisfactory condition.

! ASME/ ANSI Operation and Maintenance Code Ohia-1988, Part 6 footnote to Section 4.3, states l " Vibration measurements of pumps may be foundation, driver, and piping dependent. Therefore, ifinitial readings are high and have no obvious relationship to the pump, then vibration measurements should be taken at the driver, at the foundation, and on the piping and analyzed to ensure that the reference vibration measurements are representative of the pump and that the

measured vibration levels will not prevent the pump from fulfilling its ftmetion." This is exactly the case on the RHR C pump. The data has been analyzed in IST evaluation 97-042 and was found to be a resonant frequency between 9 - 14 HZ. This resonance frequency either alone or in combination with the mnning speed peak periodically make the overall vibration amplitude exceed the 0.325 inisec. ALERT LIMIT. The running speed peak has remained very steady (see trend
1) while the resonaut peak varies greatly from run to run (see trend 2). Each structure has it's

, own resonance frequency based on the mass and stiffness of the system. Minor changes in either l of these two components will change the resonance frequency. Differences in piping and hanger design between the four RHR pumps is the most likely cause for the difference in the resonance

frequency and therefore the vibration levels. The reason that the vibration levels change from mn to run is that for a resonance frequency to " ring" it must be excited by some forcing function. In RHR C this forcing function is flow noise, which causes a broad band forcing frequency, that l varies slightly during each run.

The required monitoring range is from % mnning speed to 1000 Hz. A filter was used to filter out the resonance below 14 Hz (<l/2 Running Speed). This helped, but periodically the filtered overall vibration still exceeds 0.325 ips. The IST data taken 2/21/98 was .3587 in./sec. even with the filter. Vibration analysis of all the vibration points did not show any signs of a pump or motor  !

problem. The only changes noted were an increase in the resonance peak.

l Given that the RHR C Pump is operating acceptably at vibration velocities at or slightly above the IST Program Alert Level with no change in running speed peak from the initial data taken in 1984, a new Alert vibration velocity level has been developed. This new velocity vibration alert level will allow for early detection of pump degradation prior to component failure while the Required Action level (0.7 in./sec.) will remain unchanged.

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g. ISI-IST Program a-Rev.4 Change 3 Page A- 27 of 33 ALTERNATE TESTING: For the vibration points on the upper motor bearing, (0VVEAl, OVVEA2 & OVVEA3), revise the ALERT Limit for the overall vibration limits to 0.4 inisec.

This exceeds the OM-6 limit of 0.325 but is well below the alternate (2.5

  • Vr) limit. Where Vr is the baseline vibration reference values. The Vr values for OVVEA1,0VVEA2 & OVVEA3 are 0.25, 0.22 & 0.29 in/sec. respectively. The required action level will remain at 0.7 inisec.

RHR C (El102C002C)

Vibration Required Alert Range Acceptable Parameter Action Range - Range Overall Velocity > 0.700 indsec. > 0.400 indsec. s 0.400 indsec.

(OVVEA1) to HorizontalInline 0.700 inisec.

Overall Velocity > 0.700 inisec. > 0.400 inisec. s 0.400 inisec.

(OVVEA2) to Horizontal 90 0.700 indsec.

Overall Velocity > 0.700 inisec. > 0.400 inisec. s 0.400 inisec.

(OVVEA3) to Vertical 0.700 indsec.

Overall Velocity > 0.700 in/sec. > 0.325 inisec. s 0.325 in/sec.

(OVVEC1) to

, HorizontalInline 0.700 inisec.

Overall Velocity > 0.700 indsec. > 0.325 inisec. s 0.325 inisec.

(OVVEC2) to Horizontal 90 0.700 in/sec.

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