View source for NG-75-2001, AO 50-261/75-16:on 751028,svc Water Booster Pump B Failed to Start.Caused by Actuation of Pump Suction Pressure Switches Provided to Protect Pumps from Low Npsh.Containment Recirculation Fans Stopped to Prevent Overheating Motors

{{Adams
| number = ML20086F545
| issue date = 11/11/1975
| title = AO 50-261/75-16:on 751028,svc Water Booster Pump B Failed to Start.Caused by Actuation of Pump Suction Pressure Switches Provided to Protect Pumps from Low Npsh.Containment Recirculation Fans Stopped to Prevent Overheating Motors
| author name = Utley E
| author affiliation = CAROLINA POWER &amp; LIGHT CO.
| addressee name = Moseley N
| addressee affiliation = NRC OFFICE OF INSPECTION &amp; ENFORCEMENT (IE REGION II)
| docket = 05000261
| license number = 
| contact person = 
| document report number = AO-50-261-75-16, NG-75-2001, NUDOCS 8401030393
| package number = ML20086F548
| document type = ABNORMAL OCCURRENCE REPORTS (SEE ALSO LER &amp; RO), TEXT-SAFETY REPORT
| page count = 4
}}

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November 11, 1575 File: NG-3513 (R)                                           -
Serial: NG-75--2001 Ty,s g'                   .'j; im                .'              '
[d Mr. Norman C. Moseley, Director                                                        /;                                     >
Directorate of Regulatory Operations                                                   j        , . ,. , , n* '':q%
U. S. Nuclear Regulatory Commission                                                             '"
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Region II, Suite 818 230 Peachtree Street, P. W.
Atlanta, Georgia       30303 50-o Dear Mr. Mosd cy:
a rn2 corr H. B. ROBINS 0:: U;IT NO. 2 LICENSE NO. DPR-23                                       ,
TWO SERVICE UA'IER BOOSTER PDIPS INOPERAULE W-          -
In accordance with 6.6.2.a of the Tcchnical Specifications for H. B. Robinson Unit o. 2, the attached Abnormal Occurrence Report is submitted for your information. This report fulfills the requirem nt for a written report uithin ten days of an Abnormal Occurrence and is in accordance with the forcat set forth in Regulatory Guideline 1. M.
Yours very truly, Ty ;/,
                                                                                         ./ f'
( ' E.(/'E.Uticy,- )f ( ,l . .'
Vice-President Bulk Pouer Supply JMB:me Attachment                                                                   .
cc: Messrs. D. C. Knuth W. G. Mcdonald S
8401030393 751111 PDR ADOCK 05000261 i
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ABN0lWAT. OCCURRENCC Rl: PORT
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L. Report No.      261/75-16
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2a. Report Date - November 4, 1975 2b. Occurrence Date - October 28, 1975
: 3. Facility -       11. B. Robinson Unit No. 2 1:artsville , South Carolina    29550                          ,
: 4. Identification of Occurrence failure of Service Water Booster Punp "B" to start.        This constitutes an abnormal occurrence as defined in Technit.:1 Specification 1.8.h.
(violation of a limiting condition of operation).
: 5. Conditions Prior to occurrence The reactor was operating nornally at full rated power. All systems were normal uith the er.ception of the service water systen. As a result of =aintenance operations on a service water valvo, one service water loop usa out of service and three punps were operating.
: 6. Descr!ntion of 0:currence LTaile operatin? vith threc service uater pumps and ene wrvice unter header, it was decided to shift the operation of the service u.:ter booster purpa.      Service water booster pump "A" was operating. Action was taken to start service water Leoster pump "B", and it uas verified operable and running at 1228 hours on October 28, 1975. At 1229 service water booster pump "A" was stopped and a stopped indication was received.
Immediately after "A" pump stepped the operator received indication that "B" punp also stepped. The operater im=cdiately attenpted to restart "A" pump and received a running indication light follcwcd by an off indicatioa light.       IIc then held the control switch in the start position and the breaker tripped on overcurrent. The operator attenpted to re-start "B" pu:.p and received a run Indicatien light then an off indication light. 11e held "B" pump control switch in the start position and the breaker tripped on overcurrent. Therefore, both pumps were out of service at that time which is a violation of Technical Specification 3.3.4.1.a.
The operating containment recirculation fans were stopped due to lack of cooling water.
At 1230 hours, the breakers on hath service water houster pumps were reset. The operator started "A" pump and received indication that it was operating. lie then restarted the containment recirculation fans.
At this time, one service water booster pump was operable and there was no requirement to proceed with placing the plant in hot shutdown.
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                                                          ,. At 1417, the operator attempted to restart "B" service water booster pump and the breaker tripped. lie then started "C" service water pump so that all service water pumps would be operating. At 1424, he attempted to restart "B" service water booster pump and the breaker tripped. "B" pump was rotated by hand and was found to be frLe. Maintenan:e person-nel checked the pump and breaker and found both to be normal. At 1552 hours,  "B" service water booster pump was restarted and operated normally.
The idic service water header was returned to service at 1815 hours.
               "B" service water booster pump was thus returned to service within the
    .          24 hours provided by Technical Specification 3.3.4.2.c.
: 7. Designation o Apparent Cause of Occurrence The apparent cause of the l'nitial loss of     "B" pump followed by the loss of  "A" pump was actuation of the pump suction pressure switches provided to  protect the pumps from low MPSH. It has not been determined whether the low pressure pump trips were a result-of flow instabilitics, problem with the pressure switches or a conbination of both. Unstable flow conditions could have been caused by back leakage through the booster pumps' discharge check valves. These check valves are installed at the discharge of each pump to prevent back flow through the idle pump. It is suspected-that these check valves leak.       The apparent cause of the pump breaker tripping on overcurr nt wa., the altcmpled pump starts with a back flow through the pumps. This uastable condition could have also contributed to actuation of the suction pressure switches.
S. Analysis of Occurrence The service water booster pumps provide a pressure boost to prevent in-Icakage of contamination to the service water should an accident occur in which the containment pressure increases.        Examination revealed that there were no equipment failures. The trips resulted from pump protection instrumentation and pressure / flow instabilitics. No damage resulted from this occurrence end at no tine was there a hazard to the general public..
: 9. Corrective Action After the loss of both pumps due to breaker tripping, the~ containment rceirculation fans were stopped to prevent overheating the motors. The breaker on   "A" pump was reset and the pump started. '"B'? pump was examined for electrical faults and mechanical binding, but- no abnormal ccndition was identified. No adjustments were made to' either pump. .It was decided-that flow / pressure instabilities creatcd the trips.
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Since the Technical Specifications allows one service water header to be removed from service for only 24 hours while operating at power, the probability of recurrences of a flow prc3sure instability in conjunction with pump shifting is remote. The suction pressure switches and ' discharge check valves will be checked and.necescary' adjustments or repairs made during the November refueling outage.                                    '

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: 10.                      Failure Dat.a               .
No previous failure of this type has occurred. The following information is provided for                 "B" Service Water Booster Pump.
Pump Model -             8CNC 104 Impeller   -
11 13/16" Manufacturer '-          Worthington Motor Model -            TSLP Horsepower -             125 Manufacturer -           Westinghouse (HC:me i
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