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. 1 NUCLEAR REGULATORY COMMISSION 1
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AE00/E807 MEMORANDUM FOR: - Edward L. Jordan, Director Office for Analysis and Evaluation of Operational Data e
FPCM:
Thomas M. Novak, Director Et Division of Safety Programs.
Office for Analysis and Evaluation j
of Operational Data SUEJECT:
ENGINEERING EVALUATION REPORT - PUMP DAMAGE DUE
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TO LOW FLOW CAVITATION This memorandum and the enclosed report are our response to action item 5-d by the EDO in.his memorandum dated April 6, 1988, related to the i
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. ass gne This action-diagnostic evaluation team report for McGuire Nuclear Station.
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l item requested thr.t AE00~ corduct an evaluation of' insufficient pump mini-flow recirculation problem and-determine:
(1) if a potential generic issue-~ exists, and (2) if generic communications are warranted.
This evaluation incicates that cperation of centrifugal pumps at a:certain l
range of flows below the design flows, can create flow recirculation'in3ide the-These internal. recirculations' induce cavitation, hydraulic pressure:
pumps.
-pulsation and vibration which can cause damage to the pumps following an' extended period ofl operation at.such low flows. The pump mini-flow recircula--
. tion lines have traditionally been sized solely on the basis of pumpIfluid; continuous minimum flow-operation, and thus the flow rate may not be1 sufficient _
j temperature-rise. Temperature rise is not the only factor influencing safe, to avoid' damage due~to internal recirculation.
In' addition, the recirculation i
configuration may not ha,v.e'been fully considered for pumps. designed for a: wide range of flows. Since maily.of the safety-related cooling system pumps. in most operating plants are designed to operate with a wide range of flows and use a'.
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mini'-flow line for inservice' testing for pumps and/or for protection againsti operation of pumps at shutoff heads, there is' the potential that some: pumps may -
be run at a low flow within the recirculation zone, without;the. awareness of :
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the plant operators. Our review has identified cases in which major,
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- degradation of impe11ers and"casi_ngs have, occurred to centrifuga1' pumps.
1 running. continuously at low flows.
2 Near the completion of this study, NRR issued Bulletin 88-04',." Potential l Safety.
Related Pump Loss," on May-5,11988 which addressesicertain aspects of'the' 3D internal-recirculation problem. The: actions addressed in the bulletin appear
'I specific to the. mini-flow line. However, this evaluation has found that the; pump damage induced.by internal recirculation can.'also be caused by operating
' pumps: at: low flow. By separate memorandum, the enclosed AEOD report and.
suggestions have been forwarded to NRR for further action.
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Edward L. Jordan I I would be pleased to provide any clarification or further infonnation that you may desire.
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I Thomas M. Novak, Director Division of Safety Programs Office for Analysis and Evaluation of Operational Data
Enclosure:
As stated cc w/ enclosures:
C. Heltemes Distribution:
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