ML20079A859
| ML20079A859 | |
| Person / Time | |
|---|---|
| Site: | Cooper  |
| Issue date: | 12/29/1994 |
| From: | Horn G NEBRASKA PUBLIC POWER DISTRICT |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| IEB-88-004, IEB-88-4, NLS940141, NUDOCS 9501040114 | |
| Download: ML20079A859 (9) | |
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GENE'.AL OFFICE P O box 499, COLUMBUS. NEBRASKA 686024499 Nebraska Public Power District "T#l"Sfe'lE?"
GUY R. HORN Vice-President. Nuclear (402) 563-5518 NLS940141 December 29, 1994 U.S. Nuclear Regulatory Commission Attn: Document Control Desk Washington, D.C.
20555 Gentlemen:
Subject:
Supplemental Response to NRC Bulletin No. 88-04 Cooper Nuclear Station NRC Docket No. 50-298, DPR-46
References:
1.
NRC Bulletin No. 88-04, dated May 5, 1988, " Potential Safety Related Puup Loss" 2.
Letter from L.G. Kuncl (NPPD) to R.D. Martin (NRC) dated July 8, 1988 (NLS8800347), " Response to Bulletin No. 88-04" 3.
Letter from L.G. Kuncl (NPPD) to R.D. Martin (NRC) dated September 26, 1989 (NLS8900264), ' Response to Bulletin No. 88-04" The Nebraska Public Power District (District) hereby supplements its previous responses to NRC Bulletin No. 88-04, " Potential Safety Related Pump Loss" (Reference 1).
NRC Bulletin No. 88-04 raised concerns regarding minimum flow protection for safety-related pumps.
The District originally responded to NRC Bulletin No. 88-04 by letters dated July 8, 1988 (Reference 2) and September 26, 1989 (Reference 3).
During a recent NRC Inspection of CNS activities, the NRC questioned the adequacy of the District's response to Bulletin No. 88-04.
In j
response to these concerns, the District performed a re-evaluation of the minimum flow capability of CNS safety-related pumps.
The District's re-evaluation concludes that all CNS safety-related pumps nave sufficient minimum flow capability to protect against pump damage.
A description of the additional evaluations performed and the results of those evaluations are detailed in the Attachment.
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U.S. Nuclear Regulatory Commission December 29, 1994 Page 2 of 3 Please contact me if you have any questions or require any additional j
information.
Si erely 4.
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. Horn ice President, Nuclear Attachment cc:
Regional Administrator USNRC - Region IV NRC Resident Inspector Office Cooper Nuclear Station NPG Distribution i
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U.S. Nuclear Regulatory Commission December 29, 1994 Page 3 of 3 STATE OF NEBRASKA )
)ss PLATTE COUNTY
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G. R. Horn, being first duly sworn, deposes and says that he is an authorized representative of the Nebraska Public Power District, a public corporation and political subdivision of the State of Nebraska; that he is duly authorized to submit this response on behalf of Nebraska Public Power District; and that the statements contained herein re true o the best of his knowledge and belief.
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G. R'.
Horn Subscribed in my presence and sworn to before me this day of hCI M A-
, 1994.
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Attachment to NLS940141 Page I of 6 I.
BACKGROUND On May 5,1988, the NRC issued Bulletin No. 88-04, " Potential Safety Related Pump Loss".h NRC Bulletin No. 88-04 requested licensees to evaluate all safety-related pumps for 1) pump-to-pump interaction during miniflow operation that could result in the dead-heading of one or more pumps, and 2) the adequacy of the minimum flow bypass capacity for operation of even a single pump.
By letter dated July 8,1988,2' the District provided its initial response to NRC Bulletin No.
88-04. That response indicated that, with the exception of additional testing and evaluation required for the Core Spray and Service Water Booster pumps, sufTicient minimum flow capability was verified for the CNS safety-related pumps. The District committed to perform additional evaluation of the Core Spray and Service Water Booster pumps, put in place interim measures to ensure protection of these pumps, and submitted a justification for continued operation until completion of the long-term actions.
By letter dated December 20,1988,l' the NRC responded to the District's submittal, indicating that the District had fulfilled the requirements for responding to NRC Bulletin 88-04.
26,1989,f he District provided, as a follow-up to the initial By letter dated September t
response to Bulletin 88-04, funher information concerning the additional testing and evaluation of the Core Spray and Service Water Booster pumps. Based on testing perfonned on the Core Spray pumps, and procedural changes to prohibit operating two Service Water Booster pumps in parallel, the District concluded that adequate minimum flow protection existed for CNS safety-related pumps, and the District's response to NRC Bulletin 88-04 was complete.
During a recent NRC inspection, the District's actions concerning the unexpected cycling of a Core Spray minimum flow valve were reviewed. As a result of this review, the NRC questioned the adequacy of the District's response to NRC Bulletin No. 88-04, with regard to the Core Spray pumps. In response to these concerns the District has re-evaluated its response to NRC Bulletin 88-04 for the Core Spray Pumps. This re-evaluation included contacting the pump manufacturer to establish the required minimum operating flows for the Core Spray Pumps and comparing the safe minimum flow to the flow measured during testing and obtained by calculation. In addition, the District has re-examined its evaluation for the remainder of the CNS safety-related pumps completed in response to Bulletin No.
88-04 to assure the adequacy of the evaluation and the completeness of the District's response. The specific event concerning the minimum flow valve was reported in CNS LER 94 002 and the actions to correct the valve problem were subsequently completed. This submittal supplements the information contained in the District's previous response to Bulletin No. 88-04.
II.
DISCUSSION A.
Core Spray Pump Minimum Flow Adequaev Re-evaluation During pre-operational testing, the Core Spray minimum flow by-pass line flowrate was determined to be at least 550 gpm.1' The flowrate was detennined by throttling the flow through valves CS-MO-26 A/B to approximately 3000 gpm and then opening minimum flow valves CS-MO-5 A/B. The reduction in indicated flow through valves CS-MO-26 A/B (i.e.,550 gpm) was considered the amount flowing through the minimum flow by-pass line. The actual flow through the minimum flow
Attachment to NLS940141 Page 2 of 6 line would be greater than the indicated change in flow due to the lower system head which results from opening minimum flow valves CS-MO-5 A/B.
To confirm the minimum flow at pump design flow, NPPD performed Calcalation NEDC 94-190.t' This calculation conservatively shows that the flow through minimum flow bypass is 414 gpm at a pump head of approximately 379 psig. In addition, the minimum flow bypass line flowrate was measured with a portable ultrasonic flow meter during Station motor operated valve testing. The measured minimum flow for CS-MOV-MOSA was approximately 444 gpm. The measured minimum flow for CS-MOV-MO5B was 390 gpm.
The pump manufacturer, BW/IP International Inc. (formerly Byron Jackson),
completed an analysis at the District's request which established the required minimum operating flow for the Core Spray pumps.2' That analysis established that the required minimum flow is 370 gpm for a total accumulation of 60 hours6.944444e-4 days <br />0.0167 hours <br />9.920635e-5 weeks <br />2.283e-5 months <br /> between overhauls. BW/IP confinned that the 60 hours6.944444e-4 days <br />0.0167 hours <br />9.920635e-5 weeks <br />2.283e-5 months <br /> run time could be continuous.
Comparing the manufacturer required minimum flow with the measured and calculated minimum flows verifies that the Core Spray pump by-pass line minimum flow is sufficient to avoid pump damage. The expected pump operating time on minimum flow is well under 60 hours6.944444e-4 days <br />0.0167 hours <br />9.920635e-5 weeks <br />2.283e-5 months <br /> since they are limited to approximately 30 seconds of operation on minimum flow during surveillance testing and would not likely operate for more than 15 minutes on minimum flow during any postulated accidentJ This confirms the conclusions drawn from the pump vibration data on i
which the District relied in its original response to Bulletin No. 88-04. The foregoing adequately addresses the issues described in Bulletin No. 88-04 regarding j
sufficient Core Spray Pump minimum flow.
1 B.
Re-examination of Hulletin No. 88-04 Response 1
Our findings from this re-examination are as follows:
I 1.
Pumn-to-Pump Interaction All CNS safety-related systems with centrifugal pumps were evaluated for pump-to-pump interaction during miniflow operation which could have resulted in dead-heading of one or more of the pumps. Specific systems j
evaluated were-1 Core Spray (CS)
Residual lleat Removal (RilR)
"igh Pressure Coolant injection (llPCI) ih-actor Core Isolation Cooling (RCIC) heactor Equipment Cooling (REC)
Service Water (SW) and Gland Seal Residual lleat Removal Service Water Booster (RilRSWB) & Gland Seal Diesel Generator Jacket Water (DGJW)
Diesel Generator Diesel Oil Transfer (DGDO)
Control Rod Drive (CRD)
Reactor Recirculation (RR)
Of the above systems, CS, RCIC, liPCI, and CRD have a minimum flow bypass line for each pump. Therefore, pump interaction during minimum
)
i Attachment' to NLS940141 Page 3 of 6 now operation for these systems is not possible and these systems are i
excluded from further consideration.
l The REC, SW, DGJW, DGDO, and RR systems would not, by design, have to run without an established flow path and, therefore, have no minimum flow bypass line. Accordingly, pump interaction during minimum flow operation for these systems is not possible and these systems are excluded from further consideration.
The RIIRSWB pumps were determined to be susceptible to pump interaction as described in the District's original response to this Bulletin. At that time procedural changes were implemented to preclude pump interaction. Since the R11RSW~B pumps are manually started, these procedural changes ensure either that only one pump per loop is used during normal operation or that an -
adequate flow path is established if two pumps are running. Therefore, pump minimum flow interaction is no longer a concern for the RIIRSWB pumps.
This leaves the RilR system as the only system at CNS to have a pump minimum flow bypass design which is common to two pumps. liowever, as was verified during DC 86-125,1' the RiiR pumps do not exhibit any interaction during parallel pump minimum flow operation as described in the District's original response to this Bulletin. During system surveillance testing, only one RilR pump is in operation at any time precluding and pump interaction. Therefore, the District's re-examination has concluded that pump interaction during minimum flow operation is not a concern for the RllR pumps.
i 2.
Minimum Flow Pump energy level and suction sgecific speed criteria were developed'in Engineering Study NED 88-001,- for the safety-related pumps at CNS listed in 2.1 above. These criteria were used to determine which of the 3
pumps were potentially susceptible to severe short-term vibration damage if operated under low flow conditions.
The following pumps were determined nqt to have an energy level and i
suction specific speed above the threshold level for concern and were eliminated from consideration:
Service Water and Gland Seal i
Residual 11 eat Removal Service Water Booster & Gland Seal i
Diesel Generator Jacket Water Diesel Generator Diesel Oil Transfer Reactor Core Isolation Cooling Reactor Equipment Cooling Control Rod Drive The RCIC pump, though having a high suction specific speed, did not meet the energy criteria. This pump would not be required to operate more than a few seconds at a flow rate less than 80-90 percent ofits best efficiency point, and therefore, would not encounter low flow rates which could cause short-term damage. In addition, the Reactor Recirculation pumps were excluded since they have variable speed drives. Also, none of these pumps
Attachraent to-NLS940141 Page 4 of 6 are required, by design, to operate on minimum flow for any appreciable time frame. As a result, only four pump models (RllR, llPCI main &
l booster, and CS) were determined to have energy levels and suction specific l
speeds such that they had the potential to be susceptible to severe shon-term vibration damage if operated under low flow conditions. NPPD's findings on the CS pumps are discussed in 1.0 above and findings on the RHR and i.
IIPCI pumps are provided below.
l l
a.
RilR Pumps Field vibration test data taken at the minimum flow bypass flowrate for the RilR pumps was evaluated by General Electric as part of DC i
86-125, Rev. IF which eliminated the restriction orifice in the j
minimum flow bypass lines. During the test, the pumps were operated for nearly one hour on two pump minimum flow. The vibration data was taken for the B pump under test flow, single pump minimum flow, and under two pump minimum flow conditions.
Vibration data was also taken for the D pump under test flow, two pump minimum flow conditions. GE's evaluation of the results concluded that pump vibration velocities were within operating i
guideline limits and piping vibration displacements were within i
fatigue endurance limits. Calculation NEDC 86-2141!' calculated l
the minimum flow through the bypass during single pump operation l
at 1862 gpm and during two pump operation at 1450 gpm.
l l
The pump manufacturer (Bingham International, Inc.) concurred with the District's conclusion from the vibration testing that the minimum flow capacities are adequate and parallel RilR pump operation (two pump operation) on minimum flow for a duration of 15 minutes will not stress the pumps to the point ofimminent failure. As stated earlier, General Electric advised that the maximum duration that c LPCI or Core Spray pump may operate in the minimum flow mode for the sim:trum of hypothetical loss-of-coolant accidents (LOCAs) is less than 'i5 rninutes.0 Accordingly, the present RilR pump minimum flow capacity is verified as adequate by the pump manufacturer, b.
IIPCI The llPCI main and booster pumps would not be required to operate more than a few seconds at a flow rate less than 80-90 percent of their best efficiency point, and therefore, will not encounter low flow l
rates which could cause shon-term damage. Per a General Electric analysis:!
l l
"The llPCI and RCIC systems have specified minimum flow rates of ten to twelve and one-half percent, respectively. The llPCI system is used only for test and emergency conditions, while the RCIC system can also be used for normal post-isolation core cooling. The minimum flow mode is intended for pump protection and is not specifically required for any safety function. Therefore, since no operational difliculties base been experienced with these systems in the minimum flow mode, the current
~
Attechment to NLS940141 Page 5 of 6 specified minimum flow rates for these systems are judged to be adequate."
In addition to the above, per Engineering Study NED 88-001 E he t
llPCI pumps will only be on minimum flow for a few seconds minimizing any potential for low How damage. This is because the turbine controller senses pump discharge flow and allows enough steam to the turbine to quickly provide a pump discharge flow of 4,250 gpm.
During system surveillance testing, the test flow path to the emergency condensate storage tanks is established before beginning the test with only the test How line throttling valve llPCI-MOV-MO21 closed. Therefore, pump operating time on minimum flow is too short (less than 10 seconds) to be of concern.
Ilelow is a comparison of the required minimum flow, and design minimum flow for the llPCI pumps which shows that the minimum flow is within the GE recommendations.
Pump Required Minimum Flow Design Minimum Flow IIPCI 425 gpm?
450 gpmE Therefore, the District's re-examination has concluded that minimum flow operation is not a concern for the RIIR and 11PCI pumps and that the infonnation in the District's original response to this Bulletin was adequate.
III.
CONCLUSION in summary, the District has determined that concerns regarding piping system configurations which could have allowed pump-to-pump interaction or other minimum flow problems have been identified and resolved. Of the safety-related pumps at CNS, only four pump models, RilR, IIPCI (main & booster), and CS were found potentially susceptible to severe short-term vibration damage if operated under low flow conditions. With this submittal, the adequacy of the current miniflow capacity to preclude severe shon-term vibration damage if operated under low flow conditions has been verified for the CS and RilR pumps based on test data, field experience, and confirmation by the respective pump manufacturers. In addition, the adequacy of the current miniflow capacity to preclude severe short-tenn vibration damage if operated under low flow conditions has been verified for parallel RilR pump operation with confinnation by the pump manufacturer. The llPCI main 1
and booster pumps are only required to operate for a few seconds at a flow rate less than 80-90 percent of their best efficiency point during pump startups and shutdown, and l
therefore, will not be subjected to low flow rates long enough to cause short-term damage.
IlPCI (and RCIC) are able to inject at high reactor pressures and will not operate on minimum flow during postulated transients that these pumps respond to. Accordingly, the District has concluded that the concerns identified in NRC Bulletin No. 88-04 have been adequately addressed at CNS.
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O Attachment to NLS940141 Page 6 of 6 REFERENCES 1.
NRC Bulletin No. 88-04, dated May 5,1988, " Potential Safety Related Pump Loss".
2.
Letter from L.G. Kunci (NPPD) to R.D. Martin (NRC), dated July 8,1988, " Response to llulletin No. 88-04" 3.
Letter from P.W. O' Conner (NRC) to G.A. Trevors (NPPD), dated December 20, 1988,
" Response to NRC Bul!etin 88-04 (TAC No. 69904)".
4.
Letter from L.G. Kunci (NPPD) to R.D. Martin (NRC), dated September 26,1989, " Response to Bulletin No. 88-04".
5.
Preoperational Test GE-12, Revision 1, dated March 9,1973, " Core Spray System".
6.
Calculation NEDC 94190, Revision 0, approved August 22,1994," Core Spray Pump Miniflow Ana'ysis".
7.
Letter from J. Bartholomew (BW/IP) to G.S. McClure (NPPD), dated August 17, 1994,
" Minimum Flow Analysis - Cooper Station".
8.
Letter from A.E. Rogers (GE) to J.M. Meacham (NPPD), dated September 24,1986, "RIIR Minimum Flow Bypass" 9.
General Electric Test Record, DRF-A00-02433, dated January 1987, " Residual 11 eat Removal System Minimum Flow Test, Cooper Nuclear Station, Nebraska Public Power District" 10.
Engineering Study NED-88-001, dated June 1988, " Evaluation of Minimum Flow Stability for CNS Essential Centrifugal Pumps".
I1.
Calculation NEDC 86-214, Revision 0, approved February 19,1987, " Removal of RilR Orifice" 12.
Letter from 1. Gabel (Burns & Roe) to D.A. Fitzpatrick (Jelco), dated May 14,1970, " Contract E-69-4 Orifice Plates" I