ML17262A435
| ML17262A435 | |
| Person / Time | |
|---|---|
| Site: | Ginna  |
| Issue date: | 03/27/1991 |
| From: | Mecredy R ROCHESTER GAS & ELECTRIC CORP. |
| To: | Andrea Johnson Office of Nuclear Reactor Regulation |
| References | |
| IEB-88-004, IEB-88-4, NUDOCS 9104100244 | |
| Download: ML17262A435 (29) | |
Text
t ACCELERATED DISTRIBUTION DEMONSTRATION SYSTEM
/
REGULATORY INFORMATION.DISTRIBUTION SYSTEM (RIDS).
CESSION NBR:9104100244 DOC.DATE: 91/03/27 NOTARIZED: NO
'OCKET FACIL:50-244 Robert Emmet Ginna Nuclear Plant, Unit 1, Rochester G
05000244 AUTH.NAME AUTHOR AFFILIATION MECREDY,R.C.
Rochester.
Gas 6 Electric Corp.
RECIP.NAME RECIPIENT AFFILIATION JOHNSON,A.R.
Project Directorate I-3
SUBJECT:
Responds to Insp,.50=244/90-24
'on 910114 re "Review of RG&E Actions Taken in Response to NRC Bulletin Number 88-04,.
Potential Safety Related Pump Loss."
DISTRIBUTION CODE IE37D COPIES RECEIVED:LTR ENCL SIZE TITLE: Bulletin 88-004 re Potential Safety-Related Pump Loss D
NOTES:License Exp date in accordance with 10CFR2,2.109(9/19/72).
05000244
/
RECIPIENT ID CODE/NAME PD1-3 LA JOHNSON,A INTERNAL: AEOD/DOA ALEXIONiT 13E2 1 NRR/DET/EMEB 7E NRR/DOEA/OGCB11 NRR/DST 8E2 F L 02 RG 01 EXTERNAL: NRC PDR COPIES LTTR ENCL 1
0 1
1 1
1 1
1 1
1 1
1 1
1 1
1 1
1 1
1
'ECIPIENT ID CODE/NAME PDl-3 PD AEOD/DSP/TPAB
- MCCOY, M
8E23 NRR/DOEA/OEAB11
, NRR/DREP/PEPB9D NRR/PMAS/ILRB12
-RES/DSIR/EIB NSIC COPIES LTTR ENCL 1
1 1'
1 1
1 1
1 1
1 1
1 1
1 D
D D
NOTE TO ALL"RIDS" RECIPIENTS:
D D
PLEASE HELP US TO REDUCE iVASTE! CONTACT THE DOCUMENT CONTROL DESK, ROOM Pl-37 (EXT. 20079) TO ELIMINATEYOUR NAME FROM DISTRIBUTION LISTS FOR DOCUMENTS YOU DON'T NEED!
TOTAL NUMBER OF COPIES REQUIRED:
LTTR 18 ENCL 17
,ROCHESTER GAS AND. ELECTRIC CORPORATION ROBERT C. MECREOY Vice President Ctnne Nucfeer Production
~
89 EAST AVENUE, ROCHESTER N.Y. 14649-Q001 TEt.ESsHONE AREA CODE 716 546 2700 March 27, 1991 U.S. Nuclear Regulatory Commission Document Control Desk Attn:
Allen R. Johnson Project Directorate I-3, Washington, D.C.
20555
Subject:
Response
to Inspection No. 50-244/90-24, dated January 14, 1991 Review of RG&E Actions Taken in Response to NRC Bulletin No. 88-04, Potential Safety Related Pump Loss R.E.
Ginna Nuclear Power Plant Docket No. 50-244
Dear Mr. Johnson:
The subject inspection report concluded that the engineering resolution and documentation for those systems that were susceptible to the concerns of the bulletin were detailed and technically sound.
However, it was noted that the documentation for the evaluation of those systems that were acceptable.,
was not adequately maintained.,
Additionally, it was noted that the as-built recirculation line for the High Head Safety Injection System did not agree with that proposed in our response to NRC Bulletin 88-04, dated July 7, 1988.
Modification (EWR) 3881 was implemented in 1989 to provide a
1",
inch recirculation line for each pump.
Our response had indicated a 1-inch line would be installed,.
The use of the 1~~-inch line was documented in modification package for EWR 3881 and a description was also provided in our December 1989 update of the UFSAR in Section 6.3.2.2.1.
The as-built system configuration is shown on the Piping and Instrumentation Drawing provided as Figure 6.3-1 of the UFSAR.
l As agreed during the exit meeting, RG&E agreed to review these documentation issues in a timely manner.
A document entitled "Basis of Design for the Minimum Flow Recirculation Systems for Residual Heat Removal, High Head Safety Injection, and Auxiliary'gpgo 75 Odd
Peedwater Pumps as Related to NRC Bulletin 88-04" was transmitted to the Region I Office on October 31, 1990.
An updated copy of that document is provided as Attachment 1.
Very truly yours; GAH/1,46 Attachment Robert C. Mecredy xc: Mr. Allen R. Johnson (Mail Stop 14D1)
Project Directorate I-3 Mashington, D.C:-
20555 U.S. Nuclear Regulatory Commission Region I 475 Allendale Road King of Prussia, PA 19406 Ginna Senior Resident Inspector A
ATTACHMENT 1 BASIS OF DESIGN FOR THE MINIMUM FLOW RECIRCULATION SYSTEMS FOR RESIDUAL HEAT REMOVAL, HIGH HEAD SAFETY INJECTION, AND AUXlLIARYFEEDWATER PUMPS AS RELATED
,TO NRC BULLETIN 88-04 REV.
1 Rochester Gas and Electric Corporation 89 East Avenue Rochester, NY 14649 EWR 3881 SI PUMPS RECIRCULATION EWR 4675 RHR PUMP RECIRCULATION FEBRUARY 13, 1991
BASIS OF DESIGN FOR THE MINIMUM FLOW RECIRCULATION SYSTEMS FOR RESIDUAL HEAT REMOVALg HIGH HEAD SAFETY INJECTION ~
AND AUXILIARYFEEDWATER PUMPS AS RELATED TO NRC BULLETIN 88-04 PURPOSE The purpose of this document is to provide additional clarification of the design basis for the minimum flow recirculation systems for the safety related pumps applicable to NRC Bulletin 88-04 concerns at the R. E. Ginna Nuclear Power Plant.
Systems applicable are as follows:
~ High Head Safety Injection (SI)
~ Main Auxiliary Feedwater, both motor driven and turbine driven (MDAFW, TDAFW)
~ Standby Auxiliary Feedwater (SBAFW)
INTRODUCTION Several letters and correspondence (Refs.
c, d,
g) documented concerns relative to the adequacy of miniflow in safety related pumps.
NRC Bulletin 88-04 (ref. g) specifically requested license evaluation and actions to be taken.
The concerns were as follows:
1)
Systems where pumps may operate in parallel with both pumps recirculating through a common recirculation line that does not preclude pump-to-pump interaction during miniflow operation.
2)
The adequacy of minimum flow bypass lines with respect to damage resulting from operation and testing in the minimum flow mode.
The first concern would result from the design of the piping system.
The second concern relates to the system design as well as how the pumps are operated and tested, and the pump application and design.
Damage to a pump may result from excessive heatup inside the pump which could as a worst case lead to seizure and failure.
Damage may also result from hydraulic forces and instability while operating at low flows.
This condition can in the worst case lead to pump failure, but can only occur when operating at low flows for extended periods or where the cumulative number of operating hours is relatively large.
It can lead to accelerated degradation of "
pump internals and impeller cavitation damage.
Cavitation so severe that it could cause damage in the short term would be detectible during testing.
The required minimum flow design must, therefore, address both these conditions.
The flow values
necessary to prevent pump damage due to heatup are much less than the flows necessary to prevent damage due to suction recirculation or instability.
Since the latter requires, operation at low flows for extended duration-and
. generally provides indications of degrading conditions.such as trends in pressure, vibration, and temperature of the bearings (ref; b), plant operating limits and testing can provide adequate assurance that this type of failure will not occur.
NRC found RG&E responses to Bulletin 88-04 (ref.
h and j) acceptable (ref. 1).
REFERENCES (a)
'b)
(c)
(d)
(e)
(f)
(g)
(h)
{k)
(m)
(n)
(o)
Letter from S. A..Herrick, Worthington (McGraw Edison) to M.
P. Lilley, RG&E, Safety Injection Pump, dated October 25, 1982.
NUREG/CR-4597-Vol.
1, Aging and 'ervice Wear of Auxiliary Feedwater Pumps for PWR Nuclear Power Plants, July 1986.
NRC Information Notice 87-59: Potential RHR Pump Loss, dated November 17, 1987.
Letter from S.
P. Swigert, Westinghouse Electric Corporation, to S.
M. Spector, RG&E, Emergency Core Cooling System Pumps Miniflow Concern, RG&E-87-670, dated December 8,
1987-.
Letter from Bill McClaskey, Pacific Pumps/Dresser, to G.
- Hermes, RG&E, 6" SVC Residual Heat Removal Pumps, dated March 24, 1988 (Response to ref. f).
Letter from G. Hermes, RG&E to William McClaskey, Dresser Pump Division, 6" SVC Residual Heat Removal Pumps, dated January 7, 1988.
NRC Bulletin No. 88-04:
Potential Safety Related Pump Loss, dated May 5, 1988.
Letter from B. A. Snow, RG&E to C. Stahle, NRC, Response to NRC Bulletin 88-04, dated July 7, 1988.
Telecon memorandum with M.
P.
Lilley-,
RG&E, and Frank Ferrarese, Dresser
- Pump, Turbine Driven Auxiliary Feedwater
- Pump, dated November 1, 1988..
Letter from R.
C. Mecredy, RG&E to A. R. Johnson, NRC, Status Report of Plant Modifications Pursuant to NRC Bulletin 88-04, dated July 24, 1989.
Safety Evaluation 10CFR50.59 RHR Pump Recirculation 1989 Installed Modification, EWR 4675, Rev.
0, dated May 25, 1989.
Letter from A.
R.
- Johnson, NRC to R.
C.
- Mecredy, RG&E, NRC Bulletin 88-04 (TAC No. 69918), dated August 16, 1989.
Interoffice Correspondence from E.
K. Uoci, RG&E, to D.
R.
- Gent, RG&E, S.I.
Pump Recirculation Flow, dated March 9, 1990.
Kypipe Analysis, ECCS Hydraulic Analysis, file "ECCS 47", dated October 26, 1990.
Letter from R.
C. Mecredy,'G&E, to A. R.
- Johnson, NRC, NRC Bulletin 88-04, dated March 12, 1990.
(p) Letter from Car1 Stahle, NRC to R.
C. Mecredy, RGKE, Issuance of Amendment to Operating License, Amendment 33, dated March 30, 1990.
(q) Letter from R. E. Smith, RGGE; to Carl Stahle, NRC, Application for Amendment to Operating License, dated November 29, 1988.
(r) Telefax from R. Joines, Dresser Pump Division, to G. Hermes, RG&E, Minimum Flow, RHR pumps, dated October 25, 1990.
1 (s)
NUS Report 0499-M-02, Rev.
0, dated December'0,
'989, Auxiliary Feedwater Hydraulic Analysis.
(t) Ingersoll Rand Drawing Line Notes, 29HMTA86X8A, Sheet 1, Rev.
2, for Ingersoll Rand order 016-36370, GAI order 55190 (date stamped April 26, 1976).
(u)
ECCS Hydraulic Analysis Report, NUS 3S61-M-10, Rev.
0, dated September 6, 1990.
t (v) Kypipe Analysis, AFW Hydraulic Model, file "TD100",
dated February 13, 1991 (w) Safety Analysis, EWR 3881, SI Pump Recirculation, Rev. 4, dated December 5,
1989.
(x) Kypipe Analysis, ECCS Hydraulic Analysis, file "ECCS 26", dated September ll, 1989.
DISCUSSION Residual Heat Removal S stem Performance Characteristics 2 pumps Model 6" SVC Single Stage 0 Close-Coupled-Horizontal RPM 1770 Rated Flow 1560 GPM P&ID 33013-1247 Rated Head 280ft.
UFSAR Fig. 5.4-7 Rated Horsepower 200 HP Flow at Best Efficiency Point (BEP) 1800 GPM Pump S/N 43513 ('A')
43514 ('B')
Manufacturer Pacific Pump/Dresser
'riginal-recirc.
design one recirc. line for both pumps; 200gpm if 1 pump operating; 100 gpm if operated in parallel RG&E provided a
response to NRC Bulletin 88-04 in ref.
(h).
Attachment B to ref.
(h) provided a detailed evaluation and operability justification.
It also described a
planned modification (EWR 4675).
The operability determination showed. that a flow of 100 gpm per pump was adequate for short periods of time.
The pump manufacturer supported this conclusion for durations of 30 minutes.
This time is sufficient to perform monthly periodic testing (ref. e).
The concern raised in the NRC Bulletin, (ref. g), over parallel pump operation existed in the original R.
E.
Ginna design.
consequently, RG&E took immediate corrective action through procedures to preclude parallel pump operation at flowrates that could conceivably result in the pump-to-pump interaction referenced earlier.
The plant modification was designed and was planned to be installed in two phases (refer to Figure B-1 ref. h).
First, the parallel pump operation concern would be eliminated by installing separate minimum flow recirculation lines.
Each line would be provided with a pressure breakdown orifice to provide 200 gpm in the event that the discharge line was closed (Safety Evaluation in ref. k), or system pressure was above shut'off head.
Although the recirculation lines came together in one common line, the system
- design, with orifices would preclude a pump-to-pump interaction, even if the pump performance characteristics between the two pumps were different by 10%
or
- more, which they are not (ref.
n).
Therefore, the recirculation lines can be termed as independent of each other in the context of Bulletin 88-04.
This modification was made during the 1989 outage.,The second phase. was the replacement of the 200 gpm orifice with a 100 gpm orifice and install'ation of an air operated control
- valve, in parallel with the 100 gpm orifice, sized to provide 350 gpm minimum recirculation flow, so that the total would be 450 gpm.
This flowrate was chosen because it represented a
value of 25t of BEP and satisfied the manufacturers recommendation for continuous operation (ref. e).
Attachment B of (ref.
h)
- showed, however, that only short term operation at low flows can occur.
The second phase of the above described modification has not'een installed as described for,the following reasons:
1) 2)
Continued delivery delays prevented obtaining the control valves (ref. j and o).
RGGE's plan to perform a revised 10CFR50.46 ECCS Analysis (ref.
o) which could subsequently revise the recirculation flowrate.
3)
Lack of approval of a
change to an existing technical specification requirement to perform monthly periodic testing at other than 200 gpm.
(An Amendment was later approved by ref. p).
4)
Continued interest to utilize the
- fixed, orifice type recirculation system which would provide the desired minimum
- flows, but with much less complexity than the originally proposed air operated control system.
The modification installed, during the 1989 outage consisted of a fixed orifice sized for 200 gpm in lieu of the 100 gpm described in the original submittal (ref. h).
Adequacy of this modification and the recirculation system was based.
on the safety evaluation, (ref.
k) and=as follows:
a)-
b) 200 gpm,met the technical specification which existed prior to NRC approval of Amendment 33 by (ref. p).
200 gpm was the value utilized in all previous monthly periodic testing
- and, therefore, provided the database for trending parameters such as developed
- pressure, temperature
'and vibration.
c) d)
200 gpm was the maximum value that still conservatively provided for adequate injected flow into the reactor vessel during LOCA events.
This is described.
in detail in RGGE Amendment request (ref. q).
Hydraulic Analyses (ref. x) showed that a maximum recirculation flow of 260 gpm (not including instrument uncertainty),
a 5'%egraded RHR pump and assuming the RWST level was at the switchover limit for RHR pumps of 28%, would meet the delivery requirements in the UFSAR Figure 15.6-13.
A value of 200 gpm guaranteed margin over the delivery requirements considering instrument uncertainty.
200 gpm exceeds the manufacturers recommendation of 100 gpm for short term operation of 30 minutes (time generally sufficient to conduct monthly testing).
It also exceeds a
value recommended by the manufacturer for longer term operation when using an interpolation technique as described below.
The manufacturers recommendation for operation up to 100 hours0.00116 days <br />0.0278 hours <br />1.653439e-4 weeks <br />3.805e-5 months <br /> per month (1200 hour0.0139 days <br />0.333 hours <br />0.00198 weeks <br />4.566e-4 months <br />s/year) is 260 gpm and for continuous operation
(24 hour2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />s/day) is 520 gpm.(ref. e).
The only. modes where RHR pumps could operate at recirculation flow are:
- 1) Accidents initiating a safety injection; small break
- LOCA, steam line breaks and otheis
- 2) Monthly periodic testing
- 3) Inadvertent safety injection Based upon emergency operating procedures, operation at recirculation flow for 1) and 3) above would not be expected. to exceed 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br />.
Operation in mode
- 2) above is generally about'0 minutes.
Mode 3) is expected only infrequently and mode 1) is not expected during the life of the plant.
Therefore, operation at recirculation flow for all modes can be represented as short term o eration.
When interpolated between the manufacturers suggested operating time for 100 gpm and. 260
- gpm, a flow of 200 gpm would result in an operating guideline of
. 140 minutes/day or 2.3 hour3.472222e-5 days <br />8.333333e-4 hours <br />4.960317e-6 weeks <br />1.1415e-6 months <br />s/day to assure reasonable trouble free operation.
e)
The manufacturer concurred (ref. r) that operation for periods on the order of 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> at 200 gpm are not injurious to the pump.
The manufacturer also recommended that once per year the pump be tested at a higher flow than minimum flow to trend data.
RG&E has been performing a yearly test at 700 gpm during the refueling outage which satisfies this recommendation.
f)
The RHR pump design provides operation at very moderate
- speed, temperature, brake horsepower, and with ambient temperature water.
, Catastrophic failure is not a
concern (ref.
e).
Periodic test data has not indicated a degrading trend, since the initial plant operation in 1970.
I4
SAFETY INJECTION SYSTEM Performance characteristics 3 pumps Model 3-WT-811 11 stage horizontal - coupled, to A.C. motor RPM 3550 Rated. Flow 300 gpm PAID 33013-1262 Rated Head 27'00 ft.
UFSAR Fig. 6.3-1 Rated Horsepower 350 HP Flow at BEP 425 gpm Pump S/N 1613234,5,66 (Curves E-207328,E-207348, E-207340)
Manufacturer Worthington/McGraw Edison Original recirc design 30 gpm per pump Attachment A to ref.
(h) provided a detailed evaluation and operability-justification for continued operation.
It also described a
planned modification (EWR 3881).
The operability determination showed that for short periods of operation a flow of 30 gpm met the design basis and no significant difference could, be detected in pump vibration between 30 gpm and 100 gpm.
The plant modification was installed during the 1989 outage.
The safety evaluation was ref.
(w).
The pump manufacturers recommendation is to provide 1/3 or 150 gpm (ref. a).
This value was applicable for operation.
The manufacturer noted that operation at than 150 gpm is a
function of owner 'experience, manufacturer did. not possess substantial testing at low manufacturer did not provide a
recommended flow for operation or testing.
of BEP flow continuous flows less since the flows.
The short, term RG&E designed and installed the plant modification (EWR 3881) so as to provide a recirculation flow of 100 gpm for each pump through a fixed orifice.
The modification replaced the 3/4" recirculation piping with 1 1/2" pipe.
(See Figure A-2= attached).
Each pumps recirculation piping comes together in a common 2" header.
Since the tie-in is downstream of the fixed. pressure breakdown orifices, there will not be a
pump-to-pump interaction as described in Bulletin 88-04.
Hence, the systems are independent in. the context of Bulletin 88-04.
(The original design depicted in ref.
(h) contained 1" lines in lieu of 1 1/2" as described above).
The SI system is equipped with a test line in addition to the recirculation lines.
During monthly periodic testing it is, therefore, possible to obtain the flow of 150 gpm even though this testing duration is only about 30 minutes (ref. m).
The value of 150 gpm, recommended for continuous. operation, provides assurance that accelerated internal wear will not result due to monthly tests.
(Refer to ref. h, Attachment A).
The cumulative hours logged by the SI pumps occurs almost solely during these monthly tests.
For the first 18 years of operation of
R. E. Ginna, the cumulative operating time for all three pumps was about 600 hours0.00694 days <br />0.167 hours <br />9.920635e-4 weeks <br />2.283e-4 months <br />; pump 'c'ogged the most hours, 280.
During power operation the test line is closed.
Therefore, i'f the pump were
- called, upon to operate at recirculation flow during accident scenarios or due to an inadvertent safety injection
- signal, a
maximum of 100 gpm would be provided.
This value is based upon the following:"
a) 100 gpm is the maximum flow that can be recirculated while still meeting the delivery flow required by the Accident Analysis Figure 15.6-12 of the UFSAR.
b) 100 gpm represents 25% of BEP which has been generally regarded as a conservative design value for low flow operation.
(Ref.
b, Section 6.3.1).
c)
.100 gpm recirculation flow has been shown by calculation to reduce the internal fluid temperature rise through the pump four fold, to a 10'F temperature rise, as compared to 30 gpm.
d)
The operating mo'des wherein 100 gpm would exist would not be expected to exceed 1
hour.
An'nadvertent SI would be terminated prior to this duration.
Accident scenarios are not postulated to occur throughout the life of the plant.
Consequently, accelerated wear due to operation at 100 gpm is not possible.
FIGURE A-2 MODIFICATION SCHEMATI C AS INSTALLED PER ERR 588I 2>>
(f>>
) $
"C", PUMP B" PUMP LO IOO GPM ORIFICE I
I I
I I
I I
I I
I I
"C PUMP r- "B" PUMP
'~ w%- ~<il- ~
I I
I I
I 30 GPM ORIFICE LO TO RV HOT/
COLD LEGS FROM CS FLOW TEST LOOP 9I6 2
I I
I
I t "~
2" f~i TO RWST SI PUMP "A" (TYP.)
LEGEND EXISTING LINE AND EQUIPMENT RETAINED EXISTING LINE AND EQUIPMENT REMOVED NEW LINE AND EQUIPMENT INSTALLED
AUXILIARYFEEDWATER SYSTEM This system consists of three different systems and pump types:
Motor Driven Auxiliary Feedwater (MDAFW); Turbine Driven Auxiliary Feedwater (TDAFW); Standby Auxiliary Feedwater (SBAFW)
Performance Characteristics 2 pumps Model 2 WTF-87 7-stage horizontal-coupled to 1800 rpm A.C. Motor through gear box RPM 4650 Rated Flow 200 gpm PAID 33013-1237 Rated Head 2850 ft.
UFSAR Fig. 10.5-1 S. 10.7-5 Rated Horsepower 250 (motor) Bill of Material, Gilbert, GAI WO 4155 g Item RC 9
Flow at BEP 230 gpm Pump S/N 1614811, 1614812 (Curves E-195763, 4)
Manufacturer Worthington/Dresser Pump. Division Original and current recirculation design Minimum flow line designed for 40 gpm through control valve and orifice Attachment C of ref.
(h) provided a detailed discussion of the current configuration and.
design of the recirculation system.
There were no changes made as a result of Bulletin 88-04.
The recirculation flow through the pump is the combined flow through the minimum flow piping plus the main discharge line to the steam generator.
The MDAFW system is designed and operated so that the, discharge line is always open to provide flow to the steam generator.
Depending on the steam generator pressure, flow through the discharge line to the steam generator is 200 gpm against a
pressure of 1100 psia.
This design value, is based.
upon meeting accident conditions.
The minimum flow line, which has an air operated control valve and pressure breakdown orifice, is designed so that if the discharge line pressure were to increase to minimum flow, the control valve would be fully open as well.
The control valve would be fully closed when the discharge pressure decreases to a
value corresponding to a flow of 125 gpm discharge flow.
This control scheme is to assure that water is not unnecessarily recirculated during conditions when the flowrate into the steam generated is critical.
Since the pump would still "see" a high flowrate (125 gpm),
there is no purpose in recirculating flow for pump protection.
The minimum flow control valve is designed. with a fail open position.
The minimum flow lines for each of two pumps come together in a common 2" header downstream of the pressure breakdown
- orifices, therefore, there is no potential for the parallel flow deadheading concern discussed in Bulletin 88-04.
11
The minimum flow pressure breakdown orifice and piping system is designed to provide 40 gpm (control valve fully open) when the discharge flow is throttled to 80 gpm.
- Hence, a
pump flow of 120 gpm would exist.
This represents 50% of BEP flow. Tf-it,were postulated that the discharge line were closed, the pump flow= has been shown by analysis (ref. s) to be 41 gpm or 17% of BEP.
(The fact that the minimum flow recirculation piping has a substantial pressure drop leads to a recirculation line flow being just slightly higher at shutoff conditions as compared to the 80 gpm discharge flow condition).
Monthly periodic testing is performed at full discharge line flow (200 gpm) and pressure, flow and vibration data are recorded and trended..
Therefore, RGGE is confident that long term wear could. be identified and corrected well before any undue risk of failure of the pump results.
The pump manufacturer's most recent recommendation regarding minimum flow for the pump is 25% of BEP (ref. i).
The original specified value was 53 gpm (23% BEP) in Gilbert Associates Bill of Material.
These are consistent with ref. (b) recommendations also.
During plant startup at low decay heat levels it is necessary to throttle the valves in the discharge flow lines to the steam generators, while continuing to maintain the minimum flow through the recirculation path.
Since the recirculation flow path provides 17'-o of BEP flow to protect the pump, it is preferable to throttle the discharge line to a closed position rather than to continually stop and restart the pump in order to maintain steam generator level.
The startup evolution is conducted infrequently and is of relatively short duration.
The recirculation flow of 17% of BEP flow also limits water temperature rise within the pump to a modest 18 F.
Based on the above, the MDAFW system design is adequate to prevent pump damage due to thermal temperature rise as well as the potential for long term accelerated wear for which the 25%
BEP value given by the manufacturer and discussed in ref.
(b) were specifically provided.
12
TDAFW Perf ormance characteristic one
- pump, Model 3WTL-87 7 stage horizontal coupled, to variable speed turbine driver RPM Turbine driven through govenor set between 4350 and, 4400 rpm Rated Flow 400 gpm P&ID 33013-1237 Rated Head 3000.ft.
9 4675rpm UFSAR Fig. 10.5-1 and 10.7-5 Rated Horsepower 449bhp 9 400 gpm Flow at BEP 450 gpm Pump S/N 1614756 Manufacturer Worthington/Dresser Pump Division Original and recirculation design minimum flow'ine designed for 95 gpm through control valve and orifice Bill of materials, Gilbert Assoc.,
GAI WO 4155, Item RC-6 Attachment C of ref.
(h) provided a detailed discussion of the current configuration and the design of the recirculation system.
There were no changes made as a result of Bulletin 88-04.
The conceptual design and operation of the recirculation system, air-'perated valve, and.pressure breakdown orifice is similar to that of the MDAFW.
The numerical values are different, since the TDAFW pump is rated at a higher flow.
The air operated control valve
'will move to the full open position when the discharge line flow is decreased to 100 gpm.
(The control valve is controlled by flow in the discharge line whereas the MDAFW valves are controlled by discharge line pressure).
- Thus, the pump flow is about 190 gp'm, 100 through the discharge and about 90 gpm through the minimum flow line (ref.
v).
This represents over 42%
of BEP and is substantially higher than that recommended by the manufacturer, ref. (i).
The value of 25%
BEP flow is based on long term operation to reduce the potential for accelerated wear.
As is the case with the MDAFW pumps, there are no modes of operation which subject this equipment to long term operation at. reduced flows.
'ince there is only one pump in the 'system, the parallel pump operation concern is not applicable.
In the event that the discharge line were closed with the pump operating, the minimum flow would be 94 gpm (ref.
s).
This condition is beyond the design, operating, and accident modes.
The minimum flow would represent a value of 21% of BEP, in this case, but for the short time that such a condition could be reasonably assumed to exist the flowrate is acceptable based on it being close to 25% and demonstrated acceptability of test results during the 48 hour5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br /> endurance test conducted in 1981.
[See ref. (b) of Attachment Cto ref. (h)].
13
i
SBAFW Performance characteristics 2 pumps Model 2HMTA9 9-stage horizontal - coupled. to A.C. motor RPM 3560 Rated Flow 200 gpm P&ID 33013-1238 Rated Head 3000 ft.
UFSAR Fig. 10.5-2 Rated Horsepower 300 HP Flow at BEP 450 gpm Pump S/N 0275156, 0275157 (Curve N-775)
Manufacturer Ingersoll Rand Original and Current recirculation design minimum flow line designed for 40 gpm through control valv'e and orifice Bill of Material Gilbert Assoc.,
GAI WO 044594-011, order N-GAI-55190 Attachment C of ref.
(h) provided.
a detailed discussion of the current configuration-and the design of the recirculation system.
There were no changes made as a result of Bulletin 88-04.
A recirculation
- line, air-operated control
- valve, and pressure breakdown orifice is provided for each pump.
The lines come together into one common header downstream of the orifices leading back to a 10,000 gal. test tank.
Therefore, the parallel pump operation concern raised in the bulletin does not exist, due to the de-sensitization of any strong weak pump interaction.
Similar to the main motor driven auxiliary feedwater
- system, the air-operated control valves are configured so that they will be full open when the discharge line flow to the steam generator is 80 gpm.
The minimum flow line is,designed to provide 40 gpm under this condition.
- Hence, the pump flow would be 120 gpm or 27% of BEP.
The pump manufacturers recommendation (ref. t) was 40 gpm to prevent heating of the fluid during operation.
Per'iodic testing (PT-16Q) conducted on the pumps must show that with a discharge flow of 50 gpm, the control valve must be in the full open position.
Periodic tests are conducted. quarterly and are of short duration.
By procedure the flow allowed could be as low as 90 gpm (20% of BEP).
Therefore, there is no concern over long term accelerated wear in the test
- mode, because the cumulative operating hours are very low.
Stable peration at low flow conditions was also demonstrated during a 48 hour5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br /> endurance test
[ref. (c) of Attachment C to ref. (h)].
The standby AFW pumps would only be operated as a backup if the main motor driven or turbine driven AFW pumps were inoperable.
The standby pumps are operated manually and have no automatic actuation.
It is unlikely that the discharge lines to the steam generators would ever be closed inadvertently when the pumps were called upon (discharge valves are normally open).
Therefore, there are no known modes of operation, testing or accident conditions which would allow operation at
-low flows below 90 gpm (when utilizing the flow value established in PT-16Q procedure) for other than short period 'of time.
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