A07218, Responds to NRC Bulletin 88-004, Potential Safety-Related Pump Loss. Data Collected to Date Continues to Support Conclusions Included in Util Stating That Problems Do Not Exist at Plants
| ML20246K025 | |
| Person / Time | |
|---|---|
| Site: | Millstone, Haddam Neck, 05000000 |
| Issue date: | 05/03/1989 |
| From: | Mroczka E, Sears C CONNECTICUT YANKEE ATOMIC POWER CO., NORTHEAST NUCLEAR ENERGY CO., NORTHEAST UTILITIES |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| A07218, A7218, IEB-88-004, IEB-88-040, IEB-88-4, IEB-88-40, NUDOCS 8905170229 | |
| Download: ML20246K025 (27) | |
Text
__
4 F MOdflW.ASTUTILITIES T*4 COseNEC7lctif Ls0Hf .ND.ovesM Cow.ssv con , i Omc.. . s io n si,.. . B.,iin. Connect,cui i
l m'em ass.c.usem saciac c ""
P.O. BOX 270 k k 7,C',',',*,,7,"Ec[, HARTFORD, CONNECTICUT 06141-0270 J .,0.,w.n .,uca . co e, (203) 665-5000 May 3, 1989 Docket Nos. 50-213 50-245 50-336 50-423 A07218 Re: NRC Bulletin 88-04 U.S. Nuclear Regulatory Commission Attention: Document Control Desk Washington, DC 20555
References:
(1) C. E. Rossi Letter to Licensees, dated May 5, 1988, Transmitting NRC Bulletin 88-04, " Potential Safety Related Pump Loss."
(2) E. J. Mroczka Letter to USNRC, dated June 30, 1988, Response to NRC Bulletin 88-04, " Potential Safety Related Pump Loss."
(3) E. J. Mroczka Letter to USNRC, dated January 10, 1989, Response to NRC Bulletin 88-04, " Potential Safety Related Pump Loss."
Gentlemen:
Haddam Neck Plant Millstone Nuclear Power Station, Unit Nos. 1, 2, and 3 Response to NRC Bulletin 88-04,
" Potential Safety-Related Pump Loss" Reference (1) requested licensees to evaluate safety-related centrifugal pumps to ensure that pump damage will not occur during norttal or emergency operation at or near shutoff head with inadequately designed minimum flow lines. References (2) ar.d (3) reported the status of our investigation into the concerns of Reference (1). The purpore of this letter is to update the NRC Staff on the status of the ongoing analyses. {
l 4 .
1
~Z6fl l
l 8905170229 890503 ADOCK 05000213 ffi PDR l
7 4
t
. U.S. Nuclear Regulatory Commission.
4 8 ' A07218/Page 2 May 3, 1989 Data collected to date continues to support the conclusions included in Reference (3) that these problems do not exist at the Haddam Neck plant or Millstone plants. However, vendor contact has not yielded conclusive results.
Therefore, our emphasis has shifted to evaluations of pump performance and maintenance histories. Attachments 2 and 3 to Reference (3) provided preliminary evaluations. Attachments 1 and 2 to this letter provide a reiteration of those evaluations with additional evaluations performed since Reference (3) was issued. Completion of those evaluations is still expected by June 30, 1989, as stated in Reference (3).
During accident conditions, some of the subject pumps may be run at minimum flow for some time. However, the time during which operators vould leave unneeded pumps running is limited and is not expected to exceed one hour. Based on the evaluation of actual operation at minimum flow, no degradation of pump performance is expected, even if this one hour period vere exceeded.
If there are any questions, please do not hesitate to contact us.
Very truly yours, l
CONNECTICUT YANKEE ATOMIC POWER COMPANY NORTHEAST NUCLEA.' ENERGY COMPANY E.h.6 4 w
E. J. Mroczka Senior Vice President b <~LILA/2 - ._
i By: C. F. Sears Vice President cc: W. T. Russell, Region I Administrator M. J. Boyle, NRC Project Manager, Millstone Unit No.1 G. S. Vissing, NRC Project Manager, Millstone Unit No. 2 D. H. Jaffe, NRC Project Manager, Millstone Unit No. 3 A. B. Vang, NRC Project Manager, Haddam Neck Plant W. J. Raymond, Senior Resident Inspector, Millstone Unit Nos. 1, 2, !
and 3 J. T. Shediosky, Senior Resident Inspector, Haddam Neck Plant a
w U.S. Nuclear Regulatory Commission
' t A07218/Page 3 i Hay 3, 1989 STATE OF CONNECTICUT )
) ss. Berlin COUNTY OF HARTFORD )
Then personally appeared before me, C. F. Sears, who being duly svorn, did state that he is Vice President of Northeast Nuclear Energy Company and Connecticut Yankee Atomic Power Company, Licensees herein, that he is i
authorized to execute and file the foregoing information in the name and I on behalf of the Licensees herein, and that the statements contained in said information are true and cort act to the best of his knowledge and belief.
(WPublic bNotary O. hM '
%Commbsion Expires March 31,1992
r 6
a , :
Docket Nos. 50-213 50-245 50-336 50-423 A07218 ATTACHMENT 1 HADDAM NECK PLANT MILLSTONE NUCLEAP POVER STATION, UNIT NOS. 1, 2, AND 3 NRC BULLETIN 88-04, " POTENTIAL SAFETY RELATED PUMP LOSS" CUMULATIVE PUMP OPERATING TIME AT HIN-FLOV, MAINTENANCE HISTORY, AND ASSESSMENT OF POTENTIAL DAMAGE i
I i
MAY 1989 l
i U.S. Nuclear Regulatory Commission l
" A07218/Page 1 May 3, 1989
- 1RC t1ULLETIN 83-04 q CUMULATIVE PUMP OPERATING TIME AT MIN-FLOV MAINTENANCE HISTORY AND AC,SESSMENT OF POTENTIAL DAMAGE
GENERAL COMMENT
S Centrifugal pumps are started against isolated discharge piping to prevent the possibility of runout and cavitation. Therefore, centrifugal I pumps are limited to min-flow until their discharge paths are opened at each start-up. The estimation of cumulative pump operating time at min-flow is done primarily by estimating the number of times a pump is started in a given time period and how long it operates at minimum flow during each start. Since mini-flow operation has not been limited by pump manufacturers, total time at shut-off/ min-flow operation has not been restricted or logged for each pump start-up. The start frequencies were estimated by taking into consideration increased operation as a result of inservice testing requirements and tank charging as well as normal surveillance testing. These estimations are provided for each pump.
A pump's maintenance history can give an indication of the occurrence of damage due to cumulative operating time at shut-off/ min-flow. This mode of pump operation generally results in higher operating temperatures and increased vibration. High temperature and vibration can produce the following types of pump damages o Vear or scoring of wear rings.
o Premature wear in bearings.
o Erosion of impellers or pump casings.
o Accelerated packing or seal deterioration, vear, or failure, o Blackening of lubricating oils due to the production of carbon particles.
o Crack formation at mounting lugs.
o Degradation of mounting pedestals.
If maintenance records indicate that these types of problems are occurring on a regular basis, it can be assumed that there may be a min-flow related problem in the affected pump. If there is no history of these types of problems, it can be tecsanably a.psured thNt operations at the provided min-flow r.ra not produtiny; measurable damage. Normal mainienanca is no2cted to correct or limit 3.ny dauge accumulation due to n In-flov '.n the l at ter cat,e.
(
. U.S. Nuclear Regulatory Commission
[ f " A07218/Page 2 May 3, 1989 Millstone Unit No. 1 Estimated Cumulative Operating Time (at min-flev since start of commercial operations in 12/70):
o 28 hours3.240741e-4 days <br />0.00778 hours <br />4.62963e-5 weeks <br />1.0654e-5 months <br /> for the most used low pressure coolant injection pump (based on 648 starts in 18 years, 2.6 minutes at min-flow start).
o 9.4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br /> for each core spray pump (based on 216 starts in 18 years, 2.6 minutes at min-flow per start).
o 9 hours1.041667e-4 days <br />0.0025 hours <br />1.488095e-5 weeks <br />3.4245e-6 months <br /> for each shutdown cooling (SC) pump (based on an estimated 36 min-flow tests in 18 years, 15 minutes at min-flow / test).
Maintenance History (only nonroutine maintenance, or maintenance that could be attributed to min-flow damage is listed here):
Lov pressure coolant injection (LPCI) pumps (Note: All LPCI pumps had their supports upgraded in 7/87).
M8-75A o Sediment in oil on 4/21/86.
o Disassembled, inspected, and overhauled in 1980, due to site engineering recommendation based on inservice Testing (IST) vibration data.
o This pump is the most frequently used pump. Its vibration has been increasing, although this increase has been small and has remained acceptable. It is judged to be from normal wear and other nonminimum-flow related phenomena.
M8-75B o Sediment in oil on 4/21/86.
M8-75C o Leaking cartridge seal in 7/88; checked motor bearing end play at the same time--nothing unusual recorded with work order.
M8-75D o In 11/77, the pump was disassembled, inspected, and overhauled when its discharge pressure dropped significantly. An eyebolt was found to be interfering with the pump's rotating parts.
7
. U.S. Nuclear Regulatory Commission A07218/Page 3 May 3, 1989 o In 10/87, the pump started to approach its vibration IST limits. Rebalancing dropped vibration back into an acceptable range.
o In 8/88, the shaft cartridge seal leaked after a period of use for torus cooling, then it stopped leaking. The seal was ;
repositioned and the coupling was realigned.
Core spray (CS) pumps (Note: Both CS pumps had their supports upgraded .
in 7/87). l H8-74A o This pump has a history of lubricating oil leaks. (The pump is water lubricated. The motor bearings are oil lubricated.)
M8-74B o This pump has a history of bearing cooling water to bearing lubricating oil leakage. Occurrences of this leakage vere noted in 1982, 1985, 1986, and 1988. This pump also shows a history of increasing vibration. This increase is small and acceptable. It is judged to be from normal wear and other nonminimum-flow related phenomena.
Shutdown Cooling Pumps M8-53A o An oil leak at the pump vas repaired on 4/7/81.
o A deteriorating pump / motor coupling was repaired on 1/14/86; both were loosening. Some damaged gasket material was replaced.
o The coupling was disassembled and inspected on 8/27/86, due to i
^
excessive grease leakage. It was noted that the wrong parts vere installed. The correct parts were re-installed at this time, o The pump vas overhauled and inspected in February 1987.
Previous coupling problems and vibrations appear to be the motivations for this inspection. llany new pat tr veic installed. No damage or wear was noted.
HB-53B o Pump was overhauled in November 1982.
o Re-tightened coupling bolts (1/14/86).
~*
. U.S. Nuclear Regulatory Commission
- A07218/Page 4..
May 3, 1989 o Removed and inspected motor / pump coupling on 8/27/86 due to excessive grease leakage. Re-installed the correct parts at this time after it was r.oted that parts with incorrect numbers
. vere being used<
o Disassembled.and inspected pump on 8/29/86. Pump was found to be in satisfactory condition. It is believed the overhaul was ,
performed to verify that the use of the wrong coupling did not i damage the pump. j i
Assessment of Potential Damage j There'are no clearcut indications that the pumps are being damaged due to l operation at min-flow or inadequate min-flow.'
.i The overhauls of the LPCI pumps performed in 1978 and 1980 did not reveal any of the following indications of min-flov' induced wear: J o Scoring of vear rings.
o Premature shaft sleeve or bearing deterioration.
I o Flow induced erosion on the impeller or pump case. i o Crack' formation at mounting points.
The following potential symptoms of min-flow induced damage have been evaluated:
o Mechanical cartridge seal failures on the "C" and "D" LPCI i pumps - one failure per pump, during.18 years of service.. This is not considered conclusive evidence of min-flow damage.
o Sediment in lubricating oil--this is not considered symptomatic of min-flow damage because it is occurring on the oil lubricated motor end of these vertical pumps. The pumps are water-lubricated. Overheating at min-flow would occur at the pump, not at the motor bearings.
o Degradation of the mounting pedestals--this problem may be due to vibration, which has been increasing on the most used, "A" LPCI pump and the "B" CS pump. However, this vibration may be due to transmission of vibration from downstream piping back to the pump, manual readjustments to the balancing (e.g., "D" LPCI l
l
, U.S. Nuclear Regulatory Commission f
- A07218/Page 5-May 3, 1989 in 1997), or improper mounting. (Stud embedment problems, aggravated by a cantilevered mounting design. Note that the mountings were modified in 7/87 to correct this problem .) i l The cartridge seal, bearing oil / vater contamination, and increased vibration discussed above could be indications of impeller recirculation at min-flow. If impeller recirculation is severe enough to induce vibration, it could produce seal and bearing cooling related damage.
However, these results could be random, or due to other vibratory modes not associated with min-flow (e.g., vibrating piping driving the pump into a damaging vibratory mode).- The most frequently used LPCI pump (the "A" pump) experiences the most vibration. The "D" LPCI pump has also had problems (vibration and otherwise). This could be the result of the 1977 incident in which an eyebolt was found to be interfering with operation
'of the pump.
The shutdown cooling pump maintenance history outlined above does not give any indications of persistent min-flow related problems.
In summary, it can be stated that there is no pattern of min-flow related pump demage in the unit's pumps after 18 years of operation. If pump vibration increases, a pump overhaul vill be considered. Therefore, it is concluded that inservice testing of :ach of these pumps on a monthly basis vill provide a means of identifying and correcting min-flow related damage before it can significantly degrade the availability or performance of these pumps.
Hillstone Unit No. 2 Estimated Cumulative Operating Time (at min-flow since start of commercial operations 12/75):
o All of the Millstone Unit No. 2 ECCS pumps discussed in this section are estimated to have the same cumulative operating time at min-flow: 50 hours5.787037e-4 days <br />0.0139 hours <br />8.267196e-5 weeks <br />1.9025e-5 months <br />.
o The cumulative times for these pumps are the same because they receive the same inservice tests on the same test schedule. This testing has resulted in approximately 174 min-flow tests, with an average duration at min-flov of 20 minutes per test, in 13 years of commercial operation.
1.' For ' additional details, see E. C. Venzinger let ter to E. J. Mroczka, " Routine-Inspection 50-245/87-12 (6/23/87 - 8/10/87)," dated August 24, 1987.
l
__ j
- U.S. Nuclear Regulatory Commission A07218/Page 6 May 3, 1989 o The motor driven auxiliary feed water pumps have an as yet undetermined time at min-flow due to steam generator filling during start-up and shutdown.
Maintenance History (only non-routine maintenance, or maintenance that could be attributed to min-flow damage is listed here) l High Pressure Safety Injection Pumps P-41A o Pump overhaul in 8/76; machining of pump internals was done at this time.
o There are several notations of the need for motor oil between 1976 and 1979, o An outboard thrust bearing was replaced in 7/78.
o The pump seized on 6/18/84, due to improper reassembly after overhaul. The pump was overhauled due to failure as a result of operation with min-flow inadvertently isolated.
l 1
o One instance of boric acid leakage at both ends of the pump shaft was reported on 9/26/87; repair was limited to cleanup.
P-41B l o Several instances of lube oil refill reported in 1979.
o Leaks and boron buildup on suction flanges; corrective action limited to cleaning (10/5/87).
P-41C o Outboard pump thrust bearing failed and replaced (3/11/88).
Low Pressure Safety Injection Pumps P-42A o Repaired pump seal (3/76).
c Impeller nut fell off; pump disassembled to repair (10/16/86).
l i
1 l
l 1
l
T l
e i e
U.S. Nuclear Regulatory Commission 1
.' A07218/Page 7 {
Hay 3, 1989 P-42B o Leaks at casing seam and boron buildup; special gaskets ordered i (10/27/87).
Containment Spray Pumps P-43A i o Nothing of significance to this bulletin was identified.
P-43B o Abrasive pump sound during 8/09/85 shutdown led to pump disassembly; pump bearings and seals were replaced.
Auxiliary Feed Pump (Turbine Driven; P-4) o Required bearing oil in 1976.
o Inboard pump packing leak was observed during operation (repaired on 4/25/83).
Auxiliary Feed Pumps (Motor Driven)
P-9A o Replaced pump shaft (3/11/78; P-9B's shaft was replaced at same time).
o Repacked pump seals to stop leakage (2/22/80).
o Water in outboard bearing compartment (10/10/85 and 12/5/85).
o Shaft seal leak on 11/09/85.
o Removed and overhauled on normal preventive maintenance schedule on 11/01/86.
P-9B o Replaced thrust bearing (7/77).
o Replaced pump shaft (3/11/78); P-9A was replaced at the same time.
o Installed new packing to stop leakage (3/23/80).
o Adjusted packing to stop leakage (1/11/83 and 12/29/83).
. U.S. Nuclear Regulatory Commission A07218/Page 8 May 3, 1989 o Repacked seals (inboard and outboard '/4/84).
o Seal leakage between pump and motor (6/18/84); tightened packing.
Assessment of Potential Damage There are no clear-cut indications that the pumps listed above are being damaged due to operation at min-flow or inadcquate min-flow.
The high pressure safety injection (HPSI) pumps did have a significant amount of internal modification in the first year of operation (1975-1976). This work was primarily due to re-machining of ths balancing druw and sleeve to achieve proper shaft thrust balance. Some thrust bearing replacements are also reported in this time period, which is to be expected if shaft thrust balancing is not correct. The incidence of thrust bearing replacement has gone down significantly since completion of this early hydraulic balancing effort (i.e., the "A" HPSI pump had a thrust bearing replacement in 1978; the "C" hPSI pump had a bearing replacement in 1988).
The thrust balancing achieved by properly sizing the balancing drum and sleeve of pumps like the HPSI pumps is achieved by building an internal min-flov into the pump. The space between the balance drum and sleeve provides a leakage path from the pump discharge chamber to the pump suction chamber (i.e., en internal recirculation / min-flow path). The early modifications to the HPSI pumps were additions of min-flow to that provided externally by the orificed min-flow lines.
The few incidents of flange leakage, shaft seal leakage and motor oil addition reported for the three HPSI pumps in their 13 years of operation are considered routine and insignificant.
The low pressure safety injection (LPSI), containment spray (CS) and turbine driven auxiliary feed (AP) pumps do not show any consistent patterns of maintenance that are symptomatic of min-flow induced damage.
The few occurrences of leakage or overhaul appear to be random.
Consequently, they are concluded to be of no significance to min-flow evaluations.
The maintenance histories of the two motot driven AF pumps does indicate that seal leakage repairs are required sporadically. Since the frequency of these repairs varies from six months (1/4/84 to 6/18/84 tor P-9B) to five years (2/22/80 to 11/9/85 for P-9A), it is not considered to be evidence of a min-flow related problem.
Both motor driven AF pumps had their shafts replaced in 1978. Pump shaft replacement would not generally be associated with min-flow related problems unless seal or bearing problems due to inadequate min-flow resulted in shaft scoring, varping, etc. There is no evidence of bearing 1
a U.S. Nuclear Regulatory Commission
/ ' A07218/Page 9 May 3, 1989 or' seal problems before these shaft replacer.ents. Also, these one time replacements have been followed by 10 years of trouble free operation.
Therefore, this shaft replacement is considered to be of no significance to min-flov evaluations for these pumps.
In summary, it can be stated that there are no patterns of min-flow related pump dan, age in 13 years of maintenance history. The frequent inservice testing (IST) the subject pumps receive vill lead to identification and correction of any min-flow related problems.before l
they can result in significant damage.
L Millstone Unit No. 3 Estimated Cumulative Operating Time (at min-flow since start of periodic
-testing in 11/85; commercial operations began in 4/86):
o 6.5 hours5.787037e-5 days <br />0.00139 hours <br />8.267196e-6 weeks <br />1.9025e-6 months <br /> for the most tested charging pump (based on 13 min-flow tests at 30 minutes per test).
l o 4.7 hours8.101852e-5 days <br />0.00194 hours <br />1.157407e-5 weeks <br />2.6635e-6 months <br /> for either high pressure safety injection pump (based on 14 min-flow tests at 20 minutes per test).
l 1
o 15 hours1.736111e-4 days <br />0.00417 hours <br />2.480159e-5 weeks <br />5.7075e-6 months <br /> for the most tested residual heat removal pump (based on 15 min-flow tests at one hour per test),
o 9.75 hours8.680556e-4 days <br />0.0208 hours <br />1.240079e-4 weeks <br />2.85375e-5 months <br /> for the motor driven auxiliary feed pumps (based on 39 min-flov tests at 15 minutes per test). The motor driven auxiliary feed pumps are run at shut-off/ min-flow for extended periods during steam generator filling. Cumulative time at min-flow due to this operational evolution has not been determined.
o 39 hours4.513889e-4 days <br />0.0108 hours <br />6.448413e-5 weeks <br />1.48395e-5 months <br /> for the turbine driven auxiliary feed pump (based on 39 min-flow tests at I hour per test).
Maintenance History (only nonroutine maintenance er maintenance that could be attributed to min-flow damage is listed here):
Charging Pumps 3CHS*P3A o Nothing significant to the subject bulletin was found.
3CHS*P3B o Motor bearing oil became dirty during a two-hour run; this run was during start-up of the plant (i.e., precommercial operations; date was 12/3/84).
- U.S. Nuclear Regulatory Commission .
A07218/Page 10 May 3, 1989 3CilS*P3C o Pump siezed during operation with suction valve shut (5/17/88);
pump was replaced.
Safety Injection Pumps 3 Sill
- PIA o Vater leaks at suction flange and casing joints during start-up program; also dirty motor oil (1/21/85).
o Mechanical seal leakage (on shaft of pump) recorded on 7/15/88; seal replaced on 8/29/88.
3S1H*PIB o Hechanical shaft seal leakage reported on 8/29/88; no work perforr.ad at this time.
Residual heat Removal Pumps 3RilS* PIA o Vater contamination of motor bearing oil noted during plant start-up program (3/26/85); miscellaneous small oil leaks during start-up.
3RilS*PIB o Vater contamination of motor bearing oil noted during plant start-up program (3/26/85).
Auxiliary Feed Motor Driven Pumps 3FVA*P1A o No significant maintenance entries were found.
3FVA*P1B o The motor tripped for an unknown reason at startup (1/29/87).
Electric checkout of motor and mechanical cheel out of the pump did not disclose any problems. Pump performed normally after this faulty start and checks.
1 1
I l
l l
_ _ _ _ _ _ _ _ _ - - _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ - __ -.-__- .- - _J
> U.S. Nuclear Regulatory Commission {
/ '
A07218/Page 11 May 3, 1989 Auxiliary Feed Turbine Driven Pump 3FWA*P2 k
o Nothing of significance to Bulletin 88-04 was discovered in maintenance history. ,
1 Assessment of Potential Damage There are no ir.dications that the pumps are being damaged due to operation at min-flow.
None of the charging pump maintenance discussed above is indicative of excessive pump vibration or overheating.
The water leakage and dirty motor bearing oil reported during start-up for the safety injection pumps are considered to be normal occurrences related to installation and initial testing. The incidents of mechanical shaf t seal leakage reported for both safety injection pumps may have significance. More operating / maintenance history is necessary before any association of this seal leakage with min-flow can be made.
The residual heat removal pump maintenance provided above is not considered to be related to pump operation at min-flow.
I Nothing indicative of problems at min-flow was found in the maintenance histories of the auxiliary feed pumps.
In summary, it can be stated that there are no patterns of min-flow related pump damage at Millstone Unit No. 3 after approximately three years of commercial operation. It is also concluded that inservice testing of these pumps will identify and lead to correction of min-flow related damage, if it should occur, before it can significantly degrade pump performance and availability.
Haddam Neck Plant Estimated Cumulative Operating Time (at min-flow since start of commercial operations in 1/68) remains to be determined.
Maintenance history (only non-routine maintenance that could be attributed to min-flow damage is listed here):
, Auxiliary Feed Pumps P-32-1A o Pump was disassembled and inspected for damage after unexplained debris was found in a pump discharge check valve.
No significant damage (6/3/80).
i
- _ _ _ _ _ - _ _ - _ _ _ _ _ _ _ _ _ - _ _ _ _ _ -. - _ __A
- U.S. Nuclear Regulatory Commission A07218/Page 12 May 3, 1989 o Pump overhauled (10/28/87) due to high vibration (in the alert range),
o Seal leakage was found and repaired (3/14/88).
o Pump disassembled and overhauled due to binding (5/23/88).
l o- Add!tional vibration testing performed to identify the source of vibration in the alert range (6/9/88).
o Coupling alignment is suspected as the source of excessive vibration. Coupling re-alignment performed on 7/11/88.
o Vibration is still a problem on 8/11/88. Coupling re-alignment is performed again. A thrust bearing is replaced.
o Vibration is found to be in the action range (9/9/88).
Dimension checks on coupling are performed. Coupling key is moved 90' from its original location as a possible cure. No further vibration problems have been encountered.
P-32-1B o Repacked a water supply seal on bottom of pump to stop leakage (2/4/76).
o Pump is disassembled to check for possible debris damage after unexplained debris is found in a discharge check valve (6/3/80). No damage was found.
o Replaced shaft cartridge seal and a thrust bearing (11/7/81).
o Replaced shaft packing, sleeve, and bearing on 1/31/83.
o Dark oil reported on both ends of pump. Oil is changed (12/22/87).
o Adjusted packing to stop a shaf t leak (3/14/88).
Charging Pumps P-18-1A o A pump seal was removed, inspected, and reinstalled with a new 0-ring; probably due to leakage (1/26/76).
- - _ _ - _ _ _ _ _ _ - _ _ _ _ _ _ _ _ _ _ _ _ _ - _ _ -_ _ __ _____ ___ - _-____ _ _____ _ _ _ _ _ _ _ - _ = _ _ - _ _ _ _ _ _ _ _ _ - _ _ _ _ _ _ _ _ _ _ _ _ _ - _ -
~.
- U.S. Nuclear Regulatory Commission
, A07218/Page 13 May 3, 1989 o Pump was replaced in the summer of 1984. Objective was to get a new pump in place with a modified rotating assembly. This modification was made to eliminate stress concentrations that vere leading to shaft failures.
o Pump shaft broke (5/22/85). Rotating assembly replaced at this time.
o Found brass chips in motor bearing oil, esp. at coupling end (1/18/86),
o Shaft breaks again on 7/9/86. Replaced with a reworked impeller at this time.
o Noisy recirculation leads to measurement of min-flow (3/12/87).
High-pitched noise observed at 102 gpin. Noise vent away when orifice bypass throttle valve adjusted to produce 109 gpm total min-flow.
o Found debris in lube oil filter (8/28/87). Identified as gasket material and possibly some babbitt material. Gasket material replaced; oil changed.
o Shaft breaks again (8/8/88). Pump disassembled and shaft is replaced.
P-18-1B o Pump motor bearing replaced on 6/16/75.
c Replaced pump shaft on 1/10/83; seems to be the result of three IST reports.
o Install new shaft cartridge seal, shaft housing sleeve (for seal), and locking collar (10/17/83).
o Replaced outboard seal (7/10/80).
o Motor bearing failure. Pump noise also reported. Start circuitry modifications and electrical tests seem to have been initiated because of this failure. A new motor was installed on 10/24/84.
o Miscellaneous minor oil leaks (usually at sight glasses) reported from 1984 - present.
l
. U.S. Nuclear' Regulatory Commission
,' - A07218/Page 14 l May 3, 1989 High Pressure Safety Injection (HPSI) Pumps P-15-1A l
o overhauled pump (5/25/73).
. o Misalignment of booster pump to this HPSI pump vas producing an abnormal axial load. Problem was corrected (9/11/84).
o Vibration and temperature readings checked with pump at min-flow (3/3/87). No problems reported.
o Boric acid buildup on seal housing was found and cleaned up (4/14/88). A seal bolt was tightened to correct the problem.
o Periodic problems with hold down bolt tightness on booster pump end.
P-15-1B o Overhauled pump (3/12/73).
o Repaired seal vater leaks (6/5/81).
o Problems with loose hold-down bolts reported several times.
o Vibration and temperature readings taken with pump at min-flov (3/3/87). No problems reported.
o Vibration in the alert range recorded (9/6/88). Corrective action was the tightening of loose hold-down bolts.
Low Pressure Safety Injection (LPSI) Pumps P-92-iA o checked vibration during monthly ECCS IST (10/7/88). No problems recor6ed in work order history.
P-92-1B o Checked vibration daring monthly ECCS IST (10/7/88). No problems recorded in work order history.
Residual Heat Removal (RHR) Pumps P-14-1A o Replaced Icaky gland ceal (8/9/84). Rebuilt pump in the process of making this repair.
l ,. ,
' U.S. Nuclear Regulatory Commission ,
I A07218/Page 15 l May 3, 1989 j l o Pump is found to be ,nissing alignment jacking bolts and brackets (9/10/87). These are fabricated and installed at this time.
o Repaired leaking fittings on gland seal cooler (12/23/87).
P-14-1B o High seal water temperature (3/5/81).
o Black pump motor bearing oil reported during scheduled preventative maintenance (1/5/87). Oil drained and replaced.
o Pump is found to be missing alignment jacking bolts and brackets (9/10/82). These are fabricated and installed at this j time. 1 Assessment of Potential Damage Auxiliary Feed Pumps These pumps demonstrate a history of maintenance that could be attributable to cunulative damage occurring at min-flow. For examples l o The P-32-1A pump has experienced vibration, binding, and seal leakage since June 1980, o The P-32-1B pump has experienced darkened oil and frequent shaft seal replacements since June of 1980.
The key factor in this history seems to be the overhauls that both pumps received in 1980. These overhauls were performed to look for damage when debris was discovered downstream of the pumps in a discharge check valve.
There is no evidence that debris damage was found.
There is evidence that vibration problems developed in P-32-1A from pump to motor coupling misalignment after the 1980 overhaul. The coupling changes made in September of 1988 should cure any persistent alignment problems and their resultant vibration.
The blackening of pump bearing oil reported for P-32-1B may not be attributable to pump heatop at min-flow. The bearings on Vorthington model #3VTF pumps are supported away from the impeller tetaining section of the pump casing. Therefore, they vill not be heated directly by water churning at min-flow. The bearing heating that darkened the oil of P-32-1B in December of 1987 could be due to incorrect bearing preloeding, 1 cyclic bearing loading due to coupling misalignment, or bearing loading due to inadequate radial shaft support on the thrust bearing end of the
)
. U.S. Nuclear Regulatory Commission
.' A07218/Page 16 May 3, 1989 pump (i.e., one end of pump is supported on a sleeve and a thrust bearing). These types of problems could also explain the frequent recurrence of shaft seal leakage on P-32-1B.
Charging Pumps
! The charging pumps do not show any history of maintenance attributable to l inadequate min-flow. This is logical considering that the charging pumps are provided with min-flows that are greater than 28 percent of rated design flow (note the maintenance entry that min-flov whine occurs when min-flows are set belov 109 gpm).
The dominant failure mode reported for the charging pumps is shaft failure. This type of failure is not generally attributable to inadequate min-flow. Shaft failures explain some of the other maintenance reported for the P-18-1A and P-18-1B pumps.
The P-18-1B pitmp has demonstrated a history of motor problems. It is believed that one of the motor bearing failures reported for this pump is a random failure, while the second is attributed to a motor start circuitry problem.
The outboard shaft seal failure reported for P-18-1B in July of 1980 is considered to be a random occurrence.
In summary, there is no evidence of inadequate min-flow in the charging pump maintenance history.
HPSI Pumps It appears that vibration in these pumps tends to loosen their hold down bolts. The vibration that is being experienced is primarily due to periods of operation at min-flow. This could be a manifestation of a min-flow related problem, or it could be a manifestation of a putap i mounting problem. The latter seems more consistent with the maintenance entries reported. Vibration appears to start out in an acceptable range after pump overhaul. It increases as hold down bolts loosen. If I min-flow vas the cause of excessive vibration, it would be evident j immediately after overhaul and consistently throughout the years. i The other maintenance items entered for these pumps are considered to be !
random and normal (i.e., not significant indicators with respect to NRC Bulletin 88-04).
In summary, the maintenance histories of the HPSI pumps do not indicate the presence of min-flow problems. Pump vibration test history will be important in assessing the adequacy of min-flow. j
)
i
_ _ - - _ _ _ _ _ _. _ _ _ _ -- J
, , ' U.S. Nuclear Regulatory Commission A07218/Page 17 Hay 3, 1989 LPSI Pur.ps There is no evidence of min-flov related problems in the LPSI pump maintenance histories.
RHR Pumps There is very little in the maint-enance history of the the RHR pumps that can be associated with problems at min-flow. The "A" pump has two occurrences of gland seal repairs (in 1984 and 1987). The "B" pump has one occurrence of blackened motor hearing oil. This was attributed to improper throttling of cooling water flow during a special test.
The two gland seal maintenance entries are considered insignificant in 21 years of operating history.
In summary, the maintenance history for the CY RHR pumps does not show evidence of inadequate min-flow.
Conclusions There are no patterns of min-flow related damage in the charging, LPSI and RHR pump mair.tenancc histories.
There are some patterns in the maintenance histories for the auxiliary feed and HPSI pumps that could be attributed to inadequate min-flow.
However,, there are other tactors which could be leading to maintenance.
Therefore, it can be stated that there are no clearcut indications of min-flow related problems in the auxiliary feed and HPSI pumps.
J
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ - _ _ _ _ _ _ _ _ _ _ J
o 1
. . i Docket Nos. 50-213 l- 50-245 50-336 50-423 A07218 ATTACHMENT 2 j HADDAM NECK PLANT MILLSTONE NUCLEAR POWER STATION, UNIT NOS. 1, 2, AND 3 NRC BULLETIN 88-04, "P0TENTIAL SAFETY RELATED PUMP LOSS" ASSESSMENT OF PUMP SECTION XI TEST HISTORY MAY 1489
e U.S. Nuclear Regulatory Commission A07219/Page 1 Hey 3, 1989 Millstone Unit 1 Core Spray (CS) and Low Pressure Coolant Injection Pumps In general, there has been no significant change in the discharge pressure and flow of the LPCI and CS pumps in 18 years of periodic testing. The "D" LPCI pump has shown a slight increase in 6P (Attributable to a decrease in dynamic suction pressure). This is I explained by instrumentation accuracy (12 percent) and readability, I rather than a change in pump performance. 1 Vibration data for the LPCI and CS pumps is ulthin inse vice testing standards. However, the vibration of the "A" LPCI and "B" CS pumps (i.e., velocity in inches /second) has been increasing. This upward trend is presently believed to be due to the following, nonminimum flow related factors:
o Flow-induced vibration in piping downstream of the pumps could be transmitted back to the pumps. Changes in this piping vibration increase pump vibration.
o Improper mounting stud embedment and pump grouting deterioration may l have caused the "A" LPCI and "B" CS pumps to gradually go out of balance. (Note: mounting modifications for all LPCI and CS pumps were completed in 1987).
o The "A" LPCI pump seems to be the most used of all of the subject pumps. Its increased usage is leading to a gradual increase in i imbalance or bearing wear.
o A pump that is balanced for smooth operation at rated flow will vibrate differently at min-flow. This is more of a reflection of vibratory harmonics that occur when the pump is operated off of its peak efficiency point than it is of the inadequacy of the min-flow i provided. These vibrations may be due to hydraulic forces that have no bearing on pump degradation.
A special test of the LPCI and CS pumps was performed in December of 1986. This test was performed to look for the presence of impeller recirculation induced vibration. If this vibratory mode was found, it was to be assumed that min-flow is gradually contributing to pump vear and imbalance. If this vibratory mode was not encountered, it was to be assumed that the min-flows provided are acceptable for th" cohjert pmogn.
Test results do not indicate the presence of damaging impeller recirculation induced vibration.
1 1
l
- , ,-' U;S. Nuclear Regulatory Commission
>A07218/Page 2 May 3, 1989 The special test demonstrated that pump interaction through shared orificed min-flow lines is not a problem where the orificed lines lead into a larger common header. This is because of the pressure drop imposed by the orifices as flow is reduced before entry into the larger common line.
In summary, the min-flows of individual LPCI pumps. vere not diminished when pairs of pumps were run together with flow routed through their.
shared min-flov lines.
Shutdown Cooling Pumps Shutdown cooling pump test data is difficult to interpret becr;use of differences in plant conditions during testing. Operational objectives during plant shutdown have led to tests at low reactor vessel level (i.e.. low NPSH), high vessel level, at min-flow, and at full flow.
Since the testing of these pumps is limited to shutdowns, the total number of tests performed to date is relatively small (it is estimated that'there have been 36 tests per pump in 18 years of operation).- Since the estimated 36 tests per pump have been performed at varying test conditions, the database for performance evaluation at any given I condition is small. From this perspective, it is inappropriate to assign too much significance to the attempt at performance trending crovided here.
The shutdown cooling pumps appear to be performing consistently.
Discharge pressures and 6Ps have been acceptable most of the time in 18 years'of testing. Requests for repairs are noted whenever these performance parameters have dropped below acceptance limits. However, major maintenance seems to be related to vibration rather than deterioration of performance parameters. Vibration has led to coupling repairs and overhauls in 1986 and 1987 (one pump overhauled in each year). l l The shutdown cooling pumps did not have any significant internal damage at the overhauls discussed above. This implies that the pumps are not being damaged by operation at min-flow or any other condition. Tne vibration that has been experienced in these pumps has been attributed to !
coupling deterioration and misalignment, not inadequate min-flow. Also, l this vibration has not been significant enough to produce any noticeable ;
I damage.
Conclusions It is concluded that the min-flows provided for the LPCI, CS, and snutdown ecoling pumps are not producing pump damage.
i b ___ _ _ _ _ _ _ . _ _ . _ _ _ _ _ . _ _ _ _ _ _ _ _ _ _ _
.['%U.S. Nuclear Regulatory Commission A07218/Page 3
'May 3, D89 Millstone Unit 3 General In general, it can be stated that the three years of test data available for these pumps may not be sufficient to notice any degradation due to j operatien at min-flow. '
Safety Injuction, Chargsng, and Residual Heat Removal The safety injection, charging, and residual heet removal pumps have not shown any deterioration in performance parameters (e.g., differential pressure and min-flow). Vibration measurements for these pumps have remained within inservice testing standards. These pumps are tested at min-flow.
Auxiliary Feed Vater (Motor Driven)
These min-flow tested pumps have shown some excessive vibrations at vane pass and running spced frequencies. The occurrence of these vibrations has not been consistent in the three years of monthly testing performed to date. However, the few incidents of excessive vibration have been considered significant enough to justify an evaluation of increasing min-flow and other performance improvements. Final results of these analyses are not in.- Preliminary results indicate that min-flow modifications are not required.
A critical bushing within these pumps is being monitored (by means of i special instrumentation) for signs of deterioration that could produce increased vibration and rotor failure. These problems are related to bushing material, not min-flow.
Auxiliary Feed Water (Turbine Driven) ;
This pump did experience excessive vibration during two consecutive min-flow tests in 1986. This pump is also being evaluated as described above (for the motor driven auxiliary feed pumps). The high vibrations ,
experienced have been attributed to bad transducer cables. !
l The pump experienced low discharge pressure at one test in 1988.
Apparently, it passed based on backup instrumentation readings.
Vibration - Evaluation of Multi-Spectra Plots The vibration data collected during min-flow testing of the subject pumps ]
may not span enough time to provide meaningful data on the possibility of slowly accumulating min-flow damage.
It is dif ficult to make projections from one min-flow test. Ideally, min-flow vibration spectra vould be compared to full flow vib, ration spectra over a period of tilne. This nethod would point out any increases I
l I
___ _ _ _ _ _ _ _ _ - _ - _ l
, g n
- U.S. Nuclear Regulatory Commission A07218/Page 4 Hay 3, 1989 in vibratory amplitudes due to the slow accumulation of puep damage. It would also show that certain vibratory modes are characteristic of a pump. The presence of these vibratory modes at min-flow is lets of a concern when it is known that these modes are observed at design flow.
Also, the availability of full flov vibratory spectra makes it easier to identify cavitation in min-flow vibratory spectra. Without the 'enefit u of all this data, cnly the following limited observations can be made.
o Charging pump data does not seem to indicate the presence of any min-flow problems.
o Safety injection pump data may indicate the presence of cavitation at min-flow. More test and maintenance history vill be required to conclude whether cavitation is present or not. Both safety injection pumps had shaft seal repairs in 1988. This type of maintenance could be due to cavitation induced vibration.
o The residual heat removal pumps show their highest vibratory amplitude points at running speed, which is normal. There are lover amplitude spikes at harmonics of vane pass. There is also indication of cavitation in the rough " grass" in the lov amplitude regions of the vibratory spectra. There is nothing in maintenance history of these pumps to indicate any min-flow problems.
o The auxiliary feed pumps (turbine and motor driven) have their highest amplitude vibratory modes at vane pass and vane pass harmonics. This could be indicative of impeller recirculation. The fact that these peak points have a higher amplitude and frequency than the normal spikes at run speed implies that damage could be occurring at min-flow. These pumps are the subject of special evaluation for these reasons as described above.
Conclusions Three years of test experience may not be erough to assess the impact of running these safety related pumps at min-flou.
The auxiliary feed pumps do show some indications that some damage may be accumulating due to operation at min-flow. NNECO does not believe there ir a setious problem with the min-flows provided for these pumps.
Engineering evaluations of these pumps are continuing.
Charging pump test data does not indicate the existence of min-flow problems.
Residual heat removal pump test data implies the possibility of cavitation and impeller recirculation induced vibration due to min-flow.
The existence of cavitation and damaging impeller recirculation is not supported by maintenance histo;y to date.
- .1
, , o.
- U.S. Nuclear Regulatory Commission
^
. A07218/Page 5 Hay 3, 1989 The safety injection pumps may be experiencing cavitation at min. flow.
More test and maintenance history vill be requ! red for conclusions on this possibility to be made.
I 1
1 i
1.
L _ __ -_ i