ML20010E847

Advises That Util Response to IE Bulletin 79-15, Deep Draft Pump Deficiencies, Is Inadequate to Demonstrate & Assure long-term Operability of Pumps.More Detailed Info Should Be Provided within 60 Days.Guidelines Encl

ML20010E847
Person / Time
Site:	LaSalle
Issue date:	08/13/1981
From:	Tedesco R Office of Nuclear Reactor Regulation
To:	Delgeorge L COMMONWEALTH EDISON CO.
References
IEB-79-15, NUDOCS 8109080368
Download: ML20010E847 (19)

Text

{{#Wiki_filter:_ 1-AUG 13199i Docket No. 50-373 b and 50-374 ~ qg "5 /._ft? @U f. A O tir. Louis 0. Del George /o Director of Huclear Lict;nsing 5 4 .~T! Coimionweoith Edison Compt :y 7-M, Post Offi:e Box 767 e Vv x Chicago, Illinois 60690 6 4' \\g S ~

Dear Hr. Del George:

subject: Long Tem Operability of Deep Draf t Pumps l IE Bulletin 79-15, dated July 11, 1979, was issued to all licensees and holders of construction pemits as a result of deep draf t pump deficiencies that were identified at facilities both operating and under construction. In your response to-tne bulletin you toentified deep draft pumps as being utilized at your facility. However, your response to the bulletin did not include enough infomation to demonstrate and assure the long tem operability of these pumps. Enclosed is a docuaent entitled, " Guidelines for Demonstration of Operability i of Deep Draf t Pumps." Within 60 days from the issuance date of this leter, you should provide information on all the deep draf t pumps identified in your bulletin response and describe the extent to which your deep draf t pump long j tem operability assurance program conforms to the various portions of these Guidelines. Emphasis should be placed on (1) the establishment of installation procedures that are followed each time these pumps are disassembled and reinstalled, and (2) the testing requirements and bearing wear criteria. The instrumentation called for in the Guidelines should not be considered a requirement. ihese Guf delines establish an acceptable nethod of assuring long term operability of r.eep draft pumps. They do not necessarily constitute the l only metnod for denonstrating long term operability. Tne staff will review i the infomation you su' mit to determine unether your long term opr ability o assurance progran for deep draft pumps is in sufficient Confomance with these Guidelines to assure long term operability. If not, the staff will determine whether you have estaalished and utilized other methods and procedures, preferably with the assistance of the pump manufacturer, that also demonstrate and assure that these pumps will perforu their intended function for the length of time required. t 1 l \\ ~ito y,o.oase eso 1a - - nooo g ...,,..................i....................i......... - nac ronu m co-somacu oso. OFFICIAL RECORD COPY usceo: w-mee.

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-6 4 4 sE I ,. I m =_ e If you have any c4 estions regarding this matter, please contact the Licensing Projet c itanager. l Sincerely, Robert L. Tedesco, Assistant Director for Licensing Division of Licensing Office of Nuclear Reactor Regulation

Enclosure:

Guidelines for Demonstration of Operability of Deep I Draft Pumps .cc w/ enclosure: See next page Distribution Docket File NRC PDR Local PDR LB#2 Project Manager, ABournia l ASchwencer MService RLTedesco/LBerry DGEisenhut/RPuple TERA NSIC TIC ASRS(16) OI&E(3) RHVollmer' WJohnston JSniezek ZRosztoczy RBosnak f aib / 3 j A; am">.. ta e2. tBe .. abo.urba.... z... ASchwe (ccr...R $#90...

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.,, c, f Mr. Louis 0. Dal George Director of Nuclear Licensing Commonwealth Edison Company 'P.O. Box 767 Cl.icago,- Illinois 60690 cc: Phillip P. Steptoe, Esq. Suite 4200 One First National Plaza Chicago, Illinois 60603 Dean Hansell, Esq. Assistant Attorney General 188 West Randolph Street Suite 2315 Chicago, Illinois 60601-Mr. Roger Walker, Resident Inspector U.S. Nuclear Regulatory Commission P.O. Box 224 Marseilles, Illinois 61364 Mr. John Hasselbring i Operations Co-Ordinator Public Utilities Division . Illinois Commerce Commission 527 East Capitol Street Springfield, Illinois 62706 l l l l {

M ENCLOSURE = GUIDELINES FOR DEMONSTRATION OF OPERABILITY OF DEEP DRAFT PUMP 5 DISCUSSION I.E. Bulletin 79-15 dated July 1979, identified problems associated 1 l with deep-draft pumps found at operating facilities and near tern operating licensee faciliti-s. Deep draft pumps,which are also called " vertical turbine pumps" are usually 30 to 60 feet in length 4 with impe11ers located in casing bowls at the lowest elevation of 4 the pump. The motor (driver) is located at the highest pump elevstion with the discharge nozzle just below the motor. Bulletin 79-15 was initiated because several nuclear power plant facilities could not demonstrate operability o' their pumps. The pumps were experiencing excessive vibration ann' bearing wear. The" - i rapid bearing wear suggested that these pumps could not perform j their required functions during or following an accident. As a result of the staff's initial review of the responses to IEB 79-15,. l several plants were identifled as having potential problems with their deep draft pumps. These guidelines are provided for these ' i plants so that the licensee or applicant involved may~have a method l acceptable to the staff for demonstrating the operability of deep-draft pumps. ~ 2 dd g o#[ U gif7$$g O ~

= GUIDELINES FOR DEMONSTRATION OF OPERABILITY OF DEEP DRAFT PUMPS DISCUSSION .I.E. Bulletin 79-15 dated July 1979, identified problems associated with deep-draft pumps found at operating facilities and near term operating licensee facilities. Deep draft pumps,which are also ' called " vertical turbine pumps! are usually 30 to 60 feet in length j with impe11ers located in casing bowls at the lowest elevation of the pump. The motor (driver) is located at the. highest pump i elevnton with the discharge nozzle,iust below the motor. I j Bulletin 79-15 was initiated because several nuclear power plant facilities could not demonstrate operability of their pumps. The The' - - ] pumps were experiencing excessive vibration and bearing wear. rapid bearf 4g wear suggested that these pumps could not perform their required functions during or following an accident. As a f i i result of the staff's initial review of the responses to IEB 79-15,. j several plants were identif'ied as having potential problems with their deep draft pumps. These guidelines are provided for these ' plants so that the licensee or applicant involved may have a method ~ j acceptable to the staff for demonstrating the operability of deep-draft pumps. + i e 9 e ._,e,-

~. - e3 q i e - DEEP DRAFT PUMF OPERATING CNARACTERISTICS In order to better understand the operating characteristics of 1 these pumps, a rotor _@namics analyses was performed to ascertain the response of the pump rotor under stea@ state operation. The analyses considered journal' bearing to shaft @namic response at various eccentricities and fluid viscosities. The model for the analysis depicted a typical deep draft pump utilized by the nuclear industry. The analysis resulted in rec,omendation,s for improving the stability of the pump rotor from external' applied inputs and by self-generated inputs. L The conclusions which were derived from the analysis and staff evaluations of North Anna, Beaver Valley and Surry facilities with similar pumps include: 1.) Pumps with this type of configuration are prone to bearing whirl vibration problems due to the flexibility of the rotor i and casing structure. This phenomenon is accentuated as journal bearing clearance becomes large. This phenomenon leads to bearing wear (Journal bearings). ,.2 a ~ i 1 " Low Head Safety Injection Pump Rotor Dynamic Analyses", by Franklin Research Center, Report FC4982, dated May 1980. 9 S 4 m. 7 m+- - { -

g..,, 4, - 2.) There may be natural frequencies associated with the pump assembly which occur near the operating speed of the pump. Pump operation will drive these frequencies and can cause bearing wear. The severity of this condition is dependent on bearing diametral clearance, rotor unbalance conditions and housing flexibility. As an example, if the wear in column journal bearings becomes sufficiently large (twice the original diametral cidarance)'so that ~ these bearings are no longer active and the undamped critical frequency near the operating speed of the pump is allowed to expand, the additio'nal uncontrolled bearing wear will occur. This wear can continue until the shaft rubs against the support struc,ture of the bearing and can potentially sever the shaft. 3.) One acceptable method for correcting instabilities in the-pump shaft is to utilize a journal bearing design which 1 l exhibits stable characteristics. One such design is the

• Taper land bearing". This design is nore stable than the plain journal bearing, is less susceptible to wear because i

i of the taper and will cause the bearing to form a hydro-dynamic film quickly during startup. L t

r, i. = \\ . 4.) Stiffening of the column sections of the pump is advantageous if there is a column frequency near the operating speed of the pump. The shifting of the column frequency to a higher level will eliminate any coupling between the pump operating speed and the column frequency. ~ ~ 5.) Flow inlet conditions to the pumps and sump designs can ~ be important to pump operability. Certain installations have demonstrated flow characteristics which produced vortexing at the be11 mouth of the pump. This ;ortexing ~ is due to sump design or sump supply line entrance con-4 ditions. This condition can contribute to additional pump vibration and wear. Flow straightener devices, i reduction of be11 mouth diameters, and bottom clearance 4 reductions have proven to be effective in eliminating i this problem. s. 6.) This type of pump has exhibited operational problems i due to design and installation deficiencies. The high flexibility of the shaft and column make this design ~

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ratb8-forgiving when it comes to installation deficien-cies such as misalignment between the shaft and column, 4 4

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low-precision coupling assemblies, and non-perpendicular 4 mounting flanges. This fact however, can lead to excessive bearing wear without significant noticeable change in pump 4 l operating characteristics. To ensure proper pum,9 operation, proper alignment should be established between all mating surfaces and measures should be emphasized which prev ~ent column and shaft eccentricities. These measures can include optical alignment of the column segments, use of high precision a couplings and use of. accurate techniques to establish that 1 the sump plumb line is perpendicular to the pump mounting fl ange. j The above findings and conclusions have contributed significantly to the development of these guidelinese The guidelines listed 1-below are divided into installation and test areas. The subjects l to be addressed in these areas are considered to be of prime 1 importance when establishing a pump operability assurance program. I l l-The extent to which each of the two are'as are impleme'nted at a l specific facility is dependent on specif1c symptoms which have i an identified with these pumps while in operation and during service periods. \\

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q a s. =* Impleme'nting the measures outlined below, at North Anna 18 2 in total, has been shown to provide reasonable assurance that the pumps will be operable when required for their safety function. These guidelines are not intended to replace the requirements of Standard Review Plan 3.9.3, Regulatory Guide 1.68 or any other i requirements presently enforced by the staff. Rather, the guidelines are to be used as supplementary material for establishing { deep-draft pump operability. 1 GUIDELINES FOR OPERABILITY INSTALLATION { 1.0 INSTALLATION PROCEDURLS j Experience has shown that these pumps are prone to having operability i problems as a result of poor installation procedures. The guidelines emphasize those areas of the installation procedure,which if implemented, ' could significantly improve the likelihood of an operable pump. The { procedures utilized should be submitted to the staff fcr review. i 1.1 PUMP INSTALLATION Detennine by measurement that all shaft segments are straight a. within tolerances specified by the manufactur'er. b. Detennine by measurement or provide certification that all i couplings (fo. shaft segments & ' pump to motor coupling) are of high precision as specified by the m.anufacturer. Determine by measurement that all pump segment flanges are c. perpendicular to the centerline of the segment, that the segments are straight and that any mating surfaces are concentric to an established datum. Where journal j l l

l-7 , bearing guides (SPIDERS) are used, establish con-centricity between this assembly and its mating surface. d. Align full pump casing assembly optically to assure maxicum straightness and concentricity of the assembly. Any equivalent method is acceptable, as long as the procedure stresses column straightness and concentricity., ] Assure pump to motor flange perpendicularity and tiiat ~ e. i proper coupling installation is perforned. l f. Assure that all mating surface bolting is properly attached and that manufacturer torquing sequences are i adhered to. j 1.2 SUMP INSTALLATION a. Assure (where used) that sump / pump mating flange is perpendicular to the sump pump line. ( ,2 b. Assure that sump design prevents fluid anomalies ~ such as vortexing or turbulence near the intake 1 .% 's to the pump bellmsdf.h and that incoming piping is not so designed as to allow fluid conditions favorable to these anomalies (i. e., sharp. ' bends in piping prior to entrance.into sump). c. Assure that interference does 'not exist between the sump and arty pump appendage such as a seismic ~ restraint. 9

L a N* 8-2.0 Testing Requirements The installation procedures are essential in establishing pug operability. In addition to careful installation, testing r.uy be required which will verify proper operation of these pugs. Afterregletionoftheinstallationchecks,licenseesorappli-cants should evaluate the need for further testing and report the.results of this evaluation together with the details of any test plans to the staff. Should tests be required, an acceptable ^ test procedure should include the items / listed.below. The staff recognizes that the instrumentation and procedures outlined below may be difficult to implement at all facilities and, therefore, the staff is emphasizing good installation practices which lead to operable cogonents. If tests demonstrating operability cannot encogass all the items listed below, then alternative procedures l should be proposed for evaluation by the staff. The tes,ts should i ermhrsize measurement of pump dynamic characteristics and wear data at different stages of testing, culminating with an extrapolation of the data to the desired life goal for the pump. i 2.1 Test Instrumentation The following instrumentation should be incorporated into the test procedure aside from normal flow measu'rement, pressure and vibration instrumentation: O U g -Q

^ u. e .g. ~ a.) X, Y proximity probes at three axial locations on the pump column, for measuring and recording radial positions of shaft with respect to the column. b.) X, Y, accelerometers (at proximity probe locations) for measuring and recording radial accelerations of the Columne c.) Dynamic pressure transducers for measuring fluid pressure at the following locations: 1. Bottom of Column (suction) ] 2. Mid-Column 3. Top of Column. j d.) Shaf t Rotational speed and dynamic variation instrument, i 2.2 ' PRE-TEST DATA ~ ~ l With the pump disassembled, measure all journal bearing 0.D.'s, bearing 1.D.'s and calculate bearing diametral clacrances. In addition with pumps fully assembled and using the proximity probes, obtain the " clearance circle" at each of the '.nree axial stations by rolling the shaft section within the clearance volume of'its bearings and in this way, establish proper operation of the p, robes. p .g-9 O e t. l O

a, r, l'. 3.1 PH'ASE 1 Testing (6 hours plus start-stop) This phase of testing should be comprised of 6 hours of testing (Break-in) followed by start-stop testing. Test conditions should simulate as nearly as possible normal and accident conditions. Parameters to be considered are flow, temperature, debris, and chemical composition of fluid being pumped. Static torque tests should be performed before'and after the test (i.e. measure mount of ~ torque required to turn shaft by hand). Data should be taken during the six' hour test at 1/2 hour intervals. A total of 12 start-stop tests will be performed con-eisting of a start up from zero speed up to. full-speed, ~~ ~ i 10-minute dwell at full-speed and a shutdown from full speed to zero speed, with recording of all instrumentation during full cycle of start-stop. Upon completion of Phase 1 testing,the following data should be obtained and recorded: 1.) Obtain the " clearance circles" using the three sets of i proximity probes. ) 2Tests at North Anna 1 & 2 and Manufacturers input indicates that 6 hours is an adequate time interval for bearing " break in" period. n-

l 2.) Measure and record the following dimensions for each bearing: a.) Journal 0.D. b.) Bearing 1.0. c.) Bearing to Journal diametral clearance d.) Establish Phase 1 test bearing wear. THE ACCEPTANCE CRITERIA IS AS FOLLOW 5: 3, 1.) If wear is> 5 mils for any bearing, wear is unacceptable ~~ and test -should be terminated. 3 2.) If waar is( 5 mils for all bearings a.) Reassemble the pump

b. ) Obtain " clearance circles"

c. ) Reinstall pump in test loop. -

2.4 Phase 2 Testing (48 hours) Phase 2 testing is to be performed at full system pressure. and tenperature and fluid conditions sinulating those expected during accident and normal operation. Before start and at conpletion of Phase 2 test,obtain measurement of static torque. 5 Data should be recorded continuously during the start-up period. . s y-3This acceptable wear value may be modified based on manufacturers recomendation. 9 e L b

and during the shutdown period. Data should also be recorded at 1-hour time intervals during the 48 hour test. The following measurements should be made at the completion of Phase 2 of the test: 4 1.) Obtain the " clearance circles" using the three sets of proximity probes. 2.) Measure and record the following dimensions for'eacli bearing: a.) Journal 0.D. b.) Bearing I.D.

c. ) Bearing to Journal diametral clearance.

d.) Establish accuculated bearing wear. THE ACCEPTANCE CRITERIA IS AS FOLLOW 5: 5 1.) If accumulated bearing wear on any bearing is >7 mils, wear is unacceptable and test should be terminated. 2.) If accunulated wear on all bearings is(7 mils forallbearings$. f ^, a.) Reassemble pump

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Obtain " clearance circles" c.) Reinstall pump in test loop. j l c e

2 _ 13 5.) Phase 3 Testing (96 hours) Phase 3 testing is to be performed at full system pressure and temperature and fluid conditions simulating those expected s turing accident and normal operation. The same procedures should be follo'wed as in Phase 2 testing except that data ~ ~ . may be taken with less frequency. The same measurements should be taken at the completion of this phase as with the other phases with the following acceptance criteria: 1.) If accumulated bearing wear is> 8 mfis for any bearing3 wear is unacceptable and test should be terminated. 2.) If accumulated wear is ( 8 mils for al1 bearings,3, '~ decision needs to be made to establish: a.) the need for additional testing or e-b.) whether or not the bearing wear will be acceptably l ow. 1 The recommended decis.on process is outlined below. l Plot the values of accumulated wear versus time (H) for each bearing after Phase 2 and Phase 3 tests, namely. Wear at H2 = 54 hour Wear at H3 = 150 hours O 1 g

s,- a s, Straight ifnes are then drawn through the plotted values of wear and extended to the right (See exaople Figure 1). If the extension intercepts tha maximum acceptable value of wear (8 mils) at a value H less than the life goal for this pump, additional testing should be performed. If the intercept of the line with wear of 8 mils exceeds the life poal for this pump, no additional testing is required and bearing wear is acceptable. If addition.a1 testing } is deemed necessary it should be done in a similar manner to that I' performed during Phase 3 with similar acceptance criteria and decision process. It is expected that such additional testing 1 will either show a stable pump operation with no increase in bearing wear or increased bearing wear with unacceptable results. 3 2.6 Evaluation of Pump Acceptability If bearing wear (after all testing phases) is acceptably low (as per decision process) and if vibration levels over the frequency spectrum i of 3 cps to 5000 cps are acceptably low and show no unfavorable trend of increasing magnitude during the testing, the pump may be judged acceptable for its intended use. ?

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