ML20005B774

Advises That Response to IE Bulletin 79-15 Re Deep Draft Pump Deficiencies Did Not Include Info to Demonstrate & Assure long-term Operability.Response Should Be Submitted within 60 Days.Guidelines Encl

ML20005B774
Person / Time
Site:	Grand Gulf
Issue date:	08/18/1981
From:	Tedesco R Office of Nuclear Reactor Regulation
To:	Mcgaughy J MISSISSIPPI POWER & LIGHT CO.
References
IEB-79-15, NUDOCS 8109020140
Download: ML20005B774 (18)

Text

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y T 4' ag p- %f' ' AUG 18 1981 y ~V, nocket No. 50-416/417 Yg@y ~ 2t, c #,.jp #,f Ii6;- igg / Mr. J. P. McGauchy, Jr. Assistant Vice President - Nuclear x M Production ^ c Q/ g g ' Mississippi Power A Light Company /i P. O. Box 1640 ~ Jackson, Mississippi 39205 {

Subject:

Long Term Operability of Deep Draft Pumps IE Bulletin 79-15, dated July. 11, 1979, was issued to all licensees and holders of constructica pemits as a result of deep draft pump deficiencies that were identified at facilities both operating and under construction. In your response to the bulletin you identified deep draft pumps ar. beino utilized at your facility. However, your response to the bulletin did not include enouch information to demonstrate and assure the long tem ooerability of these pumps. Enclosed is a document entitled, " Guidelines for Demonstration of Goerability of Deep Draft Pumps." Within 60 days from the issuance date of this letter, you should provide information on all the deep draft pumps identified in your bulletin response and describe the extent to which your deen draft pump lone term 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 reoufrements and' bearing wear criteria. The instrumentation called for in the Guidelines should not be considered a requirement. These Ruidelines establish an acceptable method of assuring long term l operability of deep draft pumps. They do not necessarily constitute the l only method for demonstrating long term operability. The staff will review the information you submit to determine whether your long tem operability assurance procram'for deep draft ptmps is in sufficient conformance with these Guidelines to assure long term operability. If not, the staff will determine whether you have established and utilized other methods and procedures, preferably with the assistance of the pump manufacturer, that also demonstrate and assure that these pumps will perfom their intended function for the length of time required. l l l ( l c ~ ~ ~ - 'SURNAMEk PDR ADOCK 05000416 'Y -l- ~~ - - ~ ~ ~ - ...........y... Lunc ronu me no.comacu ouo c6)770CIAL RECORD COPY ,w e 2n24

i t f.~ ~ ^ .. If you have any auestions regarding this matter, please contact the Licensino Profect Manager. Sincerely, Robert L. Tedesco, Assistant Director for Licensing Division of Licensing Office of Nuclear Reactor Regulation

Enclosure:

tiuidelines for Demonstration of Operability of Deep Draft Punos cc w/ enclosure: See next pace Distributior.: bccs; nocket File NRC POR Local PDR LB32 File Attorney, OELn NSIC DEisenhut/ RPurple TERA TIC RTedesco ACRS (16) ASchwencer nHouston MService I&E(3) RVollmer r Ma,rance qm (=^- " ' ' ' >....LB A2...... ..LR F.h... ...L%} i sunuco,p nHouston dn ASchkencer Teds co " " > E/d/@.1.. .6/.h.6... . 6/.hf/.S.. 1 ' " '*6o-32* 82' OFFICIAL RECORD COPi . w NRC FORM 318 410 80) N RCM O2 4 0

j b ENCLOSURE .s 4 GUIDELINES FOR DEMONSTRAT10N OF OPERABILITY OF, DEEP DRAFT PUMP 5 DISCUSSION 1.E. Bulletin 79-15 dated July 1979,1dentified problems associated. with deep-draft pumps found at operating facilities and nea'r term operating licensee facilities. Deep draf t pumps,which are also called " vertical turbine pumpst are usually 30 to 60 feet in length with impe11ers located in casing bowls at the lowest elevation of the pump. The motor (driver) is located at the highest pump elevation with the discharge nozzle just below the motor. Bulletin 79-15 was initiated because several nuclear power plant : facilities could not demonstrate operability of their pumps. The pumps were experiencing excessive vibration and bearing wear. The'- ~ rapid, bear,ing wear suggested that these pumps could not perform their required functions du-ing or following an accident. As a result of the staff's initial review of the responses to IEB 79-15,. ~ ceveral plants were identified 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 i l acceptable to the staff for demonstrating the operability of deep-draft pumps. 9 + 4

r O s sg s GUIDELINES FOR DEMONSTRATION OF OPERABILITY OF DEEP DRAFT. PUMPS DISCl!5SION I.E. Bulletin 79-15 dated July 1979,ide'ntified problems associateu with deep-draft pumps found at operating facilities and near term' M. '/ operating licensee facilities. Deep draft pumps,which are also called " vertical turbine p. umps" are usually 30 to 60 feet in length with impe11ers located in casing bowls at the lowest elevation of the pump. The motor (driver) is located at the highest pump elevntion with the discharge nozzle just below the motor. Bulletin 79-15 was initiated because several nuclear power plant facilities could not demonstrate operability of their pumps. Tne ~ pumpswereexperiencingexcessivevibrationandlearingwear. The" rapid bearing wear suggested that these pumps could not perform their required functions during or following an accident. As a l result of the staff's initial review of the responses to IEB 79-15,. several plants were identif'ted as having potential problems with l their deep draft pumps. These guidelines are provided for these ' l plants so that the licensee or applicant involved may have a method. l i acceptabl.e to the' staff for demonstrating the operability of deep- ~ draft pumps. 9 (

z-a +. s. DEEP DRAFT PUMP OPERATING CHARACTERISTICS, In order to better understand the operating characteristics of _ '1 these pucps, a rotor dynamics analyses was perforned to ascertain ^ the response of the pump rotor under steady state operation. ff The analyses considered journal bearing to shaft dynamic response at various eccentricities and fluid viscosities. The model fo'r the analysis depicted a typical deep draft pump utilized by the nuclear industry. The analysis resulted in recommendations for improving the stability of the pump rotor from externally applied inputs and by self-generated inputs. 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 probleas due to the flexibility of the rotor and casing structure. This phenomenon is accentuated as i Journal bearing clearance becomes large. This phenomenon l leads to bearing wear (Journal bearings). ~ 1 " Low Head Safety Injection Pucp Rotor Dynamic Analyses", by Franklin Research Center, Report FC4982, dated May 1980. ~ l S e e se me,e ee e

s sg 3-2.) There may be natural freque'ncies associate' with the pump d assembly which occur near the bperating 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 cicarance)'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 additional 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. l 3.) One acceptable method for corr'ecting instabilities in the-pump shaft is to utilize a journal bearing design which exhibits stable characteristics. One such design is th'e ' Taper land bearing". This design is more stable than the pisin journal bearing, is less susceptible to wear because i of the taper and will cause the bearing to form a hydro-l dynamic film quickly during startup. e e e y e e

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(, a 5,' , s 4.) Stiffening of the column sections.of the pump is advantageous if there is a column frequenqy near the 7, operating speed of the pump. The shifting of the column frequenqy 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 vortexing is due to sump design or sump supply line entrance con- ~ ~ ~ , i ti ons. This condition can contribute to additional d pump vibration and wear. Flow straightener. devices, reduction of be11 mouth diameters, and bottom ci :rance i reductions have proven to be effective in eliminating this problem. , 6.) Thi,s type of pump hr exhibited operational problems due to design and installation deficiencies. The high flexibility of the shaft and column make this design } rather forgiving when it comes to insta11ation deficien-cies such as misaligament between the shaft and column, e m

. o, - e -s low-precision coupling assemb1'ies, and non-perpendicular. mounting flanges. This fact however, can lead to excessive, bearing wear without significant noticeable change in ' pump 3 operating characteristics. To ensure proper pump operation, proper alignment should be established between all mating surfaces and measures,.ould be emphasized which prevent column and shaft eccentricities. These measures can include optical alignment of the column segments, use of high precision couplings and use of. accurate techniques to establish that the sump plumb line is perpendicular to the pump mounting fl ange. The above findings and conclusions have contributed significantly to the development of these guidelines. The guidelines listed below are divided into installation and test areas. The subjects to be addressed in these areas are considered to be of prime importance when establishing a pump operability assurance prograln. The extent to wh,ich each of the two are'as are implemented at a specific facility is dependent on specific symptoms which have i been identified with these pumps while in operation and during service periods. k s ,. ~. -.

s. a (. 4 n ', Impicmenting the measures outlined below,.at Noi th Anna 1 & 2.in total, has been shown to provide regsonable assurance, that the pumps will be operable when required for thelr safety function. Theie guidelines are not intended to replace the requirements of 7 Standard Review Plan 3.9.3, Regulatory Guide 1.68 or any other requirements presently enforced by the staff. Rather, the guidelines are to be used as supplementary caterial for establishing deep-draft pump operability. GUIDELINES FOR OPERABILITY INSTALLATION 1 <. 0 INSTALLATION PROCEDURES ~ Experience has shown that these pumps are prone to having operabi1ity ~ problems es a result of poor in:ta11ation procedur es. The guidelines emphasize those areas of the installation procedure,which if implemented, ' could, significantly improve the itkelihood of an operable pu.mp. The procedures utilized should be submi,tted to the staff for review. 1 1.1 PUWP INSTALLATION a. Determine by measurement that all shaft segments are straight within tolerances specified by the manufactur'er.

b..' Determine by measurement or provide certification that all couplings (for shaft segments & ' pump to motor coupling) are,'

of high precision as specified by the manufacturer. c. Determine by measurement that all pump segment flanges are 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'

= 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. 7 {,; maxicum straightness and concentricity of the asser$1y. Any equivalent method is acceptable, as long as the procedure stresses column straigh'tness and concentricity. e. Assure pump to motor flange perpendicularity and that proper coupling installation is performed. 1 f. Assure that all mating surface bolting is troperly attached and that manufacturer torquing sequences are = adhered to. / 1.2 SUNP INSTALLATION s ~ a. Assure (where used) that sump /purp mating flange is perpendicular to the sump purp line. b. Assure that sump design prevents fluid anomalies such as vortexing or turbulence near the intake to the pump be11 mouth 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 sunp). c. Assure that interference does 'not exist between the sump and any pump appendage such as a seismic restraint. e S 9 e

~ i S. a s, s s3 2.0 Testing Requirements The ins +111ation procedures are essent,ial in' establishing pump operability. In addition to careful, installation, testing may be required which will verify proper operation of these pumps. After cocpletion of the installation checks, licensees or app,li- ' 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 conponents. If tests demonstrating operability cannot enconpass all the items listed below, then alternative procedures should be proposed for evaluation" by the staff. The tests should emphasize 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. 2.1 Test Instrumentation The following instr'umentation should be incorporated into the test procedure aside from normal 1 low measu'rement, pressure and vibration instnamentation:

= . s, a.- ) X, Y proximity probes at three axia1 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 column. c.) Dynamic pressure transdu,3ers for measuring fluid pressure at the following locations: 1. Bottom of Column (suction) '~ ~ 2. Mid-Column 3. Top of Column. d.) Shaft Rotational speed and dynamic variation instrument.' 2.2. PRE-TEST DATA k'ith the pump disassembled, measure all journal bearing 0.D.'s, W e bearing I.D. 's and calculate bearing diametral clearances. In addition with pumps fully assembled and using the proximity probes, obtain the." clearance circle" at each of the three axial stations by rolling the shaft section within the clearance volume of'iti bearings and in this way, establish proper operation of the. probes. I ~ , ~ ~

s. a s, a. g PNASE 1 Testing (6 hours p us. start-stop)2' 3.1 This phase of testing should be domprised of 6 hours of ~ testing (Break-in) followed by start-stop testing. Test w. / conditions should simulate as nearly as possible normal and accident conditions. Parameters to be cor;idered are flow, temperature, debris, and chemical composition of fluid being pumped. Static torque tests should be ~ (i.e. measure amount of performed before and after the test 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-l ~ ~~ ~ sisting of a start up from zero speed up to full-speed, 10-minute dwell at full-speed and a shutdown from full speed to zero speed, with recording of all instri mentation during full cycle of start-stop. Upon completion of Phase 1 testing,the foll.owing data should be obtained and recorded: 1.) Obtain the " clearance circles" using the ihree sets of i proximity probes. i 2Tests at Nortt Anna 1 & 2 and Manufacturers input indicates l that 6 hours is an adequate time interval for bearing " break in" period. L

i .s - 2.) Heasure an,d record the following did. ens' ions for e?ch bearing: a.) Journal 0.D. b.) Bearing I.D. c.) Bearing to Journal diametral clearance 3?

d. ) Establish Phase 1 test bearing wear.

THE ACCEPTANCE CRITERIA IS AS FOLLOWS:. 3-1.) If wear is)r5 ails for any bearing, wear is unacceptable and test -should be terminated. ' 3 2.) If wear is(5 mils for all bearings

a. ) Reassemble the pump

b. ) Obtain " clearance circ 12s"

c. ) Reinstall pump in test loop. ~-

2.4 Phase 2 Testing (48 hours) Phase 2 testing is to be perforced at full system pressure. and temperature and fluid condit' ions simulating those expected 1 during accident and nornal operation. Before start and at coapletion of Phase 2 test,obtain reasurement of static torque. Data should be recorded continuously during the start-up period, 3This acceptable wear value ray be modified based on nanufacturers recommendation. ,-,w,,.-,,.,_,_,.n.,,ng, _s,..., e g.e e .-v.-

~( i. a 4 ss s 12 - and during the shutdown period. Data should also, be recorded at 1-hour time intervals during th'e 48 hour test. The following measurements should be made at the completion y of Phase 2 of the test: 1.) Obtain the " clearance circles" using the three sets of proximity probes. 2.) Measure and record the following dimensions for~each bearing: a.) Journal 0.D. b.) Bearing I.D. c.) Bearing to Journal diametral clem ence. d.) Establish accuculated bearing wear. THE ACCEPTANCE CRITERIA IS AS FOLLOWS: 1.) If accunulated bearing wea' on anh bearing is >7 mils, wear is unacceptable and test should be t ermi nated. l 2.) If accunulated wear on all bearings is(7 mils for all bearings $. / i a.) Reassemble pump

b. )

Obtain " clearance circles" c.) Reinstall pump in test loop. /

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1 4 ss 13 5.) Phase 3 Testing (96 hours) Phase 3 testing is to be perfonmed at full system pressure and temperature and fluid conditions simulating those expected \\ during accident and normal operation. The same procedures 7.3 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 wi~th the other phases with the following acceptance criteria: 1.) If accumulated bearing wear is> 8 mils for any bearing 3 wear is unacceptable,and test should be terminated. 2.) If accumulated wear is ( 8 mils for"all bearings,3, decision needs to be made to establish: a.) the need for additional testing or a ~ b.) whether or not the bearing wear will be acceptably low. ~ ~ The recommended decision process is outlined below. Plot the values of accumulated. wear versus time (H) for each bearing after Phase 2 and Phase 3 tests, namely. s Wear at H2 =.54 hour ~ Wear at H3 = 150 hours .~ e e

a u 3 r 14 - ! raight line's are then drawn through the plotted values of wear ~ and extended to the right (See example Figure 1). If the, extension. intercepts the maximum acceptable value of wear (8 mils) at a value H less than the life goal fcr this pump, additional testing shsuld be perfomed. If the intercept of the line with wear of 8 mils exceeds the life goal for this pump, no additional testing is required and bearing wear is acceptable. If additional testing is deemed necessary it should be done in a similar manner to that perfomed during Phase 3 with similar acceptance criteria and decision process. It is expected that such additional testing will either show a stable pump operation with no increase in' bearing wear or increased bearing wear with unacceptable results. 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 l 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 l ~ l acceptable for its intended use. t l' s l ,,---,e g g e r---, a ,---a,

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