ML20155A933
| ML20155A933 | |
| Person / Time | |
|---|---|
| Site: | Palo Verde  |
| Issue date: | 12/24/1987 |
| From: | ABB COMBUSTION ENGINEERING NUCLEAR FUEL (FORMERLY |
| To: | |
| Shared Package | |
| ML17303B141 | List: |
| References | |
| NUDOCS 8806130028 | |
| Download: ML20155A933 (74) | |
Text
{{#Wiki_filter:._ _ a f s' ANALYSIS OF REACTOR COOLANT PUMP SHAFT WITH MODIFIED KEY REGION PREPARED FOR ARIZONA NUCLEAR POWER PROJECT PALO VERDE NUCLEAR GENERATING STATION
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- UNIT 1 1
DECEMBER 24, 1987 , i COMBUSTION ENGINEERING, INC ; l
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COMBUSTION' ENGINEERING 8886288ERSS8%!go G .
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PCD-125.DJA Table of contente I. Introduction
'II., Design of Shaft
't. Location of Cracking Loadings on Shaft Shaft Modifications .
VI. Finite Element Model and Loading
- a. Axial Load Distribution
- b. Load Distribution on Keyway Wall
- c. Shaft Keyway Region Three Dimensional Medel VII. Results of Shaft Analysis
- a. Bending Loads
- b. Axial Loads
- c. Torsion Loads
- 1. CASE 1: Loading to tangent point
- 2. CASE 2: Modified key design
- 3. CASE 3: Modified key with taper
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- 4. CASE 4: Loadir g above- tangent point
- 5. Comparison of cases VIII. Load Combinations for Hodified Key Design
- a. Hot Condition Steady Loads b .~ Hot Condition Cyclic Loads
- c. Cold condition Steady Loads
- d. Cold condition Cyclic Loads IX. Material Limits X. Evaluation of Shaft XI. Conclusions XII. References I:
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PCD-125.DJA
- 1. Introduction Inspections of four (4) Reactor Coolant Pump Shaf ts at the palo Verde Nuclear Generating Station, Unit 1, were conducted during the first refueling outage. A combination of Ultrasonic Inspections, Magnetic Particle Inspections, and destructive metallurgical examinations-indicated that cracking in the area of the sheft keyways had occurred.
Circumferential cracking of similar reactor coolant pump shaf ts had been reported in Europe (Reference 1), as well as instances of shaft failures. The inspections at Palo Verde revealed three types of cracks in the shafts: (1) circumferential cracking initiating in the chrome plating of the shaff an propagating into the base metal in areas of high stress; (2) axial cracking along the bottom of the keyway corners which arrested within a short distance; and (3) one instance of a circumferential crack initiated in the keyway wall associated with wear marks. As a result of the European experience and based ob the inspection results . from Palo Verde, several modifications were performed on the replacement shafts installed in Palo Verde Unit 1. This report presents a detailed finite element analysis of the Reactor Coolant Pump shafts to l compare the effects of the modifications with the original design. The report shows that the peak stresses anticipated in the modified shaf ts l are well below allowable values and that cracking due to high cycle I fatigue is not expected. l II. Design of Shaft The shaft original design in the keyway region is shown in Figure la and Ib. The surface of the shaft was chrome plated to enhance impeller fitup and preclude gauling so that the impeller could be removed easily. 1 The key extended into the round portion of the keyway and fit fairly l tightly, although the key loading on the shaft was assumed occur only on the straight side portion of the keyway. The intersection of the k.
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.PCD-125.DJA straight side and the rounded top part of the keyway will be referred to
(; as the ' tangent point'. III. Location of Cracks Cracks in the shafts were first detected by an ultrasonic examination pr.oc to removal from the pump (Reference 2). Subsequently other
. examinations contirmed the presence of cracks and provided details of the cracks detected by the ultrasonic exam as well as other cracking.
The types of cracks are illustrated in Figure 2. The first type of cracking, shown as Typs (1) in the Figure, is initiated in the chrome layer near the tangent point of the round part of the keyway. These ' cracks are essentially identical to those found in European plants. These cracks appear to start some distance away from the keyway, merge together and extend into the keyway. They are predominately on the loaded side of the keyway. The cracks are extended by high cycle fatigue. m The second type of cracking was found on the bottom of the keyways, on the loaded side, axtending from the relatively sharp corners. The third type of crack was found in one instance in the keyway sidewall above the tangent point. This crack was associated with severe wear on the sidewall due to key contact. This crack linked up with some Type (1) cracks. i IV. Shaft Loading The dominant loading in the shaft is the torsion load imposed via the key f rom the impeller. In addition to the steady load a r.1 L1 cyclic torsion loading, occurring each chaft rotation is ovpccteu. A steady axial load due to the fluid prescure and hydraulic load which is tensile during cold operations and compressive during hot operations also occurs. Eccentricities, imbalances and hydraulic forces due to the
- impeller radial discharge produce a steady and a once por shaft
(, revolution cyclic bending load. These bending loads are relatively t i I a
'PCD-125.DJA s
small,' but have been judged to be the dominant factor in the growth of ( the Type (1) cracks once initiated. The value of these loads is shown in Table 1. The bending loads apply specifically to the shaft location corresponding to the tangent point of the keyway. These values are based on KSB report US4 14550 (Reference
- 3) and meetings with KSB personnel.
V. Shaft Modifications Several modifications were made to replacement shaf ts to address the various types of cracking. First the chrome plating was removed from tha region near the top of the keyway since the chrome plating was Judged to degrade the fatigue life of the shaf t material and contribute to crack initiation. The stop seal was modified to prevent direct exposure of seal injection water to the shaft surface. Thermal stresses due to loss and restoration of seal injection were also judged to i contribute to crack initiation of Typo (1) cracks. The cracks at the bottom of the keyway, Type (2) cracks, were attributed to the sharpness of the corner. The stress concentration was reduced by grinding a larger radiur at the corner. i The t.hird type of crack was addressed by shortening the key so that key contact does not occur in the region of high stress due to torsion (as will be seen later) . Careful attention to the fitup of the keys will ! also address the keyway wear problem. The modified key and keyway is f shown in Figure 3. ( l The analysis discussed in the following sections addresses the change in stress in the shaft due to tb9 shaft and key modifications. 1 VI. Finite Element Modola and Loadinq In order to perform a three dimensional analysis of the shaft, the way l in which the loads are applied had to be established. In the case where
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PCD-125.DJA various parts interact, a decision had to be made whether to perform the
'([ analysis of all parts simultaneously with properly modeled interaction, or to analyze each part separately and estimate the loading pattern each part imposes in its neighbors. For this analysis, in order to minimize the time and ef fort required, the latter approach, of analyzing each part separately was employed.
Using this approach for the analysis of the keyway region of the shaf t, the first requirement is to determine how the load from the impeller acts through the key on the shaft. This load r attern is established by determining how the loading is distributed along the axial direction of the shaft and, separately, up the keyway wall. The load is arsumed to be evenly distributed between the two keys.
- a. Axial Load Distribution KSB had previously performed an analysis of the combined impeller, key, and shaft system (Reference 1). Although this analysis was of
.(, a slightly different geometry and the shaf t had only one key, the axial load distribution trend should be similar to the palo Verde shaft. The axial load transmission pattern from the KSB analysis l
1s shown in Figure 4. This curve is smoothed and replotted as a percent of the average load value in Figure 5. In order to independently assess the axial distribution, a l simplified finite element model of the impeller hub and shaf t was constructed. This model is shown in Figure 6. The key is represented by nodal connections between the hub and shaf t. To l l simulate the torsion load distribution on the shaf t, the shaft is modeled as fixed above the key region and a unit torque is applied to the lower end of the hub. The stress distribution resulting from this condition is shown in Figure 7. Note that the coarseness of the model concentrates the stress at the mesh points. However, the trend in the axial distribution can be evaluated by plotting the nodal point stresses k-t.
PCD-125.DJA h as a function of distance as shown in Figure 8. By smoothing and l plotting as a function of the average load value, the results are shown along with the . corresponding KSB results in Figure 9.
. The KSB results and the coarse finite element results are in general agreement, with the KSB result producing higher peaks. The higher peaks are judged to result from the more refined mesh. The coarse mesh results confirm that the KSB computed results provide a reasonable distribution in the axial direction of the torsion load on the shaft.
- b. Load Distribution on Keyway Wall The load distribution on the keyway wall was addressed in a previous calculation at the keyway corner (Reference 4). The previous analysis considered various ways that the key could act depending on clearances which might exist in the keyway. All cases addressed resulted in compression on most of the keyway wall with tensile stresses developing due to the overturning effect near the lower portion near the keyway corner. In evaluating the pattern of key / keyway interaction, the most realistic case appears to be case 2 of the previous analysis which is shown in Figures 10 and
- 11. In this analysis a slice of the shaft, key and hub are considered with a unit torque applied to the hub with the shaf t fixed. The keyway sidewall distribution extracted from Figure 11 is shown in Figure 12.
The distribution is linearized 'for simplicity as a triangular load with the peak value at the top of the keyway wall. The triangular distribution is considered more realistic than a constant distribution which was used in previous scoping and trending analyses. The combination of the axial distribution developed in Figure 9 and the Key sidewall distribution developed in Figure 12 was used to
PCD-125.DJA apply the torsion load on the shaft in the subsequent three ( dimensional analyses.
- c. Shaft Keyway Region Three Dimensional Model The stresses in the keyway region result from axial loads and bending moments applied to the shaft remote from the top of the keyway and the torsion load applied by the key to the keyway sidewall. The axial and bending stresses were determined from the model shown in Figure 13. This model properly represents the shaft symmetry when the bending stress near the keyway is the greatest.
The bending and axial loads were applied separately to the lower end of the shaf t with the upper end being held fixed. The model was constructed to simplify the combination of the axial, bending and torsional loads. The stresses due to the torsion load were determined from the model shown in Figure 14. The half shaf t model is held fixed at the top and an antisynnetry deformation condition is applied at the longitudinal cut to represent the loacing. and deformation symmetry due to the two key configuration. In ti.a analysis, the loaded side is opposite to the actual loaded side. This affects only the view of the results. Loading conditions were imposed on the keyway wall to represent the following four different key loading situations.
- 1) loading to the tangent point (original key design)
- 2) loading to 9mm below the tangent point (modified key design)
! 3) load tapered to zero at the new key contact point from about one inch below to simulate a taper over a one inch length on a i new key design l
- 4) loading extending past the tangent point, 22 1/2* around the
(_ circle to represent the key situation suspected to have caused wear on the sidewall and the sidewall initiated cracking. l 48-l . i . L
PCD-125.DJA VII. Results of Shaft Analysis The three dimensional analysis was performed with the C-E MARC finite element analysis program with the pATRAN graphics program as pre- and post- processor. All loading cases were performed separately so that combinations of loads can be evaluated as linear combinations of the various load cases. The shaf t axis corresponds to the a coordinate direction, and the bearing load of the key on the shaf t corresponds to the X coordinate direction.
- a. Bending Loads The axial stress in the entire shaf t due to bending is shown in Figure 15, for the cyclic bending load during hot conditions given in Table 1. The detailed axial stresses near the top of the keyway are shown in Figure 16. This figure shows that the peak stresses occur near the keyway tangent point near the location of the Type (1) cracking and type-(3) cracking.
( The stress due to the other bending moments in Table 1 would scale with the moment value. These values will be considered with various loading combinations.
- b. Axial Loads l
The stress in the axial direction due to the axial load given for steady hot conditions in Table 1 is shown in Figure 17. This stress is very small and not cyclic, thereby having a negligible impact on the shaf t cracking. However, for completeness, it will be considered in load combinations,
- c. Torsion Loads The four torsion load cases are different only in the way that the load is applied by the key on the shaf t. The stresses of interest in these cases are the stress in the direction of the bearing load (s.
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PCD-125.DJA on the shaf t, called the X stress (essentially circumferential at l the keyway wall), and the axial stress, called the B stress.
- 1) CASE 1: Loading to tangent point The stress in the X and B directions for this load case with the torsion load equal to the steady value at hot conditions frem Table 1 are shown in Figures 18 and 19, respectively.
This case defines the base case for comparisen of the different key configurations. The axial loading distribution is seen to be reflected in the X direction stress plot. The peak stress in X is near the top of the keyway with a secondary peak near the bottom end. The axial stress peak occurs in the keyway sidewall near the location of the type 3 crack as previous preliminary analyses have-also shown, and has a value of 32.7 ksi.
- 2) CASE 2: Modified key design (D
The hot, steady torsion load is applied over the area of contact of the modified key, stopping at 9mm below the tangent point. The results of this analysis are shown in Figures 20 and 21 for the stresses in th, X and B directions .respectively. The peak axial stress, in the keyway sidewall is 23.9 ksi, significantly lower than the 32.7 ksi found in the base case.
- 3) CASE 3: Modified key design with taper i
In order to reduce the effect of t he sharp peak in load at the top , of the key, it has been suggestel that a slight taper in the bearing surface be made starting about one inch below the key contact point. An analytical representation of the most optimistic effect of such a taper would be to blend the load from a high peak to zero over the length of the taper. This axial load distribution was imposed on the model, again using the hot steady torsion load. The results are shown in Figures 22 and 23 for the X and a stress i
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- pCD-125.DJA respectively. In this case the axial stress peak of 21.8 -ksi is
( slightly lower than the corresponding case without the taper. The improvement is small compared to the improvement achieved with the shorter key without the taper.
- 4) CASE 4: Loading beyond tangent point The keyway sidewall crack, Type 3 of. Figure 2 was judged to be caused by significant wear- resulting from contact between the key and the keyway wall. In this case, the loading peak is extended 22 1/2' past the tangent point to simulate key contact in that region. The results of this analysis for the hot steady torsion load are shown in Figures 24 and 25 for the stresses in the X and a directions respectively. The peak axial stress in the sidewall is seen to increase slightly from the base case and to move further away from the tangent point. It appears therefore that the higher contact point. does not itself produce significantly higher
, stresses. The observed wear, however, is separate and could exacerbate the conditions at the high stressed location. The modified key, hcwever, since it is much shorter cannot contact or cause wear in a highly stressed region so this type of cracking is unlikely to continue to be a concern.
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- 5) Comparison of Cases The results of the analysis of the different loading conditions representing different key configurations clearly indicate that the peak stress in the sidewall near the locatior, of the sidewall crack is significantly reduced by shortening the key. The addition of the taper, however, does' not provide a significant improvement in the peak stress value. Additionally, the taper may be subject to local yielding which would eliminate the beneficial effect.
The stress on the surface which assists the initiation of cracks in the chrome layer are also reduced by shartening the key as can be seen by comparing Figures 19 and 21. Therefore, the shorter key will add additional margin over that achieved by the elimination of the chrome layer. The stresses in the bottom corner of the _ keyway are not
. significantly affected by the shorter key, as seen by comparing Figures 18 and 20. The increased radius of the corner, however from r = 0.7mm (Figure la) to r = 2mm (Figure
- 3) decreases the stress concentration factor from 4.5 to 3.1 according to Reference 5. Since this cracking was observed only in one shaft, it is judged that the radius improvement is sufficient to prevent future corner cracking.
VIII. Load Combinations The combination of axial, bending and torsion loads are addressed here for the case of the modified key only, since this is the configuration that is actually installed at palo Verde Unit 1. The load combinations for the steady loads are seen to be dominated by the steady torsion load. The cyclic loading stresses caused by bending and torsion are of the same magnitude and are shown here added together to produce the highest stress. / (
7 PCD-125.DJA 1 I e i
- a. CASE 1: Hot condition steady loads ,
[ The combined stresses for the loads in Table 1 for the hot steady condition are shown in Figures 26 and 27a for the X and 3 stresses respectively. As noted before, the torsion. load clearly dominates the combined loading. Figure 27b shows the von Mises stress intensity which relates to yield stress. The peak value of 46 ksi is well below the hot material yield of 92 ksi.
- b. CASE 2: Hot condition cyclic loads The combined bending and torsion stresses for the loads in Table 1 for the hot cyclic conditions are shown in Figures 28 and 29a for the X and B stresses respectively. The cyclic stress amplitude can be conservatively estimated from the von Mises stress intensity of the cyclic stress. This stress, shown in Figure 29b is quite small, about 3.8 ksi which is well below the fatigue strength of the shaft material,
- c. CASE 3: Cold conditions ateady loads The combined stresses for the loads in Table 1 for the cold steady conditions are shown in Figures 30 and 31a for the X and a stresses respectively. Figure 31b shows the von mises stress intensity for this case. These stresses are somewhat higher than the hot loads as anticipated, but are still less than the yield stress of 110 ksi at cold conditions. This is acceptable for steady loads.
- d. CASE 4: Cold conditions cyclic loads The combined bending and torsion stresses for the loads in Table 1 for the cold cyclic conditions are shown in Figures 32 and 33a for the X and a stresses respectively. The cyclic stress amplitude is shown in Figure 33b. These stresses are higher than the corresponding stresses for the cyclic hot conditions, but are still below the fatigue strength for non chrome plated material.
The steady load stresses are clearly within a reasonable percentage ( of the yield stress and therefore are acceptable. The cyclic f-
F PCD-125.DJA stresses will be compared to the shaft material fatigue data in the (' next section. IX. Material Limits The influence of the chrome plating on the fatigue strength of the shaft material has been shown in Reference 1. This influence is shown here as Figure 34. The ratio of minimum to maximum stress in ' the cycle, known as the stress ratio, R, is clearly very close to one since the cyclic stresses are a small portion of the steady values. The lower curve labeled "C", with chrome plating, water environment and high stresa 8 ratio, shows a strength as low as 3 ksi at 10 cycles. This is in the range of cyclic stresses computed in Section VIII. . The curve labeled "B" shows the fatigue strength with chrome plating and environmental effects, but a low stress ratio. Cu rve A directly corresponds to the loading and environmental conditions of curve B, but is determined for shaf t material with no chrome plating. The fatigue (, strength for the material without the chrome plating is at least 60% 8 higher than that with chrome plating at 10 cycles. previous studies of the impeller material (a cast version of the shaf t material) indicated a high cycle fatigue strength of at least 10 ksi. Therefore the value of 10 kai appears to be a sufficiently conservative value for the f atigue strength. The cyclic stress amplitude of 5.1 ksi for cold conditions from Figure 33b and 3.8 ksi for hot conditions from Figure 29b are clearly well below the very conservative estimate of 10 ksi fatigue strength. X. Evaluation of Shaft The stresses in the shaf t as modified and with the modified key design are significantly lower than the stresses in the original shaf t. With the removal of the chrome plating, the outer surface where most of the cracks originated has significantly higher fatigue strength. The cyclic stresses have been shown to be well below the high cycle fatigue k_
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PCD-125.DJA strength. indicating that .the modified shaf ts will endure a long ( operating life. In th3s analysis it was assumed that the impeller loading is shared equally between the two keys. The margin between cyclic stress and strength values is sufficient to account for a significant variation in this loading pattern. XI. Conclusions All the cracks which were found during the shaf t inspections have been addressed and the corrective action taken is anticipated to prevent similar cracking in the future. Type (1) cracks have been addressed by the elimination of the chrome layer and the reduction in stresses due to the shorter key. Type (2) cracks have been addressed by the increased radius of the bottom keyway corner. The Type (3) crack has been addressed by the reduction in stress due to the shorter key and the elimination of the possibility of wearing contact at the high stress point on the keyway sidewall. r, Since all types of cracking have been addressed and the peak stresses in the modified shaf ts are well below the fatigue strengths for high cycle fatigue, no further similar fatigue cracking is anticipated. i (- l
PCD-125.DJA XII. References-
- 1. Loehberg, R.,. Ullrich, W., Gaffal, K. , "Failure Analysis and Remedies",_
Presented at 13th MPA Seminars at Stuttgart, October 8-9, 1987,
- 2. "Ultrasonic Inspection Report of Reactor Coolant Pump Shaf t for PVNGS Unit One and Spare Shaft." Bechtel Job 19292-001, Prepared by Bechtel, Universal Testing Laboratories Kraftwerk Union AG and KSBAG, October 28, 1987.
- 3. "Stresses at the Maximum Loaded Locations of the Shaf t as Base for the Crack Propagation Calculation", KSB report US4 14550 Rev 1, December 1987.
- 4. CE letter to ANPP "Stress Analysis of Reactor Coolant Pump Shaf t and Impeller Keyways", V-CE35548, Dec. 3, 1987.
- 5. Peterson, R. E., "Stress Concentration Design Factors", J. Wiley and
. Sons, Inc., New York, 1953.
I
PCD-l25.DJA-
' TABLE'l PALO VERDE RCP SHAFT LOADS
- a. Hot Operating Conditions METRIC ENGLISH NOMINAL STRESS STEADY 55,360 NM 490,766 In lb 5.27 ksi TORSION CYCLIC 2,160 NM 19,148 In 1b .21 ksi STEADY 4,520 NM 40,070 In Ib .86 ksi BENDING CYCLIC 7,664 NM 67.941 In lb 1.46 ksi STEADY -256,510 N -57,715 lb -1.21 ksi
(, AXIAL j
- KSB comments that the correct value is -256,610N. The difference is considered to be inconsequential to the analysis and the analysis was not adjusted.
PCD-125.DJA TABLE 1 (Cont'd) PALO VERDE RCP SHAFT LOADS (Continued)
- b. Cold Cperating Conditions METRIC ENGLISH NOMINAL STRESS STEADY 72,440 NM 642,181 In Ib 6.89 ksi TORSION CYCLIC 2,610 NM 23,138 In Lb .25 ksi STEADY 6,142 NM 54,444 In lb 1.17 ksi BENDING CYCLIC 10,412 NM 92,302 In Lb 1.96 ksi STEADY +258,305 N +57,894 lb +1.21 ksi
( AXIAL i
- KSB comments that the correct value is -257,305N. The difference is considered to be inconsequential to the analysis and the analysis was not adjusted.
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APPENDIX 5 ANPP Report Field Inspection of Units 1 and 2 Reactor Coolant Pd:np Shaft Keys and Keyways l l l l i 4 I _m
. FIELD INSPECTION OF UNITS 1 AND 2 REACTOR C001 ANT PUMP SilAFT KEYS AND KEYWAYS C
Introduction The Units 1 and 2 Reactor Coolant Pump (RCP) shaft keyways and keys were visually examined- for evidence cf wear ano fretting. The examinations were condu:ted by ANPP Engineering and Engineering Evaluations personnel. The results of the shaft examinations are documented in this report, with photographs illustrating the condition of the keys and keyways. Unit 1 Table 1 summarizes the inspection results of the four Unit 1 shafts. Figure 1 is a sketch of a keyway and key, noting where cracks and wear are typically present. Heavy fretting wear was observed to be present at both the O' and 180' keyuays on shaft 2A. Figure 2 shows the shaft 2A 180* keyway. Circuraferentially criented cracks extending down the sidewall of these keyways were determined to be present, in the region of the fretting wear by magnetic particle ( testing. The shaft keys (Figures 3 and 4) were found to have experienced l significant localized wear corresponding to the keyway wear. Because of the similar wear locations- on both keys and the presence of grinding marks it is ( apparent that the keys had been swapped between the 0' ar.d 180' keyway at sometime since initial assembly of the pump. The keys were also apparently , ground to facilitate fit-up. l The keys and keyways for the remaining three pump shafes (Figures 5 through 8)
- l. exhibited varying degrees of minor fretting wear. No sidewall cracks were j
detected on these shafts. i Unit 2 i~ l' Table 2 summarizes the inspection results of the four Unic 2 shafts. The O' l and 180* keyways ori shaf t 1A exhibited moderate to light wear. Figure 9 shows ! the shaft 1A 0' keyway. The corresponding keys, Figure 10, also exhibited l moderate wear. Magnetic particle examination revealed the presence of a very l small linear indication in the wear region at the shaft 1A 180' keyway. l l The keys and keyways for the remaining three pump shafts (Figures 11 through l 16) exhibited wear ranging from none to moderate. None of the remaining ! keyways had crack indications associated with the observed wear. l Summary The Unit 2 keyways and keys did not show as frequent or as severe of wear as the Unit 1 RCP shaf ts' keyways and keys. Every Unit 1 shaft keyway and key 0350A/2263A
examined showed some degree of wear, while Unit 2 RCP shafts 2A and 2B had keyways and keys that showed no wear. Further comparisons show that the Unit C 1 2A shaft O' keyway had a 14mm long keyway sidewall crack with associated heavy fretting wear. The Unit 2 1A shaft 180' keyway had a slight 1.6mm long sidewall linear indication, with light wear. No sidewall indications were detected on any other Unit 1 or 2 RCP shafts. Conclusions Based on inspection results, we conclude the keyway fretting wear is a major contributor to sidewall crack initiation. Moreover, it appears that the amount of fretting wear also plays a role in the actual size of '2e crack being initiated, before fatigue takes over as the mode of propagatior l n , l t 1 s. 1 l l l 2-
f O b Page 3
~ ~
TABLE I: UNIT 1 RCP SHAFT CRACKING DATA 1 1 I I i l l Crack Initiation Site l l l l Identification I Chrome. I Side l Corner l Keyway Wear l Key Wear 1 i i i i i l I I l IA l 0* l 7.6mm l 0 1 0 1 Minor Rubbing I Light Wear 1 I l l 180* I I I I I I ! l 6.0mm l 0 1 0 l Small Amount of Fretting l Light Wear l 1 I I I I I I 1 I in 1 0* I O I O I 7mm i Light Wear i Not Available l 180" l I I I I l l l 1 l l 0 1 0 1 2mm l Light Wear l Not Available l
~
l 1 l I l l l l 1 2A l 0* l 3mm 1 14mm I 3mm 1 Ileavy Fretting Below Crack l Significant Localized Wearl l l 180* l l l l Heavy Fretting Above & Below l l l l l 12.7mm l 0 1 0 l Sidewall Crack l Significant Localized Wearl I I I I l I I I l 2n 1 0* l 7.6mm l 0 1 0 l Light Wear ' l Light, Uniform Wear l 1 1 180* I I I I l. I
-l 0 0 1 0 l Light Wear l Light, Uniform Wear !
l_ l 1 b
(' n R Page 4 Table 2 : Unit 2 RCP Shaf t Inspection Data l l Crack Initiating l l l l l Site and Depth l (1) l (2) l [ T denti fi ca tion i Chrome i Side I Corner i Keyway Wear i Kev Wear l 1 1 I I I I I I l 1A l 0* I O I O I N/T* I Moderate wear i Moderate wear. 1/4 " wida han l l t 180* I 0.4mm i 1.6mm I I I,1cht wear I Moderate wear. 1/4" wide han l 1 1 I I I I I i l 1B l 0* I O I O I I Linhe wear I T.i ch t wear l [ l 180* I O I O I I Licht mark. no noticeable wear i Li cht wear [ l i I I I i l I l 2A l O' I 17.7mm 1 0 l I None I None [ l I 180* I O I O I I I,1cht wear I Superficial wear l 1 i l i l ! I i l 2B l 0* I 1.6mm 1 O I I None i None l l l l l l l Moderate wear, parallel scratches l Superficial wear l l t 180* 1 1.6mm 1 0 I I noted 1 l ON/I - Not Inspected (1) See Figure 1 for location of vear on a typical keyway and key. (2) It was not posr.ible to confirm which key was for a 0* or 180* keyway. Therefore, identification was based on s ir.ila r wear inside the keyway wall.
6KE.TLW OF 6 HAFT KEYWAY ANP KEY ( - KEY' - ARE.AS OF LOCALIZED WE.AR s (AVN -
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Figure 3. Close-up of ends of Unit 1 0* (Left) and 180' (Right) Keys. Note similar wear locations and grinding mark on the O' key. gass, _ Figure 4. Unit 1 Shaft 2A 0' key showing wear and grinding marks. s i
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ATTACllMFKr 2 PALO VERDE RCP OPERATIONAL HISTORY,, UNIT 1 (REFUELING 10/2/87) RCP 1A RCP 1B RCP 2A RCP 2B Total RC? Run Time (hrs.) 19,382 19,473* 17,842* 17,601 Total Starts (Includes Test Loop Starts) 102 176 126 120 Run Time Tc 4 300*F 1,030 869 304 284 Tc > 300'F 18,302 17,993 17,444 17,140 Test Loop Run Time (hrs.) 50 611 94 177 Loss of Seal Injection (Quantity) 4 13** 4 4
- Pumps with impellar vane failures during 1983 HFT
** Nine loss of seal inject'on tests performed at C-E test facilities UNIT 2 (REFUELING 2/21/88)
RCP 1A RCP 1B RCP2A RCP 2B Total RCP Run Time (hrs.) 15,S90 15,842 15,167 15,079 Total Starts (Includes Test Loop Starte) 86 102 88 94
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Run Time Tc<300*F 425 367 204 174 Tc> 300*F 15,415 15,403 14,913 14,855 Test Loop Run Time (hrs.) 50 72 50 50 Loss of Seal Injection (Quantity) 2 2 2 2 UNIT 3 (AS OF 5/20/88) RCP 1A RCP IB RCP 2A RCP 2B Total RCP Run Time (hrs.) 3.548 5,531 5,520 5,420 Total Starts (Includes Test Loop Starts) 41 45 47 47 Run Time Tc( 300*F None Recorded Icy 300'F None Recorded Test' Loop Run Time (hrs.) 50 52. 150 83 Loss of Seal Injection (Quantity) 0 0 0 0 l
ATTACHMENT 3 STELLITE VEAR RING AREAS OF PVNGS REACTOR COOLANT PUMP IMPELLERS The Reactor cue. ant Pumps (RCPs) at PVNGS use stellite wear ring areas on the impellers. Stellite was selected by the manufacturer because of its known resistance to wear and galling. It was applied as a thin plasma sprayed coating, approximately 12 mils thick. Each impeller has two coated areas, totaling approximately 633 square inches. The upper ring is approximately 11.4" in diameter by 5.2" high. The lower ring is approximately 32.3" in diameter by 4.4" high (Figure 1). During the first refueling outage for Unit 1, the coated areas were 100% visually examined. All four impellers had some area of coating damage. Two impellers had extensive damage on tha upper ring, while the other two had minor damage on the lower ring. At the lower wear surface, only two small areas suffered any degree of damage out of the four (4) impellers. During the repair of the lower wear surfaces on the 1A and 1B impellers no additional areas of poor bonding became evident as a result of the machining activity. Thus, it is concluded that all areas of poor bonding on the lower wear surfaces have manifested themselves and no additional damage is expected. Based on field inspection of the impellers, the root cause of the stellite damage is ccacluded to be local insufficient bond strength between the stellite hardfacing and the base metal. This condition appears to be more prevelant at the upper wear surface. CE/KSB has evaluated the problem and their recommendations have been implemented. It involves stellite removal from all four upper rings, and removal of stellite in the small areas of damage on the lower rings. The stellite has been completely removed from the upper wear surface since an evaluation by CE/KSB has determined removal of the hardfacing will not be detrimental to pump operation. The stellite hardfacing on the lower wear surface has been removed for approximately 1/2 inch up from the bottom of the impeller inlet shroud for the full circumference on the 1A and 1B impellers. Complete removal of the stellite would affect the gap between the impeller inlet shroud and the suction pipe, which is critical to hydraulic performance and shaft stability. Due to the potential increase in occupational radiation exposure from stellite particles in the reactor coolant system, a program was started in order to develop an alternative wear ring material. The objective was to replace all of the lower ring stellite on the Unit 2 impellers. Despite a conserted effort including the use of consultants, a successful replacement coating could not be developed in time to support the Unit 2 refueling schedule. However, an effort to develop a suitable alternative is still in progress. The Unit 2 impellers were 1001 visually examined and no abnormal wear or damage was observed. The stellite was removed from the upper ring areas and the pumps were then reassembled. The Unit 3 impellers will be examined during its next refueling outage.
v l e . . FIGURE 1 f STE LLITE SURFACE
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