ML20246F630
| ML20246F630 | |
| Person / Time | |
|---|---|
| Site: | Rancho Seco |
| Issue date: | 02/28/1989 |
| From: | Atwell J, Khan T, Peabody W SACRAMENTO MUNICIPAL UTILITY DISTRICT |
| To: | |
| Shared Package | |
| ML20246F605 | List: |
| References | |
| NUDOCS 8903170153 | |
| Download: ML20246F630 (73) | |
Text
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/ 1/1g-6
. U-NUCLEAR ENGINEERING DEPARTMENT l
AUXILIARY FEEDWATER SYSTEM (AFW) i l
OVERPRESSURIZATION EVENT ,
4 J
l ENGINEERING EVALUATION REPORT i l
i FEBRUARY 1989 .l i
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Prepared By: Reviewed By: Approved By:
Obitfb-ld Wt U 4 & .
W, h y /g;, , f John K. Atwell Taj 94. Khan Warren" Pea ody 11 l
AGM Concurrence: PRC Concurrence:
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_ _ _ _ . _ _:____ _J
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TABLE OF CONTENTS
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Section Descr'iotion Pagg 1.0 Introduction 1 1.1 Background 1 1.2 Objective 2 1.3 Methodology 3 2.0 Scope 5 l 8
2.1 Piping and' Valves 5 f
2.1.1 Piping 6 ]
2.1.1.1 Inspection 6 L 2.1.1.2 Evaluation 9 2.1.1.3 Disposition 13 i I
2.1.2 Valves 14 j 2.1.2.1 Inspection 14 2.1.2.2 Evaluation 15 2.1.2.3 Disposition 17 2.2 Instrumentation 19 2.2.1 Inspection 19 2.2.2 Evaluation 20 l 2.2.3 Disposition 22 1
2.3 Electric Motor 24 i
2.3.1 Inspection 24 2.3.2 Evaluation 25 2.3.3 Disposition 26 1
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1 TABLE OF CONTENTS Description Pace Section AFW Pump P-318 28 2.4 Inspection 28 ,
l 2.4.1 30 2.4.2 Evaluation 33 2.4.3 Disposition Turbine, overspeed 35 2.5 Trip Device & Stop Valve 35 2.5.1 Turbine 36 2.5.1.1 Inspection 36 2.5.1.2 Evaluation 38 2.5.1.3 Disposition Overspeed Trip 39 2.5.2 Device & Stop Valve Inspection 40 2.5.2.1 41 2.5.2.2 Evaluation Disposition 43 2.5.2.3 Turbine Governor 45 2.6 2.6.1 Inspection 46 l Evaluation 47.
2.6.2 Disposition 48 2.6.3 3.0 System and Component Testing 50 4.0 Reconstruction and Evaluation 55 I
of the Event 5.0 AFW Operability Status 58 8
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1.0 INTRODUCTION
1.1 Background
On January 30, 1989, maintenance activities began on the P-318 Auxiliary Feedwater (AFW) Pump. This work included replacement of the governor for the turbine driver (K-308) as well as several other minor maintenance activities. After completion of the maintenance work, (January 31, 1989)'the 1
post-maintenance testing _ activities were~ initiated. . The pump
~l was first tested using the electric motor driver. This test !
l Was comple,ted successfully and the motor was secured. The !
P-318 pump turbine driver was then started for post-maintenance testing to verify-its functionality after the governor. replacement. Opening valve HV-30801'to allow steam flow to the turbine resulted in a rapid run up'in the steam driven turbine speed to a level of 6020 rpm. As a j 1
consequence of this overspeed of the- turbine :(overspeed trip I setpoint is 4450 rpm), the discharge pressure from the pump-was calculated to have exceeded the system design pressure i
(1325 psig). This overpressure condition existed for several minutes prior to closure of valve HV 30801 by plant. operators and termination of steam flow and-the AFW system overpressure conditions.
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As a result of evaluations made immediately after-the overpressurization event, both trains of AFW were declared inoperable.
Under this condition, Technical Specification 3.4.2.F (2) requires the reactor be made sub-critical withinL '
four hours and the reactor be on decay heat cooling within the next twelve hours. Efforts were immediately' initiated'to' assess the impact of this event-on plant equipment.
1.2 OBJECTIVE This report provides a summary-of the' Nuclear Engineering Department's investigation and evaluation of the AFW system condition following the overpressurization~ event. It specifically. addresses the six component categories-identified in the Action Plan (89-M-101), as well as providing an overall Engineering evaluation of the event.
l This report provides a definitive assessment of the.AFW system and its ability to operate and fulfill its safety function.
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l 1.3 METHODOLOGY In approaching the overpressurization event, Nuclear Engineering utilized the PDQ (Potential Deviation from Quality) and the Work Request (WR) processes. The effected components were identified by the Nuclear Engineering Department, and PDQs were written for each component and/or category of components. Each PDQ was dispositioned on an
" Interim" basis by identifying specific inspection, testing and disassembly requirements for the components identified within the body of the PDQ. The disposition requirements were converted to Work Requests for implementation of the interim actions. Prior to implementation, each Work Request was reviewed by Engineering and Maintenance to assure that all the identified actions within the PDQ were addressed.
The information obtained from the completed WRs was used by Engineering to evaluate the condition of the effected components. This information provided vital input to the final disposition (e.g. replace,~ repair, etc.) of each of the components as documented in the respective PDQs. As noted previously, the WR process was used to implement the final disposition of each PDQ to assure that all work items identified in the PDQ were translated into actions in the field.
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For the purpose of permanent Quality-Assurance record keeping, the activities described above and the final dispositions of these activities as documented on the.PDQ/WRs will serve as the documents of. record.
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2.0 SCOPE 2.1 PIPING AND VAINES During the period of time that the turbine was in an ,
1 overspeed condition, the AFW components were exposed to )
l pressures in excess of the system operating pressure of 1325 psig. The rapid increase in pressure and the duration of -
this overpressure period was obtained from IDADS data. A plot of the pressure vs. time obtained from pressure transmitter PT-31801 is provided herein as Figure 2.1-1. As can be seen from this figure, the increase in pressure occurred quite rapidly (less than 3 seconds) and lasted for a l period of approximately 3 minutes and 15 seconds. Since the IDADS information does not indicate pressures in excess of 1500 psig, a calculation was performed to determine the i maximum pressure.
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Calculation Z-FWS-M2492 was generated to determine the maximum pressure using theoretical dynamic similitude relationships based on the existing pump performance curve.
The analysis was based on the calibrated (and reverified) tachometer reading made at the time of the event of 6020 rpm.
The resulting pressure was determined to be 3850 psig, which was assumed to exist for the duration of the event. It is at 5
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To identify the extent of the overpressurization on the system, the system configuration as it existed immediately l
after the event was reviewed. Figure 2.1-2 provides a l l
picture of the effected portions of the AFW system and the j valve lineups that existed at the time of the event. _It is the piping and valves within this boundary that this section l ]
of the report will address. The P& ids associated with the AFW system and the drawings from which the figure was l l
generated are M-533, sheet 3, M-545 and M-532, sheet 1.
l 2.1.1 PIPING I
, 1 The inspections, evaluations and inal disposition of the effect of the overpressurization event on the AFW piping was addressed and documented in PDQ 89-0143 and its associated WRs.
2.1.1.1 INSPECTION 1
To evaluate the as found condition as well as determine the damage, if any, the inspection process was broken i into several general steps.
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- A walkdown-of the above-ground portions of the piping (See Figure 2.1-3) was performed prior to insulation removal to observe any obvious signs of damage and/or leakage. This walkdown identified.no obvious damage. Some minor leakage was observed at flanged joints and packing.
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- Preparation was made for further inspection of the piping by hanging clearance tags, draining the .
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individuals certified in accordance with ASME Section XI requirements for VT-1 examination.
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- To assess the physical condition of the piping and fittings, thickness measurements were taken using i calibrated Ultrasonic Testing (UT) equipment and certified personnel at approximately 600 points on the piping system. Each flanged connection was f also visually inspected prior to its disassembly and component evaluation. The areas receiving UT examination and the resultant thicknesses obtained 1 are tabulated in the PDQ.- This data was obtained' to verify minimum wall thicknesses in support of I the analysis performed for the component: stress f evaluations.
- The underground portion of pipe was excavated in two locations, which are identified on Figure 2.1-3. This was performed in order to determine the general condition of the pipe coating and to provide additional confidence in the preservation ]
of the underground piping from corrosion / degradation.
- Additional non-destructive examinations (PT) were performed on a sample of above-ground weld' locations to confirm their integrity.
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2.1.1.2 EVAIDATION The piping contained within the overpressurized boundary (Figure 2.1-2) was designed and procured as B31.1-1967, Quality Class 1, seismic class 1 in accordance with Bechtel Specification 6292-M21.01, July 1970. It was constructed to B31.1-1967 in accordance with Bechtel Specifications 6292-M870 and 6292-M875. The system has been maintained in accordance with B31.1 and ASME. ,
1 Section XI.
Subsequent modifications and evaluations of this system i have supported the classification of Quality Class 1. I It has been evaluated to ASME Section III-1977, Summer-78 addenda (IE Bulletin 79-14). Modifications have been i
to the original construction code with appropriate j i
traceability and NDE. This is consistent with the guidance in ASME Section XI.
i In consideration of the above, the current overpressurization event was evaluated to the-same edition and addenda of Section III.' The district considers this to be consistent with its original design philosophy of maintaining this system at a Quality Class 1 level.
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The focus of the evaluation of the overpressurization event.was the determination of the maximum pressures / stressed and the acceptance criteria against which they would be evaluated. of concern was the-hoop and primary piping stresses. The appropriate sections of the B31.1-67, Section III-ND-77, and Section III-ND-86 were reviewed to establish the upper limit for the j 1
acceptance criteria to be used for-the evaluation. The I
. maximum hoop stress permitted during testing was found to be 90% of the yield strength (Sy). The primary-stresses were limited to 1.2 times the code allowable stress (Sh)*
A similar review was performed for the flanged l connectors. The concern here was longitudinal hub, radial flange, and tangential flange stresses. The upper limit, according to the code, was 1.5Sh (ND-3658).
The input information for the calculations utilized ;
actual thickness' measurements obtained during the inspection phase (2.1.1.1) and the available Certified Material Test Reports (CMTRs) for the piping and fittings. Figure 2.1-4 provides a flow chart which reflects the criteria and methods used in the stress calculations.
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s 1 FIGURE 2.1-4 CRITERIA A.'lD METH000L3GY FOR TriE AUXILIARY FEE 0W/TE? PIPI'iG STRESS El;LUATIE e FIPIM e n.scsa e !II e EDUCZ3ts o
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The results indicate that at no point did the piping exceed the allowable stress levels as indicated on Figure 2.1-4.- All piping and fittings for which both CMTRs and thicknesses were available were found to have ;
seen a stress level less than 83% of'the actual yield. j Generally, the stress levels in the piping system were on the order of 60%'of yield.
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As indicated, the flanges were evaluated against an upper limit of 1.SSh. For cases.that did not' meet this criteria, a more rigorous finite element analysis was i
performed using the ANSYS computer code with quarter I 1
symmetry and optimum nodalization. The flange results -]
also indicated that none of the flanges were stressed.
beyond the allowable stress level-of the code. The ;
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.j stress analysis results can be found in calculation <
l Z-FWS-M2497. !
k A 100% inspection and analysis was not possible since a portion of the piping and fittings was inaccessible.
Additionally, some of the CMTRs were unavailable to be 1
factored into the analysis. .This being the case, a statistical evaluation was performed to provide reasonable assurance that the piping system components are capable of performing their design functions.
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A sample size was chosen which provided a 95% confidence j l
that-5% or fewer of the piping and fittings experienced l
stresses that exceed the stress limits. ]
The components in the Auxiliary Feedwater System were considered to be members of a homogeneous population for the purposes of the sampling plan for the following 1
reasons:
- All of the components are of stainless steel' seamless construction. They were all manufactured to similar fabrication specifications and l l
manufacturing controls.
- The properties being evaluated are yield stress from the CMTRs and wall thickness measurements.
These are material properties that are dependent solely on the chemistry and manufacturing process.
The components in the sample were evaluated for acceptability using the following criterion:
- The wall thickness of all accessible components were measured and compared to the calculated minimum required wall thickness.
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- All CMTRs were reviewed for minimum yield values and- compared to the calculated minimum yield required.
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If a sampled components wall thickness was greater than )
J the calculated, minimum required for the yield obtained ]
l from the CMTR, then the component passed the criterion.. ]
'y The results of the evaluation of the stresses experienced by the components in the sample are that at i
a 95% confidence level,-5% or fewer of the AFW piping i j
system components experienced stresses that exceeded the applicable stress limits. For the components evaluated, none was calculated to have experienced stresses that J l
exceeded the applicable stress' criteria.
t The details of the piping analysis and evaluation have y 1
been documented in ERPT M-0162. I 2.1.1.3 DIS POSITION
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i In response to the overpressurization event, the j i
affected piping and fittings were inspected (2.1.1.1) l 1
and evaluated (2.1.1.2). As a~ result of the.above evaluations, there is a reasonable assurance that the
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piping and fittings are capable of. fulfilling =their q 13 1
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design functions and, upon completion of the testing (Section 3.0), will be declared to be operable.
2.1.2 VALVES The inspections, evaluations, and final disposition of the overpressurization on the AFW valves were addressed and documented in PDQs 89-0149, 89-0150, 89-0177 and 89-0184 and their associated WRs.
2.1.2.1 INSPECTION l
i All the valves (Figure 2.1-2) impacted by the overpressurization event were visually inspected. Some valves were measured for signs of degradation. The results of the inspections performed indicated that no l visible or measured degradation to-the valving had occurred.
Documentation for each valve was obtained as necessary, and the valve characteristics were reviewed. This review included, but was not limited to, the following ,
information: Rating, Size, Materials, Type and pertinent Codes and Standards. Once the data was collected for all the valves of concern, an evaluation was performed, with vendor input, to determine the 14
capability of the valves to withstand the elevated pressure and be returned to service.
2.1.2.2 EVALUATION An extensive evaluation of the data was performed and is documented in Engineering Report ERPT M-0160. This evaluation considered the effect of overpressurization on:
- Pressure Boundary Integrity
- Seal Effectiveness (e.g. O-rings, gaskets)
- Valve Operators and operability After reviewing the data collected and conducting discussions with vendors as needed to support the I
review the evaluation team used the following criteria to determine if the valves were acceptable for continued operation:
- For valves that were open during the event (per A. 51) , the shell hydrotest capability, as determined by the appropriate codes or the valve manufacturer, must be greater than 3850 psig.
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- Valves that were closed during the event (per A.51)
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were evaluated in one of two' ways:
- 1) To determine if the valve seat design capability multiplied by a factor of 1.1 was greater than 3850 psig; ,
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- 2) The manufacturer provided documentation j
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l indicating that there was no adverse effect on the valve as a result of exposure l to a pressure of 3850 psig.
- For the power-operated val e, the design stem 1 thrust was evaluated against the additional thrust l
created by the 3850 psig to determine if the design thrust value was exceeded. (NOTE: None'of the 1 1
i motor-operated valves were exercised during the event; therefore, only static load conditions existed.) l 1
l As a result of the evaluation, all the AFW process and I
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root valves were determined to be capable of I
withstanding the overpressure condition without loss of-pressure integrity or operability with the exception of FWS-738, 702 and 703 (Whitey Valve Company), which were !
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- k. I designed to 3000 psig. The detailed evaluation.for each of the valves is provided in ERPT M-0160.
2.1.2.3 DISPOSITION I
In response to the'overpressurization event, the affected valves were inspected (2.1.2.1): and evalu'ted- a (2.1.2.2). As a result of this effort,.the'following actions were taken to return.the components' described in-this section to operable status:
FWS-738, 702 & 703 were replaced with Whitey-valves.
which are rated for 5000 psig.
Valve numbers HV-20581, 20582, 31826, and'31827 had i their bonnet gaskets replaced / reworked and seating surface tested. Upon reas=cably, they-were tested and successfully passed the MOVATS. requirements.
The operators for HV-20581 and HV-20582 will be replaced during the next refueling outage as a ~
result of a previous commit tent from the MOVATS effort (DCP 88-0024).
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9 .. ll Having completed'these actions, the valves which were reviewed have been determined to be capable of i fulfilling their design functions and, upon completion of the: required testing (Section 3.0), will be declared to.be operable.
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2.2 INSTRUMENTATION' The AFW system instrumentation ~affected by the event a local consisted of several flow transmitters (FT),
and a pressure transmitter (PT),
Figure their associated tubing, hoses and fittings.
2.2-1 provides a diagram that indicates the relative locations of each of the impacted instrumentation _
camponents. This section describes the evaluation that was performed on the AFW instrumentation.
The inspections, evaluations and final disposition of the overpressurization of the AFW instruments and associated connections and fittings were addressed and documented in PDQ 89-0147 and its associated WRs.
2.2.1 INSPECTION The instruments affected by the event are as follows:
FT-31803 FT-20501 FT-31802 FT-20502 PI-31801A FT-20503 PT-31801 FT-20504 19
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. .e r j 9 s Each of these instruments was visually inspected and its documentation was reviewed to determine if its design '
conditions were exceeded. In addition,'the as-found calibration points for FT-20501, FT-20502, FT-20503, FT-20504, FT-31802, FT-31803 and PT-30801 were I 1
documented and evaluated.
l The instrument lines shown on, Figure 2.2-1. consist of 3/8" instrument valves, valve manifolds, stainless steel l tubing, tube fittings and flexible stainless steel hose.
i The valves were visually # inspected and the documentation l ~for all the items were reviewed to determine if the l ,
)
l design condition of any of these components was j exceeded.
2.2.2 EVALUATION l
l The transmitters listed in Section 2.2.1 were supplied by Rosemount and are one of the following model numbers: 1153DB5, 1153HB6RA or 1153GB9. A review of the vendor information indicated that models 1153HB6RA and 1153GB9 were designed to withstand hydrostatic test pressures to 4500 psig without damage. The model 1153DB5 transmitters have the same pressure casing parts
~
l with the only difference being the pressure cell.
l Discussions with the vendor, which were' 20
i a
followed up by correspondence, indicate that all the !
transmitters were designed to withstand the pressure ]
f experienced during the overpressurization event. The !
t vendor stated that overpressurization could cause a zero shift in calibration and recommended that the d
instruments be recalibrates. u i
i Review of the information available on the Ashcroft pressure indicator (PI-31801A) did not provide <
sufficient evidence to confirm its ability to withstand j
( :l
'the overpressurization condition. With insufficient information available, it was determined that this l
indicator and its associated instrument valves would be l I
replaced.
The instrument lines were reviewed to determine the impact, if any, as a result of pressurization to 3850 psig. All the 3/8" tubing (304SS) was found to have a working pressure of 6500 psig. The fittings used with these instruments are Swagelock (SS) and have, at a 1
minimum, a 3938 psig working pressure limit. Review of 1
l the flexible metal hose indicated a proof pressure of 5330 psig. Thus, the' instrument line components were found to be designed to withstand pressures in. excess of 3850 psig.
21
- e
=
The instrument valves and valve manifolds were-manufactured by either Dragon Valve or by Whitey Valve-Company. Discussions with Whitey Valve indicate that l Model #1KS4. valves manufactured prior to September 1987 were rated at 3000 psig. This being the case, replacement of the Whitey valves was recommended. For.
the remaining Dragon Valve components (Part #s 14564 and u
14563), the manufact'rer indicated that the ratings of their components should be determined using ANSI B16.34-
- 81. This Standard indicates a working pressure of 3600 !
psig (100 F) and allowable hydrotest pressure at 150% of the working pressure for.the shell and 110% for seat 1
closure. Using these code allowables, the Dragon Valve I l
components were determined to be acceptable.
2.2.3 DISPOSITION In response to the overpressurization event, the affected instrumentation and associated tubing and l l
fittings were inspected (2.2.1) and evaluated (2.2.2).
As a result of this effort, the following actions were taken to return the components described in this section to operable status:
22
A .
4
- PI-31801A and its associated Whitey instrument valves were replaced in a like-for-like replacement.
- Based on the results and evaluation in Section, 2.1.2.2, all Whitey valves were replaced with Whitey model #1KS4 valves manufactured after September 1987 (design pressure of 5000 psig).
l i
I
- All instrumentation was re-calibrated to within l their design allowable settings.
l
-l
- A DCO was generated to resolve a drawing discrepancy discovered during the review (M-533, Sheet 3).
Having completed these actions, the instrumentation and l
associated tubing / fittings have been determined to be capable of fulfilling their design. functions and, upon completion of the required testing (Section 3.0) will be declared to be operable.
)
l l
I l
1 23 4
s, .
l 2.3 ELECTRIC MOTOR .;
l AFW pump P-318 is driven by a 1000 hp induction moter i l
(P-318-M) or a 920 hp steam turbine driver in tandem.
This motor was successfully tested and deenergized prior to the overpressurization event. Figure 2.3-1 shows the orientation of the pump / motor / turbine assembly. Figure j 2.3-2 identifies the major components of the motor for the event evaluation.
PDQ 89-0146 documents the inspections, evaluations and ]
1 final disposition of the overspeed on the AFW P-318 motor.
2.3.1 INSPECTION The AFW pump induction motor was visually inspected to document the as-found condition and alignment before ;
being shipped to the Westinghouse Class 1E motor repair facility in Compton. Westinghouse inspected and tested the motor per the instructions in the PDQ in the presence of SMUD representatives. Hitachi, the motor manufacturer, provided information on the components which may have been overstressed.
24
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The shop inspection included:
- Disassembly and cleaning of the motor.
- Visual inspection of the major internal components of the motor.
- Visual inspection and selective dye penetrant testing of the components that may have been overstressed by the overspeed.
2.3.2 EVALUATION l
All work performed in the Westinghouse shop was observed by individual' District representatives from Nuclear Engineering, Maintenance, Quality Control and Plant Performance.
During disassembly, there was visible evidence that damage had occurred to the bearings and labyrinth oil i seals which would require repair. Rotor runout was measured to verify that the shaft had not been deformed.
25 :
)
__ i
-=, ',
The shop inspection included:
- Disassembly and cleaning of the motor.
- Visual inspection of the major internal components of the motor.
- Visual inspection and selective dye penetrant
. testing of the components that may have been overstressed by the overspeed.
2.3.2 . EVALUATION All work performed in the Westinghouse shop was. observed by individual District' representatives from Nuclear Engineering, Maintenance, Quality Control and Plant < l l
Performance. 1 During disassembly, there was visible evidence that' damage had occurred to the bearings and labyrinth oil 1
seals which would require repair. Rotor runout was H measured to verify that the shaft had not been deformed.-
f 25
. D,
- 9 Hitachi provided a list ~of components that were potentially overstressed.- !
These included the radial fan j side plates, fan vanes, fan vane rivets, rotor core clamping ring boss, core back and upper end ring. !
Inspection of these components was performed.. Dye-penetrant testing was also performed on the radial fan side plate,-fan vane rivets, andaupper end ring. The
_1 results of these inspection activities indicated that no i
. damage had occurred to the identified components. The District and Westinghouse performed stress calculations j to provide additional-verification and justification for :{
i acceptance.
4 2.3.3- DISPOSITION In response to the overspeed event, the pump motor P-318-M was inspected (2.3.1) and' evaluated (2.3.2).
Based on the results of this effort, the-following actions were taken:
The bearings were rebabbitted with certified material.
The labyrinth oil seals were dressed and the shaft-polished.
26
- c. . .
- The motor was reassembled.and painted, the motor
-was balanced, and the shaft / seal clearances were cher'ed. The motor was tested and vibration meas uaments were recorded and favorably compared to previous values. Results indicated that the motor was within design tolerances.
- . Rotor balance and vibration measurements provide-additional evidence of rotor integrity. All of the manufacturer's concerns have been successfully addressed and all visual-inspections and tests indicate that the rotor-has not been-damaged.
1 As a result of the above actions,'the pump motor P-318-M has been determined to be capable of fulfilling its design function and, upon completion of the required testing (Section 3.0) will be declared to be operable.
]
1 l
27
I 2.4 AFW PUMP P-318 AFW pump P-318 can be driven by either an induction motor or a steam driven turbine (Figure 2.3-1). The pump is a Hayward-Tyler (formerly B&W of Canada) horizontal, 6-stage, centrifugal, split case pump. A cross-section showing the internals of the pump is provided as Figure 2.4-1. The results of the inspections and evaluation of the P-318 pump are provided in the sections that follow.
The inspections, evaluations and final disposition of the overpressurization of the AFW P-318 pump were addressed and documented in PDQ 89-0144 and its associated WR.
2.4.1 INSPECTION Inspection of the pump was approached in these phases.
The first phase consisted of inspection of the as-found condition of the pump prior to disassembly. This included:
Visual inspection of the pump for signs of degradation was performed.
28
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- Torque measurements of various components as described in the PDQ were taken and recorded.
The upper half of the pump casing was removed and '
additional inspections were performed as follows:
- A visual inspection of the pump internals was performed.
- Several measurements were taken and recorded including lateral and radial impeller clearances and runout, and shaft end float.
The final phase of the pump inspection consisted of removal and inspection of the rotor, stuffing boxes and bearings.
- Visual inspection of numerous internal components was performed as described in the PDQ.
- Measurements as described by the PDQ were taken and recorded for numerous components, including wear ring clearances, shaft sleeve clearances and radial sleeve bearing clearances.
29
... 's H
1
. Additional information was also collected such as serial and heat numbers, casing stud conditions, and flatness / texture of the casing flanges.
1 k
Areas of the casing were ultrasonically tested to' l verify as-found wall thicknesses.
I 2.4.2 EVALUATION l
4 i
l l
The torque measurements were taken. prior to upper casing removal.
Drag torque for the pump-turbine-motor coupled together was measured and found acceptable. An~ attempt was made to determine the drag torque for the-decoupled motor but was stopped and performed after upper casing .
removal due to resistance encountered and the desire to prevent damage by forcing the shaft. Subsequent inspection, after casing removal, indicated ~some corrosion material between the impellers and the casing.
After checking each impeller, the shaft was easily l rotated by hand.
)
Visual inspection of the stuffing box, bearing cooling and pump balance piping indicated no abnormalities or damage.
Inspection of the pump casing indicated that some rubbing of the casing had occurred,'with. minimal material removal.
30 l
~
l
,\
t
, r a
Upon upper casing removal,. rotor shaft float was measured and found acceptable. The impellers were checked for lateral and radial' clearances, looseness, and axial'and radial runout. As'a result of incorrect sleeve locknut adjustment, the impellers were found to-be loose, resulting in lateral clearances being tighter on one side of the impeller than the other. Runout measurements were taken and appeared to be acceptable.
Due to the looseness of the impellers, these j measurements were not relied upon. I l
The discovery of the loose impellers led to the disassembly, inspection and reassembly of the rotor I assembly and the associated components. The results 1 l
were evaluated by the vendor and found to be acceptable.
l All shaft sleeves (e.g. shaft, balance) were inspected and sleeve clearances measured. Clearances were evaluated by the vendor and found to be acceptable.
However, due to excessive rub and burn marks, the inboard shaft sleeve was replaced. This inboard shaft sleeve was the only component detrimentally affected by !
the overspeed event.
l 1
31 l
1
=., .
Thrust and radial sleeve bearings were visually and dimensionally inspected-for any deterioration. Thrust bearings were found acceptable.- Due to the necessity of-destroying one of the thrust bearings, in order to l
perform inspection, both thrust bearings were replaced. -l Radial sleeve bearings showed no signs.of overheating or galling. The inboard bearing was within vendor tolerances and reused. The outboard bearing-was inadvertently damaged during removal and,;therefore, replaced. ,
j i
Packing and wear rings were inspected'. 'The clearances- l measured on the wear rings were evaluated by the vendor j to assure that no detrimental impact on the pump would l l
occur. The packing showed signs of overheating; thus, j replacement of the packing was performed. i j
l The casing wall thickness, flange rubbing and studs were reviewed by Engineering and the pump vendor. No deformation was found to have occurred. The casing !
i halves and studs were analyzed by the vendor and found !
acceptable. Additional evaluation of the studs by 3 Nuclear Engineering concurred with the vendor acceptance. !
I 1
32 l
1
4 1 H
Due to:the looseness of'the impellers and the close tolerances, the impollers and casing were checked ~for wear marks. e
'Small: wear marks were found in both' impellers and the. casing.- These were evaluated by the. -
.q vendor and found to be acceptable.
~
2.4.3 DISPOSITION i
In response to the overspeed event, the P-318 pump was 1 il inspected (2.4.1) and evaluated (2.4.2). As a' result of
\
this effort, the following. actions were taken:- 1 l
Both thrust bearings were replaced.
l The inboar'd shaft sleeve was replaced.
.i
)
The rotor assembly was reassembled with the locknuts properly adjusted to. assure appropriate lateral clearances. In addition, Plant-Maintenance Manual M.22 was revised to provide clear and precise information on how those locknuts should be adjusted.
The outboard radial sleeve bearing was replaced.
33
.j
. I As a result of the above actions, the pump (P-318) has
-been determined to be capable of fulfilling its design-i function and, upon completion of the required testing' j (Section 3.0) will be declared to be operable.
1 l
i
'I 34
'l
.I i
2.5 TURBINE, OVERSPEED TRIP DEVICE AND STOP VALVE j i
l The turbine driver as shown in Figure 2.5-1, is a.920 hp l single stage, non-condensing model GS-2 turbine J l
manufactured by Terry Turbine. Its normal operating 4 i
speed is 3550 rpm with inlet steam conditions of ,
I approximately 1000 psi and 550 F. Turbine speed is f controlled by a Woodward Type'PG-PL hydraulic governor.
H Steam flow to the turbine and overspeed protection ~is i
provided by a 4" Gimpel motor-operated stop valve. .This .j
]
valve is tripped to close in the event of an overspeed j 1
condition by a centrifugally operated mechanical. trip
- {
device attached to the turbine driver shaft. Figure j l
2.5-2 provides a sketch of the valve-(HV-30801) and the associated mechanical overspeed trip device. This j section of the report will address the investigation of these devices and their disposition.
2.5.1 TURBINE The inspections, evaluations and final disposition of the turbine are addressed and documented in PDQ 89-0145 and its WRs.
35
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2.5.1.1 INSPECTION The inspection of the turbine (K-308) was performed as described in the PDQ. This inspection included the following:
- The shaft was spun by hand and the drag torque and runout measured and documented.
l l
i
- Visual inspections were performed on the journal j and thrust bearings, exhaust nozzle, governor valve, the internals of the mechanical overspeed 1
trip mechanism, and the turbine wheel buckets (boroscopic exam). ]
1 Check valve MSS-068 and the sentinel. relief valve were removed for further examination.
2.5.1.2 EVALUATION i
The shaft inspection results and measurements were evaluated and found to be within allowable ranges as documented by the Dresser-Rand service representative.
Inspection of the bearings revealed that replacement' would be necessary for both the coupling and governor.
l 36
.1 .
end shaft bearings. Replacement of the bearings was expected since they were designed for a' maximum speed of i
4700 rpm with oil ring lubrication.
]
1 The thrust bearings were found to be in good condition and required no further work. ,
J i
The inspection of the wheel buckets as well as.the L
mechanical overspeed trip weights and tappet. indicated j no degradation of these components. Inspection of the i
governor valve found it to be in acceptable condition ,
I 1 '
I and i,t was re-installed. The sentinel valve was inspected and calibrated to its set' point of 25 psig and re-installed.
Removal and inspection of MSS-068 (turbine exhaust check valve) was also performed. MSS-068 was found to have a broken spring leg resulting in one of the internal flappers being ineffective (open). It was also noted that the cross-sectional area of the valve was much less than the exhaust port for the turbine. The results indicate a need for modifications with respect to the i MSS-068 valve.
l 37
l l
1 I
i The restriction of the exhaust port caused by MSS-068 j i
was the contributing factor in the lifting of the sentinel valve during the event. Design for the exhaust-port is an 8" ID with a 50 square inch cross-sectional area at a pressure of 2 psig. MSS-068, as originally configured, provided a 26 square inch exhaust' port which
'I resulted in a back pressure sufficient to lift the i sentinel valve.
Additionally, the bearing oil coolers were pressure j tested to 113 psig for 10 minutes and no leakage was found. This was performed as a preventive maintenance measure, taking advantage of the.K-308 turbine being
'I H
l 1 l available for testing. I l
1 2.5.1.3 DISPOSITION In response to the overpressurization event,'the turbine l
driver (K-308) was inspected (2.5.1.1) and evaluated (2.5.1.2). Based on the results of this effort, the following actions were taken:
l
drained and cleaned, then filled with clean oil.
l
- New governor and coupling end shaft bearings were 38
1 i
- . '. l installed, their pedestals re-installed and'the' )
. .l shaft runout and float was reverified and found to: j be acceptable. ,
I i
- The governor, valve was re-installed.without
.j modification.. ,)
1
- MSS-068 was modified by removal'of its internals' '
and the increase of the internal cross-sectional i J1 are to equal that of the exhaust pipe. 1This 1 modification is complete and documented'in DCPT#
89-0031.
As a. result of the above actions, the: turbine driver-(K-308).has been determined to be capable ofLfulfilling.
its design function and, upon completion of.th'e required testing (Section 3.0) will be declared'to be operable.
2.5.2 OVERSPEED TRIP DEVICE & STOP VALVE The inspections, evaluations, and final disposition of the turbine overspeed trip device and' shutoff valve and their malfunction during the post-maintenance testing .,
are addressed and documented in PDQs89-152, 89-175 and'89-145 and their associated WRs.
l 39
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2.5.2.1 INSPECTION To determine the as-found condition of the stop valve-and the overspeed trip device, the following inspections were performed:
- An initial visual inspection was made.of the external components of the stop valve (HV-30801) and the 6verspeed trip device. The PDQ and associated WRs describe the inspection and details 1
the measurements taken.
- The functionality of several mechanical devices was tested. fhis included operation of the trip switch, stroking HV-30801 and manual reset of the mechanical'overspeed trip (MOT) followed by manual tripping of the device to observe the function of the mechanical trip. The exact steps and sequence of this testing can be found in the implementing WR.
- The force to disengage the valve trip latch was l
measured and found to vary from L. to 41 pounds.
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- Interna 1' inspection of.the overspeed trip' device was accomplished by removal of the. governor end bearing pedestal. The-emergency' trip weight'and
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. tappet springs condition were evaluated during the inspection.
i 2.5.2.2 EVALUATION The inspections of the overspeed tripfdevice found the 1
trip weight and tappet spring to be undamaged and usable ]
without modification or repair. The trip' weight' spring compression was determined to be adequate for continued i
service. Based on the inspection results, no'further action was considered to be necessary;for.the overspeed' trip-device.
During the event, as determined by-as-found-inspections, the trip tappet was moved upward by the emergency: weight- ;
1 as designed. However, insufficient force was app' lied by the trip rod in order to trip valve HV-30801. .This provides further indication'.that the' turbine end'of the overspeed device was functioning properly.
Through the Work Request process, a. systematic trouble shooting program was implemented to determine and duplicate the failure mechanism. Spring scales were 41
used to simulate the. forces. It was established through the trouble shooting technique that the primary cause was a weak trip rod spring. However, it.was also learned that there may have been other. contributing causes, (e.g. improper lubricating, trip switch adjustments, etc.).which by themselves may not have caused the overspeed trip mechanism to fail,'but may-have contributed to the. event. It was also established-that it required'31 pounds force in.the'as-found condition to operate the mechanism properly. Section 2.5.2.3 describes th9 actions taken to resolve the deficiencies in the trip rod and valve trip latch assembly.
t Valve HV-10801 was stroked numerous times during the inspections and found-to move without binding when actuated by handwheel, motor operator and by trip.
Based on observation of the valve during operation and due to the fact that it is designed to prevent entry of loose parts / debris (greater than 1/8") into the valve, the valve was not disassembled. The valve is considered to be acceptable without further repair or modification.
1 42 1
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2.5.2.3 DISPOSITION In response to the overspeed event, the overspeed trip device and stop valve were inspected (2.5.1.1) and evaluated (2.5.1.2). As a result of this effort, the following actions were taken:
- On valve HV-30801, the trip hock shaft, spring and-
- washer were removed, cleaned, lubricated and.the whole assembly reinstalled.
- The brass link was adjusted so that it better fits the trip rod clevis. Washers were used to keep the brass link centered in the clevis.
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- The weak trip rod spring was replaced and adjusted to provide a minimum of 32 pounds force in the reset position. l
- The spring hook pad, which contacts the trip alarm switch lever, will be held in position with nuts and lockwashers to maintain proper alignment of the components.
43
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As a result of the above actions, the overspeed trip ;
device and stop valve have been determined to b'e capable of fulfilling their decign functions and, upon. l I
completion of the required testing (Section 3.0) will be declared to be operable.
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" ' - - - - - -----___m___________ ,_, _
2.6 TURBINE GOVERNOR 1
1 The AFW turbine governor controls the turbine speed by controlling the amount of steam admitted to the turbine driver (K-308). -This is accomplished using a type PG-PL governor manufactured by Woodward. Figure 2.6-1 I
provides a schematic of the governor and its interface l l
with the governor valve and its relationship to the stop l 1
I valve and turbine. The figure depicts the differences between the Model #9903-305 (original).and the model
- 9903-340 that had been installed during the maintenance outage (as configured on the day of'the event) with respect to the internal hydraulic piping and valves.
The section that follows describes the inspection and l
results of the evaluation of the governor failure that occurred.
The inspections, evaluations, and final disposition of the K-308 Turbine governor and its failure to control l turbine speed during the post-maintenance testing are i
addressed and documented in PDQ 89-148 and its associated WRs.
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1 2.6.1 INSPECTION l The governor inspection was approached in two phases.
The first was the inspection of the as-found l 1
condition, and the second phase consisted of inspection at the vendor's. shop (Woodward).
Phase 1 I
- A visual inspection was performed, in which the as )
i found condition of the governor and its associated-components was documented. This inspection .
included documentation of the name plates (governor i j components and N2 purge-line valve), oil level and l
l several dimension measurements as called out by the PDQ.
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Positions of the compensation needle valve and the
-l manual speed setting were determined..
Stroking of the servo and governor valve and 1 measurement of the associated stroke lengths were performed to determine if adequate stroke existed to perform their functions.
46
- .The oil was removed from the governor and samples-
'taken and analyzed for water, metal,; viscosity and any other particulate matter.-
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' Phase 2 l
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- The governor was: returned to the manufacturertand.
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. tested lper the-PDQ as witnessed by SMUD representatives u
- A report was written by the manufacturer and-submitted to SMUD, which discussed 'the: as found condition and its implications.
2.6.2 EVALUATION
'I The investigation into the failure of the governor indicates that the new governor that was~ installed (model #9003-340) just' prior'to-the event had been- 1 i
modified as indicated on Figure 2.6-1.- This- J modification results in the governor, as it was installed, functioning properly with only a clockwise shaft rotation. The previous governor ~(model #9903-305)-
was designed to operate properly with either a clockwise or counter-clockwise shaft rotation. As installed, the governor operated with a counter-clockwise shaft-
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I rotation, resulting in a lack of oil pressure to. power the servo and speed control. Without power to the servo, the opening of valve HV-30801 allowed steam to force the governor valve fully open and, consequently,-
the turbine overspeed occurred.
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Inspection at the vendor's shop indicates that the 1
governor was properly configured and-adjusted. Testing )
indicates that, had the. governor been set up with the proper shaft rotation, the pump would have been adequately controlled. Shop testing indicates that the as-found, manually set speed setting would have 1
controlled the pump to a speed of approximately l 1530 rpm.
Evaluation by the vendor indicates that the governor sustained no damage as a result of this event.
2.6.3 DISPOSITION In response to the overpressurization event, theLturbine governor was inspected (2.6.1) and evaluated (2.6.2).
As a result of this effort, the following actions were-taken to return the governor to operable status.
48
- The governor was re-assembled and tested as
" described in pDQ 89-148 by the vendor.
- The governor was installed on the turbine.(K-308)-
with the proper orientation as shown on Figure 2.6-1 for counter-clockwise rotation. Testing was l
also performed to assure operability prior to being placed into service.
- Plant documentation was revised to provide specific detail to assure that the governor, Model #9903-340, would be installed with the correct rotation orientation.
Having completed these actions, the turbine. governor has been determined to be capable of fulfilling its design function and, upon completion of the required testing (Section 3.0) will be' declared to be operable.
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- - _ _ - _ - - _ - _ - _ _ _ _ _ _l
3.0 SYSTEM AND COMPONENT TESTING Testing of the system and components will be performed to ensure compliance with the Technical Specification requirements (4.8) and to provide additional assurance of system operability via the performance of several special test procedures (STP's).
Prior to exiting cold shutdown, the AFW system and components will be subjected to the following required Technical Specification Surveillance Procedures (SP) :
SP.20 " Monthly Turbine / Motor Driven Auxiliary ,
Feedwater Pump P-318 In Service Test" (NOTE: -
l The steps from this procedure have been incorporated into STP.1212.)
i SP.23 " Quarterly Auxiliary Feedwater Pump Flow Test and Check Valve Full Stroke Test (cold l shutdown)" (NOTE: The steps from this procedure have been incorporated'into STP.1212).
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SP.21 " Monthly Motor Driven Auxiliary Feedwater Pump l P-319 In Service Test" l
- Verify proper operation of the motor l l
driven AFW pump P-319.
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- Verify proper operation of check valves ]
FWS-047, MCM-060 and FWS-048.
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- Fulfills requirements of Tech. Spec. l Sections 4.8.1, 4.8.3 and 4.2.2 for AFW j Pump P-319. i i
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SP.98 " Monthly test of Auxiliary Feedwater and j l
Atmospheric Dump Valve Control Valve Manual l i
Controls" l
- Contr61 valve manual controls testing for ;
1 HIC-20527, 20528, 20831, 20532.
l 1
- Stroke and time: FV-20527, 20528 and HV-20577, 20578, 20581, 20582, 31826, 31827 to satisfy Tech. Spec. Section j 4.8.1.
.- 51
t
- Verify ability to transfer control of HV-20577, 20578, 20581, 20582, 31827 from the control room to their respective remote control stations.
- Verify AFW system valve alignment per Tech. Spec. Section 4.8.3.
Additional testing will be performed via.STP's 1212, 1213 and 1223. As noted above, SP's 20 and 23 have been incorporated into STP 1212 for this evolution only. .)
These STP's provide testing of the AFW system as described below.
STP 1212 " Auxiliary Feedwater Pump P-318 Performance Test".
- . To verify AFW pump P-318 minimum flow rat'e and to obt'ain Head / Capacity data for at least 3 different flow rates.
- Perform the initial service run for the P-318.
motor driver.
52 ;
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- Obtain baseline vibration and performance data i
for Pump-318 with both the motor driver and j turbine (K-308) driver.
I
- Verify AFW turbine speed response to a start initiation signal.
1
- Obtain. baseline dynamic alignmont data for the 4 turbine-to-motor and motor-to-pump couplings. j J
- Verify proper operation of AFW pump P-318 and associated valves in accordance with ASME l Section XI and the requirements of Tech. Spec, l 4.8.1 and 4.8.3.
- Verify the capability of AFW pumps P-318 and 319 to deliver flow from the condensate storage tank to the OTSGs as' required by Tech.
Spec. 4.8.4.
STP 1213 " Woodward Governor and Terry Turbine Mechanical Overspeed Trip Verification and Functional Test"
- Perform initial setup and operational verification of the AFW turbine K-308 Woodward Governor.
53
=. .
- Perform initial setup and operational verification of the-AFW turbine K-308 mechanical overspeed trip device.
STP 1223 " Auxiliary Feedwater Piping Leak Test"
- Verify integrity of the AFW piping within the test boundary. A test pressure of 2240 psig was used, which is conservative with respect l to the calculated pressure (Z-FWS-M2128) corresponding to the overspeed trip setpoint of 4450 rpm. The test is performed in accordance with ASME Section XI IWD-5000.
1
- Identify and repair leaking joints found during testing.
The above discussion has outlined the testing'that will ,
be performed on the AFW system. Satisfactory test results will provide the evidence that the system is ready to be declared operable. j i
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r 4.0 RECONSTRUCTION AND EVAIliATION OF THE EVENT !
From the inspections and evaluations performed by Nuclear Engineering, the sequence of events that j J
occurred and which resulted in the overspeed have been-pieced together. 3 1
The opening of HV-30801 by the operators initiated the event by allowing steam to flow into the governor valve.
As described in Section 2.6.2,.the Woodward Model
- 9903-340 governor installed at the time was operable only in the clockwise direction. Since the rotation of the turbine (K-308) results in the governor being rotated in the counter-clockwise direction, this resulted in a lack of oil pressure to the servo, which is mechanically connected to, and controls, the 79vernor valve. Without the oil pressure to the servo, the proper modulation was not provided to the governor valve, which allowed the steam flow to drive.the valve to the full-open position.
i With the governor valve in the full-open position, the increased steam flow resulted in the turbine overspending to 6020 rpm. This condition lasted for-approximately 3 minutes and 15 seconds. During this runup in turbine speed, the mechanical overspeed device 55
1 operated properly when the centrifugal device caused the trip weight to irract the tappet and provide a trip.
However, due to insufficient tension in the trip rod string on HV-30801, the valve failed to' trip. Therefore, the turbine continued to run to the maximum speed attained during the event (6020 rpm). Upon radioing the control room, HV-30801 was closed remotely. As the valve was being closed, the latch mechanism actuated and tripped the valve. Once closed, the overspeed event was terminated and AFW system pressure decayed rapidly as the turbino coasted to a stop.
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For this event to have occurred as described, two I
failures were necessary. Had either of these occurred 1 l
independently, the overspeed event would not have happened. For example, had HV-30801. failed to close, the governor and governor valve would have controlled the steam flow and prevented overspeed. With proper operation of the overspeed trip linkage, the governor failure would have been sensed by the mechanical overspeed trip device and the steamflow would have been-terminated.
56
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t Thus, the overspeed event can be attributed to the
^
governor being configured'so as to.be inoperable in the-direction it was being rotated and deterioration of th'e condition of the trip rod spring.resulting-in insufficient tension in the spring to actuate the trip l rod to trip valve HV-30801 so that is would close.
l 57 i
(
5.0 AFW OPERABILITY STATUS For a system to be declared operable, it must meet the Technical Specification definition of Operable, which is defined as follows for Rancho seco.
(Tech. Spec. Section 1.3): I "A component or system is operable.when it is capable of performing its intended function within the required range. The component or system shall be considered to have this capability when: (1) it 1
satisfies the limiting conditions for operation defined in Specificat' ion 3, (2) it has been tested periodically in accordance with Specification 4, and has met its l performance requirements, (3) the system has l available its normal and emergency sources of power, and (4) its required auxiliaries are capable of performing their intended-function".
The intended function of the AFW system as described in USAR Section 10.2.2.2 is to deliver water to the Once Through Steam Generators (OTSGs) in order to provide reactor decay heat removal in the event of a loss of 58 i _ - - - - _ _ _ . _ _ _ _ _ _ _ _ _ _ _ _ _ _ .
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\
normal feedwater supply. It is-designed to provide a.
^
nominal f80 gpm flow to the OTSGs. The minimum AFW flow required is a total flow of 475 gpm to either OTSG at 1050 psig within 70 seconds.
1 I
This functional criterion is met by the use of the j instrumentation, piping & valves and pumps.provided by.
I L the AFW system in conjunction with the surveillance testing program. Within the body of this report-(Section 2.0) each of these components and-their sub-
~
components have.been evaluated to determine the impact; if any, resulting from the.overpressurization. As'noted in each component disposition section, the. components-have been inspected, evaluated and with completion of the actions noted, have been determined to be capable.of 1
fulfilling their design function.
I Successful completion of the appropriate surveillance test requirements and the-augmented testing described in l Section 3.0 will assure that the operability l requirements of T.S. 1.3 have been met and the system-will be declared to be operable.
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e__-_-_.-__________ _ . . _ _ _ _ _ _ _ _ _ - _ - __- - . _ . . _ _ _ _ - _. _ - _ _ . ,