ML18067A572
| ML18067A572 | |
| Person / Time | |
|---|---|
| Site: | Palisades  |
| Issue date: | 06/11/1997 |
| From: | NRC (Affiliation Not Assigned) |
| To: | |
| Shared Package | |
| ML18067A571 | List: |
| References | |
| NUDOCS 9706160350 | |
| Download: ML18067A572 (8) | |
Text
UNITED STATES
- NUCLEAR REGULATORY COMMISSION
. WASHINGTON, D.C. 20555-0001 SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO THE INSERVICE TESTING PROGRAM RELIEF REQUEST NUMBER 8 CONSUMERS POWER COMPANY PALISADES PLANT DOCKET NUMBER 50-255
1.0 INTRODUCTION
The Code of Federal Regulations, 10 CFR 50.55a, requires that inservice testing (IST) of certain American Society of Mechanical Engineers (ASME) Code Class 1, 2, and 3 pumps and valves be performed in accordance with Section XI of the ASME Boiler and Pres$ure Vessel Code and applicable addenda, except where relief has been requested and granted or proposed alternatives have been authorized by the Commission pursuant to 10 CFR 50.55a (f)(6)(i), (a)(3)(i), or (a)(3)(ii). In order to obtain authorization or relief, the licensee must demonstrate that: (1) conformance is impractical for its facility; (2) the proposed alternative provides an acceptable level of quality and safety; or (3) compliance would result in a hardship or unusual difficulty without a compensating increase in the level of quality and safety. Section 50.55a (f)(4)(iv) provides that inservice tests of pumps and valves may meet the requirements set forth in subsequent editions and addenda that are incorporated by reference in 10 CFR 50.55a(b), subject to the limitations and modifications listed, and subject to Commission approval. NRC guidance contained in Generic Letter (GL) 89-04, "Guidance on Developing Acceptable lnservice Testing Programs," provided alternatives to the Code. requirements determined to be acceptable to the staff and authorized the use of the alternatives in Positions 1, 2, 6, 7, 9, and 10 provided the licensee follows the guidance delineated in the applicable position. When an alternative is*
proposed which is in accordance with GL 89-04 guidance and is documented in the IST program, no further evaluation is required; however, implementation of the alternative is subject to NRC inspection.
Section 50.55a authorizes the Commission to grant relief from ASME Code requirements or to approve propose_d alternatives upon making the hecessary findings. The NRC staff's findings with respect to granting or not granting the relief requested or authorizing the proposed alternative as part of the licensee's IST program are contained in this safety evaluation (SE).
Pump Relief Request Number 8 was submitted with the l_icensee's third 10-year IST program submittal on March 5, 1996. This particular relief request was granted on an interim basis in an SE dated August 30, 1996, for a period of 6 months for investigation to
- determine.final resolution... A revised relief.request was submitted on February 28, 1997, along with a request to extend the interim period. The licensee stated that recent plant events had prevented plant personnel from addressing the issues of the relief request. By letter dated March 7, 1997, the staff extended the interim period to August 28, 1997, to allow time for review of the relief request.
The third 10-year interval for the Palisades plant began on August 21; 1995, and ends on August 20, 2005. The current IST program is based on the requirements of the 1989 Edition of ASME Section XI, which specifies that rules for the IST of pumps and valves are stated in the ASME/ANSI Operations and Maintenance (OM) Standards, Part 6, "lnservice Testing of Pumps in Light-Water Reactor Power Plants" (OM-6), and Part 10, "lnservice Testing of Valves in Light Water Reactor Power Plants" (OM-10).
2.0 RELIEF *REQUEST PRR-008 The licensee has requested relief from the frequency response range requirements of OMa-1988, Part 6 (OM-6), paragraph 4.6.1.6, for charging pumps P-55A, P-558, and P-55C.
The licensee has proposed to take vibration measurements over a frequency response range from 6 hertz (Hz) to 16 kHz. The licensee will also perform spectral analysis testing quarterly and oil analysis will be performed monthly, with uncontaminated samples shipped off site for analysis.
2.1 Licensee's Basis for Requesting Relief The licensee states:
The following information is applicable for the Palisades Charging Pumps:
Motor Pinion Pump ID
- Speed Speed Crankshaft Speed P-55A P-558 P-55C 1786 rpm 1790 rpm 1790 rpm 620 rpm 1100 rpm 1100 rpm 115.5 rpm (1.9 Hz) 203.2 rpm (3.4 Hz) 203.2 rpm (3.4 Hz)
To satisfy OMa-1988 requirement, the frequency response range for a vibration monitoring system would need to be from 0.64 Hz to 1000 Hz for Pump P-55A and from 1.13 Hz.to 1000 Hz for Pumps P-558/C due to the low speed design of the pumps.
Palisades currently uses Predict/DU hardware and software. The system is well established and has been in place for six years although the low frequency response is 6 Hz. Predict/DU does not offer any equipment with a. better frequency response than is currently being used.
Three other manufacturers, CSI, Entek IRD, and SKF, have also been contacted to determine if their equipment is capable of operating at the required calibrated
- frequen_cies.. The result of the investigation into the vendor.capabilities is that no data collector manufacturer has successfully completed any iristrument calibration to frequencies below 2 Hz that is NIST [National Institute of Standards and Technology] certified to within 5% accurate. Therefore, no standard data acquisition systems were found that could satisfy OM-6 requirements down to 0.64 Hz or even down to 1. 13 Hz. Palisades has therefore determined that the procurement of standard, commercially available equipment, capable of accurately measuring the extremely low frequency vibrations required by OM-6, is not currently possible. Without the equipment capable of measuring these low frequencies, it is impractical to test the charging pumps in accordance with OM-6 due to their low speed design. This revised Relief Request Number 8 is therefore based on the basis that meeting the existing code requirement is impractical. This spec_ifically follows the responses to Comments 5.4-2 and 5.4-3 in NUREG-1482 that addressed similar problems. These responses stated that "a relief request must be submitted when it is impractical to meet the frequency response range," and "Apparently, the code committee did not establish the frequency response range for all types of pumps.
When the requirements appear to be impractical, the licensee may request relief;"
Pump Description.
Palisades' Charging Pumps are reciprocation pumps and _have components both above and below 600 rpm. Pump P-55A (P-558/C) input shaft and pinion rotate at 620 rpm (1050 rpm) and have two rotating element bearings. The bullgear and crankshaft rotate at 115.5 rpm (203.2 rpm) and are supported by two sleeve or journal bearings. There are no seals or couplings within the pump crankcase, nor is component rub a vibration concern based upon the pump design.
Vibration Monitoring The OM-6 Code committee has recommended that velocity measurement be used for rotational shaft speeds above 600 rpm and that displacement measurements be used for speeds below 600 rpm, This recommendation was made because vibration readings in velocity units may not be indicative of certain problem severity in slow speed machines,. while vibration readings in displacement units may not be.
indicative of problem severity in higher speed machines (Reference NUREG-1482 Section 5-4). Velocity units are used for vibration monitoring of the Charging Pumps at Palisades due to their design.
The high speed pinion, supported by rolling element bearings and the reduction gears, is the largest concern when examining vibration and overall performance.
Problems in these components will appear at frequencies well above their running speeds and any degradation will be best detected using units of velocity.
Shaft alignment problems, intermediate gearbox problems, or [problems] associated with one times the pinion speed will be adequately detected using current equipment and the available frequ~ncy response range. The contribution of the low
~ 4 -
frequency vibrations associated with the crankshaft and bull gear will not be accurately proportioned due to roll off of the frequency response. However, the contribution of vibration at these frequencies (in velocity units) to the overall vibration readings would not be signific<mt due to the extremely low operating speed. As assurance that problems with low speed components will be identified, problems associated with the crankshaft/bull gear assembly will result in higher vibration amplitudes at gear mesh frequencies which are well within the frequency response range of c.urrent vibration equipment being used. By using velocity in lieu of displacement, we can more accurately monitor the more failure prone components within the pump crankcase.
Typical rotating element bearing problems are indicated by vibrations at noninteger multiples of running speed. With the exception of cage defects, these faults appear at frequencies well above running speed. Additionally, rotating element bearing defects are generally not detectable by any overall vibration reading. until the degradation has progressed into later stages. By that point, harmonics of the fault frequencies and the general noise floor (both well above running speed) have elevated and begun to increase the overall vibration levels. Therefore, vibrations at subsynchronous frequencies caused by rotating element bearing defects (cage fault frequencies) offer no measurable amplitude increase in overall vibration readings until accompanied by fault frequency harmonics and noise floor elevation, both at higher frequencies.
Journal bearings are susceptible to some problems detectable by subsynchronous vibrations such as oil whirl and looseness. However, these problems are nearly always accompanied with higher order harmonics of shaft running speed. and the fault frequencies. This is especially true for conditions that are truly detrimental to the bearings and.overall pump performance. Additionally, the contribution of subsynchronous amplitudes to an overall velocity vibration level, especially from a slow speed rotor, is likely negligible in comparison to the vibrations at and above the dominating running speed(s). As previously discussed, any such journal bearing problem would also result in elevated gear 'mesh frequencies.
In addition to overall vibration readings, Palisades obtains vibration readings for spectral analysis as a requirement of each inservice test procedure. No matter what the shaft running speed is, vibration problems associated with any bearing can be identified by spectral analysis long before they are detectable by overall vibration readings. Although roll off is present at lower frequencies in spectral data as well, the analysis is not necessarily based on peak vibration readings at low frequencies (or at any frequency); it is based on trends and the mere presence of signals at particular frequencies. Spectral analysis is a significant part of Palisades' vibration monitoring program because we initiate action based on spectral analysis before overall vibrations fall into the required action or alert ranges.
- Periodic Maintenance*
Palisades follows vendor recommendations for charging pump oil change frequencies unless detailed oil sample analysis provides information to extend this interval. The vendor recommends quarterly changes for continuously running pumps and semi-annual oil changes for idle, or intermittently operated pumps.
During oil changes, the crankcase cover is removed to examine for particles and to wipe out the sump. Gear and bearing wear particles would be visible during this evolution, A general inspection of internal components is also performed during oil changes.*
Oil samples are drawn on a monthly basis for all running and standby charging pumps. Occasionally, the oil is radiologically contaminated and can not be released off-site for detailed analysis. When the sample is radiologically contaminated, it is tested on-site for acidity, water content, *and viscosity, When the samples are not radiologically contaminated, they are sent off-site and analyzed for acidity, water, viscosity, particle contents, and a wide array of other contaminants and additives.
Extension of the oil change interval can only be made following an acceptable off-.
site analysis.
Equipment Monitoring During pump operation, auxiliary operators regularly monitor all equipment for abnormal noise. Additionally, the system engineer is required to perform weekly walkdowns of equipment which also provides opportunity for monitoring noise emanating from the pumps. Occasionally, recordings of audible noise are made in the vicinity of the operating pumps. This provides a means to identify and verify changes in audible noise., Although there is no acceptance criteria, this noise monitoring has been responsible for detection of several indirect pump problems in the charging pump cubicles such as failed accumulator bladders and motor winding problems. In particular, suction bladder failures have resulted in audible cavitation at low frequencies of occurrence. Similar audible banging or ticking would be expected if problems were to be present associated with the pump crankshaft or pistons.
Preventative Maintenance Charging Pump P-55A which is continuously run has been thoroughly inspected and/or overhauled four times in the last ten years. A qualified representative of a pump manufacturer has been present to oversee and direct each evolution. With the exception of pitting on the bull gear teeth, no significant findings have been recorded.. No.unusual bearing wear or degradation has been noted. All major maintenance evolutions are controlled per a permanent maintenance procedure (CVC-M-1) which incorporates vendor* recommendations and original equipment manufacturer specifications for acceptance criteria. Additionally, Palisades regularly participates in NMAC [Nuclear Maintenance Assistance Ceriter (Electric Power
- Research Institute)] and CE [Combustion Engineering] Owners Group charging pump workshops which provides information as to modes of failure and possible generic issues.
Summary of Findings on Available Data Collectors Data collectors are available that can obtain data at frequencies within the vicinity of 0.64 Hz. However, no data collector manufacturer has been requested to or successfully completed any instrument calibration to frequencies below 2 Hz that is NIST certified to within 5% accurate. In many cases, data collector manufacturers would need to modify their existing hardware and develop an elaborate calibration process. Since there is no industry demand for such an accurate system at low frequencies over such a wide range, there are no off-the-shelf instruments available.
Transducers are available that may satisfy a 5 % accuracy from 0.64 Hz through 1000 Hz, but when combined with an instrument loop, it is not practical to achieve a 5% accuracy over this entire range. Even if such a system was engineered, calibration remains a challenge. Shaker tables are limited in low end frequency and transducer voltages become essentially DC. Calibration standards that will provide a reasonable ratio are not very common.
2.2 Alternate Testing The licensee proposes:
As an alternative to the code requirement, overall (IPS-RMS [Inches per second-root mean square]) vibration readings will be obtained over a frequency response range of approximately 6 Hz to 16 kHz. Additional readings are taken and used in a spectral analysis to determine trends in the vibration information. Additionally, oil analysis will be performed on a monthly basis with detailed sample analysis being performed when the samples are not contaminated and may be free released for shipment off-site.
In the event that the oil samples cannot be analyzed by an off-site facility, the vendor recommended oil change intervals will be observed and an inspection of the crankcase internals performed at that time.
2.3 Evaluation The Code requires that the frequency response range of the vibration measuring transducers and their readout system for safety-related pumps shall be from one-third minimum shaft rotational speed to at least 1000 Hz. The Code committees instituted this change from the previous requirements of ASME Section XI because this range of frequencies would more adequately envelop all potential noise contributors. It was recognized by the staff that when plants started to convert to OM-6 from ASME Section XI, Subsection IWP, that slow speed pumps may have problems meeting the Code frequency response range requirements. In the comments and responses on Draft NUREG-1482, Response 5.4-3 states that it appeared that the Code committees did not establish
- _'the frequency response range for.all types of _pumps and licensees may request relief when the requirements appear to be impractical. One particular type of pump that appears to be affected is certain types of positive displacement pumps.
The licensee has stated that the low end of the Code-required frequency response range vibration measurements was 0.64 Hz for charging pump P-55A and 1.13 Hz for charging pumps P-558/C. All three pumps are positive displacement pumps. The licensee conducted a search of manufacturers to locate vibration instrumentation that meets the Code requirements and concluded that such instrumentation that meets both the frequency response range and accuracy requirements was not available. A study of vibration equipment manufacturers conducted l:>y Brookhaven National Laboratory in 1 993
- concluded that vibration instrumentation within the Code instrument accuracy requirements was readily available for frequency response ranges from 2 Hz to 1000 Hz. Therefore, the Code requirements are impractical for these particular pumps because the crankshaft speed for each charging pump is less than 2 Hz. It would be a burden for the licensee to meet the Code requirements because it would require either redesigning the pumps or developing vibration instrumentation that could meet the Code requirements.
The licensee has proposed to perform, in addition to the regular pump inservice test, spectral analysis on each charging pump during its respective inservice test. Spectral analysis provides insight to determine the sources of the major vibration contributors.
Although, the licensee stated that the accuracy of their instrumentation is not within the ASME Coc:le requirements at low running speeds, it is a valuable tool which can aid in the identification of vibration trends at specific frequencies. In addition, the licensee states that oil analysis will be performed monthly on each charging pump. Specific analysis performed on the oil samples will depend on whether a particular sample has been radiologically contaminated. Specific examinations in th_e offsite analysis, especially determination of particle concentrations; will provide additional information about the journal bearing condition not required by the ASME Code. Therefore, the licensee's proposed alternative test provides reasonable assurance Qf operational readiness.
3.0 CONCLUSION
Relief from the vibration measurement requirements of OM-6 Paragraph 4.6.1.6, for charging pump~ P-55A, P-558, and P-55C is granted pursuant to 10 CFR 50.5.5a (f)(6)(i) based on the impracticality of performing testing. in accordance with Code requirements, and in consideration of the burden on the licensee if the Code requirements were imposed on the facility.
- Principal Contributor: Joseph Colaccino Date:
June 11, 1997
I. t DISTRIBUTION FOR LETTER TO MR. THOMAS C. BORDINE DATED: June 11, 1997
~q~~.!5~i~~i1:e~_(&o~i5_~J:::
PUBLIC PD#3-1 Reading J. Roe J. Hannon C. Jamerson R. Schaaf SEDB (TLH3)
- J. Colaccino OGC G. Hill (2)
ACRS B. McCabe B. Burgess, Riii