ML20137D457
| ML20137D457 | |
| Person / Time | |
|---|---|
| Site: | Saint Lucie  |
| Issue date: | 08/05/1994 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20136C539 | List:
|
| References | |
| FOIA-96-485 NUDOCS 9703260170 | |
| Download: ML20137D457 (4) | |
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SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO THE INSERVICE TESTING PROGRAM RE00EST FOR RELIEF FLORIDA POWER & LIGHT CO.
ST. LUCIE PLANT. UNIT 1 DOCKET NUMBER 50-335
1.0 INTRODUCTION
i The Code of Federal Regulations, 10 CFR 50.55a, requires that inservice testing (IST) of certain ASME Code Class 1, 2, and 3 pumps and valves be i
performed in accordance with Section XI of the ASME Boiler and Pressure Vessel Code (the Code) and applicable addenda, except where alternatives have been i
authorized or relief has been requested by the licensee and granted by the Commission pursuant to Sections (a)(3)(1), (a)(3)(ii), or (f)(6)(1) of 10 CFR l
50.55a.
In proposing alternatives or requesting relfef, the licensee must demonstrate that:
(1) the proposed alternatives provide an acceptable level l
of quality and safety; (2) compliance would result in hardship or unusual l
difficulty without a compensating increase in the level of quality and safety; or (3) conformance is impractical for its facility. NRC guidance contained in Generic Letter (GL) 89-04, " Guidance on Developing Acceptable Inservice Testing Programs," provides alternatives to the Code requirements determined acceptable to the staff without further NRC review.
Implementation of the GL 89-04 positions is subject to inspection.
Section 10 CFR 50.55a authorizes the Commission to approve alternatives and to grant relief from ASME Code requirements upon making the necessary findings.
The NRC staff's findings with respect to authorizing alternatives and granting or not granting the relief requested as part of the licensee's IST program are contained in this Safety Evaluation (SE).
Florida Power & Light Company's letter dated January 7, 1994, submitted modified Relief Request PR-12. The staff was also informed that Relief Request PR-13 was deleted following further evaluation by the licensee. PR-12 had been previourIy granted in NRC's SE dated January 29, 1993, on an interim basis to allow the licensee to further review the basis for relief. The revised relief request containing additional information to support the licensee's proposed alternate method of testing is evaluated below.
2.0 EVALUATION OF RELIEF REQUEST PR-12 Relief from the requirements of IWP-4520(b) has been requested for the reactor coolant charging pumps IA, 18, and IC.
IWP-4520(b) requires that the frequency response range of the readout system for measuring vibration amplitude shall be from one-half minimum speed to at least maximum pump shaft rotational speed.
9703260170 970301 PDR FOIA BINDER 96-485 PDR 4
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l 2.1 Licensee's Basis for Relief The licensee states:
The reactor coolant charging pumps operate at approximately 210 -
215 rps which equates to a rotational frequency of 3.50 Hz. The one-half minimum speed frequency response required for the vibration instrumentation correlates to 1.75 Hz (105 cpm [ cycles i
per minute]).
The vibration instrumentation presently in use at St. Lucie is the Bently Nevada model TK-81 with 270 cpm probes. The TK-81 i
l integrator frequency response is essentially flat down to 120 cpm (cycles per minute) where the displayed output of the instrument 9
slightly increases to approximately +1 dB at 100 cpm. The -3 d8 frequency response is reached at approximately 54 cpm. The velocity probes used with the TK-81 are a special low frequency probe nominally rated down to 270 cpm (-3 dB). This is only slightly higher than the expected rotational (IX) speed of the i
charging pump (205 - 210 cpm). The IX (205 cpm) vibration frequency cociponents will be somewhat attenuated by the probes, but not cut off. Overall vibration levels would still show an increasing value if some problem developed whose characteristic frequency was IX running speed.
There are virtually no mechanical degradations where only a sub-synchronous vibration component would develop on the charging pumps.
For example:
Oil whirl (0.38X - 0.48X) is not applicable to a horizontal, a.
triplex, reciprocating pump, b.
A light rub / impact could generate 0.5X (102.5 cpm) vibration components, but would also usually generate a sequence of integer and half integer running speed components. A heavy rub generates increased integer values of multiple running speed components, as well as precessing the IX phase measurement.
In either case, the overall vibration level would still show an increase from both the attenuated sub-synchronous and IX vibration components as well as the higher harmonic vibration components.
c.
Looseness in the power train would likely be indicated by increasing IX and 2X vibration components. These signals would be_slightly attenuated but again not completely cut off.
Based on the above information, it is our evaluation that the present use of the Bently Nevada 270 cpm probes with the portable TK-81 instrument is capable of collecting sufficiently reliable data to identify changes from baseline readings to indicate possible problems with the pumps.
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2.2 Alternative restina The licensee proposes:
During testing of these pumps, the vibration instrumentation used will be the Bently Nevada model TK-81 with 270. cpm probes or i
equivalent.
2.3 Evaluation IWP-4520(b) requires that the frequency' response range of the readout system
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for measuring vibration amplitude be from one-half minimum speed to at least maximum pump shaft rotational speed.
In ASME Operations and Maintenance Standards, Part 6, " Inservice Testing of_ Pumps in Light-Water Reactor Power Plants,"_the frequency response is changed to one-third minimum pump rotational speed to at least 1000 Hz.
In a paper entitled " Introduction to ASME/ ANSI OMa-1989A, Part 6
' Inservice Testing of Pumps in Light-Water Reactor Power Plants' - and Technical Differences Between Part 6 and ASME Section XI, Subsection IWP," by John Zudans of Florida Power and Light Company, included in NUREG/CP-Olll, " Proceedings of the Symposium on Inservice Testing of Pumps and Valves," the change in the frequency response range is i
discussed. According to the paper, the change in the frequency response range from "l/2 minimum speed to at least maximum pump shaft rotational speed" in i
Section XI, IWP, to "l/3 minimum pump shaft rotational speed to at least 1000 Hertz" in OM-6 was based on a publication on measuring vibration for -
" velocity" testing, to more adequately envelope all potential noise contributors. OM-6 allows the use of either velocity. units (inches per second) or amplitude units (mils displacement) for vibration measurements.
The Code requirements for frequency response ranges are general in order to cover the various types of pumps installed in safety-related applications in nuclear power plants. The vibration monitoring requirements apply most generally to pumps operating above 600 rpm and may be either too prescriptive or not prescriptive enough for other specific pump applications. Moreover, i
the frequency spectrum of the complex signals generated by machines is characteristic of each machine or each pump, constituting a unique pattern, i
referred to as the " machine signature." Analysis of the signature allows identification of vibration sources, and monitoring of the change over time permits evaluation of the mechanical condition of the pump. Though vibration instrumentation in low frequency response ranges is available, it is not in j
wide use, is difficult to calibrate, and may not be as commercially available as other instrumentation.
To identify sources of noise and vibration, the peaks of the measured frequency spectra are correlated with data pertaining to the possible i
vibration source components in the machine. Vibrations at one-half of running speed, or lower, may indicate " oil whip" in journal bearings,. or looseness in other types of bearings. Although the relief request basis does not describe i
the type of bearings in the charging pumps, it does indicate that oil whip is not applicable to this type of pump.
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4 Although the instrumentation does not conform with the lower frequency response range requirements of IWP (1/2 rotational speed), the probes are designed for low frequency responses. The pumps are very low speed and are the only group of pumps that pose a concern in meeting the requirements.
Using the proposed instrumentation will allow the licensee to obtain data and monitor for changes from the baseline conditions, providing an acceptable level of assurance of the operational readiness of the pumps in consideration of the limitations of vibration monitoring for the very slow-speed reciprocating pumps.
It would be a hardship to require the licensee to procure new vibration instrumentation, which is not currently widely available in the commercial market at very low frequency ranges, for application to only one group of pumps in the inservice testing program when the available instruments provide an adequate means of monitoring for degradation.
Imposition of the requirements could result in performance of inservice tests using specialized vibration equipment or possibly necessitate the replacement of pumps if no means of meeting the code requirements was available.
For pumps of very low speed design, there are limitations in the commercially available vibration monitoring equipment. Therefore, compliance with the Code 1
requirements would result in a hardship or unusual difficulty without a compensating increase in the level of quality and safety.
2.4 Conclusion 1
The alternative is authorized to use the proposed vibration monitoring equipment pursuant to 10 CFR 50.55a(a)(3)(ii) based on the limitations in commercially available vibration equipment and on the hardship without a compensating increase in the level of quality and safety for charging pumps of the very low speed design. The alternative method provides adequate assurance i
of the operational readiness of the reactor coolant charging pumps by comparing changes in amplitude to a baseline value.
This relief is authorized by law and will not endanger life or property or the common defense and security and is otherwise in the public interest giving due consideration to the burden upon licensee that could result if the requirements were imposed.
Principal Contributor:
P. Campbell, DE/EMEB 1