ML20046C197
| ML20046C197 | |
| Person / Time | |
|---|---|
| Site: | Haddam Neck File:Connecticut Yankee Atomic Power Co icon.png |
| Issue date: | 07/20/1993 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20046C192 | List: |
| References | |
| NUDOCS 9308090333 | |
| Download: ML20046C197 (4) | |
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UNITED STATES f
NUCLEAR REGULATORY COMMISSION P
W ASHINGTON. D C. 20555-0001
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j ENCLOSURE 1 SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO THE INSERVICE TESTING PROGRAM RELIEF RE0 VESTS CONNECTICUT YANKEE ATOMIC POWER COMPANY HADDAM NECK PLANT DOCKET NUMBER 50-213
1.0 INTRODUCTION
The Code of Federal Regulations, 10 CFR 50.55a(f), requires that inservice testing (IST) of certain ASME Code Class 1, 2, and 3 pumps and valves be performed in accordance with Section XI of the ASME Boiler and Pressure Vessel Code and applicable addenda, except where relief has been requested by the licensee and granted by the Commission pursuant to S 50.55a(f)(6)(i), or where the alternative has been authorized pursuant to s 50.55a(a)(3)(i) or (a)(3)(ii).
In requesting approval of alternatives tofor relief from the Code requirements, the licensee must demonstrate that:
(1) the proposed alternatives provide an acceptable level of quality and safety; (2) compliance would result in hardship or unusual difficulty without a compensating increase in the level of quality and safety; or (3) conformance with certain requirements of the appli able Code Edition and addenda is impractical for its facility.
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 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 Developino Acceptable Inservice Testino Proorams, 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 follow 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.
Furthermore, in rulemaking to 10 CFR 50.55a effective September 8, 1992, (See 57 Federal Reaister 34666), the 1989 edition of ASME Section XI was incorporated in 50.55a(b).
The 1989 edition provides that the rules for IST of pumps and valves shall meet the requirements set forth in ASME Operations and Maintenance Standards Part 6 (DM-6), Inservice Testing of Pumps in Light-Water Reactor Power Plants, and Part 10 (OM-10), Inservice Testing of Valves in Light-Water Reactor Power P7 ants.
Pursuant to (f)(4)(iv), portions of editions or addenda may be used provided that all related requirements of the
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. respective editions or addenda are met, subject to Commission approval, and therefore, relief is not required for those inservice tests that are conducted in accordance with OM-6 and OM-10, or portions thereof. Whether all related requirements are met is subject to NRC inspection.
These regulations authorize the Commission to grant relief from or approve alternatives for ASME Code requirements upon making the necessary 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).
An evaluation of Relief Request P-9 for the Haddam Neck IST program submitted by the licensee in their letter dated March 3,1993, is included below.
2.0 RELIEF RE0 VEST P-9 The licensee has requested relief from the vibration testing requirements of ASME Section XI, Paragraph IWP-4510, for service water pumps.P-37-1A, P-37-1B, P-37-10, and P-37-ID.
These pumps provide cooling water to various plant equipment and have a safety function during accident conditions to provide cooling water for emergency systems. Alternatively, the licensee has proposed to take vibration measurements at the associated motor bearing housing for each pump.
2.1.1 Licensee's Basis For Reauestina Relief The licensee states: "The service water pumps are vertical multistage pumps submerged in their process fluid.
Their shafts are enclosed by sleeves inside their discharge pipes for a vertical distance of 19 feet.
Therefore, vibration measurement at or near the pump is not feasible with this configuration. Alternate testing is performed."
2.1.2 Alternate Testina The licensee proposes: " Vibration measurements are taken on the service water pumps' associated motor bearing housings for indication of pump bearing degradation. These measurements are taken in three orthogonal directions, one of which is the direction of the pump axis."
2.1.3 Evaluation The licensee's inservice testing program for vibration monitoring is based on their Relief Request P-8 which proposed to measure velocity rather than amplitude as required by IWP-4510.
In addition to the velocity measurements, a signature analysis program was implemented for the overall vibration program described in P-8.
The acceptance criteria for the vibration monitoring program is based on ASME publication 78-WA/NE-5, " Suggested Improvements in the Measurement of Pump Vibration for Inservice Inspection," which does not address the location or direction of the measurements.
Relief Request P-8 was approved by NRC in a Safety Evaluation issued to the licensee August 24, 1987.
. The service water pumps are included in the scope of P-8.
Therefore, the evaluation of P-9 incorporates the alternative method of measuring velocity as described in P-8.
The service water pumps are vertical line shaft pumps which have enclosed pump shafts. The pump shaft bearings are inaccessible for obtaining vibration measurements without permanently mounted, remote readout, sensing equipment.
In the application of the service water pumps, the failure rates of this type of sensing devices are high, making the use of such a configuration unacceptable.
In recognition of the difficulties in obtaining vibration measurements on the pump bearings for vertical line shaft pumps, ANSI /ASME OMa-1988, Part 6 (OM-6), requires vibration measurements on the upper motor bearing housing of these type of pumps. OM-6 requires this alternate location because it is generally more indicative of pump vibrations than other accessible locations on the driver.
The licensee's IST program currently does not comply with the requirements of OM-6 for vibration testing, as noted above. However, the alternative testing described by Relief Request P-8_is similar to OH-6 because it-is based on measurement of pump vibration by utilizing velocity measurements. -The licensee's proposed alternative does not stipulate if the measurements will be taken on the lower or upper motor bearing; however, the vibration measurement provisions in OM-6 specifically addressing vertical line shaft pumps would require the measurements to be taken on the upper motop bearing housing. The licensee should use the requirements of OH-6 for the location of vibration measurement for the service water pumps.
If the velocity in the axial direction cannot be measured at the upper motor bearing housing due to interferences, the lower motor bearing housing may provide a practical location for the axial direction. The procedures used for obtaining the measurements should clearly identify the appropriate location (s) on the pump motor assemblies.
Imposition of IWP-4510 requirements, based on measurement of amplitude, would be inappropriate because of the previous approval of Relief Request (RR) P-8, based on measurement of velocity. However, because RR P-8 does not specify the location for obtaining the measurements, it was assumed that the locations specified in IWP-4510 would be used.
Because IWP-4510 does'not address vertical line shaft pumps, as OM-6 does, imposing measurement of vibration in accordance_with IWP-4510 is inappropriate for-these pumps. Measuring-vibration on the bearing housing of these pumps would. require significant system redesign and modification.
Implementing such modifications would be burdensome to the licensee. The licensee's alternative to IWP-4510 requirements provides a reasonable assurance that degradation of the pump shaft bearing would be identified.
OM-6 reflects the recognition by the Code committee that vibration measurements of vertical line shaft pump bearings are difficult to obtain and specifies that the measurements will be taken on the upper motor bearing housing of vertical pumps. Due to the limitations in the design configuration of vertical line shaft pump, the upper motor bearing housing is the most e
. acces_ible location for obtaining the vibration measurements.
However, a study performed by EPRI entitled "On-Line Vibration Monitoring for Submerged Vertical Shaft Pumps," EPRI NP-5704M, found that vibration measurements taken on pump motor bearing housings may not detect all pump bearing and shaft problems. The portion of the vibration level at these locations generated by the pump is small when compared to the total level. Therefore, an increase in pump vibration due to degradation could be difficult to detect at the measurement location or masked by other vibration sources. This makes it difficult to detect changes in pump mechanical condition either by measuring vibration on the pump driver or at a location away from the pump. As such, i
the acceptance criteria for vertical line shaft pumps hydraulic parameters are more restrictive than for other centrifugal pumps in OH-6.
Future advances in techniques and equipment may improve the capability to accurately. monitor the i
mechanical condition of vertical line shaft pumps and may resolve the high failure rates of the sensing equipment for this application. The licensee should follow technological developments in this area and employ improved vibration testing for these pumps when feasible.
2.1.4 Conclusion
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Relief is granted pursuant to 50.55a(f)(6)(i) based on the determination that compliance with the vibration amplitude measurement location requirements is impractical, that imposition of the requirements would be a considerable burden, and considering the licensee's proposed alternative to measure vibration velocity on the pump motor bearing housing. The relief this action provides is authorized by law and will not endanger life, property, or the common defense and security, and is otherwise in the public interest. The relief has been granted giving due consideration to the burden upon CYAPC0 that could result if the requirements were imposed on the facility.
Principal Contributor: Joseph Colaccino Date:
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