L-PI-11-044, Inservice Testing Program Fourth Ten-Year Interval Relief Request 12 - Proposed Alternative for Pump Vibration Testing
| ML112650095 | |
| Person / Time | |
|---|---|
| Site: | Prairie Island  |
| Issue date: | 09/21/2011 |
| From: | Schimmel M Northern States Power Co, Xcel Energy |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| L-PI-11-044 | |
| Download: ML112650095 (7) | |
Text
SEP 81 1 2011 Prairie Island Nuclear Generating Plant 1717 Wakonade Drive East Welch, MN 55089 L-PI-11-044 10 CFR 50.55a U. S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555-0001 Prairie Island Nuclear Generating Plant Units 1 and 2 Dockets 50-282 and 50-306 Renewed License Nos. DPR-42 and DPR-60 lnservice Testing Program Fourth Ten-Year Interval Relief Request 12 - Proposed Alternative for Pump Vibration Testinq Pursuant to the provisions of 10 CFR 50,55a(a)(3)(i), the Northern States Power Company, a Minnesota Corporation (NSPM), doing business as Xcel Energy, hereby requests NRC authorization of the attached proposed alternative for the Fourth Ten-Year Interval of the lnservice Testing (IST) Program for the Prairie Island Nuclear Generating Plant (PINGP) Units 1 and 2.
NSPM requests approval of alternative American Society of Mechanical Engineers (ASME) OM code ranges for vibrations with measured reference values at or below 0.05 inlsec for the PINGP Control Room Chiller pumps. This proposed alternative is being submitted for NRC review and authorization in accordance with 10 CFR 50.55a(a)(3)(i).
The pumps identified in the proposed alternative are tested in accordance with the PINGP IST Program. Each of these pumps has at least one vibration reference value that is currently less than 0.05 inlsec. Because a small reference value produces a small ASME OM code Acceptable Range for pump operation, a smooth running pump could be subject to unnecessary corrective action if it exceeds this limit. Per the 1998 Edition of the ASME OM Code, Section ISTB-6200(a), "Corrective Action - Alert Range" if measured values fall within the alert range of Table ISTB-5100-1 the frequency of testing specified in ISTB-3400 shall be doubled until the cause of the deviation is determined and the condition is corrected.
In order to avoid unnecessary corrective actions, a minimum reference value of 0.05 inlsec is proposed, which would be applied to those pumps with individual vibration locations with reference values less than or equal to 0.05 inlsec. In this way, pumps with a measured reference value below 0.05 inlsec for a particular vibration
Document Control Desk Page 2 Xcel Energy lnc.
measurement location will have subsequent test results for that location compared to an ASME Acceptable Range limit of 0.1 25 inlsec and an ASME Alert Range limit of 0.300 inlsec.
NSPM requests authorization of this proposed alternative by September 30, 2012. to this letter contains the Proposed Alternative request.
This letter makes no new commitments and no revisions to existing commitments.
Mark A. Schimmel Site Vice President Prairie Island Nuclear Generating Plant Units 1 and 2 Northern States Power Company - Minnesota Enclosure cc: Regional Administrator, Region Ill, USNRC Project Manager, Prairie Island Nuclear Generating Plant, USNRC Resident Inspector, Prairie Island Nuclear Generating Plant, USNRC
ENCLOSURE 1 Relief Request 12 Proposed Alternative for Pump Vibration Testing Proposed Alternative In Accordance with CFR 50H55a(a)(3)(i)
Alternative Provides Acceptable Level of Quality and Safety
- 1.
Smooth Running Pumps - Components affected by this request are identified in Appendix A to this request.
2. Applicable Code Edition and Addenda
The Prairie Island Nuclear Generating Plant (PINGP) Fourth 10-Year Interval lnservice Testing (IST) program is based on the American Society of Mechanical Engineers (ASME), OM Code-1998, through 2000 Addenda.
3. Applicable Code Requirement
ISTB-3300, "Reference Values" (reference 1)
ISTB-3300(a), states: "Initial reference values shall be determined from the results of testing meeting the requirements of ISTB-3100, 'Preservice Testing, ' or from the results of the first insenlice test. "
ISTB-3300(d), states: "Reference values shall be established at a point(s) of operation (reference point) readily duplicated during subsequent tests. "
ISTB-3300(f), states: "All subsequent test results shall be compared to these initial reference values or to new reference values established in accordance with ISTB-3310, ISTB-3320, or ISTB-6200(c). "
ISTB-5120, "lnservice Testing" (reference 2) (Centrifugal Pumps, Except Vertical Line Shaft Centrifugal Pumps)
ISTB-5121 (e) "Group A Test Procedure," and ISTB-5123(e), "Comprehensive Test Procedure," state: "All deviations from the reference values shall be compared with the ranges of Table ISTB-5100-1 and corrective action taken as specified in ISTB-6200. Vibration measurements shall be compared to both the relative and absolute criteria shown in the alert and required action ranges of Page 1 of 5 L-PI-11-044 Table-ISTB-5100-1. For example, if vibration exceeds either 6 V, or 0.7 in./sec (I. 7 cm/sec) the pump is in the required action range."
The ASME OM Code, paragraph ISTB-3540, requires that for centrifugal pumps, vibration measurements shall be taken in a plane approximately perpendicular to the rotating shaft in two approximately orthogonal directions on each accessible pump-bearing housing. Measurement shall also be taken in the axial direction on each accessible pump thrust bearing housing. The paragraph requires that for vertical line shaft pumps that the vibration measurements are taken on the upper motor-bearing housing in three orthogonal directions including the axial direction. These measurements are required to be compared with the ASME OM Code vibration acceptance criteria as specified in Table ISTB-5100-1 (reference 3) to determine if the measured values are acceptable.
Table ISTB 51 00-1 states that, if during an inservice test, a vibration measurement exceeds 2.5 times the previously established reference value (V,), the pump is considered in the alert range. The frequency of testing is then doubled in accordance with paragraph ISTB-6200(a), until the cause of the deviation is determined and the condition is corrected and the vibration level returns to the acceptable range level. Pumps whose vibration is measured as greater than 6 times V, are considered to be in the required action range, and must be declared inoperable until cause of the deviation has been determined and the condition is corrected. Per ISTB-3300, the vibration reference values shall be established only when the pump is known to be operating acceptably.
For pumps whose absolute magnitude of vibration is an order of magnitude below the absolute vibration limits in Table ISTB-5100-1, a relatively small increase in vibration magnitude may cause the pump to enter the alert or required action range.
These instances may be attributed to variation in flow, instrument accuracy, or other noise sources that would not be representative of actual pump degradation. Pumps that operate in this region are typically referred to as "smooth-running." Based on a small acceptable range, a smooth running pump could be subjected to unnecessary corrective action.
The pumps identified in Appendix A represent pumps in the PlNGP Inservice Test Program. Each of these pumps has at least one V, value that is currently less than 0.05 inlsec.
In order to avoid unnecessary corrective actions, a minimum value for V, of 0.05 inlsec is proposed. This minimum value would be applied to individual vibration locations for those pumps in Appendix A with reference vibration values less than or equal to 0.05 inlsec. Therefore, the smallest ASME OM Code Acceptable Range limit for any IST pump vibration measurement location would be no lower than 2.5 times V,, or 0.125 inlsec, which is within the "fair" range of the "General Machinery Page 2 of 5 L-PI-11-044 Vibration Severity Chart" (reference 7). Likewise, the smallest ASME OM Code Alert Range limit for any IST Pump vibration measurement location for which the pump would be inoperable would be no lower than 6 times V,, or 0.300 inlsec.
ASME OM, Table ISTB-5100-1 specifies a vibration Acceptable Range of 0.325 to 0.7 inlsec for pumps 2 600 rpm. These limits are equivalent to the Vibration Severity Chart range of "Good" to "Very Rough." Pumps that fall within this range have their test frequency doubled to monitor the vibration trend. The limits proposed by this relief request are well below these limits.
In addition to the requirements of ISTB for inservice testing, pumps in the PlNGP Inservice Test Program are also included in the PlNGP Predictive Maintenance (PdM) Program. The PlNGP PdM Program currently employs predictive monitoring techniques such as: vibration monitoring and analysis beyond that required by ISTB, bearing temperature trending, oil sampling and analysis, and/or thermography analysis as applicable.
If the measured parameters are outside the normal operating range or are determined by analysis to be trending toward an unacceptable degraded state, appropriate actions are taken that may include: initiation of a Condition Report (CR),
increased monitoring to establish a rate of change, review of component specific information to identify the cause of the condition, and removal of the pump from service to perform maintenance. Experience gathered by the PlNGP PdM Program has shown that changes in vibration levels in the range of 0.05 inlsec do not normally indicate significant degradation in pump performance.
It should be noted that pumps in the PlNGP IST Program would remain in the PlNGP PdM Program even if certain pumps have very low vibration readings and are considered to be smooth running pumps.
5. Proposed Alternative and Basis for Use
In lieu of applying the vibration acceptance criteria ranges specified in Table ISTB-51 00-1 smooth running pumps with a measured reference value at or below 0.05 inlsec for a particular vibration measurement location would have subsequent test results for that location compared to an Acceptable Range limit of 0.125 inlsec and an Alert Range limit of 0.300 inlsec (based on a minimum reference value of 0.05 inlsec). These proposed ranges would be applied to vibration test results during both Group A tests and Comprehensive tests.
Using the provisions of this relief request as an alternative to the specific requirements of ISTB identified above, it has been determined that this alternative would provide adequate indication of pump performance and continue to provide an acceptable level of quality and safety without unnecessarily imposing corrective action since changes in vibration levels in the range of 0.05 inlsec do not normally indicate significant degradation in pump performance.
Page 3 of 5 L-PI-11-044 Using the provisions of this relief request as an alternative to the vibration acceptance criteria ranges specified in Table ISTB-5100-1 provides an acceptable level of quality and safety since the alternative provides reasonable assurance of pump operational readiness and the ability to detect pump degradation.
The proposed alternative would be effective immediately and be effective during the Fourth Ten-Year lnservice Testing Interval.
7. Precedents
By letter dated May 21, 2004, as supplemented by letter dated July 9, 2004, Beaver Valley Power Station (BVPS) submitted a similar relief request (Relief Request PRR8). The BVPS relief request was approved by the NRC in a letter dated December 27,2004 (ADAMS Accession No. ML043430042).
On March 28, 2007 BVPS again requested this relief request as part of transition to an updated ten-year interval IST program plan. The NRC approved the relief request again in a letter dated September 27, 2007 (ADAMS Accession No.
1\\11 L072420376).
- 8. References
- 1) ISTB-3300, "Reference Values"
- 2) ISTB-5120, "lnservice Testing", (Centrifugal Pumps, Except Vertical Line Shaft Centrifugal Pumps)
- 3) Table ISTB-5100-1, "Centrifugal Pump Test Acceptance Criteria"
- 4) Not Used
- 5) Not Used
- 6) NUREG-1482, Rev.1, Section 5.4, "Monitoring Pump Vibration in Accordance with ISTB"
- 7) General Machinery Vibration Severity Chart provided by IRD Mechanalysis, Inc.
Page 4 of 5 L-PI-11-044 Appendix A ASME Code Components Affected Smooth Running Pumps Page 5 of 5 Unit 1
1 System ZH ZH Pump ID 045-591 045-592 Description 121 Control Room Chilled Water Pump 122 Control Room Chilled Water Pump Class 3
3 Speed (rpm) 1750 1750