SBK-L-09194, 10 CFR 50.55a Request: PR-2, Increase of Vibration Alert Range Absolute Limit to 3.50 Ips for All Containment Building Spray Pump Bearings for the Third 10-Year Interval
| ML092890325 | |
| Person / Time | |
|---|---|
| Site: | Seabrook  |
| Issue date: | 10/13/2009 |
| From: | St.Pierre G NextEra Energy Seabrook |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| PR-2, SBK-L-09194 | |
| Download: ML092890325 (13) | |
Text
NExTeraM S
SEA BROO K October 13, 2009 Docket No. 50-443 SBK-L-09194 U. S. Nuclear Regulatory Commission Attention: Document Control Desk Washington, DC 20555-0001 Seabrook Station 10 CFR 50.55a Request: PR-2, Increase of Vibration Alert Range Absolute Limit to 3.50 ips for All Containment Building Spray Pump Bearings for the Third 10-Year Interval Pursuant to 10 CFR 50.55a(a)(3)(i), NextEra Energy Seabrook, LLC (NextEra Energy Seabrook) hereby requests NRC approval of the following request for the third 10-year interval: Increase of Vibration Alert Range Absolute Limit to 3.50 ips for all containment building spray (CBS) pumps during inservice testing (IST). The request is provided as to this letter.
NextEra Energy Seabrook requests approval by the end of the second 10-year interval, August 17, 2010.
A similar request for the second 10-year interval was approved by the NRC on February 4, 2004 (NRC Accession No. ML033440009). The circumstances and basis for the prior NRC approval have not changed. NextEra Energy Seabrook is near the end of its second 10-year interval using ASME OM Code, 1995 Edition, 1996 Addenda, and will be transitioning to the latest edition of the ASME OM Code incorporated by reference in 10CFR50.55a(b) - ASME OM Code, 2004 Edition, for the third 10-year interval. A line by line comparison has shown the new ASME OM Code, 2004 Edition to be consistent with ASME OM Code, 1995 Edition, 1996 Addenda for the issue described below.
ASME OM Code, 2004 Edition, Table ISTB-5121-1, Centrifugal Pumps Test Acceptance Criteria, contains limits established in the previous references of ASME OM Code, 1995 Edition, 1996 Addenda, ISTB Table 5.2.1-1, Group A and Comprehensive Tests Vibration Acceptance Test Criteria. Both CBS pumps are challenging the Alert Range of
< 0.325 ips established in this table. NextEra Energy Seabrook is requesting relief to establish an absolute Alert Limit of < 3.50 ips for each bearing for the third 10-year interval for Seabrook Station per the 10 CFR 50.55a Request PR-2 in Attachment 1 to this letter. Pump vibration data to support the request is provided in Attachment 2.
NextEra Energy Seabrook, LLC, P.O. Box 300, Lafayette Road, Seabrook, NH 03874 A047A
U. S. Nuclear Regulatory Commission SBK-L-09194 Page 2 Through spectrum analysis, the cause of the vibration is well understood and is attributed to the original pump design and the size of the recirculation line. It is not a result of any material degradation from the original installation.
Accelerated testing under these conditions does not add to the reliability of the pumps, and correcting this condition would require a design change to the pump impeller or the installation of a test line capable of meeting the +/- 20% of pump design flows.
If you have any questions regarding this submittal, please contact-Mr. Michael O'Keefe, Licensing Manager, at (603) 773-7745.
Sincerely, NextEra Energy Seabrook, LLC Gene St. Pierre Vice President - North cc:
S. J. Collins, NRC Region I Administrator D. L. Egan, NRC Project Manager W. J. Raymond, NRC Resident Inspector to SBK-L-09194
Proposed Alternative In Accordance with 10 CFR 50.55a(a)(3)(i)
--Alternative Provides Acceptable Level of Quality and Safety--
Relief Request PR-2, Increase of Vibration Alert Range Absolute Limit for All CBS Pump Bearings to 0.350 ips
- 1. ASME Code Component(s) Affected Containment Building Spray Pumps CBS-P9A, CBS-P9B
2. Applicable Code Edition and Addenda
3. Applicable Code Requirement
Table ISTB 5121-1, Centrifugal Pump Tests Acceptance Criteria.
4. Reason for Request
" Pump casing resonance amplification causes the CBS-P-9-B pump bearing vibration to exceed the ISTB Table 5121-1, Centrifugal Pump Tests Acceptance Criteria Alert Range absolute limit.
" Pump casing resonance amplification causes the CBS-P-9-A pump bearing vibration to approach the ISTB Table 5121-1, Centrifugal Pump Tests Acceptance Criteria Alert Range absolute limit leaving very little room for test repeatability.
The ASME Code provides both a relative multiplier on the reference value, or an absolute limit. The lower of the relative multiplier or the absolute limit is used to define test acceptance criteria. The Code established that the absolute limit for the ALERT limit will be applied to all of the bearings. Based on the forcing function (e.g. pump casing resonance caused by the four vane impeller) being the same on both CBS-P-9-A and CBS-P-9-B, the absolute limit of 0.325 ips needs to be increased to 0.350 ips to provide test margin.
The cause of the vibration is well understood and is a result of our original pump design and the sizing of our re-circulation line. It is not the result of any material degradation from the original installation. An impeller design change would be required to obtain vibration test margin; however, this design change would not fix any material degradation or restore lost margin.
The pump casing resonance amplification issue impacts both pumps, although only the CBS-P-9-B pump has gone into the ALERT condition.
The corresponding vibration levels on Containment Spray Pump CBS-P A are similar but have not reached the Alert Range.
CBS pump design uses a wide, four-vane impeller that is susceptible to elevated vane pass vibration. This induced vibration amplitude, along with casing resonance near vane pass frequency, results in elevated overall vibration levels. There are no corrective actions to minimize this condition without replacing the pump impeller, or to modify the stiffness of the pump bearing housings. Implementing either of these design changes to prevent entering the Alert Range, would require extensive work and testing, with no improvement to equipment reliability.
Pump bearing housing resonance amplification results in testing challenges due to the lack of any margin between our reference value and the ISTB Table 5121-1, Centrifugal Pump Tests Acceptance Criteria Alert Range absolute limit. Exceedance of the 0.325 ips Alert limit would result in additional testing. Reduced interval testing does not provide any compensating increase in the level of quality and safety. The pumps are infrequently run, on the order of 200 hours0.00231 days <br />0.0556 hours <br />3.306878e-4 weeks <br />7.61e-5 months <br /> for an 18 month cycle.
Increasing the ISTB Table 5121-1 Alert Range Absolute Limit from 0.325 ips to 0.350 ips for all of the pump bearing limits on both 1-CBS-P-9-A and 1-CBS-P-9-B, will provide adequate margin for test repeatability.
Additional vibration data collection and analysis identified high pump vane pass spectral responses. Pump casing resonance testing identified that the pump has a resonance frequency similar to that of pump vane pass. This condition results in vibration amplitude amplification that is responsible for much of the vibration magnitude. A review of past pump history, including plant pre-operational test data identified similar pump vane pass vibration amplification.
Pump bearing resonance test results and vibration spectrum analysis are consistent with tests performed during initial plant startup (1986). These results identify that the casing resonance contributes to the overall vibration amplitude. Continued pump operation at these levels is acceptable. Additionally, high resolution vibration data analysis has not found any indications of bearing wear or degradation.
As part of the Second Ten Year Interval PR-3 alternative testing, Seabrook Station committed to the use of proven Condition Based Monitoring techniques. The implementation of the Predictive Maintenance Monitored Equipment Program which includes the industry recognized techniques of Infrared, Lube Oil Sampling, and Vibration
Spectrum Analysis are used in determining the operational readiness of the CBS pumps.
Seabrook Station has also recognized the impact of the Silica Removal Program that will periodically be using the CBS pumps to recirculate the RWST for the removal of silica. The CBS Pumps were considered Category B pumps during the Second Interval. The CBS pumps have already been classified as Category A pumps and now have vibration data taken on a quarterly basis. The increased frequency of testing will provide a larger and more frequent sample of trend data to be used in analysis of the pumps performance.
Both CBS pumps are challenging the Alert Range of >0.325 ips established in Table 5121-1. If a pump were to exceed the Alert limit, it would be tested at an accelerated frequency (6 weeks) until the condition could be corrected. To address these requirements, Seabrook Station will again be requesting the NRC for relief to establish an absolute Alert Limit of >0.35 ips for each bearing.
Based on this test history, and the current vibration values, an ISTB 5121-1 Alert Range Absolute Limit increase of the lower vibration limit from 0.325 ips to 0.350 ips for the pump vibration readings is warranted.
The bases for the 0.350 ips are to simply provide some margin for test repeatability and to define a limit for additional actions.
5. Proposed Alternative and Basis for Use
Using the 0.350 ips as the absolute Alert limit for all pump bearings will provide adequate indication of pump performance.
The CBS Pumps will be subject to additional testing, trending, and diagnostic analysis as required by the Seabrook Station Predictive Maintenance Program. This program employs predictive monitoring techniques that go beyond the vibration monitoring and analysis required by ISTB. These techniques also now include thermography and lube oil sampling and analysis. Station personnel will also perform Static Motor Testing using the Baker Advanced Winding Analyzer Series IV (AWAIV) equipment and Dynamic Motor Monitoring utilizing the Baker EXP3000 equipment. On-line testing using the EXP3000 utilizes a multitude of tests to determine the power quality, motor operating conditions, motor performance, and load originated issues. If the measured parameters were found to be outside the normal operating range or were determined to be trending toward an unacceptable degraded state, then appropriate actions would be taken. These actions include monitoring additional parameters,
review of specific information to identify cause, and potential removal of the pump from service to perform necessary maintenance.
Increase the ISTB Table 5121-1, Centrifugal Pump Tests Acceptance Criteria Alert Range Absolute limit from 0.325 ips to 0.350 ips for all pump bearing absolute limits on both 1-CBS-P-9-A and 1-CBS-P-9-B.
6. Duration of Proposed Alternative
The compensatory actions associated with this alternative method for testing will extend for the Third Interval.
7. Precedents
See TAC MB 8941 NRC Letter dated February 4, 2004 (ML033440009) and NYN-03080 Letter dated September 23, 2003 (ML32731415).
Relief Request PR-2, Vibration Data
CBS Pump Relief Request PR-2 Supporting Information CBS-P-9-A and CBS-P-9-B have had stable but elevated vibrations since original installation and testing in 1985. During the Preoperational Test, PT-12.1 vibrations were 0.35 ips and 0.38 ips on CBS-P-9-A and CBS-P-9-B, respectively. A review of data from 1991 to 2009 shows stable trends in the overall vibration magnitudes. Vibration spectrums on these pumps have been collected and archived since 1999. A review of the data from 1999 to 2009 shows similar vibration signatures. The predominant peaks in the spectrums are 1-times vane pass (4-times running speed of pump), 2-times vane pass (8-times running speed of pump) and 1-times running speed of the pump.
Seabrook Station was licensed to the OM Code 1983 Edition, Summer 1983 Addenda for its First Interval. The vibration limitations listed in that revision addressed vibration in displacement and had a larger acceptable range. Seabrook Station voluntarily upgraded to a later version of the code (OM Code 1995 Edition, 1996 Addenda) at the start of the Second Interval which incorporated a more stringent acceptance criteria for vibration. Vibration limits were established in velocity and absolute limits were assigned for the Alert and Required Action Limits. Seabrook Station requested and received relief from the 0.325 ips Alert Limit at that time (NHY-03080, Docket No. 50-443).
Seabrook submitted the original Relief Request for vibrations on March 21, 2000 (Reference NHY-00027) with later revisions on May 9, 2003 and September 23, 2003 (Reference NHY-3039 and NHY-3080)
We have reviewed the referenced information as well as data from 1985 to 2009. The vibrations have been stable for over 20 years. To significantly reduce vibrations would probably require the installation of a new pump design or structural modifications to the pump or connected piping. A trend of the vibrations magnitudes from 1991 to 2009 and spectral trends from 1998 to 2009 for CBS-P-9-A and CBS-P-9-B are provided below.
Table 1 1 -CBS-P-9-A Vibration Historical Data (readings in ips)
Date POH POV POA PIH PIV 5/14/2009 0.267 0.300 0.183 0.211 0.235 1/12/2009 0.280 0.284 0.194 0.216 0.231 2/22/2008 0.276 0.287 0.179 0.218 0.259 2/14/2008 0.276 0.295 0.180 0.221 0.233 3/12/2007 0.286 0.317 0.183 0.212 0.259 9/26/2006 0.296 0.282 0.188 0.244 0.222 5/9/2005 0.301 0.307 0.185 0.243 0.266 2/14/2005 0.287 0.333 0.190 0.222 0.256 7/9/2003 0.288 0.322 0.185 0.228 0.254 8/9/2002 0.277 0.300 0.177 0.223 0.233 5/18/2002 0.312 0.315 0.189 0.273 0.253 9/7/2001 0.284 0.319 0.185 0.233 0.261 7/13/2000 0.290 0.315 0.189 0.236 0.293 11/5/1999 0.272 0.322 0.155 0.234 0.305 11/4/1999 0.332 0.332 0.178 0.324 0.338 8/12/1999 0.277 0.330 0.175 0.251 0.296 5/20/1999 0.294 0.315 0.150 0.239 0.297 2/25/1999 0.257 0.304 0.155 0.224 0.302 12/3/1998 0.309 0.213 0.224 0.310 9/1 0/1 998 0.253 0.270 0.190 0.232 0.290 6/22/1998 0.253 0.284 0.144 0.215 0.288 4/20/1998 0.324 0.350 0.178 0.214 0.310 1/7/1 998 0.286 0.327 0.188 0.233 0.302 11/4/1997 0.240 0.310 0.330 0.270 0.320 5/1/1 997 0.270 0.320 0.230 0.260 0.300 2/24/1 997 0.220 0.300 0.210 0.240 0.280 12/2/1996 0.280 0.330 0.220 0.300 0.260 9/9/1 996 0.280 0.350 0.220 0.240 0.250 6/1 7/1 996 0.280 0.330 0.210 0.250 0.320 3/25/1 996 0.300 0.400 0.200 0.300 0.300 1/2/1996 0.290 0.310 0.200 0.240 0.290 10/1 0/1 995 0.300 0.320 0.230 0.260 0.320 7/1 7/1 995 0.270 0.310 0.200 0.240 0.280 6/4/1995 0.280 0.350 0.220 0.260 0.280 4/24/1 995 0.280 0.320 0.260 0.260 0.320 1/30/1995 0.300 0.370 0.220 0.320 0.300 11/7/1994 0.300 0.300 0.200 0.250 0.340 8/15/1994 0.280 0.310 0.190 0.250 0.310 7/23/1994 0.280 0.320 0.190 0.270 0.270 2/28/1994 0.290 0.320 0.190 0.250 0.310 12/6/1993 0.280 0.320 0.180 0.260 0.320 9/1 3/1 993 0.310 0.280 0.020 0.280 0.330 6/21/1993 0.280 0.300 0.200 0.280 0.300 3/29/1993 0.300 0.280 0.200 0.300 0.290 1/4/1 993 0.240 0.320 0.200 0.270 0.300 10/31/1992 0.290 0.380 0.240 0.300 0.300
9/1/1992 0.280 0.330 0.220 0.280 0.350 7/31/1992 0.300 0.300 0.220 0.270 0.280 4/27/1992 0.300 0.300 0.220 0.250 0.300 2/4/1992 0.280 0.340 0.220 0.270 0.290 11/11/1991 0.300 0.300 0.200 0.270 0.250 9/30/1991 0.300 0.300 0.200 0.280 0.250 5/27/1991 0.320 0.360 0.280 0.260 0.360 Notes: POH - Pump Outboard Horizontal; POV - Pump Outboard Vertical; POA - Pump Outboard Axial; PIH - Pump Inboard Horizontal; PIV - Pump Inboard Vertical
Table 2 1-CBS-P-9-B Vibration Historical Data (readings in ips)
Date POH POV POA PIH PIV 8/6/2009 0.318 0.315 0.184 0.285 0.301 7/7/2009 0.321 0.302 0.189 0.254 0.323 5/28/2009 0.324 0.318 0.196 0.259 0.322 2/23/2009 0.303 0.278 0.185 0.237 0.329 12/1/2008 0.322 0.281 0.197 0.243 0.350 3/27/2008 0.348 0.307 0.217 0.263 0.273 12/31/2007 0.331 0.268 0.195 0.244 0.328 4/23/2007 0.307 0.294 0.181 0.220 0.300 1/29/2007 0.318 0.268 0.196 0.242 0.320 2/27/2006 0.318 0.287 0.188 0.248 0.322 3/29/2005 0.323 0.278 0.201 0.244 0.323 4/26/2004 0.333 0.303 0.212 0.245 0.315 5/27/2003 0.335 0.300 0.198 0.238 0.343 6/24/2002 0.311 0.304 0.190 0.248 0.322 5/18/2002 0.334 0.324 0.206 0.245 0.321 1/9/2002 0.352 0.275 0.236 0.248 0.250 7/25/2001 0.347 0.280 0.196 0.248 0.274 7/25/2001 0.337 0.275 0.192 0.265 0.256 12/1/2000 0.331 0.296 0.211 0.257 0.284 5/31/2000 0.340 0.281 0.212 0.279 0.337 6/30/1999 0.318 0.314 0.193 0.224 0.383 3/19/1999 0.304 0.287 0.180 0.230 0.345 10/20/1998 0.273 0.253 0.212 0.215 0.333 7/29/1 998 0.335 0.289 0.192 0.250 0.366 3/13/1998 0.318 0.302 0.197 0.245 0.371 12/23/1997 0.380 0.320 0.250 0.280 0.360 9/22/1 997 0.310 0.330 0.240 0.280 0.320 6/30/1997 0.350 0.300 0.250 0.260 0.350 4/7/1 997 0.300 0.300 0.220 0.300 0.320 1/1 3/1 997 0.290 0.290 0.220 0.240 0.340 10/21/1996 0.340 0.340 0.210 0.270 0.370 7/29/1 996 0.300 0.300 0.200 0.300 0.400 5/7/1 996 0.290 0.340 0.200 0.250 0.340 2/1 3/1 996 0.350 0.350 0.240 0.300 0.370 12/6/1995 0.350 0.210 0.210 0.320 0.350 8/28/1 995 0.340 0.280 0.220 0.260 0.340 6/5/1995 0.300 0.270 0.210 0.260 0.380 3/1 3/1 995 0.300 0.290 0.240 0.280 0.340 12/19/1994 0.290 0.290 0.240 0.260 0.380 9/26/1994 0.310 0.270 0.220 0.260 0.320 8/1/1994 0.300 0.220 0.200 0.280 0.280 1/18/1994 0.300 0.300 0.220 0.250 0.370 10/15/1993 0.350 0.160 0.200 0.250 0.320 8/2/1 993 0.300 0.320 0.220 0.290 0.400 5/13/1993 0.310 0.300 0.220 0.240 0.390 2/1 5/1 993 0.300 0.320 0.200 0.260 0.400 11/23/1992 0.320 0.340 0.250 0.270 0.400 f-
11/5/1992 0.310 0.320 0.230 0.270 0.400 8/31/1992 0.300 0.300 0.250 0.260 0.400 6/8/1992 0.320 0.300 0.230 0.260 0.380 3/17/1992 0.340 0.320 0.250 0.300 0.400 1/28/1992 0.310 0.310 0.240 0.270 0.390 12/20/1991 0.330 0.310 0.200 0.240 0.380 9/15/1991 0.300 0.320 0.240 0.280 0.400 7/7/1991 0.300 0.350 0.250 0.270 0.400 Notes: POH - Pump Outboard Horizontal; POV - Pump Outboard Vertical; POA - Pump Outboard Axial; PIH - Pump Inboard Horizontal; PIV - Pump Inboard Vertical