CNL-20-052, American Society of Mechanical Engineers Operation and Maintenance Code, Request for Alternative IST-RR-8
| ML20245E518 | |
| Person / Time | |
|---|---|
| Site: | Watts Bar  |
| Issue date: | 09/01/2020 |
| From: | Jerrica Johnson Tennessee Valley Authority |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| CNL-20-052 | |
| Download: ML20245E518 (17) | |
Text
Tennessee Valley Authority, 1101 Market Street, Chattanooga, Tennessee 37402 CNL-20-052 September 1, 2020 10 CFR 50.55a ATTN: Document Control Desk U.S. Nuclear Regulatory Commission Washington, D.C. 20555-0001 Watts Bar Nuclear Plant, Unit 1 Facility Operating License No. NPF-90 NRC Docket No. 50-390
Subject:
Watts Bar Nuclear Plant (WBN) Unit 1, American Society of Mechanical Engineers Operation and Maintenance Code, Request for Alternative IST-RR-8 In accordance with Title 10 of the Code of Federal Regulations (10 CFR) 50.55a, "Codes and Standards," paragraphs (z)(2), Tennessee Valley Authority (TVA) requests an alternative to the inservice testing requirements of the American Society of Mechanical Engineers (ASME) Operation and Maintenance (OM) Code, Subsection ISTB-6200(a),
Corrective Action, which mandates that when a measured performance test parameter of an lnservice Testing Program pump falls within the alert range in Table ISTB-5121-1, Centrifugal Pump Test Acceptance Criteria, the frequency of testing specified in Subsection ISTB-3400, Frequency of Inservice Tests, shall be doubled. This alternative request applies to the Watts Bar Nuclear Plant (WBN) Unit 1 residual heat removal (RHR) pump 1B-B.
As discussed in Enclosure 1 to this letter, compliance with Subsection ISTB-6200(a) would cause a hardship or unusual difficulty without a compensating increase in the level of quality or safety due to the need to perform a mid-cycle shutdown in order to perform the increased testing frequency required by ISTB-3400. Therefore, TVA is submitting this alternative request in accordance with 10 CFR 50.55a(z)(2). Enclosure 1 to this letter describes the proposed alternative and the basis for use.
TVA requests approval of this alternative request by May 15, 2021. Enclosure 2 contains the new commitments in this submittal. Please address any questions regarding this submittal to Gordon Williams, Senior Manager, Fleet Licensing (Acting), at (423) 751-2687.
Respectfully, Jonathan T. Johnson Director, Nuclear Regulatory Affairs (Acting)
Enclosures cc: See Page 2
U.S. Nuclear Regulatory Commission CNL-20-052 Page 2 September 1, 2020
Enclosures:
- 1. Watts Bar Nuclear Plant Unit 1 American Society of Mechanical Engineers Operation and Maintenance Code Request for Alternative IST-RR-8
- 2. New Regulatory Commitments cc (Enclosures):
NRC Regional Administrator - Region II NRC Senior Resident Inspector - Watts Bar Nuclear Plant NRC Project Manager - Watts Bar Nuclear Plant CNL-20-052 E1-1 of 14 Watts Bar Nuclear Plant, Unit 1 American Society of Mechanical Engineers Operation and Maintenance Code Request for Alternative IST-RR-8 I.
ASME OM Code Components Affected Site/Unit Pump ID Pump Description Pump Type Code Class OM Group WBN Unit 1 1-PMP-74-20-B Residual Heat Removal (RHR)
Pump 1B-B Centrifugal Vertical 2
A II.
ASME Code Edition and Addenda American Society of Mechanical Engineers (ASME) Operation and Maintenance (OM) Code 2004 Edition through 2006 Addenda III.
Applicable Code Requirement
ISTB-6200(a), Alert Range, states If the measured test parameter values fall within the alert range of Table ISTB-5121-1, Table ISTB-5221-1, Table ISTB-5321-1, or Table ISTB-5321-2, as applicable, the frequency of testing specified in para. ISTB-3400 shall be doubled until the cause of the deviation is determined and the condition is corrected.
IV.
Reason for Request
The Watts Bar Nuclear Plant (WBN) RHR 1B-B Pump comprehensive pump test (CPT) is performed during refueling outages (18 month cycle) with the reactor head removed from the reactor vessel, allowing flow to be directed into the reactor cavity in order to achieve the required CPT flow rate. On May 21, 2020, during the WBN Unit 1 Cycle 16 refueling outage (U1R16) performance of the CPT, vibration measurements for the 1B-B RHR pump motor outboard horizontal and vertical locations entered the alert range of Table ISTB-5121-1.
The corrective actions of ISTB-6200(a) require the test frequency to be doubled. Therefore, another performance of the CPT is required in 12 months (one half of the two-year CPT frequency stated in ISTB-3400), which would require the unit to be shutdown and reactor head removed.
The proposed alternative would permit continued performance monitoring of RHR pump 1B-B by performing quarterly Group A tests in lieu of performing the CPT at the increased test frequency of ISTB-6200(a). The Group A test can be performed safely while the unit is operational.
This alternative request will eliminate the need to shutdown the plant in order to perform the CPT, which would result in an undue hardship due to the risks associated with plant transients. This alternative request will only apply to ISTB-6200 requirements as they relate to doubling of the CPT test frequency. With subsequent Group A testing, if any measured inservice test (IST) parameter exceeds the alert criteria, the requirements of ISTB-6200(a) will be followed (i.e., the Group A test would be performed at the prescribed increased frequency).
CNL-20-052 E1-2 of 14 V.
Proposed Alternative and Basis for Use Tennessee Valley Authority (TVA) is proposing to supplement the regularly scheduled quarterly RHR 1B-B Group A pump test with spectral analysis of the resulting vibration data in lieu of performing the increased frequency (12 months) CPT. The other requirements of the Group A test will continue to be met, including any corrective actions required by ISTB-6200 (e.g., doubling the quarterly test frequency if data falls into the alert range).
Additionally, TVA plans to perform a follow-up analysis of the RHR 1B-B pump motor bearing oil and submit the results of the oil analysis to the Nuclear Regulatory Commission (NRC). TVA will also submit to the NRC the results of the next quarterly Group A test for RHR pump 1B-B.
The purpose of performing the CPT at double the normal test frequency while in the alert range is to monitor for additional pump performance degradation until the cause of the deviation is determined and the condition is corrected.
The required alert performance of the CPT would be twelve months from the U1R16 performance date of May 21, 2020 (i.e., May 21, 2021). Applying the provisions of ASME OM Code Case OMN-20, the late date for the alert performance of the CPT can be extended to August 21, 2021, which is approximately two months prior to the commencement of the U1R17 outage. During normal plant operation, this pump is only placed into service for periodic quarterly testing and, as such, is not exposed to any degradation mechanism while remaining in its normal standby condition.
Using the provisions of this alternative request, as an alternative to the specific requirements of ISTB-6200(a) identified above, which have been identified to be a hardship without a compensating increase in quality and safety, will provide adequate indication of pump performance. Therefore, pursuant to 10 CFR 50.55a(z)(2), TVA requests an alternative to the specific ISTB Code requirements identified in alternative request.
Additional information supporting this alternative request is provided below.
In accordance with ISTB-3300, the reference point flow rate values shall be established within +/-20% of pump design flow for the CPT, or at the highest practical flow rate for the Group A test if the CPT flow rate cannot be achieved. Currently, the Group A test reference flow rate is 700 gallons per minute (gpm) and the CPT reference flow rate is 4262 gpm, which exceeds the design basis accident analysis flow of 4018 gpm. In order to achieve the CPT reference flow rate, the unit must be shutdown and reactor head removed to allow flow through the reactor vessel into the refueling cavity.
A comparison of RHR 1B-B vibration data taken at the Group A flow rate and CPT flow rate show increasing trends at both flow rates. While the vibration level at the Group A flow rate cannot be directly correlated to the vibration level at the CPT flow rate, the fact that the general trends are in agreement demonstrates the Group A test is an adequate means of monitoring of pump performance degradation.
The RHR system (RHRS) is a safety-related system designed to perform post-accident safety-related functions, normal safety-related functions, and normal nonsafety-related functions. The post-accident safety functions of the RHRS are to (1) operate as an emergency core cooling system (ECCS) subsystem, (2) operate as a subsystem of the containment spray system (CSS), and (3) provide a flow path to the reactor coolant system (RCS) from the spent fuel pool cooling and cleaning system (SFPCS) during flood mode when the reactor vessel head is removed.
CNL-20-052 E1-3 of 14 RHR pump 1B-B is a safety-related, vertical, single stage, centrifugal, motor driven pump, with the motor installed on a supporting head, which is supported by the stuffing box extension/casing. The pump impeller is mounted to the motor shaft and the RHR pump flow is limited to 3000 gpm per pump during two pump operation (normal cooldown mode). Five vibration monitoring data collections are obtained at two separate locations (three directions at location A and two directions at location B), which have been established in accordance with section ISTB of the ASME OM Code. The location of each monitoring point is depicted below:
A B
Table 1 provides a comparison of the baseline vibration reference values for the quarterly Group A and the two-year CPT. The baseline reference values for the CPT are considered to be smooth-running utilizing a baseline of 0.050 inches per second (ips) as a default value per Relief Request IST-RR-01 (Reference 1), with the exception of bearing location A in the vertical direction. None of the bearing location/directions are considered to be smooth-running for the Group A test.
Table 1 Comparison of the Baseline Vibration Reference Values Bearing Location Measurement Direction Quarterly Group A Test (700 gpm)
Comprehensive Test (4262 gpm)
A Horizontal 0.160 ips 0.03394 ips A
Vertical 0.186 ips 0.06652 ips A
Axial 0.114 ips 0.02837 ips B
Horizontal 0.074 ips 0.02591 ips B
Vertical 0.145 ips 0.02685 ips CNL-20-052 E1-4 of 14 During preoperational testing in 1994 to support initial WBN Unit 1 startup in 1995, RHR Pump 1B-B was tested during vessel floodup from the refueling water storage tank (injection mode) and a five point curve was developed. In order to move the CPT from the refueling outage critical path schedule, the testing sequence was changed from occurring during reactor vessel and refueling cavity fill to after cavity level has been established.
Testing was performed during the U1R11 and U1R12 refueling outages using a cavity neutral test loop to allow recirculation from the reactor vessel to the pump and back to the reactor vessel. A six-point curve was developed in the U1R11 outage and a seven point curve in the U1R12 outage. These three pump curves along with the current Group A and CPT test points are shown in Figure 1. The region of shutdown flow obtained during the troubleshooting activities in U1R16 is also indicated.
275 295 315 335 355 375 395 415 435 455 475 500 1000 1500 2000 2500 3000 3500 4000 4500 5000 Head (ft)
Flow (gpm)
Figure 1 RHR Pmp 1B Curves FSAR Head (ft) 1994 RHR Pmp 1B PTI (ft)
During Floodup U1R11 RHR Pmp 1B Preservice Head (ft) Recirc U1R12 RHR Pmp 1B Preservice Head (ft) Recirc Group A Test Point CPT Test Point Group A Test Point 5/24/20 ~Troubleshooting Flow Rate CNL-20-052 E1-5 of 14 The RHR 1B-B CPT was initiated in 2008 as part of the second IST Interval. The CPT hydraulic performance has remained relatively stable. Transitioning performance of the CPT from the period during floodup to cavity neutral has also improved repeatability of results. Results of the last six RHR 1B-B CPT performances using the cavity neutral test methodology are provided in Figure 2.
140.0 145.0 150.0 155.0 160.0 165.0 170.0 4/1/2012 8/14/2013 12/27/2014 5/10/2016 9/22/2017 2/4/2019 6/18/2020 10/31/2021 Differential Pressure, psid Date of Test Figure 2 RHR Pump 1B-B Differential Pressure at CPT Flow Delta P Req. Action Low Alert Req. Action High CNL-20-052 E1-6 of 14 As shown in Figure 3, slightly elevated vibration levels were first noticed on RHR Pump 1B-B in May 2018 during quarterly Group A pump testing at locations A-H, A-A, and B-H.
0.00000 0.10000 0.20000 0.30000 0.40000 0.50000 0.60000 6/14/2017 8/3/2017 9/22/2017 11/11/2017 12/31/2017 2/19/2018 4/10/2018 5/30/2018 Vibration, ips Date of Test Figure 3 RHR Pump 1B-B Vibrations (Quarterly Group A)
B - H B - V A - H A - V A - A CNL-20-052 E1-7 of 14 As shown in Figure 4, in October 2018 during the Unit 1 Cycle 15 refueling outage (U1R15)
CPT, vibration levels were slightly elevated, but not to an unusual level or beyond normal data scatter, at locations A-H, B-H, and B-V. The U1R15 vibration level for bearing A-V was further elevated, but still within acceptance criteria. This reading was considered to be an anomaly potentially due to a test performer issue such as data collection technique.
0.00000 0.05000 0.10000 0.15000 0.20000 0.25000 0.30000 2/1/2008 6/15/2009 10/28/2010 3/11/2012 7/24/2013 12/6/2014 4/19/2016 9/1/2017 Vibration, ips Date of Test Figure 4 RHR Pump 1B-B Vibrations (CPT)
B - H B - V A - H A - V A - A CNL-20-052 E1-8 of 14 As shown in Figure 5, in November 2018, two quarters after the initial observation of increased vibration levels, slightly elevated vibration levels were noted in the five bearing/locations (Figure 5 is same as Figure 3, plus two additional data points).
0.00000 0.10000 0.20000 0.30000 0.40000 0.50000 0.60000 6/14/2017 9/22/2017 12/31/2017 4/10/2018 7/19/2018 10/27/2018 Vibration, ips Date of Test Figure 5 RHR Pump 1B-B Vibrations (Quarterly Group A)
B - H B - V A - H A - V A - A CNL-20-052 E1-9 of 14 As shown in Figure 6, in October 2018, after the conclusion of U1R15, vibration levels on the Group A test exhibited an approximate 50% step change and then plateaued at that level at locations A-H and A-V. Smaller step changes followed by plateaued values were observed at locations B-H and B-V (Figure 6 is same as Figure 5, plus two additional data points).
0.00000 0.10000 0.20000 0.30000 0.40000 0.50000 0.60000 6/14/2017 9/22/2017 12/31/2017 4/10/2018 7/19/2018 10/27/2018 2/4/2019 5/15/2019 Vibration, ips Date of Test Figure 6 RHR Pump 1B-B Vibrations (Quarterly Group A)
B - H B - V A - H A - V A - A CNL-20-052 E1-10 of 14 As shown in Figure 7, during Unit 1 Cycle 16, the trend indicating continued vibration level increase during Group A testing is at location A-H which has exhibited an increased level on the last two quarterly tests prior to U1R16 (December 2019 and February 2020) (Figure 7 is same as Figure 6, plus three additional data points).
0.00000 0.10000 0.20000 0.30000 0.40000 0.50000 0.60000 6/14/2017 12/31/2017 7/19/2018 2/4/2019 8/23/2019 3/10/2020 Vibration, ips Date of Test Figure 7 RHR Pump 1B-B Vibrations (Quarterly Group A)
B - H B - V A - H A - V A - A CNL-20-052 E1-11 of 14 While the Group A test was not performed in U1R16, the CPT was performed in May 2020.
As shown in Figure 8, during that test, four of the five locations exhibited an increase in level from the U1R15 test with locations A-H and A-V both entering the alert range with A-H increasing by approximately 100% and A-V increasing by approximately 50%.
Locations B-H and B-V both exhibited approximately a 25% increase over the previous level. Location A-A remained in the historical band with a slight decrease in overall level (Figure 8 is same as Figure 4, plus one additional data point).
0.00000 0.05000 0.10000 0.15000 0.20000 0.25000 0.30000 2/1/2008 10/28/2010 7/24/2013 4/19/2016 1/14/2019 10/10/2021 7/6/2024 Vibration, ips Date of Test Figure 8 RHR Pump 1B-B Vibrations (CPT)
B - H B - V A - H A - V A - A CNL-20-052 E1-12 of 14 The latest available periodic vibration data is from the Group A test performed on June 8, 2020 (Figure 9), which was performed on its routine periodic frequency. This test determined that bearing direction/location A-V exhibited another upward step change from the previous cycle historical trend with a measured vibration level of 0.297 ips. During this Group A test, the data for A-H exhibited a marked downward step change to a value of 0.159 ips, which is slightly less than the historical trend during WBN Unit Cycle 16. The remaining three data points (A-A, B-H, and B-V) all show a slight upward shift in vibration level.
0.00000 0.10000 0.20000 0.30000 0.40000 0.50000 0.60000 6/1/2019 9/9/2019 12/18/2019 3/27/2020 Vibration, ips Date of Test Figure 9 RHR Pump 1B-B Vibrations (Quarterly Group A)
B - H B - V A - H A - V A - A CNL-20-052 E1-13 of 14 On June 24, 2020, a conditional (non-routine) quarterly Group A pump test was performed in conjunction with tightening the pump support structure and monitoring the corresponding vibration levels. Vibration levels were collected on all five monitored bearing locations/directions prior to any adjustments and once again upon completion of the final adjustments. As shown in Figure 10, none of the points documented any appreciable change between the before and after vibration levels following the maintenance. Prior to the maintenance being performed, three of the five monitored bearing locations/directions (A-H, A-A, and B-H) exhibited a higher level compared to the June 8, 2020, test (See graphical representation in Figure 10 and tabulated data in Table 2) (Figure 10 is same as Figure 9, plus one additional data point).
Table 2 Comparison of June 8 and June 24, 2020 Vibration Data for Selected Points Location/Direction June 8, 2020 June 24, 2020 Delta Percent Change A-H 0.15930 0.19700
+0.0377
+23.66 A-A 0.09820 0.11700
+0.0188
+19.14 B-H 0.11900 0.15300
+0.0340
+28.57 0.00000 0.10000 0.20000 0.30000 0.40000 0.50000 0.60000 6/1/2019 9/9/2019 12/18/2019 3/27/2020 7/5/2020 10/13/2020 Vibration, ips Date of Test Figure 10 RHR Pump 1B-B Vibrations (Quarterly Group A)
B - H B - V A - H A - V A - A CNL-20-052 E1-14 of 14 VI.
Results of Troubleshooting Following discovery of the elevated vibration levels during the U1R16 CPT, troubleshooting identified looseness in the support structure. The support structure had some cracked and missing paint near certain mechanical fasteners on the northeast side of the support structure that indicated the framing had shifted. This is potentially due to the pump/motor assembly not being doweled in place with the mounting holes being slotted to allow for some assistance with installation. The motor/pump assembly itself does not show any signs of a degraded equipment condition based on the data that has been collected. This troubleshooting activity was performed at a shutdown cooling flow rate of approximately 2780 to 3150 gpm.
TVA performed a spectral analysis of the vibration data. This analysis did not identify any spectral trend that points to a degrading mechanical/electrical condition, but the overall amplitude has experienced a slight increasing trend. Based on the spectral data, RHR Pump 1B-B appears to be exhibiting some type of looseness in the equipment/structure.
An oil analysis was also performed by TVA, which determined that viscosity, wear metals, and chemistry values were within normal operating ranges. No moisture was noted within this system.
VII. Duration of Proposed Alternative The duration of the proposed alternative request will be through the completion of the U1R17 refueling outage, which is currently scheduled to be completed by November 27, 2021.
VIII.
Precedents The following similar alternative requests have been approved by the NRC.
North Anna Power Station, Unit 1, Relief Request P-9, dated February 19, 2020 (ML20031E784)
Waterford Steam Electric Station, Unit 3, Relief Request PRR-WF3-2017-3, dated December 11, 2017 (ML17341A120)
Waterford Steam Electric Station, Unit 3, Relief Request PRR-WF3-2016-1, dated July 6, 2016 (ML16182A270)
Palo Verde Nuclear Generating Station, Unit 3, Relief Request PRR-08, dated August 3, 2009 (ML091900274)
IX.
Reference
- 1.
NRC letter to TVA, "Watts Bar Nuclear Plant, Unit 2-Review of lnservice Test Program and Preservice Test Program, and Safety Evaluation of Relief Requests IST-RR-1/2/3/4 for the First 10-Year Interval of the lnservice Testing Program (TAC No. MF4118)," dated October 21, 2014 (ML14289A222)
CNL-20-052 E2-1 of 1 New Regulatory Commitments Commitment Due Date/Event TVA will submit to the NRC the results of the follow-up oil analysis for RHR pump 1B-B October 30, 2020 TVA will submit to the NRC the results of the next quarterly Group A test for RHR pump 1 B-B October 30, 2020