05000263/LER-2018-002, C Outboard Main Steam Line Isolation Valve Delayed Closure Due to Foreign Material in the Air Valve
| ML19046A002 | |
| Person / Time | |
|---|---|
| Site: | Monticello  |
| Issue date: | 02/14/2019 |
| From: | Church C Northern States Power Company, Minnesota, Xcel Energy |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| L-MT-19-011 LER 2018-002-00 | |
| Download: ML19046A002 (5) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications |
| 2632018002R00 - NRC Website | |
text
(l Xcel Energy*
R ESP O N SI BL E BY NAT UR E February 14, 2019 ATTN: Document Control Desk U.S. Nuclear Regulatory Commission Washington, DC 20555-0001 Monticello Nuclear Generating Plant Docket No. 50-263 Renewed Facility Operating License No. DPR-22 2807 West County Road 75 Monticello, MN 55362 L-MT-19-011 10 CFR 50.73 10 CFR 21 LER 2018-002-00, C Outboard Main Steam Line Isolation Valve Delayed Closure Due to Foreign Material in the Air Valve Northern States Power Company, a Minnesota Corporation (NSPM), doing business as Xcel Energy, hereby submits Monticello Nuclear Generating Plant (MNGP) Licensee Event Report (LER) 2018-002-00 "C Outboard Main Steam Line Isolation Valve Failed to Close Due to Foreign Material in the Air Valve" pursuant to 10 CFR 50.73(a)(2)(i)(B) as an operation or condition which was prohibited by the plant's Technical Specification. Additionally, this report also constitutes a 10 CFR 21 notification.
Summary of Commitments This letter m.a,kes no 1 ~2ts and no revisions to existing commitments.
C nstopher R. Church
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Site Vice President, Monticello Nuclear Generating Plant Northern States Power Company - Minnesota Enclosure cc:
Administrator, Region Ill, USNRC Project Manager, Monticello, USNRC Resident Inspector, Monticello, USNRC Minnesota Department of Commerce
NRC FORM 366 (02-2018)
NRC FORM 366 (02-2018)
U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB: NO. 3150-0104 EXPIRES: 03/31/2020
, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.
LICENSEE EVENT REPORT (LER)
(See Page 2 for required number of digits/characters for each block)
(See NUREG-1022, R.3 for instruction and guidance for completing this form http://www.nrc.gov/reading-rm/doc-collections/nuregs/staff/sr1022/r3/)
- 1. Facility Name Monticello Nuclear Generating Plant
- 2. Docket Number 05000-263
- 3. Page 1 OF 4
- 4. Title C Outboard Main Steam Isolation Valve Delayed Closure Due to Foreign Material in the Air Valve
- 5. Event Date
- 6. LER Number
- 7. Report Date
- 8. Other Facilities Involved Month Day Year Year Sequential Number Rev No.
Month Day Year Facility Name Docket Number 05000 12 20 2018 2018
- - 002
- - 00 02 14 2019 Facility Name Docket Number 05000
- 9. Operating Mode 1
)
No Abstract (Limit to 1400 spaces, i.e., approximately 14 single-spaced typewritten lines)
On November 16, 2018 at approximately 20:34 hours while operating in Mode 1 at 25% power, the plant was performing a functional test to demonstrate fast-closure of C Outboard Main Steam Isolation Valve (MSIV) AO-2-86C.
The delay of the valve closure was caused by silicone based foreign material intrusion in the air solenoid valve body attributed to manufacturing of the air control assembly. The Monticello Nuclear Generating Plant (MNGP) Technical Specifications (TS) Surveillance Requirement (SR) 3.6.1.3.6 requires that the isolation time of each MSIV is 3 seconds and 9.9 seconds. The C Outboard MSIV failed to close on the first attempt and failed stroke time acceptance criteria on the second closure attempt. During the second functional test the stroke time was measured at approximately 16 seconds. The valve was declared inoperable and subsequently repaired.
The component failure is reportable in accordance with 10 CFR 50.73(a)(2)(i)(B) as a condition prohibited by TS 3.6.1.3 Primary Containment Isolation Valves, since C Outboard MSIV was inoperable for greater then the TS 3.6.1.3 Required Action A.1, Completion Time of 8 hours9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br /> to isolate a main steam line, and the Completion Time for TS 3.6.1.3 Require Action F, to be in Mode 3 in 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> and Mode 4 in 36 hours4.166667e-4 days <br />0.01 hours <br />5.952381e-5 weeks <br />1.3698e-5 months <br /> when the completion time of A.1 is not met.
There were no actual safety consequences that affect public health and safety associated with this condition since the primary containment isolation function was maintained. Additionally, this report also constitutes a 10 CFR Part 21 notification.
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Page 2 of 4 (04-2017)
U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB: NO. 3150-0104 EXPIRES: 3/31/2020
, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.
LICENSEE EVENT REPORT (LER)
CONTINUATION SHEET (See NUREG-1022, R.3 for instruction and guidance for completing this form http://www.nrc.gov/reading-rm/doc-collections/nuregs/staff/sr1022/r3/)
- 3. LER NUMBER Monticello Nuclear Generating Plant 05000-263 YEAR SEQUENTIAL NUMBER REV NO.
2018
- - 002
- - 00
EVENT DESCRIPTION
On November 16, 2018 at approximately 20:34 hours while operating in Mode 1 at 25% power, the plant was performing a functional test to demonstrate fast-closure of C Outboard Main Steam [SB] Isolation Valve [ISV] (MSIV)
AO-2-86C. During this functional test, C Outboard MSIV was given a close signal via the control room hand switch [HS]. The C Outboard MSIV was not observed to close via light indication and no movement was observed via a locally mounted camera. After approximately 50 seconds, the hand switch was returned to auto/open. A second attempt to close the C Outboard MSIV via the control room hand switch was performed. Movement did not occur for approximately eight seconds after placing the hand switch to close, however, once the valve started to move, the stroke time was eight seconds. The MNGP Technical Specification (TS) Surveillance Requirement (SR) 3.6.1.3.6 requires that the isolation time of each MSIV is 3 seconds and 9 seconds. The measured closing time of the second functional test was approximately 16 seconds. With the SR not being met, the valve was declared inoperable.
On November 17, 2018 at approximately 02:14 hours, Operations closed and deactivated C Inboard MSIV AO 80C to comply with TS 3.6.1.3. The valve closed as expected.
Onsite troubleshooting activities commenced and the air control assembly was removed for bench testing, disassembly, and inspection. The air control assembly consists of a cluster of three AVCO solenoid valves (SV1, SV2, and SV3) which control air to three Norgren pilot air valves (V1, V2, and V3). During the bench testing, all three AVCO solenoid valves and two Norgren pilot air valves (V3 and V2) operated correctly. Minor corrosion and adhesive wear was observed inside the Norgren air valve assembly. Minor wear was also noted on AVCO SV1 and SV2 and small pieces of foreign material noted in SV2 during the troubleshooting disassembly but a conclusive failure mechanism was not determined during onsite troubleshooting activities. Most of the air control assembly, three AVCO solenoid valves and two Norgren valves (V1 and V3), was replaced and the C Outboard MSIV was declared operable after completing the functional test on November 20, 2018 at approximately 00:19 hours. The Norgren pilot air valve V2 operated correctly and did not show signs of wear; therefore, it was not replaced.
The parts were sent out to an external vendor for forensic testing. During this detailed analysis a silicone based foreign material was identified in AVCO SV2 which could restrict air flow from the solenoid vent upon de-energizing.
The external laboratory testing indicated that the corrosion and adhesive wear on the Norgren air valve assembly (V3 and V2) was not significant enough to cause the delayed closure. Using results from the vendor forensics, a causal evaluation (CE) was completed on December 20, 2018 which concluded that the failure mechanism would have rendered the MSIV incapable of meeting the TS closure time requirement since the previous fast closure test. The last time the C Outboard MSIV demonstrated the capability of performing the fast closure was May 3, 2017 during the performance of the functional test.
EVENT ANALYSIS
The event was determined to be reportable in accordance with 10 CFR 50.73 (a)(2)(i)(B), Any operation or condition which was prohibited by the plants Technical Specifications. Specifically this component failure is reportable with 10 CFR 50.73(a)(2)(i)(B) as a condition prohibited by TS 3.6.1.3 Primary Containment Isolation Valve, since C Outboard MSIV was inoperable for greater than the TS 3.6.1.3, Required Action A.1, Completion Time of 8 hours9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br /> to isolate a main steam line, and the Completion Time for TS 3.6.1.3, Required Action F, to be in Mode 3 in 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> Page 3 of 4 (04-2017)
U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB: NO. 3150-0104 EXPIRES: 3/31/2020
, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.
LICENSEE EVENT REPORT (LER)
CONTINUATION SHEET (See NUREG-1022, R.3 for instruction and guidance for completing this form http://www.nrc.gov/reading-rm/doc-collections/nuregs/staff/sr1022/r3/)
- 3. LER NUMBER Monticello Nuclear Generating Plant 05000-263 YEAR SEQUENTIAL NUMBER REV NO.
2018
- - 002
- - 00 and Mode 4 in 36 hours4.166667e-4 days <br />0.01 hours <br />5.952381e-5 weeks <br />1.3698e-5 months <br /> when the completion time of A.1 is not met. Additionally, this report also constitutes a 10 CFR Part 21 notification.
This event is not classified as a safety system functional failure as the C Inboard MSIV was operable during the period from May 3, 2017 through November 20, 2018.
SAFETY SIGNIFICANCE
There were no actual safety consequences that affect public health and safety associated with this condition. The C Inboard MSIV on C Main Steam line was operable from May 3, 2017 until the C Outboard MSIV was declared operable on November 20, 2018. The C Inboard MSIV was tested for both leak rate and closing time during the last refueling outage (Spring 2017) and each test was completed satisfactorily. Additionally, the inboard MSIVs and their air actuators are a different design than those on the outboard MSIVs. The station performs maintenance and testing activities on the inboard MSIVs and the sites operational history does not indicate a performance issue with the inboard MSIVs. Therefore, the primary containment isolation capability of the main steam lines remained operable which ensured the required isolation safety function was maintained.
CAUSE
The direct cause of C Outboard MSIV delayed closure was attributed to silicone based foreign material intrusion in the solenoid valve body attributed to manufacturing of the air control assembly. The foreign material was introduced during original manufacturer fabrication as the air control assembly was delivered to the site as a complete unit and no additional silicone based thread sealant was applied during plant installation. In addition, foreign material is not expected to originate from the plant air system as the air supply filters out 99.99% of all particles 1 micron and larger and 98% of all particles 0.07 microns and larger.
The laboratory testing and third party vendor analysis concluded that the most likely cause of the anomalous behavior of the C Outboard MSIV was debris within AVCO solenoid valve SV2 interfering with the closure of port 2 and the withdrawal of control air from the Norgren pilot valves V1 and V3. The corrosion and adhesive wear observed on the components of the Norgren pilot valve V1 would have contributed to the sluggish response of the C Outboard MSIV but could not have been the sole cause of the failure to close.
CORRECTIVE ACTION
The immediate corrective action was to replace the air control assembly and complete the functional test for fast closure for the C Outboard MSIV. Then the valve was declared operable.
The functional bench test for the MSIV air control assembly was developed to address a previous concern of binding and misalignment that caused the Norgren valves to stick (LER 2017-002-00). The functional bench test for the MSIV air control assembly will be revised to include a step for air venting to remove potential foreign material left over from the manufacturing process.
The functional bench testing is planned to be performed for the A, B, C, and D Outboard MSIV valves Page 4 of 4 (04-2017)
U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB: NO. 3150-0104 EXPIRES: 3/31/2020
, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.
LICENSEE EVENT REPORT (LER)
CONTINUATION SHEET (See NUREG-1022, R.3 for instruction and guidance for completing this form http://www.nrc.gov/reading-rm/doc-collections/nuregs/staff/sr1022/r3/)
- 3. LER NUMBER Monticello Nuclear Generating Plant 05000-263 YEAR SEQUENTIAL NUMBER REV NO.
2018
- - 002
- - 00 air control assemblies during the next refueling outage.
FAILED COMPONENT INFORMATION
Description
Rotork-Hiller MSIV Actuator AVCO Solenoid Manifold Sub-Assembly Manufacturer: Appendix B Supplier: Rotork-Hiller, subcomponent AVCO solenoid valve Part Number: Rotork-Hiller Actuator Serial Number 1526309, AVCO solenoid valve series B6930-081
PREVIOUS SIMILAR EVENTS
There were two previously similar LERs 2017-002-00 and LER 2015-006-00. The cause of these events was determined to be binding and misalignment of the Norgren valves on the D Outboard MSIV. The cause of the delayed closure of the C Outboard MSIV on November 16, 2018 was due to foreign material in the AVCO solenoid valve. Therefore, the corrective actions from LER 2017-002-00 would not have prevented the silicone based foreign material from being introduced into the C Outboard MSIV air control assembly.
ADDITIONAL INFORMATION
The Institute of Electrical and Electronics Engineer codes for equipment are denoted by [XX].