05000324/LER-2017-003

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LER-2017-003, 1 OF 4
Brunswick Steam Electric Plant (Bsep) Unit 2
Event date: 06-05-2017
Report date: 08-03-2017
Reporting criterion: 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications
3242017003R00 - NRC Website
LER 17-003-00 for Brunswick, Unit 2, Regarding Setpoint Drift in Main Steam Line Safety/Relief Valves Results in Three Valves Inoperable,
ML17215A990
Person / Time
Site: Brunswick Duke energy icon.png
Issue date: 08/03/2017
From: Gideon W R
Duke Energy Progress
To:
Document Control Desk, Office of Nuclear Reactor Regulation
References
BSEP 17-0065
Download: ML17215A990 (6)


At the time the condition was identified, Unit 2 was in Mode 1 at 87 percent of rated power and was increasing in power after a preplanned control rod improvement evolution.

valves (SRVs) to be operable. Per Surveillance Requirement (SR) 3.4.3.1, each valve is required to open within +/-3 percent of its opening setpoint. As-found testing of the valves indicated that three of the valves had lift setpoints outside this tolerance. Based on the causes of the inoperability described below, it was concluded that three SRVs were inoperable when the unit was in operation. Consequently, the plant operated in a condition which is prohibited by the TS, that is, with fewer than the required number of SRVs having lift setpoints within the +/-3 percent tolerance. Therefore, the condition is being reported per 10 CFR 50.73(a)(2)(i)(B) for operation in a condition prohibited by the plant TSs.

The change in SRV lift setpoints resulted from corrosion bonding between the discs and seats of the pilot valves. Corrosion bonding between the pilot disc and seat is an inherent problem with the two-stage SRV During the spring 2017 Unit 2 refueling outage, all 11 Model 7657F Target Rock Two-Stage pilot valve assemblies in the SRVs were replaced with certified spares. The removed SRV pilot valves were sent to National Technical Systems (NTS) to determine the as-found set pressure. On June 5, 2017, test results were reported to BSEP. The test results showed that three of the 11 valves actuated at pressures outside of the +/-3 percent tolerance allowed by TS 3.4.3. The test data for the valves found out of tolerance are shown below:

Reportability Criteria

Event Description

Event Cause (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/)

CONTINUATION SHEET

Valve Identification TS Setpoint (psig) As-Found Lift Pressure (psig) Percent Difference S/N 1098 1140 1244 +9.1 S/N 1109 1130 1227 +8.6 S/N 1106 1150 1208 +5.0 APPROVED BY OMB: NO. 3150-0104 EXPIRES: 03/31/2020 comments regarding burden estimate to the Information Services Branch (T-2 F43), U.S. Nuclear Regulatory Commission, Washington, DC 20555-0001, or by e-mail to used to impose an information collection does not display a currently valid OMB control number, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.

2017 - 003

3. LER NUMBER

- 000 Therefore, it is concluded that the SRVs always remained capable of performing their safety function of preventing overpressurization of the reactor coolant system.

Based on the foregoing analysis, it is concluded that this event had no adverse impact on nuclear safety.

Corrective Actions

All the SRV pilot assemblies were replaced with certified spares during the spring 2017, Unit 2 refueling outage.

Procedure 0CM-VSR509, “Main Steam Relief Valves Target Rock Model 7567 Air Operators and Pilot Assembly Disassembly, Inspection, and Reassembly,” has been revised to reduce the probability of have been prepared with this revised procedure.

design used at Brunswick. Brunswick mitigates corrosion bonding of SRVs by coating each pilot disc surface with platinum to prevent oxygen from interacting with the underlying Stellite. The integrity of the platinum coating is critical to mitigating corrosion bonding. In SRV pilots 1106 and 1109, the platinum coating was degraded in large areas of the pilot disc. The coating was degraded because adhesion to the underlying Stellite was not optimal. Adhesion was less than optimal because a recently devised surface preparation method (i.e., precision grinding to minimize micro-cracking) had not yet been implemented at the time these SRVs were built.

On SRV pilot 1098, extensive steam erosion changed the geometry of the pilot disc. The altered geometry required additional steam pressure to develop sufficient force to overcome the set pressure spring. The change in geometry likely resulted in wedging of the disc into the seat. Steam erosion occurred because the pilot was leaking for a significant portion of the cycle.

The purpose of the safety/relief valves is to provide overpressure protection for the reactor coolant system.

The as-found condition of the Unit 2 SRVs was analyzed per Engineering Change (EC) 409048. The analysis compares each of the 11 SRVs in its as-found condition to the most limiting case addressed in the Brunswick Unit 2 Cycle 22 Reload Safety Analysis Report (RSAR). EC 409048 shows that every SRV opened in its as-found state at a pressure lower than at least one valve in the RSAR analysis. Since each as-found SRV was bounded by the opening pressures assumed in the analysis, the overall RSAR analysis bounds the overall as-found condition of the SRVs. The peak steam dome pressure would therefore not reach the plant safety limit of 1325 psig even in the worst-case analyzed transient.

Safety Assessment (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/)

CONTINUATION SHEET

APPROVED BY OMB: NO. 3150-0104 EXPIRES: 03/31/2020 comments regarding burden estimate to the Information Services Branch (T-2 F43), U.S. Nuclear Regulatory Commission, Washington, DC 20555-0001, or by e-mail to used to impose an information collection does not display a currently valid OMB control number, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.

2017 - 003

3. LER NUMBER

- 000 In the past three years, two Licensee Event Reports have been submitted to the NRC describing events in which SRVs have been found with setpoint drift which made the valves inoperable.

In these events, the causes of corrosion bonding were analyzed, and corrective actions were implemented in subsequent groups of SRVs being rebuilt. However, the platinum coating process is still being advanced. Previous corrective actions could not benefit from improvements which were developed later.

This report contains no new regulatory commitments.

Commitments

Previous Similar Events

(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/) 05000325 / 2014-005, dated July 21, 2014 (ADAMS Accession Number ML14212A031) 05000324 / 2015-002, Revision 1, dated June 26, 2015 (ADAMS Accession Number ML15196A033)

CONTINUATION SHEET

APPROVED BY OMB: NO. 3150-0104 EXPIRES: 03/31/2020 comments regarding burden estimate to the Information Services Branch (T-2 F43), U.S. Nuclear Regulatory Commission, Washington, DC 20555-0001, or by e-mail to used to impose an information collection does not display a currently valid OMB control number, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.

2017 - 003

3. LER NUMBER

- 000