05000366/LER-2017-003

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LER-2017-003,
Edwin I. Hatch Nuclear Plant Unit 2
Event date: 02-19-2017
Report date: 4-13-2017
Reporting criterion: 10 CFR 50.73(a)(2)(v)(C), Loss of Safety Function - Release of Radioactive Material

10 CFR 50.73(a)(2)(ii)(A), Seriously Degraded
LER closed by
IR 05000321/2017003 (14 November 2017)
3662017003R00 - NRC Website
LER 17-003-00 for Edwin I. Hatch, Unit 2, Regarding Primary Containment Isolation Penetration Exceeded Overall Allowable Technical Specification Leakage Limits
ML17104A292
Person / Time
Site: Hatch Southern Nuclear icon.png
Issue date: 04/13/2017
From: Vineyard D R
Southern Nuclear Operating Co
To:
Document Control Desk, Office of Nuclear Reactor Regulation
References
NL-17-0640
Download: ML17104A292 (6)


Primary Containment Isolation Penetration Exceeded Overall Allowable Technical Specification Leakage Limits 8. OTHER FACILITIES INVOLVED 5. EVENT DATE 6. LER NUMBER 7. REPORT DATE

FACILITY NAME DOCKET NUMBER REV

MONTH YEAR DAY YEAR MONTH DAY YEAR

DOCKET NUMBER FACILITY NAME

02 19 2017 2017 - 003 - 00 4 13 2017 11. THIS REPORT IS SUBMITTED PURSUANT TO THE REQUIREMENTS OF 10 CFR 10 CFR : (Check all that apply) q 20.2203(a)(3)(i) 0 50.73(a)(2)(viii)(A) q 20.2201(b) 50.73(a)(2)(ii)(A) 0 20.2201(d) 0 50.73(a)(2)(viii)(B) 0 20.2203(a)(3)(ii) 0 50.73(a)(2)(ii)(B) 0 20.2203(a)(1) 0 50.73(a)(2)(ix)(A) 0 20.2203(a)(4) 0 50.73(a)(2)(iii) 0 20.2203(a)(2)(i) 0 50.73(a)(2)( 0 50.36(c)(1)(i)(A) 0 50 73(a)(2)(iv)(A) 0 20.2203(a)(2)(ii) 0 73.71(a)(4) 0 50.36(c)(1)(ii)(A) 0 50.73(a)(2)(v)(A) 0 20.2203(a)(2)(iii) 0 73.71(a)(5) 0 50.36(c)(2) 0 50.73(a)(2)(v)(B) 0 20.2203(a)(2)(iv) 0 73.77(a)(1) 0 50.46(a)(3)(ii) 50.73(a)(2)(v)(C) 0 20.2203(a)(2)(v) q 73.77(a)(2)(i) 0 50.73(a)(2)(i)(A) 0 50.73(a)(2)(v)(D) 0 20.2203(a)(2)(vi) 0 73.77(a)(2)(ii) 0 50.73(a)(2)(i)(B) 0 50.73(a)(2)(vii) 0 50.73(a)(2)(i)(C) 0 OTHER Specify in Abstract below or in NRC Form 366A TELEPHONE NUMBER (Include Area Code) ICENSEE CONTACT Edwin I. Hatch / Jimmy Collins - Licensing Supervisor 912-537-2342

13. COMPLETE ONE UNE FOR EACH COMPONENT FAILURE DESCRIBED IN THIS REPORT

1 MANU- REPORTABLE COMPONENT CAUSE SYSTEM COMPONENT FACTURER TO EPIX

REPORTABLE

TO EPIX

MANU-

FACTURER CAUSE SYSTEM

4 X BB ISV F130 Y

15. EXPECTED

SUBMISSION

DATE

DAY YEAR MONTH

outboard drywell ventilation penetration isolation valve 2T48F320 (EIIS Code: ISV) failed local leak rate testing (LLRT).

Previously on February 7, 2017 at 1427 EST, the inboard drywell ventilation penetration isolation valve 2T48F319 had also failed LLRT. Therefore, due to both primary containment isolation valves (PCIVs) in this penetration flow path exceeding the maximum allowable leakage rate (La), this event represents a failure of the associated penetration (2T23X26) to maintain primary containment integrity per Technical Specifications (TS).

Actions were taken to repair both of the PCIVs and on February 21, 2017, the valves were successfully retested. During the next scheduled Unit 2 refueling outage, the 2T48F320 isolation valve will be completely rebuilt. Also a corrective maintenance rebuild procedure will be developed for Fisher Series 9200 butterfly valves.

Reported lessons learned are incorporated into the licensing process and fed back to industry Send comments regarding burden estimate to the FOIA, Privacy and Information Collections Branch (T-5 F53), U.S. Nuclear Regulatory Commission, Washington, DC 20555-0001, or by e-mail to Infocollects.Resource@nrc.gov, and to the Desk Officer, Office of Information and Regulatory Affairs, NEOB-10202, (3150-0104), Office of Management and Budget, Washington, DC 20503. If a (See NUREG-1022, R.3 for instruction and guidance for completing this form means 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.

CONTINUATION SHEET

http://www.nrc.00v/readino-nn/doc-collections/nureps/staff/sr1022/r3/) 05000-366

Event Description

On February 19, 2017 at 2323 EST, with Unit 2 at 0 percent rated thermal power due to a refueling outage, the Unit 2 outboard drywell ventilation penetration isolation valve 2T48F320 (EIIS Code: ISV) failed local leak rate testing (LLRT). Previously on February 7, 2017 at 1427 EST, the inboard drywell ventilation penetration isolation valve 2T48F319 had also failed LLRT. Therefore, due to both primary containment isolation valves (PCIVs) in this penetration flow path exceeding the maximum allowable leakage rate (La), this event represents a failure of the associated penetration (2T23X26) to maintain primary containment integrity per Technical Specifications (TS).

The as-found results of the LLRT rendered penetration 2T23X26 inoperable. Actions were made to repair both of the PCIVs and on February 21, 2017, the valves were successfully retested. Observed leakage rates were determined to be acceptable.

Failed Components Information:

Master Parts List Number 2T48F319 and 2T48F320 Manufacturer: Fisher Controls Co.

Model Number. Model 9220 Type: Isolation Valves Event Cause Analysis The cause of the both the 2T48F319 and 2T48F320 PCIVs exceeding their acceptable maximum allowable leakage limits was attributed to inadequate conditions related to the disc sealing ring that was found on both valves. Specifically for the 2T48F320 isolation valve, it was revealed that the set screws that are used to hold in place the retaining plate for the disc sealing ring were all loose. This allowed the ring to loosen over time, creating a gap between the valve disc and the ring.

Safety Assessment This event is reportable per 10 CFR 50.73(a)(2)(ii)(A) due to an event or condition that resulted in the condition of the nuclear power plant, including its principle safety barriers, being seriously degraded. This event is also reportable per 10 CFR 50.73(a)(2)(v)(C) as an event or condition that could have prevented the fulfillment of the safety function of structures or systems that are needed to control the release of radioactive material due to the failure of the penetration flow path to meet its maximum allowable leakage rate.

The function of the PCIVs, in combination with other accident mitigation systems, is to limit fission product release during and following postulated Design Basis Accidents (DBAs) to within limits. Primary containment isolation ensures that the release of radioactive material to the environment will be consistent with the assumptions used in the analyses for a DBA. Operability requirements for the PCIVs help ensure that an adequate primary containment boundary is maintained during and after an accident by minimizing potential paths to the environment. This provides assurance that the primary containment function as assumed in safety analyses is maintained. Two barriers in series are provided for each penetration such that no single credible failure or malfunction of an active component can result in a loss of isolation or leakage that exceeds limits assumed in the safety analyses.

`NRC FORM 366A U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB: NO. 3150-0104 EXPIRES: 10/31/2018 LICENSEE EVENT REPORT(LER) Reported lessons learned are incorporated into the licensing process and fed back to industry.

Send comments regarding burden estimate to the FOIA, Privacy and Information Collections

CONTINUATION SHEET

Branch (T-5 F53), U.S. Nuclear Regulatory Commission, Washington, DC 20555-0001, or by e-mail to Infocollects.Resource@nrc.gov, and to the Desk Officer, Office of Information and Regulatory Affairs, NEOB-10202, (3150-0104), Office of Management and Budget, Washington, DC 20503. If a (See NUREG-1022, R.3 for instruction and guidance for completing this form means 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.

Edwin I. Hatch Nuclear Plant Unit 2 05000-366 NUMBER NO.

A calculation was performed to determine the impact of drywell ventilation penetration 2T23X26 leakage exceeding La on post-LOCA doses, where La is the maximum allowable primary containment leakage rate per TS 5.5.12. The calculation evaluated doses to the main control room (MCR), the technical support center (TSC), the exclusion area boundary (EAB), and the low population zone (LPZ). The results of the calculation show that with an assumed containment leakage rate of 3 times La, and an assumed MSIV leakage of twice the as-found leakage rate, doses to the MCR, TSC, EAB and LPZ were all within the regulatory limits. The actual as-found overall leakage rate of primary containment was determined to be 2.3 times La, 23 percent less than the assumed value.

Therefore, based on the aforementioned calculation results, the potential safety consequences of exceeding the maximum allowable TS primary containment leakage rate by a factor of 2.3 are very low due to radiation doses in the MCR, TSC, EAB and LPZ all being within regulatory limits. Radiation doses would not have exceeded federal limits during a design basis event.

Corrective Actions

The ring assemblies on both the 2T48F319 and 2T48F320 valves were replaced and the set screws were adjusted. The valves were successfully retested with an observed acceptable leakage rate. During the next scheduled Unit 2 refueling outage, the 2T48F320 isolation valve will be completely rebuilt Also a corrective maintenance rebuild procedure will be developed specifically for Fisher Series 9200 butterfly valves.

Previous Similar Events

On April 16, 2011, during the Hatch Nuclear Plant 2R21 refueling outage, a local leak rate test (LLRT) was performed on torus purge supply primary containment isolation valve (PCIV) 2T48-F324 which is associated with primary containment penetration 2T23-X205. At that time, plant engineers and technicians were performing an LLRT for penetration 2T23-X205 when it was discovered that both PCIVs (2T48-F309 and 2T48-F324) had failed their LLRTs for this penetration. This resulted in the penetration leakage exceeding the overall allowable leakage (La) requirements by the Technical Specifications (TS) for primary containment.

Although the event documented above is similar, the corrective actions taken did not prevent the 2T48F319 or 2T48F320 valves from failing their LLRT.

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