05000440/LER-2023-002, Main Steam Line Leakage Exceeded Technical Specification Limit
| ML23117A063 | |
| Person / Time | |
|---|---|
| Site: | Perry  |
| Issue date: | 04/26/2023 |
| From: | Penfield R Energy Harbor Nuclear Corp |
| To: | Office of Nuclear Reactor Regulation, Document Control Desk |
| References | |
| L-23-107 LER 2023-002-00 | |
| Download: ML23117A063 (1) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications 10 CFR 50.73(a)(2)(ii)(B), Unanalyzed Condition 10 CFR 50.73(a)(2)(v), Loss of Safety Function |
| 4402023002R00 - NRC Website | |
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harbor Rod L. Penfield Site Vice President, Perry Nuclear April 26, 2023 L-23-107 ATTN: Document Control Desk U.S. Nuclear Regulatory Commission Washington, DC 20555-0001
SUBJECT:
Perry Nuclear Power Plant Docket No. 50-440, License No. NPF-58 Licensee Event Report Submittal Energy Harbor Nuclear Corp Perry Nuclear Power Plant 10 Center Road Perry, Ohio 44081 440-280-5382 724-462-0816 (cell) 10 CFR 50.73(a)(2)(i)(B) 10 CFR 50.73(a)(2)(ii)(B) 10 CFR 50.73(a)(2)(v)(C)
Enclosed is Licensee Event Report (LER) 2023-002, "Main Steam Line Leakage Exceeded Technical Specification Limit." There are no regulatory commitments contained in this submittal.
If there are any questions or if additional information is required, please contact Mr. Glendon Burnham, Manager - Regulatory Compliance, at (440) 280-7538.
Enclosure:
LER 2023-002 cc:
NRC Project Manager NRC Resident Inspector NRC Region Ill Regional Administrator
Enclosure L-23-107 LER 2023-002
Abstract
On March 4, 2023, with the reactor shutdown for a planned refueling outage (Mode 5 and 0% rated thermal power), an evaluation of data from the scheduled Main Steam Line (MSL) valve penetration Local Leak Rate Testing (LLRT) determined that the 'as found' maximum pathway leakage for all four Main Steam Isolation Valves (MSIVs) to be in excess of the Technical Specification (TS) Surveillance Requirement (SR) 3.6.1.3.10 leakage limit of less than or equal to 250 standard cubic feet per hour (scfh). In addition, when the 'B' outboard MSIV was tested, the leakage was indeterminate due to a large packing leak.
The two B MSIVs required rework due to leakage beyond the TS SR limit. An Engineering calculation was performed based on the MSL B leakage and showed that in the event of a Loss of Coolant Accident (LOCA) on MSL B (worst case), the resulting radiological dose at the Exclusion Area Boundary (EAB) would be 44.29 rem, which is greater than the Updated Safety Analysis Report (USAR) limits for the station.
The direct cause of leakage on the inboard MSIV B valve was attributed to normal wear, due to the as found condition during valve rework. The plausible cause of the packing gland leak on the outboard MSIV B is due to a previous misalignment of the stem. Both valves were reworked so that as-left LLRT leakage values complied with the limits established in TS SR 3.6.1.3.1 0.
This event is reportable due to a condition prohibited by TS under 10 CFR 50. 73(a)(2)(i)(B), an unanalyzed condition under 10 CFR 50.73(a)(2)(ii)(B), and under 10 CFR 50.73(a)(2)(v)(C) as a condition that could have prevented the fulfillment of a safety function of structures or systems needed to control the release of radioactive material.
Energy Industry Identification System (EIIS) codes are identified in the text as [XX].
EVENT DESCRIPTION
YEAR 2023 SEQUENTIAL NUMBER 002 REV NO.
00 On March 4, 2023, with the unit shutdown for a planned refueling outage (Mode 5, Refueling, 0% power), the Main Steam Line (MSL) [SB] Local Leak Rate Test (LLRT) for Containment penetrations [BD] was being performed for the MSL B inboard and outboard Main Steam Isolation Valves (MSIV) [ISV] to determine leakage. The LLRT testing found that the MSL B leakage was unable to be measured due to a packing leak on the outboard MSIV.
The Technical Specification (TS) Surveillance Requirement (SR) 3.6.1.3.10 states in part, "Verify leakage rate through each main steam line is less than or equal to 100 scfh and the total leakage rate through all four main steam lines is less than or equal to 250 scfh."
The TS SR was not met following the LLRT and the outboard MSIV B packing was replaced, in order to be able to quantify the inboard MSIV leakage. Reperformance of the LLRT, following the packing replacement, showed that the combined MSL B leakage was at 158.96 scfh, with the overall leakage for all main steam lines at 304.3 scfh. The outboard MSIV B leakage was now 2.8 scfh, with the as-found inboard MSIV leakage at 156.2 scfh.
The inboard and outboard MSIV B valves were reworked during the refueling outage after the two initial LLRT tests. The inboard MSIV was reworked due to excess seat leakage, and the outboard MSIV was reworked due to the gouges on the stem, which likely damaged the packing. Final performance of the LLRT testing, following rework, showed MSL B leakage at 4. O scfh and the total leakage of all Main Steam Lines at 153.4 scfh, which is within the TS SR 3.6.1.3.10 criteria.
CAUSES OF EVENT The direct cause of the inboard MSIV B leakage was valve seating surface wear/degradation over the previous operating cycle. The plausible cause of the outboard MSIV B leakage from the packing gland was attributed to stem misalignment during the work on the valve in 2021 (1R18). This misalignment caused gouges on the stem and ultimately the packing gland leakage.
EVENT ANALYSIS
Engineering calculation 3.2.15.22 was performed to determine the past operability of the four Main Steam Lines. The calculation results are based on the as-found leakage values for all four MSIV inboard valves and for MSIV outboard valves A, C, and D (B leakage was unable to be quantified). The model scenario is a Loss of Coolant Accident (LOCA) on Main Steam Line B and all of the four Main Steam Shutoff Motor Operated Valves [SHV] failing open. This is the worst case MSL.
The result of the engineering calculation is that the dose consequences of the postulated accident scenario are above the limits of the Updated Safety Analysis Report (USAR). The USAR limits in Table 15.6-15 are 21.32 rem for the Exclusion Area Boundary (EAB), 9.56 rem for the Low Population Zone (LPZ), and 3.01 rem for the Control Room. The calculated dose rates are 44.29 rem, 9.56 rem, and 4.03 rem respectively. The EAB result of 44.29 rem is also above the 10 CFR 50.67 Regulatory Limit of 25 rem at the EAB. The calculation does not support past Operability of the four Main Steam Lines.
- 2. DOCKET NUMBER i----....,.--3._L_E_R_N_U,..M_BE_R ____
t YEAR 00440 2023 SEQUENTIAL NUMBER 002 REV NO.
00 In April 2021, the results of the as-left LLRT testing, during the 1 R18 refueling outage, show the MSL B leakage results being 96.9 scfh against the TS SR limit of 100 scfh. The total leakage of all four Main Steam Lines was 193.8 scfh against the TS SR limit of 250 scfh.
Condition Report 2022-08499 documented a rated-pressure walkdown of the outboard MSIVs during a unit forced outage shutdown in November of 2022, which identified a packing gland leak on outboard MSIV B with wetting and minor evidence of spray on the bottom of the valve flange. No steam plume was identified.
Based upon the preliminary cause and history, there is firm evidence that the condition existed during the last operating cycle for longer than allowed by TS SR 3.6.1.3.10. The condition is being reported in accordance with 1 O CFR
- 50. 73(a)(2)(i)(B) as a condition prohibited by Technical Specifications. The condition is also being reported under 1 O CFR 50.73(a)(2)(ii)(B) as an unanalyzed condition and under 10 CFR 50.73(a)(2)(v)(C) as a condition that could have prevented the fulfillment of a safety function of structures or systems needed to control the release of radioactive material.
A Probabilistic Risk Assessment (PRA) evaluation was performed for the March 2023 MSL B Outboard MSIV event, assuming a full 1-year unavailability and using the full power PRA model. Fire and other external hazards were qualitatively addressed to be of low risk. The analysis of this event results in delta Core Damage Frequency (CDF) and delta Large Early Relief Frequency (LERF) values that are below the acceptable thresholds of 1.0E-06/yr and 1.0E-07/yr, as discussed in Regulatory Guide 1.17 4. Sensitivities performed that added the postulated unavailability of the Inboard MSIV for the same 1-year period did not change these conclusions. The risk of this event is therefore considered to be of very low safety significance in accordance with the Regulatory Guidance.
CORRECTIVE ACTION
MSIV B inboard and outboard valves were reworked during the refueling outage. The as-left LLRT leakage results are 4.0 scfh for MSL B, and 153.4 scfh for all four Main Steam Lines, which are within the TS SR limits. The valve stem and packing on the MSIV B outboard valve have been replaced, and the disc and seat were machined on the MSIV B inboard valve.
PREVIOUS SIMILAR EVENTS
There have been no Licensee Event Reports in the past three years related to the Main Steam System. Page 3 of 3