L-25-024, 10 CFR 50.55a Request BV-ISI-2025-01, Quench Spray Pinhole Leak
| ML25017A395 | |
| Person / Time | |
|---|---|
| Site: | Beaver Valley |
| Issue date: | 01/17/2025 |
| From: | Blair B Vistra Operations Company |
| To: | Office of Nuclear Reactor Regulation, Document Control Desk |
| References | |
| L-25-024 | |
| Download: ML25017A395 (1) | |
Text
Beaver Valley Power Station Barry N. Blair Site Vice President P.O. Box 4 200 State Route 3016 Shippingport, PA 15077 724-682-5234 L-25-024 January 17, 2025 10 CFR 50.55a ATTN: Document Control Desk U.S. Nuclear Regulatory Commission Washington, DC 20555-0001
Subject:
Beaver Valley Power Station, Unit No. 1 Docket No. 50-334, License No. DPR-66 10 CFR 50.55a Request BV-ISI-2025-01, Quench Spray Pinhole Leak Pursuant to 10 CFR 50.55a(z)(2), Vistra Operations Company LLC (VistraOps) hereby requests Nuclear Regulatory Commission (NRC) approval of the attached relief request for the Beaver Valley Power Station, Unit No. 1 (BVPS-1).
Approval is requested for deferral of a code repair of a through-wall leak in the BVPS-1 quench spray (QS) system. A through wall weld flaw has been identified in the fillet weld of a coupling connecting sections of piping together. The flaw is in a section of piping that would present a hardship without commensurate increase in safety to implement code repair within the time period permitted by the applicable Technical Specifications (TS)
Limiting Condition for Operation (LCO).
In accordance with Generic Letter (GL) 90-05, code repair of the identified flaw at this time is not practical since a plant shutdown would be required. Evaluation of the flaw in accordance with the fracture mechanics methodology provided in GL 90-05 has determined that the structural integrity of the QS piping is maintained.
Therefore, VistraOps requests NRC approval to defer implementation of code repairs to no later than the next scheduled refueling outage, as permitted by GL 90-05.
The attached relief request addresses the present condition of the weld and implementation of the compensatory actions taken per GL 90-05. Operability and functionality of the system have been maintained and VistraOps has concluded that deferring repair of the flaw will not affect the health and safety of the public. Since compliance with the specified Code requirements would result in unnecessary hardship without a compensating increase in the level of quality and safety, VistraOps requests verbal approval of this relief request, pursuant to 10 CFR 50.55a(z)(2), by January 18, 2025 to be within the time period permitted by TS.
Beaver Valley Power Station, Unit No. 1 L-25-024 Page 2 There are no regulatory commitments contained in this submittal. If there are any questions, or if additional information is required, please contact Jack Hicks, Senior Manager, Licensing, at (254) 897-6725 or jack.hicks@luminant.com.
Sincerely, Barry N. Blair Attachments:
- 1. 10 CFR 50.55a Request Number: BV-ISI-2025-01
- 2. Generic Letter 90-05 Flaw Evaluation cc: NRC Region I Administrator NRC Resident Inspector NRC Project Manager Director BRP/DEP Site BRP/DEP Representative
L-25-024 10 CFR 50.55a Request Number: BV-ISI-2025-01 Page 1 of 6 Proposed Alternative In Accordance with 10 CFR 50.55a(z)(2)
-- Hardship or Unusual Difficulty without Compensating Increase in Level of Quality and Safety --
- 1. ASME Code Component(s) Affected Component:
Quench Spray (QS) System piping line 12-QS-1-153B-Q3 System:
QS Code Class:
3 (Pipeline is classified as Q3, which is equivalent to ASME III Class 3 as described in the Beaver Valley Power Station, Unit No. 1 (BVPS-1) Updated Final Safety Analysis Report (UFSAR))
==
Description:==
Defect is located at a fillet weld connecting a pipe coupling and a section of pipe in pipeline QS-1 Size:
12 inch, Schedule 10S Nominal Outside Diameter:
12.75 inches Nominal Wall Thickness:
0.180 inches Pipe Material:
A358 TP304 CL1 Design Temperature:
140°F Design Pressure:
30 pounds per square inch gauge (psig)
2. Applicable Code Edition and Addenda
The fifth inspection interval for BVPS-1 began on August 29, 2018 and is scheduled to end August 28, 2028. The American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code (ASME Code),Section XI, 2013 Edition with no Addenda is the code of record for inservice inspection and repair/replacement programs for this inspection interval.
The QS piping line was designed to American National Standards Institute (ANSI) B31.1 1967, including 1971 addenda with supplemental requirements as necessary for use in nuclear applications described in the BVPS-1 UFSAR.
3. Applicable Code Requirement
ASME Section XI, 2013, Article IWA-4421, General Requirements, requires that defects be removed or mitigated in accordance with code requirements IWA-4340, IWA-4411, L-25-024 Page 2 of 6 IWA-4461, or IWA-4462 (Note: Use of IWA-4340 is prohibited by 10 CFR 50.55a(b)(2)(xxv)(A).).
4. Reason for Request
On January 16, 2025, a minor leak (flaw) was identified in the QS piping line 12-QS-1-153B-Q3 during non-destructive examination (NDE) activities unassociated with the weld, due to weepage coming from the toe of the weld.
The piping that contains this flaw is two sections of piping welded together with use of a coupling between the refueling water storage tank (RWST) and the A train QS pump.
The flaw is in the toe of the welded joint at the 12 inch socket and appears to be at the stop-start interface of the socket weld. A drawing of the flaw location and photographs of the flaw are shown in Figures 1 and 2 of this request.
Figure 1: Drawing of the Flaw Location L-25-024 Page 3 of 6 Figure 2: Photographs of the Flaw ASME Code,Section XI, 2013 Edition, requires a code repair. The QS system is designed to cool and depressurize containment following a design basis accident (DBA). This is a reactor safeguard system and has an associated Technical Specification (TS), TS 3.6.6. This TS requires two independent trains of QS to meet the limiting condition of operation. With one train removed from service for repair, the inoperable train would need to be restored within 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> or the plant would have to be in hot standby in the following 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br />.
Isolation of the affected line is not practical given the location of the line relative to the only drain location on the header. Repair will require removing the affected train of QS from service for the repair duration. Consideration was given to performing a flaw evaluation per Code Case N-513-4, however, this code case excludes evaluating flaws in socket welds. Generic Letter (GL) 90-05, Guidance for Performing Temporary Non-Code Repair of ASME Code Class 1, 2, and 3 Piping, contains a through-wall flaw evaluation in Enclosure 1, which may be used to assess the structural integrity of Class 3 piping and does not exclude socket welds.
An accurate measurement of the pinhole diameter could not be obtained since the size of the pinhole leak is small enough that it cannot be accurately measured. The area of the leak was observed weeping with no measurable drops of water. The flaw is a small defect that most likely extends in the radial direction from the pipe to outer edge of the coupling (from where there is stagnant water between the outer diameter of the pipe and the inside diameter of the fitting). Ultrasonic testing (UT) measurements taken adjacent to the weld indicate nominal pipe/fitting thickness with a maximum thickness of 0.248 inches and a minimum thickness of 0.172 inches. Therefore, it is concluded that there is no general wall thinning and the flaw does not extend into the base metal.
The flaw appears to be at the stop-start interface of the socket weld and is likely the result of a lack of fusion or other defect at this location following installation. The result would be a small crevice created between the inner diameter and outer diameter of the weld and fitting interface, which would permit stagnant water between the outer L-25-024 Page 4 of 6 diameter of the pipe and the inside diameter of the fitting. This defect could be a result of impurities, work practices or workmanship. The low design pressure and temperature of the pipe, along with low induced mechanical stress, precludes the pipe from primary water stress corrosion cracking (PWSCC). Additionally, the flaw was not a result of vibration as the QS system is mostly in a static environment (not in service) with little changes when in operation, i.e., little to no vibration occurring. There was no vibration detected on line 12-QS-1-153B-Q3 during a field walkdown with the system not in service. Finally, transgranular stress corrosion cracking (TGSCC) is not a likely failure mode because the line is typically insulated and is subjected to little exposure to outside contaminants that could result from poor house-keeping practices. This is considered an isolated incident, with no programmatic or widespread deficiencies currently identified.
GL 90-05 states, The staff has determined that an ASME Code repair is required for code Class 1, 2 and 3 piping unless specific written relief has been granted by the NRC.
However, the staff has determined that temporary non-code repair of Class 3 piping that cannot be isolated without a plant shutdown is justified in some instances. Guidance in GL 90-05 Enclosure 1 for assessing the acceptability of relief, based on the structural integrity of the flaw along with factors such as potential flooding, water spraying on equipment, and loss of flow for design loading conditions. Based on the difficulty of isolating the affected area of QS piping and performing a code repair within the time period permitted by the limiting condition of operability, relief is being requested from ASME Code, Section Xl, 2013 Edition, Article IWA-4421, in accordance with 10 CFR 50.55a(z)(2) to prevent an unnecessary hardship caused by requiring a unit shutdown without a compensating increase in quality and safety.
5. Proposed Alternative and Basis for Use
Vistra Operations Company LLC (VistraOps) proposes the following alternative.
As an alternative to the code repair required by IWA-4421, VistraOps is proposing the following strategy to address the identified flaw. VistraOps proposes to defer the code repair of the identified flaw until the next planned outage of sufficient duration, but no later than the next refueling outage, currently scheduled to begin in October 2025.
During the interim period, VistraOps intends to implement augmented inspections on a 30-day frequency, not to exceed the 3-month frequency required by GL 90-05, to detect changes in the condition of the identified defect. This testing will use suitable nondestructive examination methods, including UT. Additionally, VistraOps intends to perform a daily qualitative assessment of leakage, not to exceed the weekly requirement by GL 90-05, to determine if there is additional degradation of structural integrity.
Basis for Request Complying with IWA-4421 requirements to remove defective portions of this piping prior to performing a repair/replacement activity represents a hardship or unusual difficulty without a compensating increase in the level of quality and safety for the following reasons:
L-25-024 Page 5 of 6 Rendering the A train of the QS inoperable for the repair of the flaw is a 72-hour shutdown condition per limiting condition of operation (LCO) 3.6.6. In addition, the recirculation spray system is a supported system by QS, which also makes the A train of recirculation spray inoperable and results in entry into a 72-hour shutdown condition per LCO 3.6.7. Both action statements require Mode 5 entry upon failure to meet the LCO completion time.
Removal of defective portions of this piping would require that the piping be isolated and depressurized. Based upon the piping design only one vent or drain valve on the system exists between the clearance boundaries. This vent valve would need to be dismantled and a hose connected to a pump would be utilized to drain the system as the valve is not at the low point in the system. Once the valve is dismantled, any leak-by through the upstream valve, 1QS-1 would drain the RWST until the valve could be reassembled, or the line sufficiently capped.
The current loss of flow from the QS system is negligible compared to the total system volume. The leak rate is weeping with no measurable drip rate at normal standby pressure. The allowable leak for the piping is 75 gallons per minute (gpm),
which is bounded by the allowable flaw size of 0.158 inches.
Currently, there is no water spray from the pinhole leak. There is no equipment in the area that would be damaged due to spray from the leak, should spray develop.
The leakage present does not present any flooding concerns in the area.
Augmented UT will be completed per GL 90-05 on five additional accessible locations deemed most susceptible to a similar flaw.
GL 90-05 "through-wall" flaw evaluation criteria was used to assess the structural integrity of the pipe with the flaw. This evaluation determined that flaw length did not exceed either 3 inches or 15 percent of the length of the pipe circumference, with a total flaw length allowed calculated to be 0.158 inches. Total flaw length in the socket weld was conservatively assumed to be 0.125 inches. The current stress intensity factor is below allowable limits. Therefore, the piping associated with 12-QS-1-153B-Q3, including the socket weld, is structurally adequate in accordance with GL 90-05 to accept as-is until the next repair opportunity. Currently, the flaw is stable and shows no signs of growth or propagation.
Based on the structural integrity evaluation, the low risk of impact to nearby components, and the monitoring, VistraOps believes deferring the repair to the next refueling outage is acceptable.
6. Duration of Proposed Alternative
Repair of the defect will be deferred until the next scheduled outage exceeding 30 days, but no later than the next refueling outage scheduled to begin in October 2025, provided L-25-024 Page 6 of 6 the condition continues to meet the acceptance criteria of GL 90-05. VistraOps personnel are currently monitoring the leak location.
- 7. Precedent
- 1. Shearon Harris Nuclear Power Plant, Unit 1, Relief Request RA-20-0312, November 4, 2020, Agencywide Documents Access and Management System (ADAMS) Accession Number ML20309A774
- 2. Shearon Harris Nuclear Power Plant, Unit 1, Relief Request I3R-06, April 21, 2011, ADAMS Accession Number ML110060442
- 3. Millstone Power Station, Unit 3, Relief Request IR-4-03, July 16, 2020, ADAMS Accession Number ML20189A206
- 8. References
- 1. Beaver Valley NDE Report BOP-UT-25-004
- 2. BVPS-1 Drawing 8700-06.024-0102, Sheet 1, Yard Piping West Reactor Containment
- 3. VistraOps Condition Report CR-2025-00331
- 4. Beaver Valley Design Basis Document, 1DBD-13, Revision 18, Design Basis Document for Containment Depressurization System
- 5. Generic Letter 90-05, Guidance for Performing Non-Code Repair of ASME Code Class 1, 2, and 3 Piping, dated June 15, 1990
L-25-024 Generic Letter 90-05 Flaw Evaluation Page 1 of 3
NP(B)-00228-X-001: Min-Wall Thickness Evaluation 12"-QS-1-153B-Q3 at Node 40 Run of Record: Rev. 1 Vendor document 2706.009-000-002 from Structural Integrity Associates provides code reconciliation for Unit 1 & 2 RW / SWS A106 Gr. B piping allowable stress.
The Lesser of 0.7Su or 2.4 Sm may be used for past operability determinations per NRC IM-0326 and Section III Appendix F Piping Information:
For A358, TP304 CL 1,
Sh 17870 psi Design Pressure,
P 30 psi Manufacturer's Tolerance,
Mt 1.143 Outside Diameter,
D 12.75 in Inside Diameter,
ID 12.39 in EQ. B.2-4:
DMFsustained
=
Sh Mt 1016 psi 20.10 Nominal Pipe Thickness,
tnom 0.180 in EPRI, 20% Nominal Thickness,
t20
tnom 0.20 EQ. B.2-5:
DMFocc.n.u
=
Sh 1.2 Mt 1751 psi 14.00 Joint Efficiency Factor,
E 1.0 Additional Thickness,
Atk 0.0 in EQ. B.2-7:
DMFthermal
=
Sh 2.5 1016 psiMt 1364 psi 36.59 Thermal-Pressure Factor,
y 0.40 EQ. B.2-6:
DMFocc.f
=
Sh 1.8 Mt 2486 psi 14.79 Code Min-Wall Evaluation:
tmin.code
=
+
P D 2
+
Sh E
P y Atk 0.011 in Mechanical Loading Evaluation:
Design Margin Factor,
DMFmin
=
min DMFsustained DMFocc.n.u DMFthermal DMFocc.f 14.00
Znom
=
0.0982
D4 ID4 D
22.032 in3 Set
Zmin
=
Znom DMFmin 1.574 in3 therefore, Zmin can be defined as
0.0982 D4 d4 D
solving for d,
d
=
D4
Zmin D 0.0982
1 4
12.725 in
tmin.mechanical
=
D d
2 0.012 in Therefore,
tmin max tmin.mechanical tmin.code
=
tmin 0.012 in
GL 90-05 Through-wall Flaw Evaluation This approach assumes a through-wall flaw and evaluates the stability by a linear elastic fracture mechanics methodology. The code-required minimum wall thickness "t min" defined above will be replaced via the governing "t min" from mechanical stresses as the difference between the them is negligible. The maximum length of the portion of the flaw that extends beyond "t min", independent of orientation with respect to the pipe, is the through-wall flaw length "2a".
Use tm= 0.012" for through-wall flaw evaluation (conservative)
=
tmin 0.012 in Minimum value for equations: ND-3641-1, 8 & 9 The following through-wall flaw evaluation is per GL 90-05 Enclosure 1 Section C.3.a.
a
.079 in Half the length of the flaw diameter
R
=
D tmin 2
6.369 in Mean Radius
c
=
a
R 0.004
s 3.850 ksi Sum of stresses from Above ((1364+2486)/1000) Ref: GL90-05 "s" definition
r
=
R tmin 515.258
A
=
+
+
-3.26543 1.52784
R tmin
0.072698
R tmin
2 0.0016011
R tmin
3 200507.795
B
=
+
11.36322 3.91412
R tmin
0.18619
R tmin
2 0.004099
R tmin
3
-513301.523
C
=
+
+
-3.18609 3.84763
R tmin
0.18304
R tmin
2 0.00403
R tmin
3 504672.795
F
=
+
+
+
1
A c1.5
B c2.5
C c3.5 50.245 Allowable Stress Intensity Factor
Kact
=
1.4 s F ((
a))
0.5 134.919
ksi in0.5 Kact Ksi Ksi is defined as 135 ksi in^0.5 as defined in GL90-05
=
2 a 0.158 in Total Flaw Length allowed