NL-26-0051, Request for Revision to Approved Relief and Alternative Requirements for Squib (Explosively Actuated) Valves First Test Interval (V34-IST-ALT-04)
| ML26044A119 | |
| Person / Time | |
|---|---|
| Site: | Vogtle  |
| Issue date: | 02/13/2026 |
| From: | Coleman J Southern Nuclear Operating Co |
| To: | Office of Nuclear Reactor Regulation, Document Control Desk |
| References | |
| NL-26-0051 | |
| Download: ML26044A119 (0) | |
Text
3535 Colonnade Parkway Birmingham, AL 35243 205.992.5000 Regulatory Affairs February 13, 2026 Docket Nos.52-025 NL-26-0051 52-026 10 CFR 50.55a U. S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, D. C. 20555-0001 Southern Nuclear Operating Company Vogtle Electric Generating Plant Units 3 & 4 Request for Revision to Approved Relief and Alternative Requirements for Squib (Explosively Actuated) Valves First Test Interval (V34-IST-ALT-04)
On July 19, 2024, the Nuclear Regulatory Commission (NRC) approved a Southern Nuclear Operating Company (SNC) Request for Relief and Alternative Requirements to allow for no testing or replacement of the squib valve pyrotechnic charges or its associated electrical circuitry, and no disassembly for internal examination during the first refueling outages for Vogtle Electric Generating Plant (VEGP), Units 3 and 4 (ML24191A456). During preparation for the upcoming second refueling outage for VEGP Unit 3, SNC determined that some changes (that continue to meet the Code requirements) would be beneficial to the outage schedule.
Specifically, the proposed relief and alternative requirements of May 7, 2024 (ML24128A245) identified that the valves chosen for testing and replacement of the squib valve pyrotechnic charges and its associated electrical circuitry would include all twelve of the units squib valves during the second refueling outage. After further investigation, this proposal to test the squib charge of all twelve valves was unnecessary to meet the ASME OM Code requirements for the first two refueling outages and requests to reduce the proposed second refueling outage testing and replacement to only six of the squib valve charges. The valves chosen for squib charge testing would be the same valves for which operational readiness of the actuation logic and associated electrical circuits would be verified. Following the second refueling outage of each unit, testing and replacement of three of the squib valve charges will continue to meet the ASME OM Code.
The proposed relief and alternative requirements of May 7, 2024 (ML24128A245) also identified specific valves chosen for disassembly and inspection. SNC now proposes that specific identification of the valves chosen for disassembly and inspection was unnecessary to meet the ASME OM Code requirements and requests to disassemble and inspect the equivalent number of valves but without specifying the specific valves.
The revised relief and alternative requirements are provided in the Enclosure.
U. S. Nuclear Regulatory Commission NL-26-0051 Page 2 SNC requests the NRC authorize this proposed relief by April 1, 2026, which is prior to the upcoming second refueling outage for VEGP Unit 3.
This letter contains no regulatory commitments. This letter has been reviewed and confirmed to contain no security-related information.
If you have any questions, please contact Mr. Ryan Joyce at (205) 992-6468.
Respectfully submitted, Jamie M. Coleman Director, Regulatory Affairs Southern Nuclear Operating Company
Enclosure:
Request for Revision to Approved Relief and Alternative Requirements for Squib (Explosively Actuated) Valves First Test Interval (V34-IST-ALT-04) cc:
NRC Regional Administrator, Region ll NRR Project Manager - Vogtle 3&4 Senior Resident Inspector - Vogtle 3&4 Document Services RTYPE: VND.LI.L00 File AR.01.02.06 Digitally signed by JAMIEMCO Date: 2026.02.13 09:32:05
-06'00'
Southern Nuclear Operating Company NL-26-0051 Enclosure Vogtle Electric Generating Plant (VEGP) Unit 3 and Unit 4 Request for Revision to Approved Relief and Alternative Requirements for Squib (Explosively Actuated) Valves First Test Interval (V34-IST-ALT-04)
Enclosure to NL-26-0051 Request for Revision to Approved Relief and Alternative Requirements for Squib (Explosively Actuated) Valves First Test Interval (V34-IST-ALT-04)
E-2 Plant Site-Unit:
Vogtle Electric Generating Plant (VEGP) - Unit 3 and Unit 4 Interval-Interval Dates:
Applies to the initial inservice test (IST) interval for Units 3 and 4 beginning April 1, 2023, and ending March 30, 2033 Requested Date for Approval:
Authorization is requested by April 1, 2026 ASME Code Components Affected:
3/4-PXS-V123A and B - In-Containment Refueling Water Storage Tank (IRWST) Injection Isolation Valves 3/4-PXS-V125A and B - IRWST Injection Isolation Valves 3/4-PXS-V118A and B - Containment Recirculation Sumps to Reactor Coolant System (RCS) Actuation Squib Valves 3/4-PXS-V120A and B - Containment Recirculation Sumps to RCS Actuation Squib Valves 3/4-RCS-V004A, B, C and D - Automatic Depressurization System (ADS) Stage 4 Valves Applicable Code Edition and Addenda:
ASME Operation and Maintenance of Nuclear Power Plants (OM)
Code, 2012 Edition for 1st Inservice Test Interval (Ref. 1)
Applicable Code Requirements:
OM Code ISTC-5260(c), "Explosively Actuated Valves," states: At least 20% of the charges in explosively actuated valves shall be fired and replaced at least once every 2 years.
OM Code ISTC-5260(e)(2), states: At least once every 2 yr, one valve of each size shall be disassembled for internal examination of the valve and actuator.
(a) This examination will verify the operational readiness of the valve assembly by evaluating the internal components for their operational functionality, ensuring the integrity of individual components, and removing any foreign material, fluid, or corrosion in accordance with the Owner's examination procedures.
(b) All valves shall be disassembled for internal examination at least once every 10 yr.
Enclosure to NL-26-0051 Request for Revision to Approved Relief and Alternative Requirements for Squib (Explosively Actuated) Valves First Test Interval (V34-IST-ALT-04)
E-3 OM Code ISTC-5260(e)(3), states: For the valves selected in the test sample for subpara. ISTC-5260(c), the operational readiness of the actuation logic and associated electrical circuits must be verified for each sampled valve following removal of its charge.
This verification must include confirmation that sufficient electrical parameters (voltage, current, resistance) are available for each actuation circuit.
OM Code ISTC-5260(e)(4), states: For the valves selected in the test sample for subparagraph ISTC-5260(c), the sampling must select at least one explosively actuated valve from each redundant safety train every 2 yr. Each sampled pyrotechnic charge shall be tested in the valve or a qualified test fixture to confirm the capability of the charge to provide the necessary motive force to operate the valve to perform its intended function without damage to the valve body or connected piping.
Reason for Request:
Prior to the first refueling outage for Vogtle Units 3 and 4 (3/4R01),
replacement charges were unavailable for testing of the identified squib valves.
On July 19, 2024, the Nuclear Regulatory Commission (NRC) approved a Southern Nuclear Operating Company (SNC) Request for Relief and Alternative Requirements to allow for no testing or replacement of the squib valve pyrotechnic charges or its associated electrical circuitry, and no disassembly for internal examination during the first refueling outages for Vogtle Electric Generating Plant (VEGP), Units 3 and 4 (ML24191A456) (Ref. 5).
During preparation for the upcoming second refueling outage (3/4R02) for VEGP Unit 3, SNC identified that identification of the specific valves selected for disassembly in the request for relief V34-IST-ALT-03 and subsequent revisions created excessive burden to the site to execute due to physical limitations and coordination. This relief request revision eliminates the specificity of valve selection for disassembly.
Additionally, it was identified during a design review that the previously specified selection scheme of explosively actuated valve cartridges to be removed and test fired is overly conservative to meet ASME OM code requirements based on redundant flow paths within a single safety train. This relief request revision aligns site IST requirements to the AP1000 specific design.
Enclosure to NL-26-0051 Request for Revision to Approved Relief and Alternative Requirements for Squib (Explosively Actuated) Valves First Test Interval (V34-IST-ALT-04)
E-4 Proposed Alternative and Basis for Use:
Proposed Alternative:
SNC proposes modifying the existing relief request (Ref. 4) to meet the following:
- Disassembly inspections were not performed during the first outage for each unit. Disassembly inspections conducted in each units second outage will be increased to two of each size as previously approved. Selection choices will be modified by site as necessary. Following the second outage, disassembly inspections will revert to one valve of each size per 2yr to meet code requirements.
- Due to supplier limitations, pyrotechnic charge testing was not completed in the first outage for each unit. SNC will increase the number of charges tested in the second outage, to catch up to cumulative total sample requirements for that timeframe.
Following the second outage, pyrotechnic charge testing will be resumed at the sample requirements specified per the ASME OM Code.
Based on the AP1000 design with 4 redundant flow paths for each function, the application of code requirements to test at least one explosively actuated valve from each redundant safety train will result in a normal test plan of 3 total charges tested each outage, which meets the code minimum of 20%. The sampling will be made up of a selection of at least one explosively actuated valve from each of the following safety functions:
- 1. Stage 4 ADS (RCS-V004A/B/C/D)
- 2. IRWST Injection (PXS-V123A/B and PXS-V125A/B)
- 3. Containment Recirculation (PXS-V118A/B and PXS-V120A/B)
This will result in 6 cartridges being tested during the second outage (50% of total population) for each unit.
All other code requirements will be met for testing based on the selections specified above.
Enclosure to NL-26-0051 Request for Revision to Approved Relief and Alternative Requirements for Squib (Explosively Actuated) Valves First Test Interval (V34-IST-ALT-04)
E-5 Basis for Use:
SQUIB CHARGE FIRING The basis is SNCs application of the following requirements.
ISTC-5260(c), Explosively Actuated Valves, states (emphasis added): "At least 20% of the charges in explosively actuated valves shall be fired and replaced at least once every 2 yr
[years]. If a charge fails to fire, all charges with the same batch number shall be removed, discarded, and replaced with charges from a different batch."
ISTC-5260(e)(4) states (emphasis added): "For the valves selected in the test sample for subparagraph ISTC-5260(c), the sampling must select at least one explosively actuated valve from each redundant safety train every 2 yr. Each sampled pyrotechnic charge shall be tested in the valve or a qualified test fixture to confirm the capability of the charge to provide the necessary motive force to operate the valve to perform its intended function without damage to the valve body or connected piping."
In particular, SNC has reconsidered how to apply the definition of each redundant safety train.
The previously approved alternative request (Ref. 4) was based on an understanding of redundant safety trains which identified each valve pair as a redundant safety train, i.e., each of the valve pairs identified below were considered as a redundant safety train for the identified system purpose. These purposes are consistent with those identified in Updated Final Safety Analysis Report (UFSAR) Table 6.3-1.
Code OM Component Number System (Purpose) Class Cat. Size 3/4-RCS-V004A & B ADS (Depressurization) 1 D 14" 3/4-RCS-V004C & D ADS (Depressurization) 1 D 14" 3/4-PXS-V123A & B PXS (Injection) 1 D 8"
3/4-PXS-V125A & B PXS (Injection) 1 D 8"
3/4-PXS-V118A & B PXS (Recirculation) 3 D 8"
3/4-PXS-V120A & B PXS (Recirculation) 3 D 8"
Using this understanding, the requirement to test one valve from each redundant safety train would mean testing one of each pair each refueling outage. With the approval for no testing in the first
Enclosure to NL-26-0051 Request for Revision to Approved Relief and Alternative Requirements for Squib (Explosively Actuated) Valves First Test Interval (V34-IST-ALT-04)
E-6 refueling outage, this meant testing both valves of each pair in the second refueling outage.
However, UFSAR Figure 5.1-5 (Sheet 1) and Figure 6.3-1 (Sheet 2) shows each of these valves in a different flow path, i.e.,
each valve represents a separate capability to achieve the safety function. Thus, SNC now considers that redundant safety trains should instead be based on the totality of valves in separate flow paths performing redundant capabilities to meet the system purpose. As noted above, each system purpose actually has four valves, e.g., four redundant valves for the RCS depressurization purpose, four redundant valves for the PXS injection purpose, and four redundant valves for the PXS recirculation purpose. With this understanding of four redundant valves comprising one safety train for each purpose, the requirement would be met by testing only one of the four valves (25%) for each system purpose each refueling outage. Thus, with the approval for no testing in the first refueling outage, SNC will test two of the four valves (50%) of each purpose in the second refueling outage, i.e., six valves rather than all twelve, consistent with the OM Code requirements.
OM Code language was written based on the fully-redundant, multiple-train safeguards concept used in Generation II PWRs, where a credible, postulated single failure can fail an entire active ECCS train (such as due to the loss of one emergency diesel generator).
The AP1000 safeguards systems design success basis is for any single failure in any one flow path of one safeguards system purpose, while the remaining flow paths for the safeguards system purpose function properly.
On this basis, SNC requests approval of a revision to the alternative requirements previously granted such that only six of the above valves are tested during the second refueling outage of each unit.
The same valves that are chosen for testing of the charges will also be selected for verification of the actuation logic and associated electrical circuits pursuant to ISTC-5260(e)(3).
Following the second refueling outage of each unit, VEGP Units 3 and 4 will revert to one valve of each function every 2 years, i.e.,
one of the four valves (25%) for each system purpose each refueling outage.
Enclosure to NL-26-0051 Request for Revision to Approved Relief and Alternative Requirements for Squib (Explosively Actuated) Valves First Test Interval (V34-IST-ALT-04)
E-7 DISASSEMBLY For the disassembly inspections, specifically, the previously approved alternative requirements included specific identification of particular valves chosen for disassembly and inspection pursuant to ISTC-5260(e)(2) during the second refueling outage, i.e., RCS-PL-V004A, RCS-PL-V004B, PXS-PL-V123A, and PXS-PL-V125B. SNC is now planning to disassemble and inspect different valves during the second refueling outage, for example, RCS-PL-V004D, RCS-PL-V004B, PXS-PL-V123A, and PXS-PL-V125A. These valves will continue to meet the requirements of Title 10, Code of Federal Regulations (10 CFR) Section 50.55a(f) and the American Society of Mechanical Engineers (ASME) Code for Operation and Maintenance of Nuclear Power Plants (OM Code) paragraph ISTC-5260(e)(2) and the additional inspections identified in the alternative request. Following each units second refueling outage, VEGP will return to compliance with the 10 CFR 50.55a(f) paragraph ISTC-5260(e)(2) requirements and the OM Code.
GENERAL The qualified inservice life for the squib charges is eight (8) years.
The Code requires a minimum of 20% of the charges in explosively actuated valves to be tested at each refueling outage, and only one valve of each size to be disassembled for internal examination, and thus acknowledges a service life of several cycles.
Through performance of the specified inspections and testing during the second refueling outage, cumulative sampling requirements are caught up to code requirements following the outage.
In implementation of this relief request, all other applicable code requirements will be maintained, including but not limited to:
records to ensure that service life is not exceeded and will not be exceeded (ISTC-5260(a) and (b)), replacement charges from batches which have had a sample charge tested satisfactorily (ISTC-5260), and visual inspections of each valve every two years (ISTC-5260(e)(1)). Additionally, in line with normal work preparation practices, compliance with other applicable license and Technical Specification requirements will be met.
Through performance of the inspections and testing specified above to meet ASME OM Code during the second refueling outage, combined with catch up performance from items deferred
Enclosure to NL-26-0051 Request for Revision to Approved Relief and Alternative Requirements for Squib (Explosively Actuated) Valves First Test Interval (V34-IST-ALT-04)
E-8 during each units first refueling outage, an acceptable level of safety and quality is proposed.
Thus, the alternative request satisfies the provisions of 10 CFR 50.55a(z)(1).
Duration of Proposed Alternative:
Initial reactor criticality through the end of the second two year period for Units 3 and 4.
Precedent:
Operating Experience searches were performed on the INPO website and in the NRC ADAMS database using terms such as squib and explosively actuated, instances of charges failed to fire during testing were noted, mostly in the 1970s, 1980s and 1990s, the number of test firing failures has dropped dramatically over the past decade and there was no reporting of situations involving the internal visual inspection for explosively actuated valves.
References:
- 2. Vogtle Units 3 and 4 Inservice Testing Program Plan
[ML22102A114]
- 3. Vogtle Units 3 and 4 Updated Final Safety Analysis Report Subsection 6.3.2.2.8.9, Explosively Opening (Squib) Valves
[ML23165A215]
- 4. Revised Request for Relief and Alternative Requirements for Squib Valves First Test Interval, V3/4-IST-ALT-03-R1, dated May 7, 2024 (ML24128A245)
- 5. NRC approval of SNC Revised Request for Relief and Alternative Requirements for Squib Valves First Test Interval, V3/4-IST-ALT-03-R1, dated July 19, 2024 (ML24191A456)
Status:
Awaiting NRC authorization