ML21340A120
| ML21340A120 | |
| Person / Time | |
|---|---|
| Site: | Vogtle  |
| Issue date: | 12/06/2021 |
| From: | NRC/NRR/DNRL |
| To: | |
| References | |
| Download: ML21340A120 (7) | |
Text
From:
Santos, Cayetano Sent:
Monday, December 6, 2021 10:56 AM To:
Vogtle PEmails Cc:
Gleaves, Billy; Gonzalez, Carlos
Subject:
Draft ALT-02 for pre-submittal discussion Attachments:
ND-21-0000 IST-ALT-02 for PSM 20211216.pdf
Hearing Identifier:
Vogtle_COL_Docs_Public Email Number:
629 Mail Envelope Properties (MN2PR09MB5244414126FDDDEB11C8FB3EE56D9)
Subject:
Draft ALT-02 for pre-submittal discussion Sent Date:
12/6/2021 10:56:04 AM Received Date:
12/6/2021 10:56:06 AM From:
Santos, Cayetano Created By:
Cayetano.Santos@nrc.gov Recipients:
"Gleaves, Billy" <Bill.Gleaves@nrc.gov>
Tracking Status: None "Gonzalez, Carlos" <Carlos.Gonzalez@nrc.gov>
Tracking Status: None "Vogtle PEmails" <Vogtle.PEmails@usnrc.onmicrosoft.com>
Tracking Status: None Post Office:
MN2PR09MB5244.namprd09.prod.outlook.com Files Size Date & Time MESSAGE 3
12/6/2021 10:56:06 AM ND-21-0000 IST-ALT-02 for PSM 20211216.pdf 182221 Options Priority:
Normal Return Notification:
No Reply Requested:
No Sensitivity:
Normal Expiration Date:
ND-21-0000 Request for Alternative (VEGP 3&4-IST-ALT-02)
Page 2 of 4 Plant Site-Unit:
Vogtle Electric Generating Plant (VEGP) - Units 3 and 4 Interval-Interval Dates:
Applies to the initial inservice test (IST) interval for Units 3 and 4 Requested Date for Approval:
Authorization is requested by [6 months following submittal]
ASME Code Components Affected:
Specific alternative requested is applicable to Main Turbine System (MTS):
- Turbine stop valves: MTS-PL-V001A/B and MTS-PL-V003A/B, and
- Turbine control valves: MTS-PL-V002A/B and MTS-PL-V004A/B.
These are Class N, Active, Category B valves.
Applicable Code Edition and Addenda:
ASME Operation and Maintenance of Nuclear Power Plants (OM)
Code, 2012 Edition for 1st Inservice Test Interval Applicable Code Requirements:
Quarterly exercise (ISTC-3510), full stroke exercise (ISTC-3521(a)
Reason for Request:
10 CFR 50.55a(z) allows for alternatives to the requirements when the licensee can demonstrate that: 1) the proposed alternative would provide an acceptable level of quality and safety; or 2) compliance with the specified requirements of this section would result in hardship or unusual difficulty without a compensating increase in the level of quality and safety.
The proposed alternative test methodology and frequency provides an acceptable level of quality and safety, while reducing the risk of a unplanned turbine trip and associated potential challenges to safety systems.
DRAFT
ND-21-0000 Request for Alternative (VEGP 3&4-IST-ALT-02)
Page 3 of 4 Proposed Alternative and Basis for Use:
Proposed Alternative:
In lieu of the Code requirement for full-stroke testing of these valves on a quarterly frequency per ISTC-3510 and ISTC-3521(a), it is proposed to establish partial stroke testing on a semi-annual basis (six-month frequency per Code Case OMN-20).
Basis for Use:
The turbine stop and control valves close to perform the function of providing backup isolation in the event of a main steam line break (MSLB) with the single failure of a main steam isolation valve (MSIV) to mitigate the event, and to prevent the generation of turbine missiles in the event of a turbine overspeed condition. When Westinghouse was designing the AP1000, the stroking of these valves was assumed, as documented in the DCD, to be informed by industry initiatives to minimize the chances of an unanticipated turbine trip (turbine valve testing is the most common cause of unplanned reactor trips), while maintaining the probability of generating a turbine missile at an appropriately low probability (see UFSAR Subsection 10.2.3.6). This testing frequency (every six months) was input into the PRA which demonstrated an acceptable overall risk, including the use of these valves in their MSIV backup function. Additionally, the change from full-stroke to partial stroke exercising minimizes the required power reduction (to 90% for partial stroke testing vs. to 75% for full stroke testing) and associated secondary transient which also contributes to reducing the risk of a turbine trip event. The UFSAR discussion of the turbine maintenance and inspection program in Subsection 10.2.3.6 indicates:
Turbine valve testing is performed at six-month intervals. The semi-annual testing frequency is based on nuclear industry experience that turbine-related tests are the most common cause of plant trips at power. Plant trips at power may lead to challenges of the safety-related systems. Evaluations show that the probability of turbine missile generation with a semi-annual valve test is less than the evaluation criteria.
The Unit 3 Turbine Maintenance and Inspection Program (submitted on July 9, 2020) identifies this testing at six-month intervals as partial stroke testing.
The partial stroke testing on a six-month frequency, provides an acceptable level of quality and safety. As such, SNC proposes this alternative to the OM Code under 10 CFR 50.55a(z)(1).
DRAFT
ND-21-0000 Request for Alternative (VEGP 3&4-IST-ALT-02)
Page 4 of 4 Duration of Proposed Alternative:
Through the end of the first Vogtle Unit 3 & Unit 4 IST interval
References:
- 1. Vogtle Electric Generating Plant Units 3&4 INSERVICE TESTING PROGRAM PLAN - 1st INTERVAL (ADAMS Accession No.
ML########)
submitted to NRC on December ##, 2021
- 2. Vogtle Electric Generating Plant Units 3&4 TURBINE MAINTENANCE AND INSPECTION PROGRAM (ADAMS Accession No. ML20192A048) submitted to NRC on July 09, 2020
- 3. UFSAR Subsection 10.2.3.6, Maintenance and Inspection Program Plan (relative to turbine rotor integrity)
Status:
Awaiting NRC authorization DRAFT
ND-21-0000 Markup of Vogtle Unit 3 Inservice Testing Program Plan - 1st Interval Page 1 of 2 Revise the MTS stop and control valve stroke testing Frequencies as follows:
MTS Valve ID Description Class Aug Cat A/P Valve Size Valve Type Act.
Type Drawing
& Coord Normal Safety Fail-Safe Required Test Freq Code Dev.
Plan Notes SV3-MTS-PL-V001A Main Stop Valve #1 N
Y B
A 28 GL EH SV3-MTS-M6-002 F-6 O
C C
CSJ-MTS-1 Note X Note Z SV3-MTS-PL-V001B Main Stop Valve #3 N
Y B
A 28 GL EH SV3-MTS-M6-002 C-6 O
C C
CSJ-MTS-1 Note X Note Z SV3-MTS-PL-V002A Control Valve #1 N
Y B
A 28 GL EH SV3-MTS-M6-002 F-6 O
C C
CSJ-MTS-1 Note X Note Z SV3-MTS-PL-V002B Control Valve #3 N
Y B
A 28 GL EH SV3-MTS-M6-002 C-6 O
C C
CSJ-MTS-1 Note X Note Z SV3-MTS-PL-V003A Main Stop Valve #2 N
Y B
A 28 GL EH SV3-MTS-M6-002 E-6 O
C C
CSJ-MTS-1 Note X Note Z SV3-MTS-PL-V003B Main Stop Valve #4 N
Y B
A 28 GL EH SV3-MTS-M6-002 D-6 O
C C
CSJ-MTS-1 Note X Note Z SV3-MTS-PL-V004A Control Valve #2 N
Y B
A 10 GL AO SV3-MSS-M6-001 E-6 C
C C
CSJ-MTS-1 Note X Note Z SV3-MTS-PL-V004B Control Valve #4 N
Y B
A 10 GL AO SV3-MSS-M6-001 D-6 C
C C
CSJ-MTS-1 Note X Note Z
ND-21-0000 Request for Alternative (VEGP 3&4-IST-ALT-02)
Page 2 of 2 Unit 3 IST Program Plan markups shown - Unit 4 markups would show identical changes Select IST Program Plan Legend information (for reviewer information):
Class N - non-safety related Aug Y - Augmented scope (not required by ASME OM Code)
Cat. B - OM Code Category B Valve (see OM Code)
A/P A - Active valve Valve Type GL - Globe Valve Act. Type AO - Air Operated actuator Act. Type EH - Electro-Hydraulic Operated actuator Position O - Open Position C - Closed Required Test PI - Remote Position Indication Verification Required Test STC - Stroke Time Closed test Required Test FST - Fail-Safe Test Freq 2y - Two-year frequency Freq Q - Quarterly frequency Freq SA -Semi-Annually or six-month frequency (new - not previously used)
Freq CS - Cold shutdown frequency