ML21225A031
| ML21225A031 | |
| Person / Time | |
|---|---|
| Site: | Hatch  |
| Issue date: | 08/31/2021 |
| From: | Southern Nuclear Operating Co |
| To: | Office of Nuclear Reactor Regulation |
| Lamb J | |
| References | |
| Download: ML21225A031 (20) | |
Text
Hatch Pre-Submittal Meeting Request to Eliminate the Requirement for Automatic Main Steam Isolation on High Turbine Building Area Temperature August 2021
Meeting Purpose
- The purpose for this meeting is to discuss proposed license amendment request (LAR) to eliminate the requirement for automatic main steam isolation on High Turbine Building Area Temperature, and to add new TS 3.7.10 to monitor turbine building area temperature
- Follow-up to October 14, 2020 pre-submittal meeting (Meeting Summary -
ML20289A424) based on scope change
- October 14, 2020 meeting proposed to remove Function 1.f (Main Steam Line Isolation - Turbine Building Area Temperature - High) from Technical Specification (TS) and relocate to Technical Requirements Manual (TRM)
- Revised proposal retains turbine building area temperature monitoring requirement in TS, but removes automatic main steam isolation 2
Meeting Agenda
- LAR Summary Description
- System Design and Operation
- Current Licensing Basis Requirements
- Reason for Proposed Change
- Description of Proposed Change
- Technical Evaluation of Proposed Change 3
LAR Summary Description LAR Summary Description
- Revision to TS 3.3.6.1, Primary Containment Isolation Instrumentation, Table 3.3.6.1-1, to eliminate the requirement for automatic main steam isolation on high turbine building area temperature (Function 1.f)
- TS requirements for turbine building area temperature monitoring will be relocated to a new TS 3.7.10 5
System Design and Operation System Design and Operation
- Main Steam Line (MSL) leakage in the turbine building is monitored to protect the assumptions of the accident dose analyses.
- Allowable Value chosen to detect a leak equivalent to between 1% and 10% rated steam flow
- Credit for temperature instruments is not taken in any transient or accident analysis in the updated final safety analysis report (UFSAR), since bounding analyses are performed for large breaks such as main steam line breaks (MSLBs) 7
System Design and Operation
- The Turbine Building Area Temperature - High Function monitors area temperature around the MSLs in the turbine building, and isolates the Main Steam Isolation Valves (MSIVs) on high temperature
- Normally energized; de-energized to trip 8
Turbine Building Temperature Main Steam Line Isolation Logic 9
Current Technical Specification Requirements
Current Technical Specification Requirements
- Technical Specification (TS) requirements are 32 (of 64) channels Operable to ensure no single instrument failure can preclude isolation function
- Each trip stream must have 2 channels per main steam line (8 total channels)
- No more than 40 feet may separate any two Operable channels
- Allowable Value 200°F 11
Reason for Proposed Change Reason for Proposed Change
- Due to area configuration, indicated temperature can trend close to isolation set points for reasons other than small steam leak (e.g. issues with turbine building area chillers, temperature monitoring instrument drift)
- Has resulted in numerous half-Group 1 isolations, none of which were caused by a steam leak
- Removing automatic MSIV isolation will reduce the probability of an unnecessary plant transient (either an unplanned maintenance outage or a complicated scram)
- New TS requirements will allow for a controlled shutdown if a small steam leak exists, which is more commensurate with the safety significance
- If temperature exceeds setpoint for reasons other than a small steam leak, new TS will provide appropriate remedial actions to ensure plant is operating safely and within assumed plant conditions 13
Description of Proposed Change LCO 3.7.10 TB maximum area temperature shall be 200 °F.
Description of Proposed Change APPLICABILITY: MODES 1, 2, and 3.
ACTIONS CONDITION REQUIRED ACTION COMPLETION TIME A. TB maximum area A.1 Initiate action to verify Immediately temperature no main steam line
> 200°F. leak.
AND A.2 Verify no main steam Once per 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> line leak. thereafter B. Required Action and B.1 Be in MODE 3. 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> associated Completion Time not met. AND B.2 Be in MODE 4. 36 hours4.166667e-4 days <br />0.01 hours <br />5.952381e-5 weeks <br />1.3698e-5 months <br /> SURVEILLANCE REQUIREMENTS SURVEILLANCE FREQUENCY SR 3.7.10.1 Verify TB maximum area temperature is within In accordance with limit. the Surveillance Frequency Control Program 15
Technical Evaluation Technical Evaluation
- Evaluation of design basis showed basically two criteria for MSL turbine building isolation function:
- 1. Leak Before Break
- Early intergranular stress corrosion cracking (IGSCC) showed isolating on a small leak provided assurance that the leak would not grow to a break
- Small cracks in main-steam piping are not subject to IGSCC due to high quality steam and corresponding lack of corrosive environment
- Furthermore, TS 3.7.10 will require a shutdown if a leak is confirmed
- 2. Dose Limits
- Dose limits may be exceeded if a LOCA were to occur concurrent with an on-going (undetected) leak in the main steam piping in the turbine building
- Proposed TS 3.7.10 provides assurance that a leak would be properly identified
- If TS 3.7.10 Condition B were entered based on confirmed steam leak, impact to radiological consequences would be insignificant 17
Technical Evaluation - Small Leak Detection Indications
- In addition to TS Table 3.3.6.1-1 Main Steam Line Isolation Instrumentation, other methods to detect a small leak in the turbine building include:
- Verifying no unexpected, sudden rise in maximum area temperature
- Verifying no unexpected change in radiation monitors
- Verifying no unexpected rise in turbine building sump levels
- Verifying no unexpected change in megawatts electric (MWe)
- Visual (e.g. cameras, drones) and sound indications 18
Technical Evaluation - Risk Insights
- Risk insights provided related to proposed change
- Risk analysis demonstrates with reasonable assurance that eliminating the requirement for automatic main steam isolation on high turbine building area temperature is within RG 1.174 acceptance criteria
- Analysis calculates CDF and LERF that results from assuming the turbine building steam line break high temperature function fails
- The following conservatisms are assumed in the risk evaluation:
- No credit of reduced chance of spurious actuation from a fire
- No assumption of operator action to detect a steam leak
- Unisolated breaks of any size result in core damage and large early release 19
Questions?