ML23291A156

NRC Pre-Submittal Meeting Watts Bar & Sequoyah LAR, TVA Presentation Slides

ML23291A156
Person / Time
Site:	Watts Bar, Sequoyah
Issue date:	10/18/2023
From:	Tennessee Valley Authority
To:	Plant Licensing Branch II
Wentzel M
References
Download: ML23291A156 (1)

Text

License Amendment Request Application to Revise Function 5 of Technical Specification Table 3.3.2-1, "Engineered Safety Feature Actuation System Instrumentation," for the Sequoyah Nuclear Plant and Watts Bar Nuclear Plant October 24, 2023

Agenda

• Introduction

• Description of the Proposed Change

• Reason for the Proposed Change

• System Description

• Technical Evaluation

• Precedent

• Schedule Milestones

• Closing Remarks 2

Introduction

• The purpose of this meeting is to discuss a proposed license amendment request (LAR) for the Sequoyah Nuclear Plant (SQN),

Units 1 and 2 and the Watts Bar Nuclear Plant (WBN) Units 1 and 2.

• The proposed license amendment would add a new note to SQN Units 1 and 2 and WBN Units 1 and 2 Technical Specification (TS) 3.3.2, Engineered Safety Feature Actuation System (ESFAS)

Instrumentation, Table 3.3.2-1, Function 5, Turbine Trip and Feedwater Isolation, for Modes 1, 2, and 3 regarding the turbine stop valves or governor valves,

• Proposed change will avoid an unnecessary entry into LCO 3.0.3 if the turbine stop valves or governor valves are already closed (in the required turbine trip condition) and are incapable of opening.

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Description of the Proposed Change l 4

• The proposed license amendment would add the following note to SQN Units 1 and 2 and WBN Units 1 and 2 TS 3.3.2, Table 3.3.2-1, Functions 5a and 5b for Modes 1, 2, and 3:

Turbine trip function is not required when all turbine stop valves or governor valves are closed and are incapable of opening.

• The remaining footnotes in TS 3.3.2, Table 3.3.2-1 are renumbered accordingly.

Description of the Proposed Change (contd) l 5

• SQN Units 1 and 2 TS 3.3.2, Table 3.3.2-1

Description of the Proposed Change (contd) l 6

• SQN Units 1 and 2 TS 3.3.2, Table 3.3.2-1

Description of the Proposed Change (contd) l 7

• WBN Unit 1 TS 3.3.2, Table 3.3.2-1

Description of the Proposed Change (contd) l 8

• WBN Unit 1 TS 3.3.2, Table 3.3.2-1

Description of the Proposed Change (contd) l 9

• WBN Unit 2 TS 3.3.2, Table 3.3.2-1

Description of the Proposed Change (contd) l 10

• WBN Unit 2 TS 3.3.2, Table 3.3.2-1

Reason for the Proposed Change

• SQN and WBN TS Table 3.3.2-1, Function 5 requires two trains of the Turbine Trip function to be operable in Mode 1 and in Modes 2 and 3 [except when all main feedwater (MFW) isolation valves, MFW regulating valves (MFRVs), and MFRV bypass valves are closed or isolated by a closed manual valve].

• This function requires the four main turbine stop valves to be capable of closing within the prescribed time limits.

• However, SQN and WBN TS 3.3.2 does not provide any specific condition/action for the main turbine stop valves.

• Therefore, if one or more of the turbine stop valves is inoperable (e.g., fails to meet the required closure time), then both trains of the Turbine Trip function must be declared inoperable, which requires entry into SQN and WBN TS Limiting Condition for Operation (LCO) 3.0.3 due to two trains inoperable with no applicable TS required action.

• However, entry into LCO 3.0.3 is unnecessary if the turbine stop valves or governor valves are already closed (in the required turbine trip condition) and are incapable of opening.

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System Description===

• The primary functions of the Turbine Trip and Feedwater Isolation signals are to prevent damage to the turbine due to water in the steam lines, and to stop the excessive flow of feedwater into the steam generators (SGs). These Functions are necessary to mitigate the effects of a high water level in the SGs, which could result in carryover of water into the steam lines and excessive cooldown of the primary system. The SG high water level indication is due to excessive feedwater flows.

• The Function is actuated when the level in any SG exceeds the high setpoint, and performs the following functions:

Trips the main turbine,

Trips the MFW pumps,

Initiates feedwater isolation, and

Shuts the MFW regulating valves and the bypass feedwater regulating valves.

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System Description (contd)

• Each of the two main steam chests includes two turbine stop valves and two turbine control valves. The steam lines are cross-connected upstream of the turbine stop valves. The turbine provides anticipatory trips to the reactor protection system from contacts which change position when the turbine stop valves close or when the emergency trip header pressure goes below its setpoint.

• For a turbine trip, the reactor would be tripped directly (unless below approximately 50% power) from a signal derived from the turbine emergency trip header pressure or the turbine stop valve position. The turbine stop valves close on loss of emergency trip header pressure actuated by one of a number of possible turbine trip signals.

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Technical Evaluation

• A turbine trip signal into the digital electric hydraulics (DEH) system (see Figures 1 and 2) must be present for the turbine stop and governor valves to be closed and incapable of opening. While the turbine is in the tripped state the trip block solenoid valves will de-energize and remain open removing hydraulic fluid pressure needed for valve movement. The trip block solenoid valves will energize only when all turbine trips are clear and the turbine is latched. These actions will allow system pressure to build therefore enabling valve movement when demand is present.

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Figure 1 l 15

Figure 2 l 16

Precedent l 17

• There is no precedent for the proposed change.

Schedule Milestones l 18

• TVA to submit LAR to NRC by December 22, 2023.

• Request NRC approval within 1-year from submittal.

• 60-day implementation following NRC approval.