ML19210D451

Abeyance Seal Preapplication Meeting Slides

ML19210D451
Person / Time
Site:	Prairie Island
Issue date:	07/22/2019
From:	Northern States Power Co, Xcel Energy
To:	Northard S Division of Operating Reactor Licensing
Kuntz R
References
EPID L-2019-LRM-0045
Download: ML19210D451 (16)

Text

Prairie Island Nuclear Generating Plant (PINGP)

Pre-Application Meeting Request for NRC Approval of PRA Model for Flowserve N-Seal Abeyance Seal and Dynamic Testing for the Prairie Island Nuclear Generating Plant July 22, 2019

Meeting Agenda

• Describe future submittal requesting NRC approval

• Discuss scope of the new PRA model

• Background information

• Abeyance seal design and operation

• Basis of the N-Seal PRA model

• Proposed schedule

• Questions 2

Proposed Submittal NRC approval of Flowserve Report:

PRA Model for Flowserve N-Seal Abeyance Seal and Dynamic Testing for the Prairie Island Nuclear Generating Plant 3

Proposed Submittal (continued)

Reasons for submittal:

• Reflect the risk benefit of the N-9000 seal package abeyance seal in the PRA models

• Allows closure of the open Fact & Observation (F&O) Finding SY-A17-01 from the PRA Peer Review

• Supports risk-informed NFPA 805 licensing basis and 10 CFR 50.69 application 4

Scope of RCP Seal PRA Modeling

• Static (RCP off) modeling of Abeyance seal

• Dynamic (RCP running) modeling of N-Seal (Time to trip RCPs)

• Update on operating history data of N-Seal

• Not an overall RCP seal model

- Abeyance seal is modeled per the Flowserve Report stage face-type seal is modeled per NRC-approved WCAP 16175-P-A, Model for Failure of RCP Seals Given Loss of Seal Cooling in CE NSSS Plants 5

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Background===

• Xcel Energy installed Flowserve N-9000 RCP seal packages

- PINGP Unit 2: Dec 2013

- PINGP Unit 1: Nov 2014

• PINGP PRA updated accordingly stages of face-type seals modeled per WCAP 16175-P-A consistent with NRC SE conditions/limitations for use by non-CE plants

- Abeyance seal modeled per Flowserve PRA model

- 2014 Focused-scope Peer Review of Flowserve N-Seal Abeyance Seal PRA Model conducted

• F&O Finding SY-A17-01 addressed model assumptions for loss of power to RCPs when safeguards power is lost.

- 2017 Closure Review Team determined the closure was acceptable, but determined SY-A17-01 could not be closed due to lack of NRC-approved abeyance seal PRA model 6

Background (continued)

• RCP seal model (in particular, allowing credit for the abeyance seal) is discussed in PINGP risk-informed applications:

- NFPA 805

- TSTF-425

- 10 CFR 50.69

• Enercon developed Flowserve N-Seal Abeyance Seal PRA Model

- Updates for abeyance seal, hot dynamic tests, and 20+ years of operating experience at several plants 7

Background (continued)

NRC SE for NFPA 805:

• Licensee used the best available applicable information, (i.e., the Flowserve RCP seal PRA model), to estimate the associated change-in-risk

• Licensee will take action if replacing the current model with a final, NRC-approved PRA model increases risk beyond risk acceptance guidelines

• Implementation Item 66: PINGP PRA to be reviewed and updated when NRC approves a seal model.

- Compensatory measures remain in place until the seal model is approved or the PRA model removes credit for the abeyance seal 8

Background (continued)

NRC SE for TSTF-425:

• Licensee performed a sensitivity study that removed credit for abeyance seals.

• Staff concluded the Flowserve N-9000 RCP seal model did not have a significant impact on the Surveillance Frequency Control Program (SFCP) 9

Background (continued) 10 CFR 50.69 (under NRC review):

• NRC staff noted there is no NRC accepted methodology to model the abeyance seal in PRAs.

• Xcel Energy proposed Implementation Item #1, PRA model used for categorization will only credit the abeyance RCP seal after NRC approval 10

Abeyance Seal Design and Operation Simplicity of design provides reliable actuation

• Abeyance seal is a diverse sealing mechanism located above top stage

• Inert until significant leak from all three primary seal stages occurs

• Passive, self-actuated device with no reliance on sub-assemblies -

actuated by pressure of leakage flow across seal package

• Does not rely on elastomers

- Metallic sealing ring is main sealing device

- Supplemented by PEEK actuation ring (initial sealing until pressure loading collapses metal sealing ring onto shaft sleeve)

• Near zero leakage provided RCP has tripped

• Non-contacting during normal operation - no wear

• Testing demonstrated no credible mechanism for inadvertent actuation 11

Abeyance Seal Design and Operation Abeyance Seal Actuation Sequence RCP shaft Sealing ring Actuation ring Seal injection or reactor coolant Normal Operation Initialization Full Deployment 12

Basis of N-Seal PRA Model

• Abeyance seal modeling

- Failure modes considered Abeyance

• Fail to actuate (per demand) 3rd Stage

• Fail to hold once sealed (per hour)

• Failure due to installation error 2nd Stage

- Failure data from development testing

• Modes precluded by design excluded

• Conservative values used 1st Stage

• N-Seal dynamic operation without cooling

- Additional testing was completed (beyond what was used to develop WCAP-16175-P-A) to demonstrate extended operation at full RCS conditions

- N-Seal design-specific data supports significantly greater time than generically-approved 20 minutes for operators to trip RCPs 13

Schedule

• Projected submission in August 2019 with a requested issuance of September 2020

• Implement in time to coincide with implementation of final NFPA 805 modifications consistent with Transition License Condition 3 and Implementation Item 66

- Not required for NFPA 805 implementation, but highly desired 14

Questions

• Questions or comments?

15