ML19045A269

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Public Meeting Presentation Slides on February 19, 2019
ML19045A269
Person / Time
Site: Fermi DTE Energy icon.png
Issue date: 02/19/2019
From: Jonathan Haas, Hullum-Lawson K, Vukonich C
DTE Energy
To: Polson K
Division of Operating Reactor Licensing
Goetz S
References
EPID L-2018-LLA-0246
Download: ML19045A269 (23)
v • d • e


Text

Fermi-2 Risk Assessment of ECCS Strainer Performance Christopher Vukonich, Kendra Hullum-Lawson, Jason Haas February 19th, 2019 1

Agenda

  • Objectives
  • Background
  • Risk Discussion
  • Schedule
  • Summary / Questions / Feedback 2

Objectives

  • Provide the NRC with an overview of the proposed license amendment request (LAR):

- Scope and content for LAR

  • Changes to licensing basis for ECCS suction strainers

- Methodology

- Submittal schedule

  • Obtain NRC feedback

- Content for LAR

- Approval schedule

- Lessons learned 3

=

Background===

  • NRC inspections identified non-cited violations1

- NCV 05000341/2016007-09, Failure to Evaluate the Acceptability of Drywell Coatings with Respect to Potential ECCS Suction Strainer Blockage

- NCV 05000341/2016007-10, Non-Conservative ECCS Suction Strainer Min-K Combined Generation and Transport Factors

- NCV 05000341/2016007-15, Failure to Identify that a Non-Conservative Min-K Insulation Volume Calculation Error Was Nonconforming to the ECCS Suction Strainer Licensing Basis

  • Fermi has evaluated the impact of these violations in the corrective action program 4
1. INSPECTION REPORT 05000341/2016007

=

Background===

  • Fermi is proposing a risk-informed analysis of additional debris beyond current design basis values

- Insulation in containment penetrations

- Sensitivity studies for coatings / labeling

  • Results of this risk-informed analysis will form the basis of a request to amend the license basis to accept the additional debris sources based on low risk following the guidance in Reg. Guide 1.174
  • This will provide an analysis of the impacts of insulation in containment penetrations and additional margin to support emergent analysis 5

Fermi-2 Containment Geometry 6

Drywell Liner Penetrations Feedwater x2 Main Steam x4

Penetration Photos 7

Penetration Cross Section 8

Background:

Current Methodology

- Strainers were sized to meet the requirements of Reg Guide 1.82 R2

- Strainers were designed and installed in RF06 are of the GE optimized stacked-disk (OSD) design

- Strainer debris loads were developed utilizing the methodology provided in NEDO-32686, BWROG Utility Resolution Guidance (URG)

- Strainer head loss uses GE LTR Methodology (NEDO-32721P-A) as modified by GE SC 08-02 corrections

  • Fermi is predominately a Reflective Metal Insulation plant with spot locations of NUKON/Min-K insulation at several whip restraints and Min-K in penetrations
  • Participated fully in BWROG studies regarding NRC twelve issues 9

Penetration Min-K Debris Loads 10

  • There is no specific guidance in the URG methodology regarding a ZOI for a break inside a penetration
  • A break in the penetration is unique in that it is highly restrained, directed and becomes automatically isolated as part of the containment isolation system
  • All breaks at the penetration (Weld A and Weld D) are between the inboard and outboard containment isolation valves and part of the Containment Isolation System Weld D Weld A Outboard Isolation Inboard Isolation

Risk Informed Analysis Approach

  • Leverage industry precedent including NRC SE for South Texas Project (PWR) GSI-191 LAR and recent BWROG ECCS Risk Informed Resolution studies
  • Risk over Deterministic (RoverD) Approach

- Maintain current design basis deterministic methods for existing debris loads

- Calculate the delta risk associated with the new debris loads over the baseline risk of the current design basis debris loads

- Utilize NUREG-1829 LOCA Frequencies

- Categorization of risk based on Regulatory Guide 1.174

  • Interface with plant PRA

- Provides isolation valve failure probabilities 11

Break Locations and Risk Analysis

  • Current design basis analysis utilizes a deterministic analysis for all break locations

- Conservatively assumes those in the penetrations are non-isolated

  • New risk analysis takes into consideration isolation of breaks between inboard and outboard isolation valve and valve failure probability

- Utilize NUREG-1829 break frequencies and assumptions for inboard welds

- Valve failure probability from Fermi PRA based on generic industry data from NUREG/CR-6928

- Adapt NUREG-1829 break frequencies and assumptions to estimate isolable break frequencies (breaks between the isolation valves, i.e., in the penetration) 12 Outboard Inboard Inboard Isolation Valves

Background Fermi PRA

  • The Fermi 2 PRA Full Power Internal Events (FPIE) models are highly detailed and include a wide variety of initiating events, modeled systems, operator actions, and common cause events. The Fermi 2 FPIE model of record and supporting documentation has been maintained as a living program, with periodic updates to reflect the as-built, as-operated plant
  • The Fermi 2 PRA FPIE models have been the subject of several assessments (e.g., industry peer reviews) to establish the technical adequacy of the PRA
  • Fermi 2 has used the F&O Closure process and Focused Scope Peer Reviews to close all open findings and currently meets all supporting requirements to at least Capability Category II 13

Risk Evaluation

  • Utilize Fermi Mark I Containment CAD Model with plant specific debris locations (geometry), weld locations, and equipment configuration
  • Develop strainer failure probabilities for all break locations

- Strainer failure is defined as any debris load greater than the design basis debris load (loss of NPSH)

- Conservatively assume core damage for every non-isolated outboard break (between isolation valves)

  • For risk calculation, the specific LOCA initiating event frequency for size and location is multiplied by the associated ECCS suction strainer failure probability and conservatively assumed to lead directly to core damage 14

Risk Evaluation Assumptions Inboard Weld Break Locations (Between Vessel and Isolation Valve)

  • Use URG debris generation and transport fractions
  • Debris accumulates on strainer as a function of flow
  • Assume failure of the first ECCS suction strainer represents common cause failure of all ECCS suction strainers in the suppression pool 15

Risk Evaluation Assumptions (Cont.)

Penetration Weld Break (Valves Failing to Isolate)

  • Assume ECCS suction strainer failure (debris load exceedance)
  • Apply failure to automatically isolate LOCA based on valve isolation failure probabilities from Fermi-2 PRA
  • LOCA frequency x valve isolation failure probability x ECCS suction strainer probability (1.0) assumed to lead directly to core damage and contribute directly CDF 16

Risk Evaluation Assumptions (Cont.)

Penetration Weld Break (Valves Successfully Isolate)

  • RPV makeup requirements for isolated LOCA events are significantly reduced such that the risk impact of these scenarios is judged to be very small
  • RPV makeup can be provided automatically from clean water sources such as HPCI, RCIC, and CRD. Standby Feedwater System (two high pressure motor driven pumps with 600 gpm/pump from CST) can be manually aligned from the Control Room with a high reliability 17

Preliminary Min-K Results

  • Core Damage Frequency (#/year) for Min-K
  • Results are in Region III of R.G. 1.174
  • CDF due to external events (e.g., fire and seismic) judged to be small or negligible and will not change the risk conclusions based on similar risk evaluations developed for the BWR risk evaluation
  • LERF not expected to be the bounding risk metric, which would also be consistent with BWROG risk evaluation Break Location CDF Inboard Breaks 0

Penetration Breaks 7.22E-07 Total 7.22E-07 18

Sensitivity Studies and Operational Margin

  • Goal is to support additional operational margin and evaluation of potential debris sources
  • Sensitivities performed to address potential debris sources (e.g., non-conforming coatings or labeling) identified during plant walkdowns or vendor safety communications that may exceed the current design limits
  • Sensitivity #1 - impact of degraded or failed coatings
  • Sensitivity #2 - impact of reduced strainer area due to labels, tags, or foreign material 19

Sensitivity Studies and Operational Margin

  • Sensitivity #1 - impact of failed coatings (particulate)

- Strainer failure criteria is development of 1/8 of fibrous debris; sufficient to filter coatings particulate Preliminary results indicate this will be in Region II/III

  • Sensitivity #2 - impact of reduced strainer area of 80 sqft with and without thin-bed strainer failure criteria

- Preliminary results indicate that limited credit for operator actions may be required to remain in Region II/III for thin-bed criteria 20

Change to License Basis

  • LAR explains basis of risk-informed analysis, quantifies change in risk, and describes changes in licensing basis
38) to permit use of a risk-informed approach to evaluate the residual risk associated with those effects that have not been explicitly addressed using deterministic methods
  • Schedule

- Planned LAR Submittal - Spring/Summer 2019

- Requesting NRC Approval - 2020 21

Closing Remarks

  • Penetration breaks (i.e., breaks between containment isolation valves) represent unique break locations that are designed to be automatically isolated
  • Removal of the insulation associated with these break locations incurs considerable dose with minimal improvement in safety
  • Additional risk associated with debris effects relative to RG 1.174 criteria calculated to be small (Region II/III) based on preliminary analyses
  • Plan is to submit LAR to utilize a risk informed approach to address the debris effects and resolve the issues raised in the referenced Fermi NCVs and provide operational margin
  • Consistent with the Commissions Policy Statement on the Use of Probabilistic Risk Assessment Methods in Nuclear Regulatory Activities that the use of PRA technology in NRC regulatory activities should be increased to the extent supported by state of the art in PRA methods and data and in a manner that complements the NRCs deterministic approach and consistent with defense in depth concepts 22

NRC Feedback

  • Comments / Feedback
  • Lessons Learned from recent submittals 23
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