ML20315A158

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Presentation Meeting Slides for the 11/17/20 Teleconference
ML20315A158
Person / Time
Site: Arkansas Nuclear  Entergy icon.png
Issue date: 11/17/2020
From:
Entergy Operations
To:
Plant Licensing Branch IV
Wengert T, NRR/DORL/LPL4, 415-4037
References
EPID L-2020-LRM-0105
Download: ML20315A158 (19)
v • d • e


Text

Arkansas Nuclear One (ANO)

Resolution of In-Vessel Downstream Effects Pre-Submittal Meeting with NRC November 17, 2020 1

Agenda

  • Meeting Objectives
  • Overview of ANO Approach for Resolving In-Vessel Downstream Effects

- ANO Fiber Bypass Testing

- ANO In-Vessel Fiber Load Analysis

- Applicability of WCAP-17788 AFP Analysis for ANO

  • Submittal Format and Schedule 2

Meeting Objectives

  • Communicate ANOs approach for resolving in-vessel downstream effects
  • Communicate content and schedule of upcoming supplemental GL 2004-02 response
  • Obtain staff feedback on the technical approach
  • Identify areas of concern from the NRC 3

Overview of Sump Strainers (Unit 1)

  • Unit 1 strainer features multiple modules of filtering cartridges installed on top of containment sump
  • Cartridge lengths: 300 mm and 400 mm
  • Total strainer surface area: 2715 ft2 4

Overview of Sump Strainers (Unit 2)

  • Unit 2 strainer has modules of filter cartridges along containment wall connected to a suction plenum
  • Cartridge lengths: 100 mm, 200 mm and 400 mm
  • Total strainer surface area: 4837 ft2 West Branch 5

Overview of Sump Strainers (Unit 2)

East Branch 6

Current GL 2004-02 Resolution Status

  • ANO chose a deterministic resolution path (Option 2b) for both strainer head loss and in-vessel effects
  • All outstanding issues related to strainer head loss have been resolved as of 2010
  • ANO presented the fiber bypass testing approach to the NRC in March 2017
  • ANO conducted fiber bypass testing in May 2017
  • ANO evaluated in-vessel fiber loads in 2017

- Evaluation updated in 2020 per latest NRC review guidance

ANO Fiber Bypass Testing

  • Performed large-scale bypass tests at Alden
  • Used three spare 400 mm cartridges as test strainer with key perforated plate dimensions matching those of plant strainers
  • Figure below shows a plan view of test tank Debris Addition 8

ANO Fiber Bypass Testing Test Strainer Mixing Lines Mixing Region for Debris Addition 9

ANO Fiber Bypass Testing

  • Performed two large-scale fiber-only bypass tests

- Similar to other tank tests observed by the NRC at Alden

  • Test parameters represented plant conditions of both units: fiber load, approach velocity and water chemistry (i.e., max pH and buffer type)
  • Used only fine heat-treated Nukon fiber for testing
  • Followed NEI guidance on fiber debris preparation
  • Added debris in 5 batches with increasing batch size
  • Prevented settling by mixing from return flow into test tank without disturbing debris bed on test strainer 10

ANO Fiber Bypass Testing Prepared Nukon Fiber Debris Loading on Test Strainer 11

ANO Fiber Bypass Testing

  • Collected fiber bypass by routing all flow through 5-micron filter bags with retention rate > 97%

- Parallel filter housings used to facilitate swapping filter bags without disturbing system flow

  • Collected time-dependent fiber bypass testing data:

bypass vs. fiber load on strainer

- New filter bags placed online before adding a new batch

- At least one additional set of filter bags placed online for >30 min to capture shedding fiber for each batch

  • Filter bags dried and weighed before and after testing
  • Test 2 showed slightly higher bypass and used to develop a curve fit for bypass fraction vs. fiber load on strainer 12

In-Vessel Analysis

  • Determined in-vessel fiber load for hot leg breaks (HLBs) using WCAP-17788 methodology

- Divided recirculation phase into small time steps

- Calculated debris arrival at sump strainers for each time step based on pool fiber concentration and pump flow rates

- Evaluated fiber penetration fractions based on strainer fiber load for each time step using curve-fit from testing

- Analyzed most limiting equipment configurations (both ECCS trains operating with failure of one spray pump)

- Performed sensitivity to capture the worst combination of inputs (e.g., pool volume, ECCS pump flow rate)

- Assumed all fiber that reaches reactor accumulates at core inlet with no credit of alternate flow paths (AFPs) 13

In-Vessel Effects Resolution (Unit 1)

  • ANO-1 used Box 2 path from NRC guidance for B&W plants to resolve in-vessel issue
  • Largest in-vessel fiber load of 77.9 g/FA is less than the limit in Section 6.5 of WCAP-17788 Vol 1, Rev. 1
  • Boric acid precipitation precluded by inherent design of B&W reactor without requiring operator actions

- Flow through gaps between reactor vessel outlet nozzles and core support shield dilutes boron concentration

- This flow path becomes active during reflooding period following an accident

- Additional operating procedure in place as defense-in-depth measure 14

In-Vessel Effects Resolution (Unit 2)

  • ANO-2 used Box 4 path from NRC guidance for CE plants to resolve in-vessel issue Parameters WCAP-17788 Revision 1 Values ANO Unit 2 Values NSSS Design Various CE Fuel Type Various Westinghouse 16 x 16 NGF Fuel Minimum Chemical Precipitation Time 333 minutes (5.6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br />) 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> after accident (tchem) (tblock from WCAP-17788, Vol. 1, Table 6-1)

Max Hot Leg Switchover (HLSO) Time 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> after accident 5 hours5.787037e-5 days <br />0.00139 hours <br />8.267196e-6 weeks <br />1.9025e-6 months <br /> after accident Max Core Inlet Fiber Load for HLB WCAP-17788, Vol. 1, Table 6-3 72.52 g/FA Max In-Vessel Fiber Load for HLB WCAP-17788, Vol. 1, Section 6.4 72.52 g/FA Min Sump Switchover (SSO) Time 20 minutes 30.03 minutes Max Rated Thermal Power 3458 MWt 3026 MWt Max AFP Resistance WCAP-17788, Vol. 4, Table 6-3 WCAP-17788, Vol. 4, Table RAI-4.3-8 ECCS Flow per Fuel Assembly (FA) 3.8 - 11.4 gpm/FA 4.1 - 10.2 gpm/FA 15

In-Vessel Effects Resolution (Unit 2)

  • Chemical precipitation occurs after tblock and switchover to hot leg recirculation

- Chemical precipitation timing based on sump pH, Al concentration from WCAP-16530 evaluation and precipitation boundary equation from WCAP-17788

  • Max in-vessel fiber load (72.5 g/FA) exceeds core-inlet fiber limit but bounded by total in-vessel fiber limit

- WCAP core-inlet fiber limit conservatively low based on assumption of uniform fiber bed at core inlet

- Licensees may justify that a non-uniform debris bed will form at the core inlet allowing adequate flow to assume LTCC, even though the average debris load per FA metric is exceeded 16

In-Vessel Effects Resolution (Unit 2)

  • Earliest ANO-2 sump switchover time (30.03 minutes) is greater than that assumed in the WCAP analysis
  • ANO-2 thermal power (3026 MWt) is lower than that analyzed in WCAP-17788 for CE plants (3458 MWt)
  • ANO-2 AFP resistance is lower than that analyzed in WCAP-17788 for CE plants
  • ANO-2 ECCS flow rate per fuel assembly (4.1 - 10.2 gpm) is within the range tested in WCAP-17788 (3.8 -

11.4 gpm) for CE plants 17

Licensing Actions and Submittal

  • ANO will update the UFSAR to incorporate in-vessel downstream effects analysis and conclusions before submittal
  • Submittal will have one enclosure for each unit, focusing on the resolution of in-vessel effects
  • Submittal is currently going through ANO licensing review and engineering certification
  • Projected submittal date: December 2020 18

Closing

  • Questions?

19

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