0CAN122001, Final Response to NRC Generic Letter 2004-02

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Final Response to NRC Generic Letter 2004-02
ML20353A115
Person / Time
Site: Arkansas Nuclear  Entergy icon.png
Issue date: 12/10/2020
From: Gaston R
Entergy Operations
To:
Document Control Desk, Office of Nuclear Material Safety and Safeguards, Office of Nuclear Reactor Regulation
References
0CAN122001, GL-04-002
Download: ML20353A115 (34)
v • d • e


Text

Entergy Operations, Inc.

1340 Echelon Parkway Jackson, MS 39213 Tel 601-368-5138 Ron Gaston Director, Nuclear l.Jcensmg 0CAN122001 December 10, 2020 ATTN: Document Control Desk U.S. Nuclear Regulatory Commission Washington, DC 20555

Subject:

Final Response to NRC Generic Letter 2004-02 Arkansas Nuclear One, Units 1 and 2 NRC Docket Nos. 50-313, 50-368, and 72-13 Renewed Facility Operating License Nos. DPR-51 and NPF-6 The purpose of this submittal is to provide the Entergy Operations, Inc. (Entergy) final supplemental response for Arkansas Nuclear One, Unit1 (ANO-1) and Unit 2 (ANO-2) to Generic Letter (GL) 2004-02, dated September 13, 2004, "Potential Impact of Debris Blockage on Emergency Recirculation during Design Basis Accidents at Pressurized-Water Reactors (PWRs)."

On May 16, 2013, Entergy submitted a letter of intent per NRC Commission Paper SECY-12-0093, "Closure Options for Generic Safety Issue - 191, Assessment of Debris Accumulation on PWR Sump Performance,* indicating ANO-1 and ANO-2 would pursue Closure Option 2 (deterministic approach) of the SECY recommendations (refinements to evaluation methods and acceptance criteria) (Reference 1). The final outstanding issue for ANO-1 and AN0-2 with respect to GL 2004-02 was the in-vessel downstream effects evaluation, which addresses that long-term core cooling can be adequately maintained for postulated accident scenarios that require sump recirculation.

The in-vessel downstream effects evaluation has been completed for ANO-1 and ANO-2 and is documented in Enclosures 1 and 2, respectively, to this letter. This satisfies the final Generic Safety Issue (GSl)-191 commitment identified in the May 16, 2013, Closure Option letter (Reference 1).

In addition, this submittal supplements References 2 and 3 and satisfies the commitments previously made in Reference 4 for GSl-191.

There are no new regulatory commitments contained in this submittal. ft!) 4, fl)t--f 5 5 2 l.

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0CAN122001 Page 2 of 2 If there are any questions or if additional information is needed, please contact Riley Keele, Manager, Regulatory Assurance, ANO, at (479)858-7826.

I declare under penalty of perjury that the foregoing is true and correct.

Executed on December 10, 2020.

Respectfully, L.,____

Ron Gaston RWG/nbm : ANO-1 Final Response to NRG Generic Letter 2004-02 : ANO-2 Final Response to NRG Generic Letter 2004-02 References. 1. Entergy letter to NRG, "Generic Letter 2004-02 Closure Option,"

(0CAN051301) (ML13137A126), dated May 16, 2013.

2. Entergy letter to NRG, "GL 2004-02 Final Supplemental Response,"

(0CAN090801) (ML082700499), dated September 15, 2008.

3. Entergy letter to NRG, "Generic Letter 2004-02 Revision to the Final Supplemental Response and Requests for Additional Information,"

(0CAN091001) (ML102730943), dated September 29, 2010.

4. Entergy letter to NRG," Generic Letter 2004-02 Commitment Extension,"

(0CAN111701) (ML173258078), dated November 20, 2017.

cc: NRG Region IV Regional Administrator NRG Senior Resident Inspector -Arkansas Nuclear One NRG Project Manager - Arkansas Nuclear One

ENCLOSURE1 0CAN122001 AN0-1 FINAL RESPONSE TO NRC GENERIC LETTER 2004-02

0CAN122001 Page 1 of 17 ANO-1 FINAL RESPONSE TO NRC GENERIC LETTER (GL) 2004-02 Updated Resolution to In-Vessel Downstream Effects for AN0-1 Table of Contents Section Page 1 Overall Compliance .................................................................................................. 1 2 General Description of and Schedule for Corrective Actions ......................................... 3 3 Specific Information Regarding Methodology for Demonstrating Compliance ................. 3 4 References .....................................................................................................................17

1. Overall Compliance Provide information requested in Generic Letter (GL) 2004-02, "Potential Impact of Debris Blockage on Emergency Recirculation during Design Basis Accidents at Pressurized-Water Reactors (PWRs)," Requested Information Item 2(a), regarding compliance with regulations.

GL 2004-02 Requested lnfonnation Item 2(a): Confinnation that the emergency core cooling system (EGGS) and reactor building spray system (RBSS) recirculation functions under debris loading conditions are or will be in compliance with regulatory requirements listed in the Applicable Regulatory Requirements section of this GL. This submittal should address the configuration of the plant that will exist once all modifications required for regulatory compliance have been made and this licensing basis has been updated to reflect the results of the analysis described above.

Response

In accordance with SECY-12-0093 and as identified in Entergy Operations, Inc. (Entergy) letter to the NRG dated May 16, 2013 (Reference 11 ), Entergy elected to pursue Generic Safety Issue (GSl)-191 Closure Option 2a, utilizing a deterministic methodology for both strainer and in-vessel effects for Arkansas Nuclear One, Unit 1 (ANO-1 ). Topical Report WCAP-17788-P, "Comprehensive Analysis and Test Program for GSl-191 Closure (PA-SEE-1090)," Revision 1 (Reference 5), provides evaluation methods and results to address in-vessel downstream effects. As discussed in the NRG Technical Evaluation Report of in-vessel effects (Reference 10), the NRG has performed a detailed review of WCAP-17788-P. Although the NRG did not issue a Safety Evaluation for WCAP-17788, as discussed further in NRG Memorandum, "U.S. Nuclear Regulatory Commission Staff Review Guidance for In-Vessel Downstream Effects Supporting Review of GL 2004-02 Responses (Reference 2),

  • the NRC expects that many of the methods developed in the WCAP may be used by pressurized water reactor (PWR) licensees to demonstrate adequate long-term core cooling (LTCC). Completion of the analyses with acceptable results for parameters of interest identified by the review guidance demonstrates compliance with 10 CFR 50.46(b)(5) as it relates to in-vessel downstream debris effects for ANO-1.

0GAN122001 Page 2 of 17 This enclosure follows the NRG review guidance (Reference 2) and PWR Owners Group (PWROG) implementation guidance (Reference 3) to describe the fiber penetration testing and in-vessel analysis, establish in-vessel acceptance criteria, and demonstrate that the criteria are met for ANO-1. Note that this enclosure is a supplement to the previous submittals on GL 2004-02.

Overview of AN0-1 Resolution to GL 2004-02 The following provides a listing of correspondences issued by the NRC or submitted by Entergy for ANO-1 with respect to GL 2004-02 since 2010.

Table 1-1 Correspondence between Entergy and the NRC on GL 2004-02 Correspondence Document (ADAMS Document Date Accession No.)

0GNA011002 NRG letter to Entergy regarding the NRG's conclusion 1/26/2010 (ML100190320) with respect to the review of the previous submittals.

Informed the NRG that Entergy is performing additional 0GAN041001 analysis for both units since the use of WGAP-16568-P 4/8/2010 (ML100980614) zone-of-influence (ZOI) sizes for inorganic zinc primer is no longer acceptable.

Follow-up to the previous letter to inform the NRG that there is sufficient coatings debris margin to address the coating ZOI issue for both units; this letter included a 0GAN091001 9/29/2010 supplement to the previous submittal dated 9/15/2008 (ML102730943)

(0CAN090801) (ML082700499) which included information from submittal dated 9/24/2009 (0CAN090901) (ML092720684).

Informed the NRG that new insulation was discovered 1GAN121101 12/21/2011 inside containment for ANO-1 and committed to (ML120040124) disposition by 3/24/2013.

1GAN031303 Informed the NRC that the newly discovered insulation for 3/20/2013 (ML13080A347) ANO-1 would be removed from containment.

Informed the NRG that Entergy has selected Option 2a 0GAN051301 5/16/2013 using a deterministic methodology to resolve the in-vessel (ML13137A126) downstream effects for ANO-1.

0GAN111402 Request for extension on the resolution of in-vessel 11/26/2014 (ML14330A638) effects.

0GAN051606 Request for extension on the resolution of in-vessel 5/31/2016 (ML16152A662) effects.

0GAN111701 Request for extension on the resolution of in-vessel 11/20/2017 (ML17325B078) effects.

0GAN122001 Page 3 of 17 The January 26, 2010, NRG letter (Reference 12) stated that the NRG had reviewed Entergy's submittals prior to that date and had no further questions regarding the completion of corrective actions for GL 2004-02, except for the resolution of in-vessel downstream effects. At the time, the methodology and acceptance criteria required for the evaluation of in-vessel downstream effects were being reviewed by the NRG.

In March 2017, Entergy held a public meeting with the NRG to discuss the technical approach for new fiber debris penetration testing. Entergy completed the testing at Alden Research Laboratory (Alden) in August 2017. Using the test results, Entergy perforn,ed in-vessel calculations to quantify the fiber debris that could accumulate at the reactor core inlet and within the heated core region using the methodology in WGAP-17788, Revision 0 (Reference 4). In September 2019, the NRG issued the review guidance on the resolution of in-vessel effects (Reference 2), which laid out four different paths that licensees may take to resolve the issue based on the alternative flow path (AFP) analysis in WGAP-17788. Entergy reviewed the new guidance and revised the in-vessel calculations accordingly. Additionally, Entergy adopted the method in the NRG review guidance (Reference 2) and demonstrated that the method is applicable to ANO-1, and that the AFP analysis in WGAP-17788 bounds ANO-1 plant conditions. Refer to Section 3 of this enclosure for further details.

2. General Description of and Schedule for Corrective Actions Provide a general description of actions taken or planned, and dates for each. For actions planned, reference approved extension requests or explain how regulatory requirements will be met as per Requested Information Item 2(b).

GL 2004-02 Requested Information Item 2(b): A general description and implementation schedule for all corrective actions, including any plant modifications that you identify while responding to this GL.

Response

This supplemental response addresses the remaining ANO-1 commitments related to GL 2004-02 as identified in the November 20, 2017, letter (Reference 1) from Entergy to the NRG:

  • Update the ANO-1 in-vessel downstream effects calculation and licensing basis.
  • Submit a final supplemental response to support closure of GL 2004-02.

Entergy has detern,ined that ANO-1 does not require any new modifications or other remediation measures for the closure of GL 2004-02. There are no other outstanding corrective actions associated with GL 2004-02 for AN0-1.

3. Specific Information Regarding Methodology for Demonstrating Compliance 3.n Downstream Effects - Fuel and Vessel The objective of the downstream effects, fuel and vessel section is to evaluate the effects that debris carried downstream of the containment sump screens and into the reactor vessel has on core cooling.

0CAN122001 Page 4 of 17 3.n.1 Show that the in-vessel effects evaluation is consistent with, or bounded by, the industry generic guidance (WCAP-16793-NP), as modified by NRC comments on that document. Briefly summarize the application of the methods. Indicate where the WCAP methods were not used or where exceptions were taken and summarize the evaluation of those areas.

Response

The NRC review guidance for the resolution of in-vessel downstream effects (Reference 2) provided four different paths (identified as Box 1 through Box 4 paths) that PWR licensees may use to resolve the issue based on the AFP analysis in WCAP-17788-P, Revision 1 (Reference 5). Entergy has elected to use the Box 2 path from the NRC review guidance (instead of WCAP-16793-NP) to address in-vessel downstream effects for ANO-1. This response summarizes the fiber penetration testing and in-vessel analyses and demonstrates the applicability of the Box 2 resolution path and the WCAP-17788 AFP analysis for ANO-1. Per the NRC review guidance, the loss-of-coolant accident (LOCA) deposition model analysis and in-vessel analysis for cold leg breaks are not necessary to ensure LTCC and are, therefore, not discussed in the sections below. As summarized in this response, post-accident LTCC is not challenged by accumulation of debris inside the reactor vessel at ANO-1.

Sump Strainer Fiber Penetration Testing Entergy conducted fiber penetration testing in 2017. The purpose of the testing was to collect time-dependent fiber penetration data of the plant strainers. The penetration test program included two tests and was designed with test parameters selected to be representative of the most conservative conditions between ANO-1 and ANO, Unit 2 (ANO-2) (e.g., strainer approach velocity, fiber load, and water chemistry). The second test (Test 2) resulted in slightly higher penetration and was used to derive a model to quantify fiber penetration for the strainers at plant conditions. The penetration test is described below.

Test Loop Design The test loop layout is shown in Figure 3.n.1-1. The main recirculation pump took suction from the test strainer plenum. Discharge from the recirculation pump travels through an isokinetic sampler and was then directed through one of two parallel filter bag housing assemblies. Filter bag housings were outfitted with upstream and downstream isolation valves such that flow could be aligned to either set of filter housing without disruption to flow. This allowed for the online filter housing to be switched during the test in order for clean bags to be brought online while providing continuous filtration.

A portion of flow downstream of the strainers can be diverted through a heat exchanger to maintain the test temperature. Downstream of the heat exchanger a branch was diverted to the plenum which was located behind the test strainer to provide cross-flow that simulated the flow through the duct system or plenums that interconnect the plant strainer modules. The flow rate of this branch was measured and controlled to achieve a cross-flow velocity that is representative of the plant condition.

0CAN122001 Page 5 of 17 Downstream of the branch the flow was split for return discharge into the test tank via the debris introduction hopper or through the flow mixing nozzles in the upstream section of the test tank.

The mixing flow was controlled by a throttle valve to maintain appropriate level of turbulence in the upstream section of the test tank which prevents fiber from settling without disturbing the debris bed on the test strainer. The mixing flow rate was measured by subtracting the hopper flow (from flow meter (FM) 2 as designated in Figure 3.n.1-1) from the total strainer flow (from FM1 ).

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0CAN122001 Page 6 of 17 Test Strainer The ANO-1 strainer is made up of six sections of pocket cartridge strainer modules installed over the containment sump as shown in Figure 3.n.1-2. All but six of the 98 cartridges in the ANO-1 strainer have a pocket depth of 400 mm. The remaining cartridges have a depth of 300 mm.

Figure 3.n.1-2: AN0-1 Plant Strainer

0CAN122001 Page 7 of 17 The test strainer (see Figure 3.n.1-3) consisted of three 400 mm cartridge strainer modules and each module had pockets arranged in a 1Ox 2 array. Being actual plant components, the cartridges have the same key characteristics as the plant strainer. The total surface area of the test strainer was 81.05 ft2

  • The resulting scale factor for ANO-1 was 0.0299 based on plant strainer surface area of 2715 ft2
  • Figure 3.n.1-3: Test Strainer for Fiber Penetration Testing Debris Types and Preparation Debris penetration testing considered only fibrous debris sources. The fibrous debris types at AN0-1 are Temp-Mat, High-Density Fiberglass (HDFG), Thermal Wrap, Cera-Fiber, Cold Leg Penetration Fiber, and latent fiber. Nukon fines were used in testing. This is appropriate since Nukon fibers have similar characteristics as Thermal Wrap and are finer than Temp-Mat and HDFG.

The fiber fines were prepared according to the Nuclear Energy Institute (NEI) protocol (Reference 7). Nukon blankets were heat-treated and cut into 2" x 2" cubes prior to processing.

The tough outer un-burnt layer of the Nukon pieces was separated and torn into smaller pieces to promote a more consistent fiber breakup during processing. A sample of Nukon pieces prior to processing is shown in Figure 3.n.1-4.

0CAN122001 Page 8 of 17 Figure 3.n.1-4: Base Material for Nukon Fines Fiber was placed in a preparation vessel that included a manifold with three high pressure nozzles. The fiber was then wetted with the pre-heated test water until the base material was saturated and the pressure washer nozzle assembly was submerged. The debris was then sprayed with test water pressurized to 1500 psi. The prepared fiber consisted of predominantly Class 2 fibers as defined in NUREG/CR-6224 (Reference 9, Table B-3) including mostly individual fibers with lesser quantities of fiber shards and small entanglements. The duration of the spray was controlled to provide consistent fiber slurry characteristics between different batches. Each batch of prepared fiber was photographed and an example is shown in Figure 3.n.1-5.

Figure 3.n.1-5: Prepared Nukon Fiber Fines

0CAN122001 Page 9 of 17 Debris Introduction Fine fiber debris was introduced via a debris hopper in five separate batches. As shown in Figure 3.n.1-6, debris was added to the hopper via the top opening. Velocity and turbulence from the hopper inflow from the bottom of the hopper was sufficient to break up any debris agglomerations that occurred.

Figure 3.n.1-6: Debris Introduction Hopper Debris added to hopper The debris batching schedule was set to introduce smaller debris batches first when the strainer has more surface area that was free of debris and then larger fiber batches as the fiber bed grew. The first two batches had a theoretical uniform bed thickness of 1/16" each and the last three were 1/8" each. The testing evaluated a fiber quantity equivalent to the total ANO-2 fibrous debris load of 213 lbm which bounds the ANO-1 fiber load of 115 lbm.

Before adding a batch of debris, the test tank and debris hoppers were visually checked to verify that all introduced debris had transported to the strainer. Between batches the debris introduction rate was controlled to maintain a prototypical concentration in the test tank.

There was no settled or floating debris observed after the addition of each debris batch. Debris bed development on the test strainer was relatively uniform throughout the duration of the test.

The strainer loading after the final debris batch is shown in Figure 3.n.1-7.

0CAN122001 Enclosure 1 Page 10 of 17 Figure 3.n.1-7: Penetration Test Strainer Fiber Loading Debris Capture Fiber can penetrate through the strainer by two different mechanisms (prompt penetration and shedding). Prompt penetration occurs when fiber reaching the strainer travels through the strainer immediately. Shedding occurs when fiber that already accumulated on the strainer migrates through the bed and ultimately travels through the strainer. Both mechanisms were considered during testing.

After passing through the strainer the flow traveled through five-micron filter bags where fiber that passed through the strainer was collected. The capture efficiency of the filter bags was verified to be above 97%. The filtering system had two sets of filter bags installed in parallel lines such that one set of filter bags was left online at all times, and switchover between filter bag sets was allowed .

0CAN122001 Page 11 of 17 A clean set of filter bags was placed online before a debris batch was introduced to the test tank and was left online tor a minimum of three hopper turnovers and one tank turnover to capture the prompt fiber penetration. For each batch, at least one additional set of filter bags was used tor a minimum of 30 minutes to capture the fiber penetration due to shedding. After adding the third debris batch, the second set of shedding filter bags was left online tor one hour to characterize longer-term shedding. The final set of shedding filter bags after Batch 5 was left online for over tour hours to further characterize the long-term fiber shedding. This approach allowed the testing to capture time-dependent fiber penetration data which was used to develop a model tor the rate of fiber penetration as a function of time and fiber quantity on the strainer.

Before and after each test the filter bags required tor the test were uniquely marked and dried, and their weights were recorded. The weight gain of the filter bags during testing was used to quantify fiber penetration. After testing, the debris-laden filter bags were rinsed with deionized (DI) water to remove residual chemicals before being dried and weighed. When processing the filter bags, in either a clean or debris laden state, the bags were placed in an oven for at least an hour before being cooled and weighed inside a humidity-controlled chamber. This process was repeated for each bag until two consecutive bag weights were within 0.05 g of each other.

Test Parameters The chemical condition selected for Test 2 had a boron concentration of 2154 ppm and a sodium tetraborate (NaTB) buffer concentration of 7.545 g/L which are the concentrations associated with the maximum pH during recirculation (8.0) for ANO-2. Test water was prepared by adding pre-weighed chemicals to DI water per the prescribed concentrations. ANO-1 water chemistry corresponding to the maximum pH during recirculation (9.0) has a boron concentration of 1861 ppm and a sodium hydroxide (NaOH) buffer concentration of 0.0803 mol/L. This water chemistry was used for Test 1, which resulted in slightly less penetration than Test 2.

The target strainer flow rate for the penetration testing was 290 gpm which corresponds to a test approach velocity of 0.008 ft/s. This is equivalent to the average approach velocity for one-train operation at ANO-1 . The test flow rate was maintained within -0% to +5% of the target flow rate tor 100% of the test duration. Note that the average approach velocity for two-train operation at ANO-1 of 0.004 ft/s was used in Test 1 which resulted in slig htly less penetration than Test 2.

ANO-1 Strainer Penetration Model Data gathered from Test 2 were used to develop a model tor quantifying the strainer fiber penetration under plant conditions. The model was developed per the following steps:

  • Governing equations were developed to describe both the prompt fiber penetration and shedding through the strainer as a function of time and fiber quantity on the strainer. The equations contain coefficients with values determined separately tor each test based on the individual test results.
  • The results for each test were fit to the governing equations using various optimization techniques to refine the coefficient values. This produced a unique set of equations and thus a unique penetration model for each test. Figure 3.n.1-8 compares the Test 2 penetration results (shown as circles) with the fiber penetration model results using the Test 2 conditions (shown as blue solid line). As Figure 3.n.1-8 shows, the model results adequately represent the test data.

0CAN122001 Enclosure 1 Page 12 of 17 Figure 3.n.1-8: Test 2 Cumulative Fiber Bypass Fit 100 f;()O -

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The penetration models from the previous step can then be used to determine the prompt fiber penetration fraction and shedding fraction for a given time and amount of fiber accumulated on the strainer. Coupled with a fiber transport model, a time-dependent evaluation can be performed to quantify the total amount of fiber that could pass through the strainer under certain plant conditions.

An example application of the model using ANO-1 conditions, which demonstrates how time-dependent penetration can be determined for the in-vessel analysis, is shown below. For the time-dependent analysis, the recirculation duration was divided into smaller time steps. For each time step, the fiber penetration rates and quantities were calculated. The transportable fiber in the pool is assumed to be uniformly distributed. Figure 3.n.1-9 shows the resulting cumulative fiber penetration through the strainer over time.

0CAN122001 Page 13 of 17 Figure 3.n.1-9: Test 2 Penetration Model at Plant Scale 1AOOO 1lOOO UIOOO V

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0CAN122001 Page 14 of 17 Figure 3.n.1-11: ANO Shedding Rate Calculated

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Evaluation for Accumulation of Fiber inside Reactor Vessel The accumulation of fiber debris that passes through the strainer during the post-accident sump recirculation phase inside the reactor vessel was evaluated for hot leg break (HLB) scenarios using the methodology of WCAP-17788-P, Revision 1 (Reference 5). Cold leg break scenarios are not discussed, as the NRC review of the cold leg break fiber amounts is not necessary to assure compliance with LTCC requirements (Reference 10). The evaluation used time-dependent fiber penetration fractions obtained from ANO testing, as described earlier in this response. The penetration fraction varies with the amount of fiber on the strainer and the amount of time passed since the onset of recirculation.

A bounding evaluation for ANO-1 breaks was performed, and the duration of the overall recirculation phase was divided into small time steps. For each time step, the following computation was performed to quantify the fiber that passes through the strainer:

  • The fractions of prompt and shedding penetration are calculated using the ANO fiber penetration model equations based on the quantity of fine fiber collected on the strainer at the beginning of the time step.
  • The amount of fine fiber that arrives at the strainer during the current time step is calculated by multiplying the fine fiber concentration in the pool by the strainer flow rate and time step.
  • The amount of prompt penetration is calculated by multiplying the prompt penetration fraction from Step 1 by the amount of fine fiber arriving at the strainer during the current time step from Step 2.

0CAN122001 Page 15 of 17

  • The amount of shedding penetration is calculated by multiplying the shedding penetration fraction from Step 1 by the amount of fiber collected on the strainer at the beginning of the time step.
  • The fiber that passes through the strainer is then split based on the ratio in flow rate between the ECCS pumps and RBSS pump.
  • The fiber transported by the ECCS pumps reaches the reactor and is assumed to accumulate at the core inlet only, without crediting the AFPs. This is consistent with the NRG review guidance. The fiber carried by the RBSS pump is returned to the sump pool.

The pool fiber concentration is updated as an initial condition for the next time step.

The total in-vessel fiber load was calculated by summing up the amount of fiber that reaches the reactor during each time step. The calculated fiber load was increased by 7% to account for the uncertainty in the curve-fit of the fiber penetration test data.

The evaluation included eight cases using different combinations of input parameters to ensure the largest in-vessel fiber load is captured. The bounding HLB analysis case had two ECCS trains in operation at the maximum flow rate, maximu~ sump pool volume, maximum fiber load and one RBSS train in operation at minimum flow rate. The worst case in-vessel results of the hand calculation are summarized in the table below.

Table 3.n.1-1: Bounding In-vessel Fiber Loads for HLB Scenarios Maximum Core Inlet Fiber Load (g/FA) 77.94 Maximum Total Reactor Vessel Fiber Load (g/FA) 77.94 The ANO-1 in-vessel downstream effects analysis has the following conservatisms:

  • All fiber that reaches the reactor was conservatively assumed to accumulate at the reactor core inlet. Some fraction of fibrous debris would actually penetrate the core inlet or bypass the core inlet via AFPs.
  • The in-vessel analysis was continued until less than 0.1 % of the sump fiber load remains in the sump pool. This is an order of magnitude less than the WCAP-1 naa acceptance criteria and allows for a longer period of shedding bypass to occur.
  • The evaluation used the full surface area of the strainer, conservatively neglecting the potential reduction in strainer surface area due to blockage by miscellaneous debris.

Resolution of In-Vessel Downstream Effects using WCAP-17788 AFP Analysis As discussed above, Entergy has elected to use the Box 2 path from the NRG review guidance (Reference 2) to address in-vessel downstream effects for ANO-1, which is outfitted with a Babcock & Wilcox (B&W) nuclear steam supply system. The Box 2 path is specifically for B&W units and is therefore applicable for ANO-1.

0CAN122001 Page 16 of 17 For the Box 2 resolution path, the following infonnation is required:

  • Confirmation that the maximum amount of fiber that may arrive at the core inlet and heated core for HLB is below the WCAP-17788-P, Revision 1 (Reference 5) fiber limit.

The largest total in-vessel fiber load is 77.94 g/FA which is less than the fiber limit shown in Section 6.5 of WCAP-17788-P Volume 1, Revision 1 (Reference 5).

  • Confirmation that boric acid precipitation (BAP) mitigation measures are taken prior to 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> after a LOCA.

BAP is precluded by the inherent design of the B&W reactor without requiring operator actions. Specifically, during post-LOCA long-tenn recirculation,, flow through the leakage gaps between the reactor vessel outlet nozzles and the core support shield is shown to be adequate to dilute the boron concentration sufficiently to avoid precipitation. The NRC previously reviewed and concurred with this conclusion (Reference 8). The evaluation also showed that the leakage gap flow paths become active during the reflooding period following an accident. Aside from the passive leakage flow paths, ANO-1 has an operating procedure with operator actions to mitigate BAP as a defense-in-depth measure.

Since both criteria are satisfied, in-vessel downstream effects for ANO-1 are bounded by the WCAP-17788 AFP analysis and would not challenge LTCC.

3.p Licensing Basis The objective of the licensing basis is to provide infonnation regarding any changes to the plant licensing basis due to the sump evaluation or plant modifications.

3.p.1 Provide the infonnation requested in GL 2004-02 Requested Information Item 2(e) regarding changes to the plant-licensing basis. The effective date for changes to the licensing basis should be specified. This date should correspond to that specified in the 10 CFR 50.59 evaluation for the change to the licensing basis.

GL 2004-02 Requested Information Item 2(e): A general description of and planned schedule for any changes to the plant licensing bases resulting from any analysis or plant modifications made to ensure compliance with the regulatory requirements listed in the Applicable Regulatory Requirements section of this GL. Any licensing actions or exemption requests needed to support changes to the plant licensing basis should be included.

Response

The ANO-1 Safety Analysis Report has been updated to incorporate the in-vessel downstream effects analysis and conclusions. No other licensing actions or exemption requests are required.

0CAN122001 Page 17 of 17

4. References
1. Entergy Operations, Inc. (Entergy) letter to U.S. Nuclear Regulatory Commission (NRC), "Generic Letter 2004-02 Commitment Extension," Arkansas Nuclear One -

Units 1 and 2, (OCAN111701) (ML17325B078), dated November 20, 2017.

2. NRC Memorandum, "U.S. NRC Staff Review Guidance for In-Vessel Downstream Effects Supporting Review of GL 2004-02 Responses,* (ML19228A011), dated September 4, 2019.
3. PWROG-16073-P, "TSTF-567 Implementation Guidance, Evaluation of In-Vessel Debris Effects, Submittal Template for Final Response to GL 2004-02 and FSAR Changes," Revision 0, dated February 2020.
4. WCAP-17788-P, Volumes 1 - 6, "Comprehensive Analysis and Test Program for GSl-191 Closure (PA-SEE-1090)," Revision 0, dated July 2015.
5. WCAP-17788-P, Volumes 1 - 6, "Comprehensive Analysis and Test Program for GSl-191 Closure (PA-SEE-1090)," Revision 1, dated December 2019.
6. WCAP-16530-NP-A, "Evaluation of Post-Accident Chemical Effects in Containment Sump Fluids to Support GSl-191,
  • dated March 2008 (this reference is not utilized for ANO-1 but kept in the list to maintain consistency with ANO-2 references).
7. Nuclear Energy Institute, "201 Fibrous Debris Preparation, Processing, Storage, and Handling," Revision 1 (ML120481057), dated January 2012.
8. NRC letter to B&W Owners Group, "Post-LOCA Reactor Vessel Recirculation to Avoid Boron Precipitation," dated March 9, 1993.
9. NUREG/CR-6224, "Parametric Study of the Potential for BWR ECCS Strainer Blockage due to LOCA-Generated Debris," (ML083290498), dated October 1995.
10. NRC Technical Evaluation Report, "Staff Technical Evaluation of In-Vessel Debris Effects,* (ML19178A252), dated June 13, 2019.
11. Entergy letter to NRC, "Generic Letter 2004-02 Closure Option," ANO - Units 1 and 2, (0CAN051301) (ML13137A126), dated May 16, 2013.
12. NRC letter to Entergy, *Arkansas Nuclear One, Units 1 and 2 - Generic Letter 2004-02 Supplemental Response (TAC Nos. MC4663 and MC4664)," (0CNA011002)

(ML100190320), dated January 26, 201 0.

ENCLOSURE 2 0CAN122001 AN0-2 FINAL RESPONSE TO NRC GENERIC LETTER 2004-02

0CAN122001 Page 1 of 13 AN0-2 FINAL RESPONSE TO NRC GENERIC LETTER (GL) 2004-02 Updated Resolution to In-Vessel Downstream Effects for AN0-2 Table of Contents Section Page 1 Overall Compliance ............................................................................. ..................... 1 2 General Description of and Schedule for Corrective Actions ......................................... 3 3 Specific Information Regarding Methodology for Demonstrating Compliance ................. 3 4 References .....................................................................................................................12

1. Overall Compliance Provide information requested in Generic Letter (GL) 2004-02, "Potential Impact of Debris Blockage on Emergency Recirculation during Design Basis Accidents at Pressurized-Water Reactors (PWRs)," Requested Information Item 2(a), regarding compliance with regulations.

GL 2004-02 Requested Information Item 2(a): Confirmation that the emergency core cooling system (EGGS) and containment spray system (GSS) recirculation functions under debris loading condffions are or will be in compliance with regulatory requirements listed in the Applicable Regulatory Requirements section of this GL. This submittal should address the configuration of the plant that will exist once all modifications required for regulatory compliance have been made and this licensing basis has been updated to reflect the results of the analysis described above.

Response

In accordance with SECY-12-0093 and as identified in Entergy Operations, Inc. (Entergy) letter to the NRC dated May 16, 2013 (Reference 11), Entergy elected to pursue Generic Safety Issue (GSl)-191 Closure Option 2a, utilizing a deterministic methodology for both strainer and in-vessel effects for Arkansas Nuclear One, Unit 2 (ANO-2). Topical Report WCAP-17788-P, "Comprehensive Analysis and Test Program for GSl-191 Closure (PA-SEE-1090)," Revision 1 (Reference 5), provides evaluation methods and results to address in-vessel downstream effects. As discussed in the NRC Technical Evaluation Report of in-vessel effects (Reference 10), the NRC has performed a detailed review of WCAP-17788-P. Although the NRC did not issue a Safety Evaluation for WCAP-17788, as discussed further in NRC Memorandum, "U.S. Nuclear Regulatory Commission Staff Review Guidance for In-Vessel Downstream Effects Supporting Review of GL 2004-02 Responses" (Reference 2), the NRC expects that many of the methods developed in the WCAP can be used by pressurized water reactor (PWR) licensees to demonstrate adequate long-term core cooling (LTCC). Completion of the analyses with acceptable results for parameters of interest identified by the review guidance demonstrates compliance with 10 CFR 50.46(b)(5) as it relates to in-vessel downstream debris effects for ANO-2.

0GAN122001 Page 2 of 13 This enclosure follows the NRG review guidance (Reference 2) and PWR Owners Group (PWROG) implementation guidance (Reference 3) to describe the fiber penetration testing and in-vessel analysis, establish in-vessel acceptance criteria, and demonstrate that the criteria are met for AN0-2. Note that this enclosure is a supplement to the previous submittals on GL 2004-02.

Overview of AN0-2 Resolution to GL 2004-02 The following provides a listing of correspondences issued by the NRG or submitted by Entergy for ANO-2 with respect to GL 2004-02 since 2010.

Table 2-1 Correspondence between Entergy and the NRC on GL 2004-02 Correspondence Document (ADAMS Document Date Accession No.)

0GNA011002 NRG letter to Entergy regarding the NRG's conclusion 1/26/2010 (ML100190320) with respect to the review of the previous submittals.

lnfonned the NRG that Entergy is perfonning additional 0GAN041001 analysis for both units since the use of WGAP-16568-P 4/8/2010 (ML100980614) zone-of-influence (201) sizes for inorganic zinc primer is no longer acceptable.

Follow-up to the previous letter to inform the NRG that there is sufficient coatings debris margin to address the coating 201 issue for both units; this letter included a 0GAN091001 9/29/2010 supplement to the previous submittal dated 9/15/2008 (ML102730943)

(0GAN090801) (ML082700499) which included information from submittal dated 9/24/2009 (0GAN090901) (ML092720684).

lnfonned the NRG that Entergy has selected Option 2a 0GAN051301 5/16/2013 using a deterministic methodology to resolve the in-vessel (ML13137A126) downstream effects for ANO-2.

0GAN111402 Request for extension on the resolution of in-vessel 11/26/2014 (ML14330A638) effects.

0GAN051606 Request for extension on the resolution of in-vessel 5/31/2016 (ML16152A662) effects.

0GAN111701 Request for extension on the resolution of in-vessel 11/20/2017 (ML17325B078) effects.

The January 26, 2010, NRG letter (Reference 12) stated that the NRG had reviewed Entergy's submittals prior to that date and had no further questions regarding the completion of corrective actions for GL 2004-02, except for the resolution of in-vessel downstream effects. At the time, the methodology and acceptance criteria required for the evaluation of in-vessel downstream effects were being reviewed by the NRG.

0CAN122001 Page 3 of 13 In March 2017, Entergy held a public meeting with the NRC to discuss the technical approach for new fiber debris penetration testing. Entergy completed the testing at Alden Research Laboratory (Alden) in August 2017. Using the test results, Entergy perfonned in-vessel calculations to quantify the fiber debris that could accumulate at the reactor core inlet and within the heated core region using the methodology in WCAP-17788, Revision 0 (Reference 4). In September 2019, the NRC issued the review guidance on the resolution of in-vessel effects (Reference 2), which laid out four different paths that licensees may take to resolve the issue based on the alternative flow path (AFP) analysis in WCAP-17788. Entergy reviewed the new guidance and revised the in-vessel calculations accordingly. Additionally, Entergy adopted the method in the NRC review guidance (Reference 2) and demonstrated that the method is applicable to ANO-2, and the AFP analysis in WCAP-17788 bounds ANO-2 plant conditions.

Refer to Section 3 of this enclosure for further details.

2. General Description of and Schedule for Corrective Actions Provide a general description of actions taken or planned, and dates for each. For actions planned, reference approved extension requests or explain how regulatory requirements will be met as per Requested lnfonnation Item 2(b).

GL 2004-02 Requested Information Item 2(b): A general description and implementation schedule for all corrective actions, including any plant modifications that you identify while responding to this GL.

Response

This supplemental response addresses the remaining AN0-2 commitments related to GL 2004-02 as identified in the November 20, 2017 letter (Reference 1) from Entergy to the NRC:

  • Update the AN0-2 in-vessel downstream effects calculation and licensing basis.
  • Submit a final supplemental response to support closure of GL 2004-02.

Entergy has determined that ANO-2 does not require any new modifications or other remediation measures for the closure of GL 2004-02. There are no other outstanding corrective actions associated with GL 2004-02 for ANO-2.

3. Specific Information Regarding Methodology for Demonstrating Compliance:

3.n Downstream Effects - Fuel and Vessel The objective of the downstream effects, fuel and vessel section is to evaluate the effects that debris carried downstream of the containment sump screens and into the reactor vessel has on core cooling.

3.n.1 Show that the in-vessel effects evaluation is consistent with, or bounded by, the industry generic guidance (WCAP-16793-NP), as modified by NRC comments on that document. Briefly summarize the application of the methods. Indicate where the WCAP methods were not used or where exceptions were taken and summarize the evaluation of those areas.

0GAN122001 Page 4 of 13

Response

The NRG review guidance for the resolution of in-vessel downstream effects (Reference 2) provided four different paths (identttied as Box 1 through Box 4 paths) that PWR licensees may use to resolve the issue based on the AFP analysis in WGAP-17788-P, Revision 1 (Reference 5). Entergy has elected to use the Box 4 path from the NRG review guidance (instead of WGAP-16793-NP) to address in-vessel downstream effects for ANO-2. This response summarizes the fiber penetration testing and in-vessel analyses and demonstrates the applicability of the Box 4 resolution path and the WGAP-17788 AFP analysis for ANO-2. Per the NRG review guidance, the loss-of-coolant (LOGA) deposition model analysis and in-vessel analysis for cold leg breaks are not necessary to ensure LTGG and are therefore not discussed in the sections below. As summarized in this response, post-accident LTGG is not challenged by accumulation of debris inside the reactor vessel at ANO-2.

Sump Strainer Fiber Penetration Testing ANO fiber penetration testing is described in Enclosure 1.

Test Loop Design The ANO test loop design is described in Enclosure 1.

Test Strainer The ANO-2 strainer consists of sections of pocket cartridge strainer modules installed on two opposite sides of suction plenums where each module is made up of multiple strainer pocket cartridges as shown in Figure 3.n.1-12. The strainer modules vary by pocket depth, with pocket depths of 100 mm, 200 mm, and 400 mm. The total area of the strainer is 4,837 ft 2

  • The test strainer is described in Enclosure 1. The area ratio of the test strainer to the plant strainer results in a test scale of 0.0168 for ANO-2.

Figure 3.n.1-12: AN0-2 Strainer

0CAN122001 Page 5 of 13 Debris Types and Preparation The fibrous debris types at AN0-2 are Thennal-Wrap, Cera-fiber, and latent fiber. Nukon fines were used in testing. Test fiber debris types and preparation are discussed in Enclosure 1.

Debris Introduction Test debris introduction is discussed in Enclosure 1.

Debris Capture Debris capture is discussed in Enclosure 1 .

Test Parameters AN0-2 water chemistry corresponding to the maximum pH during recirculation (8.0) has a boron concentration of 2154 ppm and a sodium hydroxide (NaTB) buffer concentration of 7.545 g/1.

The water chemistry used in penetration testing is discussed in Enclosure 1.

The average approach velocity for two-train operation at AN0-2 is 0.00325 ft/s.

The approach velocity used in penetration testing is discussed in Enclosure 1.

AN0-2 Strainer Penetration Model Development of the penetration model is discussed in Enclosure 1.

Evaluation for Accumulation of Fiber inside Reactor Vessel The accumulation of fiber debris that passes through the strainer during the post-accident sump recirculation phase inside the reactor vessel was evaluated for hot leg break (HLB) scenarios using the methodology of WCAP-1TT88-P, Revision 1 (Reference 5). Cold leg break scenarios are not discussed, as the NRC review of the cold leg break fiber amounts is not necessary to assure compliance with LTCC requirements (Reference 10). The evaluation used time-dependent fiber penetration fractions obtained from ANO testing, as described earlier in this response. The penetration fraction varies with the amount of fiber on the strainer and the amount of time passed since the onset of recirculation.

A bounding evaluation for the ANO-2 breaks was perfonned, and the duration of the overall recirculation phase was divided into small time steps. For each time step, the following computation was perfonned to quantify the fiber that passes through the strainer:

  • The fractions of prompt and shedding penetration are calculated using the ANO fiber penetration model equations based on the quantity of fine fiber collected on the strainer at the beginning of the time step.
  • The amount of fine fiber that arrives at the strainer during the current time step is calculated by multiplying the fine fiber concentration in the pool by the strainer flow rate and time step.

0CAN122001 Page 6 of 13

  • The amount of prompt penetration is calculated by multiplying the prompt penetration fraction from Step 1 by the amount of fine fiber arriving at the strainer during the current time step from Step 2.
  • The amount of shedding penetration is calculated by multiplying the shedding penetration fraction from Step 1 by the amount of fiber collected on the strainer at the beginning of the time step.
  • The fiber that passes through the strainer is then split based on the ratio in flow rate between the ECCS pumps and CSS pump.
  • The fiber transported by the ECCS pumps reaches the reactor and is assumed to accumulate at the core inlet only, without crediting the AFPs. This is consistent with the NRC review guidance. The fiber carried by the CSS pumps is returned to the sump pool.

The pool fiber concentration is updated as an initial condition for the next time step.

The total in-vessel fiber load was calculated by summing up the amount of fiber that reaches the reactor during each time step. The calculated fiber load was increased by 7% to account for the uncertainty in the curve-fit of the fiber penetration test data.

The evaluation included eight cases using different combinations of input parameters to ensure the largest in-vessel fiber load is captured. The bounding HLB analysis case had two ECCS trains in operation at the maximum flow rate, maximum sump pool volume, maximum fiber load and one CSS train in operation at minimum flow rate. The worst case in-vessel results of the hand calculation are summarized in the table below.

Table 3.n.1-2: Bounding In-Vessel Fiber Loads for HLB Scenarios Maximum Core Inlet Fiber Load (g/FA) 72.52 Maximum Total Reactor Vessel Fiber Load (g/FA) 72.52 Resolution of In-Vessel Downstream Effects using WCAP-17788 AFP Analysis As discussed above, Entergy has elected to use the Box 4 path from the NRC review guidance (Reference 2) to address in-vessel downstream effects for ANO-2 which is outfitted with a Combustion Engineering (CE) nuclear steam supply system. To use this method, key in-vessel parameters of ANO-2 need to be compared with those assumed in the WCAP-17788 analysis to demonstrate applicability, as required in the NRC review guidance. Table 3.n.1-3 compares the plant parameters with those used in the WCAP-17788. More detailed discussions of the comparison are presented following Table 3.n.1-3.

0CAN122001 Page 7 of 13 Table 3.n.1-3: Summary of In-Vessel Effects Parameters Parameters WCAP-1TT88 Revision 1 Values AN0-2 Values NSSS Design Various CE Westinghouse 16 x 16 Next Fuel Type Various Generation Fuel (NGF)

Minimum Chemical 333 minutes (lti1ock from 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> after accident Precipitation Time WCAP-17788, Volume 1, Table 6-1)

Maximum Hot Leg N/A Five hours after accident Switchover (HLSO) Time Maximum Core Inlet WCAP-17788, Volume 1, Table 6-3 72.52 g/FA Fiber Load for HLB Maximum In-Vessel Fiber WCAP-17788, Volume 1, 72.52 g/FA Load for HLB Section 6.4 Minimum Sump 20 minutes 30.03 minutes Switchover (SSO) Time Maximum Rated Thermal 3458 MWt 3026 MWt Power Maximum AFP WCAP-17788, Volume 4, WCAP-17788, Volume 4, Table 6-3 Resistance Table RAl-4.3-8 ECCS Flow per Fuel 3.8 - 11.4 gpm/FA 4.1 -10.2 gpm/FA Assembly (FA)

Comparison of AN0-2 Chemical Precipitation Time with HLSO Time and tb1ock For ANO-2 chemical precipitation was shown to occur after the latest HLSO time and after the time that complete core inlet blockage can be tolerated which is defined in WCAP-17788 as lti1ock,

  • ANO-2 chemical precipitation time (barn) - Chemical precipitation is shown not to occur within 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> for containment sump temperatures above 135 °F following the accident based on the autoclave testing in WCAP-17788, Volume 5. This was determined using a precipitation map to compare the sump aluminum concentration estimated with the WCAP-16530 methodology with the sodium tetraborate (NaTB) group autoclave test results and the WCAP-17788 precipitation boundary equation (see Figure 3.n.1-13).

The aluminum concentration results from the WCAP-17788 autoclave tests that used NaTB buffer are shown in Figure 3.n.1-13 as plus signs. Test results where precipitation was detected are overlaid with red dots. The WCAP-17788 precipitation boundary equation is also plotted on the figure for pH values from 7.1 to 8.0, which is representative of the ANO-2 long-term containment sump pH range. The WCAP precipitation boundary at a pH of 7.1 (solid gray curve) is used in this analysis for pH values from 7.1 to 8.0 because it conservatively minimizes aluminum solubility (high p[AI]).

0CAN122001 Page 8 of 13 Using the minimum ANO-2 containment sump pH of 7.1 and the maximum sump aluminum concentration after 30 days from the WCAP-16530 methodology (3.6 ppm), the pH + p[AI] was calculated to be 10.97 which crosses the precipitation boundary at a temperature of 102 °F (black dashed line). Note that the ANO-2 WCAP-16530 analysis used the maximum containment sump pH profile to maximize aluminum release, which is conservatively combined with the minimum pH to determine the pH + p[AI] value. To provide additional aluminum margin, an aluminum concentration of 12 ppm is used to determine a lower pH+[AI] value than determined using plant specific values. This results in a pH+ p[AI] of 10.45 {black solid line) which crosses the precipitation boundary in Figure 3.n.1-13 at approximately 135 °F.

Post-accident sump conditions following a 0.01 ft2 break showed that, even for this small break, the sump temperature stays above 180 °F after switchover to sump recirculation up to 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> following the accident. Therefore, containment sump temperatures below 135 °F by 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> would be indicative of a significantly less severe accident than simulated using the WCAP-16530 methodology. It is concluded that, for ANO-2, chemical precipitation would not occur within 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> after a LOCA.

Site-specific autoclave testing was previously performed by Entergy to credit aluminum solubility for containment sump strainer head loss. This testing was described in the September 15, 2008, Supplemental Response in Section 3.o.2.9.iii of Attachment 2 (Reference 13). The autoclave tests with aluminum content representative of the ANO-2 amounts did not show evidence of chemical precipitation starting via increased filtration times until the solution was cooled to near ambient temperatures (84 °F). The autoclave tests with approximately 18 times the aluminum in the ANO-2 containment did not identify chemical precipitation until, at most, a temperature of 130 °F, indicated by slightly higher filtration times. These results support, with margin, the temperatures determined using the WCAP-17788 precipitation boundary methodology with aluminum concentrations determined using the WCAP-16530 methodology as described above.

  • ANO-2 HLSO time -ANO-2 maximum HLSO time is five hours after the event.
  • Time of fb1ock used in WCAP-17788 - WCAP-17788 used a foo:k of 333 minutes for the CE plants which is applicable to ANO-2.

0CAN122001 Page 9 of 13 Figure 3.n.1-13: Aluminum Precipitation Map for NaTB Buffer 13.500 13.000 +

++

12.500 t

+ +

12.000 i+ *

+

~

~ 11 .500 I

a. ..... ....

11 .000 - - - - - -

. . . ::::- -....-~ - - - - - *-- - - - - - - - - - - -

+/- ..... ..... .

  • ..._ .... , ...._ I 10500

. ------------------- - .t.._ -

  • -- ~--..

10.000 9.500 t*

-i--

60 70 80 90 100 110 120 130 140 150 160 170 lenl)erature ("F)

- WCN'P.Boundary - pl-l 7.1 WCN' P.Boundary - pl-I 7.5

- * - WCAP P.BoundaJy - pl-I 8.0 + WCAP-17788-NP Autoclave Tests

- - - ANO Unit 2 Min pH+p(AI) (3.6 ppm Al)

  • Al Preq,itation Detected

- Min. pH+p[~) w/Margin (12 ppm Al)

Comparison of AN0-2 In-Vessel Fiber Load with WCAP-17788 Limit The maximum amount of fiber that may arrive at the core inlet for ANO-2 during a HLB exceeds the core inlet fiber limit but is less than the total in-core fiber limit presented in WCAP-17788.

  • WCAP-17788 HLB core inlet fiber limit- The core inlet fiber limit that is applicable for ANO-2 (i.e., CE NSSS with Westinghouse fuel) is in Table 6-3 of WCAP-17788 Volume 1 (Reference 5). The ANO-2 FA pitch matches that of the 16 x 16 NGF fuel shown in Table RAl-1 .1-1 of WCAP-17788, Volume 1 (Reference 5). The core inlet fiber limit was adjusted by applying a scaling factor Rm as defined in Section 6.5.5 of WCAP-17788, Volume 1 (Reference 5).
  • WCAP-17788 HLB total in-core fiber limit- The total in-core fiber limit is in Section 6.4 of WCAP-17788, Volume 1 (Reference 5).

0CAN122001 Page 10 of 13

  • ANO-2 HLB core inlet fiber load - The maximum core-inlet fiber load during a HLB for ANO-2 is 72.52 g/FA. As stated previously in this response, the evaluation analyzed various combinations of input parameters to ensure the maximum core inlet fiber load is captured. Per the latest NRC review guidance (Reference 2), the flow split between the core inlet and AFPs was not credited. All the fiber that reaches the reactor is assumed to accumulate at the core inlet.

The WCAP-17788 core inlet fiber limit was derived based on the assumption that debris accumulates uniformly at the reactor core inlet. In reality, the debris bed at the core inlet would not be uniform due to non-uniform flow, and it would therefore take more debris than determined by WCAP-17788 to completely block the core inlet and activate the AFPs, as discussed in the NRC review guidance (see Reference 2, Appendix B). Because of the expected non-uniform debris loading, the debris head loss at the core inlet would be lower than predicted in WCAP-17788. Lower head loss would allow additional fiber accumulation beyond the core inlet fiber limit where complete core blockage is predicted to occur in the WCAP. By definition, if the head loss at the core inlet is not high enough to activate flow through the AFPs, the core is continuing to receive sufficient flow for LTCC through the core inlet. As described in WCAP-17788, LTCC is assured as long as the total amount of fiber to the Reactor Coolant System (RCS) remains below the total in-core fiber limit. Therefore, it is reasonable to use the total in-core fiber limit as the acceptance criterion for HLBs. For ANO-2, the maximum.quantity of fiber predicted to reach the reactor core (72.52 g/FA) is lower than the WCAP-17788 total in-core fiber limit. As a result, the accumulation of fiber inside the reactor core would not challenge LTCC.

Comparison of AN0-2 SSO Time with that Assumed in WCAP-17788 The earliest SSO times for AN0-2 are greater than that assumed in the WCAP-17788 analysis.

  • ANO-2 SSO time - The SSO time marks the beginning of sump recirculation and fiber accumulation inside the reactor vessel. For ANO-2, the shortest duration for injection from the refueling water tank is 30.03 minutes.
  • The SSO time assumed in the WCAP-17788 analysis is 20 minutes (Reference 5, Volume 4, Table 6-3).

Compa,rison of Maximum Thermal Power with that Assumed in WCAP-17788 The maximum rated thermal power for ANO-2 is less than the analyzed power level in WCAP-17788 for a CE plants.

  • ANO-2 rated thermal power - ANO-2 maximum rated thermal power is 3026 MWt.
  • Thermal power assumed in WCAP-17788 - The WCAP analysis used a thermal power of 3458 MWt for the CE plants, as shown in Table 6-3 of WCAP-17788, Volume 4 (Reference 5).

The later SSO time and lower thermal power for ANO-2, compared with those analyzed in WCAP-17788, resulted in lower decay heat at the SSO time for ANO-2 than the WCAP analysis. The ANO-2 LOCA containment analysis used a decay heat curve determined using

0CAN122001 Page 11 of 13 the methodology in the 1981 NRG Branch Technical Position A8B-9.2, Revision 2. The methodology included an uncertainty factor of 20% up to 1000 seconds and a factor of 10%

from 1000 to 107 seconds after shutdown. From this curve, the decay heat ratio at the earliest ANO-2 880 time of 30.03 minutes (or 1801.8 seconds) was calculated to be 0.02173 from linear interpolation. The decay heat at this 880 time is then calculated to be 65.8 MWt based on the ANO-2 thennal power of 3026 MWt. This decay heat for ANO-2 is lower than and, therefore, bounded by that analyzed in WCAP-17788 for CE plants based on the assumed 880 time of 20 minutes and thennal power of 3458 MWt.

Comparison of AN0-2 Reactor AFP Resistance with that Assumed in WCAP-17788 The ANO-2 AFP resistance is less than that analyzed in WCAP-17788.

  • ANO-2 reactor AFP resistance - The ANO-2 AFP resistance is presented in Table RAl-4.3-8 of WCAP-17788, Volume 4 (Reference 5) as "Total Adjusted K/A 2 (ft4)."
  • AFP resistance assumed in WCAP-17788 - The AFP resistance used in the WCAP-17788 analysis that is applicable for ANO-2 (i.e., CE Plant) is provided in Table 6-3 of WCAP-17788, Volume 4 (Reference 5) as "Barrel/Baffle Total K/A2 " for the Max Resistance Cases.

As discussed in the PWROG guidance (Reference 3), comparing the ANO-2 total adjusted AFP loss coefficient with the AFP resistance used in the WCAP-17788 analysis is appropriate because the adjusted loss coefficient accounted for the dtfference in thennal power between ANO-2 and that assumed in the WCAP AFP analysis. The adjusted ANO-2 AFP loss coefficient, when applied with the thermal power assumed in the WCAP analysis for CE plants (3,458 MWt), results in the pressure drop for ANO-2 AFPs. This thermal power is also used in the WCAP analysis, along with an assumed AFP resistance to ensure that the resulting pressure drop across the AFP in the WCAP analysis bounds the CE plants, including ANO-2.

Comparison of AN0-2 EGGS Flow Rate with that Analyzed in WCAP-17788 The ANO-2 ECC8 flow per FA is within the range of flow rates analyzed in WCAP-17788.

  • ANO-2 ECC8 flow rate - The ANO-2 ECC8 flow rate per FA is between 4.1 gpm/FA and 10.2 gpm/FA, calculated by dividing the minimum and maximum ECC8 flow rates by the number of fuel assemblies.
  • ECC8 flow rates analyzed in WCAP-17788 - For the CE plants, the analyzed ECC8 flow rate is 3.8 gpm/FA to 11.4 gpm/FA (Reference 5, Volume 4, Table 6-3).

Based on the comparisons shown above, the AFP analysis in WCAP-17788 for CE plants is applicable for and bounds ANO-2 plant conditions, following the Box 4 resolution path in the NRG review guidance for in-vessel downstream effects. As a result, accumulation of debris inside the reactor core would not challenge LTCC at ANO-2.

0CAN122001 Page 12 of 13 3.p Licensing Basis The objective of the licensing basis is to provide information regarding any changes to the plant licensing basis due to the sump evaluation or plant modifications.

3.p.1 Provide the information requested in GL 2004-02 Requested Information Item 2(e) regarding changes to the plant-licensing basis. The effective date for changes to the licensing basis should be specified. This date should correspond to that specified in the 10 CFR 50.59 evaluation for the change to the licensing basis.

GL 2004--02 Requested Information Item 2(e): A general description of and planned schedule for any changes to the plant licensing bases resulting from any analysis or plant modifications made to ensure compliance with the regulatory requirements listed in the Applicable Regulatory Requirements section of this GL. Any licensing actions or exemption requests needed to support changes to the plant licensing basis should be included.

Response

The ANO-2 Safety Analysis Report has been updated to incorporate the in-vessel downstream effects analysis and conclusions. No other licensing actions or exemption requests are required.

4. References
1. Entergy Operations, Inc. (Entergy) letter to U.S. Nuclear Regulatory Commission (NRG), *Generic Letter 2004-02 Commitment Extension," Arkansas Nuclear One -

Units 1 and 2, (0CAN111701) (ML173258078), dated November 20, 2017.

2. NRC Memorandum, "U.S. NRC Staff Review Guidance for In-Vessel Downstream Effects Supporting Review of GL 2004-02 Responses," (ML19228A011), dated September 4, 2019.
3. PWROG-16073-P, "TSTF-567 Implementation Guidance, Evaluation of In-Vessel Debris Effects, Submittal Template for Final Response to GL 2004-02 and FSAR Changes,* Revision 0, dated February 2020.
4. WCAP-17788-P, Volumes 1 - 6, "Comprehensive Analysis and Test Program for GSl-191 Closure (PA-SEE-1090),* Revision 0, dated July 2015.
5. WCAP-17788-P, Volumes 1 - 6, "Comprehensive Analysis and Test Program for GSl-191 Closure (PA-SEE-1090),* Revision 1, dated December 2019.
6. WCAP-16530-NP-A, "Evaluation of Post-Accident Chemical Effects in Containment Sump Fluids to Support GSl-191,
  • dated March 2008 (this reference is not utilized for ANO-1 but kept in the list to maintain consistency with ANO-2 references).
7. Nuclear Energy Institute, "ZOI Fibrous Debris Preparation, Processing, Storage, and Handling,* Revision 1 (ML120481057), dated January 2012.

0CAN122001 Page 13 of 13

8. NRC letter to B&W Owners Group, "Post-LOCA Reactor Vessel Recirculation to Avoid Boron Precipitation," dated March 9, 1993.
9. NUREG/CR-6224, "Parametric Study of the Potential for BWR ECCS Strainer Blockage due to LOCA-Generated Debris," (ML083290498), dated October 1995.
10. NRC Technical Evaluation Report, "Staff Technical Evaluation of In-Vessel Debris Effects,* (ML19178A252), dated June 13, 2019.
11. Entergy letter to NRC, "Generic Letter 2004-02 Closure Option," ANO - Units 1 and 2, (0CAN051301) (ML13137A126), dated May 16, 2013.
12. NRC letter to Entergy, "Arkansas Nuclear One, Units 1 and 2- Generic Letter 2004-02 Supplemental Response (TAC Nos. MC4663 and MC4664)," (0CNA011002)

(ML100190320), dated January 26, 2010.

13. Entergy letter to NRC, "GL 2004-02 Final Supplemental Response Arkansas Nuclear One - Units 1 and 2,* (0CAN090801) (ML082700499), dated September 15, 2008.
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