ML21242A279

ANO Slides Presentation for 9-1-21 Public Meeting

ML21242A279
Person / Time
Site:	Arkansas Nuclear
Issue date:	08/30/2021
From:	Thomas Wengert Plant Licensing Branch IV
To:	Entergy Operations
Wengert T
References
L-2017-LRC-0000
Download: ML21242A279 (14)

Text

ANO GL 200402 Final Response Requests for Additional Information 9/1/21 1

Agenda

• Introduction

• Entergy Presentation

• Discussion/Questions 2

Purpose

• The purpose of this meeting is to discuss the NRCs requests for additional information provided on July 16, 2021, for Entergys final submittal for resolution of GL 200402 which was submitted on December 10, 2020.

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RAI 1

In Enclosure 1, on pg. 11 of 17 (PDF pg. 14), the second paragraph under test parameters appears to have one-train flow and two-train flow reversed. The velocities for one-train flow is listed as 0.008 feet per second (ft/s) (used for Test 1) and two-train as 0.004 ft/s (used for Test 2). Provide the one and two-train flow rates and state which flow rate was used for each test. State which test resulted in greater penetration.

Response

The description of the two velocities in the submittal is a typographical error. For ANO-1, the strainer approach velocity is 0.004 ft/s for one-train operation, and 0.008 ft/s for two-train. The strainer flow rate for one-train operation is 4,867 gpm, and the flow rate for two-train operation is 9,734 gpm.

The ANO fiber bypass Test 1 used the approach velocity of 0.004 ft/s, and Test 2 used the approach velocity of 0.008 ft/s. As correctly stated on Page 4 of Enclosure 1 in the submittal, Test 2 resulted in higher fiber penetration than Test 1.

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RAI 2

Provide additional details on how the penetration models at plant scale were developed.

a) Describe how the penetration amounts determined from the testing were scaled to the plant condition for each unit.

Response

The model derived from Test 2 describes the fiber prompt and shedding penetration fractions as functions of cumulative fiber load on the test strainer. It is an important distinction to note that the plant strainer in-vessel analyses used the penetration fractions (not penetration debris quantities) calculated from the model. As stated in the submittal, the in-vessel analysis for reactor core inlet fiber load divided the recirculation phase into time steps. The fiber penetration model was used to determine the fiber prompt penetration and shedding fractions for each time step.

In the plant evaluation, the cumulative quantity of fiber on the plant strainer at the beginning of a time step was determined. This quantity was then scaled down to the test strainer surface area (i.e.,

multiplied by the ratio in surface area between the test strainer and plant strainer). The scaled fiber load was substituted into the model derived from Test 2 to calculate the fiber prompt penetration and shedding fractions for the given time step. These fractions were then applied to the plant strainer analysis to determine the fiber prompt penetration and shedding amounts for each time step, as stated in the last bullet on Page 14 and the first bullet on Page 15 of Enclosure 1 in the submittal.

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RAI 2

Provide additional details on how the penetration models at plant scale were developed.

b) It appears that the model depicted in Figure 3.n.1-9 (PDF pg. 16) was used for both units. Provide justification that the same model is applicable to both units even though the strainer sizes and fiber amounts are significantly different between the units.

Response

The penetration model derived from Test 2 was applied for both units.

Figure 3.n.1-9 shows the results of an example application of the fiber penetration model: cumulative fiber penetration through the ANO-1 sump strainer as a function of time. The results shown in this figure are for demonstration purposes and were not directly used for the actual in-vessel analysis of either unit.

As stated in the submittal, Test 2 used a test strainer that is prototypical to the plant strainers of both units. Additionally, other testing conditions (e.g., fiber loads, approach velocity, water chemistry) were either representative of or bounded the plant strainer operating conditions of both units. The test was designed to characterize how fiber penetration varies as the quantity of fiber accumulated on the strainer increases. This was achieved by introducing debris into the test tank in five batches, allowing a gradual accumulation of fiber on the test strainer, and changing filter bags multiple times for each debris batch to collect long-term shedding penetration. The model derived from the test data describes the fiber prompt and shedding penetration fractions as functions of cumulative fiber load on the test strainer.

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Response (contd):

As stated in the response to Part a of this RAI, in the plant strainer in-vessel analysis, the accumulated fiber load on the plant strainer was scaled down to the test strainer surface area first before being used to calculate the fiber penetration fractions from the model. These fractions were then applied to determine the fiber penetration quantities during a time step for the plant strainer. This methodology is different from the application of simply scaling up the measured total fiber penetration quantity to the plant strainer surface area to quantify the plant strainer penetration.

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RAI 2

Provide additional details on how the penetration models at plant scale were developed.

c) Describe the relevance of the time scale on the x-axis of Figure 3.n.1-9. The NRC staff concluded that the axis implies time at a plant scale. Describe the assumptions used to develop the time scale or justify that it is not important to the calculations.

Response

The time on the x-axis of Figure 3.n.1-9 is at plant scale. As discussed above, this figure shows results of an example application, which uses similar methodology as the actual in-vessel analysis.

The prompt and shedding penetration fractions calculated from the model were used to determine the fiber penetration quantities of the plant strainer during each time step. The figure shows cumulative fiber penetration quantity over time.

Both the example application and actual in-vessel analyses assumed that the fibrous debris is uniformly distributed in the containment sump pool, consistent with the WCAP-17788 methodology.

The in-vessel analysis was terminated when the pool fiber concentration is 0.1% of the initial fiber concentration, which is more conservative than the 1% concentration termination criteria in WCAP-17788. As shown in Figure 3.n.1-9, the cumulative fiber penetration quantity plateaus well before the termination criterion is reached.

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RAI 2

Provide additional details on how the penetration models at plant scale were developed.

d) Describe the application of Figures 3.n.1-10 and 11 to each unit (PDF pgs. 16 and 17). Explain how the difference in strainer area between units is accounted for in the analysis, considering that the ANO-2 strainer has approximately 1.8 times the area of the ANO-1 strainer.

Response

It should be clarified that the prompt penetration and shedding fractions shown in Figures 3.n.1-10 and 3.n.1-11 are not inputs to the ANO in-vessel analysis of either unit. Instead, they resulted from the example application of the model to the ANO-1 strainer as shown in Figure 3.n.1-9.

As discussed in the response to Part a of this RAI, for a given time step, the amount of fiber accumulated on the plant strainer is first scaled down to the test scale (i.e., multiplied by the ratio in surface area between the test strainer and plant strainer) before being substituted into the model to calculate the fiber penetration fractions. For example, if the same amount of fiber accumulates on the plant strainers of both units, the fiber loads scaled to the test scale will be greater for ANO-1 than ANO-2 due to much larger surface area of the ANO-2 plant strainer. As a result, when using these scaled fiber loads in the model, the calculated fiber penetration fractions for ANO-1 would be lower than those of ANO-2. In other words, the resulting fiber penetration fraction curves for ANO-2 would be different from those shown in Figures 3.n.1-10 and 3.n.1-11 for ANO-1. In summary, the penetration model derived from testing only provided fiber penetration fractions for the in-vessel analyses. Although the same model was applied to both units, the difference in plant strainer surface areas between the two units was accounted for when the model was applied.

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RAI 3

In Enclosure 1, on pg. 15 (PDF pg. 18), the ANO-1 in-vessel fiber calculation credits one Reactor Building Spray System (RBSS) pump at minimum flow. Provide the basis for the assumption that one RBSS pump will start and continue to operate (not be shut off) during the period of interest for fiber accumulation at the core inlet. That is, confirm that the RBSS pumps start for large break scenarios and continue to run.

Response

For ANO-1, the RBSS operation is initiated by a reactor building high-high pressure signal. This occurs when the reactor building pressure exceeds 44.7 psia. This pressure is exceeded early in the event for a design basis accident, ensuring RBSS is actuated. Once actuated, the sprays remain active for the duration of the event. After spray initiation the operator is directed to throttle the RBSS flow prior to the beginning of recirculation and maintain spray flow throughout the event. With the exception of indication of sump blockage, the RBSS remains active during the recirculation phase.

As stated in the submittal, the ANO-1 in-vessel analysis conservatively used the minimum throttled RBSS flow. While the RBS operates for the entire 30-day event, the ANO-1 in-vessel analysis reached the termination criteria (as discussed in the response to RAI 2.c) approximately eight hours after initiation of the accident. Therefore, the RBSS is active during the entire period of interest for fiber accumulation at the core inlet.

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RAI 4

In Enclosure 2, on pg. 6 (PDF pg. 27), the ANO-2 in-vessel fiber calculation credits one Containment Spray System (CSS) pump at minimum flow. Provide the basis for the assumption that one CSS pump will start and continue to operate (not be shut off) during the period of interest for fiber accumulation at the core inlet. That is, confirm that the CSS pumps start for large break scenarios and continue to run.

Response

In the ANO-2 analysis, the time when containment spray is terminated was assumed to be ten hours after the LOCA. Containment spray actuation signal is automatically initiated when the containment pressure exceeds the containment pressure high-high (CPHH) setpoint of 25.7 psia. Containment spray is terminated once the containment pressure and temperature drop below 22.5 psia and 140°F, respectively.

Since a minimum spray operating time is conservative for the in-vessel analysis, the containment pressure and temperature curves from analysis of a small-break LOCA (SBLOCA) were used to derive the spray duration. The peak containment pressure for the SBLOCA is approximately 32 psia which exceeds the containment spray actuation setpoint. The earliest time the SBLOCA containment temperature drops to 140°F is approximately 300,000 seconds, or 83 hours9.606481e-4 days <br />0.0231 hours <br />1.372354e-4 weeks <br />3.15815e-5 months <br />. The earliest time the SBLOCA containment pressure drops below 22.5 psia is at 70,000 seconds, or 19 hours2.199074e-4 days <br />0.00528 hours <br />3.141534e-5 weeks <br />7.2295e-6 months <br />. For conservatism, this value was rounded down to ten hours for the spray duration in the in-vessel analysis for ANO-2.

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RAI 5

The NRC staff recognizes that substantial chemical effects information was provided in the licensees letter dated December 10, 2020, Final Response to NRC Generic Letter 2004-02. Please also provide the WCAP-17788, Comprehensive Analysis and Test Program for GSI-191 Closure, Test Group Number(s) that are considered representative of plant conditions for ANO-1 and ANO-2.

Response

As discussed in Enclosure 1 of the submittal, Entergy has elected to use the Box 2 path from the NRC review guidance to address in-vessel downstream effects for ANO-1, which is outfitted with a Babcock

& Wilcox (B&W) nuclear steam supply system. The minimum chemical precipitation time is not required for the Box 2 path. Therefore, comparison of the WCAP-17788 autoclave test groups with the ANO-1 plant conditions are not necessary.

For ANO-2, Entergy elected to use the Box 4 path from the NRC review guidance, and chemical precipitation was 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 by using a precipitation map based on an array of representative autoclave tests from WCAP-17788, Volume 5. Additionally, WCAP-17788 autoclave Test Group 18, including Test 18-01 and Test IBOB 18-02, is considered representative of the ANO-2 post-LOCA plant conditions for the in-vessel analysis. No chemical precipitation was observed during the Test Group 18 autoclave tests down to a filtration test temperature of 160°F for the 24-hour test duration.

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Response (contd):

The below table provides the critical projected ANO-2 post-LOCA conditions and debris loads at plant scale and test scale for comparison with the Test Group 18 parameters.

ANO-2 ANO-2 Parameter (Plant Scale) (Test Scale, 50 L)

Buffer Sodium Tetraborate Sodium Tetraborate Sump pH (Long-term) 7.2 - 8.0 7.2 - 8.0 1,765,085 L Minimum Sump Volume 50 L (384,000 gal + 82,286 gal)

Maximum Sump Pool Temperature 241.3°F 241.3°F Maximum Calcium Silicate 1,447,000 g 40.99 g Maximum E-Glass 900 g 0.0255 g Maximum Silica 0g 0g Maximum Mineral Wool 0g 0g Maximum Aluminum Silicate 25,400 g 0.720 g Maximum Concrete 49.3 g (4900 ft2) 0.00140 g (0.14 ft2)

Maximum Interam' 0g 0g Aluminum 301.0 ft2 0.00853 ft2 Galvanized Steel Not Determined Not Determined 13

Summary

• Anticipated submittal date is midSeptember, 2021.

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