ML20280A524

International - Submittal of Holtec Spent Fuel Pool Heat Up Calculation Methodology Topical Report

ML20280A524
Person / Time
Site:	99902086
Issue date:	09/29/2020
From:	Sterdis A Holtec
To:	Document Control Desk, Office of Nuclear Reactor Regulation
Shared Package
ML20280A523	List: ML20280A524
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HI-2200750, Rev 0
Download: ML20280A524 (8)

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Holtec Technology Campus, One Holtec Blvd, Camden, NJ 08104 Telephone (856) 797-0900 Fax (856) 797-0909 September 29, 2020 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555-0001 Docket No. 99902086 - HDI Spent Fuel Pool Heat Up Calculation Methodology

Subject:

Submittal of Holtec Spent Fuel Pool Heat Up Calculation Methodology Topical Report

Dear Sir or Madam:

Holtec is pleased to submit for NRC review and approval a topical report that provides an expanded methodology for calculating spent fuel pool thermal conditions. This methodology is straight-forward and validated against NRC-approved calculational methodologies, as well as NRC methods themselves. Due to the improvement in safety that can be realized through use of the methodology and its straightforward and robust validation, we request that the NRC staff review and approve this topical report by March 31, 2021.

The report is included as Attachment 1 this letter. Since this document is considered proprietary, includes an affidavit according to 10CFR2.390 requesting that it be withheld from public disclosure.

If you have any questions, please contact me at 856-797-0900 ext. 3813.

Sincerely, Andrea L. Sterdis VP, Regulatory and Environmental Affairs Holtec Decommissioning International Digitally signed by Andrea L. Sterdis DN: cn=Andrea L. Sterdis, c=US, o=HDI, ou=Holtec Decommissioning International, email=andrea.sterdis@holtec.com Date: 2020.09.29 16:35:22 -04'00' Andrea L.

Sterdis

Holtec Technology Campus, One Holtec Blvd, Camden, NJ 08104 Telephone (856) 797-0900 Fax (856) 797-0909 Document 65000001 Page 2 of 2 Attachments:

Method for Determining Spent Fuel Assembly Heat Up During a Theoretical Drain Down Event, HI-2200750, Revision 0 (Holtec Proprietary) :

Affidavit Pursuant to 10 CFR 2.390 to Withhold Information from Public Disclosure cc:

Robert Lucas, NRC, NRR/DORL/LLPB Dennis Morey, NRC, NRR/DORL/LLPB Ekaterina Lenning, NRC, NRR/DORL/LLPB Christopher Regan, NRC, NMSS/DFM

Affidavit Pursuant To 10 CFR 2.390 Non-Proprietary

U.S. Nuclear Regulatory Commission ATTN: Document Control Clerk Non-Proprietary Attachment 2 AFFIDAVIT PURSUANT TO 10 CFR 2.390 I, Andrea L. Sterdis, being duly sworn, depose and state as follows:

1) I have reviewed the information provided in Topical Report HI-2200750 which is sought to be withheld, and am authorized to apply for its withholding.

2) The document provided in Attachment 1 to this letter (Topical Report HI-2200750) is proprietary to Holtec International.

3) In making this application for withholding of proprietary information of which it is the owner, Holtec International relies upon the exemption from disclosure set forth in the Freedom of Information Act (FOIA), 5 USC Sec. 552(b)(4) and the Trade Secrets Act, 18 USC Sec. 1905, and NRC regulations 10 CFR Part 9.17(a)(4), 2.390(a)(4), and 2.390(b)(1) for trade secrets and commercial or financial information obtained from a person and privileged or confidential (Exemption 4). The material for which exemption from disclosure is here sought is all confidential commercial information, and some portions also qualify under the narrower definition of trade secret, within the meanings assigned to those terms for purposes of FOIA Exemption 4 in, respectively, Critical Mass Energy Project v. Nuclear Regulatory Commission, 975F2d871 (DC Cir. 1992),

and Public Citizen Health Research Group v. FDA, 704F2d1280 (DC Cir. 1983).

4) Some examples of categories of information which fit into the definition of proprietary information are:

a. Information that discloses a process, method, or apparatus, including supporting data and analyses, where prevention of its use by Holtecs competitors without license from Holtec International constitutes a competitive economic advantage over other companies;

b. Information which, if used by a competitor, would reduce his expenditure of resources or improve his competitive position in the design, manufacture, shipment, installation, assurance of quality, or licensing of a similar product.

c. Information which reveals cost or price information, production, capacities, budget levels, or commercial strategies of Holtec International, its customers or its suppliers;

U.S. Nuclear Regulatory Commission ATTN: Document Control Clerk Non-Proprietary Attachment 2 AFFIDAVIT PURSUANT TO 10 CFR 2.390

d. Information which reveals aspects of past, present, or future Holtec International customer-funded development plans and programs of potential commercial value to Holtec International;

e. Information which discloses patentable subject matter for which it may be desirable to obtain patent protection.

The information sought to be withheld is considered to be proprietary for the reasons set forth in paragraphs 4.a and 4.b above.

5) The information sought to be withheld is being submitted to the NRC in confidence. The information (including that compiled from many sources) is of a sort customarily held in confidence by Holtec International, and is in fact so held. The information sought to be withheld has, to the best of my knowledge and belief, consistently been held in confidence by Holtec International. No public disclosure has been made, and it is not available in public sources. All disclosures to third parties, including any required transmittals to the NRC, have been made, or must be made, pursuant to regulatory provisions or proprietary agreements which provide for maintenance of the information in confidence. Its initial designation as proprietary information, and the subsequent steps taken to prevent its unauthorized disclosure, are as set forth in paragraphs (6) and (7) following.

6) Initial approval of proprietary treatment of a document is made by the manager of the originating component, the person most likely to be acquainted with the value and sensitivity of the information in relation to industry knowledge. Access to such documents within Holtec International is limited on a need to know basis.

7) The procedure for approval of external release of such a document typically requires review by the staff manager, project manager, principal scientist or other equivalent authority, by the manager of the cognizant marketing function (or his designee), and by the Legal Operation, for technical content, competitive effect, and determination of the accuracy of the proprietary designation. Disclosures outside Holtec International are limited to regulatory bodies, customers, and

U.S. Nuclear Regulatory Commission ATTN: Document Control Clerk Non-Proprietary Attachment 2 AFFIDAVIT PURSUANT TO 10 CFR 2.390 potential customers, and their agents, suppliers, and licensees, and others with a legitimate need for the information, and then only in accordance with appropriate regulatory provisions or proprietary agreements.

8) The information classified as proprietary was developed and compiled by Holtec International at a significant cost to Holtec International. This information is classified as proprietary because it contains detailed descriptions of analytical approaches and methodologies not available elsewhere. This information would provide other parties, including competitors, with information from Holtec Internationals technical database and the results of evaluations performed by Holtec International. A substantial effort has been expended by Holtec International to develop this information. Release of this information would improve a competitors position because it would enable Holtecs competitor to copy our technology and offer it for sale in competition with our company, causing us financial injury.

9) Public disclosure of the information sought to be withheld is likely to cause substantial harm to Holtec Internationals competitive position and foreclose or reduce the availability of profit-making opportunities. The information is part of Holtec Internationals comprehensive decommissioning and spent fuel storage technology base, and its commercial value extends beyond the original development cost. The value of the technology base goes beyond the extensive physical database and analytical methodology, and includes development of the expertise to determine and apply the appropriate evaluation process.

The research, development, engineering, and analytical costs comprise a substantial investment of time and money by Holtec International.

The precise value of the expertise to devise an evaluation process and apply the correct analytical methodology is difficult to quantify, but it clearly is substantial.

Holtec Internationals competitive advantage will be lost if its competitors are able to use the results of the Holtec International experience to normalize or verify their own process or if they are able to claim an equivalent understanding by demonstrating that they can arrive at the same or similar conclusions.

The value of this information to Holtec International would be lost if the

U.S. Nuclear Regulatory Commission ATTN: Document Control Clerk Non-Proprietary Attachment 2 AFFIDAVIT PURSUANT TO 10 CFR 2.390 information were disclosed to the public. Making such information available to competitors without their having been required to undertake similar expenditure of resources would unfairly provide competitors with a windfall, and deprive Holtec International of the opportunity to exercise its competitive advantage to seek an adequate return on its large investment in developing these very valuable analytical tools.

U.S. Nuclear Regulatory Commission ATTN: Document Control Clerk Non-Proprietary Attachment 2 AFFIDAVIT PURSUANT TO 10 CFR 2.390 STATE OF NEW JERSEY)

)

ss:

COUNTY OF CAMDEN )

Andrea L. Sterdis, being duly sworn, deposes and says:

That she has read the foregoing affidavit and the matters stated therein are true and correct to the best of her knowledge, information, and belief.

Executed at Camden, New Jersey, this __lj__ day of September 2020.

~~--~.:

Andrea L. Sterdis Holtec Decommissioning International Holtec International VP, Regulatory & Environmental Affairs Subscribed and sworn before me this ~

day of

~e..p\\.e.ro'l.r-.-er 2020 KORIN M FAGAN No t ar y P\\Jblic, State of New Jersey My Commission Expires February 15, 2024

Method for Determining Spent Fuel Assembly Heat Up During a Theoretical Drain Down Event Holtec Proprietary Information HI-2200750 Rev. 0 Page i of v Copyright © 2020 Holtec International, all rights reserved Revision Log Revision Description of Changes 0

Initial issue.

Method for Determining Spent Fuel Assembly Heat Up During a Theoretical Drain Down Event Holtec Proprietary Information HI-2200750 Rev. 0 Page ii of v Copyright © 2020 Holtec International, all rights reserved EXECUTIVE

SUMMARY

Holtec International has developed a conservative method for calculating the transient heat up of spent fuel assemblies under a hypothetical spent fuel pool drain down event. Following defueling of the reactor, the ignition of the zirconium cladding of the spent fuel assembly within the spent fuel pool due to a loss of spent fuel pool cooling becomes one of the highest consequence potential accidents. Traditional NRC approved adiabatic calculations, such as the ones presented in NUREG-1738 [1], [

] 4.a, 4.b will take longer than 10 hours1.157407e-4 days <br />0.00278 hours <br />1.653439e-5 weeks <br />3.805e-6 months <br /> to reach a temperature associated with a zirconium fire (zirc fire). These calculations are very conservative, [

] 4.a, 4.b In other words, [

] 4.a, 4.b This approach can be modified to [

] 4.a, 4.b The results from this modified approach can [

] 4.a, 4.b By using this method [

] 4.a, 4.b a significant and real safety benefit can be recognized.

A recent NRC study RES/DSA/FSCB 2016-03 [2] explores the conservatisms embodied by the adiabatic calculation and summarizes the results of several strategies for calculating a more realistic heat up time. Principal among these are inclusion of the mass of the spent fuel racks in the heat up equation and, through use of the MELCOR code, introduction of convective heat dissipation. [

] 4.a, 4.b following a post shut-down drain down event in the pool. [

] 4.a, 4.b The results presented in this report are shown to be consistent with those found in RES/DSA/FSCB 2016-03 [2]. Holtec further validated this method by performing the Computational Fluid Dynamics (CFD) calculations presented in Appendix D. [

] 4.a, 4.b These CFD calculations further demonstrate the conservative nature of the method presented in this report, as the CFD results illustrate the significant levels of conservative margin in the proposed method.

Method for Determining Spent Fuel Assembly Heat Up During a Theoretical Drain Down Event Holtec Proprietary Information HI-2200750 Rev. 0 Page iii of v Copyright © 2020 Holtec International, all rights reserved Based upon the results of the method presented in this report, as validated against the NRC and Holtec CFD calculations, [

] 4.a, 4.b and can be leveraged to [

] 4.a, 4.b

Method for Determining Spent Fuel Assembly Heat Up During a Theoretical Drain Down Event Holtec Proprietary Information HI-2200750 Rev. 0 Page iv of v Copyright © 2020 Holtec International, all rights reserved Table of Contents Executive Summary.................................................................................................................... ii Purpose.......................................................................................................................... 1 Acceptance Criteria........................................................................................................ 2 Methodology................................................................................................................... 2 Overview............................................................................................................. 2

] 4.a, 4.b............................................. 3

[

] 4.a, 4.b...................... 5 Material Specific Heats....................................................................................... 8 Assembly Material Weights................................................................................. 8

[

] 4.a, 4.b............................................................................. 9

[

] 4.a, 4.b............................................................... 9 Assumptions and Conservatisms...................................................................................11 Conservatisms...................................................................................................11 Assumptions......................................................................................................12 Input Data......................................................................................................................13 Generic Input Data.............................................................................................13 Site Specific Input Data......................................................................................14 Example Calculations....................................................................................................15 Results of Example Calculations...................................................................................15

[

] 4.a, 4.b..................................................15 Interpretation of Results.....................................................................................16

[

] 4.a, 4 b.......................................17 Results for Example Plants................................................................................17 Comparison to NRC Calculations.......................................................................18 Comparison to Computational Fluid Dynamics (CFD) Calculations....................19 Conclusion....................................................................................................................19 References....................................................................................................................20 Tabulation of Zircaloy Specific Heat Values By Temperature........................... A-1 Example Calculation [

] 4.a, 4.b........... B-1 Example Calculation [

] 4.a, 4.b................ C-1 Validation Studies Using CFD Method............................................................. D-1

Method for Determining Spent Fuel Assembly Heat Up During a Theoretical Drain Down Event Holtec Proprietary Information HI-2200750 Rev. 0 Page v of v Copyright © 2020 Holtec International, all rights reserved List of Tables Table 5.1: Constants Used in UO2 Specific Heat Capacity Correlations....................................13 Table 5.2: Additional Coefficients and Parameters....................................................................13 Table 5.3: Example Site Fuel Assembly Parameters.................................................................14 Table 7.1: Calculated Heat Load Limits for Example Plants......................................................17 Table 7.2: [

] 4.a, 4b.........................18 List of Figures Figure 3.1: [

]

4.a, 4.b 3

Figure 3.2: [

] 4.a, 4.b....................... 7 Figure 3.3: [

] 4.a, 4 b...........................................10 Figure 7.1: [

] 4.a, 4.b.....15 Figure 7.2: [

] 4.a, 4.b................................................................................................................16 Figure 7.3: Comparison of Results [

] 4 a, 4.b..........................................................................................................19

Method for Determining Spent Fuel Assembly Heat Up During a Theoretical Drain Down Event

~4eltee Prei:irietary I AferR'latieA 1.0 PURPOSE HOLTEC INTERNAT I O NA L Spent fuel pools safely store spent nuclear fuel (SNF) from nuclear power plants in fuel racks.

The fuel racks are cellular structures with design features that facilitate the circulation of water through the storage cells to maintain the fuel rods in a cooled state. The racks are staged on the pool's slab with an elevated baseplate which supports the fuel assemblies and provides a bottom plenum of water that feeds the coolant to each storage cell. High reactivity fuel or fuel recently removed from the reactor is stored in flux-trap (FT) type fuel racks. Flux-trap type racks are characterized by a small lateral gap around each storage cell. Other fuel assemblies can be stored in the so-called non-flux trap (NFT) type racks which feature no gap between adjacent storage cells. Most PWR plants have racks of both flux trap and non-flux trap types 1. BWR fuel, due to its relatively lower reactivity, is typically stored in NFT racks only.

Because keeping the fuel cool is a principal function of fuel racks, they are equipped with appropriate features to promote efficient fuel decay heat removal. The bulk temperature of the water in the pool is maintained in a desired range using a set of pumps and heat exchangers with redundancy to ensure reliable cooling. The pool's heat removal system and robust design that protect against abnormal conditions have proven to be reliable, making in-pool storage a credibly safe means to store the fuel.

Once a reactor is permanently defueled, a drain down of the water in the spent fuel pool, while highly unlikely, has one of the highest consequences of the remaining potential accidents in terms of public health and safety. Because the heat rejection rate via air cooling is several orders of magnitude smaller than via water cooling, the fuel temperature will rise until the heat generation rate equilibrates with the heat dissipation rate. It is known that the zirconium fuel cladding becomes sensitive to combustion in an oxygen environment at temperatures above 900°C. To reduce or prevent the fuel's vulnerability to a zirconium fire (zirc fire) during a drain down event of the pool, it is desirable to adopt measures to minimize the fuel cladding's temperature rise in the air environment. In the event that preventing exceedance of the allowable limit is not possible, as is the case immediately following reactor shutdown, it is essential [

] 4.a. 4.b Historically, permanently shut down plants have computed the period of zirc fire vulnerability after a reactor's shutdown, to establish the basis for adjusting requirements that are needed to ddress the hypothetical zirc fire event. Such analyses have been often performed [

1 The racks with FT are commonly referred to as Region 1 racks and the NFT types are referred to as Region 2 racks. This terminology is adopted for the remainder of the report.

Hl-2200750 Rev. 0 Page 1 of 21 Copyright © 2020 Ho/tee International, all rights reserved 4.a, 4.b

Method for Determining Spent Fuel Assembly Heat Up During a Theoretical Drain Down Event Holtec Proprietary Information HI-2200750 Rev. 0 Page 2 of 21 Copyright © 2020 Holtec International, all rights reserved The objective of this topical report is to present a generic methodology that [

] 4.a, 4.b This method can thus be used to [

] 4.a, 4.b It is shown in this report that:

i.

[

] 4.a, 4.b ii.

The method developed maintains large levels of conservatism through its assumptions.

iii.

The method can be used to analyze any fuel pool with any kind of fuel.

iv.

analyses performed both by the NRC using a MELCOR model and by Holtec using a Computational Fluid Dynamics (CFD) model.

[

] 4.a, 4.b ACCEPTANCE CRITERIA While the method presented in this report does not itself have a specific acceptance criteria, it is intended for use in determining the elapsed time until loss of spent fuel pool water cooling results in the ignition of the spent fuel assembly zirconium cladding. NUREG-1738 [1]

establishes 900ºC as a reasonable temperature limit to protect against a runaway oxidation, and thus a zirc fire, in an air environment, in combination with a 10-hour time window to take actions.

SECY-99-168 [3] deems an elapsed time of at least ten hours as being generally sufficient time from the lo and consequence of a zirc fire is sufficiently diminished to warrant adjustment cy plan.

As such, the results presented in Section 7.0 of this report [

] 4.a, 4.b to reach 900ºC is ten hours or longer.

METHODOLOGY Overview This section presents the methodology used to calculate the spent fuel assembly bulk temperatures as a function of time following a theoretical drain down event. The assumptions inherent to the methodology are discussed in more detail in Section 4.0.

The methodology presented in this report considers [

] 4.a, 4.b The calculations are conservative [

4.a, 4.b

Method for Determining Spent Fuel Assembly Heat Up During a Theoretical Drain Down Event Holtec Proprietary Information HI-2200750 Rev. 0 Page 3 of 21 Copyright © 2020 Holtec International, all rights reserved

] 4.a, 4 b is discussed further in Sections 3.6 and 3.7.

Figure 3.1: [

] 4.a, 4.b

[

] 4.a, 4.b

[

] 4 a, 4 b Eq. 3-1 Where:

4.a, 4.b 4.a, 4.b 4.a, 4.b 4.a, 4.b

Method for Determining Spent Fuel Assembly Heat Up During a Theoretical Drain Down Event Holtec Proprietary Information HI-2200750 Rev. 0 Page 4 of 21 Copyright © 2020 Holtec International, all rights reserved

[

] 4.a, 4.b Eq. 3-2 Where:

[

] 4.a, 4.b Eq. 3-3 Eq. 3-4 Where:

4.a, 4.b 4.a, 4.b 4.a, 4.b 4.a, 4.b 4.a, 4.b 4.a, 4.b

Method for Determining Spent Fuel Assembly Heat Up During a Theoretical Drain Down Event Holtec Proprietary Information HI-2200750 Rev. 0 Page 5 of 21 Copyright © 2020 Holtec International, all rights reserved Eq. 3-5 Where:

[

] 4.a, 4.b Eq. 3-6 Where:

Eq. 3-7 4.a, 4.b 4.a, 4.b 4.a, 4.b 4.a, 4.b 4.a, 4.b 4.a, 4.b

Method for Determining Spent Fuel Assembly Heat Up During a Theoretical Drain Down Event Holtec Proprietary Information HI-2200750 Rev. 0 Page 6 of 21 Copyright © 2020 Holtec International, all rights reserved Where:

Eq. 3-8 Eq. 3-9 Where:

Eq. 3-10 4.a, 4.b 4.a, 4.b 4.a, 4.b

Method for Determining Spent Fuel Assembly Heat Up During a Theoretical Drain Down Event Holtec Proprietary Information HI-2200750 Rev. 0 Page 7 of 21 Copyright © 2020 Holtec International, all rights reserved Eq. 3-11 Eq. 3-12 Eq. 3-13 Figure 3.2: [

] 4.a, 4.b 4.a, 4.b 4.a, 4.b 4.a, 4.b

Method for Determining Spent Fuel Assembly Heat Up During a Theoretical Drain Down Event Holtec Proprietary Information HI-2200750 Rev. 0 Page 8 of 21 Copyright © 2020 Holtec International, all rights reserved Material Specific Heats The specific heats of the UO2 and zircaloy are determined based on the methods presented in NUREG/CR-0479. The specific heats of UO2 are calculated from the specific heat capacity correlation provided in Appendix A of NUREG/CR-0479 [5] at each time step for each fuel assembly. This correlation is reproduced below:

Eq. 3-14 Where:

, and are each constants.

is temperature in K is the oxygen to metal ratio of is the gas constant.

The specific heats of zircaloy are linearly interpolated based upon the experimental data presented in Appendix B of NUREG/CR-0479. [5] These results are tabulated in intervals of 5ºC in Appendix A of this report. For each timestep in the calculation, the specific heat of zircaloy at the nearest lower bound temperature increment are used to determine the incremental temperature increase. This approach yields conservative results as the specific heat of zircaloy in this temperature range increase with rising temperature.

Assembly Material Weights In instances where the masses of UO2 or zircaloy within an assembly are not directly available, these values can be calculated from other assembly characteristics. The mass of UO2 in the fuel assembly is estimated by scaling the mass of heavy metal by the mass fraction of U in UO2, which simply multiplies the mass of heavy metal by a factor of 1.134.

The mass of zircaloy in the assembly is calculated as:

Eq. 3-15 Where:

is the density of zirconium is the length of the active region is the typical number of rods per assembly is the mathematical constant is the outer diameter of the fuel rod cladding.

is the inner diameter of the fuel rod cladding.

Method for Determining Spent Fuel Assembly Heat Up During a Theoretical Drain Down Event Holtec Proprietary Information HI-2200750 Rev. 0 Page 9 of 21 Copyright © 2020 Holtec International, all rights reserved It is noted that these methods for determining material weights were utilized in this report based on the materials available to be referenced, and alternative approaches for determining appropriate inputs are acceptable.

[

] 4.a, 4.b

[

] 4.a, 4.b Eq. 3-16 4.a, 4.b 4.a, 4.b 4.a, 4.b

Method for Determining Spent Fuel Assembly Heat Up During a Theoretical Drain Down Event Holtec Proprietary Information HI-2200750 Rev. 0 Page 10 of 21 Copyright © 2020 Holtec International, all rights reserved Figure 3.3:

4.a, 4.b 4.a, 4.b 4.a, 4.b

Method for Determining Spent Fuel Assembly Heat Up During a Theoretical Drain Down Event Holtec Proprietary Information HI-2200750 Rev. 0 Page 11 of 21 Copyright © 2020 Holtec International, all rights reserved ASSUMPTIONS AND CONSERVATISMS Conservatisms Only the masses of the UO2 fuel pellets and the zircaloy cladding are considered for heat up in this method. This approach conservatively neglects the mass of the spent fuel racks and other fuel assembly components, which in reality would also absorb the generated heat, further slowing the rate of increase in temperature of the spent fuel assemblies. Consideration of the racks alone has been shown in RES/DSA/FSCB 2016-03 [2] to further extend heat up times by 35-40% in BWRs and 15-20% in PWRs.

] 4.a, 4.b consistent with those used in NUREG-1738 [1], RES/DSA/FSCB 2016-03 [2], and numerous others.

The starting time of the calculation is assumed to occur when the spent fuel pool is drained. This conservatively neglects the significant period of time where a leak or other loss of spent fuel cooling would have been detected and plant staff would be able to begin taking mitigating action. Inherent in this approach is the presumption that the spent fuel pool water instantaneously vaporizes, whereas in reality the mass of spent fuel pool water is still present to absorb and dissipate heat from the spent fuel assemblies. This conservatism is consistent with that assumed in the calculations described in SECY 168 [3].

4.a, 4.b 4.a, 4.b 4.a, 4.b 4.a, 4.b

Method for Determining Spent Fuel Assembly Heat Up During a Theoretical Drain Down Event l-loltec Proprietary lnf.ormation HOLTEC IN TERNAT IO NA L 4.2 Assumptions 4.2.1

[

] 4 a. 4.b This is consistent with the approach taken for adiabatic calculations in NUREG-1738 [1], RES/DSA/FSCB 2016-03 [2], and other prior licensee calculations. It 4.a, 4.b 4.2.2 The spent fuel assembly [

4.2.3 4.2.4

] 4 a. 4.b This assumption is reasonable as the fuel and cladding are in close contact, and [

] 4 a. 4.b This is also a common assumption for calculations of this nature and is consistent with NUREG-1738

[1] and RES/DSA/FSCB 2016-03 [2]. In BWR fuel, the fuel channel is similarly assumed

[

] 4.a. 4.b 4.a, 4.b 4.a, 4.b 4.2.5 The starting temperatures of the spent fuel assemblies [

] 4 a. 4.b This choice of starting temperature is realistic and appropriate, [

] 4.a. 4.b Hl-2200750 Rev. 0 Page 12 of 21 Copyright © 2020 Ho/tee International, all rights reserved

Method for Determining Spent Fuel Assembly Heat Up During a Theoretical Drain Down Event Holtec Proprietary Information HI-2200750 Rev. 0 Page 13 of 21 Copyright © 2020 Holtec International, all rights reserved INPUT DATA Generic Input Data The subsequent tables present the standardized coefficients and values associated with the equations provided in Section 3.0.

Table 5.1: Constants Used in UO2 Specific Heat Capacity Correlations Parameter Value [Ref]

K1 296.7 J/kg/K [5]

K2 2.43 x 10-2 J/kg/K2 [5]

K3 8.745 x 107 J/kg [5]

535.285 K [5]

ED 1.577 x 105 J/mol [5]

O/M of UO2 2.0 [8]

R 8.3143 J/mol/K [5]

Table 5.2: Additional Coefficients and Parameters Parameter Value [Ref]

4.a, 4.b

[

] 4.a, 4.b 4.a, 4.b

[

] 4 a, 4.b 4.a, 4.b [

] 4.a, 4 b Density of z

6490 kg/m3 [5]

Method for Determining Spent Fuel Assembly Heat Up During a Theoretical Drain Down Event Holtec Proprietary Information HI-2200750 Rev. 0 Page 14 of 21 Copyright © 2020 Holtec International, all rights reserved Site Specific Input Data The subsequent tables present the site-specific values used to generate the example results in Section 7.0.

Table 5.3: Example Site Fuel Assembly Parameters Parameter Example Plant A (W 15x15 OFA)

Example Plant B (CE 15x15 Palis. PWR)

Example Plant C (GE GNF2)

Active Length 3.657 m [8]

3.098 m [10]

3.689 m [11]

[

] 4.a, 4.b

[

] 4 a, 4.b

[

] 4.a, 4.b

[

] 4.a, 4 b Typical Number of Rods 204 [8]

204 [8]

[

] 4.a, 4.b

[

] 4.a, 4.b

[

] 4.a, 4.b [

] 4.a, 4.b Cladding Outer Diameter 10.718 mm [12]

10.591 mm [10]

10.261 mm [11]

Cladding Inner Diameter 9.474 mm [12]

9.321 mm [10]

[

] 4.a, 4.b

[

] 4.a, 4.b

[

] 4.a, 4 b

[

] 4.a, 4 b

[

] 4.a, 4.b

[

] 4 a, 4.b

[

] 4.a, 4.b

[

] 4.a, 4.b Mass of Heavy Metal 462.664 kg [8]

412.769 kg [8]

Mass of UO2 524.660 kg

• 468.080 kg

• 208.011 kg [11]

Mass of Zircaloy 95.516 kg

• 81.461 kg

• 41.666 kg [11]

Notes:

1 Some values in the table are converted from the values in the provided reference to the units stated here, rounded as shown.

2 For some parameters, multiple values can be found in the listed reference. In that case, the most conservative (smallest) value is used.

3 Values marked by an asterisk (*) are calculated from other values provided in this table and Table 5.2.

[

] 4.a, 4.b

Method for Determining Spent Fuel Assembly Heat Up During a Theoretical Drain Down Event Holtec Proprietary Information HI-2200750 Rev. 0 Page 15 of 21 Copyright © 2020 Holtec International, all rights reserved EXAMPLE CALCULATIONS Example calculations for two representative cases are presented in Appendix B and Appendix C RESULTS OF EXAMPLE CALCULATIONS

[

] 4.a, 4.b Figure 7.1: [

] 4.a, 4.b 4.a, 4.b 4.a, 4.b

Method for Determining Spent Fuel Assembly Heat Up During a Theoretical Drain Down Event Holtec Proprietary Information HI-2200750 Rev. 0 Page 16 of 21 Copyright © 2020 Holtec International, all rights reserved Figure 7.2: [

]

Interpretation of Results Based upon the results in Section 7.1, [

] 4.a, 4.b While the proposed method could be used to [

] 4.a, 4.b which in turn introduces additional conservatism.

4.a, 4.b

Method for Determining Spent Fuel Assembly Heat Up During a Theoretical Drain Down Event Holtec Proprietary Information HI-2200750 Rev. 0 Page 17 of 21 Copyright © 2020 Holtec International, all rights reserved As described in Sections 3.6 and 3.7, [

[

] 4.a, 4.b Results for Example Plants Table 7.1 presents the results for three example plants. [

] 4.a, 4.b Table 7.1: Calculated Heat Load Limits for Example Plants 4.a, 4.b 4.a, 4.b 4.a, 4.b

Method for Determining Spent Fuel Assembly Heat Up During a Theoretical Drain Down Event Holtec Proprietary Information HI-2200750 Rev. 0 Page 18 of 21 Copyright © 2020 Holtec International, all rights reserved Comparison to NRC Calculations

]4.a, 4.b The MELCOR calculations were performed using the average power from Figure 1 in [2] for a BWR assembly with a burnup of 60 GWd/MTHM across a variety of cooling times. [

]4.a, 4.b In order to closely replicate the scenarios evaluated, the heat load values used in the study were estimated from the respective figure, [

]4.a, 4.b Calculations were performed using these same heat load values used by [2] under the developed method for Example Plant C, also a BWR. These results are presented beside the MELCOR results in Figure 7.3. [

]4.a, 4.b This trend is indicative of significant conservatism [

]4.a, 4.b This further illustrates the conservatism of the method proposed in this report as a whole.

Table 7.2: [

]

4.a, 4.b 4.a, 4.b 4.a, 4.b

Method for Determining Spent Fuel Assembly Heat Up During a Theoretical Drain Down Event Holtec Proprietary Information HI-2200750 Rev. 0 Page 19 of 21 Copyright © 2020 Holtec International, all rights reserved Figure 7.3: [

]

Comparison to Computational Fluid Dynamics (CFD) Calculations As discussed in Appendix D, CFD calculations were performed to further confirm the conservative nature of the model, [

]4.a, 4.b As shown by the comparison of the CFD cases with the corresponding results from Figure 7.2 and Table 7.1, the method presented in this report results in shorter heat up times and is therefore conservative.

CONCLUSION This topical report presents a simple and effective method for determining PWR and BWR spent fuel assembly heat up in spent fuel pools during a hypothetical drain down event. Results are 4.a, 4.b 4.a, 4.b

Method for Determining Spent Fuel Assembly Heat Up During a Theoretical Drain Down Event Holtec Proprietary Information HI-2200750 Rev. 0 Page 20 of 21 Copyright © 2020 Holtec International, all rights reserved compared against more sophisticated models and show significant levels of conservatism, [

]4.a, 4.b REFERENCES

[1] "NUREG-1738 Technical Study of Spent Fuel Pool Accident Risk at Decommissioning Nuclear Power Plants (ML010430066)," 2001.

[2] "RES/DSA/FSCB 2016-03 Spent Fuel Assembly Heat Up Calculations in Support of Task 2 of User Need NSIR-2015-001 (ML16110A431)," 2016.

[3] "SECY-99-168 Improving Decommissioning Regulations for Nuclear Power Plants (ML992800087)," 1999.

[4] S. Middleman, An Introduction to Mass and Heat Transfer, New York: John Wiley & Sons, Inc., 1998.

[5] "NUREG/CR-0479 MATPRO-Version 11 (Revision 2) A Handbook of Materials Properties for Use in the Analysis of Light Water Reactor Fuel Rod Behavior," 1981.

[6] "NSIR/DPR-ISG-02 Emergency Planning Exemption Requests for Decommissioning Nuclear Power Plants (ML14106A057)," 2015.

[7] EPRI, "Severe Accident Management Guidance Technical Basis Report, Volume 2: The Physics of Accident Progression," 2012.

[8] "DOE/RW-0184-Vol. 3 Characteristics of Spent Fuel, High-Level Waste, and other Radioactive Wastes Which May Require Long-Term Isolation," 1987.

[9] Holtec International, "HI-2002444R20 Final Safety Analysis Report for the HI-STORM 100 Cask System," 2020.

[10] "Palisades Final Safety Analysis Report, Revision 29, Table 3-2".

[11] "Response to Request for Additional Information (RAI) and Supplemental Information Regarding Request for Changing Emergency Preparedness License Amendment No. 294 Effective Date (Change to Adiabatic Heat-up Calculation) (ML19044A643)," 2019.

[12] "EN-DC-141R17-190605, Design Input Record, Attachment-9.1".

[13] "C-1302-226-E310-459R0 Oyster Creek Reactor Building Heat Up and Fuel Cladding Temperature for Drained Spent Fuel Pool," 2019.

Method for Determining Spent Fuel Assembly Heat Up During a Theoretical Drain Down Event Holtec Proprietary Information HI-2200750 Rev. 0 Page 21 of 21 Copyright © 2020 Holtec International, all rights reserved

[14] "Regulatory Improvements for Power Reactors Transitioning to Decommissioning (ML15026A316)," 2017.

[15] "NUREG-2161 Consequence Study of a Beyond-Design-Basis Earthquake Affecting the Spent Fuel Pool for a U.S. Mark I Boiling Water Reactor (ML14255A365)," 2014.

Method for Determining Spent Fuel Assembly Heat Up During a Theoretical Drain Down Event Holtec Proprietary Information HI-2200750 Rev. 0 Page A-1 of 3 Copyright © 2020 Holtec International, all rights reserved TABULATION OF ZIRCALOY SPECIFIC HEAT VALUES BY TEMPERATURE The specific heats of zircaloy are linearly interpolated based upon the experimental data presented in Appendix B of NUREG/CR-0479. [5]

K C

J/kg/K 298 25 280.6 303 30 281.6 308 35 282.7 313 40 283.7 318 45 284.8 323 50 285.8 328 55 286.9 333 60 287.9 338 65 289.0 343 70 290.0 348 75 291.1 353 80 292.1 358 85 293.2 363 90 294.2 368 95 295.3 373 100 296.3 378 105 297.4 383 110 298.4 388 115 299.5 393 120 300.5 398 125 301.6 403 130 302.4 408 135 303.0 413 140 303.6 418 145 304.2 423 150 304.8 428 155 305.4 433 160 306.0 438 165 306.6 443 170 307.2 448 175 307.8 453 180 308.4 458 185 309.0 463 190 309.6 468 195 310.2 473 200 310.8 478 205 311.4 483 210 312.0 488 215 312.6 493 220 313.2 498 225 313.8 503 230 314.4 508 235 315.1 513 240 315.7 518 245 316.3 523 250 316.9 528 255 317.5 533 260 318.1 538 265 318.7 543 270 319.3 548 275 319.9 553 280 320.5 558 285 321.1 563 290 321.7 568 295 322.3 573 300 322.9 578 305 323.5 583 310 324.1 588 315 324.7 593 320 325.3 598 325 325.9 603 330 326.5 608 335 327.1

Method for Determining Spent Fuel Assembly Heat Up During a Theoretical Drain Down Event Holtec Proprietary Information HI-2200750 Rev. 0 Page A-2 of 3 Copyright © 2020 Holtec International, all rights reserved 613 340 327.7 618 345 328.3 623 350 328.9 628 355 329.6 633 360 330.2 638 365 330.8 643 370 331.3 648 375 331.8 653 380 332.3 658 385 332.8 663 390 333.2 668 395 333.7 673 400 334.2 678 405 334.7 683 410 335.2 688 415 335.7 693 420 336.2 698 425 336.7 703 430 337.2 708 435 337.6 713 440 338.1 718 445 338.6 723 450 339.1 728 455 339.6 733 460 340.1 738 465 340.6 743 470 341.1 748 475 341.6 753 480 342.0 758 485 342.5 763 490 343.0 768 495 343.5 773 500 344.0 778 505 344.5 783 510 345.0 788 515 345.5 793 520 346.0 798 525 346.4 803 530 346.9 808 535 347.4 813 540 347.9 818 545 348.4 823 550 348.9 828 555 349.4 833 560 349.9 838 565 350.4 843 570 350.8 848 575 351.3 853 580 351.8 858 585 352.3 863 590 352.8 868 595 353.3 873 600 353.8 878 605 354.3 883 610 354.8 888 615 355.2 893 620 355.7 898 625 356.2 903 630 356.7 908 635 357.2 913 640 357.7 918 645 358.2 923 650 358.7 928 655 359.2 933 660 359.6 938 665 360.1 943 670 360.6 948 675 361.1 953 680 361.6 958 685 362.1 963 690 362.6 968 695 363.1 973 700 363.6 978 705 364.0 983 710 364.5 988 715 365.0

Method for Determining Spent Fuel Assembly Heat Up During a Theoretical Drain Down Event Holtec Proprietary Information HI-2200750 Rev. 0 Page A-3 of 3 Copyright © 2020 Holtec International, all rights reserved 993 720 365.5 998 725 366.0 1003 730 366.5 1008 735 367.0 1013 740 367.5 1018 745 368.0 1023 750 368.4 1028 755 368.9 1033 760 369.4 1038 765 369.9 1043 770 370.4 1048 775 370.9 1053 780 371.4 1058 785 371.9 1063 790 372.4 1068 795 372.8 1073 800 373.3 1078 805 373.8 1083 810 374.3 1088 815 374.8 1093 820 502.0 1098 825 524.0 1103 830 546.0 1108 835 568.0 1113 840 590.0 1118 845 596.3 1123 850 602.5 1128 855 608.8 1133 860 615.0 1138 865 641.0 1143 870 667.0 1148 875 693.0 1153 880 719.0 1158 885 743.3 1163 890 767.5 1168 895 791.8 1173 900 816.0

Method for Determining Spent Fuel Assembly Heat Up During a Theoretical Drain Down Event Holtec Proprietary Information HI-2200750 Rev. 0 Page B-1 of 3 Copyright © 2020 Holtec International, all rights reserved EXAMPLE CALCULATION [

]4a., 4.b AT EXAMPLE PLANT A 4.a, 4.b

Method for Determining Spent Fuel Assembly Heat Up During a Theoretical Drain Down Event Holtec Proprietary Information HI-2200750 Rev. 0 Page B-2 of 3 Copyright © 2020 Holtec International, all rights reserved 4.a, 4.b

Method for Determining Spent Fuel Assembly Heat Up During a Theoretical Drain Down Event Holtec Proprietary Information HI-2200750 Rev. 0 Page B-3 of 3 Copyright © 2020 Holtec International, all rights reserved 4.a, 4.b

Method for Determining Spent Fuel Assembly Heat Up During a Theoretical Drain Down Event Holtec Proprietary Information HI-2200750 Rev. 0 Page C-1 of 3 Copyright © 2020 Holtec International, all rights reserved EXAMPLE CALCULATION [

]4a., 4.b AT EXAMPLE PLANT A 4.a, 4.b

Method for Determining Spent Fuel Assembly Heat Up During a Theoretical Drain Down Event Holtec Proprietary Information HI-2200750 Rev. 0 Page C-2 of 3 Copyright © 2020 Holtec International, all rights reserved 4.a, 4.b

Method for Determining Spent Fuel Assembly Heat Up During a Theoretical Drain Down Event Holtec Proprietary Information HI-2200750 Rev. 0 Page C-3 of 3 Copyright © 2020 Holtec International, all rights reserved 4.a, 4.b

Method for Determining Spent Fuel Assembly Heat Up During a Theoretical Drain Down Event Holtec Proprietary Information HI-2200750 Rev. 0 Page D-1 of 31 Copyright © 2020 Holtec International, all rights reserved Validation Studies Using CFD Method A conservative method for calculating the transient heat up of spent fuel assemblies under a hypothetical spent fuel pool drain down event is presented in the main part of the report. This appendix presents an independently conducted analysis, utilizing a different method than in the main report, which confirms the conservative nature of that method in determining fuel pool heat up rates. The independent validation method presented in the appendix is a widely used Computational Fluid Dynamics (CFD) approach. This approach has a long history of use in solving a wide array of thermal-hydraulic problems in wet and dry storage of spent nuclear fuel (SNF).

The CFD code, FLUENT, used since the mid-1990s in virtually every Holtec docket, [

]4.a, 4.b The concept is further discussed in the next sections of this appendix. [

]4.a, 4.b presented in main part of the report, are analyzed in Section D.4 and the results from the two methods are compared.

D.1 EVALUATION METHODOLOGY D.1.1 Overview The CFD approach has a long history of use in solving a wide array of thermal-hydraulic problems in the nuclear industry. The computer code ANSYS FLUENT is a Holtec QA-validated code [D.6.4]

used for this purpose. CFD owes its origin to the safety analyses performed for Connecticut Yankee [D.6.1], Millstone Unit 1 [D.6.2] and Vermont Yankee [D.6.3] which utilized the same code (ANSYS FLUENT [D.6.4], [D.6.5]) using simplified models. Additionally, the thermal modeling methodology described in this section has been benchmarked against test data from dry storage casks containing SNF as described in Section D.3 of this appendix. The benchmarking evaluations show that the FLUENT solutions are conservative in all cases.

[

]4.a, 4.b The principal features of the thermal models are described in this section and example calculations are reported Section D.4 of this appendix.

D.1.2 Methodology and Principal Assumptions Fuel rack is a 3-D array of square shaped cells that can hold nuclear fuel assemblies. [

]4.a, 4.b Details of the methodology are provided in the following sub-sections.

Method for Determining Spent Fuel Assembly Heat Up During a Theoretical Drain Down Event Holtec Proprietary Information HI-2200750 Rev. 0 Page D-2 of 31 Copyright © 2020 Holtec International, all rights reserved D.1.2.1 Details of the [

]4.a, 4.b 4.a, 4.b

Method for Determining Spent Fuel Assembly Heat Up During a Theoretical Drain Down Event Holtec Proprietary Information HI-2200750 Rev. 0 Page D-3 of 31 Copyright © 2020 Holtec International, all rights reserved 4.a, 4.b

Method for Determining Spent Fuel Assembly Heat Up During a Theoretical Drain Down Event Holtec Proprietary Information HI-2200750 Rev. 0 Page D-4 of 31 Copyright © 2020 Holtec International, all rights reserved D.1.2.2 [

]4.a, 4.b

]4.a, 4.b This approach is used in the various dockets approved by NRC (Table D.1.1).

[

]4.a, 4 b This approach is used in the various dockets approved by NRC (Table D.1.1).

]4.a, 4.b This approach is used in the various dockets approved by NRC (Table D.1.1).

D.1.2.3 [

]4.a, 4.b 4.a, 4.b

Method for Determining Spent Fuel Assembly Heat Up During a Theoretical Drain Down Event Holtec Proprietary Information HI-2200750 Rev. 0 Page D-5 of 31 Copyright © 2020 Holtec International, all rights reserved Eq (D.1.1) where:

D.1.2.4 [

]4.a, 4.b Eq (D.1.2) 4.a, 4.b 4.a, 4.b 4.a, 4.b 4.a, 4.b 4.a, 4.b

Method for Determining Spent Fuel Assembly Heat Up During a Theoretical Drain Down Event Holtec Proprietary Information HI-2200750 Rev. 0 Page D-6 of 31 Copyright © 2020 Holtec International, all rights reserved

[

]4.a, 4.b Eq (D.1.3)

where, Eq (D.1.4) where, Eq (D.1.5) 4.a, 4.b 4.a, 4.b 4.a, 4.b 4.a, 4.b 4.a, 4.b

Method for Determining Spent Fuel Assembly Heat Up During a Theoretical Drain Down Event Holtec Proprietary Information HI-2200750 Rev. 0 Page D-7 of 31 Copyright © 2020 Holtec International, all rights reserved

where, Eq (D.1.6)

Where, Eq (D.1.7)

Where, 4.a, 4.b 4.a, 4.b 4.a, 4.b 4.a, 4.b 4.a, 4.b

Method for Determining Spent Fuel Assembly Heat Up During a Theoretical Drain Down Event Holtec Proprietary Information HI-2200750 Rev. 0 Page D-8 of 31 Copyright © 2020 Holtec International, all rights reserved D.1.2.5 Inputs The following inputs are adopted for CFD analyses [

]4.a, 4.b using the models and methodology described in the above sub-sections:

[

]4.a, 4 b 4.a, 4.b

Method for Determining Spent Fuel Assembly Heat Up During a Theoretical Drain Down Event Holtec Proprietary Information HI-2200750 Rev. 0 Page D-9 of 31 Copyright © 2020 Holtec International, all rights reserved Table D.1.1: List of Prior NRC Approval on CFD Methodology Sl.

No Description NRC Docket No.

Location in Approved Docket

1.

[

]4.a, 4 b 72-1014 Section [

]4 a, 4.b 72-1032 Section [

]4 a, 4.b 72-1040 Section [

]4 a, 4.b 71-9325 Section [

]4 a, 4.b 71-9367 Section [

]4 a, 4.b 71-9373 Section [

]4 a, 4.b 71-9374 Section [

]4 a, 4.b

2.

[

]4.a, 4.b 72-1014 Section [

]4 a, 4.b 72-1032 Section [

]4 a, 4.b 72-1040 Section [

]4 a, 4.b

3.

[

]4.a, 4.b 72-1014 Section [

]4 a, 4.b 72-1032 Section [

]4 a, 4.b

4.

[

]4.a, 4.b 72-1014 Section [

]4 a, 4.b 72-1032 Section [

]4 a, 4.b 72-1040 Section [

]4 a, 4.b

5.

[

]4.a, 4 b 72-1014 Section [

]4 a, 4.b 72-1032 Section [

]4 a, 4.b 72-1040 Section [

]4 a, 4.b

6.

[

]4.a, 4 b 72-1014 Section [

]4 a, 4.b 72-1032 Section [

]4 a, 4.b 72-1040 Section [

]4 a, 4.b 71-9325 Section [

]4 a, 4.b

7.

[

]4.a, 4.b 72-1014 Section [

]4 a, 4.b 72-1032 Section [

]4 a, 4.b 72-1040 Section [

]4 a, 4.b 71-9325 Section [

]4 a, 4.b 71-9367 Section [

]4 a, 4.b 71-9373 Section [

]4 a, 4.b

Method for Determining Spent Fuel Assembly Heat Up During a Theoretical Drain Down Event Holtec Proprietary Information HI-2200750 Rev. 0 Page D-10 of 31 Copyright © 2020 Holtec International, all rights reserved Table D.1.2: Reference Fuel Parameters [

]4.a, 4.b Notes:

1. [

]4.a, 4.b 4.a, 4.b

Method for Determining Spent Fuel Assembly Heat Up During a Theoretical Drain Down Event Holtec Proprietary Information HI-2200750 Rev. 0 Page D-11 of 31 Copyright © 2020 Holtec International, all rights reserved Table D.1.3: Normalized Distribution Based on Burnup Profile [D.6.12]

PWR DISTRIBUTION Interval Axial Distance from Bottom of Active Fuel

(% of Active Fuel Length)

Normalized Distribution 1

0% to 16-2/3%

0.88755 2

16-2/3% to 33-1/3%

1.1050 3

33-1/3% to 50%

1.0980 4

50% to 66-2/3%

1.0790 5

66-2/3% to 83-1/3%

1.0501 6

83-1/3% to 100%

0.7804

Method for Determining Spent Fuel Assembly Heat Up During a Theoretical Drain Down Event Holtec Proprietary Information HI-2200750 Rev. 0 Page D-12 of 31 Copyright © 2020 Holtec International, all rights reserved Figure D.1.1: [

]4.a, 4.b 4.a, 4.b

Method for Determining Spent Fuel Assembly Heat Up During a Theoretical Drain Down Event Holtec Proprietary Information HI-2200750 Rev. 0 Page D-13 of 31 Copyright © 2020 Holtec International, all rights reserved Figure D.1.2: [

]4.a, 4 b 4.a, 4.b

Method for Determining Spent Fuel Assembly Heat Up During a Theoretical Drain Down Event Holtec Proprietary Information HI-2200750 Rev. 0 Page D-14 of 31 Copyright © 2020 Holtec International, all rights reserved Figure D.1.3(a): [

]4.a, 4.b 4.a, 4.b

Method for Determining Spent Fuel Assembly Heat Up During a Theoretical Drain Down Event Holtec Proprietary Information HI-2200750 Rev. 0 Page D-15 of 31 Copyright © 2020 Holtec International, all rights reserved Figure D.1.3(b): [

]4.a, 4.b 4.a, 4.b

Method for Determining Spent Fuel Assembly Heat Up During a Theoretical Drain Down Event Holtec Proprietary Information HI-2200750 Rev. 0 Page D-16 of 31 Copyright © 2020 Holtec International, all rights reserved D.2 ACCEPTANCE CRITERIA The acceptance criterion stated in NUREG-1738 [D.6.6] is adopted herein. The bulk average temperature of active fuel region of a fuel assembly shall not exceed 900oC after 10 hours1.157407e-4 days <br />0.00278 hours <br />1.653439e-5 weeks <br />3.805e-6 months <br /> of dry cooling.

Method for Determining Spent Fuel Assembly Heat Up During a Theoretical Drain Down Event Holtec Proprietary Information HI-2200750 Rev. 0 Page D-17 of 31 Copyright © 2020 Holtec International, all rights reserved D.3 BENCHMARKING AND VALIDATION OF CFD METHODOLOGY The Computational Fluid Dynamics (CFD) approach has a long history of solving a wide range of thermal analysis problems in the nuclear industry. The computer code ANSYS FLUENT is a QA-validated code [D.6.5] used for this purpose. Additionally, this code has been validated under 6.10]. Numerous wet and dry storage thermal-hydraulic evaluations have been performed using FLUENT and have been approved by the NRC (Table D.4.1).

The FLUENT thermal modeling methodology has been benchmarked using data from tests conducted with dry storage casks loaded with SNF. The benchmark work is archived in QA-validated Holtec reports2. A summary of a few benchmarking studies is presented below.

D.3.1 Benchmark against Test Data from TN-24P Cask The FLUENT thermal modeling methodology has been benchmarked with full-scale cask test data (EPRI TN-A-SFS modeling of the HI-STORM System [D.6.9]. The 3D thermal modeling methodology adopted in the benchmarking analysis is similar, as described below, to that used in the CFD evaluations presented in this Appendix.

1. [

]4.a, 4.b

2. [

]4.a, 4.b

3. [

]4.a, 4.b

4. [

]4.a, 4.b The measured cladding temperature from the test data are compared against predicted temperatures from the simulations. Test data documents results from various scenarios such as vertical orientation, pressurized gas, helium backfilled, nitrogen backfilled. All these scenarios were evaluated, and the results demonstrate that the thermal analysis methodology conservatively predicts the cladding temperatures measured. Also, the variation of the predicted cladding temperatures along the height of the fuel assemblies compared favorably with the experimental data. The benchmark work is archived in a QA-validated Holtec report [D.6.11]. This provides assurance that the CFD modelling approach is appropriate for evaluating the time it takes to achieve a temperature of 900ºC associated with a zirc fire.

D.3.2 Holtec has also performed a thermal validation test on a dry storage system loaded with SNF, as required by 6.7]. As part of this validation, the total air mass flow rate through the cask system using direct measurements of air 2 Specific references are cited in the following sub-sections.

Method for Determining Spent Fuel Assembly Heat Up During a Theoretical Drain Down Event Holtec Proprietary Information HI-2200750 Rev. 0 Page D-18 of 31 Copyright © 2020 Holtec International, all rights reserved velocity in the cask inlet vents was measured. An analysis of the cask system was performed using the CFD method [D.6.15], consistent with that outlined in this appendix, and results compared with the measurements. Uncertainties in the numerical and experimental studies were included in this comparison.

All analyzed scenarios presented in the report [D.6.15] conservatively bound the mass flow rate determined through the experimental methods.

D.3.3 Benchmarking Conclusions from NUREG NRC has independently performed benchmarking studies against experimental data from casks CFD code and methodology [D.6.14] using the experimental data documented in NUREG/CR-7250 [D.6.13], to test the validity of the modeling presently used to determine cladding temperatures and air mass flow rates in vertical dry casks. Multiple data sets of varying conditions were collected and analyzed for these efforts, as described in NUREG/CR-7250.

The 3D CFD modeling methodology adopted in the NUREG studies is similar to that used in the CFD evaluations presented in this Appendix. CFD models were built for each of these configurations and tested under the same conditions to support the validation study. Steady-state and transient simulations were performed at different decay heat power values and canister helium pressures. PCT, temperature profiles for different wall structures (i.e., channel box, basket, and pressure vessel), and air mass flow rate from the CFD predictions were compared to the experimental data. The CFD results and experimental data for PCT and air mass flow rate agreed favorably within the calculated validation uncertainty for all the cases [D.6.14].

Method for Determining Spent Fuel Assembly Heat Up During a Theoretical Drain Down Event Holtec Proprietary Information HI-2200750 Rev. 0 Page D-19 of 31 Copyright © 2020 Holtec International, all rights reserved Table D.3.1: Approved Holtec Systems under NRC Dockets that use FLUENT System Name NRC Docket Number HI-STORM 100 (Storage) 72-1014 HI-STORM Flood/Wind (Storage) 72-1032 HI-STORM UMAX (Storage) 72-1040 HI-STAR 100 (Transportation) 71-9261 HI-STAR 180 (Transportation) 71-9325 HI-STAR 180D (Transportation) 71-9367 HI-STAR 60 (Transportation) 71-9336 HI-STAR 100MB (Transportation) 71-9378 HI-STAR 80 (Transportation) 71-9374 HI-STAR 190 (Transportation) 71-9373

Method for Determining Spent Fuel Assembly Heat Up During a Theoretical Drain Down Event Holtec Proprietary Information HI-2200750 Rev. 0 Page D-20 of 31 Copyright © 2020 Holtec International, all rights reserved D.4 [

]

To illustrate that the method presented in main part of the report is bounding, CFD calculations are performed [

] 4.a, 4.b results from the two methods are compared. [

] 4.a, 4.b CFD evaluations presented in this section are performed using the methodology articulated in Section D.1. The principal steps are as follows:

] 4.a, 4.b presented herein demonstrates the acceptance criteria from Section D.2 is satisfied. Additionally, all the results demonstrate that the results

[

] 4.a, 4.b in the main report are bounding.

In addition to the above, [

]4.a, 4.b Therefore, these additional studies further ascertain the results presented in the main report are conservative.

4.a, 4.b 4.a, 4.b 4.a, 4.b 4.a, 4.b

Method for Determining Spent Fuel Assembly Heat Up During a Theoretical Drain Down Event Holtec Proprietary Information HI-2200750 Rev. 0 Page D-21 of 31 Copyright © 2020 Holtec International, all rights reserved Table D.4.1: [

]4 a, 4.b 4.a, 4.b

Method for Determining Spent Fuel Assembly Heat Up During a Theoretical Drain Down Event Holtec Proprietary Information HI-2200750 Rev. 0 Page D-22 of 31 Copyright © 2020 Holtec International, all rights reserved Table D.4.2: Fuel Data for Plant A Parameter Value Array Size 15 x 15 Fuel Cladding OD 10.72 mm Fuel Cladding ID 9.48 mm Fuel Pellet Diameter 9.29 mm Fuel Rod Pitch 14.30 mm Number of Guide Tubes 20 Number of Instrument Tubes 1

Guide Tube / Instrument Tube OD 10.72 mm Guide Tube / Instrument Tube thickness 0.43 mm Rod Height 3860.8 mm Active Height 3657.6 mm Weight of UO2 530 kg Weight of Zr 104 kg

Method for Determining Spent Fuel Assembly Heat Up During a Theoretical Drain Down Event Holtec Proprietary Information HI-2200750 Rev. 0 Page D-23 of 31 Copyright © 2020 Holtec International, all rights reserved Table D.4.3: Fuel Racks Region 2 Geometrical Data for Plant A Parameter Value Rack Cell ID 8.83 in Rack Height 165 in Bottom Rack Support Height 11 in Flux Trap Width Not Applicable Neutron Absorber Thickness3 0.075 in 3[

]4.a, 4.b

Method for Determining Spent Fuel Assembly Heat Up During a Theoretical Drain Down Event Holtec Proprietary Information HI-2200750 Rev. 0 Page D-24 of 31 Copyright © 2020 Holtec International, all rights reserved Table D. 4.4: [

]4.a, 4.b 4.a, 4.b

Method for Determining Spent Fuel Assembly Heat Up During a Theoretical Drain Down Event Holtec Proprietary Information HI-2200750 Rev. 0 Page D-25 of 31 Copyright © 2020 Holtec International, all rights reserved Table D.4.5: [

]4.a, 4.b Table D.4.6: [

]4.a, 4.b 4.a, 4.b 4.a, 4.b

Method for Determining Spent Fuel Assembly Heat Up During a Theoretical Drain Down Event Holtec Proprietary Information HI-2200750 Rev. 0 Page D-26 of 31 Copyright © 2020 Holtec International, all rights reserved Figure D.4.1: [

]4.a, 4.b 4.a, 4.b

Method for Determining Spent Fuel Assembly Heat Up During a Theoretical Drain Down Event Holtec Proprietary Information HI-2200750 Rev. 0 Page D-27 of 31 Copyright © 2020 Holtec International, all rights reserved Figure D.4.2: [

]4.a, 4.b 4.a, 4.b

Method for Determining Spent Fuel Assembly Heat Up During a Theoretical Drain Down Event Holtec Proprietary Information HI-2200750 Rev. 0 Page D-28 of 31 Copyright © 2020 Holtec International, all rights reserved Figure D.4.3: [

]4.a, 4.b 4.a, 4.b

Method for Determining Spent Fuel Assembly Heat Up During a Theoretical Drain Down Event Holtec Proprietary Information HI-2200750 Rev. 0 Page D-29 of 31 Copyright © 2020 Holtec International, all rights reserved Figure D.4.4: [

]4.a, 4.b 4.a, 4.b

Method for Determining Spent Fuel Assembly Heat Up During a Theoretical Drain Down Event Holtec Proprietary Information HI-2200750 Rev. 0 Page D-30 of 31 Copyright © 2020 Holtec International, all rights reserved D.5 CONCLUSIONS The CFD predictions in all cases support the conservative nature of the fuel pool heat up calculations from the simplified model in the main body of this report. These results from the CFD model and its use of the most widely used and QA-validated code for gaseous flow conditions in the nuclear industry (FLUENT) provides the confidence that the method presented in the main report can serve as a reliable vehicle for analyzing fuel pools in a drain down condition.

Method for Determining Spent Fuel Assembly Heat Up During a Theoretical Drain Down Event Holtec Proprietary Information HI-2200750 Rev. 0 Page D-31 of 31 Copyright © 2020 Holtec International, all rights reserved D.6 REFERENCES

[D.6.1]

Holtec Report #HI-971717 to the USNRC; Evaluation of Haddam Neck Fuel Storage System under complete water loss scenario (1997).

[D.6.2]

Holtec Report # HI-992135 to the USNRC; Evaluation of Millstone Point Unit 1 pool under complete loss of water (1999).

[D.6.3]

Holtec Report #HI-2022858 to the USNRC; Thermal Evaluation of the potential of Zirc Fire in the Vermont Yankee pool under loss of water assumption (2002).

[D.6.4]

ANSYS FLUENT Commercial Software, Lebanon, NH.

[D.6.5]

Holtec Report #HI-992252 to the USNRC, Topical Report on the Validation of FLUENT (1999).

[D.6.6]

Technical Study of Spent Fuel Pool Accident Risk at Decommissioning Nuclear Power Plants, NUREG-1738, February 2001.

[D.6.7]

HI-STORM 100 Safety Analysis Report, Holtec Report No. HI-2002444, Latest Revision.

[D.6.8]

HI-STORM FW Safety Analysis Report, Holtec Report No. HI-2114830, Latest Revision.

[D.6.9]

TN-24P PWR Spent-Fuel Storage Cask: Testing and Anal EPRI NP-5128, (April 1987).

[D.6.10]

-2177807, Revision

4.

[D.6.11]

2166981, Latest Revision.

[D.6.12] Evaluation of Axial Burnup and Void Profiles, Holtec Report HI-2167312, Revision

2.

[D.6.13]

-Hydraulic Experiments Using

-7250, October 2018.

[D.6.14]

Cask

-2238, June 2020.

[D.6.15]

I-2188214, Revision 1.