BVY 13-097, Proposed Change 306, Areva Document No. 32-9145461-001, Vynpp - Re-analysis of Ast/Fha Radiological Consequences with Open Containment

Proposed Change 306, Areva Document No. 32-9145461-001, Vynpp - Re-analysis of Ast/Fha Radiological Consequences with Open Containment

ML13323A519
Person / Time
Site:	Vermont Yankee
Issue date:	11/14/2013
From:	Entergy Nuclear Operations
To:	Office of Nuclear Reactor Regulation
References
BVY 13-097 32-9145461-001
Download: ML13323A519 (37)

Text

BVY 13-097 Docket 50-271 Attachment 4 Vermont Yankee Nuclear Power Station Proposed Change 306 AREVA Document No. 32-9145461-001, "VYNPP - Re-analysis of AST/FHA Radiological Consequences with Open Containment"

0402-01-FOl (Rev. 017,11/19/12)

A CALCULATION

SUMMARY

SHEET (CSS)

AREVA Document No. 32 - 9145461 - 001 Safety Related: M Yes 0i No Title VYNPP - Re-analysis of AST/FHA Radiological Consequences with Open Containment PURPOSE AND

SUMMARY

OF RESULTS:

The present calculation deals with the radiological evaluation of a design-basis fuel handling accident (FHA) taking place at the Vermont Yankee Nuclear Power Plant, based on the AST methodology (Ref. [1]), an open containment, and ground-level releases. The objectives in the original analysis (in Rev. 000) were as follows:

• Determination of the minimum required decay time after reactor shutdown that would ensure MCR habitability in its existing configuration (i.e., during normal operation with 3700 cfm of unfiltered air supplied for ventilation), and also under a pre-isolation condition (with an assumed 50 cfm of unfiltered inleakage for demonstrative purposes), and the required decay time for meeting the EAB dose,

• The benefits of upgrading the MCR HVAC system to include emergency intake-flow filtration, and

• The viability of MCR isolation prior to fuel movement, followed by MCR purge a few hours after an FHA.

Other objectives implemented in Rev. 001 include the following:

• Determination of the required decay time at which the EAB TEDE dose would be less than 1 rem (the recommended Protective Action Guide (PAG) limit for Evacuation (Ref. [2], Table 2-1),

• Clarification that the analysis covers a fuel assembly drop ineither the reactor cavity pool or in the SFP during a full-core offload, and

• Re-issuance of the calculation as "Non-Proprietary."

The starting point of the analysis was confirmation of the FHA results inthe VYNPP calculation of record (Ref. [3]). A summary of the results and conclusions appear in Section 6.0. Points of interest are as follows:

(a) The EAB TEDE dose with open containment is less than the regulatory limit (6.3 rem) even with a 24-hr pre-FHA decay time, and the required decay time for an EAB dose of less than 1 rem TEDE is 17 days.

(b) Adecay time of about 11 to 13 days would be needed to achieve an MCR dose less than 5 rem, for intake flows ranging between 50 cfm (with the MCR pre-isolated) and 3700 cfm (current MCR configuration).

(c) Upgrade of the MCR HVAC system to include intake-flow emergency filtration can reduce the required decay time to 5 days.

(d) Pre-isolation of the MCR followed by MCR purge appears to be a viable option.

This work was performed under AREVA's Quality Assurance Program and is appropriate for safety-related design work. The latest revision of AREVA NP Procedure 0402-01, Calculations, was followed.

THE DOCUMENT CONTAINS ASSUMPTIONS THAT SHALL BE THE FOLLOWING COMPUTER CODES HAVE BEEN USED IN THIS DOCUMENT: VERIFIED PRIOR TO USE CODENERSION/REV CODENERSION/REV ELISA-2, Version 2.4ZN SViYES Page 1 of 34

.A. 0402-01-FOI (Rev, 017,11119h12)

A .V.A Document No. 32-9145461-001 WNPP - Re-analysis of AST/FHA Radiological Consequences with Open Containment Review Mothod: I Design Revlow (DetaUed Check)

E] Attertate Calculation Signature Block Note: P/R/A designates Prep*aer (P), Reviewer (R), Approver (A);

LP/LR designates Lead Preparer (LP), Lead Reviewer (LR)

Project Manager Approval of Custotner References (NIA if not applicable)

Name Title (printed or typed) (printed or typed) Signature Date Tamnny Natou' ProjectManager Qo \ 4 IA 1115113 lVMentorIng Information (not required per 0402-01)

Name Title Mentor to:

(printed or typed) (printed or typed) (PIR) Signature Date N/A Page 2 I

A 0402-01-F01 (Rev. 017, 11/19/12)

AREVA Document No. 32-9145461-001 VYNPP - Re-analysis of AST/FHA Radiological Consequences with Open Containment Record of Revision Revision Pages/Sections/Paragraphs No. Changed Brief Description / Change Authorization Rev. 000 N/A Original issue Rev. 001 CSS Updated the cover sheet to include the objectives of the new revision, and the additional results.

Section 1.1 Inserted comment clarifying that, for either an open or closed containment, the FHA analytical model and associated assumptions are applicable to a fuel assembly drop in either the reactor cavity pool or in the SFP during a full-core offload.

Section 1.2 Added the PAG limit of 1 rem TEDE as part of the acceptance criteria.

Table 3-1 Added table Note (a) clarifying the use and implications of the radial peaking factor.

Table 3-3 Added table note regarding the applicability of the 1995-1999 hourly meteorological data in the current applications.

Section 4.1 Identified the operating platform for the new ELISA-2 computer run (differs from than in Rev. 000).

Section 4.2 Updated the ColdStor location name for the Rev. 000 computer files, and included the location for the new files.

Updated the title for Table 4-1 to identify it as being solely for the Rev. 000 computer files, and added new Table 4-2 for the Rev. 001 files.

Section 5.2.2 Updated the documentation to include the EAB doses following the additional decay times of 17 and 19 days, and updated the corresponding entries in Table 5-3 and Figure 5-1.

Section 6.0 Updated the Summary of Results and Conclusions to address the new objectives added in Rev. 001.

Section 7.0 Added new Ref. [2], the EPA PAG manual; remaining references were automatically renumbered.

All Minor editorial changes, as needed, including identification of the correct RG 1.183 Appendix B section (namely, Section 5.3 instead of 4.1) for the release rate from the containment to the atmosphere. Section 4.1 is for releases from the fuel building, which for BWRs is within the containment.

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A ARE VA Document No. 32-9145461-001 VYNPP - Re-analysis of AST/FHA Radiological Consequences with Open Containment Table of Contents Page SIG NATURE BLOCK ............................................................................................................................. 2 RECO RD O F REVISIO N ....................................................................................................................... 3 LIST O F TABLES .................................................................................................................................. 6 LIST O F FIG URES ................................................................................................................................ 7 1.0 ANALYTICAL METHODO LOGY ............................................................................................ 8 1.1 G e n e ra l.............................................................................................................................................. 8 1.2 A cce pta n ce C rite ria ........................................................................................................................... 8 1.3 R o u n d off E rro rs ................................................................................................................................. 9 2.0 ASSUM PTIO NS ........................................................................................................................ 9 2.1 Assumptions Requiring Justification ........................................................................................... 9 2 .2 J u stifie d A ss u m ptio n s ........................................................................................................................ 9 2.3 Modeling Simplifications ................................................................................................................. 10 3.0 DESIG N INPUT ........................................................................................................................ 11 4.0 SO FTW ARE AND CO MPUTER FILES .................................................................................. 15 4 .1 S o ftw a re ......................................................................................................................................... 15 4.2 C o m p u te r F ile s ............................................................................................................................... 15 5.0 ANALYSIS AND RESULTS ...................................................................................................... 17 5.1 Confirmatory Analyses - Closed Containment and Elevated Release ...................................... 17 5.1.1 Accident Scenario ....................................................................................................... 17 5.1.2 Radiological Consequences and Comparison with Calculation of Record ................ 20 5.2 FHA with Open Containment, Ground-Level Release and Existing MCR Design .................... 21 5.2.1 Accident Scenario ....................................................................................................... 21 5.2.2 Radiological Consequences ....................................................................................... 21 5.3 FHA with Open Containment, Ground-Level Release and MCR Upgraded Design .................. 27 5.3.1 Accident Scenario ....................................................................................................... 27 5.3.2 Radiological Consequences ....................................................................................... 27 5.4 FHA with Open Containment, Ground-Level Release, Pre-FHA MCR Isolation and Post-FHA MC R Pu rge .................................................................................................................................... 29 Page 4

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ARE VA Document No. 32-9145461-001 VYNPP - Re-analysis of AST/FHA Radiological Consequences with Open Containment Table of Contents (continued)

Page 5.4 .1 A ccident S cenario ..................................................................................................... . . 29 5.4.2 Radiological Consequences ........................................................................................ 30 6.0

SUMMARY

OF RESULTS AND CONCLUSIONS ................................................................. 32 7 .0 R E F E R E N C E S ......................................................................................................................... 34 Page 5

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ARE VA Document No. 32-9145461-001 VYNPP - Re-analysis of AST/FHA Radiological Consequences with Open Containment List of Tables Page Table 2-1: Fractional Release of Radioactivity to Atmosphere at 2 Air Changes per Hour ................ 9 Table 3-1: VYNPP - Design Input for FHA ..................................................................................... 11 Table 3-2: VYNPP Undecayed Core Inventory for Radionuclides Important in the Radiological E va lua tio n o f D B As ....................................................................................................................... 13 Table 3-3: Atmospheric Dispersion Factors for the Postulated FHA ................................................ 14 Table 4-1: List of Computer Files Transferred to the AREVA ColdStor Server for Rev. 000 ............ 15 Table 4-2: List of Computer Files Transferred to the AREVA ColdStor Server for Rev. 001 ............ 16 Table 5-1: Undecayed Activity Available for Release from FHA Damaged Fuel Rods ..................... 19 Table 5-2: FHA Re-Analysis - Comparison with Calculation of Record ........................................... 20 Table 5-3: VY FHA - EAB and MCR TEDE Dose vs. Decay Time .................................................. 22 Table 5-4: Time Dependence of MCR Cumulative Dose - Sample Cases ...................................... 23 Table 5-5: VY FHA - MCR TEDE Dose with ESF Filtration vs. Decay Time and Unfiltered Inleakage. 28 Table 5-6: VY FHA - MCR TEDE Dose with 5-Day Decay, Pre-FHA Isolation and Post-FHA Purge... 31 Page 6

A AREVA Document No. 32-9145461-001 VYNPP - Re-analysis of AST/FHA Radiological Consequences with Open Containment List of Figures Page Figure 5-1: VY FHA - EAB TEDE Dose vs. Decay Time ................................................................ 24 Figure 5-2: VY FHA - MCR TEDE Dose vs. Decay Time and Intake/Inleakage Flow Rate ............. 25 Figure 5-3: Time Dependence of MCR Cumulative TEDE Dose - Sample Cases ........................... 26 Page 7

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ARE VA Document No. 32-9145461-001 VYNPP - Re-analysis of AST/FHA Radiological Consequences with Open Containment 1.0 ANALYTICAL METHODOLOGY 1.1 General The postulated accident scenarios were based on the Alternative Source Term (AST) Methodology in Ref. [1]

(RG 1.183, Appendix B). Two main configurations of the reactor building during fuel movement were considered, as follows:

A closed containment, for the purpose of replicating the current licensing basis (in Ref. [3]) and thus provide a valid starting point for the re-analyses documented in the present calculation, and An open containment, for the purpose of identifying the required decay time prior to fuel movement and the various pre- and post-FHA Main Control Room (MCR) ventilation configurations that would support refueling with open containment.

It is noted that, for either configuration, i.e., open or closed containment, the analytical model and associated assumptions are applicable to a fuel assembly drop in either the reactor cavity pool or in the SFP during a full-core offload.

The analysis was based on the ELISA-2 computer code [4]. The dose conversion factors in ELISA-2 are from Federal Guidance Reports 11 and 12 (Refs. [5] and [6]). Dose rates and cumulative doses are computed for each organ, TEDE, skin and air. Of these, only the TEDE doses are presented in the main body of the calculation for comparing with regulations, which only specify TEDE limits; all other doses may be found in the ELISA-2 computer outputs, along with time-dependent dose rates.

Reference [1] (RG 1.183, Appendix B, Sec. 5.3, Footnote 3) states that the following provisions need to be implemented for refueling operations with open containment:

"The (NRC) staff will generally require that technical specifications allowing such operations (i.e., open containment during fuel handling operations) include administrative controls to close the airlock, hatch, or open penetrations within 30 minutes. Such administrative control will generally require that a dedicated individual be present, with necessary equipment available, to restore containment closure should a fuel handling accident occur. Radiological analyses should generally not credit this manual isolation."

This provision is discussed further in Ref. [7] (NUMARC 93-01, Sec. 11.3.6.5).

1.2 Acceptance Criteria The basic radiological acceptance criteria associated with the AST methodology are spelled out in 10 CFR 50.67, and amount to 25 rem TEDE for offsite receptors and 5 rem for control room personnel. These criteria, however, are for evaluating potential reactor accidents of exceedingly low occurrence probability and low risk of public exposure to radiation. For events with higher probability of occurrence, such as a fuel handling accident, the acceptance criteria for the offsite receptors are more stringent, while that for the control room operators remains the same. The applicable AST criteria for an FHA are as follows (Ref. 1, and 10 CFR 50.67):

Exclusion Area Boundary (EAB): 6.3 rem TEDE Page 8

A ARE VA Document No. 32-9145461-001 VYNPP - Re-analysis of AST/FHA Radiological Consequences with Open Containment Low Population Zone (LPZ): 6.3 rem TEDE Control Room (CR): 5.0 rem TEDE The EAB and LPZ criteria are referred to as being "well within" the regulatory limits (i.e., 25%).

The LPZ doses were not addressed in the present calculation since the release occurs within two hours, and as a result they are bounded by the corresponding doses at the EAB.

In Rev. 001, an additional objective was added to determine the required decay time that would preclude Evacuation as a protective action following an FHA. The limit for such an action is 1 rem TEDE (Ref. [2], Table 2-1).

1.3 Roundoff Errors Some of the entries in the various tables in this calculation were generated using a Microsoft Office EXCEL-2003 spreadsheet. As a result, some results may not be exactly duplicated by hand calculation due to round-off of significant figures. Validations of the spreadsheet results are included as footnotes to the tables, where applicable.

2.0 ASSUMPTIONS 2.1 Assumptions Requiring Justification There are no unjustified assumptions employed in the present calculation.

2.2 Justified Assumptions Release Rate from Reactor Building In line with Ref. [1] (RG 1.183, Appendix B, Sec. 4.1 for an FHA in the SFP, and Sec. 5.3 for an FHA in the reactor cavity pool), the radioactive material that escapes the water pool was assumed to get released to the environment over a 2-hour interval. Analytically, this was accomplished by using a building air exchange rate of 2.0 air changes per hour (ACH, equivalent to 48 air changes per day, an ELISA-2 input). This air exchange rate leads to [1.0 - exp{-2.0 (hr-')*15 (min) / 60 (min/hr)}] = 39.3% of the airborne activity within the reactor building getting released within 15 minutes. Other release fractions as a function of post-FHA time are listed below.

Table 2-1: Fractional Release of Radioactivity to Atmosphere at 2 Air Changes per Hour Post-FHA Activity Post-FHA Activity Released to Released to Time(min) Atmosphere Time (min) Atmosphere 15 39.3% 60 86.5%

30 63.2% 90 95.0%

45 77.7% 120 98.2%

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AREVA Document No. 32-9145461-001 VYNPP - Re-analysis of AST/FHA Radiological Consequences with Open Containment The 2 ACH is the RB release rate that was used in the majority of the computer runs. Four sensitivity cases (ELISA-2 Run Cases K10 through K13 in Section 5.4) make use of 1 and 0.25 ACH release rates to assess the dose impact on MCR purge initiation time.

It is noted that, for the MCR 30-day dose computations, the releases from the RB were assumed to continue for 30 days. Included in the releases beyond 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br /> are the (100 - 98.2) = 1.8% still airborne within the RB at 2 hrs (from Table 2-1), as well as the noble gases generated by the decay of iodines retained by the pool water.

MCR Filtered Intake Flow and Unfiltered Inleakage For the cases with filtered MCR intake (postulated upgrade of HVAC system), the total exhaust flow from the MCR was assumed to be 3700 cfm, and to consist of both the intake flow and any unfiltered inleakage. For these cases, the filtered intake flow was assumed to be 3700 cfm less the unfiltered inleakage. This is conservative since it increases the fraction of unfiltered flow entering the MCR, while maintaining a fixed clean-up rate.

The unfiltered intake flows were assumed to include 10 cfm due to ingress and egress, in line with Ref. [8].

The atmospheric dispersion factors for the transport of RB releases to the MCR main intake and to the MCR inleakage location were assumed to be the same.

MCR Finite Cloud Correction Doses to MCR personnel due to the external gamma radiation from airborne radioactivity within the MCR were adjusted using the Murphy/Campe finite-cloud correction model in Ref. 1 (Sec. 4.2.7). Even though this model tends to be non-conservative for nuclides emitting low gamma radiation, it was used in the present application in lieu of the nuclide-specific finite-cloud model in ELISA-2. This selection is immaterial since the MCR doses are primarily due to the inhalation pathway, with the submersion pathway contributing less than about 1% (from the ELISA-2 output files, summary pages, showing the percent contribution of the inhalation pathway to the total dose).

2.3 Modeling Simplifications There are no modeling simplifications employed in the present calculation. ELISA-2 was modeled to handle the pre-FHA decay correction, the time-release from the RB, and the time-dependence of the MCR flows (as applicable). The ELISA-2 built-in logic accounts for the time-dependent generation and release of noble gases from the decay of halogens retained by the pool water, and on the MCR intake filter where applicable; these releases extend beyond the end of the 2-hr release from the RB.

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A AREVA Document No. 32-9145461-001 VYNPP - Re-analysis of AST/FHA Radiological Consequences with Open Containment 3.0 DESIGN INPUT The design input employed in the analyses, and the associated references, are summarized in Table 3-1 through Table 3-3.

Table 3-1: VYNPP - Design Input for FHA No. DESCRIPTION VALUE REFERENCE / COMMENTS A - FHA Source Term Al Power level for DBA analysis 1950 MWt

[Includes

' 2 % measurement uncertainty]

A2 Number of assemblies in core 368 Ref. [3]

A3 Maximum allowed radial peaking factor(a) 1.65 A4 Pin failure fraction 0.571%

Equivalent number of damaged peak assemblies, and Calculated:

A5 fractions thereof 2.101 [368 assemblies

• 0.571% failure fraction]

Power level associated with damaged rods in peak Calculated:

A6 assemblies 18.37 MWt [1950 MWt

• 0.571% failure assemblies fraction

• 1.65 Peaking Factor]

Fuel rod gap fractions (AST Methodology) 1-131 0.08 A7 Kr-85 0.10 Ref. [1]

Other noble gases 0.05 (Reg. Guide 1.183, Table 3)

Other halogens 0.05 Alkali metals (Cs and Rb) 0.12 A8 Undecayed core inventory for radionuclides important in the See Table 3-2 Ref. [9], Table 4.5

___evaluation of FHAs A9 Post-shutdown decay time prior to postulated accident Various Assumed values B - Atmospheric Release Resulting from Postulated FHA B 1 Percent of damaged-fuel rod gap activity release 100 %

Noble gases I B2 Overall pool decontamination factor (DF) Halogens 200 Alkalis Infinite Ref. [1]

B3 Required water depth above fuel for above DFs 23 ft (Reg. Guide 1.183, Appendix B)

B4 Halogen composition in airborne release Elemental 57 %

(composition above pool) IOrganic 43%

B5 Reactor building configuration during refueling operations Open B6 Potential release point to the atmosphere RB blowout Ref, [10]

______________________________ ___________ panel BaseCase 2 hrs Ref. [1]

B7 Release duration to atmosphere, and (2 ACH)r.183, (Reg. Guide Appendix B) corresponding air changes per hour (ACH) Certain Others (0.25 and 1 Sensitivity analyses ACH)

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ARE VA Document No. 32-9145461-001 VYNPP - Re-analysis of AST/FHA Radiological Consequences with Open Containment Table 3-1 (Continued)

VYNPP - Design Input for FHA No. DESCRIPTION VALUE REFERENCE I COMMENTS C - Control Room Characteristics Cl Control room free air volume 41534 ft3 Ref. [3]

Nominal unfiltered intake flow Ref. [3] (Sensitivity analyses for accident duration (assumed include various pre-FHA decay C2 to include fresh air and air from 3700 cfm times ranging from Ito 15 days) surrounding areas as a result of [See Sections 5.1 and 5.2]

ingress, egress and inleakage)

With MCR isolation prior to fuel Minimized value for sensitivity C3 movement, and unfiltered 50 cfm analysis, along with various pre-inleakage, for accident duration FHA decay times (same as in Case C2) [See Section 5.2]

MCR HVAC With operator-initiated ESF Filtration actuation at 20 Sensitivity analyses, along with configuration filtration (4" charcoal beds with and 30 minutes post FHA, vity ale s, ay tith C4 99% halogen removal efficiency, and 50, 100 and 200 cfm vanious pre-FHA decay times or 2" beds with 95% efficiency), unfiltered inleakage; 3700 ranging from 3 to 8 days and unfiltered inleakage cfm total exhaust. [See Section 5.3]

100 and 150 cfm unfiltered With MCR isolation prior to fuel leakage,Sensitivity analyses, with 5-day C5 movement, followed by post- release rates, time-shifted pre-FHA decay time FHA purge atmospheric dispersionSection 5.4]

factors, and various purge initiation times D - Other Variables D1 Atmospheric dispersion factors from release point to See Table 3.3 Ref, [3], and Ref. [10], Section 6

___locations of interest_______________

D cations oiterest Control Room 0 - 720 hrs 3.5E-04 m33/sec Ref. [1], pg 1. 183-18 D2 Breathing rates EAB 0 - 2 hr 3.5E-04 M /sec Ref. [I], pg 1. 183-16 0 - 24 hrs 1.0 D3 Control room occupancy factors 24 - 96 hrs 0.6 Ref. [1], pg 1.183-18 96 - 720 hrs 0.4 D4 Exposure IntervalsNb) Control room 30 days Ref. [1], Sections 4.1.3, 4.1.5 and EAB 2 hrs 4.2.6 iRef. [1], pg 1.183-19, and Control room TEDE 5 rem Ref. [1], Sec.183(19,iand D5 Regulatory dose limits EAB TEDE 6.3 rem Ref [1], Te 6 ILPZ TEDE 6.3 rem D6 PAG Evacuation dose limit (EAB TEDE) 1 rem Ref, [2], Table 2-1 (a) Item #A3: In line with RG 1.183 (Ref. [1], Sec. 3.1), the radial peaking factor is applied to the average fuel-assembly inventory based on the core inventory in Table 3-2. This is a conservative approach and bounds any potential variations in the FHA source term resulting from variations in the EFPDs and burnup in any given cycle.

(b) Item #D4: Even though all radioactivity is released to the atmosphere within 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br /> following a design-basis FHA, the exposure intervals for the CR personnel was assumed to be 30 days. This provides adequate time for cleanup of the airborne radioactivity still present within the CR after termination of the 2-hr release, and also accounts for the delayed release of noble-gas decay products from the refueling pool water produced upon decay of halogens retained therein.

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A AREVA Document No. 32-9145461-001 VYNPP - Re-analysis of AST/FHA Radiological Consequences with Open Containment Table 3-2: VYNPP Undecayed Core Inventory for Radionuclides Important in the Radiological Evaluation of DBAs (From Ref. [9], Table 4.5, based on 1950 MWt, an enrichment range from 3.0 to 4.65 wt % U-235, and core-average burnup from 5 to 58 GWD/MTU)

Nuclide Core Ci Nuclide Core Ci Br-83 8.267E+06 1-132 7.900E+07 Kr-83m 8.265E+06 Te-133 6.602E+07 Br-85 1.874E+07 Te-133m 4.493E+07 Kr-85 9.852E+05 1-133 1.130E+08 Kr-85m 1.894E+07 Xe-133 1.128E+08 Rb-86 2.496E+05 Xe-133m 3.428E+06 Kr-87 3.788E+07 Te-134 1.036E+08 Kr-88 5.355E+07 1-134 1.254E+08 Kr-89 6.755E+07 Cs-134 2.971E+07 Sr-89 6.724E+07 1-135 1.051E+08 Sr-90 7.999E+06 Xe-135 4.540E+07 Y-90 8.363E+06 Xe-135m 2.232E+07 Sr-91 8.684E+07 Cs-136 7.602E+06 Y-91 8.270E+07 Xe-137 9.893E+07 Sr-92 8.987E+07 Cs-137 1.186E+07 Y-92 9.008E+07 Ba- 137m 1.124E+07 Y-93 9.857E+07 Xe-138 9.851E+07 Zr-95 9.645E+07 Ba-139 1.043E+08 Nb-95 9.673E+07 Ba-140 1.004E+08 Zr-97 9.596E+07 La-140 1.009E+08 Mo-99 1.034E+08 La-141 9.573E+07 Tc-99m 9.05 IE+07 Ce- 141 9.255E+07 Ru-103 9.889E+07 La-142 9.387E+07 Ru-105 7.844E+07 Ce-143 9.228E+07 Rh-105 7.183E+07 Pr-143 9.181E+07 Ru- 106 5.554E+07 Ce- 144 7.268E+07 Sb-127 7.194E+06 Nd-147 3.736E+07 Te-127 7.151E+06 Np-239 1.496E+09 Te-127m 9.705E+05 Pu-238 7.668E+05 Sb-129 1.976E+07 Pu-239 2.864E+04 Te- 129 1.947E+07 Pu-240 6.061E+04 Te-129m 2.890E+06 Pu-241 1.281E+07 Te- 131 m 8.405E+06 Am-241 1.702E+04 1-131 5.564E+07 Cm-242 6.669E+06 Xe-131m 6.192E+05 Cm-244 2.358E+06 Te-132 7.739E+07 II Page 13

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AR EVA Document No. 32-9145461-001 VYNPP - Re-analysis of AST/FHA Radiological Consequences with Open Containment Table 3-3: Atmospheric Dispersion Factors for the Postulated FHA (From Ref. [3], and Ref. [10], Section 6)

Release Receptor Post-FHA x/Q No. Point Point Interval (sec/m 3)

I Main stack (Calculation EAB Instantaneous 1.35E-04 of record with closed release 2 containment, for Control Room Instantaneous 6.04E-05 confirmatory analyses) Fresh Air Intake release 3 EAB 0 - 2 hrs 1.69E-03 0 - 2 hrs 5.89E-03 RB blowout panel, for 2 - 8 hrs 1.53E-03 present application with Control Room open containment Fresh Air Intake 8 - 24 hrs 6.41E-04 24 - 96 hrs 6.64E-04 96 - 720 hrs 5.1OE-04 Note: The atmospheric dispersion factors in this table were based on the analysis of a combined 5-years' worth of hourly meteorological data collected on site (1995-1999), and were used in the AST implementation at VYNPP. According to Reg. Guide 1.183 (Ref. [1], Section 5.3, Meteorology Assumptions), "Atmospheric dispersion values (x/Q)for the EAB, the LPZ, and the control room that were approved by the staff during initial facility licensing or in subsequent licensingproceedingsmay be used in performing the radiologicalanalyses identified in this guide." The FHA analysis is addressed in Appendix B of the guide.

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A AREVA Document No. 32-9145461-001 VYNPP - Re-analysis of AST/FHA Radiological Consequences with Open Containment 4.0 SOFTWARE AND COMPUTER FILES 4.1 Software Computation of the EAB and MCR radiological consequences for the postulated FHA were based on the ELISA-2 computer code (Ref. [4], Version 2.4) for all the analyzed scenarios. ELISA-2 is in the AREVA NP Engineering Application Software Index (EASI). There are no software errors that affect its application in the present calculation.

All ELISA-2 runs were carried out on the following platforms:

Rev. 000: HP 9000/785 CPU running HP UX B.10.20.

Rev. 001: HP 9000/800 CPU running HP UX B. 11.11 4.2 Computer Files The input and output files for the computer runs associated with the present document are available on the AREVA ColdStor System, under the following folders:

Rev. 000: \cold\General-Access\32\32-9000000\32-9145461 -000\official Rev. 001: \cold\ General-Access\32\32-9000000\32-9145461-001 \official The list of files in these folders are presented in Table 4-1 and Table 4-2. It is noted that each listed case has a number of stacked sub-cases, bringing the total number of analyzed scenarios to 72 for Rev. 000 and to 3 for Rev.

001.

Table 4-1: List of Computer Files Transferred to the AREVA ColdStor Server for Rev.

000 File Name Size (Bytes) Date/Time ELISA-2 Input (*.ell) and Output (*.el2) Files for Section 5.1 (Confirmatory Anal ses - Closed Containment and Elevated Release)

Ii2-VY-FHA-A.ell 6430 Sep23 2010 16:01:04 eli2-VY-FHA-A.e12 157935 Sep 23 2010 16:01:12 ELISA-2 Input and Output Files for Section 5.2 (FHA with Open Containment, Ground-Level Release and Existing MCR Design) eli2-VY-FHA-B.ell 8918 Sep 21 2010 09:22:42 eli2-VY-FHA-B.eI2 330662 Sep 21 2010 09:29:58 eli2-VY-FHA-C.ell 10989 Sep 24 2010 09:50:42 eli2-VY-FHA-C.eI2 398144 Sep 24 2010 09:51:38 eli2-VY-FHA-D.ell 10980 Sep 24 2010 09:51:16 eli2-VY-FHA-D.eI2 398144 Sep 24 2010 09:51:28 Page 15

- .~ ~~K.f' U A

AR EVA Document No. 32-9145461-001 VYNPP - Re-analysis of AST/FHA Radiological Consequences with Open Containment Table 4-1 (Continued)

List of Computer Files Transferred to the AREVA ColdStor Server for Rev. 000 File Name Size (Bytes) Date/Time ELISA-2 Input and Output Files for Section 5.3 (FHA with Open Containment, Ground-Level Release and MCR Upgraded Design) eli2-VY-FHA-E.ell 9646 Sep 24 2010 11:41:04 eli2-VY-FHA-E.e12 257679 Sep 24 2010 11:41:14 eli2-VY-FHA-F.ell 6417 Sep 24 2010 12:24:02 eli2-VY-FHA-F.e12 174641 Sep 24 2010 12:24:12 eli2-VY-FHA-G.ell 9670 Sep 24 2010 11:43:50 eli2-VY-FHA-G.e12 257679 Sep 24 2010 11:44:06 eli2-VY-FHA-H.ell 6425 Sep 24 2010 12:24:48 eli2-VY-FHA-H.e12 174641 Sep 24 2010 12:24:54 eli2-VY-FHA-I.ell 9670 Sep 24 2010 11:47:26 eli2-VY-FHA-I.e12 257679 Sep 24 2010 11:47:36 eli2-VY-FHA-J.ell 6425 Sep 24 2010 12:25:24 eli2-VY-FHA-J.e12 174641 Sep 24 2010 12:25:32 ELISA-2 Input and Output Files for Section 5.4 (FHA with Open Containment, Ground-Level Release, Pre-FHA MCR Isolation and Post-FHA MCR Purge) eli2-VY-FHA-K.ell 19053 Sep 23 2010 13:53:52 eli2-VY-FHA-K.e12 717635 Sep 23 2010 13:54:44 Table 4-2: List of Computer Files Transferred to the AREVA ColdStor Server for Rev.

001 File Name Size (kBytes) Date/Time ELISA-2 Input and Output Files for Section 5.2 (FIA with Open Containment, Ground-Level Release, Additional Decay Times for EAB Dose - Supplements Case B in Table 4-1) eli2-VY-FHA-B1.el1* 3346 Oct 23 2013 13:58:00 e1i2-VY-FHA-B1.e12* 127291 Oct 23 2013 14:51:44 Includes Case B8 as a confirmatory subcase duplicating the results in Rev. 000 (files el2-VY-FHA-B.eI*)

Page 16

A ARE VA Document No. 32-9145461-001 VYNPP - Re-analysis of AST/FHA Radiological Consequences with Open Containment 5.0 ANALYSIS AND RESULTS Presented in the subsections which follow are the following FHA evaluations:

• Confirmatory analyses for comparison with the calculation of record (with closed containment and elevated release),

0 Analyses similar to those in the calculation of record, but for a ground-level release, with extended pre-FHA decay times to determine the acceptable scenario that would meet the dose acceptance criteria at all receptors of interest (EAB and MCR), along with a sensitivity runs with MCR isolation prior to fuel movement, 0 Sensitivity analyses under the assumption that the MCR HVAC system will be upgraded to include emergency ESF filtration of the intake flow, and 0 Sensitivity analyses with pre-FHA MCR isolation and post-FHA MCR purge (without ESF filtration).

Details follow. It is noted that the description which follows deals with an FHA taking place in the reactor cavity pool. Nonetheless, the analytical model and associated assumptions are applicable to a fuel assembly drop in either the reactor cavity pool or in the SFP during a full-core offload.

5.1 Confirmatory Analyses - Closed Containment and Elevated Release 5.1.1 Accident Scenario Pertinent assumptions employed in the calculation of record (Ref. [3]) are as follows:

(a) The reactor has been operating at full power (1950 MWt) for an extended period of time.

(b) The reactor is shutdown, refueling operations are initiated and an FHA takes place at either 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> after shutdown (all rods in)', or at 96 hours0.00111 days <br />0.0267 hours <br />1.587302e-4 weeks <br />3.6528e-5 months <br />.

(c) The accident was assumed to involve the dropping of an assembly onto other assemblies, leading to the equivalent clad failure of the fuel rods in 2.101 assemblies (from Table 3-1, Item #A5). All failed rods are peak powered, with a radial peaking factor of 1.65 (from Table 3-1, Item #A3).

(d) All activity within the gaps of the failed fuel rods is released to the reactor cavity pool. The released activity corresponds to 8% of the entire inventory of 1-131 in the rods (i.e., within the fuel matrix and gaps), 10% of the Kr-85, 5% of the remaining halogens and noble gases, and 12%

of the alkalis (Cs and Rb), from Table 3-1, Item #A7. The activity released from the damaged fuel rods is presented in Table 5-1.

(e) All the noble gases and ( 1/ 2 0 0 )t" of the halogens escape from the pool and are released to the refueling level. All the alkalis are retained by the pool. The halogen composition above the pool is 57 % in elemental form and 43 % in organic form2 , from Table 3-1, Items #B2 and #B4.

Fuel movement initiation at 96 hours0.00111 days <br />0.0267 hours <br />1.587302e-4 weeks <br />3.6528e-5 months <br /> after shutdown is more typical (Ref. [3]).

Page 17

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ARE VA Document No. 32-9145461-001 VYNPP - Re-analysis of AST/FHA Radiological Consequences with Open Containment (f) In line with Ref. [1] (Appendix B, See. 5.3), the radioactive material that escapes the reactor cavity pool was assumed to get released to the environment over a 2-hour interval. As a simplification, the calculation of record assumed the release to the atmosphere to be instantaneous; the same assumption was made in the confirmatory analyses.

(g) The reactor building was assumed to be closed during the refueling operations, such that all releases to the environment would be via the main stack, with no credit for any filtration by the SGTS system, or any in-transit decay and plateout. A sensitivity analysis assuming a ground-level release was also evaluated in the MCR habitability, in both the calculation of record and the current calculation.

(h) Transport of the released radioactivity to the receptors of interest is dictated by the applicable atmospheric dispersion factors in Table 3-3.

(i) The MCR ventilation system was assumed to remain in the normal operating mode during the entire exposure interval (30 days). The air intake flow is 3700 cfm (includes additional flow from surrounding areas as a result of ingress, egress and leakage) and is unfiltered.

(j) Breathing rates and MCR occupancy factors are as given in Table 3-1, Items #D2 and #D3.

(k) The control room operators were assumed to be located at the base of a hemispherical cloud having a volume equal to the free air volume of the control room. Finite-cloud correction to the submersion dose was based on the Murphy/Campe equation in Reg. Guide 1.183 (Sec. 4.2.7).

2 The halogen composition has no impact in this analysis since the filtration efficiencies in the sensitivity cases with ESF filters was assumed to be the same for all halogen species.

Page 18

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A AREVA Document No. 32-9145461-001 VYNPP - Re-analysis of AST/FHA Radiological Consequences with Open Containment Table 5-1: Undecayed Activity Available for Release from FHA Damaged Fuel Rods Activity FHA Source Core Specific within Failed Gap Term Nuclide Inventory Activity Peak- Fraction(a) (Ci Available (Ci) (Ci / MWt) Powered Fuel for Release)

Rods (Ci)

Kr-83m 8.265E+06 4.238E+03(') 7.786E+04(c) 0.05 3.893E+03(d)

Kr-85 9.852E+05 5.052E+02 9.281E+03 0.10 9.281E+02 Kr-85m 1.894E+07 9.713E+03 1.784E+05 0.05 8.921E+03 Kr-87 3.788E+07 1.943E+04 3.568E+05 0.05 1.784E+04 Kr-88 5.355E+07 2.746E+04 5.045E+05 0.05 2.522E+04 Kr-89 6.755E+07 3.464E+04 6.364E+05 0.05 3.182E+04 Xe-131m 6.192E+05 3.175E+02 5.833E+03 0.05 2.917E+02 Xe-133 1.128E+08 5.785E+04 1.063E+06 0.05 5.313E+04 Xe-133m 3.428E+06 1.758E+03 3.229E+04 0.05 1.615E+03 Xe-135 4.540E+07 2.328E+04 4.277E+05 0.05 2.138E+04 Xe-135m 2.232E+07 1.145E+04 2.103E+05 0.05 1.051E+04 Xe-137 9.893E+07 5.073E+04 9.320E+05 0.05 4.660E+04 Xe-138 9.851E+07 5.052E+04 9.280E+05 0.05 4.640E+04 Br-83 8.267E+06 4.239E+03 7.788E+04 0.05 3.894E+03 Br-85 1.874E+07 9.610E+03 1.765E+05 0.05 8.827E+03 1-131 5.564E+07 2.853E+04 5.242E+05 0.08 4.193E+04 1-132 7.900E+07 4.051E+04 7.442E+05 0.05 3.721E+04 1-133 1.130E+08 5.795E+04 1.065E+06 0.05 5.323E+04 1-134 1.254E+08 6.431E+04 1.181E+06 0.05 5.907E+04 1-135 1.051E+08 5.390E+04 9.901E+05 0.05 4.950E+04 Rb-86 2.496E+05 1.280E+02 2.351E+03 0.12 2.822E+02 Cs- 134 2.971E+07 1.524E+04 2.799E+05 0.12 3.359E+04 Cs-136 7.602E+06 3.898E+03 7.161E+04 0.12 8.594E+03 Cs- 137 1.186E+07 6.082E+03 1.117E+05 0.12 1.341E+04 Te- 131 m(e) 8.405E+06 4.310E+03 7.918E+04 0.08 6.334E+03 Te-132(e) 7.739E+07 3.969E+04 7.291E+05 0.05 3.645E+04 Te- 133'e) 6.602E+07 3.386E+04 6.219E+05 0.05 3.11OE+04 Te-133m(e) 4.493E+07 2.304E+04 4.233E+05 0.05 2.116E+04 (a) The gap fractions are from Table 3-1, Item #A7.

(b) Kr-83m specific activity: 8.265E+06 (Ci) / 1950 (MWt) = 4.238E+03 (Ci/MWt)

(c) Kr-83m activity in failed rods: 4.238E+03 (Ci/MWt)

• 18.37 (MWt, from Table 3-1, Item #A6) = 7.786E+04 (Ci)

(d) Kr-83m FHA source term: 7.786E+04 (Ci)

• 0.05 (gap fraction) = 3.893E+03 (Ci)

(e) The Te isotopes were used only in the confirmatory analysis, for consistency with the calculation of record (Ref.

[3]). In line with Ref. [1], Reg. Guide 1.183, Appendix B, Section 1.2, only the nobles, halogens and alkalis are to be assumed as present in the fuel rod gaps.

Page 19

A AREVA Document No. 32-9145461-001 VYNPP - Re-analysis of AST/FHA Radiological Consequences with Open Containment 5.1.2 Radiological Consequences and Comparison with Calculation of Record The dose consequences for the FHA scenario described in this subsection are presented in Table 5-2. It is seen that there is very good agreement between the calculation of record and the analyses documented in the present calculation. The only relatively large difference (about 10%, which is still acceptable) is due to the underestimation of the Xe-135m contribution to the dose, resulting from this noble-gas isotope not being identified in the calculation of record as a daughter product of 1-135 in the decay correction. The corresponding EAB dose in Case A3 is not impacted due to the long pre-FHA decay time for this isotope. The MCR doses in all cases are not affected by the Xe- 13 5m underestimation primarily due to the finite-cloud correction to the submersion dose.

Table 5-2: FHA Re-Analysis - Comparison with Calculation of Record

[From ELISA-2 output file eli2-VY-FHA-A.e12, last page of each case analyzed]

TEDE Dose (rem)

ELISA-2 Release Decay Calc. of Percent Run Case Point (days) (A) Difference(a)

A] EAB Elevated 1 0.5215 0.472 -10.5 A2 MCR Elevated 1 0.1555 0.153 -1.6 A3 EAB Elevated 4 0.2771 0.274 -1.1 A4 MCR Elevated 4 0.1081 0.107 -1.0 A5 MCR Ground-Level 14 4.387 <5 N/A (a) Percent difference = [(B - A) / B]*100 Page 20

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AREVA Document No. 32-9145461-001 VYNPP - Re-analysis of AST/FHA Radiological Consequences with Open Containment 5.2 FHA with Open Containment, Ground-Level Release and Existing MCR Design 5.2.1 Accident Scenario Assumptions associated with this accident scenario are as follows:

(a) The reactor has been operating at full power (1950 MWt) for an extended period of time.

(b) The reactor is shutdown, refueling operations are initiated and an FHA takes place at various assumed decay times after reactor shutdown, ranging from I to 19 days for the EAB dose and from I to 15 for the MCR dose.

(c)-(e) See Section 5.1.1 for details on the FHA source term. It is noted, however, that the Te isotopes in Table 5-1 .were not included, as clarified in the table notes.

(f) In line with Ref. [1 ] (Appendix B, Sec. 5.3), the radioactive material that escapes the reactor cavity pool was assumed to get released to the environment over a 2-hour interval, based on 2 air changes per hour. See Section 2.2 for further details.

(g) The reactor building was assumed to be open during the refueling operations, with all post-FHA releases to the environment assumed to be at ground level, via the RB blowout panels.

(h) Transport of the released radioactivity to the receptors of interest is dictated by the applicable atmospheric dispersion factors in Table 3-3 for ground-level releases.

(i) Two MCR ventilation configurations were assumed: (1) Normal operating mode during the entire exposure interval (30 days), with an intake flow of 3700 cfm, unfiltered, and (2) Fully isolated prior to fuel movement, with an unfiltered inleakage of 50 cfm. [Note: The 50-cfm unfiltered inleakage requires a very tight MCR envelope. It was selected solely for demonstrative purposes.]

(j)-(k) See Section 5.1.1 for details on the breathing rate, MCR occupancy factors and MCR finite-cloud correction to the submersion dose.

5.2.2 Radiological Consequences The dose consequences for the FHA scenario described in this subsection are presented in Table 5-3 and shown graphically in Figure 5-1 and Figure 5-2. It is seen that the EAB TEDE dose with open containment is less than the regulatory limit of 6.3 rem limit even with a 24-hr pre-FHA decay time. Also, a decay time of 17 days is required for this dose to drop below the EPA PAG Evacuation limit of 1 rem TEDE.

On the other hand, a decay time of about 11 to 13 days is needed to achieve an MCR dose less than 5 rem, for intake flows ranging between 50 cfmn (with the MCR pre-isolated) and 3700 cfm (current MCR configuration).

It is noted that simple pre-isolation of the MCR does not provide much relief. This is because the MCR cleanup rate is also reduced. Thus even though much less activity enters the MCR envelope, it stays therein for a much longer time. Examples of the time dependence of the MCR cumulative dose are shown in Table 5-4 and Figure Page 21

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A AREVA Document No. 32-9145461-001 VYNPP - Re-analysis of AST/FHA Radiological Consequences with Open Containment 5-3. These results suggest the possibility of reducing the pre-FHA decay time by MCR isolation prior to fuel movement, followed by MCR purge a few hours after the postulated FHA; see Section 5.4 for further details.

Table 5-3: VY FHA - EAB and MCR TEDE Dose vs. Decay Time

[Ground-level release with open containment at 2 air changes per hour]

Decay Time (days) EAB TEDE Dose MCR TEDE Dose (rem) vs. Intake Flow (rem) 3700 cfm 50 cfm 1 5.895 14.48 12.47 3 3.643 11.14 9.834 5 2.953 9.185 8.152 7 2.451 7.691 6.835 9 2.042 6.464 5.746 11 1.705 5.437 4.834 13 1.424 4.575 4.067 15 1.190* 3.849 3.422 17 0.9957 N/A N/A 19 0.8333 N/A N/A ELISA-2 Run Case eli2-VY-FHA-B.e12 (last output of each (Subcases B I-B8) and eli2-VY-FHA-C.eI2 eIi2-VY-FHA-D.eI2 uepage ofyeah (last eli2-VY-FHA-B1 .el2 (Subcases C1-C8) (Subcases DI-D8) case analyzed) (Subcases B9-B 10)

(See Figure 5-1 and Figure 5-2 for graphical presentations)

The EAB dose at 15 days (1.190 rem TEDE, from eli2-VY-FHA-B.eI2) was reproduced in eli2-VY-FHA-BI .e12 (for Rev. 001) to confirm consistency in the input files and continuity of results.

Page 22

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AREVA Document No. 32-9145461-001 VYNPP - Re-analysis of AST/FHA Radiological Consequences with Open Containment Table 5-4: Time Dependence of MCR Cumulative Dose - Sample Cases MCR Cumulative 13-day decay, 3700 TEDE Time (hr) Dose (rem) 11-day decay, 50 cfm intake cfm inleakage 0.0 0.0 0.0 0.1 0.1956 0.003727 0.25 0.8733 0.02111 0.5 2.106 0.07238 1 3.651 0.2199 1.5 4.271 0.3906 2 4.502 0.5654 4 4.574 1.214 6 4.575 1.773 8 4.575 2.253 12 4.575 3.019 24 4.575 4.312 45 4.575 4.728 96 4.575 4.832 720 4.575 4.834 eli2-VY-FHA-C.el2, eli2-VY-FHA-D.eI2, ELISA-2 Run output page 106 output page 95 (Case C7) (Case D6)

(See Figure 5-3 for graphical presentations)

Page 23

A AREVA Document No. 32-9145461 -001 VYNPP - Re-analysis of AST/FHA Radiological Consequences with Open Containment Figure 5-1: VY FHA - EAB TEDE Dose vs. Decay Time (Ground-level release with open containment at 2 air changes per hour) 8.0 6.0 EA to 0

Q LLI aLLI 4.0 Cý 2-0 0.0 0 2 4 6 8 10 12 D 4 16 18 20 Post-Shutdown Decay Time (days)

I *--EABDose --a -90% of DoseLuimit Page 24

A AREVA Document No. 32-9145461 -001 VYNPP - Re-analysis of AST/FHA Radiological Consequences with Open Containment Figure 5-2: VY FHA - MCR TEDE Dose vs. Decay Time and Intakellnleakage Flow Rate (Ground-level release with open containment at 2 air changes per hour) 15 Ge 10 0

0 ILl 0

I-0, 0

0 2 4 6 8 10 12 14 16 Post-Shutdown DecayTime (days)

---

3700 cfm (intake + inleakage) - -a--- 50 cfm (inleakage) - - 90% of Dose Limit Page 25

A AR EVA Document No. 32-9145461 -001 VYNPP - Re-analysis of AST/FHA Radiological Consequences with Open Containment Figure 5-3: Time Dependence of MCR Cumulative TEDE Dose - Sample Cases

[Note the difference in decay times between the two cases.]

5 -i 3 i

- Vi ' i I

• 2 - ,,

(0 LW 0.1 1 10 100 1000 Post-FHA "1ime (hr) 13-day decay, 3700 cfm intake - -a- day decay, 50 cfm inleakage Page 26

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AR EVA Document No. 32-9145461-001 VYNPP - Re-analysis of AST/FHA Radiological Consequences with Open Containment 5.3 FHA with Open Containment, Ground-Level Release and MCR Upgraded Design This subsection evaluates the benefits of upgrading the MCR HVAC system to include charcoal intake filters.

5.3.1 Accident Scenario The associated assumptions are as listed in Section 5.2.1, with the following exceptions:

(1) Based on scoping analyses, the pre-FHA decay times were assumed to range from 4 to 8 days.

(2) The MCR ventilation configuration was assumed to be in the normal mode at the time of the accident, drawing in 3700 cfm of outside air. At either 20 or 30 minutes after the accident (both cases analyzed), emergency filtration is actuated diverting the intake flow through 2-inch or 4-inch charcoal beds (with 95% or 99% efficiency, respectively, for the removal of iodines and particulates). Unfiltered inleakage is also assumed, at 50, 100 or 200 cfm, as part of the total intake flow of 3700 cfm (i.e., the exhaust flow is 3700 cfm).

5.3.2 Radiological Consequences The FHA dose consequences with the postulated upgrade to the MCR HVAC system are presented in Table 5-5.

It is seen that the MCR TEDE doses can be maintained below the 5 rem TEDE limit under the following alternative conditions:

(a) Decay prior to fuel movement: 5 days Unfiltered inleakage: 50 to 200 cfm Filtration efficiency: 99% (4" charcoal beds)

Delay in emergency filtration actuation: 20 minutes (b) Decay prior to fuel movement: 5-6 days (depending on unfiltered inleakage)

Unfiltered inleakage: 50 to 200 cfm Filtration efficiency: 95% (2" charcoal beds)

Delay in emergency filtration actuation: 20 minutes (c) Decay prior to fuel movement: 8 days Unfiltered inleakage: 50 to 200 cfm Filtration efficiency: 99% (4" charcoal beds)

Delay in emergency filtration actuation: 30 minutes The 20-minute delay time in the MCR filtration actuation was based on SRP Section 6.4 (Ref. [8]), while the 30-min delay is what is typically allocated for operator action. The 20-min delay is expected to be acceptable for an FHA, and provides a significant reduction in the decay time prior to fuel movement.

Page 27

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ARE VA Document No. 32-9145461-001 VYNPP - Re-analysis of AST/FHA Radiological Consequences with Open Containment Table 5-5: VY FHA - MCR TEDE Dose with ESF Filtration vs. Decay Time and Unfiltered Inleakage

[Ground-level release with open containment at 2 air changes per hour; MCR total exhaust rate of 3700 cfm, continuous; from ELISA-2 output files eli2-VY-FHA-E.el2 through eli2-VY-FHA-J.eI2, last page of each case analyzed.]

Pre-FHA MCR Dose (TEDE rem) vs. Unfiltered Decay Time Inleakage (days) 50 cfm 100 cfm 200 cfm MCR ESF Filtration Actuation in 20 minutes (99% charcoal filters) 4 5.114 5.182 5.318 5 4.659 4.721 4.845 6 4.259 4.316 4.429 ELISA-2 Run EI-E3 G1-G3 11-13 Cases _________ _________ _________

MCR ESF Filtration Actuation in 20 minutes (95% charcoal filters) 4 5.314 5.380 5.510 5 4.842 4.901 5.020 6 4.426 4.481 4.590 ELISA-2 Run E4-E6 G4-G6 14-16 Cases __________I_______ __

MCR ESF Filtration Actuation in 30 minutes (99% charcoal filters) 5 5.981 6.025 6.113 6 5.468 5.508 5.588 7 5.007 5.044 5.118 8 4.589 4.623 4.690 ELISA-2 Run F1-F4 H1-H4 J14 Cases (Bold entries are for MCR TEDE doses that are above the 5 rem regulatory limit)

Page 28

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A AREVA Document No. 32-9145461-001 VYNPP - Re-analysis of AST/FHA Radiological Consequences with Open Containment 5.4 FHA with Open Containment, Ground-Level Release, Pre-FHA MCR Isolation and Post-FHA MCR Purge This subsection evaluates the potential of ensuring the MCR habitability following an FHA based on isolation of the MCR prior to fuel movement, followed by purge of the MCR atmosphere a few hours after an FHA has taken place. These analyses are to demonstrate feasibility. The capability to identify less contaminated air at the MCR air intake than that within the MCR as a pre-condition for the purge credit would likely be required.

5.4.1 Accident Scenario The associated assumptions are as listed in Section 5.2.1, with the following exceptions:

(1) Based on scoping analyses, the following scenario (which meets the MCR dose limit of 5 rem TEDE) was selected as a base case:

• Pre-FHA decay of 5 days.

Refueling operations with open containment, vented at the rate of 2 air changes per hour (the assumed value described in Sec. 2.2), with no delay in the start of the atmospheric release following the accident.

• MCR isolation prior to fuel movement, with a total unfiltered intake flow plus unfiltered inleakage of 150 cfm (where the intake flow would be for maintaining an acceptable CO 2 level within the MCR envelope).

• MCR purge at 3.5 hours5.787037e-5 days <br />0.00139 hours <br />8.267196e-6 weeks <br />1.9025e-6 months <br /> after the postulated FHA, at the normal flow rate of 3700 cfm.

(2) Sensitivity analyses were then carried out to determine acceptable variations in the following parameters:

• Purge delay,

• Release delay from the reactor building, along with or without associated time shifting of the accident atmospheric dispersion factor,

• MCR unfiltered inleakage,

• Reduced release rate from the reactor building (with no delay in the release initiation),

and

• Time shifting of the atmospheric dispersion factor for a reduced release rate from the Reactor Building.

Page 29

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AREVA Document No. 32-9145461-001 VYNPP - Re-analysis of AST/FHA Radiological Consequences with Open Containment 5.4.2 Radiological Consequences The dose consequences of the various FHA scenarios evaluated are presented in Table 5-6. The folloW.ing are noted:

(a) The base-case dose is about half of that without purge. Delaying the purge by 30 minutes increases the dose by about 0.5 rem to a value beyond the acceptance criterion.

(b) Should the radioactivity released from the failed fuel rods get retained within the RB atmosphere for more than 3 hours3.472222e-5 days <br />8.333333e-4 hours <br />4.960317e-6 weeks <br />1.1415e-6 months <br />, the MCR dose rate would exceed the limit. This implies that purge initiation needs to be coupled to the start of the release from containment.

(c) A reduced MCR unfiltered inleakage would result in a lower dose.

(d) A reduced RB release rate would also result in a lower dose.

(e) For a slow RB release rate, time-shifting of the atmospheric dispersion factor does not lead to a significant change in the overall dose.

In general, pre-isolation of the MCR followed by MCR purge appears to be a viable option. However, it may only be acceptable as an interim measure for refueling operations with open containment, with the premise that suitable improvements will be made to the MCR HVAC system to mitigate the radiological consequences of an FHA.

Page 30

A AREVA Document No. 32-9145461-001 VYNPP - Re-analysis of AST/FHA Radiological Consequences with Open Containment Table 5-6: VY FHA - MCR TEDE Dose with 5-Day Decay, Pre-FHA Isolation and Post-FHA Purge

[Ground-level release with open containment at various air changes per hour, RB release delay, and x/Q time shifting; from ELISA-2 output file eli2-VY-FHA-K.e12, last page of each case analyzed.]

RB Air MCR 3700-cfm ELISA-2 Run CUnfiltered MCR Purge RB Release xIQ Time MCR TEDE CASE Changes Inleakage Initiation Delay Shift Dose (rem)

(cfm) Time (hr)

Impact of No Purge or Purge Delay K1 2 150 No purge no no 9.014 K2 2 150 4 no no 5.036 K3 (Base Case) 2 150 3.5 no no 4.571 Impact of RB Release Delay and x/Q Time Shifting K5 2 150 3.5 no yes, 1 hr 1.542 K6 2 150 3.5 yes, 1 hr yes, I hr 3.472 K7 2 150 3.5 yes, 2 hr yes, 2 hr 2.422 K8 2 150 3.5 yes, 3 hr yes, 3 hr 3.831 K9(a) 2 150 3.5 1 yes, 3.5 hr yes, 3.5 hr 9.064 Impact of Reduced MCR Unfiltered [nleakage K3 (Base Case) 2 150 3.5 no no 4.571 K4 2 100 3.5 no no 3.388 Impact of Reduced Release Rate from Reactor Building K3 (Base Case) 2 150 3.5 no no 4.571 K10 1 150 3.5 no no 3.930 K11 0.25 150 3.5 no no 2.516 Impact of x/Q Time Shifting with a Slow Release Rate from Reactor Building K11 0.25 150 3.5 no no 2.516 K12 0.25 150 3.5 no yes, 2 hr 1.887 K13 0.25 150 3.5 no yes, 3.5 hr 2.422 (a) Case K9 is equivalent to no pre-FHA MCR isolation, and a total decay of 5 days + 3.5 hrs.

Page 31

A AREVA Document No. 32-9145461-001 VYNPP - Re-analysis of AST/FHA Radiological Consequences with Open Containment 6.0

SUMMARY

OF RESULTS AND CONCLUSIONS The present calculation dealt with the radiological evaluation of a design-basis fuel handling accident (FHA) taking place at the Vermont Yankee Nuclear Power Plant, based on the AST methodology (Ref. [1]), an open containment, and ground-level releases. It is noted that, regardless of the containment configuration (open or closed), the FHA analytical model and associated assumptions are applicable to a fuel assembly drop in either the reactor cavity pool or in the SFP during a full-core offload.

The starting point of the analysis was confirmation of the FHA results in the VYNPP calculation of record, as described in Section 5.1. This was followed by different scenario sets to evaluate the following:

• The minimum required decay time after reactor shutdown that would ensure the MCR habitability under its current configuration during normal operation, and also under a pre-isolation condition,

• The benefits of upgrading the MCR HVAC system to include emergency filtration of the intake flow, and

• The viability of MCR isolation prior to fuel movement, and MCR purge following an FHA.

Reference is made to Sections 5.2, 5.3 and 5.4 for details. A summary of the conclusions is present below.

(a) The EAB TEDE dose with open containment is less than the regulatory limit of 6.3 rem TEDE even with only a 24-hr pre-FHA decay time. hi addition, a decay time of 17 days is required for this dose to drop below the EPA PAG Evacuation limit of 1 rem TEDE. It is noted that since the release occurs within two hours, the 2-hr doses at the EAB bound the corresponding 30-day doses at the LPZ (which is farther out).

(b) A decay time of about 11 to 13 days would be needed to achieve an MCR dose less than 5 rem, for intake flows ranging between 50 cfm (with the MCR pre-isolated) and 3700 cfm (current MCR configuration).

(c) Simple pre-isolation of the MCR does not provide much relief. This is because the MCR cleanup rate is also reduced, thus extending the exposure interval (see Figure 5-3).

(d) Upgrade of the MCR HVAC system to include intake-flow emergency filtration will result in acceptable MCR doses under the following alternative conditions:

1. Decay prior to fuel movement: 5 days Unfiltered inleakage: 50 to 200 cfm Filtration efficiency: 99% (4" charcoal beds)

Delay in emergency filtration actuation: 20 minutes (SRP Section 6.4 (Ref. [8])

2. Decay prior to fuel movement: 5-6 days (depending on unfiltered inleakage)

Unfiltered inleakage: 50 to 200 cfm Filtration efficiency: 95% (2" charcoal beds)

Delay in emergency filtration actuation: 20 minutes

3. Decay prior to fuel movement: 8 days Page 32

I~~ ~,L 1.-'Z- ,lI_'7U" V_ , '1 A

AREVA Document No. 32-9145461-001 VYNPP - Re-analysis of AST/FHA Radiological Consequences with Open Containment Unfiltered inleakage: 50 to 200 cfm Filtration efficiency: 99% (4" charcoal beds)

Delay in emergency filtration actuation: 30 minutes (e) Pre-isolation of the MCR followed by MCR purge appears to be a viable option. The base-case scenario analyzed consisted of the following:

I. Pre-FHA decay of 5 days.

2. Refueling operations with open containment, vented at the rate of 2 air changes per hour, with no delay in the start of the atmospheric release following the accident.

3. MCR isolation prior to fuel movement, with a total unfiltered intake flow plus unfiltered inleakage of 150 cfm (where the intake flow would be for maintaining an acceptable CO 2 level within the MCR envelope).

4. MCR purge at 3.5 hours5.787037e-5 days <br />0.00139 hours <br />8.267196e-6 weeks <br />1.9025e-6 months <br /> after the postulated FHA, at the normal flow rate of 3700 cfm.

However, such a configuration may only be acceptable as an interim measure for refueling operations with open containment, with the premise that suitable improvements (such as ESF filtration, or relocation of the air intake) will be made to the MCR HVAC system to mitigate the radiological consequences of an FHA.

Page 33

A AREVA Document No. 32-9145461-001 VYNPP - Re-analysis of AST/FHA Radiological Consequences with Open Containment

7.0 REFERENCES

1. US NRC Regulatory Guide 1.183, "Alternative Radiological Source Terms for Evaluating Design Basis Accidents at Nuclear Power Reactors" (Rev. 0, July 2000)

2. EPA 400-R-92-001, Manual of Protective Action Guides and Protective Actions for Nuclear Incidents (1991) 3.* ENTERGY Calculation VYC-2299, "Radiological AST Fuel Handling Accident Analysis [PSAT 3019CF.QA.05, Rev. 0]" (Jun. 2003)

4. AREVA NP Document 32-9053350-001, "ELISA A Software Package for the Radiological Evaluation of Licensing and Severe Accidents at Light-Water Nuclear Power Plants Based on the Classical and Alternative-Source-Term Methodologies" (Aug. 2008) [See also AREVA NP Document 2A4.26-2A4-ELISA2-2.4_UsersManual-000, "ELISA-2 Version 2.4 User's Manual - Revision 2".]

5. EPA 520/1-88-020, Federal Guidance Report No. 11, "Limiting Values of Radionuclide Intake and Air Concentration, and Dose Conversion Factors for Inhalation, Submersion, and Ingestion" (ORNL, September 1988)

6. EPA 402-R-93-08 1, Federal Guidance Report No. 12, "External Exposure to Radionuclides in Air, Water, and Soil" (ORNL, September 1993)

7. NUMARC 93-01, "Industry Guidelines for Monitoring the Effectiveness of Maintenance at Nuclear Power Plants"

8. NUREG-0800, Standard Review Plan, See. 6.4, "Control Room Habitability System" (Rev. 3, Mar. 2007) 9.* ENTERGY Calculation VYC-2260, "Bounding Core Inventories of Actinides and Fission Products for Design-Basis Applications at 1950 MWt" (Rev. 0, Feb. 2003) 10.* ENTERGY Calculation VYC-2275, "Control Room Air Intake X/Q Due to Release from Reactor Building Blowout Panel Using Arcon96 Methodology" (Rev. 0, April 2003)

11. Code of Federal Regulations Title 10 Part 50.67 (10CFR50.67).

References identified with an (*) are maintained within the VYNPP Records System and are not retrievable from AREVA Records Management. These are acceptable references per AREVA Administrative Procedure 0402-01, Attachment 8. See page 2 of the present document for Project Manager Approval of customer references.

Page 34

BVY 13-097 Docket 50-271 Attachment 5 Vermont Yankee Nuclear Power Station Proposed Change 306 List of Regulatory Commitments

BVY 13-097 / Attachment 5 / Page 1 of 1 List of Regulatory Commitments This table identifies actions discussed in this letter for which Entergy commits to perform. Any other actions discussed in this submittal are described for the NRC's information and are not commitments.

TYPE (Check one) SCHEDULED ONE-TIME CONTINUING COMPLETION DATE COMMITMENT ACTION COMPLIANCE (If Required)

During fuel handling/core alterations,, x Commitment will be ventilation system and radiation monitor implemented prior availability (as defined in NUMARC 91-06) to use of the will be assessed, with respect to filtration amendment and monitoring of releases from the fuel.

The goal of maintaining ventilation system and radiation monitor availability is to reduce doses even further below that provided by the natural decay.

A single normal or contingency method to x Commitment will be promptly close primary or secondary implemented prior containment penetrations will be to use of the established. Such prompt methods need amendment not completely block the penetration or be capable of resisting pressure.

Contingency plans for prompt closure of openings will include the following:

- Equipment and tools needed to facilitate closure will be staged,

- Personnel responsible for closure will be knowledgeable and trained in the procedures for establishing building integrity,

- The closure response team will be accompanied by a Radiation Protection (RP) technician for radiation protection monitoring,

- Hoses and cables routed through openings will employ a means to allow rapid, safe disconnect and removal, and

- One door in each airlock will be capable of expeditious closure Revise VY UFSAR to reflect revised fuel x Completed in handling accident analysis. accordance with next scheduled UFSAR update following amendment approval