ML082140237

Response to Request for Additional Information Concerning License Amendment - Application of Alternative Source Term

ML082140237
Person / Time
Site:	Peach Bottom
Issue date:	07/29/2008
From:	Cowan P Exelon Nuclear
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
Download: ML082140237 (24)

Text

Exelon Nuclear www.exeloncorp.com 200 Exelon Way Nuclear Kennett Square, PA 19348 10 CFR 50.90 July 29, 2008 U. S. Nuclear Regulatory Commission Attn: Document Control Desk Washington, DC 20555-0001 Peach Bottom Atomic Power Station, Units 2 and 3 Renewed Facility Operating License Nos. DPR-44 and DPR-56 Docket Nos. 50-277 and 50-278

Subject:

Response to Request for Additional Information Concerning License Amendment Request - Application of Alternative Source Term

References:

1. Letter from Pamela B. Cowan, Exelon Generation Company, LLC, to U. S. Nuclear Regulatory Commission, "License Amendment Request - Application of Alternative Source Term," dated July 13, 2007

2. U.S. Nuclear Regulatory Commission e-mail dated July 18, 2008, draft Request for Additional Information (RAI), Peach Bottom Atomic Power Station, Units 2 and 3, License Amendment Request (LAR), Alternative Source Term Application (five questions)

3. U.S. Nuclear Regulatory Commission updated e-mail dated July 25, 2008, draft Request for Additional Information (RAI), Peach Bottom Atomic Power Station, Units 2 and 3, License Amendment Request (LAR), Alternative Source Term Application (one question)

In Reference 1, Exelon Generation Company, LLC (Exelon) submitted an application requesting a change to the Technical Specifications (TS), Appendix A, of Renewed Facility Operating License Nos. DPR-44 and DPR-56 for Peach Bottom Atomic Power Station (PBAPS), Units 2 and 3, respectively. The proposed change was requested to support the application of Alternative Source Term (AST) methodology at PBAPS, Units 2 and 3. In References 2 and 3, the U.S. Nuclear Regulatory Commission (NRC) issued draft requests for additional information concerning the PBAPS License Amendment Request (LAR). In particular, the NRC requested that Exelon provide additional information pertaining to meteorological and dose consequences issues related to AST.

U.S. Nuclear Regulatory Commission License Amendment Request Alternative Source Term Docket Nos. DPR-44 and DPR-56 July 29, 2008 Page 2 During teleconferences on July 21, July 22, July 24, and July 25, 2008, NRC and Exelon representatives further discussed the draft RAI questions (References 2 and 3). As a result of these discussions, Exelon agreed to provide a response to four of the six questions identified in the RAI by July 29, 2008. The response to the remaining questions will be the subject of a subsequent supplemental response. The supplemental response will include changes to X/Q values, and the submittal of revised supporting calculationsi. As a result of the revised calculations, it is predicted that there will be some increases in the dose values. However, predicted increases will still result in acceptable doses with ample margin to the regulatory limits. Although some of the calculated doses may change, the methodologies for their determination remain the same. Attachment 1 to this letter restates each of the NRC's questions followed by Exelon's response. Attachments 2 and 3 contain revised: tables (Tables A and B) and figures (Figures 1 and 2) previously submitted in the May 23, 2008, RAI response.

Exelon has concluded that the information provided in this response does not impact the conclusions of the: 1) Technical Analysis, 2) No Significant Hazards Consideration under the standards set forth in 10 CFR 50.92(c), or 3) Environmental Consideration as provided in the original submittal (Reference 1).

This letter does include a regulatory commitment as described in Attachment 4. Ifyou have any further questions or require additional information, please contact Richard Gropp at 610-765-5557.

I declare under penalty of perjury that the foregoing is true and correct. Executed on the 29th day of July 2008.

Respectfully, a{ W Ci)a Pamela B. Co an Director - Licensing and Regulatory Affairs Exelon Generation Company, LLC : Response to Request for Additional Information : Revised Tables A and B : Revised Figures 1 and 2 : List of Regulatory Commitments cc: Regional Administrator - NRC Region I w/ Attachments NRC Senior Resident Inspector - PBAPS "

NRC Project Manager, NRR - PBAPS Director, Bureau of Radiation Protection - Pennsylvania Department of Environmental Protection S. T. Gray, State of Maryland "

U. S. Nuclear Regulatory Commission License Amendment Request Alternative Source Term Docket Nos. DPR-44 and DPR-56 July 29, 2008 Page 3 bcc: P. Steinhauer, PSEG w/o Attachments Senior Vice President, Mid-Atlantic Operations II Site Vice President - PBAPS Plant Manager - PBAPS II Director, Operations - PBAPS II Director, Engineering - KSA II Director, Site Engineering - PBAPS Director, Site Training - PBAPS wI/Attachments Manager, Regulatory Assurance - PBAPS n' Manager, Licensing J. Rommel - Manager - Engineering Safety Analysis - Cantera T. Mscisz - Engineering, KSA-2A Records Management - KSA-1 N1

ATTACHMENT 1 Peach Bottom Atomic Power Station Units 2 and 3 Docket Nos. 50-277 and 50-278 License Amendment Request Response to Request for Additional Information Alternative Source Term (AST)

Alternative Source Term Response to RAI Page 1 of 12

Background

By letter dated July 13, 2007, Exelon Generation Company, LLC (Exelon) submitted an application requesting a change to the Technical Specifications (TS), Appendix A, of Renewed Facility Operating License Nos. DPR-44 and DPR-56 for Peach Bottom Atomic Power Station (PBAPS), Units 2 and 3, respectively. The proposed change was requested to support the application of Alternative Source Term (AST) methodology at PBAPS, Units 2 and 3.

By electronic mail (e-mail) on July 18, 2008- (five questions) and an updated e-mail on July 25, 2008 (one question), the U.S. Nuclear Regulatory Commission (NRC) transmitted draft Request for Additional Information (RAI) questions pertaining to the meteorological and dose consequence issues related to AST. During teleconferences on July 21, July 22, July 24, and July 25, 2008, NRC and Exelon representatives further discussed the draft RAI questions. As a result of these discussions, Exelon agreed to provide a response to four of the six questions identified in the RAIs by July 29, 2008. The response to the remaining questions identified as AADB RAI 23 and AADB RAI 25 below will be the subject of a subsequent supplemental response. The specific questions are restated below followed by Exelon's response.

NRC Question 1 (AADB RAI 20)

Title 10 of the Code of FederalRegulations Part50.67 (10 CFR 50.67), 'Accident source term",

requires that the accident source term used in dose consequence evaluations be representative of a major accident involving significant core damage, with dose consequences not exceeded by those from any accidentconsidered credible (i.e., maximum hypothetical accident). Unlike the design basis accident (DBA) LOCA, used to evaluate the emergency core cooling system (ECCS) requirements of 10 CFR 50.46, the generalscenario used to develop a maximum hypothetical, dose consequence accidentsource term does not representany specific accident sequence. Rather, the maximum hypothetical accidentis intended to be a surrogate to enable a deterministic evaluation of the response of a facility's engineeredsafety features (ESFs) such as the primary containmentsystem. The accidentanalyses are intentionallyconservative in order to compensate for known uncertaintiesin accidentprogression,airborneactivity product transport,and atmospheric dispersion. The source term referenced in 10 CFR 50.67 is based on NUREG- 1465 and is referred to as the alternative source term (AST).

The licensee determined that the dose consequence to the Control Room (CR) operatorfor its proposed design basis maximum hypothetical accident, which assumes that activity is not deposited in the longest inboardmain steam line, is higher than assuming activity is deposited therein. This result supports the notion that the licensee's proposed design basis accident analysis is indeed more likely to be the maximum hypothetical accident,commensurate with the requirements of 10 CFR 50.67.

Exelon has analyzed a conservativelyadjusted LOCA as the PBAPS design basis, and not re-determined the major accident that would result in potential dose consequences not exceeded Alternative Source Term Response to RAI Page 2 of 12 by those from any accident consideredcredible. Therefore, please submit a proposed license condition that would ensure that the conservative assumptions used in the proposed licensing basis LOCA of the LAR will be updated and retainedin the PBAPS FSAR.

Response

Regulatory Guide (RG) 1.183, Section B, states that an accident source term is intended to be representative of a major accident involving significant core damage and is typically postulated to occur in conjunction with a large loss-of-coolant accident (LOCA). The design basis accidents (DBAs) were not intended to be actual event sequences, but rather, were intended to be surrogates to enable deterministic evaluation of the response of a facility's engineered safety features. The AST is not based upon a single accident scenario, but instead, it represents a spectrum of credible severe accident events. These accident analyses are intentionally conservative in order to compensate for known uncertainties in accident progression, fission product transport, and atmospheric dispersion.

RG 1.183, Section C.2.1, further indicates that the AST must be based on major accidents, hypothesized for the purposes of design analyses or consideration of possible accidental events that could result in hazards not exceeded by those from other accidents considered credible.

RG 1.183, Table 1, lists core inventory release fractions, by radionuclide groups, for the gap release and early in-vessel damage phases for DBA LOCAs for BWRs. For non-LOCA events, the fractions of the core inventory assumed to be in the damaged fuel gap for the various radionuclides are given in a separate table (Table 3). These release fractions are used in conjunction with the fission product inventory calculated with the maximum core radial peaking factor.

In consideration of the above, the AST LOCA analysis performed for the PBAPS, Units 2 and 3, considered a spectrum of line breaks and applicable source term guidance and has determined that the AST LOCA is representative of the maximum hypothetical accident (MHA). For the purpose of consideration of the MHA the LOCA analysis assumes a line break in a main steam line upstream of one inboard main steam isolation valve (MSIV) within the primary containment (drywell).

RG 1.183, Appendix A, Section 6.5 allows reduction in MSIV releases that is due to holdup and deposition in main steam piping downstream of the MSIVs if the components and piping systems used in the release path are capable of performing their safety function during and following a safe shutdown earthquake (SSE). Although a main steam line break (MSLB) in containment would not result in substantial fuel damage (per General Electric analysis described in GE Topical Report NEDO-24708A, "AdditionalInformation Required for NRC Staff Generic Report on Boiling Water Reactors," Revision 1, dated December 1980), the break in a steam line was chosen as the worst-case LOCA with the assumption of a non-mechanistic LOCA source term. This maximizes the dose since one steam line that would otherwise be available is postulated to be broken and cannot be credited for iodine deposition. The faulted steam line was chosen such that the line with the most deposition credit possible is not available for deposition, thereby maximizing the dose.

Alternative Source Term Response to RAI Page 3 of 12 Exelon will revise the LOCA Design Analysis (i.e., Calculation PM-1077) to include the appropriate description regarding the MHA during the next revision. It is expected that the revision to Calculation PM-1 077 will be completed in conjunction with providing the supplemental response to address NRC Question 4 (AADB RAI 23).

NRC Question 2 (AADB RAI 21)

Table A and Table B of the licensee supplement on May 23, 2008, shows columns representing the PBAPS MSIV leakage modeling. In the third column the heading states, "Between Inboard MSIV & TSV [turbine stop valve]." Also in the second column the heading states, "Between Inboard & OutboardMSIVs." Pleaseexplain the apparentdiscrepancyin these headings for Peach Bottom MSIV leakage modeling, since crediting deposition twice in piping between the inboardand outboard MSIVs would be non-conservative.

Response

The third columns in Tables A and B of the RAI response dated May 23, 2008, for "Peach Bottom AST Analysis - Parametric Study" contain a discrepancy in the heading title. These columns should be titled as "Between Outboard MSIV & TSV." The information contained in these columns is correctly applied in the design analysis and the parametric study. The revised tables are included in Attachment 2 of this submittal for clarity. As a result of the required changes to the X/Q values, the dose values are predicted to change and will be updated and included in the revision to Calculation PM-1077, which will be submitted in response AADB RAI 23.

NRC Question 3 (AADB RAI 22)

Appendix A, Section 6.1, of RG 1.183 states that "the activity available for release via MSIV leakage should be assumed to be that activity determined to be in the drywell for evaluating containment leakage (see Regulatory Position3)." Regulatory Position 3 presents the source term, in the form of activity release fractions, releasedinto containment. This containment source term accounts for phenomena that would serve to inhibitactivity release from the vessel, prior to transportthrough main steam and other bypass piping. The guidance of RG 1.183 further allows for the credit of other containment removal mechanisms (i.e., naturaldeposition or drywell spray, for example); however, applying additionalremoval mechanisms, prior,and in addition, to crediting nodalized and well-mixed pipe deposition, can substantiallychange the containmentsource term assumed to traverse the bypass piping, thus rendering the containmentsource term of Regulatory Position 3 inapplicable. Because the cumulative effect of pre-bypass pipe removal mechanisms and each pipe node was not explicitly addressedby the containmentsource term provided in Regulatory Position 3, considerationshould be given to the interactionof each removal mechanism with the source term of RG 1.183 when modeling the transportof activity from the drywell through bypass pathways.

Therefore, please provide information to show that the cumulative effect of assuming the release of the containmentsource term, naturaldeposition, and a constant deposition rate in successive piping nodes, for the postulated LOCA at PBAPS, does not compromise the conservative characteristicsof the dose analysis.

Alternative Source Term Response to RAI Page 4 of 12

Response

The applicable NRC guidance for the post-LOCA MSIV leakage release path in RG 1.183 and AEB 98-03 are listed in Table 1 below starting from the containment source term to atmospheric release. The post-LOCA MSIV leakage release paths are analyzed in the design analysis (PM-1077) with additional conservatisms with respect to the AEB 98-03.

Containment Source Term and Reduction of Airborne Activity:

The core isotopic activity is determined in a conservative manner in that the inventory is evaluated at two times during core life: beginning of core life (100 EFPD), and end of core life (711 EFPD). Since the accident could happen at any time, the isotopic activity at the higher of the two times was selected as the core inventory; thereby, generating a conservative core inventory. The treatment of containment source term complies with the regulatory guidance (Table 1 below, Items 1 and 2). Aerosol and elemental iodines are simultaneously removed by gravitational settling and adsorption by the wetted surface of the drywell, respectively (Table 1 below, Item 3). Additionally, the drywell airborne activity is further reduced by the containment and MSIV leakages.

Aerosol Removal By Gravitational Deposition:

Gravitational force naturally removes the airborne aerosol particles in the main steam piping during their migration through the pipe to the atmosphere. The horizontal main steam piping projected surface area provides a favorable condition for aerosol deposition. Items 4 through 9 of Table 1 below discuss the model for aerosol deposition in the main steam piping and its conformance with RG 1.183 and AEB 98-03.

A parametric study was performed using AEB 98-03 recommendations for the post-LOCA MSIV leakage path as applicable to PBAPS as described below. This study will be documented in the revision to the LOCA analysis (Calculation PM-1077), which is being performed in conjunction with providing the supplemental response to address NRC Question 4 (AADB RAI 23). A summary of the parametric study and its technical basis is described below.

1. The MSIV failed line consists of two well-mixed nodes - the main steam line volume between the inboard MSIV & outboard MSIV as well as the main steam line volume between the outboard MSIV and turbine stop valves (TSV).

2. The intact steam line consists of two well-mixed nodes - the main steam line volume between the RPV and outboard MSIV as well as the main steam line volume between the outboard MSIV and TSV.

3. The 5 0 th percentile settling velocity and resulting aerosol removal efficiencies are used in the first node of each line. This includes the MSIV failed line well-mixed volume representing the main steam line between the inboard and outboard MSIV, as well as the well-mixed volume representing the intact main steam line between the RPV and outboard MSIV.

Alternative Source Term Response to RAI Page 5 of 12

4. The settling velocities in the main steam lines beyond the outboard MSIVs in both release paths (failed line and intact line) are varied from the 1 0 th percentile through the 5 0 th percentile.

5. CR doses for the different settling velocities in the main steam piping beyond the outboard MSIV are then compared with the post-LOCA MSIV leakage pathway dose for the control room in Design Analysis PM-1077. The results of this study (to be contained in design analysis (Calculation PM-1077, Revision 1) further demonstrates that the method used in PM-1077, Revision 0 is conservative. AEB 98-03 states that the use of the 1 0 th percentile settling velocity with a well-mixed volume is not appropriate because it does not account for many of the other removal mechanisms and added that the use of a well-mixed volume, together with median ( 5 0th percentile) settling velocity is more appropriate (AEB 98-03, page 11).

==

Conclusions:==

Based on the parametric study performed, it is concluded that:

1. The aerosol gravitational deposition and elemental iodine removal in the post-LOCA MSIV leakage release paths are conservatively modeled in design analysis (Calculation PM-1077) such that it does not compromise the conservative characteristics of the dose analysis or the method described in AEB 98-03.

2. The MSIV leakage model is structured to provide a conservative bound for a large range of settling velocities including very fine aerosol particles represented by a lower settling velocity, lesser deposition, and higher dose as well as coarser aerosol particles represented by a higher settling velocity, larger deposition, and lower dose.

3. The conservative model used in design analysis (Calculation PM-1077) provides an appropriate and prudent safety margin against unpredicted events in the course of an accident and compensates for large uncertainties in facility parameters, accident progression, radioactive material transport, and atmospheric dispersion.

As previously indicated the results of this parametric study will be documented in more detail as an appendix to the LOCA analysis (Calculation PM-1077). The revision to Calculation PM-1 077 is being completed in conjunction with providing the supplemental response to address NRC Question 4 (AADB RAI 23).

Alternative Source Term Response to RAI Page 6 of 12 Table 1 Con.servatisms in PBAPS IMSIV Leakage Paths - From Containment Source Term to Atmospheric Release

.Item PostLOCA Design Input Regulatory PBAPS Comments NO. Position LOCA Design Analysis PM-i 077 Containment Source Term:

1 Core inventory release fractions, by groups, for the RG 1.183, Position Design Input 5.3.1.6 and RADTRAD Runs Core inventory is gap release and early in-vessel damage phases 3.2 PB3D185CL.oO & PB360MS205.oO. evaluated at for DBA LOCA are listed in RG 1.183 Table 1 for beginning of cycle BWRs. and end of cycle.

Maximum isotope values used in composite inventory for conservatism.

2 The radioactivity released from the fuel should be RG 1.183, Appendix Assumption 4.6.1 and RADTRAD Runs assumed to mix instantaneously and A, Position 3.1 PB3D185CL.oO & PB360MS205.oO.

homogeneously throughout the free air volume of the drywell in BWRs as it is released.

Reduction In Airborne Activity:,

3 Reduction in airborne radioactivity in the RG 1.183, Appendix Aerosol deposition by gravitation and elemental iodine containment by natural deposition within the A, Position 3.2 removal by containment spray are credited in AEB 98-containment may be credited. Acceptable models 03, Appendix C.1 for the MSIV leakage path. Aerosol for removal of iodine and aerosols are described in deposition (Assumption 4.6.2 and Section 7.4), and Chapter 6.5.2, "Containment Spray as a Fission elemental iodine adsorption by wetted surface Product Cleanup System," of the Standard Review (Sections 7.7 & 7.8) are credited in the PBAPS LOCA Plan (SRP), NUREG-0800 ([RG 1.183] Ref. A-i) analysis and incorporated in the RADTRAD Runs and in NUREG/CR-6189 PB3D185CL.oO & PB360MS205.oO.

___MSIV Leakage:

Alternative Source Term Response to RAI Page 7 of 12 Table 1 Conservatisms in PBAPS MSiV Leakage Paths - From Containment Source Term to Atmospheric Release ItemPost-LOCA Design Input ReuaoyPASComments No. Position LOCA Design Analysis PM-1077 4 For the purpose of this analysis, the activity RG 1.183, Appendix The activity available for release via MSIV leakage is As stated in #1 available for release via MSIV leakage should be A, Position 6.1 assumed to be same as that in the drywell for above, additional assumed to be that activity determined to be in the evaluating containment leakage. Per Assumption 4.6.1, conservatism exists drywell for evaluating containment leakage (see the activity from the reactor core is assumed to mix in the determination RG 1.183, Regulatory Position 3). No credit should instantaneously and homogeneously throughout the of the core isotopic be assumed for activity reduction by the steam drywell air volume without crediting any activity inventory.

separators or by iodine partitioning in the reactor reduction mechanism inthe reactor vessel. Please see vessel, the RADTRAD Runs PB3D185CL.oO &

PB360MS205.oO.

5 AEB 98-03 states that use of the well-mixed model AEB 98-03, page 11 Well-mixed model with 40-percentile aerosol deposition Use of 4 0th together with median (50 percentile) values for velocity is conservatively used to calculate the aerosol percentile aerosol the settling velocity produces calculated doses removal efficiencies in the MSIV failed and Intact lines deposition velocity comfortably below the acceptance limits. (Section 7.4 and Tables 3 through 7). The aerosol reduces the distribution in the MSIV leakage path becomes removal rate insignificant at later times in the accident. Therefore constant the aerosol removal is conservatively not credited in substantially and the MSIV leakage paths after 96 hours0.00111 days <br />0.0267 hours <br />1.587302e-4 weeks <br />3.6528e-5 months <br /> (see Table 6 conservatively and RADTRAD Run PB360MS205.oO). increases dose.

Alternative Source Term Response to RAI Page 8 of 12 Table 1 Conservatisms in PBAPS MSIV Leakage Paths - From Containment Source Term to Atmospheric Release Item Ps-C Dign Inpu Regulatory PBAPSR Comments No. * "-ost.LUADesign Input .. Position LOCA Design Analysis PM-1077 6 One MSIV line between the RPV & inboard MSIV AEB 98-03, Figure 1 The rupture of one MSIV line between the RPV and Based on the is postulated to fail. No credit for aerosol inboard MSIV is not credible due to the PBAPS plant- comparison of the deposition is taken in the failed segment of pipe. specific seismic design and break exclusion area CR dose in Tables consideration of the main steam lines (see discussion A& B of AADB RAI in Section 2.3.3). However, the concept of maximizing 8 (letter to NRC the dose is conservatively incorporated by not crediting dated 05/23/08), the aerosol deposition and elemental iodine removal in the aerosol deposition piping from the RPV to outboard MSIV (see detailed and elemental discussion in the May 23, 2008, response to RAI AADB iodine removal RAI 8 including Tables Aand B and RADTRAD Run model for the MSIV PB360MS205.oO). failed line is consistent with the PBAPS plant-specific design of the main steam line and more conservative than the AEB 98-03 model.

Alternative Source Term Response to RAI Page 9 of 12 Table 17

'Conservatisms in PBAPS MVSIV Leakage Paths - From Containment Source Term to Atmospheric Release ItemnNo. Reost-LryOCA No. -LCADesign Input ReuaoyPASComments Position LOCA Design Analysis PM-1 077, 7 The aerosol settling velocity (removal rate) is AEB 98-03, Appendix The LOCA analysis modeled the settling velocity The post-LOCA assumed to be constant during the entire duration C.1, MSIV Release constant for the entire duration of the accident for the MSIV leakage of accident. Path Nos. 14,15 & 16 MSIV leakage release path, which is consistent with release model is in RADTRAD run AEB 98-03, Appendix C.1, and RADTRAD MSIV consistent with AEB release paths # 14, 15, & 16. Unlike PBAPS, the Perry 98-03. See Plant does not have seismically designed main steam description of the piping beyond the outboard MSIV. The additional well- parametric study mixed volumes are modeled to represent the piping performed.

between the outboard MSIV and TSV. For the given 40th percentile aerosol settling velocity, the aerosol removal rate is a function of the horizontal pipe surface area and piping well-mixed volume (see Equation 2 of AEB 98-03). Therefore, the use of a constant settling velocity and aerosol removal rate is appropriate and consistent with the AEB 98-03.

8 The use of a well-mixed volume with a median AEB 98-03, page 11, The aerosol removal rates in the post-LOCA MSIV The post-LOCA (501h percentile) value of settling velocity for Paragraph 2 leakage release paths are calculated using the 4 0 1h MSIV leakage aerosol deposition is acceptable for the MSIV percentile settling velocity because (1)The lower release model is leakage paths - settling velocity represents the deposition of the finer conservative with aerosol particles with a smaller aerosol density in the respect to AEB 98-well-mixed volume. The gravitational removal rate of 03.

the lighter (finer) aerosol particles is substantially reduced in the lightly packed well-mixed volume. The resulting reduction in aerosol deposition removal rate constant and corresponding increase in the dose will be described in the parametric study. (2) The use of a lower settling velocity provides a conservative basis for the Staff's concern about the uncertainty associated with the gravitational deposition of the lighter aerosol I __particles in the well-mixed volume.

Alternative Source Term Response to RAI Page 10 of 12 Co0sevatisms in PBAPS MSIV Leakage Paths= FrmC-pei Table 1 i PBPS Conervtiss SIVLeaagePats -From Containment Source Term to Atmospheric Release Item Regulatory ....... PBAPS1 No.... riPosition LOCA Design Aalysis eM-o 077 C men 9 Natural removal of elemental iodine in each steam AEB 98-03, page B-3 The elemental iodine removal in the MSIV leakage The use of 50%

line volume is assumed to be DF of 2 or 50%. paths is assumed to be 50% from 2 min to 96 hrs. For elemental iodine the intact main steam line between the outboard MSIV removal efficiency and TSV, the elemental iodine removal is further in the MSIV leakage reduced from 50% to 0.5% conservatively during 38 to paths is 96 hrs. The elemental iodine removal in the MSIV conservative leakage paths is conservatively not credited beyond 96 because the hrs. elemental iodine removal efficiency calculated based on the drywell gas maximum temperature is 56%,

which greatly increases as the drywell atmosphere cools down

_following a LOCA.

Alternative Source Term Response to RAI Page 11 of 12 NRC Question 4 (AADB RAI 23)

The response to NRC Question 12 (AADB RAI 12) of the licensee's May23, 2008, letter stated that the reactorbuilding stack tops are at 305 feet (ft) mean sea level (msl) and the meteorologicalTower 2 grade elevation is 367 ft msl. NRC staff agrees that the elevation of the reactorbuilding stack tops is nearer the height of the meteorological Tower 2 grade elevation than the grade elevation of the River Tower or Tower 1A which are approximately 116 feet msl.

However, the reactorbuilding stack tops are about 60 feet below the Tower 2 grade elevation and therefore appearto be below the top of at leastpart of the bluff upon which Tower 2 is located. In addition, otherpostulated release locations such as the personnel access door, railway bay door, and ground hatches are at or near the plant structures on the river valley shoreline and appear to be at a height more nearly that of River Tower and Tower 1A.

Therefore, please providejustification that these postulated releasescould not be impactedby localized air flow patterns in the valley. Further,please provide justification that use of the Tower 2 meteorologicaldata in the PA VAN computer calculations provides the limiting atmospheric dispersion factors (x/Q values) for the low populationzone dose assessment.

Response

Exelon will: 1) recalculate the LPZ X/Qs using Tower 1A data, 2) recalculate the EAB and LPZ X/Qs using PAVAN with the finer wind speed categories. The revised calculations and updated information will be provided in a subsequent supplemental response. Since the X/Q values will be revised, it is expected that there will be some increases in dose. In addition, as a result of the changes to the X/Q values the supporting calculations for the LOCA analysis (Calculation PM-1077), Fuel Handling Accident (Calculation PM-1059), and Control Rod Drop Accident (Calculation PM-1057) will be revised and resubmitted in response to this question. However, predicted increases will still result in acceptable doses with ample margin to the regulatory limits.

NRC Question 5 (AADB RAI 241 Figures 1 and 2 associatedwith the response to NRC Question 18 (AADB RAI 18) state that the Units 2 and 3 roof scuttles are at 183.5 ft (55.9 m) msl. Page 13 of Attachment 1 of the July 13, 2007 alternative source term license amendment requeststates that plant grade is 35.4 m. This would suggest that the roof scuttles are 20.55 m above plant grade. However, Table 3-1 of Attachment G to Calculation PM- 1059 of the July 13, 2007 letter lists the release height of the roof scuttles as 48.5 m. Pleaseprovide additionalinformation to clarify the height of the roof scuttles andjustify that the value of 48.5 m input to the ARCON96 computer calculations.

Alternative Source Term Response to RAI Page 12 of 12

Response

Pages 3 and 4 of Attachment G to Calculation PM-1 059, Revision 2, of the July 13, 2007T submittal provide the derivation of the release height of the roof scuttles of 48.5 m (approximately 159 ft), as stated in Table 3-1, based on the roof scuttle height at the top of the Reactor Building of approximately 294 ft msl - 135 ft msl (west face grade) = 159 ft. It is important to note, that the correct value of 48.5 m above the west face grade was properly utilized as input to the ARCON96 computer calculations.

In response to NRC Question 18 (AADB RAI 18) in the May 23, 2008 submittal, Figures 1 and 2 were provided which included an asterisked annotation indicating that the elevation for the Unit 2 and 3 roof scuttles was 183.5 ft msl. This value is not representative of the elevation of the roof scuttles. These figures were provided to help improve reader clarity in highlighting the source and receptor locations. The information depicted on the figures was based on information from Figure 3-1 in Attachment G to Calculation PM-1077, Revision 2.

The figures have been revised to reflect the appropriate elevation for the Units 2 and 3 roof scuttles (i.e., approximately 294 ft msl). In addition, Figure 3-1 of Attachment G to Calculation PM-1059, Revision 2, will also be revised during the next revision to accurately reflect the elevation of the roof scuttles. It is expected that the revision to Calculation PM-1 059 will be completed in conjunction with providing the supplemental response to address NRC Question 4 (AADB RAI 23).

NRC Question 6 (AADB RAI 25)

Updated Table 4.3-1 (LOCA Parameters)of the Enclosure to the May 23, 2008, Peach Bottom response to a request for additionalinformationprovides a set of control room atmospheric dispersion factors (X/Q values) for containmentand ESF leakage releases via an off-gas stack release. Sheet 5 of Attachment A to the Enclosure provides a second set of X/Q values for releases from the off-gas stack to the control room intake that were calculatedin accordance with Section 3.2.2 of Regulatory Guide 1.194. The two sets of values appearto be for a single release scenariousing two different methodologies. If this is the case, please identify which set you propose to establish as the new licensing basis control room X/Q values for postulated releases from the off-gas stack.

Response

Exelon will respond to this question in conjunction with responding to NRC Question 4 (AADB 23), which will be provided in a subsequent supplemental response.

ATTACHMENT 2 Revised Tables A and B (from May 23, 2008, RAI Response)

Revised Table A Peach Bottom Plant-specific MSIV Leakage Model - 100% Compliance With AEB 98-03 Methodology AEB 98-03 Peach Bottom AST Analysis - Parametric Study MSIV Failed Line Intact Line MSIV Failed Line Intact Line RPV To Between RPV To Between RPV To Between Between RPV To Between Between Variable Parameter Inboard Inboard & Inboard Inboard & Inboard Inboard & 0Utbo'al Inboard Inboard & Oulhoard MSIV Outboard MSIV Outboard MSIV Outboard MSIV & MSIV Outboard MSIV &

MSIVs MSIVs MSIVs TSV MSIVs TSV Ruptured - Ruptured -

Piping Integrity Rutured d Remains Remains Remains Rutured Remains Remains Remains Remains Remains Assumed Intact Intact Intact Intact Intact Intact Intact Intact in analysis in analysis Not Not Aerosol Deposition Credited Credited Credited Credited Credited Credited Credited Credited Credited Credited Not Not Piping Volume Credited Credited Credited Credited Credited Credited Credited Credited Credited Credited Not Not Not Not Not Not Not Not Not Not Holdup Time Credited Credited Credited Credited Credited Credited Credited Credited Credited Credited Deposition Velocity 40th Percentile 40th Percentile Distribution Elemental Iodine Not Credited Credited Credited Not Credited Credited Credited Credited Credited Removal Credited (50%) (50%) (50%) Credited (50%) (50%) (50%) (50%) (50%)

Not~ ~

Provotprided- t)itdeL be d4e1 ie in revisionjl to Cai~du n P.V-17J7in CR Dose Not Providedt4JI3 L2 Perry plant does not have the seismically supported main steam line beyond the outboard MSIV; therefore, unlike the Peach Bottom plant, the main steam line between the outboard MSIV and TSV is not modeled.

Revyised Table B Peach Bottom Plant-specific MSIV Leakage Model Used In Licensing Basis AST LOCA Analysis AEB 98-03 PBAPS Plant-secific Licensing Basis AST LOCA Analysis MSIV Failed Line Intact Line MSIV Failed Line Intact Line Variable Parameter RPV To Between RPV To Between RPV To Between Between RPV To Between Between Inboard Inboard & Inboard Inboard & Inboard Inboard & ... t.oarr Inboard Inboard & Otbdho:iir MSIV Outboard MSIV Outboard MSIV Outboard MSIV & MSIV Outboard MSIV &

MSIVs MSIVs MSIVs TSV MSIVs TSV Piping Integrity Ruptured - Remains Remains Remains Remains Remains Remains Remains Remains Remains Assumed n analysis in credite Intact

______ Intact Intact Intact Intact Intact Intact Intact Intact Aerosol Aeposon Not Not Not Cet Credited Credited Credited Cet Cet Credited Credited Credited Credited Deposition Credited Credited Credited Not Piping Volume Credited Credited Credited Credited Credited Credited Credited Credited Credited Credited Not Not Not Not Not Not Not Not Not Not Holdup Time Credited Credited Credited Credited Credited Credited Credited Credited Credited Credited Deposition Velocity 40th Percentile 40th Percentile Distribution Elemental Iodine Not Credited Credited Credited Credited Credited Credited Credited Removal Credited (50%) (50%) (50%) Not Credited Not Credited (50%) (50%) (50%) (50%)

CR Dose Not Provided 36 Ren TE per 141107, RR --iajroviidein t[h*,Way 2.3, 2)08. R41 rejii*se (to be CRpdial in ceiniunclion Kwith rcision to CalculationM 111077 i rewNonsc to.AAD13 ,114JI3J myl_crdiiot1I hc dqpfioIIoII olf acro-o I an1d emvl'~%ý o IeImentaICIILtf iodinIe1 11)that1 ilne11and als in[I th C[11601 ti o) tlli niaisaik'1in

)tL bet w e th:cinbiýoaird anI otiiboajI d MS I\

rh1is produý. 'I4ýadiullL theIQ CR wloniiito thiglo IkePAP'SIS leakage xnoýl is corlC 1yIn~oprn ic dd~s thelj CALE 96803 MSlyeV a

ATTACHMENT 3 Revised Figures 1 and 2 (from May 23, 2008, RAI Response)

ATTACHMENT 4 List of Regulatory Commitments Alternative Source Term Response to RAI Page 1 of 1 Attachment 4 LIST OF COMMITMENTS The following table identifies those actions committed to by Exelon Generation Company (Exelon), LLC, in this document. Any other statements in this submittal are provided for information purposes and are not considered to be commitments.

COMMITTED COMMITMENT TYPE COMMITMENT DATE OR ONE-TIME PROGRAMMATIC "OUTAGE" ACTION (Yes/No)

(Yes/No)

The design basis documentation for Prior to No Yes Peach Bottom Atomic Power Station implementation of (PBAPS), Units 2 and 3, will include the Approved the appropriate description regarding License the-maximum hypothetical accident Amendment (MHA) during the next revision. For the purpose of consideration of the MHA the LOCA analysis assumes a line break in a main steam line upstream of one inboard main steam isolation valve (MSIV) within the primary containment (drywell).