RS-18-016, License Amendment Request to Utilize the TORMIS Computer Code Methodology

License Amendment Request to Utilize the TORMIS Computer Code Methodology

ML18036A227
Person / Time
Site:	Braidwood
Issue date:	02/01/2018
From:	Gullott D Exelon Generation Co
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
RS-18-016
Download: ML18036A227 (75)

Text

4300 Winfield Road Warrenville. IL 60555 Exelon Generation 630 657 2000 Office RS-18-016 10 CFR 50.90 February 1, 2018 U. S. Nuclear Regulatory Commission ATIN: Document Control Desk Washington, DC 20555-0001 Braidwood Station, Units 1 and 2 Renewed Facility Operating License Nos. NPF-72 and NPF-77 NRC Docket Nos. STN 50-456 and STN 50-457

Subject:

License Amendment Request to Utilize the TORMIS Computer Code Methodology In accordance with 10 CFR 50.90, "Application for amendment of license, construction permit or early site permit," and 10 CFR 50.59, "Changes, tests, and experiments," paragraph (c)(2)(viii),

Exelon Generation Company, LLC, (EGC) requests amendments to Renewed Facility Operating License Nos. NPF-72 and NPF-77 for Braidwood Station , Units 1 and 2. This amendment request proposes to revise the Braidwood Station licensing basis for protection from tornado-generated missiles. Specifically, the Updated Final Safety Analysis Report (UFSAR) will be revised to identify the TORMIS Computer Code as the methodology used for assessing tornado-generated missile protection of unprotected plant structures, systems and components (SSCs) and to describe the results of the Braidwood Station site-specific tornado hazard analysis. The results from the Braidwood Station TORM IS analysis will be used to credit unprotected equipment for post-tornado safe shutdown. Note that there are no Technical Specifications changes associated with this request.

The Braidwood Station TORMIS analysis utilizes a probabilistic approach performed in accordance with the guidance described in the NRC TORMIS Safety Evaluation Report dated October 26, 1983, as clarified by Regulatory Issue Summary (RIS) 2008-14, "Use of TORMIS Computer Code for Assessment of Tornado Missile Protection," dated June 16, 2008. to this letter provides an evaluation of the proposed changes and a summary of the supporting analysis.

The proposed amendment has been reviewed by the Braidwood Station Plant Operations Review Committee in accordance with the requirements of the EGC Quality Assurance Program.

In accordance with 10 CFR 50.91, "Notice for public comment; State consultation," paragraph (b) ,

EGC is notifying the State of Illinois of this application for license amendment by transmitting a copy of th is letter and its attachments to the designated State of Illinois official.

February 1, 2018 U. S. Nuclear Regulatory Commission Page 2 It should be noted that Braidwood Station issued Event Notification Report No. 51959, dated May 25, 2016, "Discovery of Non-Conforming Conditions During Tornado Hazards Analysis."

This Notification Report documents non-conforming conditions in the plant design such that specific Technical Specifications equipment on both units is considered to be inadequately protected from tornado missiles. These conditions are being addressed in accordance with Enforcement Guidance Memorandum 15-002, "Enforcement Discretion for Tornado-Generated Missile Protection Noncomplicance," Revision 1, dated February 7, 2017 and DSS-ISG-2016-01 ,

"Clarification of Licensee Actions in Receipt of Enforcement Discretion per Enforcement Guidance Memorandum EGM 15-002, 'Enforcement Discretion for Tornado-Generated Missile Protection Noncomplicance,"' Draft Revision 1, dated February 2017.

EGC requests approval of the proposed license amendment request within one year of this submittal date; i.e., by February 1, 2019; which meets the timeframe specified in the EGM for addressing tornado missile non-compliances. Once approved , the amendment shall be implemented within 90 days.

A summary of regulatory commitments is contained in Attachment 1A of this letter. Should you have any questions concerning this letter, please contact Joseph A. Bauer at (630) 657-2804.

I declare under penalty of perjury that the foregoing is true and correct. Executed on the 1st day of February 2018.

Respectfully, David M. Gullett Manager - Licensing Exelon Generation Company, LLC Attachments: Attachment 1 Evaluation of Proposed Changes Attachment 1A Summary of Regulatory Commitments Attachment 1-1 TORMIS Results Tables 1-4 Attachment 1-2 TORMIS Results Figures 1-8 Attachment 1-3 Draft Markup of Updated Final Safety Analysis Report Pages cc: NRC Regional Administrator, Region Ill NRC Senior Resident Inspector, Braidwood Station Illinois Emergency Management Agency - Division of Nuclear Safety

ATTACHMENT 1 Evaluation of Proposed Changes

Subject:

License Amendment Request to Utilize the TORMIS Computer Code Methodology 1.0

SUMMARY

DESCRIPTION 2.0 DETAILED DESCRIPTION

3.0 TECHNICAL EVALUATION

3.1 Current Licensing Basis for Tornado Missile Protection 3.2 Tornado Missile Concerns at Braidwood Station Prompting TORMIS Analysis 3.3 TORMIS Methodology and Analysis Results 3.3.1 Target Hit and Damage Frequency 3.3.2 Boolean Log ic Approach 3.3.3 TORMIS Analysis Results 3.3.4 TORMIS Analysis Conservatisms 3.3.5 Compliance with the NRC Safety Evaluation Report Acceptance Criteria 3.3.6 Compliance with the NRC RIS 2008-14 Criteria

4.0 REGULATORY EVALUATION

4 .1 Applicable Regulatory Requirements/Criteria 4 .2 Precedent 4.3 No Significant Hazards Consideration 4.4 Conclusions

6.0 REFERENCES

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ATTACHMENT 1 Evaluation of Proposed Changes 1.0

SUMMARY

DESCRIPTION In accordance with 10 CFR 50.90, "Application for amendment of license, construction permit or early site permit," and 10 CFR 50.59, "Changes, tests , and experiments," paragraph (c)(2)(viii),

Exelon Generation Company, LLC , (EGC) requests amendments to Renewed Facility Operating License Nos. NPF-72 and NPF-77 for Braidwood Station , Units 1 and 2. This amendment request proposes to revise the Braidwood Station licensing basis for protection from tornado-generated missiles. Specifically, the Updated Final Safety Analysis Report (UFSAR) will be revised to identify the TORMIS Computer Code as the methodology used for assessing tornado-generated missile protection of unprotected plant structures, systems and components (SSCs); and to describe the results of the Braidwood Station site-specific tornado hazard analysis. The results from the Braidwood Station TORMIS analysis will be used to credit unprotected equipment for post-tornado safe shutdown. Revisions to the affected UFSAR sections will be performed in accordance with 10 CFR 50.59, "Changes, tests and experiments,"

after approval of the proposed amendment. Note that there are no Technical Specifications changes associated with this request.

The Braidwood Station TORMIS analysis utilizes a probabilistic approach performed in accordance with the guidance described in the NRC TORMIS Safety Evaluation Report (SER) dated October 26, 1983 (Reference 1), as clarified by Regulatory Issue Summary (RIS) 2008-14, "Use of TORM IS Computer Code for Assessment of Tornado Missile Protection ," dated June 16, 2008 (Reference 2). The Braidwood Station TORMIS analysis was performed by Applied Research Associates, Inc. (ARA) using TORMIS_ 14, an updated version of the original EPRI NP-2005 (Reference 5) version of the code .

2.0 DETAILED DESCRIPTION The proposed revision to the Braidwood Station tornado licensing basis is based on the NRC approved methodology as detailed in topical reports: EPRI NP-768, "Tornado Missile Risk Analysis," May 1978 (Reference 3), EPRI NP-769, "Tornado Missile Risk Analysis-Appendices," May 1978 (Reference 4) and EPRI NP-2005, "Tornado Missile Risk Evaluation Methodology," August 1981 (Reference 5). These reports address utilization of the TORMIS Computer Code. TORMIS uses a Monte Carlo simulation technique to assess, through a Probabilistic Risk Assessment (PRA) methodology, the probability of multiple missile hits causing unacceptable damage to unprotected safety-significant components at a plant. For each tornado strike, the tornado windfield is simulated , missiles are injected and flown , and missile impacts on structures and equipment are analyzed. These models are linked to form an integrated, time-history simulation methodology. By repeating these simulations, the frequencies of missiles impacting and damaging individual components (targets) and groups of targets are estimated. Statistical convergence of the results is achieved by performing multiple replications with different random number seeds. The statistical confidence bounds of the results can then be estimated using conventional methods.

For the Braidwood Station TORM IS analysis, the plant was divided into two separate models because of the remote location of the Essential Service Water (SX) discharge pipes in the middle of the Ultimate Heat Sink (UHS) cooling pond , nearly a mile from the closest other safety-significant targets. The Main Site Model is used to analyze all targets on and around the Reactor and Auxiliary Buildings. The SX Model is used to analyze the SX discharge pipe 2 of 33

ATTACHMENT 1 Evaluation of Proposed Changes targets only. The plant safety envelope for the SX Model has the same area and shape as the envelope for the Main Site Model but is centered on the SX discharge pipes to allow the use of the same tornado hazard inputs for both models." The information presented below is primarily focused on the Main Site Model.

Over 27.7 billion TORM IS tornado missile simulations were performed for each of the Braidwood Station models. Each simulation consists of sampling and flying a missile for a simulated tornado strike on the plant. A total of 2.31 million tornado strikes on the plant were simulated in the TORM IS analysis for each of the models.

The TORM IS results are estimated frequencies of tornado missile hit and damage, and have the units of yr-1. They represent the modeled-output frequencies of tornado missile hit/damage to a target, or group of targets. There were 74 individual unprotected safety-significant targets modeled in TORMIS as shown in Attachment 1-1 , Table 1, "TORMIS Results by Individual TORMIS Target." The average missile hit and damage frequencies were developed from 60 TORMIS replications.

Table 2-1 below shows the arithmetic sum of damage frequencies for all target groups affecting the individual units (i.e ., Unit 1 plus common unit components and Unit 2 plus common unit components) . Note that these values include the damage frequency from the SX Model for the SX discharge pipes which are the only common unit targets at Braidwood Station (see -1 , Table 3). A damage frequency acceptance value of 1.0E-06 per year was established in the Standard Review Plan , Section 2.2.3, "Evaluation of Potential Accidents."

The acceptance value of 1.0E-06 per year was also endorsed in Reference 2 and Reference 8.

As shown in Table 2-1 , if no additional missile protection is provided for the unprotected safety-significant targets, the damage frequency exceeds the acceptance value of 1.0E-06 per year for both Unit 1 and Unit 2; however, if the Refueling Water Storage Tank (RWST) hatches (i.e., -1 , Table 1, Target Numbers 1 and 2) are protected , the damage frequency acceptance criteria are satisfied for both units. Braidwood Station will install missile protection on the Unit 1 and Unit 2 RWST hatches prior to implementation of the TORM IS methodology after approval of the proposed amendment. None of the other safety-significant targets are assumed to have additional tornado missile protection installed .

Table 2-1 Mean Damage Frequency by Unit (With RWST Hatches Protected)

Damage Frequency (yr 1)

Unit 1 Unit 2 Arithmetic Sum over all Target Groups 1.19E-06 1.29E-06 Arithmetic Sum Followina Protection of RWST Hatches 5.26E-07 5.BOE-07 Additional information regarding the TORMIS analysis results is presented in Section 3.3.3 below.

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ATTACHMENT 1 Evaluation of Proposed Changes The current tornado design basis and licensing basis for tornado missile protection is discussed in the fo llowing UFSAR sections.

UFSAR Section 3.3, "Wind and Tornado Load ings" UFSAR Section 3.5, "Missile Protection" As noted above, these UFSAR sections will be revised in accordance with 10 CFR 50.59 to incorporate the TORM IS analysis after approval of the proposed amendment. Draft markups of the proposed changes to these UFSAR sections are presented in Attachment 1-3 for information . Note that the Braidwood Station UFSAR is a common "Byron/Braidwood" UFSAR.

The majority of the UFSAR revisions implemented in support of the recently approved Byron Station TORMIS license amendment are also applicable to Braidwood Station . The marked up UFSAR pages presented in Attachment 1-3 only show revisions to the "current" UFSAR pages which have already incorporated the Byron Station TORM IS-related changes .

Other UFSAR sections, impacted by the changes in Sections 3.3 and 3.5 , will also be revised in accordance with 10 CFR 50.59 after approval of the proposed amendment; however, are not included with this submittal.

3.0 TECHNICAL EVALUATION

The evaluation and description of the Braidwood Station TORM IS analysis and the associated results supporting the proposed UFSAR changes, is presented below in the following sections.

Section 3.1, "Current Licensing Basis for Tornado Missile Protection ," describes the current tornado missile protection licensing basis.

Section 3.2, "Tornado Missile Concerns at Braidwood Station Prompting TORMIS Analysis,"

briefly describes the past issues pertaining to Braidwood Station missile protection which are , in part, prompting this request.

Section 3.3, "TORMIS Methodology and Analysis Results," summarizes the TORMIS methodology, including the use of Boolean Logic. This section also summarizes the analysis results and confirms compliance with the TORM IS SER (Reference 1) and NRC RIS 2008-14 (Reference 2).

• It is worthy to note that the Braidwood Station TORMIS analysis closely parallels the Byron Station TORMIS analysis documented in Reference 13. In Reference 14, EGC also responded to an NRC request for additional information regarding the Byron Station TORMIS analysis.

The information provided in Reference 14 has been reviewed and incorporated in the below evaluation where applicable.

3.1 Current Licensing Basis for Tornado Missile Protection The current licensing basis for tornado missile protection is presented in UFSAR Sections 3.5.3, "Barrier Design Procedures," and 3.5.4 , "Analysis of Missiles Generated by a Tornado ." Most safety related systems and components are located inside structures designed to protect them from tornado-generated missiles as discussed in UFSAR Section 3.5.3.

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ATTACHMENT 1 Evaluation of Proposed Changes UFSAR Section 3.5.4 describes the licensing basis for safety-related components located outdoors. Section 3.5.4 states the following :

"Effects of tornado missiles have been assessed for safety-related components located outdoors. These components are the SXCTs [essential service water cooling towers] (Byron only), the emergency diesel generator exhaust stacks, the emergency diesel generator ventilation and combustion air intakes, the emergency diesel generator crankcase vents, and the main steam safety and power operated relief valve tailpipes (Braidwood only)."

Section 3.5.4 provides a discussion addressing the existing configuration and why the lack of tornado missile protection is acceptable.

3.2 Tornado Missile Concerns at Braidwood Station Prompting TORMIS Analysis In NRC Inspection Report, "Byron Station , Units 1 and 2, Integrated Inspection Report 05000454/2009004; 05000455/2009004," dated November 5, 2009, Byron Station received a non-cited violation, NCV 05000454/2009004-02; 05000455/2009004-02, for failure to protect the Emergency Diesel Generator (EOG) Diesel Oil Storage Tank (DOST) vent lines from tornado-generated missiles. During the extent of condition review to address this violation , additional safety related pipes vulnerable to tornado-generated missiles were identified (i.e. , the Steam Generator Power Operated Relief Valve (PORV) tailpipes, the Main Steam Safety Valve (MSSV) tailpipes, and the Auxiliary Feedwater (AF) Diesel exhaust stacks). These same missile vulnerabilities were also applicable to Braidwood Station. Compensatory measures regarding tornado missile protection for the Diesel Oil Storage Tank vent lines were discussed in Braidwood Station Condition Report AR 01051105 , "Potential Compensatory Measures for DOST Vent Lines," dated March 31 , 2010. Braidwood Station Operability Evaluation 10-004, "DOST-DG Vent Lines Crimp vs Break," also addressed tornado missile concerns ; confirmed operability and has been closed .

On May 25, 2016, Braidwood Station issued Event Notification Report No. 51959, "Discovery of Non-Conforming Conditions During Tornado Hazards Analysis." This Notification Report documents non-conforming conditions in the plant design such that specific Technical Specifications equipment on both units is considered to be inadequately protected from tornado missiles. These conditions are being addressed in accordance with Enforcement Guidance Memorandum 15-002, "Enforcement Discretion for Tornado-Generated Missile Protection Noncomplicance," Revision 1, dated February 7, 2017 (Reference 9) and DSS-ISG-2016-01 ,

"Clarification of Licensee Actions in Receipt of Enforcement Discretion Per Enforcement Guidance Memorandum EGM 15-002, 'Enforcement Discretion for Tornado-Generated Missile Protection Noncomplicance, '" Revision 1, dated November 2017 (Reference 10).

To resolve the above concerns, Braidwood Station has decided to pursue NRC approval to utilize the TORMIS Computer Code methodology for assessing tornado-generated missile protection of the Braidwood Station SSCs. Unprotected targets needed for safe shutdown after a tornado are included in the TORM IS analysis. NRC approval of the TORM IS methodology will allow Braidwood Station to avoid modifications to provide tornado missile protection to the subject unprotected equipment. The appropriate sections of the UFSAR will then be modified under the 10 CFR 50.59 process to reflect these results . In addition , as noted in RIS 2008-14, "Once the TORMIS methodology has been approved for the plant and incorporated in the plant licensing basis, it can be used to address additional tornado missile vulnerabilities identified in 5 of 33

ATTACHMENT 1 Evaluation of Proposed Changes the future without seeking NRC approval , provided its use is consistent with the approved licensing basis of the plant."

3.3 TORMIS Methodology and Analysis Results As noted in Section 2.0 above , TORMIS uses a Monte Carlo simulation technique to assess, through a PRA methodology, the probability of multiple missile hits causing unacceptable damage to unprotected safety-significant components at a plant. Over 27.7 billion TORMIS tornado missile simulations were performed for each of the Braidwood Station models (i.e., Main Site Model and SX Model). Each simulation consists of sampling and flying a missile for a simulated tornado strike on the plant. A total of 2.31 million tornado strikes on the plant were simulated in the TORM IS analysis for each of the models.

The TORM IS results are estimated frequencies of tornado missile hit and damage. They represent the modeled-output frequencies of tornado missile hit/damage to a target, or group of targets . There were 74 individual unprotected safety-sign ificant targets modeled in TORMIS .

The average missile hit and damage frequencies were developed from 60 TORMIS replications.

The TORMIS results for the 74 individual safety-significant targets are presented in -1 , Table 1, "TORMIS Results by Individual TORMIS Target." Note that, although Braidwood Station and Byron Station are of similar design , Byron Station had a significantly larger number of unprotected targets (i.e., 153 targets) primarily due to the design of the SX Cooling T ewers.

3.3.1 Target Hit and Damage Frequency Target missile hit frequencies, shown in Attachment 1-1 , Table 1, reflect the frequency of at least one tornado missile hitting a target over a period of one year. For very large targets, tornado-generated missiles are likely to hit the building for almost every tornado strike and hence the missile hit frequency may approach or be essentially equal to the tornado strike frequency for such targets . As the target size reduces, as the target is shielded by other structures, or if only one surface of the target is exposed , the missile hit frequency reduces accordingly. In general , tornado missile hit frequencies are dependent on many geometrical factors as well as missile types, numbers, and proximity. The degree to which the elevation of the target is above the elevation of the nearby missile sources can also be a critical factor.

The damage frequencies, shown in Attachment 1-1 , Table 1, reflect the modeling of damage in TORM IS. For many targets, there is a notable reduction in the damage frequency from the hit frequency. The term "target damage" is used in a general sense to mean any damage (or "loss of function") criteria caused by a tornado missile hitting the target. Target damage is not necessarily the same as target hit, but hit can equal damage for fragile equipment. The accepted (i.e. , built-in) TORMIS penetration , spall , and perforation equations were used to evaluate damage for selected targets. Missile impact and velocity exceedance was also used to evaluate damage for several targets.

It should be noted that the damage frequency values for the Division 1 and Division 2 MEER ventilation system exhaust openings for each unit (i.e., Attachment 1-1 , Table 1, Target Numbers 63 , 64 , 67 and 68) assume some amount of acceptable tornado missile damage. The MEER exhaust openings were modeled in TORMIS using the pipe penetration feature to 6 of 33

ATTACHMENT 1 Evaluation of Proposed Changes determine the missile damage frequency. When using the pipe penetration feature, exhaust system components (e.g. , HELB and/or fire dampers) within the wall opening may be impacted such that the exhaust path is blocked due to physical damage or debris accumulation .

Necessary equipment, such as instrument inverters and battery chargers, are contained in the MEERs; therefore, manual action is relied on to restore ventilation . The associated manual actions entail simple activities to open doors (to provide an exhaust path) and restart supply fans .

Structural response damage can be evaluated within TORMIS using the results from offline structural response calculations. For the Braidwood Station TORM IS analysis, a finite element analysis (FEA) was performed to provide the required missile damage threshold velocity for each missile type to cause damage to three different types of targets (shown below).

Specifically, the FEA was performed to determine the critical impact velocities for crimping damage. The critical impact velocity is defined as the minimum velocity required to crimp the pipe to its critical area. In that the intended purpose of all the targets is to release exhaust products, the critical area is the area at which proper target function would be impeded .

Analyses were performed to assess three target structures subjected to a select seven TORMIS missiles. These fragility results were extended to the remaining TORMIS missiles using a conservative energy scaling approach. The fragility results are used as inputs to the TORMIS analyses of the three targets. These three target types represent 12 of the 74 targets modeled for the analysis. The three target types evaluated for crimping in the finite element analysis include:

• Diesel Auxiliary Feed Pump (DAFP) exhaust pipe (Targets 59 and 61)

• DAFP exhaust cover plates (Targets 60 and 62)

• Power Operated Relief Valve (PORV) tailpipes (Targets 43-50)

For these targets, damage is evaluated by comparing the missile velocity to the damage threshold velocity for the particular missile type and target group. If the missile velocity meets or exceeds 90% of the critical velocity, it is scored as damage. No damage is scored if the velocity of the impacting missile is less than 90% of the critical velocity (developed in the analysis) . The critical closure values are 60% for the DAFP and 90% for the PORVs.

The following conservatisms were applied when determining the damage threshold velocities:

• In general , the finite element analysis missile models were built to be conservatively strong and stiff given the materials and connections used in their structure. Conversely, target models were built conservatively to maximize the degree of potential crimping .

• The threshold velocity for missiles causing damage to the DAFP exhaust pipes, DAFP exhaust cover plates and PORV tailpipes were input into TORM IS as 90% of the critical velocities calculated in the finite element analysis.

UFSAR Table 3.5-4, "Impact Velocities of Design-Basis Tornado-Generated Missiles," provides a list of the Design-Basis tornado missiles and their associated assumed horizontal impact velocities . It should be noted that TORMIS does not use the missile velocities listed in Table 3.5-4 of the UFSAR. Instead , TORMIS simulates 3-D missile trajectories by integrating the equations of motion . Simulated missile trajectories consider the physical properties of each 7 of 33

ATTACHMENT 1 Evaluation of Proposed Changes missile, including missile dimensions, weight and aerodynamic shape as they are released into a simulated tornado wind field . This approach produces simulated missile velocities at impact that include site specific missile sources and target characteristics.

In TORMIS , the damage threshold velocity can be specified for each target and each missile type . This approach was built into TORM IS to allow for target-specific damage calculations where analysis outside of TORM IS could be used to determine the missile impact velocity thresholds that could produce failure of the target. The damage threshold velocities are input to TORMIS for each target-missile pair.

There was no attempt to show that the above three unprotected targets were capable of withstanding UFSAR missile impact design velocities. The UFSAR missile velocities are still retained as they are applicable for the Design Basis structures (i.e., non-TORMIS targets). The purpose of the finite element analysis is to determine the missile hit velocity for each TORM IS missile that results in unacceptable crimping damage of the three subject targets.

3.3.2 Boolean Logic Approach Hit and damage frequencies for groups of targets evaluated in TORM IS are commonly combined using Boolean operators (U and n) to aid in summarizing the results and understanding the effects of the system redundancies. The union (U) operator means that if any one of the targets is damaged in a tornado, the system is assumed to fail. The intersection (n) operator means that all the intersected components must be damaged in a tornado strike for the system to fail. Combinations of union and intersection operators can be put together to describe multi-component system failure logic for plant systems and subsystems. Note that no Boolean combinations presented in the Braidwood Station analysis use the intersection (n) operator.

Several safety-significant components were broken into multiple targets within the Braidwood Station TORMIS models to account for different parts of single systems or to account for multiple failure modes of individual components. In these cases, Boolean union logic is used to prevent over counting of tornado missile damage.

Boolean union logic is applied to each TORM IS simulated tornado to determine if the missile damage results in a loss of function within each target group. For example, the unprotected PORV tailpipes are modeled as two separate targets to address two separate failure modes:

1) pipe penetration pass through , and 2) crimping due to velocity exceedance. A TORMIS tornado simulation that results in either missiles passing through the tailpipe opening (i.e. , pipe penetration failure mode) or causes unacceptable crimping of the tailpipe (i.e., velocity exceedance failure mode) results in loss of PORV function . If both of these targets are failed in the same simulated tornado , only a single failure is counted towards the damage frequency for the system for that tornado; therefore, the Boolean Union logic is used to account for these two failures as a single loss of PORV function when determining the damage frequency for that PORV target group.

The 74 individual targets were grouped together into 26 groups according to target type and/or function. Attachment 1-1 , Table 2, "Average Hit and Damage Frequency (per year) for Target Groups," presents the missile hit and damage frequencies for the 26 target groups as previously defined in Attachment 1-1 , Table 1 (i.e., the frequency values for each of the 26 groups in 8 of 33

ATTACHMENT 1 Evaluation of Proposed Changes Table 2 are the Boolean union of the individual target damage frequencies for those targets assigned to each group as shown in Table 1). These values are shown graphically in -2, Figure 2, "Target Group Hit and Damage Frequencies."

3.3.3 TORMIS Analysis Results The final results for the damage frequency for all Braidwood Station target groups, utilizing the Boolean Logic approach , are presented in Attachment 1-1 , Table 3, "Mean Damage Frequency (per Year) for Braidwood Station Target Groups."

Table 3.3.3-1 below shows a summary of the arithmetic sum of damage frequencies for all target groups affecting the individual units (i .e., Unit 1 plus common unit components and Unit 2 plus common unit components) . As shown in Table 3.3.3-1 , if no additional missile protection is provided for the unprotected safety-significant targets, the damage frequency exceeds the acceptance value of 1.0E-06 per year for both Unit 1 and Unit 2; however, if the RWST hatches (i.e. , Attachment 1-1 , Table 1, Target Numbers 1 and 2) are protected, the damage frequency acceptance criteria is satisfied for both units. Braidwood Station will install missile protection for the RWST hatches prior to implementation of the TORM IS methodology after approval of the proposed amendment. None of the other safety-significant targets are assumed to have additional tornado missile protection installed .

Table 3.3.3-1 Mean Damage Frequency Damage Frequency (yr 1)

Unit 1 Unit 2 Arithmetic Sum over all Tan:iet Groups 1.19E-06 1.29E-06 Arithmetic Sum Followino Protection of RWST Hatches 5.26E-07 5.80E-07

• Composite Site Damage Frequency for all Target 9.96E-07 Groups Following Protection of RWST Hatches

• The composite site damage frequency value is provided for information only.

Note that the acceptance criterion is applied on a unit-specific basis as documented in the NRC Safety Evaluation for use of the TORM IS methodology at the Donald C. Cook Nuclear Plant; i.e., in a letter from J. F. Stang (NRC) to R. P. Powers (Indiana Michigan Power Company) ,

"Donald C. Cook Nuclear Plant, Units 1 and 2 - Issuance of Amendments," dated November 17, 2000 (Reference 12); and at Byron Station ; i.e., in a letter from Joel S. Wiebe (NRC) to B. C.

Hansen (EGC), "Byron Station , Unit Nos. 1 and 2 - Issuance of Amendments Regarding Use of TORMIS for Assessing Tornado Missile Protection ," dated August 10 2017 (Reference 15).

It is worthy to note that the composite site damage frequency (following installation of missile protection for the RWST hatches) also meets the acceptance criteria. The composite site value is simply the sum of the Unit 1 and Unit 2 damage frequencies minus the damage frequency of common unit targets such that the common unit target damage frequencies are not counted twice. The SX Discharge Pipes are the only common unit targets at Braidwood Station (see -1 , Table 3).

Specifically: Composite Site Damage Frequency= 5.26E-07 + 5.80E 1.10E-07 = 9.96E-07 .

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ATTACHMENT 1 Evaluation of Proposed Changes In Reference 14, Byron Station specifically validated applying the acceptance criteria on a unit-specific basis . Similar to Byron Station, multiple time periods for Braidwood Station correspond to outage and non-outage conditions . Outage time periods have additional missile sources ,

which are treated by introducing additional potential missiles in the appropriate zones that reflect materials, equipment, new trailers, etc. that exist during outage conditions. These potential outage missile sources are modeled in distinct TORMIS runs representing outage time periods. Three time periods were simulated with TORM IS: (1) Unit 1 in an outage state with Unit 2 operational ; (2) Unit 2 in an outage state with Unit 1 operational ; and (3) Unit 1 and Unit 2 operational. Based on review of outage times, each unit was conservatively assumed to be in an outage condition 18% of the time . These three time periods were combined to calculate a per-unit and composite site damage frequency, consistent with the methodology in NP-2005 (Reference 5) .

3.3.4 TORMIS Analysis Conservatisms There are many conservatisms in the TORMIS modeling to offset the simplification and limitations of TORM IS . The Braidwood Station TORM IS analysis is conservative for the following reasons:

1. In TORMIS , the effects of local obstructions, buildings, and structures are neglected in simulating the tornado winds . Thus, for example, tornado winds flow through the Turbine Building without consideration of either terrain/site roughness or blockage/interference of the reinforced concrete and heavy steel frame structures.

2. All the postulated missiles at Braidwood Station were treated as minimally restrained in which each sampled missile is injected near the peak aerodynamic force, thus maximizing the transport range and impact speed and , consequently, the missile hit and damage frequency.

3. A 100% missile inventory method was used for structure-origin and zone-origin missiles.

The approach for structure-origin missiles conservatively assumes that all the structural missiles become minimally restrained for high intensity tornadoes . A maximum number of 363 ,778 missiles are simulated for the EF 1- 5 tornadoes. The missile density considers all missile sources to a distance of 2500 feet and covers all land areas around the targets.

4. Outage related increases in missile populations were estimated through observation of outage missiles during the walkdown and interviews with Braidwood Station staff regarding the staging of outage related equipment and materials. These outage related missile populations were included in the analysis using a temporal averaging approach. A conservative 5% increase in the mean surveyed missile population was used for all zone and structure origin missiles.

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ATTACHMENT 1 Evaluation of Proposed Changes

5. The missile injection heights used in the study were chosen conservatively. All missiles that originate from structures are injected into the tornado wind field at the appropriate height above grade.

6. The TORMIS transport model produces missile trajectories and missile impact speeds that are conservative when compared to ballistic (drag only) trajectory models. The highest missile speeds attained in TORMIS easily exceed the missile speeds adopted by the NRC for deterministic design.

7. The size of the safety targets vulnerable to "offset" hits was increased to account for "offset" hits. These safety components were increased in size by 1.5 feet for each free face in the three-dimensional modeling . This TORMIS modeling approach therefore conservatively estimated the damage to these targets for near misses by tumbling tornado missiles.

8. The analysis conservatively did not increase the size of missile shielding targets for offset hits. This approach produces a conservative result in compliance with the RIS comment on "tumbling missiles."

9. Statistical convergence of the TORM IS damage frequencies has been achieved for Braidwood Station through 27.7 billion tornado missile simulations .

10. The analysis uses of 90% of the critical missile velocities for evaluation of crimping damage to the DAFP exhausts and PORV exhausts.

11 . In general, the finite element analysis missile models were built to be conservatively strong and rigid. Conversely, target models were built to be conservatively weak to maximize the degree of potential crimping .

12. The TORM IS results for damage frequency also contains inherent conservatism. This conservatism stems from the assumption that a tornado missile strike that results in "target damage" also causes a radioactive release rather than performing specific evaluations to determine whether the damage can actually cause a release .

The degree of conservatism associated with these combined items has not been quantified; however, the net effect of eliminating or reducing these conservatisms is expected to result in a notable reduction in the TORMIS methodology estimated tornado missile damage frequencies for Braidwood Station .

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ATTACHMENT 1 Evaluation of Proposed Changes 3.3.5 Compliance with the NRC Safety Evaluation Report (SER) Acceptance Criteria In Reference 1 (i.e ., the TORMIS SER) , the NRC stated that licensees using the EPRI approach (i.e. , the TORMIS methodology) must consider the following points and provide the following information :

1. Data on tornado characteristics should be employed for both broad regions and small areas around the site. The most conservative values should be used in the risk analysis or justification provided for those values selected.

2. The EPRI study proposes a modified tornado classification, F'-scale, for which the velocity ranges are lower by as much as 25% than the velocity ranges originally proposed in the Fujita, F-scale. Insufficient documentation was provided in the studies in support of the reduced F'-scale. The F-scale tornado classification should therefore be used in order to obtain conservative results.

3. Reductions in tornado wind speed near the ground due to surface friction effects are not sufficiently documented in the EPRI study. Such reductions were not consistently accounted for when estimating tornado wind speeds at 33 feet above grade on the basis of observed damage at lower elevations. Therefore, users should calculate the effect of assuming velocity profiles with ratios Vo (speed at ground level) I V33 (speed at 33 feet elevation) higher than that in the EPRI study. Discussion of sensitivity of the results to changes in the modeling of the tornado wind speed profile near the ground should be provided.

4. The assumptions concerning the locations and numbers of potential missiles presented at a specific site are not well established in the EPRI studies. However, the EPRI methodology allows site specific information on tornado missile availability to be incorporated in the risk calculation. Therefore, users should provide sufficient information to justify the assumed missile density based on site specific missile sources and dominant tornado paths of travel.

5. Once the EPRI [i.e ., TORMIS] methodology has been chosen, justification should be provided for any deviations from the calculational approach [i.e. , from the original EPRI methodology].

The following information summarizes how the Braidwood Station TORM IS analysis satisfies the above criteria.

1. Data on Tornado Characteristics Employed to Identify Braidwood Station Sub-Region A site-specific analysis has been performed to generate a tornado hazard curve for Braidwood Station and a data set for the TORM IS analysis. The National Oceanic Atmospheric Administration (NOAA) Storm Prediction Center Severe Weather Database was used to identify a homogenous sub-region around the station. Tornadoes have been mapped for a large region and statistical tests have been performed to identify a suitable sub-region . The sub-region tornado occurrence rate, EF-scale intensities, path length ,

width , and direction variables have been analyzed for use in the TORMIS analysis.

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ATTACHMENT 1 Evaluation of Proposed Changes The analysis examines both broad and small regions around the site and provides justification for the final sub-region selected . Two Hundred Twenty-five (225) 1° latitude-longitude blocks and 25 3° blocks were analyzed to determine a homogeneous sub-region and to assess variation of risk within the sub-region . A tornado hazard curve for Braidwood Station was developed and the EF-scale wind speeds were used in this analysis in accordance with NUREG/CR-4461 , Revision 2 (Reference 6).

Additional detail regarding the derivation of the occurrence rate value may be of interest.

To develop the tornado frequency characteristics for Braidwood Station , a broad 15° longitude x 15° latitude square, centered longitudinally at the plant, was used as the starting region (this area corresponds the 225 1° latitude-longitude blocks and 25 3° blocks noted above) . This large area covered 668,222 square miles and included 18,926 tornados in the NOAA Storm Prediction Center data set. Within this broad region , the tornado risk was quantified for subareas of 1° longitude by 1° latitude (i.e ., 1° x 1° blocks) and 3° longitude by 3° latitude (i.e. , 3° x 3° blocks). A statistical method, termed Cluster Analysis , was used to determine how the distinct subarea blocks grouped into similar clusters of tornado risk. These procedures were performed separately for both the 1° x 1° block and 3° x 3° block areas. The 1° x 1° block cluster results coupled with the 3° x 3° block cluster results were used to select the final Braidwood Station tornado sub-region .

The Braidwood Station tornado sub-region includes 76 1° blocks that surround the site and provides a conservative area to develop the site-specific tornado risk and has the desirable features of connectivity and broad statistical homogeneity for tornado risk analysis. This area also includes the tornado small area "hot spots" identified in the 1° block analysis; therefore, this modeling approach meets the intent of the TORM IS SER requirement to use data on tornado characteristics for both broad regions and small areas around the plant.

A total of 9282 tornadoes were reported in the 64-year period (i.e ., 1950-2013), producing an average of 145.03 per year. The mean unadjusted occurrence rate is:

v = TJltoA = 5.29E-04 tornadoes/ square mile/ year In this equation , TJ = 9282 tornadoes, to= 64 years, and A= 274,085 square miles A correction for annual reporting trends and reporting inefficiencies are part of the TORM IS methodology. The adjusted occurrence rate is 1.04E-03 tornadoes I square mile/ year.

The calculated adjusted tornado occurrence rate of 1.04E-03 tornadoes/ square mile/ year (noted above) is consistent with the current values given in the UFSAR. UFSAR Section 2.3.1.2.2, "Tornadoes and Severe Winds," estimated the mean tornado probability values for 1° x 1° blocks (approximately 3600 mi 2) for the periods of 1953-1962 and 1955-1967. These values were 1.7 tornado/year and 3.3 tornado/year, respectively. As noted , these values have units of "tornadoes per year" whereas the TORM IS values have unit of "tornadoes per square mile per year."

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ATTACHMENT 1 Evaluation of Proposed Changes Converting the UFSAR values to units of "tornadoes per square mile per year" you get the following :

v = 1.7 tornado/year+ 3600 mi2 = 4.72E-04 tornadoes/mi2/year (1953 - 1962 data) v = 3.3 tornado/year + 3600 mi 2 = 9.17E-04 tornadoes/mi2/year (1955 - 1967 data)

As can be seen , these values are generally consistent with the TORMIS-calculated adjusted tornado occurrence rate of 1.04E-03 tornadoes/ square mile/ year.

As discussed below in RIS 2008-14, Item 1.a "Justification for Tornado Frequency," the Braidwood Station site-specific tornado risk used in the TORMIS analysis has been shown to be conservative when compared to the NRC Region I criteria given in NUREG/CR-4461 ,

"Tornado Climatology of the Contiguous United States, (PNNL-15112 , Rev 2)," Revision 2.

UFSAR Section 2.3.1.2.2 will be revised to acknowledge the tornado parameters and tornado frequency values used in TORM IS. Since the TORMIS methodology only applies to a limited set of unprotected targets, the UFSAR will also retain the existing UFSAR information that continues to apply to the majority of the plant structures.

2. Tornado Wind Speed Intensity The 1983 SER calls for the use of the F scale of tornado intensity in terms of assigning tornado wind speeds to each intensity category (F1-F5). However, the NRC has adopted the EF scale and confirmed in previous discussions on TORMIS that the EF scale could be used in place of the F scale. The use of the EF scale is consistent with the recently endorsed positions of NRC Regulatory Guide (RG) 1.76, Revision 1, that are based on NUREG/CR-4461 , Revision 2 (Reference 6).

It is recognized that the Braidwood Station Design Basis windspeed (290 mph rotational velocity) is consistent with the 1974 version of RG 1.76 and exceeds the EF5 windspeed of 230 mph shown below in Table 3.3.4-1; however, the use of the EF scale wind speeds is limited to evaluation of unprotected equipment using TORMIS. There is no intent to update the entire licensing basis to utilize RG 1.76, Revision 1. UFSAR Section 3.5.5, "Probabilistic Tornado Missile Risk Analysis," (included in Attachment 1-3), specifically notes the use of the EF scale in TORMIS simulations (see Attachment 1-3, UFSAR Section 3.5.5.3.a on page 3.5-26c) .

3. Characterization of Tornado Wind Speed as a Function of Height Above Ground Elevation The TORMIS simulations were performed with the TORMIS rotational velocity Profile 3, which has increased near ground wind speeds over Profile 5, which was used in the 1981 EPRI TORMIS reports (see Attachment 1-2, Figure 3, "Tornado Rotational Wind Velocity Profiles"). Therefore, the Braidwood Station runs were made with higher near ground wind speeds than in the EPRI study. The sensitivity study was conducted by running the original EPRI profiles (i.e., Profile 5). All 60 replications that contributed to the target group results in Attachment 1-1 , Table 2 were run and compared to the Profile 3 results Boolean group by Boolean group. Note that Figure 3 is a scan of Figure ll- 12(b) from Reference 5.

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ATTACHMENT 1 Evaluation of Proposed Changes The comparison showed that differences in results were negligible for missile hit (see Attachment 1-2, Figure 4, "Plot of Frequencies with Profile 5 versus Profile 3"). Some sensitivity was observed for targets with very low damage frequencies (i.e., <1 .0E-08) ;

however, differences were negligible when aggregated over the target groups. Hence, the use of Profile 3 produces results comparable to Profile 5.

4. Missile Characterization and Site-Structure Models A detailed plant survey was performed during an outage to quantify the number of potential missiles. The Braidwood missile survey walkdown was performed by ARA using ARA's plant walkdown procedures. The survey walkdown uses a systematic, documented process to provide input on what missiles are in each missile zone, the minimum and maximum injection heights for all missiles by missile type, the building characteristics for structures in the missile zone , and pictures of the missiles and buildings surveyed . This information was developed into the plant modeling inputs for the TORMIS analysis. The mean number of potential missiles simulated for EF5 tornadoes was 383,420 , including structural failure missile sources. This number also includes additional missiles in several zones to conservatively anticipate future conditions. The missiles consist of both zone missile and structure origin missiles. The missiles are distributed throughout the plant based on the missile survey. Tornadoes from any direction that strike the plant will interact with numerous missiles within 2500 feet of the targets.

The plant site is described by specifying the geometry, location , and material properties of the structures/components and the location of potential missile sources. Missile sources (buildings , houses, storage areas, vehicles, etc.) are modeled to a distance of approximately 2500 feet in all directions from safety-significant targets. This distance is based on a sensitivity study performed in the original TORMIS research (References 3 and 4). The sensitivity study concluded that missiles beyond 2000 feet did not need to be considered in the risk assessment. This value has been increased to 2500 feet in modern TORMIS analyses to be conservative. This process includes the development of missile origin zones around the plant (shown in Attachment 1-2, Figure 5, "Zone Layout for Braidwood Station Main Site Model TORMIS Analysis," and Figure 6 , "Zone Layout for Braidwood Station SX Model TORM IS Analysis") and surveying the types and quantities of missiles in each zone.

The Braidwood Station missiles include the standard TORMIS missiles in EPRI NP-769 (Reference 4) , including structural sections, pipes, wood members, other construction materials, and an automobile category. For each set, the cross-sectional geometry and the missile aspect ratio (Lid) are deterministic.

The structure-origin missiles represent the maximum number of missiles produced given destruction of the buildings. The number of missiles produced from this total inventory depends on the wind speeds (i.e. , EF scale) experienced by the building . For example , light damage might be expected in 100 mph winds, while catastrophic failure might occur in 200 mph winds. Research performed in the development of the HAZUS wind model (Reference 7) is used to determine the number of missiles available for each building type for each wind speed level considered in the TORM IS runs. When specific wind fragilities of building components are known , the calculated building fragilities are used to produce the number of available missiles in place of the HAZUS functions .

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ATTACHMENT 1 Evaluation of Proposed Changes The HAZUS vulnerability models are based on detailed 3-D modeling of buildings and simulated hurricane winds. For each simulated storm, the wind pressures are estimated over the building envelope. The wind load is then computed for each component and compared to the component resistance. Component failures occur when the load exceeds the resistance. This simulation process is repeated for all components as the storm is tracked by the building for each time step. Internal pressurization of the structure is modeled when the envelope is breached by a missile or a failed opening (window or door).

Table 3.3.5-1 below summarizes the wind speed missile functions, defined at the wind speeds for which TORMIS is typically run to produce missile fragilities in support of License Amendment Requests with the Enhanced Fujita scale wind speeds from the HAZUS research. The damage state for each building type was selected based on sufficient failure to produce structural component missiles. These criteria correspond to "Damage State 4-Destruction" for all building types except manufactured buildings, where Damage State 3 was determined to be sufficient to produce significant structural missiles.

Table 3.3.5-1 HAZUS Damage State Exceedence Probabilities for EF-Scale Mid-Point Wind Speeds E11l1a11ud Wi11d Spei'd (mpl,)

Ha::.ard Brrildi11g T_1pe Dam.age EFO EF1 EFl EFJ EF.J EF.,

State 65-85 86-110 111-13.i 136-165 166-!00 !00-!lO Trailer, Jln1111faC'rored Bldg 3 0.01 0.03 0.5 0.96 .00 .00 Wood Frame/ .\Jodrrlar 4 0.00 0.01 0.12 0.75 0.99 .00

_\Iasom;* Frame 4 0.00 0.01 0.03 0.35 LOO 1.00 Pre E11gr Steel Frame 4 0.00 0.00 0.02 0.3 0.85 0.98 E11gim.*efii'd Fmme 4 0.00 0.00 o.oo*

• 0.0 0.50 0.90 A stochastic missile modeling approach was used to model the numbers of potential missiles at the plant during outage and non-outage conditions. All the postulated missiles at Braidwood Station were treated as minimally restrained in which each sampled missile is injected near the peak aerodynamic force , thus maximizing the transport range and impact speed and , consequently, the missile hit and damage frequency. A summary of the total missile populations used in the TORMIS Main Site Model is given in Table 3.3.5-2 below.

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ATTACHMENT 1 Evaluation of Proposed Changes Table 3.3.5-2 Number of Braidwood Station TORMIS Simulated Missiles (Stochastic Model Main Site)

Zone Origin Slr11ct11re Ori ,;,, Total (A.II S011rces)

EF Scale

.V'm .Vea11 Ma.Y .Vin Jltan .Va.Y Min .Vtan .'t-fa.Y EF l 44,990 51,565 60,993 2,635 2,885 3,219 47,788 54,450 63,903 EF 2 44,990 51,565 60,993 26,278 29,361 33,638 73,082 80,926 94,020 EF 3 44,990 51,565 60,993 166,645 184,231 205,374 213,841 235,796 265,756 EF 4 44,990 51.,565 60,993 274,723 298,174 328,705 321,919 349,740 389,087 EF5 44,990 51,565 60,993 308,081 33 1,855 365,379 355,277 383,420 425,761 A summary of the total missile populations used in the TORM IS SX Model is given in Table 3.3.5-3 below. Note that the simulated missiles from the Main Site Model and the SX Model have no impact on the opposite model due to the distance between the Reactor and Auxiliary Buildings, and the SX discharge pipes (i.e., greater than 2500 feet apart) .

Table 3.3.5-3 Number of Braidwood Station TORMIS Simulated Missiles (SX Model)

Zo11e Origi11 Struc111re Origin Total .Uissiles (.4ll Sources)

EF Scale Jlin .llea11 Max .11;,, Mean .iJax Jfin .llea11 J/a.,*

EF I 12,612 14,075 16,119 47 50 51 12,660 14,125 16,176 EF2 12,612 14,075 16,1 19 303 367 477 12,926 14,442 16,596 EF 3 12,612 14,075 16,119 1,044 1,212 1,507 13,699 15,287 17,626 EF 4 12,612 14,075 16,119 2,595 2,91 5 3,386 15,366 17,050 19,220 EF 5 12,612 14,075 16, 119 3,546 4,170 4,973 16,426 18,245 20,200 It should be emphasized that the TORM IS methodology does consider vertical missiles.

Specifically, the approved TORMIS methodology explicitly considers all x, y, and z components of the missile velocity vector. The 3-D simulations integrate the equations of motion for each missile and the resulting trajectories include a continuum of trajectory paths, including horizontal, vertical , and oblique trajectory paths. NP-2005 Volume 2,Section IV, describes missile motion and orientation models. The missile velocity vector at the instant of impact; therefore, inherently includes vertical and horizontal motions of the missile. As such, a continuum of missile velocity vector orientations at impact can occur, including horizontal, near- horizontal , oblique, near vertical , and vertical.

5. Deviations from the Original EPRI Methodology:

The Braidwood Station TORMIS analysis was performed by Applied Research Associates, Inc. (ARA) using TORMIS_ 14, an updated version of the orig inal EPRI NP-2005 version of the code (Reference 5).

The TORMIS code is a legacy FORTRAN computer code that has been ported to modern computers and compilers and has had bug fixes and other enhancements since 1981 . The 17 of 33

ATTACHMENT 1 Evaluation of Proposed Changes updates and enhancements made to TORMIS since 1981 are documented in ARA TORMIS reports and Code Manuals. These changes include: porting the legacy code from mainframe to minicomputer to PC computers, post processing data routines, updates to the random number generation , ensure aerodynamic function of box/beam for Cit greater than 4 to match Figure 3-8 of Reference 4 and replace the exponential tip loss function with an equivalent polynomial (i.e ., replaced the exponential function in Equation 3.10 in Reference 4 with the Hoerner suggested polynomial); enhanced output options; and addressing compiler differences and numerical round-off issues in various functions from the legacy code. All code changes have been checked and verified through comparisons to the preceding version .

Also included in the updates were the replacement of the original mainframe based random number generator with a machine-independent algorithm and re-dimensioning of the code to allow larger numbers of targets and missiles.

The TORMIS code verification includes duplications and comparison to each preceding TORMIS version as well as the original TORMIS Sample Problem in EPRI NP 2005 (Reference 5). These statistical comparisons show that the basic TORMIS code calculational approach produces comparable results to that of the original version .

An enhanced method for evaluating missiles passing through openings, such as pipe penetrations in reinforced concrete walls was used for the Braidwood Station analysis. This method uses a screening of missile impact conditions to screen-out missile impacts that can obviously not pass through an opening . The screening is done in the processing of the missile impact data without modifying the TORMIS physics engine in the IMPACT subroutine. This calculation approach for pipe penetration type targets was introduced as an option in previous versions of TORM IS and was used in several analyses prior to the Braidwood Station analysis. This approach provides an additional output option that is conservative for estimating the probabilities of missiles passing through small openings in concrete barriers. Both the TORMIS hit probability and the pipe penetration probability is reported for all such targets where the screening approach is used. The results for individual targets are given in Attachment 1-1 , Table 1.

There was also a single change made to the code of a purely "software" nature, which was not related to the approved TORMIS physics engine and calculation approach ; i.e., the dimensioned number of possible missile types was increased to 24 for evaluation of damage from missile velocity exceedance and pipe penetration pass through . This change was made, verified and exactly reproduces previous TORMIS outputs. Note that the missiles used for the Braidwood Station FEA calculations were identical to those used for the Byron Station analysis (approved in Reference 15) with the exception of the roof paver missile which was omitted for the Braidwood Station analysis (i.e. , the Braidwood Station analysis used 23 missiles) as there are no pavers on building roofs at Braidwood Station.

In addition , it should be noted that TORSCR_MF was updated to accommodate up to 40,000 tornadoes (up from 15,000) to be evaluated for each TORMIS replication. Note that TORSCR is a FORTRAN computer code that is used to post-process TORM IS output files.

Its primary function is to compute Boolean combinations of target hit and damage probabilities over multiple targets.

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ATTACHMENT 1 Evaluation of Proposed Changes Note that all the above deviations from the original EPRI Methodology were previously identified in the Byron Station TORMIS License Amendment Request; i.e., in a letter from D.

M. Gullett (EGC) to NRC, "License Amendment Request to Utilize the TORMIS Computer Code Methodology," dated October 7, 2016 . (Reference 13). This proposed license amendment was subsequently approved by the NRC in letter from J. S. Wiebe (NRC) to B. C. Hansen (EGC) , "Byron Station , Unit Nos. 1 and 2 - Issuance of Amendments Regarding Use of TORM IS for Assessing Tornado Missile Protection," dated August 10, 2017 (Reference 15).

3.3.6 Compliance with NRC RIS 2008-14 Criteria Subsequent to the original NRC TORMIS SER (Reference 1), the NRC issued Regulatory Issue Summary 2008-14 (Reference 2) to inform licensees of the NRC's experience with shortcomings identified in submitted licensee TORMIS analyses. The RIS specifically identified items licensees should address to confirm the TORMIS methodology and computer code have been properly applied and implemented . These issues identified in the RIS are presented below.

1. Licensees did not fully satisfy the first four points identified in the SER approving the TORMIS methodology. Examples include the following:

a. not providing adequate justification that the analysis used the most conseNative value for tornado frequency

b. not including the entire TORM IS missile spectrum defined for use in the TORMIS computer code as appropriate for the plant

c. not providing adequate explanation for the number and adequacy of tornado simulations and histories

d. not providing sufficient information regarding the development and use of area ratios I

2. Licensees did not fully address the fifth point identified in the SER and explain how the methodology was implemented when the parameters used differed from those specified in the TORMIS methodology. Examples include the following:

a. inappropriately limiting the number of targets modeled

b. failing to address missile tumbling when modeling targets

c. failing to properly consider and use the variance reduction techniques and parameters specified by TORMIS

d. taking credit for nonstructural members

e. failing to consider risk significant, non-safety-related equipment

3. Licensees used the TORMIS methodology to address situations for which the methodology was not approved. Examples include the following:

a. proposing the elimination of existing tornado barriers

b. proposing Technical Specifications (TS) changes

c. proposing plant modifications 19 of 33

ATTACHMENT 1 Evaluation of Proposed Changes Braidwood Station considered these observations in the development of the TORM IS analysis and addressed each of them as shown below.

1.a. Justification for Tornado Frequency:

To meet the regulatory requirements for modeling tornado risk, TORMIS uses a statistical approach that considers both broad regions and small areas around the plant. A basic sub-region data set for Braidwood Station is identified and analyzed . The sub-region data is analyzed to produce the tornado input files needed in TORMIS . Tornado hazard curves are developed using a TORMIS-derived code called TORRISK. TORRISK is a specialized version of TORM IS that produces tornado hazard curves distinct from the missile risk analysis features of TORM IS. The TORRI SK hazard curves provide control points to ensure that the TORMIS simulations track the Braidwood Station site-specific hazard curve and are conservative for missile risk analysis.

The tornado frequency value conservatively considers regions around the plant and corrects for reporting trend and tornado classification error and random encounter errors, per the TORMIS methodology (References 3, 4, and 5) . The developed tornado hazard curve for Braidwood Station is conservative when compared to NRC Region I criteria given in NUREG/CR-4461 , Revision 2 (Reference 6). A comparison of Braidwood Station hazard curve (i.e., the "BRW 2015 Plant EF" curve) and NUREG/CR-4461 (i.e., the "BRW NUREG EF" curve) is shown in Attachment 1-2, Figure 7, "TORMIS Simulation of Braidwood Station Tornado Hazard for Plant Safety Envelope."

1.b. Spectrum of Missiles Considered:

The Braidwood Station study included the missile spectrum (26 missile aerodynamic subsets) developed for use in TORM IS. A total of 23 missile types were used for Braidwood Station , including two plant specific missiles. One plant specific missile type was the precast concrete roof deck panels found on several buildings. The second plant specific missile was the existing metal siding missile which was modified to be plant specific based on the characteristics of the insulated metal siding on the exterior of the Braidwood Turbine Building . Note that the missiles used for the Braidwood Station FEA calculations were identical to those used for the Byron Station analysis (approved in Reference 15) with the exception of the roof paver missile which was omitted for the Braidwood Station analysis as there are no pavers on building roofs at Braidwood Station .

1.c. Justification for the Number and Adequacy of Tornado Simulations:

A replication approach was used for the simulations. A total of 60 complete TORMIS replications were run with different random number seeds and missile populations for each TORMIS model. A total of 462 million missile simulations were performed for each replication , for a total of 27.7 billion missile simulations over all 60 replications. The standard deviations (cr) of these replications were computed and the standard error (E) in the aggregate mean probability(µ) was computed from E = cr/vn. The 95% confidence bounds in the mean probability were conservatively approximated by µ +/- 2*£.

Attachment 1-2, Figure 8, "Target Group Hit and Damage Frequency with Confidence Intervals," plots the two-sided 95% confidence intervals. As an example, the running 95%

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ATTACHMENT 1 Evaluation of Proposed Changes two-sided confidence bounds for Group 8 are illustrated in Attachment 1-2, Figure 9, "Convergence Plot for Damage Frequency for Target Group 8 (U1 MSSV Group 1 NE)," to demonstrate that reasonable statistical convergence had been obtained with 60 replications.

1.d. Use of Area Ratios:

No area ratios have been used as a method to adjust the TORMIS outputs for small targets, based on a ratio of hit probabilities from a large target or surface. A variance reduction approach is available in TORMIS and was used for Braidwood Station that allows for increasing the volume or size of small targets explicitly within the code.

TORMIS applies the input variance reduction weight (ka) in the TORMIS scoring equation.

These adjustments are used within TORMIS for the single missile impact probability. They are not used to "ratio down" the multiple missile impact probabilities following a TORMIS simulation . Ratioing down the results at the end of TORM IS is not technically acceptable and can lead to an underestimation of the multiple missile risk.

2.a. Inappropriately Limiting of the Number of Targets Modeled:

The Braidwood Station TORMIS model includes plant components, identified as necessary to safely shutdown the plant and maintain a shutdown condition , located in areas not fully protected by missile barriers designed to resist impact from design basis tornado missiles. The Braidwood Station TORMIS analysis includes 74 potential missile targets(seeAttachment 1-1 , Table 1).

A number of unprotected targets were reviewed and not included in the Braidwood Station TORMIS model based on the following criteria :

1. Alternate protected systems or components are available to perform the required function , or

2. Analysis or evaluation to show that a postulated tornado missile impact will not result in the loss of a safe shutdown function .

The following are examples of the equipment not included in the Braidwood Station TORMIS model with associated justification as documented in an engineering evaluation .

• The unprotected non-safety related Condensate Storage Tanks (CST) and piping from the CSTs to the AF pumps located in the Turbine Building are not included in the Braidwood TORMIS model. The safety related essential service water system is used as the backup suction source for the AF pumps if the CSTs or piping from the CSTs are damaged during a tornado event. The secondary effects (i.e., local flooding) from a CST rupture, caused by a tornado missile strike, were also considered . There are no safety-related SSCs near the CST that would be adversely affected by a CST rupture .

• The unprotected portion of the safety related Emergency Diesel Generator (EOG) exhaust stacks are not included in the TORMIS model. To prevent loss of diesel availability due to exhaust stack damage, a rupture disc pressure relief device is 21 of 33

ATTACHMENT 1 Evaluation of Proposed Changes installed on each diesel exhaust line. This relief device is located inside a missile protected structure.

• Each EOG engine is provided with a crank case breather vent line that is routed to the outdoors. Where the lines penetrate the auxiliary building the vent lines could be damaged by tornado missiles blocking the crank case vent path. Design analysis has been completed and demonstrates that the crankcase vent lines can be blocked without adversely affecting the ability of the associated EOG to perform its design function . *

• The Diesel Oil Storage Tanks (DOST) and EOG Day Tanks contain vent lines which provide a path to allow the tanks to fill and drain without developing excessive internal pressure or vacuum . The vent lines could be crimped by tornado missiles blocking the vent path at the point where they penetrate the auxiliary building. In the event the normal tank vent is blocked , an adequate alternate vent path for the DOSTs and EOG Day Tanks is provided by the DOST overflow lines and the piping that connects the air spaces of the DOSTs and EOG Day Tanks. These alternate vent paths are located inside the auxiliary building and are properly protected from tornado missiles.

• The normal fill path to the DOSTs (which are missile protected , located inside the auxiliary building) is from either the 125,000-gallon or 50 ,000-gallon, Category II outdoor oil storage tanks utilizing gravity flow. The 125,000-gallon and 50,000-gallon oil storage tanks are not protected from tornado missiles. The outside fill connection is also not protected from tornado missiles. The DOSTs are designed to provide adequate fuel supply for 7 days of post-accident load operation.

• The AF Pump Diesel Engine Day Tanks contain vent lines which provide a path to allow the tanks to fill and drain without developing excessive internal pressure or vacuum. The vent lines could be crimped by tornado missiles blocking the vent path at the point where they penetrate the auxiliary building . For the Unit 1 AF Pump Diesel Engine Day Tank, if the normal vent path is completely blocked , an adequate alternate vent path would be provided by the tank overflow line to the 1C DOST. This alternate vent path is located inside the auxiliary building and is properly protected from tornado missiles. For the Unit 2 AF Pump Diesel Engine Day Tank , the vent line has a different configuration ; therefore , a revision was made to the Abnormal Operating Procedure to establish operator compensatory actions to address a potential vent line crimp due to a tornado missile impact.

• As discussed in the Section 3.5.2 of the original Braidwood Station Safety Evaluation Report (SER) , although the fuel-handling building is designed to be tornado missile resistant, the rollup freight door which is a large opening in the building is not capable of resisting tornado-missile impact. A tornado or tornado missile could destroy the door and may allow a relatively lightweight missile of large area , such as a steel panel or the door itself to travel inside the fuel-handling building . However, the spent fuel pool is sufficiently far from the door that any resulting tornado missile and debris could not enter the spent fuel pool and cause damage to the spent fuel assemblies or block coolant flow. This is due to the low trajectory that the missile would have to follow through the door and toward the fuel pool. Further, it would then be required to turn 90° in order to enter the fuel pool.

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ATTACHMENT 1 Evaluation of Proposed Changes

• An unprotected six-inch vent pipe runs from the top of each RWST into the Fuel Handling Building . The loss of RWST vent function (i.e ., a missile hit completely crimps the vent and prevents air from entering the tank) has been analyzed to show no adverse impact on the RWST pressure boundary function . The pumps that draw suction from the RWST have been evaluated to show adequate Net Positive Suction Head is available without the vent function .

• The underground pipe tunnels from the RWSTs to the Auxiliary Building have an outdoor access shaft and hatch . The hatch cover is%" thick steel plate that is not designed as a missile barrier. An evaluation determined that no equipment required for safe shutdown would be damaged by tornado missiles that enter the hatch and travel down the access shaft into the pipe tunnel.

• Doors and ventilation openings between the Auxiliary Building and the Turbine Building below Elevation 451' are protected from tornado missiles by the concrete slabs, various Turbine building concrete walls , and large equipment located on elevations 426' and 401' of the Turbine Building .

It is also worthy to note that other targets were considered and include, for example, buildings that are expected to fail in a tornado and produce missiles (i.e. , missile source targets) and build ings that are not assumed to fail during a tornado (such as reinforced concrete structures or heavy steel frames) . Targets can be stacked on the top of one another to create , for example, a missile source on top of a safety-significant reinforced concrete building. For each target, the material type and strength are specified for each surface of the target, which is generally modeled as a prismatic box shape. These missile source targets are identified based on the site plans and aerial photos as well as plant walkdowns. Potential missiles generated by missile source buildings are estimated based on the site walkdown and building break-up models.

Missile shielding targets are buildings and other structures that are assumed to not fail in the tornado and provide missile shielding to the safety significant targets. Plant components modeled as shielding targets (also referred to as blockage) are constructed of reinforced concrete that is at least one foot thick, or clad with steel plate that is at least one inch thick. For example, the concrete structure of the Reactor Building is modeled as a missile shield target.

TORMIS target worksheets were completed for each safety-significant target. These worksheets are used to document the location , dimensions, material properties, references, and special modeling considerations for each of the safety-significant targets.

Each worksheet also includes copies of the photos taken during the target walkdown and three-dimensional CAD representations of the targets as modeled for TORM IS. -1 , Table 4, "Sequential Numbering of Safety-Significant, Shielding and Missile Source Targets," contains a list of all the safety-significant, shielding , and missile source targets included in the Braidwood Station TORMIS model. Also shown in the table is the target group to which each of the safety-significant targets belongs.

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ATTACHMENT 1 Evaluation of Proposed Changes 2.b. Consideration of Missile Tumbling:

All safety-significant targets (with the exception of pipe penetrations) were modeled to allow for tumbling missile hits (i.e. , offset hits) in accordance with the TORMIS technical reports (References 3, 4, and 5). Pipe penetration targets were not increased in size to reflect tumbling missiles since offset missiles cannot result in penetration of a small opening in a concrete wall.

EPRI TORM IS Report NP-769 (Reference 4) discusses consideration of finite missile size in modeling targets in Section 4.2.3. Since TORMIS tracks the missile as a point, missiles that just miss a target are actually likely to have hit the target by virtue of an "offset" hit.

The analysis in Reference 4 shows that each safety target dimension should be increased by L/8 for each free face or direction , where Lis the mean length of the missiles. Each shielding target can be increased by U4 in each free direction. Thus, if a safety target has two free faces in the X direction , its actual X dimension , would be increased by L/8 x 2.

This increase in target size accounts for the potential near misses (which are actually "offset" hits) that are not treated in TORMIS .

The determination of the appropriate offset hit dimension is an iterative process because a TORMIS model of a given plant needs to be run with its plant description and actual missile inventory. This was accomplished for Braidwood Station by creating a TORMIS model of the plant with an offset hit dimension of 1.5 feet per free edge.

The Braidwood Station TORMIS analysis conservatively did not increase the size of missile shielding targets for offset hits. This approach produces a conservative result in compliance with the RIS comment on "tumbling missiles."

2.c. Use of Variance Reduction Techniques:

Due to the very large simulation/replication sizes, no variance reduction techniques were used for tornado wind speed , tornado offset, tornado direction , tornado orientation , missile type, missile injection height, missile impact orientation , or trajectory termination . Variance reduction techniques were used for missile zone population and target size (ka by target surface).

2.d. Inappropriate Credit for Non-Structural Members:

The Braidwood Station TORMIS analysis did not take credit for missile resistance for non-structural members.

2.e. Failure to Consider Risk Significant, Non-Safety-Related Equipment:

Plant walkdowns were performed in support of the TORM IS analysis. Risk-significant targets (both safety-related and non-safety-related) were considered . Seventy-four (74) unprotected targets were ultimately identified and are included at the TORMIS analysis target set. Also see discussion under Item 2.a.

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ATT ACHM ENT 1 Evaluation of Proposed Changes 3.a. Using TORMIS for the Elimination of Existing Tornado Barriers TORM IS is not being used to propose the elimination of tornado barriers.

3.b. Using TORMIS to Propose TS Changes TORMIS is not being used to propose TS changes .

3.c. Using TORMIS for Plant Modifications TORMIS is not being used to design new plant equipment modifications.

4.0 REGULATORY EVALUATION

4.1 Applicable Regulatory Requirements/Criteria The TORM IS methodology was developed to estimate the probability of tornado missile impact and damage to nuclear power plant SSCs. The proposed change to utilize the TORMIS Computer Code for assessing tornado-generated missile protection of unprotected plant SSCs, is consistent with this methodology and the requirements and acceptance criteria specified in the below documents:

• Electric Power Research Institute Report- EPRI NP-768, "Tornado Missile Risk Analysis," May 1978 (Reference 3)

• Electric Power Research Institute Report - EPRI NP-769, "Tornado Missile Risk Analysis -Appendices," May 1978 (Reference 4)

• Electric Power Research Institute Report - EPRI NP-2005 Volumes, I and 2, 'Tornado Missile Risk Evaluation Methodology," August 1981 (Reference 5)

• NRC Standard Review Plan (SRP) (i.e ., NUREG-0800), Section 2.2.3, "Evaluation of Potential Accidents," Revision 2, July 1981 Specific information regarding TORMIS approval and acceptance criteria is contained in the following documents.

NRC TORMIS Safety Evaluation Report The TORMIS methodology (References 3, 4 and 5) has been reviewed and accepted for nuclear power plant tornado missile risk analyses, as documented in the NRC Safety Evaluation Report (SER) - Electric Power Research Institute (EPRI) Topical Reports Concerning Tornado Missile Probabilistic Risk Assessment (PRA) Methodology, dated October 26, 1983 (ML080870291) (Reference 1). The NRC SER concluded that:

"... the EPRI methodology can be utilized when assessing the need for positive tornado protection for specific safety-related plant features. "

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ATTACHMENT 1 Evaluation of Proposed Changes The SER also states that licensees using the EPRI approach (i.e ., the TORMIS methodology) must consider five specific points and provide the appropriate information. This information is provided in Section 3.4.5 above.

NRC Memorandum on Use of Probabilistic Risk Assessment in Tornado Licensing Actions NRC Memorandum from Harold R. Denton to Victor Stello , "Position of Use of Probabilistic Risk Assessment in Tornado Licensing Actions," dated November 7, 1983 (ML030020331), endorsed the acceptance criteria stated in NUREG-0800, Section 2.2.3. The memorandum states:

"Therefore, the guidance in SRP Section 2.2.3 is applicable to tornado missiles. This guidance, which we will use in our probabilistic tornado reviews, states that an expected rate of occurrence of potential exposures in excess of the 10 CFR 100 guidelines of approximately 10-6 per year is acceptable if, when combined with reasonable qualitative arguments, the risk can be expected to be lower."

NRC Regulatory Issue Summary 2008-14 The NRC subsequently issued Regulatory Issue Summary (RIS) 2008-14, "Use of TORM IS Computer Code for Assessment of Tornado Missile Protection," dated June 16, 2008. This RIS provided additional guidance on the use of TORM IS for assessing nuclear power plant tornado missile protection . The RIS states that:

"The TORMIS methodology is approved for situations where (1) a licensee identifies existing plant SSCs that do not comply with the current licensing basis for positive tornado missile protection of the plant and (2) it would require costly modifications to bring the plant into compliance with the current licensing basis."

In addition , the RIS identified specific items licensees should address to confirm the TORMIS methodology and computer code have been properly applied and implemented . This information is presented in Section 3.4.6 above. The RIS also reconfirms that the guidance in SRP Section 2.2.3 is applicable to tornado missiles.

4.2 Precedent The NRC previously approved use of the TORM IS methodology for use at the following facilities:

Byron Station, Units 1 and 2 This amendment is documented in a letter from J . S. Wiebe (NRC) to B. C. Hansen (EGC) ,

"Byron Station, Unit Nos. 1 and 2 - Issuance of Amendments Regarding Use of TORM IS for Assessing Tornado Missile Protection," dated August 10, 2017 (Reference 15).

In this amendment, the NRC explicitly acknowledged that it is appropriate to apply the acceptance criterion established in SRP 2.2.3 of 10-6 per year on a unit-specific basis. The Braidwood Station approach to justify application of the acceptance criteria on a unit-specific bases is the same as that used for Byron Station .

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ATTACHMENT 1 Evaluation of Proposed Changes In Reference 15, the NRC also specifically approved the use of Boolean Logic. The NRC stated the following :

"The Boolean Logic was created for the UHS based on the minimum tower requirement as described in the licensee's letter dated October 7, 2016, Section 3.4.3. The licensee stated that the Boolean Logic was modeled in the analysis with the TORMIS post-processor TORSCR using the Boolean intersection (n) operator. The licensee's application dated October 7, 2016, Section 3.4.2 described that TORSCR is a FORTRAN computer code used to post-process TORMIS output files. Its primary function is to compute Boolean combinations of target hit and damage probabilities over multiple targets. The intersection operator was only used for the UHS in the Byron TORM IS analysis because multiple components need to be damaged to cause a failure of the UHS."

"Based on the use of the intersection operator to evaluate failures that need multiple components damaged from tornado missiles, the NRG staff finds that the licensee's use of the intersection operator to be acceptable for the components of the UHS."

In Reference 15, the NRC also approved a number of deviations from the original EPRI methodology (see References 3, 4 and 5). These deviations are similar to the deviations utilized in the Braidwood Station TORM IS analysis as discussed in Section 3.3.5, Item 5, above.

Specifically, the NRC noted the following :

The licensee stated that the TORMIS code, a legacy FORTRAN computer code, has been updated to modern computers. The updates and enhancements include: porting the legacy code from the mainframe to minicomputer to PC computers; post processing data routines; updating the random number generation; updating the aerodynamic tip loss function, and addressing compiler differences and numerical round-off issues in various functions from the legacy code. An enhanced method was used for evaluating missiles passing through openings such as pipe penetrations in concrete walls. This method uses a screening of missile impact conditions to evaluate missile impacts that can obviously not pass through an opening. This approach provides an additional output option for estimating the probabilities of missiles passing through small openings in concrete barriers. Based on its review, the NRG staff finds that these methods are reasonable and are therefore acceptable.

Fermi 2 This amendment is documented in a letter from T. J. Wengert (NRC) to J. H. Plona (DTE Electric Company) , "Fermi 2 - Issuance of Amendment Re: Revise the Fermi 2 Licensing Basis Concerning Protection from Tornado-Generated Missiles," dated March 10, 2014 (Reference 11 ).

In this amendment, the NRC also approved a number of deviations from the original EPRI methodology (see References 3, 4 and 5) . These deviations are similar to the deviations utilized in the Braidwood Station TORMIS analysis as discussed in Section 3.3.5 , Item 5, above.

Of particular note, the NRC stated that following :

"An enhanced method was used for evaluating missiles passing through openings such as pipe penetrations in concrete walls, in addition to the standard TORMIS hit probability for such targets. This provides supplemental outputs intended to cover special cases of missiles going through wall openings."

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ATTACHMENT 1 Evaluation of Proposed Changes Donald C. Cook Nuclear Plant, Units 1 and 2 This amendment is documented in a letter from J. F. Stang (NRC) to R. P. Power (Indiana Michigan Power Company) , "Donald C. Cook Nuclear Plant, Units 2 and 2 - Issuance of Amendments," dated November 17, 2000 (Reference 12).

In this amendment, the NRC explicitly acknowledged that the accepta nce criterion established o-s in SRP 2.2.3 of 1 per year is applied on a unit-specific basis.

4.3 No Significant Hazards Consideration In accordance with 10 CFR 50.90 , "Application for amendment of license, construction permit or early site permit," and 10 CFR 50.59, "Changes, tests, and experiments," paragraph (c)(2)(viii),

Exelon Generation Company, LLC , (EGC) requests amendments to Renewed Facility Operating License Nos. NPF-72 and NPF-77 for Braidwood Station , Units 1 and 2. This amendment request proposes to revise the Braidwood Station licensing basis for protection from tornado-generated missiles. Specifically, the Updated Final Safety Analysis Report (UFSAR) will be revised to identify the TORMIS Computer Code as the methodology used for assessing tornado-generated missile protection of unprotected plant structures, systems and components (SSCs); and to describe the results of the Braidwood Station site-specific tornado hazard analysis. The results from the Braidwood Station TORMIS analysis will be used to credit unprotected equipment for post-tornado safe shutdown. Revisions to the affected UFSAR sections will be performed in accordance with 10 CFR 50.59, "Changes, tests and experiments,"

after approval of the proposed amendment. Note that there are no Technical Specifications changes associated with this request.

The Braidwood Station TORMIS analysis utilizes a probabilistic approach performed in accordance with the guidance described in the NRC TORMIS Safety Evaluation Report dated October 26, 1983, as clarified by Regulatory Issue Summary {RIS) 2008-14, "Use of TORMIS Computer Code for Assessment of Tornado Missile Protection ," dated June 16, 2008.

According to 10 CFR 50.92 , "Issuance of amendment," paragraph (c) , a proposed amendment to an operating license involves no significant hazards consideration if operation of the facility in accordance with the proposed amendment would not:

(1) Involve a significant increase in the probability or consequences of an accident previously evaluated; or (2) Create the possibility of a new or different kind of accident from any accident previously evaluated ; or (3) Involve a significant reduction in a margin of safety.

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ATTACHMENT 1 Evaluation of Proposed Changes EGC has evaluated the proposed change for Braidwood Station , using the criteria in 10 CFR 50.92, and has determined that the proposed change does not involve a significant hazards consideration . The following information is provided to support a finding of no significant hazards consideration .

Criteria

1. Does the proposed change involve a significant increase in the probability or consequences of an accident previously evaluated?

Response: No.

The NRC TORMIS Safety Evaluation Report states the following :

"The current Licensing criteria governing tornado missile protection are contained in

[NUREG-0800) Standard Review Plan (SRP) Section 3.5.1.4, [Missiles Generated by Natural Phenomena] and 3.5.2 [Structures, Systems and Components to be Protected from Externally Generated Missiles]. These criteria generally specify that safety-related systems be provided positive tornado missile protection (barriers) from the maximum credible tornado threat. However, SRP Section 3.5.1.4 includes acceptance criteria permitting relaxation of the above deterministic guidance, if it can be demonstrated that the probability of damage to unprotected essential safety-related features is sufficiently small."

As permitted by these SRP sections, the combined probability will be maintained below an allowable level, i.e., an acceptance criterion threshold , which reflects an extremely low probability of occurrence. SRP Section 2.2.3, "Evaluation of Potential Accidents,"

established this threshold as approximately 1.0E-06 per year if, "when combined with reasonable qualitative arguments, the realistic probability can be shown to be lower." The Braidwood Station analysis approach assumes that if the sum of the individual probabilities calculated for tornado missiles striking and damaging portions of safety-significant SSCs is greater than or equal to 1.0E-06 per year per unit, then installation of tornado missile protection barriers would be required for certain components to lower the total cumulative damage probability below the acceptance criterion of 1.0E-06 per year per unit. Conversely, if the total cumulative damage probability remains below the acceptance criterion of 1.0E-06 per year per unit, no additional tornado missile protection barriers would be required for any of the unprotected safety-significant components.

With respect to the probability of occurrence or the consequences of an accident previously evaluated in the UFSAR, the possibility of a tornado impacting the Braidwood Station site and causing damage to plant SSCs is a licensing basis event currently addressed in the UFSAR. The change being proposed (i.e., the use of the TORM IS methodology for assessing tornado-generated missile protection of unprotected plant SSCs), does not affect the probability of a tornado strike on the site; however, from a licensing basis perspective, the proposed change does affect the probability that missiles generated by a tornado will strike and damage certain safety-significant plant SSCs. There are a defined number of safety-significant components that could theoretically be struck and damaged by tornado-generated missiles. The probability of tornado-generated missile hits on these "important" systems and components is calculated using the TORMIS probabilistic methodology. The 29 of 33

ATTACHMENT 1 Evaluation of Proposed Changes combined probability of damage for unprotected safety-significant equipment will be maintained below the acceptance criterion of 1.0E-06 per year per unit to ensure adequate equipment remains available to safely shutdown the reactors, and maintain overall plant safety, should a tornado strike occur. Consequently , the proposed change does not constitute a significant increase in the probability of occurrence or the consequences of an accident based on the extremely low probability of damage caused by tornado-generated missiles and the commensurate extremely low probability of a radiological release.

Finally, the use of the TORMIS methodology will have no impact on accident initiators or precursors; does not alter the accident analysis assumptions or the manner in which the plant is operated or maintained; and does not affect the probability of operator error.

Based on the above discussion , the proposed change does not involve a significant increase in the probability or consequences of an accident previously evaluated .

2. Does the proposed change create the possibility of a new or different kind of accident from any accident previously evaluated?

Response: No.

The impact of a tornado strike on the Braidwood Station site is a licensing basis event that is explicitly addressed in the UFSAR. The proposed change simply involves recognition of the acceptability of using an analysis tool (i.e., the TORMIS methodology) to perform probabilistic tornado missile damage calculations in accordance with approved regulatory guidance. The proposed change does not result in the creation of any new accident precursors; does not result in changes to any existing accident scenarios; and does not introduce any operational changes or mechanisms that would create the possibility of a new or different kind of accident.

Therefore , the proposed change will not create the possibility of a new or different kind of accident than those previously evaluated .

3. Does the proposed change involve a significant reduction in a margin of safety?

Response: No.

The existing Braidwood Station licensing basis regarding tornado missile protection of safety-significant SSCs assumes that missile protection barriers are provided for safety-significant SSCs; or the unprotected component is assumed to be unavailable post-tornado.

The results of the Braidwood Station TORM IS analysis have demonstrated that there is an extremely low probability, below an established regulatory acceptance limit, that these "important" SSCs could be struck and subsequently damaged by tornado-generated missiles. The change in licensing basis from protecting safety-significant SSCs from tornado missiles, to demonstrating that there is an extremely low probability that safety-significant SSCs will be struck and damaged by tornado-generated missiles, does not constitute a significant decrease in the margin of safety.

Therefore, the proposed change to use the TORMIS methodology does not involve a significant reduction in the margin of safety.

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ATTACHMENT 1 Evaluation of Proposed Changes Based on the above, EGC concludes that the proposed amendment does not involve a significant hazards consideration under the standards set forth in 10 CFR 50 .92 , and accordingly, a finding of "no significant hazards consideration" is justified.

4.4 Conclusions The TORM IS methodology was developed to estimate the probability of tornado missile impact and damage to nuclear power plant structures and components. The TORMIS methodology has been reviewed and accepted for nuclear power plant tornado missile risk analyses, as discussed in the NRC TORM IS SER (Reference 1). The NRC SER concluded that the methodology " ... can be utilized when assessing the need for positive tornado missile protection for specific safety-related plant features." Each of the five points in the NRC's SER has been addressed in this evaluation ; i.e., (1) conservative site-specific tornado characteristics, (2) use of EF-Scale wind speeds per updated Regulatory Guide 1.76 (that are based on NUREG/CR-4461 , Revision 2) , (3) use of enhanced near ground tornado wind speeds, (4) conservative characterization of plant site-specific missiles; and (5) justified deviations from the calculational approach .

The conservatisms utilized in the TORM IS analysis provides high confidence that the Braidwood Station mean damage frequency values for each unit are conservatively high and "the risk can be expected to be lower," consistent with the acceptance criteria stated in SRP Section 2.2.3.

In conclusion , based on the considerations discussed above, (1) there is reasonable assurance that the health and safety of the public will not be endangered by operation in the proposed manner, (2) such activities will be conducted in compliance with the site licensing basis and Commission's regulations , and (3) the issuance of the amendment will not be inimical to the common defense and security or to the health and safety of the public.

5.0 ENVIRONMENTAL CONSIDERATION

EGC has evaluated this proposed operating license amendment consistent with the criteria for identification of licensing and regulatory actions requiring environmental assessment in accordance with 10 CFR 51 .21 , "Criteria for and identification of licensing and regulatory actions requiring environmental assessments." EGC has determined that these proposed changes to utilize the TORMIS Computer Code as the methodology used for assessing tornado-generated missile protection of plant structures, systems and components (SSCs), meet the criteria for a categorical exclusion set forth in paragraph (c)(9) of 10 CFR 51.22, "Criterion for categorical exclusion ; identification of licensing and regulatory actions eligible for categorical exclusion or otherwise not requiring environmental review," and as such , has determined that no irreversible consequences exist in accordance with paragraph (b) of 10 CFR 50.92, "Issuance of amendment." This determination is based on the fact that these changes are being proposed as an amendment to the license issued pursuant to 10 CFR 50, "Domestic Licensing of Production and Utilization Facilities," which changes a requirement with respect to installation or use of a facility component located within the restricted area, as defined in 10 CFR 20, 31 of 33

ATTACHMENT 1 Evaluation of Proposed Changes "Standards for Protection Against Radiation ," or which changes an inspection or a surveillance requirement, and the amendment meets the following specific criteria :

(i) The amendment involves no significant hazards consideration .

As demonstrated in Section 4.3, "No Significant Hazards Consideration ," the proposed change does not involve any significant hazards consideration.

(ii) There is no significant change in the types or significant increase in the amounts of any effluent that may be released offsite.

The proposed change does not result in an increase in power level, does not increase the production nor alter the flow path or method of disposal of radioactive waste or byproducts. It is expected that all plant equipment would operate as designed in the event of an accident to minimize the potential for any leakage of radioactive effluents.

The proposed changes will have no impact on the amounts of radiological effluents released offsite during normal at-power operations or during the accident scenarios.

Based on the above evaluation , the proposed change will not result in a significant change in the types or significant increase in the amounts of any effluent released offsite.

(iii) There is no significant increase in individual or cumulative occupational radiation exposure.

There is no change in individual or cumulative occupational radiation exposure due to the proposed change. Specifically, the change to utilize the TORMIS Computer Code as the methodology used for assessing tornado-generated missile protection of plant SSCs has no impact on any radiation monitoring system setpoints. The proposed action will not change the level of controls or methodology used for processing of radioactive effluents or handling of solid radioactive waste, nor will the proposed action result in any change in the normal radiation levels within the plant.

Therefore, in accordance with 10 CFR 51.22, paragraph (b), no environmental impact statement or environmental assessment need be prepared regarding the proposed amendment.

6.0 REFERENCES

1. NRC Safety Evaluation Report, "Electric Power Research Institute (EPRI) Topical Reports Concerning Tornado Missile Probabilistic Risk Assessment (PRA) Methodology,"

dated October 26, 1983 (ML080870291)

2. NRC Regulatory Issue Summary 2008-14, "Use of TORMIS Computer Code for Assessment of Tornado Missile Protection," dated June 16, 2008 (ML080230578)

3. Electric Power Research Institute Report- EPRI NP-768, "Tornado Missile Risk Analysis," May 1978 32 of 33

ATTACHMENT 1 Evaluation of Proposed Changes

4. Electric Power Research Institute Report - EPRI NP-769, "Tornado Missile Risk Analysis - Appendices," May 1978

5. Electric Power Research Institute Report - EPRI NP-2005 Volumes, I and 2, 'Tornado Missile Risk Evaluation Methodology," August 1981

6. NUREG/CR-4461 , Revision 2, "Tornado Climatology of the Contiguous United States, (PNNL-15112, Rev 2)," Ramsdell and Rishel , 2007

7. FEMA (2007), "Multi-hazard Loss Estimation - Hurricane Model, HAZUS MH MR3 Technical Manual"

8. NRC Memorandum from Harold R. Denton to Victor Stello, "Position of Use of Probabilistic Risk Assessment in Tornado Licensing Actions," dated November 7, 1983 (ML080870287)

9. Enforcement Guidance Memorandum 15-002 , "Enforcement Discretion for Tornado-Generated Missile Protection Noncomplicance," Revision 1, dated February 7, 2017

10. DSS-ISG-2016-01 , "Clarification of Licensee Actions in Receipt of Enforcement Discretion Per Enforcement Guidance Memorandum EGM 15-002, 'Enforcement Discretion for Tornado-Generated Missile Protection Noncomplicance,"' Revision 1, dated November 2017 11 . Letter from T. J. Wengert (NRC) to J. H. Plona (DTE Electric Company) , "Fermi 2 -

Issuance of Amendment Re: Revise the Fermi 2 Licensing Basis Concerning Protection from Tornado-Generated Missiles," dated March 10, 2014

12. Letter from J. F. Stang (NRC) to R. P. Powers (Indiana Michigan Power Company) ,

"Donald C. Cook Nuclear Plant, Units 1 and 2 - Issuance of Amendments," dated November 17, 2000

13. Letter from D. M. Gullett (EGC) to NRC, "License Amendment Request to Utilize the TORMIS Computer Code Methodology, " dated October 7, 2016

14. Letter from D. M. Gullett (EGC) to NRC, "Response to Request for Additional Information Regarding the License Amendment Request to Utilize the TORMIS Computer Code Methodology," dated March 20, 2017

15. Letter from J. S. Wiebe (NRC) to B. C. Hansen (EGC) , "Byron Station , Unit Nos. 1 and 2 -

Issuance of Amendments Regarding Use of TORM IS for Assessing Tornado Missile Protection ," dated August 10, 2017 33 of 33

ATTACHMENT 1A

SUMMARY

OF REGULATORY COMMITMENTS The following table identifies commitments made in this document. (Any other actions discussed in the submittal represent intended or planned actions. They are described to the NRC for the NRC's information and are not regulatory commitments.)

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

Tornado missile protection will be Prior to Yes No installed on the Unit 1 and Unit 2 implementing RWST hatches. the TORMIS methodology after NRC approval.

ATTACHMENT 1-1 TORMIS Results Tables 1-4 BRAIDWOOD STATION UNITS 1 AND 2 Docket Nos. 50-454 and 50-455 Renewed Facility Operating License Nos. NPF-37 and NPF-66

Table 1 TORMIS Results by Individual TORMIS Target Group Target Target Gro up Description Fallun, Mode Crimping Type Mlulle Hit Damage Number Number I RWST Hatch Unit 2 V > Vdam NIA 7.05E-07 7.05E-07 I RWST Hatches 2 R WST Hatch Unit I V > Vdam NIA 6.68E-07 6.68E-07 3 MSSV-SE-1-1-p Pipe Penetratioo NIA 5.04E-07 5.35E-10 4 MSSV-SE-1-2-p Pipe Penetr-atioo NIA 5. 18E-07 6.99E-IO 2 U2 MSSV Grcx1p I (SE) 5 MSSV-SE-1-3-o Pioe Penetration NIA 4.95E--07 5.22E-IO 6 MSSV-SE-1-4-o Pipe Penetratioo NIA 5.19E-07 l.62E-09 7 MSSV-SE-1-5-p Pipe Penetratioo NIA 4.90E-07 7.99E-10 8 MSSV-SE-2-1-p Pipe Penetration NIA 4.69E--07 5.13E-10 9 MSSV-SE-2-2-o Pioe Penetratioo NIA 4.95E--07 J.62E-10 3 U2 MSSV Grt<,p 2 (SE) 10 MSSV-SE-2-J-p Pipe Penetration NIA 4.45E--07 J .69E-10 II MSSV-SE-2-4-p Pipe Penetration NIA 5.02E--07 4.57E-IO 12 MSSV-SE-2-5-p Pipe Penetration NIA 4.6JE--07 l.36E--09 13 MSSV-SW-1-1-o Pine Penetration NI A 4.12E--07 l.08E-09 14 MSSV-SW-1-2-o Pipe Penetration NIA 4.28E--07 1.J?E-09 4 U2 MSSV Group 1 (SW) 15 MSSV-SW-1-J-p Pipe Penetration NIA 4.09E--07 I.IJE-09 16 MSSV-SW-1-4-p Pipe Penetration NIA 4.74E-07 6.41E-10 17 MSSV-SW-1-5-p Pipe Penetration NIA 4.29E-07 8.22E-10 18 MSSV-SW-2-1 -p Pipe Penetratioo NIA l.6JE-07 3.4JE-10 19 MSSV-SW-2-2-o Pioe Penetration NIA l.36E-07 2.97E-10 5 U2 MSSV Group 2 (SW) 20 MSSV-SW-2-3-o Pipe Penetration NIA l.90E-07 2.0lE-10 21 MSSV-SW-2-4-p Pipe Penetratioo NIA l.59E--07 5.69E-10 22 MSSV-SW-2-5-p Pipe Penetratioo NIA 2.4JE--07 9.40E-IO 23 MSSV-NW-1-1-o Pipe Penetra lion NIA 8.65E--08 2.22E-10 24 MSSV-NW-1-2-o Pipe Penetration NIA 7.20E--08 7.02E-10 6 UI MSSV Groop 1 (NW) 25 MSSV-NW-1-3-p Pipe Penetration NIA 8.0JE--08 1.97E-10 26 MSSV-NW-1-4-p Pipe Penetration NIA 7.00E--08 1.0JE-10 27 MSSV-NW-1-5-o Pioe Penetration NIA 7.90E-08 2.59E-10 28 MSSV-NW-2-1-o Pipe Penetratioo NIA 2.55E--07 3.48E-10 29 MSSV-NW-2-2-p Pipe Penetratioo NIA 2.79E--07 4.00E-10 7 U I MSSV Groop 2 (NW) JO MSSV-NW-2-3-p Pipe Penetration NIA 2. 78E--07 4.JOE-10 JI MSSV-NW-2-4-p Pioc Penetration NIA 3.14E--07 3.81E-10 32 MSSV-NW-2-5-p Pipe Penetration NIA 2.97E--07 4.43E-10 33 MSSV-NE-1-1-p Pipe Penetratioo NIA 2.50E--07 7.90E-10 34 MSSV-NE-1-2-p Pipe Penetration NIA 2.99E-07 1.66E-09 8 Ul MSSV Groop 1 (NE) 35 MSSV-NE-1-3-o Pioe Penetration NIA 2.99E-07 9.16E-10 36 MSSV-NE-1-4-p Pipe Penetration NIA J.45E--07 8.39E- IO 37 MSSV-NE-1-5-p Pipe Penetration NIA 3.79E--07 2. lOE-09 38 MSSV-NE-2-1-p Pipe Penetratioo NIA 2.74E--07 I.OIE-09 39 MSSV-NE-2-2-o Pioc Penetratia:1 NIA 2.89E--07 3.49E-10 9 U I MSSV Groop 2 (NE) 40 MSSV-NE-1-J-p Pioe Penetration NIA J.08E--07 1.14E-09 41 MSSV-NE-1-4-p Pipe Penetration NIA 3.57E--07 1.16E-09 42 MSSV-NE-1-5-p Pipe Penetratioo NIA J.89E--07 2.61E-09 10 U2 PORV SE I 43 PORV-SE-1-c V > Vdam PORV 2.05E--06 2.JOE-09 II U2 PORV SE 2 44 PORV-SE-2-c V > Vdam PORV l.20E-06 4.62E-10 12 U2PORVSW I 45 PORV-SW- 1-c V > Vdam PORV 9.04E--07 8.14E-ll 13 U2PORV SW2 46 PORV-SW-2-c V > Vdarn PORV 4. 15E--07 4.69E-II 14 U l PORVNW I 47 PORV-NW-1-c V > Vdam PORV l.1 9E--07 O.OOE-<00 15 UI PORVNW2 48 PORV-NW-2-c V > Vdam PORV 2.6JE-07 O.OOE-<00 16 UI PORVNE I 49 PORV-NE-1-c V > Vdam PORV l.56E--06 J.80E- IO 17 UI PORVNE2 50 PORV-NE-2-c V > Vdam PORV 4.85E--07 2.94E-10 10 U2PORVSE I 51 PORV-SE-1-p Pipe Penetration NIA 4.05E--07 6.02E-10 II U2 PORVSE2 52 PORV-SE-2-p Pipe Penetration NIA 3.89E--07 l.20E-09 12 U2PORVSW I 53 PORV-SW-1-p Pipe Penetratioo NIA 4.65E--07 4.59E-10 13 U2PORVSW2 54 PORV-SW-2-p Pipe Penetration NIA 2.90E--07 5.20E-10 14 UI PORVNW I 55 PORV-NW-1-o Pioe Penetration NIA l.10E--07 4.42E-10 15 Ul PORVNW2 56 PORV-NW-2-P Pioe Penetration NIA 2.93E--07 3.29E-10 16 UI PORVNE I 57 PORV-NE- 1-p Pipe Penetration NIA 2.l!E--07 J .86E-IO 17 Ul PORVNE2 58 PORV-NE-2-o Pioe Penetration NIA 2. lJE--07 5.58E-10 59 Diesel Auxiarv Feed Pwno Exhaust U2 -- Lower nnrtm V > Vdam DAFP Pioe 7. llE-06 2.82E-08 18 DAFP U2 60 Diesel Auxiary Feed Pwnp Exhaust U2 -- Upper oortion V > Vdam DAFP Cover Plate 2.09E-06 J.OJE-07 61 Diesel Auxiarv Feed Pwno Exhaust U I -- Lower nno1ion V > Vdam DAFP Pioe 6.22E-06 2.39E-08 19 DAFP Ul 62 Diesel Auxiarv Feed Pumo Exhaust UI -- Uooer nnrtim V > Vdam DAFP Cover Plate 2.06E-06 299E-07 20 UJ Divisim 2 MEER 63 U I Division 2 MEER Opening Pioe Penetration NIA l.91E-06 J.34E-08 21 U I Divisioo I MEER 64 U I Division 1 MEER Opening Pipe Penetration NIA 6.91E-07 5.78E-09 24 UICRHVAC 65 U I Control Room HV AC Intake Opening Pipe Penetration NIA 6.98E-07 2.18E-10 25 U2CRHVAC 66 U2 Control Room HVAC Intake Ooenil12 Pioe Penetration NIA 6.19E-07 1.82E-10 22 U2 Division I MEER 67 U2 Divisioo I MEER Ooenil12 Pioe Penetration NIA 7. 15E-07 1.06E-08 23 U2 Divisioo 2 MEER 68 U2 Divisioo 2 MEER Opening Pipe Penetration NIA l.95E-06 6.58E-08 20 U I Division 2 MEER 69 Pipe West of U I Divisioo 2 MEER Opening Pelforation NIA l.79E-05 l.89E-08 21 Ul Divisioo 1 MEER 70 Pioe West ofUI Divisioo I MEER Ooenin2 Pelfora lion NIA l.39E-05 l.66E-08 22 U2 Divisioo I MEER 71 Pioe West of U2 Divisioo I MEER Openin2 Pelfora lion NIA l.4JE-05 l.54E-08 23 U2 Divisim 2 MEER n Pipe West of U2 Divisim 2 MEER Openiruz Pelforation NI A l.82E-05 2.60E-08 73 SX Discharee Pine-I V > Vdam NIA 6.46E-08 6.46E-08 26 SX Discharge Pipes 74 SX Discharge Pipe-2 V > Vdam NIA 4.6JE-08 4.6JE-08

Table 2 Average Hit and Damage Frequency (per year) for Target Groups Group Target Group Failure Logic Missile Hit Damage Number 1 R WST Hatches 1U2 l.37E-06 1.37E-06 2 U2 MSSV Group 1 (SE) 3U4U5U6U7 2.51E-06 4.18E-09 3 U2 MSSV Group 2 (SE) 8 U 9 U 10 U 11 U 12 2.35E-06 3.06E-09 4 U2 MSSV Group 1 (SW) 13 U 14 U 15 U 16 U 17 2.13E-06 5.05E-09 5 U2 MSSV Group 2 (SW) 18 U 19 U 20 U 21 U 22 8.86E-07 2.35E-09 6 Ul MSSV Group 1 (NW) 23 U 24 U 25 U 26 U 27 3.87E-07 1.48E-09 7 U I MSSV Group 2 (NW) 28 U 29 U 30 U 31 U 32 l.41E-06 2.00E-09 8 U 1 MSSV Group 1 (NE) 33 U 34 U 35 U 36 U 37 1.56E-06 6.30E-09 9 Ul MSSV Group 2 (NE) 38 U 39 U 40 U 41 U 42 l.61E-06 6.27E-09 10 U2PORV SE 1 43 U51 2.45E-06 2.90E-09 11 U2PORV SE2 44U52 l.59E-06 I.67E-09 12 U2PORVSW 1 45 U53 1.37E-06 5.40E-10 13 U2PORV SW2 46U54 7.05E-07 5.67E-10 14 Ul PORVNW l 47U55 2.28E-07 4.42E-10 15 Ul PORVNW2 48U56 5.55E-07 3.29E-10 16 Ul PORV NE 1 49U 57 l.76E-06 7.66E-10 17 Ul PORVNE2 50U58 6.96E-07 8.52E-10 18 DAFP U2 59U60 9.07£-06 3.31E-07 19 DAFP Ul 61 U 62 8.18E-06 3.23E-07 20 U 1 Division 2 MEER 63 U 69 1.97E-05 5.23E-08 21 Ul Division 1 MEER 64U70 1.46E-05 2.24E-08 22 U2 Division l MEER 67U71 l.50E-05 2.60E-08 23 U2 Division 2 MEER 68U72 2.00E-05 9.19E-08 24 Ul CRHVAC 65 6.98E-07 2.18E-10 25 U2CRHVAC 66 6.19E-07 1.82E-10 26 SX Discharge Pipes 73U74 1.IOE-07 1. lOE-07

Table 3 Mean Damage Frequency (per Year) for Braidwood Station Target Groups Source Table for Unit I Damage Unit 2 Damage Target Identified by BRW Corres ponding Target Groups Target Group Approach Damage Freque ncy Freaue ncv { vr- 1) Freaue ncv (vr-1)

Boolean Union ofover separate targets for ellhaust pipe and cover plate. Separate damage frequencies computed for each unit.

Diesel AuxFW Pump Emausts DAFP Table 2 3.23E-07 3.3 IE-07 Damage to DAFP ellhaust pipes and cover plates based on Finite Flernent Analysis specifically for BRW.

PORVI 4.42E-IO 2.90E-O')

Boolean Union of targets modeled for pipe crinl)ing and pipe PORV2 penetration pass through . Separate damage frequencies computed 3.29&10 1.67&0')

PORV Tailpipes Table 2 PORV3 for each PORVon each unit. Pipe crimping damage based on Finite 7.66E-IO 5.40E- 10 Flernent Analysis completed specifically for BRW .

PORV4 8.52E-IO 5.67E-IO MSSVI l.48E-O') 4.18E-O')

MSSV2 Boolean Union ofover 5 MSSVs on each respective Main Steam 2.00E..O') 3.06E-O')

MSSVTailpipes line. Separate damage frequencies computed for each set of 5 Table 2 MSSV3 MSSVs on each unit. 6.30E-O') 5.05E-O')

MSSV4 6.27E-O') 2.35E-O')

Missile hit probability on single target representing the RWST RWST Hatches RWSTHatch Table I 6.68E-07 7.05E-07 hatch for each unit.

MEER Div 2 Opening Boolean Union of missiles passing through equivalent pipe 5.23E-08 9.19E-08 MEER Openings MEER Div I Opening penetration and perforating the pipe blocking the opening Table 2 2.24E-08 2.60E-08 CR HVAC Intake Opening Missiles passing through equivalent pipe penetration 2. 18E- IO l.82E- 10 Boolean Union of missile hit probability on the two exposed SX SX Discharge Pipes SX Pipes Table 2 I. IOE-07 l.lOE-07 Discharge Pipes in the lake.

Arithmetic Sum over all Target Groups 1.19£-06 J.29£-06 Arthlmetlc Sum assuming prote ction of RWST Hatches 5.26£-07 5.80£-07

Table 4 Sequential Numbering of Safety-Significant, Shielding and Missile Source Targets (Page 1 of 4)

TOR.lIIS BR.W Tars*t Gniap TOR.MIS I ars*t Duniptioa iw..,. I.- 1_

Targ*t" I RWST Hate.hes RWSTHalc.h nit 2 I 2 RWST Hatch Uwt I 2 3 U2 MSSV Group 1 (SE) MSSV-SE-1-1-p 3 4 MSSV-SE-1-2-p 4 5 MSSV-SE-1-3-p 5 6 MSSV-SE-1-4-p ,6 7 MSSV-SE-1-5-p 7 s U2 MSSV Group 2 (SE) MSSV-SE-2-1-p s 9 MSSV-SE-2-2-p 9 10 :MSSV-SE-2-3-p 10 11 :MSSV-SE-2-4-p ll 12 MSSV-SE-2-5-p 12 13 U2 MSSV Graap I (SW) MSSV-SW-1-1-p 13 14 MSSV-SW-1-2-p 14 15 MSSV-SW-1-3-p 15 16 MSSV-SW-1-4-p 16 17 MSSV-SW-1-5-o 17 18 U2 1SSV Group 2 (SW) MSSV-SW-2-1-p 18 19 1SSV-SW-- P 19

~o . fSSV-SW-2-3-p _o 21 1SSV-SW---4-p 2l 22 MSSV-SW---5-p 22 23 U I MSSV Group I (NW) MSSV-~-1-1-p _3 24 l\.lSSV-NW-1-2-p 24 25 l\.lSSV-NW-1-3-p _5 26 MSSV-. W-l-4-p _6 17 MSSV-NW-1-5-p 27 28 U l MSSV Group 2 (NW) MSSV-NW-2-1-p 28 29 MSSV-~---2-p _9 30 MSSV-NW---3-p 30 31 MSSV-NW-2-4-p 31 32 l\.lSSV-NW-2-5-n 32 33 U I MSSV Group I (NE) MSSV-NE-1-1-p 33

}4 1SSV-NE-l-2-p }4 35 1SSV-NE-l-3-p 35 36 . 1SSV-NE-l-4-p 36 37 MSSV-NE-1-5-p 37 38 Ul MSSV Group 2 (NE) .MSSV-NE-2-1-p 38 39 1SSV-NE-2-2-p 39 40 1SSV-NE-1-3-p 40 41 1SSV-NE-l-4-p 41 42 MSSV-NE-1-5-11 42 43 U2PORV SE l PORV-SE-1-c 43 44 U2PORVSE2 POR.V-SE-2-c 44 45 U2PORV SW I PORV-SW-1-< 45 46 U1 PORV SW2 PORV-SW-2-< 46 4 U l PORV -:-lW l PORV-NW-1-< 47 48 UlPORVXVl2 PORV-NW-2..., 48 49 Ul PORVNE I PORV-~-\..., 49

Table 4 Sequential Numbering of Safety-Significant, Shielding and Missile Source Targets (Page 2 of 4)

TOlUIIS BRWTarc*t Croup TOR.All~ Targ*I Du ~riplioa I_,. I.- 1_

Tarc*t 11 50 Ul PORVNE 2 PORV-NE-2-c 50 51 U2 PORVSE l PORV-SE-1-p 51 52 U2 POR.V SE 2 PORV-SE-2-p 51 53 U2 PORVSW I PORV-SW-l -1> 53 54 U2 PORV SW2 PORV-SW-2-1> 54 55 U l POR.V"!'.'W I PORV-NW-1-p 55 56 Ul PORV"!lfW 2 PORV-NW-2-P 56 5 Ul PORVNE I PORV-NE- l-p 57 58 Ul PORVNE 2 PORV-NE-2-P 58 59 DAFPU2 Di...el Auxiary feed Pump EJ<bau,t U2 ** Lower ponioo 59 60 Diec.elAW<iaiy feed Pump Exhau:.t U2 - ~paman 60 61 DAFPU I Diesel Auxiary feed Pump &lna."1 Ul -* Lower pomon 61 61 Die::.elAmmnv feed Pmnn Exhaust U l -* Unn,,rnnmnn 62 63 Dii.* 12 ~fEER. Ul Dil.-i,;-,n 2 MEER Ope~ 63 64 Dr.- l! ~1EER. Ul Di1.-..1>D I MEER. Opening 64 65 MCR Makem, Air Intake Ul l: l Ccmrol Room HV AC Intake nn..n..,,. 65 66 MCR Makeup Air Intake U2 U2 Control Room HV AC Intake Openmg 66 67 Dr.*21 MEER. U2 Dil.-isim I MEER Opening 67 68 Dii.* 22 ~1EER. U2 Dil.-i,;im 2 MEER O....nin.. 68 69 Dr1.* l'.l MEER. Pme Wm ofU I Dil.-ision 2 MEER On.run.. 69 70 Dr.* ll MEER. Pipe We.,t of Ul Dr."ision I MIIBR. Openmg 70 l Dr.* 21 MEER Pipe West of U2 Dil.'ision l MEER OpeD.Eg 7l 72 D11*2'> MEER. Pme We.st of U2 Dn-'ision 2 ~ff.ER Q,...n;,,,. 72 3 Mi:is ile Slrieldm; Target Re~en'l!d 1 74 ken--ed 2 75 Re.:;en--ed 9 6 Resen--ed 10 n Re::.en--ed 11 s Main TB 12 9 Left Side Secmn 1B 13 so llight Ul RB 14 SI FHB 15 82 ~ Shared Section of RB 16 83 Lower 'lught Section RB nto Reactor 17 84 Upper Riglct Section RB mto Reactor 18 85 RjghtU2 RB 19 86

• 1 Reactor _o s 2 Reactor 21 88 UISEboxbwer n 89 UlSEbox~r 23 90 Ul SW box lim*er 24 91 U I SW box upper 25 92 U2 NE box lower 26 93 U2 NE box upper 2 94 2NW boxbwer 28 95 2 NW box upper .9 96 R\VST 1 30 97 RWST 2 31 98 U! A= FW Shield South 32 99 Ul A= FW Shield West 33 100 U I A= FW Slue.Id North 34 101 U2 Aux FW Shu! South 35 102 U2 Aux FW Slrioold West 36 103 U2 A= FW Sha.Id North 3 104 Ul MSHe.1>2 38

Table 4 Sequential Numbering of Safety-Significant, Shielding and Missile Source Targets (Page 3 of 4)

TOR?tlli, T11rget "

BRW Target Croup TORAHS Targ*t Ducriprioa i..,.., i.. .... 1-...

105 l\fus.ile Shiekling Target, co11rinusd l MSHelb 3 39 106 - MSHelb5 40 10 U2 MSHelb6 41 108 Under Helb 2-3 42 109 Betwe4'nHelb 43 110 Uoder Helb 5-6 44 l1l Missi!e So\lK'e Targets Gat1>House l 112 Gate House 2 2 113 Senxe B'llilding Add l 3 114 Senxe Bmlding Add 2 4 ll5 Ful.-u,bima Iniler 5 11 6 CA fac,Ry Unit_ 6 117  !EMA Building 7 118 CA f acilfy Unit l 8 119 Old Building 9 120 Sec~- 10 121 Gas Ster.age Area 11 122 Waste Treatment Buacling 12 U3 Stora g,> Sbed-9 13 124 Warehouse- IO 14 125 Recie.-ing Bm"ldng 15 126 ~onlaminatiao f acilry 16 12 Supply W,TI!.bou,e I 17 118 Supply Wuebame 2 18 129 Supp _ Wuebou,;e 3 19 130 ~ . Ian 20 131 Emebo.A 21 13_ E.xceJon B 22 133 E.....,..bnC 23 B4 Office-15 24 135 Offi::e-16-1 25 136 Offi::e-16-2 26 13 Offi:e-16-3 27 138 Warehouse-16 2S 139 Warehouse-Attachment 29 140 Shed-17 30 141 Warebouse-485 31 142 Iron Fab Shop 32 143 Garage 33 144 Central Warehouse 34 145 Waruiou:.e 18-1 35 146 Wa:rehome 8-2 36 14 Shep-To Be &,ma,.-ed 37 148 Access 38 149 New Training Fae 39 150 TrainmgShop 40 151 Fir for Duty 41 152 Seem-it)*Scree:nmg 42 153 Ful.,isbima Buildin,g 43 154 Trailer-24 44 155 SaltSbed 45 156 ISfSI Stcrage 46 15 Buikling-25 47 158 Swhl Yard Ho,x;e 1 48 159 Swtch Ya.rd Ho,x;e 2 49 160 Ched-point 50 161 North Hc,u:;e,;-30 51 162 Mid Houses-30 52 163 South Houses-JO 53

Table 4 Sequential Numbering of Safety-Significant, Shielding and Missile Source Targets (Page 4 of 4)

TOlllJS Tars**"

164 165 166 BRW Target Groap Missile Some* Targets C'o11ti11ud TODf~ Targ*t Duuiptioa H=e~-31 S.icgle Hous*-31

• 01th Houses-32 i.~.,.

• - 1_

54 55 56 167 East Houses-32 5 168 We.st Houses-32 58 169 Hou::u-33 59 170 Y op Buildng 60 171 Park Sheds 61 172 Public Water 62 173 BBa Building 63 174 Q.ibhou:;, 64 175 Trailler-33 65 l 6 House-33 66 17 Screening House o/

178 U2 Operating Floor 68 l 9 Ul Operating Floor 69 180 TSC Roof 70 181 Operating Buildmg 71 182 U2 Bwldng Operatmg Floor 72 183 Radw-ast,, 73 184 Outage-3 74 185 Outage Tra r,;-4 75 186 Oura go Trailer-17 76 187 East Wall TB l 77 188 We.stWa TB 78 189 North Wall TB 9 190 South VJ all TB so 191 Ul RB Cbd.ch,g 81 192 UJ RB Cbd.ch,g 82 193 Sen'icoB~ S3 194 TB Roof 84 195 Hou:;e,-28 85 196 Train Car Sbed 86 19 fukushmia -3 g 198 Oubge Tr~i,,-2 88 199 Outage Trailu-22 S9 200 EutWa TB 2 90 201 EastWa TB 3 91 202 Contractor.. Facility 92 203 Huter Bay Roof 93 204 SouthWestTB 94 205 ISFSI Warehou::e 95

ATTACHMENT 1-2 TORMIS Results Figures 1-8 BRAIDWOOD STATION UNITS 1 ANO 2 Docket Nos. 50-454 and 50-455 Renewed Facility Operating License Nos. NPF-37 and NPF-66

Figure 1 Individual Target Hit and Damage Frequencies BRW Tar Hir and Damag Fr qu nd s 1 L

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Figure 2 Target Group Hit and Damage Frequencies Tar et Group a1nd D,a mage IFrequencie*s

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Figure 3 Tornado Rotational Wind Velocity Profiles (Figure ll-12(b) from NP-2005 Volume 2)

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Figure 4 Plot of Frequencies with Profile 5 versus Profile 3

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i. -09 I I I II 1111 ~ 111111 I I I I 111 I 111 L I

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Figure 5 Zone Layout for Braidwood Station Main Site Model TORMIS Analysis

Figure 6 Zone Layout for Braidwood Station SX Model TORMIS Analysis

Figure 7 TORMIS Simulation of Braidwood Station Tornado Hazard for Plant Safety Envelope

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• Figure 8 Target Group Hit and Damage Frequency with Confidence Intervals arget Group Gcmfidence Intervals for Missile H1it 1

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Figure 9 Convergence Plot for Damage Frequency for Target Group 8 (U1 MSSV Group 1 NE)

Hit ,con,v ergenoe over All 1 RepHcati o n s

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ATTACHMENT 1-3 Draft Markup of Updated Final Safety Analysis Report Pages BRAIDWOOD STATION UNITS 1 AND 2 Docket Nos. 50-454 and 50-455 Renewed Facility Operating License Nos. NPF-37 and NPF-66 REVISED UFSAR PAGES 3.3-1 3.3-2 3.3-3 (no changes; included for continuity) 3.3-4 3.3-5 3.5-11 3.5-21 (no changes; included for continuity) 3.5-21a 3.5-25 3.5-25a (no changes; included for continuity) 3.5-26 3.5-26a-d 3.5-27 (no changes; included for continuity) 3.5-28 3.5-48 3.5-49 (no changes; included for continuity) 3.5-50

8/8-UFSAR 3.3 WIND AND TORNADO LOADINGS 3 . 3.1 Wind Loadings 3.3.1.1 Design Wind Velocity A design wind velocity of 85 mph , based upon a 100-year mean recurrence interval , is used in the design of Seismic Category I structures .

For Category II structures a design wind velocity of 75 mph is used , based upon a 50-year mean recurre n ce interval.

The vertical velocity distribution and gust factors employed for the wind velocities are based on Table 5 of Reference 1 for exposure Type C.

3.3.1.2 Determination of Applied Forces The dynamic wind pressures are converted to an equivalent static force by considering appropriate pressure coefficients . The applied forces were derived in accordance with the provisions of Table 7 , Refere n ce 1 , using external pressure coefficients , Cp of 0 . 8 and -0 . 5 for windward and leeward walls respectively , and

-0 .7 for side walls and roofs .

For structural shapes other than rectangular appropriate pressure coefficients are used in accordance with Reference 2 .

3.3.2 Tornado Loadings 3.3 . 2 . 1 Applicable Design Parameters The following are the parameters for the design-basis tornado (Reference 3) :

Tangential velocity : 290 mph Translational velocity : 70 mph Radius of maximum rotational velocity from center of tornado : 150 feet Pressure drop at the center of vortex : 3 psi Rate of pressure drop: 2 psi/sec .

The characteristics and spectrum of design-basis tornado-generated missiles are found in Subsec tion 3 . 5 . 1.4 .

The tornado parameters used in the probabilistic tornado missile risk analysis (TORMIS) described in ,S ect_ion 3.5 . 5 are found in -I [ Deleted: By r o n o nl y Refere n ce s 5 and 6 .

3 . 3-1 REVISION 17 - DECEMBER 2018

B/B-UFSAR Load Factor Since the postulated tornado loading is an extreme environmental condition with a very low probability of occurrence , a load factor of 1 . 0 is used .

3.3 . 2 . 2 Determination of Forces on Structures The Category I stru ctures which have wi nd tornado loads , design-basis tornado generated missiles , and/or combination of these loads addressed in their design are as follows :

a. containment building ,

b. auxiliary building ,

c. fuel handling building ,

d. main steam tunnel ,

e. auxiliary feedwater tunnel ,

f . essential service water cooling tower (Byron) ,

g. essential cooling pond (Braidwood) ,

h. deep well enclosures (Byron) ,

i . lake screen house substructure (Braidwood) ,

j . isolation valve room , and

k. essential service water discharge (Braidwood) .

Several individual essential service water cooling tower components (Byron) , and the essential service water discharge pipes (Braidwood) not fully protected from tornado generated missiles are addressed in the probabilistic tornado missile risk analysis (TORMIS) described in ~ e~ti_9n 3 . 5 . 5 . { Deleted: Byron only 3.3.2.2.1 Tra n sformation of Tornado Winds Into Effective Pressure All tornado wind pressure and differential pressure effects are considered as static loads since the natural period of building structures and their exposed structural elements is very short compared to the rate of variation of the applied loads .

The effects of the design-basis tornado are translated into forces on structures with the use of a tornado model (Reference

4) that incorporates parameters defined in Subsection 3 . 3 . 2 . 1 .

3.3-2 REVISION 17 - DECEMBER 2018

8/8-UFSAR The tornado model considers a velocity distribution based on the following equations:

v ( r) = Ve _E_ + Vt , for _E_ ~ 1 (3 . 3-1)

Re Re v(r) = Ve Re + Vu for _E_ ~ 1 (3 . 3-2) r Re where :

v(r) = wind velocity at radius r ,

r = distance from the center of the tornado, Ve = maximum tangential velocity ,

Re distance from the center of the tornado , to the locus of the maximum wind velocity , and Vt translational velocity .

The distribution of the pressure drop with the radius from the tornado is as follo ws :

p (r l = 3 . 0 [1 - 0 . 5 (r / RJL for _E_ < 1 (3 . 3-3)

Re p(r ) = 1.5 (Re /r)2 , for _E_ ~ 1 (3 . 3-4)

Re where :

p(r) = pressure drop in psi .

The tornado velocity is converted into an equivalent static press u re using equations given in ANSI A58 . l-1972 (Reference 1) .

Neither a " gust factor " nor any change in velocity with height is considered . Figure 3.3-1 shows the variation in wind velocity and differential pressure as per Equations 3 . 3-1, 3 . 3-2 , 3 . 3-3 , and 3 . 3-4 . Figure 3 . 3-2 shows the windward and leeward wind pressure components of the tornado .

3 . 3-3 REVISION 17 - DECEMBER 2018

B/B-UFSAR The load combination equation used for tornado load and tornado generated missiles is Wt= 448 psf + Wm . Figure 3 . 3-3 shows the resulting surface pressure when the effect of tornado wind and pressure drop components are added together.

The load combination equations as per SRP Section 3 . 3 . 2 using load parameters of UFSAR Section 3 . 3 are as follows :

1. Wt Ww i . e ., Wt 265 psf

2. Wt Wp i . e ., Wt 432 psf

3. Wt Wp Wm

4. Wt Ww + . 5 Wp i . e . f Wt= 340 . 1 psf

5. Wt Ww + Wm i .e . f Wt = 265 psf + Wm

6. Wt Ww + . 5 Wp + Wm i .e . f Wt= 340 . 1 psf + Wm.

The equation (Wt = 448 psf + Wm) used in design is more conservative than the SRP equations above .

3.3 . 2 . 2 . 2 Venting of the Structure Venting of concrete structures is not relied upon to reduce the differential pressure loadings . However , all siding and roof decking of the Turbine Building above the floor at elevation 451 feet O inch is designed and detailed to blow off at tornado pressures exceeding 105 psf . Above this pressure only bare framework is considered to be exposed to design-basis tornado loads .

3 . 3 . 2 . 2.3 Tornado Generated Missiles The characteristics and spectrum of tornado generated missiles for the design-basis tornado are found in Subsection 3 . 5 . 1 . 4 .

The characteristics and spectrum of tornado generated missiles considered in the probabilistic tornado missile risk analysis (TORMIS) described in pection 3 . 5 . 5 are found in Reference s 5 and l 6 . The procedures used for desfgrilng - for the Impactive dynamlc -

i Deleted: Byron only effects of a point load resulting from tornado generated missiles are found in Subsection 3 . 5 . 3.

3 . 3.2 . 2 . 4 Tornado Loading Combinations Refer to Tables 3.8-3 through 3 . 8-9 for the load factors and load combinations associated with tornado loading . In designing for the postulated design-basis tornado , the structure in consideration is placed in various locations of the pressure field to determine the maximum critical effects of shear ,

overturning moment , and torsional moment on the structure.

3 . 3-4 REVISION 17 - DECEMBER 2018

B/B-UFSAR 3.3.2.3 Effect of Failure of Structures or Components Not Designed for Tornado Loadings All non-safety- related structures which are connected to safety-related structures are designed to prevent collapse under the design tornado loading. The only exceptions are the fuel handling building train shed , the Essential Service Water Cooling Tower Security Booth Tower Walkway (applicable to Byron only) and Walkway Access Stair Tower (applicable to Byron only) and the equipment staging structures installed adjacent to the emergency hatches . The collapse of these structures under tornado loading does not affect the structural integrity of any safety-related structures.

All other non - safety-related structures are separated from safety-related structures by a distance exceeding the height of the non-safety-related structure . This ensures that the failure of non-safety-related structures will not affect safety-related structures . Missiles generated by the collapse of non-safety-related structures were evaluated to be less critical than those considered in Subsection 3.5 . 1 . 4 or were evaluated in ~ ecti~n [ Deleted: Byr on on l y 3.5.5.

3.3.3 References

1. ANSI ASS . 1-1972 , "Building Code Requirements for Minimum Design Loads in Buildings and Other Structures, " American National Standards Institute , Inc ., New York , New York , 1972.

2. "Task Committee on Wind Forces , Committee on Loads and Stresses , Wind Forces on Structures, Final Report ," Paper No .

3269 , Transactions , ASCE, Vol . 26 . rg 1961.

3 . USNR Regulatory Guide 1 . 76 , " Design Basis Tornado for Nuclear Power Plant , " April 1974 .

4. J . D. Stevenson , "Tornado Design of Class I Structures for Nuclear Power Plants ," Proceedings of Symposium on Structural Design of Nuclear Power Plant Facilities , University of Pittsburgh , December 197 2 .

5 . Design Analysis ARA-002116002116, "Tornado Missile TORMIS Analysis of [Byron Generating Station] BGS , " Revision 3 .

6 . Design Analysis ARA-002431002431, "Tornado Missile TORMIS Analysis of [Braidwood Generating Station) BRW ," Revision 0 .

3 . 3 -5 REVISION 17 - DECEMBER 2018

B/B-UFSAR the piping pressure element assemblies are less severe than those of Table 3.5-2b .

The missile characteristics of the reactor coolant pump temperature sensor, the instrumentation well of the pressurizer ,

and the pressurizer heaters are given in Table 3.5-2c. A 10 degree expansion half angle water jet has been assumed .

3.5 . 1.3 Turbine Missiles The turbine-generators at the Byron/Braidwood Stations are manufactured by the Westinghouse Electric Corporation . Each unit consists of four double-flow turbine cylinders : one high pressure , and three low pressure . The low pressure stages employ 40-inch last row blades . The rated speed of the turbine-generator is 1800 rpm .

The current approach to evaluating turbine missile protection focuses on the probability of turbine failure resulting in the ejection of turbine disc (or internal structure) fragments through the turbine casing (P1). A risk assessment will be performed each refueling outage to ensure that the probability of a turbine missile, P1, remains at an acceptably low value . Based on this low probability, the turbine missile hazard is not considered a design - basis event for these stations . The details of the approach to ensure turbine missile protection are provided in Section 10 . 2 . 3 .

For details o n turbine overspeed protection , valve testing , and turbine characteristics , refer to Subsection 10 . 2 .2.

3.5 . 1 . 4 Missiles Generated By Natural Phenomena Tornadoes are the only natural phenomenon occ urring in the vicinity of the Byron/Braidwood Stations that can generate missiles . The characteristics of postulated design-basis tornado-generated missiles are given in Table 3 . 5- 3 . The impact velocities of these missiles resulting from the design-basis tornado (Subsection 3 . 3 . 2) are shown in Table 3 . 5-4 . Missiles A, B, C, D, and E are considered at all elevations , and missiles F and Gare postulated at elevations up to 30 feet above grade level . These missiles are assumed to be capable of striking in all directions .

The characteristics of tornado-generated missiles considered in the probabilistic tornado missile risk analysis (TORMIS) described ~ ection 3 . 5 . 5 are found in Reference s 15 and 22 . { Deleted : i n By ro n only 3 . 5-11 REVISION 17 - DECEMBER 2018

B/B- UFSAR 3.5.2 Systems to be Protected All systems and equipment which may require protection are listed in Table 3 . 2-1 . Onsite storage locations for compressed gases are provided in Table 3 . 5-10 . Table 15.1-2 must be evaluated for protection against missiles postulated in Section 3 . 5 .

The following safety-related components are located outdoors ,

away from the main building complex , installed above grade and have missile protection to the extent indicated :

Byron Station

a. At the river screen house , the essential service water makeup pumps , and associated diesel-engine drives and fuel oil storage tanks are installed at elevation 702 feet O inch . The building does not protect the components from tornado missiles . Refer to Subsection 9 . 2 . 5 . 2 and Drawing M-20 .

b. The mechanical draft fans and their respective electric motor drives are located at the essential service water cooling towers (SXCTs) (refer to Drawings NCT-683-4H and -14H) . The fans and motors are not fully protected from missiles and are evaluated in Section 3 . 5 . 5 . A combination of TORMIS analysis and tornado protection was used for the piping within the SXCTs .

c. The outside air intake openings for the SXCT ESF Switchgear rooms are not protected from a tornado missile and are evaluated in Section 3 . 5.5 .

d. The onsite wells and pumps at Byron, although not safety-related , are each protected by missile - proof walls and roofs . The onsite wells supply makeup water to the SXCTs in the event that a tornado missile renders the essential service water makeup pumps inoperative . Missile protected check valves (OSX284A/B) are installed i n t h e essential service water makeup lines to prevent back flow from the SXCT basins to the river screen house .

e. Safety-related electrical cables are adequately protected against tornado-generated missiles by the reinforced concrete ducts around them . Embedded conduits in the auxiliary building south wall and associated cable vaults supporting operation of the SXCTs and deep well pumps are evaluated in Section 3.5 . 5 .

3 . 5-21 REVISION 17 - DECEMBER 2018

B/B-UFSAR Braidwood Station

~ --~~-s~n_tic1_:l Se!:y?:_c~---~~-1:~]::___0._i._s~l"lar:ge _P~pes _ai:-e _lo_<:::?_t:~d __ _ Deleted : There are no ~afety-relat ed component:

in the middle of the Essential Service Water Cooling Pond located outdoors at Braidwood Station.I and are not fully protected from missiles . The Essential Service Water Discharge Pipes are evaluated in Section 3.5.5.

All safety- related electrical component s whi ch are located outdoors are listed in Subsection 8 . 3 . 1 . 4.4 (Class lE Equipment in Remote Structures) .

All Category I buri ed pipes on Byron/Braidwood sites and the Category II (Non-Safety Related) Well Water (WW) piping from the onsite wells and pumps to the SXCTs at Byron have adequate soil cover for protection from tornado - generated missiles . These pipes are buried to depths greater than the required minimum depth of 4 feet 1 inch , determined using Young's method .

Safety-related HVAC system air intakes a nd exhausts are indicated on the plant arrangement Drawings M-5 , M-6, M-14 , M-15 and M 2 .

Auxiliary Building and Containment Purge (VA, VQ)

Intakes Intake louvers are shown as listed above . Protection is provided by missil e walls .

Exhaust The exhaust stacks are shown as listed above . Vertical stack connected to horizontal exhaust tunnel affords missile protection .

Diesel-Generator Room Intake (VD)

Th e diesel-generator room intake is shown as listed above . Protection is provided by missile walls.

Safety-related electrica l cables are adequately protected against tornado-generated missiles by the reinforced concrete ducts around them .

Control Room Intake (VC)

The control room intake is shown as listed above .

Protection is provided by missile walls. The p o~t£ol _ ( Deleted: Byron room turbine building makeup air intakes are evaluated in p ection 3.5 . 5 . I { Deleted: Byron only 3 . 5-2 1a REVISION 17 - DECEMBER 2018

B/B-UFSAR 3.5.4 Analysis of Missiles Generated by a Tornado Effects of tornado missiles have been assessed for safety-related components located outdoors. These components are the SXCTs (Byron only), the emergency diesel generator exhaust stacks , the emergency diesel generator ventilation and combustion air intakes , the emergency diesel generator crankcase vents, the fuel handling building railroad freight door , the main steam safety ( Deleted: and and power operated relief valve tailpipes , and the essential service water discharge extension lines (Braidwood only).

3.5.4.1 Essential Service Water Cooling Towers (Byron)

A temperature and inventory analysis of the UHS after the loss of SXCT fans due to tornado-generated missiles was performed . The analysis also considers out of service fans and postulated single failures. The number of fans lost due to tornado missiles is based on the results of the TORMIS analysis described in Section 3 . 5.5 .

Based on the results of the TORMIS analysis, the deep well pumps remain available to provide makeup water if the SX makeup pumps are damaged during the tornado event .

The analysis was performed using SXCT performance curves generated using the method described in Section 9 . 2 . 5 . 3 . 1 . 1 . 2 .

Various outside air wet bulb temperatures were considered in the analysis . The results of the analysis are used to establish operating limits on the number of SXCT fans required to be operable based on the outside air wet bulb temperature and number of units operating . The analysis credits the following operator actions :

a . Manual initiation of the deep well pump(s) is assumed to occur 1. 5 hours5.787037e-5 days <br />0.00139 hours <br />8.267196e-6 weeks <br />1.9025e-6 months <br /> into the event, b . Iso l ation of essential service water blowdown within two hours ,

c . Isolation of the auxiliary feedwater telltale drains within two hours , and d . Isolation of the SXCT riser leakoff drains within two hours The analyses determined the SXCTs are capable of providing adequate heat removal and timely safe shutdown of both units .

3 . 5-25 REVISION 17 - DECEMBER 2018

B/B-UFSAR 3.5. 4.2 Emergency Diesel Generator Exhaust Stacks The diesel generator exhausts are completely protected up to the point where they penetrate the tornado proof concrete enclosure on the auxiliary building roof . Above this point , they are exposed for about 35 feet as they travel vertically . Analysis has established t hat the stacks can be damaged to the extent that the flow area is reduced to 50 % of the original flow area without reducing the diesel power output (Braidwood only) .

To prevent loss of diesel availability due to the exhaust stack damage , a rupture disc pressure relief device is installed on each diesel exhaust line . This relief device is located downstream of the silencer and inside the missile protection structure on the roof of the auxiliary building . Upon blockage of the stack, t he rupture disc will open prior to backpressure increasing to the point that required diesel power is not available . The emergency diesel generators will therefore remain functional following any postulated tornado missile impact .

3. 5 . 4.3 Emergency Diesel Generator Ventilation and Combustion Air Intakes and Crankcase Vents Venti l ation and combustion air for the emergency diesels is inducted through tornado proof intakes in the auxiliary building roof . The emergency diese l engine crankcase vents are exposed to tornado missiles . Reference 14 demonstrates that the crankcase vent lines can be blocked without adversely affecting the ability of the associated diesel to perform its design function .

3.5.4. 4 Fuel Handling Building Railroad Freight Door The railroad freight door is not designed to be tornado proof .

In the event the door is missing or open , missiles would potentially enter the tunnel to the fue l handling building . To reach the fuel handling area , missiles would have to travel over 100 feet down the tunnel which is approximately 25 feet square .

The two most vulnerable areas are the fuel pool heat exchangers on the lower level and fuel storage area on the upper level .

After negotiating the tunnel , the missile would have to make a 90 degree turn and penetrate a wall to damage either of the heat exchangers (which are redundant) or make two 90 degree turns (up and right) to reach the fuel storage area . Based on this assessment , it is concluded that tornado missiles pose no hazard to the fuel handling building .

3 . 5-25a REVISION 17 - DECEMBER 2018

B/8 - UFSAR 3.5.4.5 Main Steam Safet y and Power Op erated Relief Valve Tailpipes The main steam safety valve 16 inch diameter 1/ 2 inch thick tai l p i pes extend approximately 1 foot above the MSSV roof a n d a max i mum of 1 . 5 i n c h es above a guard pipe . The guard pipe is a 20 inch diameter , 1/2 inch t h ick pipe .~ I Deleted: The combination of a short height above the roof and the installed guard pipe Th e pi~in _s__!:_ea_I!l ~af~tya.!!_~ power ope;~ted relief valve tailejpes are evaluated in pe ctio~ ~ . 5 . 5 . _

I practically eliminate s the possibility of a horizontal missile denting or crimping the MSSV tailpipes. The exhaust of the power operated relief valve is in a recessed area 3 . 5 .4. 6 Essentia l Service Wa t er Disch arge Extension Lines between the valve room upper roof and the containment wall , and is , therefore , protecte (Braidwood only) from horizontal missiles.

Deleted: Byron The Non -Safety Related portions of the Essential Service Water (SX) discharge extension lines extend approximately 3 feet above Deleted: Byron only lake level and they are attached to the safety related portion of the SX discharge piping at t h e discharge structu re via a f l a n ged connection .

• __ _ ___ Deleted: Analysis has demonstrated that the flange connection will fail and separate before the SX extension pipe stress reaches The Braidwood essential service water discharge extension lines the yield stress of the pipe material , i.e.

are evaluated in Section 3 . 5 . 5 . the extension pipe section will remain in the elastic behavior zone without plastic deformation due to a force generated by a horizontal missile. Therefore, the SX discharge flow path is not adversely impacteC by a Tornado generated horizontal missile striking the exposed SX discharge extension lines.

3 . 5-26 REVISION 17 - DECEMBER 2018

B/B-UFSAR 3.5.5 Probabilistic Tornado Missile Risk Analysis A probabilistic tornado missile risk analysis was completed for Byron (Reference 15) and Braidwood (Reference' -22) using -the - - -

I { Deleted: (Reference 15 )

TORMIS computer code which is based on the NRC approved methodology detailed in References 16 , 17 and 18. The TORMIS analysis was performed in accordance with the guidance described in t h e NRC TORMIS Safety Evaluation Report (Reference 19) and as clarified by Reg u latory Iss u e Summary (RIS) 2008-14 (Reference 20 ).

3 . 5 . 5 . 1 Scope The TORMIS analysis (Reference s 15 and 22 ) includes plant components , identified as necessary to safely shutdown the plant and maintain a shutdown condition , located in areas not fully protected by missile barriers designed to resist impact from design-basis tornado missiles . The targets included in the TORMIS analysis are listed in Table s 3 . 5-17 (Byron) and 3.5-18 (Braidwood) and additional details regarding targets (i . e .,

specific location and identification) are included in _y~lume 3 of { Deleted: Reference 15, References 15 (Byron) and 22 (Braidwood) .

3 . 5 . 5 . 2 Computer Codes 3.5.5.2 .1 TORM IS TORMIS (TORnado MISsile Risk Analysis Methodology Computer Code) uses a Monte Carlo simulation method that simulates tornado strikes on a pla n t . For each tornado strike , the tornado wind field is simulated , missiles are injected and flown (including vertical and near vertical missile impacts) , and missile impacts on structures and equipment are analyzed . These models are linked to form an integrated , time - history simulation methodo l ogy .

By repeating these simulations , the frequencies of missiles impacting and damaging individual components (targets) and groups of targets are estimated . Statistical convergence of the results is achieved by performing multiple replications with different random number seeds .

3 . 5-26a REVISION 17 - DECEMBER 2018

B/B-UFSAR 3.5.5.2.2 TORRISK TORRISK (TORnado RISK Analysis Methodology Computer Code} is a specialized version of TORMIS that produces tornado hazard curves distinct from the missile risk analysis features of TORMIS .

TORRISK is a fast - running version of TORMIS and was spun- off in 1983 specifically for the p u rpose of tornado wind probability analysis for the different types of geometrical targets , like po ints , buildings , sites and transmission lines . TORRISK uses the same tornado input data as TORMIS a nd produces tornado wind hazard risks o n ly . TORRISK produces a more accurate wind hazard curve than TORMIS since it is not encumbered with all of the TORMIS missile simulation variance reduction methods .

3.5.5.2 .3 TORSCR TORSCR is a FORTRAN computer code that is used to post-process TORMIS output files . Its primary function is to compute Boolean combi nations of target hit and damage probabilities over multiple targets .

3.5.5.2. 4 LS - DYNA LS-DYNA is a nonli n ear explicit finite element code for the dynamic analysis of structures . Since 1987, the LS-DYNA code has been extensively developed and supported by the Livermore Software Technology Corporation and is used for a wide variety of crash , blast and impact applications . LS-DYNA was used to develop missile threshold damage velocities for selected targets which are used as an input in the TORMIS model .

3.5.5.3 Analysis Th~ TORM IS tornado missile risk analysis results s h ow that t he [ Deleted : By ron arithmetic sum of damage frequencies for all target groups affecting the i ndividual units (i . e. , Unit 1 plus common unit components and Unit 2 plus common unit components } for both Byron and Braidwood are lower than the acceptable threshold frequency of l . OE - 06 per year established in SRP Section 2 . 2 . 3 and Reference 21 .

3 . 5-26b REVISION 17 - DECEMBER 2018

B/B-UFSAR The following limiting inputs and assumptions were used in the analysis (refer to Reference s 15 and 22 for additional assumptions and engineering judgments used in the analysis) :

a . A site specific tornado hazard curve and data set for Byron and Braidwood was developed using statistical analysis of the NOAA/National Weather Service Storm Prediction Center tornado data for the years 1950 thru 2013 . The analysis utilizes the Enhanced Fujita (EF) scale wind speeds in the TORM ~S simulations . - - ( Deleted: u b . A TORMIS wind profile (#3) that adequately models increased near ground wind speeds c . The missile characteristics and locations are based on a plant walk down survey and plant drawings . The plant walk down survey was performed during a unit outage to capture both non-outage and outage conditions during the survey .

A stochastic (time-dependent) model of the missile population is implemented in TORMIS . The stochastic approach to the missile population varies the mi ssile populations in each of the TORMIS replications to account for predictable cha nges in plant conditions (i. e .,

increased mi ssiles during outages) and the randomness inherent in the total number of missiles present at the plant at any given time .

d . Finite element calculations were performed to provide the missile damage threshold velocity for each missile type to cause unacceptable crimping damage for the SXCT riser pipes (Byron only) , diesel driven auxiliary feedwater pum~

exhaust pipes and cover plates and the main steam power operated relief valve tailpipes .

e . For the UHS (Byron only) , one or two SXCT ce ll s are assumed to be randomly out of service for maintenance. A postulated single failure of an electrical bus is assumed resulting in the loss of power to two additional SXCT cells . For the TORMIS analysis , success is defined as at least 3 of the remaining 5 cells surviving when one cell is out of service or 2 of the remaining 4 cells surviving when two cells are out of service .

3 . 5-26c REVISION 17 - DECEMBER 2018

B/B-UFSAR Hit and damage frequencies for groups of targets evaluated in TORMIS are commonly combined using Boolean operators (U and n) to aid in summarizing the results and understanding the effects of the system redundancies . The union (U ) operator means that if any one of the targets is damaged in a tornado , the system is assumed to fail . The intersection (n ) operator means that all the intersected components must be damaged in a tornado strike for the system to fail . Combinations of union and intersection operators can be put together to describe multi-component system failure logic for plant systems and subsystems . The Braidwood Station analysis only used the U operator while the Byron Station analysis used both the U and n operators.

For Byron Station , t pe arithmetic sum of damage frequencies for ( Deleted : T all target groups affecting the individual units would exceed the acceptance criteria of 1 . 0E-06 per year per unit . Boolean combinations of targets were developed to aid in summarizing the results and understanding the effects of system redundancies .

This approach yielded acceptable results . Boolean Logic is applied to target groups to accou nt for redundancy in the structural or system design or TORMIS modeling of a component as multiple targets . With redundancy in the design , the system function could be met even with one or more individual targets damaged by postulated tornado missiles . The Boolean intersection operator was used for UHS targets to credit redundancy in the design . The logic is applied to each TORMIS simulated tornado to determine if the missile damage results in a loss of function of the target group .

There was a single change made to the TORMIS code of a purely "software" nature which was not related to the approved TORMIS physics engine and calculation approach ; i . e. , the dimensioned number of possible missile types was increased to 24 for evaluation of damage from missile velocity exceedance and pipe penetration pass t h rough . Note that the 24th missile type (roof paver missile) was omitted for the Braidwood Station TORMIS analysis as there are no pavers on building roofs at Braidwood Station .

3. 5-26d REVISION 17 - DECEMBER 2018

B/B-UFSAR 3.5 . 6 References 1 . J . M. Vallance , A Study of the Probability of an Aircraft Using Waukegan Memorial Airport Hitting the Zion Station ,

Pickard , Lowe and Associates , Inc ., Washington , D. C ., 1972 .

2 . Clair Billington , FAA , Telephone conversations with H. H.

Hitzeman , Senior Engineering Analyst , Sargent & Lundy , August 5 ,

1977 and August 9 , 1977 .

3. John W. Ryan , FAA , Telephone conversation with H. H.

Hitzeman , Senior En gineering Analyst , Sargen t & Lundy , September 7 , 1977 .

4 . Annual Review of Aircraft Accident Data - U. S . General Aviation - Calendar Year 1970. National Transportation Safety Board , Washington , D. C ., Report Number NTSB-ARG-74-1 , April 18, 1974 .

5 . Annual Review of Aircraft Accident Data - U. S . General Aviation - Calendar Year 1969 , National Transportation Safety Board , Washington , D. C . , Report Number NTSB-ARG-71-1 , April 28 ,

1971.

6 . A. Amirikian , " Design of Protective Structures ," Bureau of Yards a nd Docks, Pu b l ication No . NAVDOCKS P-51 , Department of the Navy , Washington, D. C., August 1950 .

7 . J . M. Doyle , H. J . Klein, and H. Shah , " Design of Missile Restraint Concrete Panels ," Second International Conference on Structural Mechanical in Reactor Technology , Berlin , Germany ,

September 197 3.

8 . W. B . Cottrell and A . W. Savolainen , " U. S . Reactor Containment Technology ," ORNL-NSIC-5, Vol . 1 , Chapter 6 , Oak Ridge National Laboratory , August 1965.

9 . R. A . Williamson and R . R . Alvy , " Impact Effect of Fragments Striking Structural Elements, " Holmes and Naver , Inc ., Revised November 1 973 .

1 0 . AC! 349 , Code Requirements for Nuclear Safety Related Concrete Structures , 1976.

11 . P . Gottlieb , " Estimation of Nuclear Power Plant Aircraft Hazards ," Probabilistic Analysis of Nuclea r Reactor Safety ,

Proceedings of the American Nuclear Society Topical Meeting (May 8 - 10 , 1978 , Los Angeles , California) , p . VIII.8 , 1 to 8 .

12 . "A Manual for the Prediction of Blast and Fragment Loadings On Structures , " DOE/TIC-11268 , U. S . Department of Energy ,

November 1980 .

3 . 5-27 REVISION 17 - DECEMBER 2018

B/B-U FSAR 13 . A. H. Motloch , " Rotational Capacity of Hinging Regions in Reinforced Concrete Beams , " from Proceedings of the International Symposium on Flexural Mechanics of Reinforced Concrete , American Society of Civil Engineers, 1965 .

14 . Design Analysis 3101-0039-01 , "Calculation of EOG (Emergency Diesel Generator) Crankcase Pressure Assuming the Crankcase Vent Line is Blocked . "

15. Design Analysis ARA-002116002116, "Tornado Missile TORMIS Analysis of [Byron Generating Station) BGS ," Revision 3.

16 . Electric Power Research Institute Report-EPRI NP-768 ,

" Tornado Missile Risk Analysis ," May 1978 .

17 . Electric Power Research Institute Report-EPRI NP-769 ,

" Tornado Missile Risk Analysis Appendices, " May 1978 .

18 . Electric Power Research Institute Report-EPRI NP-2005 Volumes 1 and 2, " Tornado Missile Risk Evaluation Methodology, "

August 1981 .

19 . NRC Safety Evaluation Report - " Electric Power Research Institute (EPRI) Topical Reports Concerning Tornado Missile Probabilistic Risk Assessment (PRA) Methodology, " dated October 26 , 1983 (ML080870291) .

20 . NRC Regulatory Issue Summary 2008-14 , " Use of TORMIS Computer Code for Assessment of Tornado Missile Protection , "

dated June 16, 2008 (ML080230578) .

21 . Memorandum from Harold Denton , NRR Director to Victor Stello , Deputy Executive Director for Regional Operations and Generic Requirements , " Position of Use of Probabilistic Risk Assessment in Tornado Licensing Actions ," dated November 7 , 1983 (ML030020331) .

22 . Design Analysis ARA-002431002431, "Tornado Missile TORMIS Analysis of [Braidwood Generating Station] BRW ," Revision 0 .

3.5-28 REVISION 17 - DECEMBER 2018

B/B-UFSAR TABLE 3.5-17 TARGETS EVALUATED IN BYRON TORMIS ANALYSIS TARGET NUMBER FAILURE NOTES OF MODE(S)

TARGETS SXCT Riser Pipes 8 Perforation SXCT Cells A-H and Crimping SXCT Fan Motors and 8 Missile Hit SXCT Cells A-H Power Feeds SXCT Fan Gear Box Oil 8 Missile Hit SXCT Cells A- H Level Gauges SXCT Personnel 8 Perforation SXCT Cells A-H Hatches SXCT Fan Inspection 8 Perforation SXCT Cells A-H Hatches SXCT Fan Blades 8 Missile Hit SXCT Cells A-H SXCT Anti-Vortex 2 Perforation North and South Boxes and Trash Screens SXCT Switchgear Room 4 Perforation Division 11 (Bus Ventilation Louvers 131Z), 12 (Bus 132Z), 21 (Bus 231Z) and 22 (Bus 232Z)

Diesel Driven 2 Crimping Unit 1 and Unit 2 Auxiliary Feedwater Pump Exhaust Pipes Diesel Driven 2 Crimping Unit 1 and Unit 2 Auxiliary Feedwater Pump Exhaust Cover Plates Steam Generator Power 8 Pipe Unit 1 (4) and Operated Relief Valve Penetration Unit 2 (4)

Tailpipes and Crimping 3 . 5-48 REVISION 17 - DECEMBER 2018

B/B-UFSAR TABLE 3.5-17 (cont'd)

TARGET NUMBER FAILURE NOTES OF MODE(S)

TARGETS Main Steam Safety 40 Pipe Unit 1 (20) and Valve Tailpipes Penetration Unit 2 (20)

Deep Well Pump 2 Spall Pumps OA and OB Enclosures Embedded Conduits 4 Perforation Division 11 (Bus (Auxiliary Building 131Z), 12 (Bus 132Z, South Wall) 21 (Bus 231Z) and 22 (Bus 232Z)

Cable Vaults - 6 Spall Division 11 (lGl),

Division 11 (Bus 12 (1H2 and 1J2), 21 131Z), 12 (Bus 132Z), (2Gl) and 22 (2H2 21 (Bus 231Z) and 22 and 2J2)

(Bus 232Z)

Auxiliary Building L 2 Pipe OA and OB Main Line Openings Penetration Control Room Turbine Building Makeup Air Intakes Auxiliary Building L 4 Pipe Division 11, 12, 21 Line Openings Penetration and 22, Miscellaneous Electrical Equipment Room Exhaust*

Non-ESF Switchgear 5 Perforation Division 11 and 21 Room Conduits SXCT Power and Control Cables (Evaluated in Segments)

• In a limited number of cases , the exhaust path may be impacted. Therefore, manual action is relied on to restore ventilation . These manual actions entail simple activities to open doors (to provide an exhaust path) and restart supply fans.

3 .5-4 9 REVISION 17 - DECEMBER 2018

B/B-UFSAR TABLE 3.5-18 TARGETS EVALUATED IN BRAIDWOOD TORMIS ANALYSIS TARGET NUMBER FAILURE NOTES OF MODE(S)

TARGETS Diesel Driven 2 Crimping Unit 1 and Unit 2 Auxiliary Feedwater Pump Exhaust Pipes Diesel Driven 2 Crimping Unit 1 and Unit 2 Auxiliary Feedwater Pump Exhaust Cover Plates Steam Generator Power 8 Pipe Unit 1 (4) and Operated Relief Valve Penetration Unit 2 (4)

Tailpipes and Crimping Main Steam Safety 40 Pipe Unit 1 (20) and Valve Tailpipes Penetration Unit 2 (20)

Auxiliary Building L 2 Pipe OA and OB Main Line Openings Penetration Control Room Turbine Building Makeup Air Intakes Auxiliary Building L 4 Pipe Division 11 , 12 , 21 Line Openings Penetration and 22 ,

Miscellaneous Electrical Equipment Room Exhaust*

SX Discharge Pipes 2 Missile Hit OA and OB SX Discharge Extension Lines

• In a limited number of cases , the exhaust path may be impacted.

is relied on to restore ventilation. These manual actions entail doors (to provide an exhaust path) and restart supply fans.

rle ual action ies to open 3 . 5-50 REVISION 17 - DEC MBER 2018