RBG-48323, License Amendment Request to Revise the Licensing Basis and Minimum Basin Water Level for the Ultimate Heat Sink

License Amendment Request to Revise the Licensing Basis and Minimum Basin Water Level for the Ultimate Heat Sink

ML24365A265
Person / Time
Site:	River Bend
Issue date:	12/30/2024
From:	Couture P Entergy Operations
To:	Office of Nuclear Reactor Regulation, Document Control Desk
References
RBG-48323
Download: ML24365A265 (1)

Text

Phil Couture Senior Manager Regulatory Assurance 601-368-5102

RBG-48323 10 CFR 50.90 December 30, 2024 ATTN: Document Control Desk U.S. Nuclear Regulatory Commission Washington, DC 20555-0001

Subject:

License Amendment Request to Revise the Licensing Basis and Minimum Basin Water Level for the Ultimate Heat Sink River Bend Station, Unit 1 NRC Docket No. 50-458 Renewed Facility Operating License No. NPF-47 In accordance with the provisions 10 CFR 50.90, Entergy Operations, Inc. (Entergy) is requesting an amendment to the license of River Bend Station Unit 1 (RBS). The proposed amendment would modify the RBS licensing basis through a revision of the Updated Safety Analysis Report (USAR) to credit makeup to the ultimate heat sink (UHS) in less than 30 days to account for system leakage and for operation with both standby service water subsystems in operation. Additionally, the proposed amendment would revise Technical Specification (TS)

Surveillance Requirement 3.7.1.1 to increase the minimum UHS cooling tower basin water level in order to maximize UHS inventory.

The Enclosure provides a description and assessment of the proposed changes. Attachment 1 provides the existing USAR pages marked up to show the proposed changes. Attachment 2 provides the existing TS pages marked up to show the proposed changes. Attachment 3 provides revised (clean) TS pages. Attachment 4 provides existing TS Bases pages marked to show the proposed changes for information only.

Entergy requests approval of the proposed license amendment within 13 months of the submission date, with the amendment being implemented within 60 days.

In accordance with 10 CFR 50.91, "Notice for public comment; State consultation," paragraph (b), a copy of this license amendment request, with enclosure, is being provided to the designated State Officials.

This letter and its enclosure do not contain any new commitments.

RBG-48323 Page 2 of 2 Should you have any questions or require additional information, please contact Randy Crawford, River Bend Regulatory Assurance Manager, at 225-381-4177.

I declare under penalty of perjury that the foregoing is true and correct.

Executed on December 30, 2024.

Respectfully, Phil Couture, Senior Manager, Fleet Regulatory Assurance - Licensing PC/dlw

Enclosure:

Description and Assessment of the Proposed Changes Attachments to the

Enclosure:

1. Proposed USAR Markups

2. Technical Specification Page Markups

3. Revised (Clean) Technical Specification Pages

4. Technical Specification Bases Page Markups (Information Only) cc:

NRC Regional Administrator - Region IV NRC Project Manager - River Bend Station NRC Senior Resident Inspector - River Bend Station Louisiana Department of Environmental Quality Digitally signed by Philip Couture DN: cn=Philip Couture, c=US, o=Entergy, ou=Regulatory Assurance, email=pcoutur@entergy.com Date: 2024.12.30 17:08:16 -06'00' Philip Couture

RBG-48323 Description and Assessment of the Proposed Changes

RBG-48323 Page 1 of 19 TABLE OF CONTENTS 1.0

SUMMARY

DESCRIPTION 2.0 DETAILED DESCRIPTION

2.1 BACKGROUND

2.2 SYSTEM DESIGN AND OPERATION 2.3 CURRENT LICENSING BASIS AND REGULATORY GUIDANCE 2.4 REASON FOR PROPOSED CHANGES

2.5 DESCRIPTION

OF THE PROPOSED CHANGES

3.0 TECHNICAL EVALUATION

3.1 EVALUATION OF UHS CAPABILITY 3.2 TS SR 3.7.1.1 3.3 SCT REPLENISHMENT USING THE DEEP WELL PUMPS 3.4 SCT REPLENISHMENT USING THE CIRCULATING WATER FLUME 3.5 PHYSICAL SEPARATION AND REDUNDANCY 3.6 NRC-REQUESTED INFORMATION

4.0 REGULATORY EVALUATION

4.1 APPLICABLE REGULATORY REQUIREMENTS/CRITERIA 4.2 PRECEDENT 4.3 NO SIGNIFICANT HAZARDS CONSIDERATION ANALYSIS

4.4 CONCLUSION

S

6.0 REFERENCES

7.0 ATTACHMENTS

RBG-48323 Page 2 of 19 DESCRIPTION AND ASSESSMENT OF THE PROPOSED CHANGES 1.0

SUMMARY

DESCRIPTION This License Amendment Request (LAR) is requesting Nuclear Regulatory Commission (NRC) approval for changes to the River Bend Station (RBS) current licensing basis as described in the Updated Safety Analysis Report (USAR) to credit makeup to the ultimate heat sink (UHS) in less than 30 days to account for operation with both standby service water (SSW) subsystems in operation. As a result of the analyses discussed in this LAR, the credited makeup sources provide an overall UHS replenishment method that meets Regulatory Guide (RG) 1.27 Revision 2 requirements to ensure the continuous capability of the UHS to perform its safety functions, taking into account the availability of replenishment equipment and limitations that may be imposed on freedom of movement following an accident, including the effects of natural phenomena. Additionally, the LAR proposes to revise Technical Specification (TS) Surveillance Requirement (SR) 3.7.1.1 to increase the minimum UHS cooling tower basin water level in order to maximize UHS inventory.

Approval for this LAR is requested to address a violation received by Entergy in 2011 where the NRC determined that changes to the RBS licensing basis, similar to those proposed in this LAR, were made by the site under 10 CFR 50.59 when prior approval by the NRC should have been obtained. The LAR additionally addresses a 2023 violation regarding failure to obtain a license amendment to correct the issue identified in the 2011 violation.

2.0 DETAILED DESCRIPTION

2.1 BACKGROUND

Currently, the RBS standby cooling tower (SCT) basin is designed in accordance with RG 1.27 Revision 2 (Reference 1) to maintain a 30-day inventory assuming the failure of an Emergency Diesel Generator (EDG), thereby limiting operations to one subsystem of SSW and its associated system leakage following a design basis accident (DBA). However, if failure of the EDG does not occur and both subsystems of SSW remain operational, the UHS inventory is depleted within approximately 21 days. Rather than securing an EDG and operating with a single SSW subsystem post-DBA, the preferred approach is to maintain all EDGs operational and instead replenish the UHS inventory as needed.

This LAR proposes to revise the current licensing bases to reflect that the UHS maintains a 21-day inventory and to credit the deep well pumps, which are the standard SCT makeup source, and the circulating water flume as two separate alternative makeup sources that can be utilized to ensure the continuous capability of the UHS to perform its safety functions for the 30-day duration required in RG 1.27 Revision 2.

History of Issue In 2002, Entergy revised the USAR and TS Bases crediting makeup to the UHS to account for system leakage during the case where the Division II Diesel Generator does not fail, and the associated Division II SSW components are operated in addition to Division I/III during the 30-day post DBA mission time. This change was made under 10 CFR 50.59 with the understanding

RBG-48323 Page 3 of 19 by Entergy at the time that this scenario was considered outside the design basis case evaluated in the USAR.

In 2011, the NRC issued Inspection Report (IR) 05000458/2011008, which contained a non-cited violation (NCV) of 10 CFR 50.59 regarding Entergy failing to obtain a license amendment prior to implementing the change to the ultimate heat sink inventory requirements in 2002.

In February 2014, Entergy submitted a LAR (Reference 2) requesting NRC approval for the change made in 2002 to address the 2011 violation. Entergy subsequently withdrew the LAR (Reference 3). In the letter of withdrawal acknowledgement (Reference 4), the NRC included 4 items required to be addressed for any future resubmittal. These items are addressed in Section 3.6 of this LAR.

On June 1, 2023, Entergy implemented compensatory measures that ensure a 30-day UHS cooling water supply. These measures included increasing the minimum SCT level, establishing alternate makeup sources, and eliminating unnecessary heat load on the SCT.

On November 13, 2023, the NRC issued IR 05000458/2023003 and a Notice of Violation (NOV) to RBS (Reference 5). The NOV detailed that from October 27, 2011, to September 30, 2023, Entergy failed to obtain a license amendment pursuant to 10 CFR 50.90.

On December 7, 2023, Entergy sent the NRC a reply to the November 13, 2023 NOV. In the reply, Entergy stated that they intend to correct the condition by submitting a LAR to credit alternate makeup sources to the SCT and reduce the SCT inventory requirements from 30 days to approximately 21 days.

2.2 SYSTEM DESIGN AND OPERATION Standby Service Water (SSW)

The SSW System consists of two redundant mechanical subsystems. Each subsystem consists of two 50-percent capacity service water pumps with associated valves and standby cooling tower fans. The Division I/III SSW subsystem receives water from the SSW pumps (SWP-P2A and SWP-P2C). SWP-P2A is powered from the Division I EDG, and SWP-P2C is powered from the Division III EDG. The redundant mechanical SSW subsystem includes Division II (SWP-P2B and SWP-P2D) pumps that are both powered from the Division II EDG. The SSW System is comprised of two equally sized, redundant piping systems, each supplying the components listed in Table 9.2-15 of the USAR. During normal plant operation, the normal service water pumps use SSW piping to supply safety-related components. The SSW System is designed to provide cooling water for the removal of heat from unit auxiliaries such as Residual Heat Removal (RHR) System heat exchangers, EDGs, High Pressure Core Spray Diesel Generator, and room coolers for Emergency Core Cooling System equipment required for a safe reactor shutdown following a Design Basis Accident (DBA) or transient. The SSW System also provides cooling to unit components, as required, during normal shutdown and reactor isolation modes.

Cooling water for normal station operation, including shutdown, is provided by the Normal Service Water (NSW) System. During normal operation, the NSW System pumps use the SSW System piping to supply cooling water to safety-related components. During a DBA with a loss of offsite power, the equipment required for normal operation only is isolated from the SSW

RBG-48323 Page 4 of 19 System, and SSW cooling is directed only to safety related equipment. Isolation of the NSW System from the SSW System is achieved via automatic closure of the SSW System supply header isolation valves (SWP-MOV57A and SWP-MOV57B) and return header isolation valves (SWP-MOV96A and SWP-MOV96B) when the SSW System pumps are initiated. The mission time of the SSW System is 30 days following a DBA LOCA.

As discussed in USAR Section 9.2.7, the SSW System operates under emergency conditions, in conjunction with the UHS, to remove heat from those plant components required for the safe shutdown and cooldown of the unit. The system provides all the necessary cooling water to the reactor plant components required to safely bring the reactor to a cold shutdown condition and to maintain it in cold shut down for a 30-day post-accident period.

The SSW System is designed to Seismic Category I requirements, and protection is provided from extreme natural phenomena such as earthquakes, tornadoes, and floods. The system is also protected from the effects of externally and internally generated missiles, as well as the effects of pipe whip and jet impingement from high and moderate-energy line breaks.

Standby Cooling Tower (SCT)

Post DBA heat loads are dissipated by the SCT, also referred to as the UHS, which is an evaporative cooling tower containing two 100% cooling tower divisions. The SCT structure is a single seismic Category I structure designed to withstand seismic, tornado, and missile loads.

Each division contains 100% capacity piping, fill, and fans capable of removing 100% of the heat load to mitigate the consequences of a DBA assuming a loss of offsite power. One 100%

common basin is provided for both divisions of fans and pumps/piping. The evaporative cooling provided by the cooling tower depletes inventory in the basin. In addition to evaporation, other losses include drift, the Main Steam Positive Leakage Control System (MS-PLCS), and system leakage. The SCT is designed to provide sufficient cooling to permit safe shutdown and cooldown of the unit following an assumed worst case LOCA DBA. The UHS is required to perform its intended safety function assuming any single active or passive failure coincident with a loss of offsite power.

The SCT, including its storage basin, is designed in accordance with RG 1.27 Revision 2, as stated in USAR Table 1.8-1. The UHS basin capacity is required by RG 1.27 Revision 2, and described in USAR Section 9.2.5, to maintain a minimum of 30 days inventory to mitigate the consequences of a DBA without replenishment assuming a loss of offsite power and a single failure. The current TS minimum water level for the UHS basin is 78%, as required by TS SR 3.7.1.1, which corresponds to an elevation of 111 10. Note that elevations and levels discussed in this LAR refer to mean sea level (MSL).

USAR Section 9.2.5.2 states that the postulated DBA is a large recirculation line break coincident with loss of offsite power. During a DBA, in determining the acceptability of the UHS with respect to the 30-day inventory requirement, the design assumes the single failure of the Division II EDG to occur immediately after the reactor trip. Therefore, only the Division I/III SSW

RBG-48323 Page 5 of 19 components are currently assumed in the USAR and design basis inventory calculations to operate following a DBA.

The SCT, including its storage basin, is designed to withstand the effects of natural phenomena such as earthquakes, tornados, hurricanes, and floods. The SCT is also designed to withstand the effects of internally and externally generated missiles, including pipe breaks.

Deep Well Pumps The normal method of replenishing water in the SCT is performed using the installed deep well pumps, which are part of the makeup water treatment system. Raw water is pumped from two deep well pumps (MWS-P1A and MWS-P1B) to maintain level in the SCT basin. The pumps are in wells that are approximately 1800 ft deep and have an approximately 14 ft discharge column above the impellers. Eighteen inches of submergence is required for the pumps to operate.

Each pump is sized to provide 150 GPM to the SCT if operated individually. The pumps can supply a combined flow of 200 GPM when operated in parallel.

The two pumps are located in the yard along the south plant access road. MWS-P1A is located east of the fire pump house and MWS-P1B is located west of the fire pump house. The pumps are located approximately 460 ft apart. Both pumps discharge above ground into pipelines that drop underground into the fire pump house. At the fire pump house, the two pump discharges combine into a common 4 line. This line goes underground in the fire pump house and is buried until it enters the auxiliary control building. The line then enters the southwest corner of the turbine building heater bay and then the service water piping tunnels. From the piping tunnels, the line enters at the southeast quadrant of the cooling tower basin.

The deep well pumps and associated piping are not classified seismic Category I, are non-safety related, and are normally powered by non-safety related power.

Circulating Water Flume and Fire Protection Piping The backup method of replenishing the SCT if the deep well pumps and piping are unavailable is to use the circulating water (circ water) flume and fire protection piping. The water is transferred to the SCT from the flume using the fire protection system piping and a temporary diesel driven pump. Site procedures are in place to implement this makeup source if needed.

The circ water flume is an open channel located between the plant cooling towers which serves to transfer the water from the cooling tower basins to the suction of the circ water pumps. It is low-profile concrete structure with walls that extend up from its base to about 3 ft above grade.

The walls are nominally 2.5 thick reinforced concrete. An outlet flume runs from the main flume channel to each of the cooling tower basins.

The fire protection piping system runs throughout the plant. The portion of the system used for replenishment of the SCT is the piping from fire hydrants FPW-FHY29 or FPW-FHY1 to either FPW-FHY10 or FPW-FHY9. Hydrant FHY29 is located to the west of the flume inside the Generation Support Building (SOCA) fence and FHY1 is located just south of the plant near the demineralized water storage tanks. FHY10 is located east of the SCT and FHY9 is located just west of the SCT. The piping is all underground except for the hydrants. Water from the flume can be pumped with fire hoses to hydrant FHY29 or FHY1, through buried fire protection piping

RBG-48323 Page 6 of 19 to either hydrant FPW-FHY10 or FPW-FHY9, and transferred from the hydrant to the SCT with fire hoses.

Per USAR Section 10.4.5, the circulating water system serves no safety function. Malfunction or failure of a component of the system does not affect the intended function of safety-related systems or components.

2.3 CURRENT LICENSING BASIS AND REGULATORY GUIDANCE Regulatory Guide 1.27 Revision 2, issued by the NRC in 1976, outlines requirements and acceptable designs for UHS. River Bend committed to this guidance, as documented in USAR Table 1.8-1. RG 1.27 Revision 2 states the following:

The capacity of the sink should be sufficient to provide cooling both for the period of time needed to evaluate the situation and for the period of time needed to take corrective action. A period of 30 days is considered to be adequate for these purposes.

The RG continues to state:

A capacity of less than 30 days may be acceptable if it can be demonstrated that replenishment can be effected to ensure the continuous capability of the sink to perform its safety functions, taking into account the availability of replenishment equipment and limitations that may be imposed on "freedom of movement" following an accident.

RG 1.27 Revision 2 further requires that, because of the importance of the UHS to safety, the UHS safety functions should be ensured during and following the most severe natural phenomena postulated for the site. In the case of RBS, these natural phenomena are the Safe Shutdown Earthquake (SSE), design basis tornado, hurricane, and flood.

The current RBS licensing basis, described in USAR Section 9.2.5 and USAR Table 9.2-13, indicates the UHS can operate for 30 days following a DBA assuming failure of the Division II EDG, leaving a single subsystem of the SSW in operation.

2.4 REASON FOR PROPOSED CHANGES The current site analysis meets the RG 1.27 30-day requirement, assuming a Division II EDG failure resulting in only Division I/III equipment in operation. However, the design and licensing basis are unclear on actions when no EDG failure occurs. Although operating procedures provide direction on securing unnecessary loads if both divisions operate, they do not address securing a division of SSW.

The NRC has questioned whether a Division II EDG failure is the most conservative scenario for UHS inventory. RBS has determined the limiting failure with respect to inventory would be failure of one of the SSW return header isolation valves, SWP-MOV96A or SWP-MOV96B, with no EDG failures and both divisions of SSW in operation. Given these concerns, a condition report was initiated in the RBS Corrective Action Program to address this licensing basis issue and compensatory measures were implemented. These compensatory measures currently

RBG-48323 Page 7 of 19 include maintaining the SCT inventory at or above 114 9 and providing makeup during accident conditions per site procedures using the circ water flume sources to keep the SCT operable. This LAR resolves this condition by revising the licensing basis to credit these SCT makeup sources within the 30-day post-DBA period to ensure the continuous capability of the UHS to perform its safety functions.

To support the revised UHS analysis, the minimum water level in the UHS basin is increased.

This maximizes the time the UHS basin provides cooling water and allows for the maximum time available to provide makeup to the UHS basin.

2.5 DESCRIPTION

OF THE PROPOSED CHANGES RBS USAR Section 9.2.5 is revised to remove the current assumption of a single failure of the Division II EDG following a trip. USAR Section 9.2.5 is instead revised to indicate that the limiting case for determining UHS water storage basin capacity is all EDGs operating following the DBA, including both SSW divisions, along with the single failure of one of the two SSW return header isolation valves. USAR Section 9.2.5 is also revised to reflect that the UHS water storage basin is sized to provide a minimum of 21 days inventory without replenishment.

Replenishment from either the deep well pumps or the circulating water flume is started by day 10 following an accident to ensure the safety functions of the UHS are maintained for 30 days.

The TS 3.7.1 minimum UHS basin water level is increased to the corresponding level of 114 5 (82.6%). Specifically, TS SR 3.7.1.1 is revised from:

Verify the water level of UHS cooling tower basin is 78%.

To:

Verify the water level of UHS cooling tower basin is 82.6%.

The increased initial inventory of the UHS water storage basin due to the TS SR 3.7.1.1 change is also reflected in the mark ups of USAR Section 9.2.5.

A summary of the proposed USAR changes is provided in Attachment 1. The TS changes are provided in Attachment 2, with clean pages provided in Attachment 3. The proposed changes are supported by changes to the TS Bases, which are provided in Attachment 4 for information only.

3.0 TECHNICAL EVALUATION

The SCT is designed to provide sufficient cooling water to permit the safe shutdown of the unit and cooldown of all units it serves and to maintain them in a safe shutdown condition. RG 1.27 Revision 2 allows a UHS capacity of less than 30 days if it can be demonstrated that replenishment can be affected to ensure the capability of the sink to perform its safety functions, taking into account the availability of replenishment equipment and limitations that may be imposed on freedom of movement following an accident.

RBG-48323 Page 8 of 19 3.1 EVALUATION OF UHS CAPABILITY Entergy calculations have determined that, with no EDG failures and both divisions of SSW in operation, the SCT basin inventory is depleted by day 21 following a DBA. These calculations assume the proposed starting UHS inventory of 114 5, a system leakage loss rate of 15 GPM per SSW subsystem, a loss rate of 1.5 GPM to supply seal water to the MS-PLCS, and a single failure of one of the return header boundary isolation valves along with a 20-minute operator manual action to close the valve. Entergy will provide these calculations to the NRC, as needed, through an audit portal.

The failure of a return header boundary isolation valve and the associated operator manual action to close the valve already exists in the RBS failure modes and effects analysis (FMEA).

In NUREG-0989 Supplement No. 3 (Reference 6), the original NRC Safety Evaluation Report (SER) related to the operation of RBS, the staff reviewed the FMEA in order to conclude the SSW system could withstand any single failure and provide sufficient cooling water to ensure a safe shutdown for all design-basis events. This FMEA included the single failure of one of the Service Water Return Header Isolation Valves, SWP-MOV96A or SWP-MOV96B, as compensated by operator actions in existing site procedures.

Based on the Entergy calculations, replenishment of the SCT basin is required in less than 30 days to ensure the continued capability of the UHS to provide its safety functions. To meet the 30-day mission time, replenishment must start by day 10 post-DBA at a minimum rate of 87.25 GPM. The required replenishment total volume needed to reach 30 days is approximately 2,512,800 gallons.

Two sources of replenishment proposed to the SCT are the deep well pumps and the circulating water flume using one of two available portable diesel driven pumps that discharge to the SCT basin through fire protection piping and fire hydrants. These two sources are evaluated below to confirm that they meet the flow rate requirements as well as RG 1.27 Revision 2 requirements.

3.2 TS SR 3.7.1.1 The current SCT basin minimum water level is 78%, corresponding to 111 10. The proposed SR 3.7.1.1 revision to change the minimum water level from 78% to 82.6% corresponds to a change from 111 10 to 114 5. The requested minimum water level 114 5 was determined based on the process safety limit (PSL) elevation of 118 4 which is the elevation where the water would overflow the basin onto the ground. The requested 114 5 level is the maximum level that the SCT basin can support after accounting for high level and minimum level alarms considering instrument accuracy and drift. This maximum water level will allow adequate time for station personnel to respond to the DBA and identify actions needed to maintain adequate UHS water levels. These actions could include replenishment by the two water sources described below.

3.3 SCT REPLENISHMENT USING THE DEEP WELL PUMPS The normal means of replenishment of the SCT basin is using the deep well pumps system.

This system includes two deep well pumps (MWS-P1A and MWS-P1B), associated Makeup Water (MWS) piping, the station blackout (SBO) diesel generator (for loss of normal power

RBG-48323 Page 9 of 19 scenarios), and structures housing the MWS piping like the Fire Pump House along with its installed electrical infrastructure.

RBS site procedures are in place to replenish the SCT using the deep well pumps and to provide temporary power using the SBO diesel generator to the pumps when normal power is not available. The deep well pumps are designed and sized to supply 150 GPM to the SCT when one pump is in operation. The pumps are capable of operating in parallel at a flow rate of 200 GPM. Since the required replenishment to meet UHS mission time is 87.25 GPM, a single pump is capable of meeting the required makeup flow.

The two deep well pumps draw water from the 1800 ft deep tertiary zone 3 aquifer. The available capacity of the aquifer has been evaluated and determined to have sufficient capacity with considerable margin to replenish the SCT with minimal drawdown of the aquifer.

Therefore, the aquifer has sufficient water to replenish the SCT following a DBA.

The SBO diesel generator is stored in the protected area adjacent to the standby diesel generator building. The generator and trailer are designed for a sustained wind speed of 100 mph. Site procedures direct relocating the generator to the fire pump house to power one of the deep well pumps. The deep well pump electrical load is less than 10% of the rated load for the generator. Analysis has determined that the minimum SBO diesel generator fuel replenishment interval is approximately 43 hours4.976852e-4 days <br />0.0119 hours <br />7.109788e-5 weeks <br />1.63615e-5 months <br /> and replenishment of fuel, with regard to freedom of movement by day 10 following an accident when SCT inventory makeup is required, will be available.

Protection from Flooding Flooding at RBS as evaluated in the USAR is assumed to be created by occurrence of the probable maximum precipitation event (PMP) due to local intense precipitation. This event results in ponding in local areas with no areas ponding to an elevation above 96 mean sea level near plant buildings.

With a flood elevation at the pump house of 96 MSL, flood waters could extend into the deep well pumps motor control center (MCC) compartments. The top of the MCC mounting pads in the fire pump house are at elevation 95 4 MSL. Deep well pump motors, local push button control stations, and the SBO diesel generator trailer are well above the PMP flood levels. As a result, the only items necessary to supply makeup from the deep well pumps potentially impacted by flooding are the MCC compartments.

Thus, the deep well pumps cannot be assured to be available following a PMP flood. In the unlikely event that the deep well pumps are impacted by flooding, the circ water flume would remain available as an alternate makeup source.

Protection from Wind (Hurricane and Tornado)

All elements of the deep well makeup flow path including the SBO diesel generator are designed to resist the site design basis wind loading of 100 mph, fastest mile wind speed.

Buildings housing piping from the deep well pumps include the Fire Pump House, Auxiliary Control Building, Heater Bay, Piping Tunnel and Standby Service Water Cooling tower. An underground pipeline from each deep well pump converges via a manifold inside the Fire Pump

RBG-48323 Page 10 of 19 House with a single line exiting the Fire Pump House underground to the Auxiliary Control Building at which point it is run within the buildings noted above to the Standby Cooling Tower.

The deep well pumps, the Fire Pump House structure, and the Auxiliary Control Building structure are not designed for tornado wind or tornado missiles. The Pipe Tunnel structure and the Standby Cooling Tower are designed to resist the site design basis tornado loadings.

The deep well pumps are protected from design basis wind loading, but cannot be assured to be available following a direct hit from a tornado. In the unlikely event that the deep well pumps are impacted by a tornado, the circ water flume would remain available as an alternate makeup source.

Protection from Seismic Events Piping from the deep well pumps through the Fire Pump House to the Pipe Tunnel, along with electrical raceway and MCC mounting in the Fire Pump House are non-seismic in design. The piping from the deep well pumps to the SCT basin is predominantly buried or located within seismic Category I areas except for piping in the fire pump house, the auxiliary control building, and the turbine building. This underground MWS piping is judged to be seismically rugged.

Portions of the MWS piping in the pipe tunnels have been evaluated to seismic Category II/I criteria to remain adequately supported to not adversely impact adjacent piping.

The deep well pumps cannot be assured to be available following a design basis SSE. In the unlikely event that the deep well pumps are impacted by an SSE, the circ water flume would remain available as an alternate makeup source.

Dose Entergy calculations have determined that the deep well pumps and fire pump house can be accessed four days following a DBA with more than a 40 hour4.62963e-4 days <br />0.0111 hours <br />6.613757e-5 weeks <br />1.522e-5 months <br /> stay time. Since makeup is not required until day 10 following a DBA, it is concluded that the fire pump house, SBO diesel generator, and deep well pumps will be accessible due to dose to execute the deep well makeup.

Conclusions In summary, the deep well pumps as a SCT makeup system meets the calculated required replenishment capacity and flow rate, and supports the UHS design in meeting the 30-day capacity requirements of Regulatory Guide 1.27 Revision 2. While portions of the deep well pump system are not considered resistant to all flooding, tornado, and seismic events, they represent a highly reliable primary replenishment source.

3.4 SCT REPLENISHMENT USING THE CIRCULATING WATER FLUME In situations where the deep well makeup source is impaired due to natural phenomena, the circulating water flume remains as an alternative replenishment path, meeting the intent of RG 1.27 Revision 2 requirements for maintaining continuous capability of the sink to perform its safety functions.

RBG-48323 Page 11 of 19 The alternate SCT makeup source will use the circ water flume and pump structure, Fire Protection piping, the high-density polyethylene (HDPE) SOCA piping, and Hale pumps stored in the FLEX buildings. Site procedures are available to direct operators to provide alternate makeup to the SCT using one of two Hale fire pumps drawing water from the circ water flume via one of two alternate flow paths. The site procedures specify relocation of either of the two Hale fire pumps from the FLEX building storage, installation of the pump near the circ water flume, installation of fire hoses, and performance of fire protection valve manipulations necessary for either of the flow paths.

The first flow path is from the circ water flume to the HDPE SOCA pipe to hydrant FHY29 via fire hoses, through buried fire protection piping on the East and North sides of the plant, and then to the SCT from hydrant FHY10 or FHY9 again via fire hoses. The second flow path is from the circ water flume to the HDPE circ water drain pipe to hydrant FHY1 via fire hoses, through buried fire protection piping on the South and West sides of the plant, and then to the SCT from hydrant FHY10 or FHY9 again via fire hoses. The two flow paths (FHY1 and FHY29) utilize different HDPE pipes through the SOCA and different fire protection piping. FHY1 utilizes fire protection piping south and west of the plant where FHY29 utilizes fire protection piping east and north of the plant. Therefore, the diversity of the available hydrants also results in diverse pipe routing. This physical layout allows flexibility in pump placement on the southwest side of the flume, which is conducive to freedom of movement considerations.

Entergy calculations indicate the required volume to replenish the SCT to meet the 30-day mission time is 2,512,800 gal. A circ water temperature of 100°F is assumed, which exceeds the maximum design circ water temperature of 96°F. Assuming a starting flume level at the minimum operating level of 105 ft, the flume has an available volume of at least 2,695,000 gal.

Therefore, the flume has adequate volume to meet the 30-day mission time for the SCT basin.

The required replenishment flow rate to the SCT to meet the 30-day mission time of the UHS is a minimum of 87.25 GPM. The Hale fire pumps have sufficient capacity to provide approximately 300 to 360 GPM from the circ water flume to the SCT basin depending on the route using the fire protection piping. Thus, replenishment from the flume has adequate flow to meet the 30-day mission time for the UHS.

The Hale Fire pumps are skid mounted diesel driven pumps. The Hale pumps and the associated fire hoses are stored separately, with one set in the north FLEX building and another approximately 3,000 feet away in the south FLEX building. This offers enhanced resilience by diversifying location and accessibility. Site calculations have determined the Hale Fire pumps have a fuel consumption rate of approximately 2.5 gal/hr. The pump skid assembly includes a minimum of 190 gallons of fuel. Fuel tank replenishment would therefore be required approximately every 76 hours8.796296e-4 days <br />0.0211 hours <br />1.256614e-4 weeks <br />2.8918e-5 months <br />, providing long operational capability.

Protection from Flooding As previously discussed, flooding at RBS is assumed to be created by occurrence of the PMP.

This event results in ponding in local areas less than elevation 96 MSL. The grade near the circulating water flume is at approximately an elevation of 105 MSL. The north FLEX building top of foundation elevation is 132 MSL and the south building top of foundation is 110 MSL.

These elevations are well above any ponding that is predicted in the PMP. It is therefore concluded that postulated flooding would not adversely impact the availability of the circulating

RBG-48323 Page 12 of 19 water flume replenishment equipment or impose limitations on freedom of movement following an accident.

Protection from Wind (Hurricane and Tornado)

The flume structure and FLEX equipment storage buildings are structurally robust to withstand design basis hurricane-level winds. The FLEX buildings are designed to withstand wind speeds in excess of the site design basis speed of 100 mph. The two FLEX Buildings are located greater than 3,000 feet apart and perpendicular to the prominent tornado paths to ensure that a single event will not damage both buildings. This FLEX building design and separation satisfies the requirements of NEI 12-06, Section 7.3.1. The flume is a low-rise structure comprised of thick concrete walls. Exposure to tornado winds or missiles is not expected to cause catastrophic damage to the flume that would cause it to lose significant water inventory. The majority of the flume walls are at least 2.5 thick with nominally 3 of the wall projecting above grade with the balance of the structure buried below grade. These walls meet site design criteria for preventing perforation from design basis tornado missiles. Three small segments of the flume have 2 thick walls, again, nominally projecting 3 above grade but with slightly less horizontal reinforcement than needed to meet the missile perforation resistance criteria given in the site Structural Design Criteria. While tornado missiles may pose localized risk, the flumes low-rise design and substantial wall thicknesses provide protection against significant water loss.

Protection from Seismic Events Seismic capability of the circ water flume was assessed by considering Operational Basis Earthquake (OBE) and SSE loadings. The limiting structural elements were evaluated using the same load combinations listed in the USAR as applied to the original SCT basin design.

Structural demand for load combinations including OBE were compared to American Concrete Institute (ACI) working stress criteria, and load combinations including SSE were compared to ultimate strength design capacities. Finite element modeling using computer program ANSYS was used to determine soil pressure on the underground portions of the flume wall due to surcharge loadings. Analysis results show that the flume meets structural acceptance criteria when considering seismic loading combined with other applicable load cases.

Entergy evaluations also address the seismic capability of underground fire protection piping and segments of HDPE that are available to convey water under the SOCA perimeter used to supply water from the circ water flume to the SCT. Stresses resulting from load combinations involving SSE were compared to 1.8 times the normal allowable stress for metallic piping and 1.2 times the normal allowable stress for HDPE piping. The piping was evaluated to ASME B31.1 using computer program AutoPIPE. ASME Code Case CC N-755-1 was applied for the HDPE piping. Analysis results show pipe stresses remain within acceptable limits when considering seismic loading combined with other applicable load cases.

The FLEX equipment storage buildings are qualified to seismic design standards ASCE 7-05 and ASCE 7-10.

RBG-48323 Page 13 of 19 Dose Entergy calculations have determined the SCT can be accessed four days following a DBA with more than a 30 hour3.472222e-4 days <br />0.00833 hours <br />4.960317e-5 weeks <br />1.1415e-5 months <br /> stay time. Since the circ water flume, pipe connections, fire hydrants, and FLEX storage buildings are remote with respect to the SCT, this evaluation bounds the flume makeup locations. As makeup is not required until day 10, it is concluded that the circ water flume, associated pipe connections, fire hydrants, and FLEX buildings will be accessible due to dose to execute the circ water flume makeup.

Conclusions In summary, the SCT replenishment via the circulating water flume meets RG 1.27, Revision 2, requirements for reliable availability and freedom of movement to support makeup within 30 days. Additionally, this method provides replenishment flow and available volume that allow the UHS to exceed the 30-day capacity requirements RG 1.27, Revision 2.

3.5 PHYSICAL SEPARATION AND REDUNDANCY Physical separation exists among the critical elements (deep well pumps, Fire Pump House, circ water flume, FLEX buildings, and SBO generator storage), minimizing the risk of a single natural phenomenon affecting both makeup sources. Makeup to the SCT is required by day 10 post-DBA, with dose rates allowing personnel access by day 4. The site has procedures in place for implementing FLEX actions that address deploying equipment in challenging conditions that include flooding, storm damage to site infrastructure, and debris accumulation. Similar methods to assure that equipment needed for SCT makeup can be safely deployed and haul paths are available may be used if needed.

The redundancy of the two makeup sources further improves the reliability of the UHS under natural phenomena scenarios and the assurance of the continuous capability of the sink to perform its safety functions in accordance with RG 1.27 Revision 2. Both makeup sources can be used simultaneously, resulting in inherent margin in the available makeup inventory and the rate at which it can be provided to the SCT.

3.6 NRC-REQUESTED INFORMATION In a letter acknowledging the withdrawal of the 2014 LAR (Reference 4), the NRC requested four items to be addressed in a resubmittal. These are listed and addressed below:

1. Provide the basis for why accounting for leakage, which compromises a safety function, is not part of RBS's design basis for UHS inventory.

Entergy has revised the design analysis calculation for UHS inventory to include leakage. This LAR includes leakage (see item 2 below) as an assumed loss from the UHS and therefore part of the design basis.

RBG-48323 Page 14 of 19

2. If leakage is determined to be part of the licensing basis, specify a leakage limit from the SSW to NSW.

The leakage limits assumed in the associated design calculations are as follows:

15 GPM per division (30 GPM total) is assumed for leakage out of SSW. This includes leakage into Normal Service Water (NSW). Leakage out of SSW is identified and tracked by operator rounds. Recent leakage rates prior to this submittal were approximately 3.55 GPM for Division I/III and 1.38 GPM for Division II. The current design limit is 6.9 GPM per division. Therefore, the leakage rate is within the current design limit.

1.5 GPM per division is assumed for unrecovered leakage at the MS-PLCS compressors.

A total of 400,000 gallons of leakage for the post DBA operating period is assumed from the single failure of one SSW return header isolation valve (SWP-MOV96A or SWP-MOV96B) failing open until it can be manually closed. This leakage would also be into NSW but is in addition to the 6.9 GPM/15 GPM discussed above.

3. Provide the basis for why the operation of one division of ECCS and SSW is the bounding single failure when determining UHS inventory requirements.

This LAR revises the assumed single failure from the Division II EDG to one of the SSW return header isolation valves (SWP-MOV96A or SWP-MOV96B) failing open, which is the bounding single failure with respect to inventory.

4. From the submittals provided, the NRC staff could not verify that the alternative sources of makeup water to the UHS provide acceptable methods to replenish the UHS. Provide more detail on the three alternate sources of makeup water with regards to capacity, implementation, and design.

The alternate sources of makeup water credited in less than 30 days are discussed above in Sections 3.3 and 3.4, which include the deep well pumps and the circulating water flume. The capacity, implementation, and design of these sources are discussed in Sections 3.3 and 3.4.

4.0 REGULATORY EVALUATION

4.1 APPLICABLE REGULATORY REQUIREMENTS/CRITERIA 10 CFR 50.36 10 CFR 50.36, Technical Specifications, defines the content required in TS. Specifically, 10 CFR 50.36(c)(3) requires that the TS include SR requirements relating to test, calibration, or inspection to assure that the necessary quality of systems and components is maintained, that

RBG-48323 Page 15 of 19 facility operation will be within safety limits, and that the limiting conditions for operation will be met. The proposed change to SR 3.7.1.1 increases the minimum UHS cooling tower basin water level in order to maximize UHS inventory. This improves the ability of the UHS to perform its design functions and continues to ensure that limiting conditions for operation will be met.

Based on this evaluation, the proposed SR revision continues to support compliance 10 CFR 50.36(c)(3).

General Design Criteria Appendix A, "General Design Criteria (GDC) for Nuclear Power Plants," to 10 CFR Part 50 establishes the minimum requirements for the principal design criteria for water-cooled nuclear power plants. The following criteria are applicable for this review:

Criterion 2 Design Bases for Protection Against Natural Phenomena, requires that SSCs important to safety shall be designed to withstand the effects of natural phenomena such as earthquakes, tornadoes, hurricanes, floods, tsunami, and seiches without loss of capability to perform their safety functions. The design bases for these SSCs shall reflect: (1) appropriate consideration of the most severe of the natural phenomena that have been historically reported for the site and surrounding area, with sufficient margin for the limited accuracy, quantity, and period of time in which the historical data have been accumulated, (2) appropriate combinations of the effects of normal and accident conditions with the effects of the natural phenomena, and (3) the importance of the safety functions to be performed.

The proposed change to the licensing basis credits use of makeup sources to meet UHS design functions. As discussed in Sections 3.3 and 3.4, these sources have been shown to be reliable, with at least one makeup source available following the effects of natural phenomena. This ensures the continuous capability of the sink to perform its safety functions in accordance with RG 1.27 Revision 2, which is an NRC-accepted basis for implementation of GDC 2.

Criterion 44 Cooling Water, requires, in part, that a system to transfer heat from SSCs important to safety, to an ultimate heat sink shall be provided. The system safety function shall be to transfer the combined heat load of these SSCs under normal operating and accident conditions. Suitable redundancy in components and features, and suitable interconnections, leak detection, and isolation capabilities shall be provided to assure that for onsite electric power system operation (assuming offsite power is not available) and for offsite electric power system operation (assuming onsite power is not available) the system safety function can be accomplished, assuming a single failure.

The design basis functions of the UHS are assured by the use of the deep well pumps and the circulating water flume as alternate makeup sources, which are evaluated in Sections 3.3 and 3.4. This meets the intent of RG 1.27 Revision 2, which is an NRC-accepted basis for implementation of GDC 44.

The proposed changes are consistent with the applicable regulations and regulatory guidance.

4.2 PRECEDENT

RBG-48323 Page 16 of 19 The crediting of alternate makeup sources to ensure UHS safety functions based on RG 1.27 requirements is similar to the following Palo Verde submittal:

Palo Verde LAR, Proposed Amendment to Bases for Technical Specification Section 3/4.7.5, dated December 7, 1994 In this LAR, Palo Verde reduced the capacity of the UHS without makeup from 27 days to 26 days. Palo Verde indicated that the RG 1.27 Revision 2 requirement to ensure continuous capability of the UHS to perform its safety functions is maintained based on the availability of a reliable makeup source prior to depletion of the initial UHS capacity. This was based on it being highly unlikely that a natural phenomenon could render all three onsite wells used for makeup inoperable; and even if the onsite wells were inoperable, a new well could be drilled and put into operation within the necessary timeframe to ensure continuous operation of the UHS.

The change to increase the UHS minimum water level is similar to changes approved in the following submittals:

Sequoyah Nuclear Plant LAR, Ultimate Heat Sink (UHS) Temperature Increase and Elevation Changes, Dated July 12, 2006 Callaway Plant LAR, Revision to Technical Specification 3.7.9, Dated December 13, 2012 4.3 NO SIGNIFICANT HAZARDS CONSIDERATION ANALYSIS Entergy Operations, Inc. (Entergy) is requesting an amendment to the license of River Bend Station Unit 1 (RBS). The proposed amendment would modify the RBS licensing basis through a revision of the Updated Safety Analysis Report (USAR) to credit makeup to the ultimate heat sink (UHS) in less than 30 days to account for operation with more than one division of standby service water in operation. Additionally, the proposed amendment would revise Technical Specification (TS) Surveillance Requirement (SR) 3.7.1.1 to increase the minimum UHS cooling tower basin water level in order to maximize UHS inventory.

Entergy has evaluated whether or not a significant hazards consideration is involved with the proposed amendment(s) by focusing on the three standards set forth in 10 CFR 50.92, "Issuance of amendment," as discussed below:

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

Response: No.

The UHS does not initiate any accidents discussed in Chapter 15 of the RBS USAR and the proposed changes will have no effect on previously evaluated accidents. The UHS is utilized to remove heat loads from plant systems during normal and accident conditions. This function is not expected or postulated to result, in the generation of any accident and continues to adequately satisfy the associated safety functions with the

RBG-48323 Page 17 of 19 proposed changes. Therefore, the probability of an accident presently evaluated in the safety analyses will not be increased because the UHS function does not have the potential to be the source of an accident. The proposed change to increase the UHS minimum water level does not alter the function, design, or operating practices for plant systems or components. The proposed addition of credit for replenishment from either the deep well pumps or the circulating water flume ensures the UHS remains capable of meeting the requirements of Regulatory Guide (RG) 1.27 Revision 2 to provide sufficient inventory to support post loss of coolant accident (LOCA) design basis accident (DBA) heat removal for 30 days. These makeup sources are highly reliable and can be implemented following a DBA in time to ensure the continuous capability of the UHS to perform its safety functions. The multiple makeup sources provide redundancy, and physical separation exists between the critical components, minimizing the risk of a single natural phenomenon affecting both makeup sources. In the unlikely event that both makeup sources are compromised, substantial time is available for repair prior to makeup being required. Since the safety functions of the UHS are maintained, the systems that ensure acceptable offsite dose consequences will continue to operate as designed.

Therefore, 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 UHS function is not an initiator of any accident and only serves as a heat sink for normal and upset plant conditions. The reliability, redundancy, and physical separation of the components for the proposed makeup sources ensure that the UHS meets the requirements of RG 1.27 Revision 2 to ensure the continuous capability to perform its safety functions. The increase to the water level of the UHS cooling tower basin only alters the parameters for UHS operation while the safety functions of the UHS and systems that transfer the heat sink capability continue to be maintained. These changes have no effect on the ability of the UHS to perform its design function. The UHS function provides accident mitigation capabilities and does not reflect the potential for accident generation. Therefore, the possibility for creating a new or different kind of accident is not created because the UHS is only utilized for heat removal functions that are not a potential source for accident generation.

Therefore, the proposed change does not create the possibility of a new or different kind of accident from any accident previously evaluated.

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

Response: No.

The proposed change does not involve a change to any fission product barrier, i.e., fuel cladding, reactor coolant system or containment structure. There is no change in the ability of the UHS to perform its safety function of providing cooling water to certain

RBG-48323 Page 18 of 19 safety-related loads post DBA. Since the safety functions of the UHS are maintained, the systems that ensure acceptable offsite dose consequences will continue to operate as designed. Additionally, the proposed changes do not require the modification of component setpoints utilized for automatic mitigation of accident conditions or other equipment necessary for accident mitigation. These changes allow the UHS to continue to meet the requirements of RG 1.27 Revision 2.

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

Based on the above, Entergy concludes that the proposed change presents no significant hazards consideration under the standards set forth in 10 CFR 50.92(c), and, accordingly, a finding of "no significant hazards consideration" is justified.

4.4 CONCLUSION

S 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 Commissions 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

A review has determined that the proposed amendment would change a requirement with respect to installation or use of a facility component located within the restricted area, as defined in 10 CFR 20, or would change an inspection or surveillance requirement. However, the proposed amendment does not involve (i) a significant hazards consideration, (ii) a significant change in the types or a significant increase in the amounts of any effluents that may be released offsite, or (iii) a significant increase in individual or cumulative occupational radiation exposure. Accordingly, the proposed amendment meets the eligibility criterion for categorical exclusion set forth in 10 CFR 51.22(c)(9). Therefore, pursuant to 10 CFR 51.22(b), no environmental impact statement or environmental assessment need be prepared in connection with the proposed amendment.

RBG-48323 Page 19 of 19

6.0 REFERENCES

1. Regulatory Guide 1.27, Ultimate Heat Sink for Nuclear Power Plants, Revision 2, (ADAMS Accession No. ML003739969), dated January 1976

2. Entergy Letter to NRC, License Amendment Request 2013-18, Revision of Ultimate Heat Sink Design Capacity, (ADAMS Accession No. ML14051A170), dated February 10, 2014

3. Entergy Letter to NRC, Withdrawal of License Amendment Request, (ADAMS Accession No. ML14212A398), dated July 7, 2014

4. NRC Letter to Entergy, River Bend Station, Unit 1 - Withdrawal of Requested Licensing Action, License Amendment Request RE: Ultimate Heat Sink Design Basis (TAC No.

MF3601), (ADAMS Accession No. ML14190B134), dated July 23, 2014

5. NRC letter to Entergy, "River Bend Station - Integrated Inspection Report 05000458/2023003 and Notice of Violation," (ADAMS Accession No. ML23310A032),

dated November 13, 2023

6. NRC NUREG-0989, Supplement No. 3, Safety Evaluation Report Related to the Operation of River Bend Station, dated August 1985 7.0 ATTACHMENTS

1. Proposed USAR Markups

2. Technical Specification Page Markups

3. Revised (Clean) Technical Specification Pages

4. Technical Specification Bases Page Markups (Information Only)

RBG-48323 Proposed USAR Markups

21 Replenishment from either the deep well pumps or the circulating water flume is credited starting by day 10 to replenish the UHS water storage basin in less than 30 days.

RBS USAR The domestic water and sanitary drains and disposal systems are in continuous use and do not require any testing after the initial testing. Before placing in service, the domestic water system will be inspected and tested hydrostatically. Sanitary waste is monitored by grab sampling on a weekly basis to verify that effluent is within discharge limitations of the NPDES permit.

9.2.4.5 Instrumentation Requirements 9.2.4.5.1 Domestic Water System Domestic water is provided by the Consolidated Water District No. 13 Water Supply System.

Each domestic hot water generator is provided with an integral thermostat to control hot water at a nominal 140°F.

9.2.4.5.2 Sanitary Drains and Disposal System Local controls are provided for manual or automatic operation of the lift station.

In the automatic mode of operation, the lift station sewage pumps start and stop according to the liquid level in the wet well. A high level condition from lift station SLS 1, which serves the protected area, activates an alarm in the auxiliary control room.

9.2.5 Ultimate Heat Sink The standby cooling tower and water storage basin forms a part of the standby service water system which functions as the ultimate heat sink (UHS) for River Bend Station (Fig. 9.2-11). The location of the UHS standby cooling tower with respect to the reactor building is shown in Fig. 1.2-2. Service water piping to and from the UHS is shown schematically in Fig. 9.2-1 b through 9.2-1f.

9.2.5.1 Design Bases The UHS is designed in accordance with the following criteria:

1.

The UHS is designed to provide sufficient cooling water to permit safe shutdown and cooldown of the unit and to maintain it in a cold shutdown condition, i.e., reactor temperature below 105°F, when normal cooling towers are unavailable. Cooling water for normal station operation, i ing shutdown, is provided by the normal cooling towers.

2.

The capaci th UHS water storage basin is designed to provide necessary cooling for the period of time :aG-days) needed to evaluate the situation, to take corrective action to mitigate the consequences of an accident, and if required to take any necessary measures to permit water replenishment. In addition, alternate methods are available for ensuring the continued capability of the sin eyond 30 days (Section 9.2.5.2).

3.

The UHS cooling tower and st rage basin is designed to withstand the effects of natural phenomena such as earthqu kes, tornadoes, hurricanes, and floods as described in Sections 3.2, 3.3, 3.5, and 3.8.

Revision 27 9.2-18

The initial inventory plus a credited replenishment of 2,512,800 Gal is available an internal inventory of 6,778,000

, and leakage For inventory analysis, the worst case single failure of either SWP-MOV96A or B (Standby Service Water Return Header Isolation Valves) is postulated to occur immediately after the trip. For temperature analysis, the worst-case single failure of the Div II SCT fans is postulated to occur immediately after the trip.

114 ft 5 in RBS USAR

4.

The UHS is designed to withstand the effects of external missiles and internally generated missiles as described in Section 3.5 and pipe whip and jet impingement forces associated with high and moderate energy pipe breaks as described in Section 3.6.

5.

The UHS is designed to operate under emergency conditions only. Normal cooling for service water including shutdown is accomplished by the cooling tower in the service water cooling system and the normal service water heat exchangers as described in Sections 9.2.1 and 9.2.12.

6.

The UHS is designed to perform its intended safety function assuming any single active or passive failure coincident with a loss of offsite power.

7.

The UHS is designed to be capable of isolating individual components, systems, or piping if required so that safety functions are not compromised.

8.

The UHS is designed to Seismic Category I criteria as described in Section 3.7.

9.

The UHS is designated Safety Class 3 as defined in Section 3.2.3.3.

10.

The UHS design performance was verified by test runs during initial plant operation in accordance with the procedures set forth in ASME Performance Test Code 23, "Atmospheric Water Cooling Towers"(2> (the issue in effect at the time of the tests).

..,,...,.'V"'V_.... 9.2.5.2 System Description c:J The UHS at River Bend Station consists of one 00 percent Seis Ic Category I c~o~~l~~e~-and one 100 percent capacity water storage basin rl"he basin holds pproximately 6,426,014 gal of usable water at the minimum water level of

• to the minimum pump submergence level of 65 ft O in to make up for drift -aRG evaporative lossesf

~

operation. ~~mponent design data are give~~

ble 9.2-15.

~

--............,._,.,..,.._,...,._,The cooling t~

designed to nominally remove ~

x 106 Btu/hr at a maximum service water flow of 33,000 gpm. Design temperature for cold water leaving the tower is 93°F, corresponding to a design tower inlet water temperature of 116°F.

The design ambient wet-bulb temperature of 81 °F, for evaluating peak UHS water storage basin temperature, was based upon the maximum mean 1-day wet bulb temperature of 80.3°F recorded on July 27, 1969.

For evaluating UHS evaporative losses, the 30-day weather data used, starting June 6, 2009, was based on the worst average combination of controlling parameters having the highest evaporation potential.

The maximum allowable cold water temperature is nominally 95°F, corresponding to the value assumed for evaluation of the containment heat removal systems (Section 6.2.2).

Heat transfer to standby service water is seen to occur immediately after a OBA, postulated as a large break of a main steam line (DBA-MSL) coincident with a complete loss of offsite power. The loss of offsite power is assumed to last for the full 30 day post shutdown period. The single faih::1re of the Di¥ision II diesel generator is postulated to oeeur irnrnediately after trip.

Revision 27 9.2-19

114 ft 5 in 6,778,000

~T =

(HR)

Q Cp where:

~ T = Cooling range (°F)

HR = Heat rejection rate (Btu/hr)

Q = Service water flow (lbm/hr)

RBS USAR Cp = Specific heat of water (Btu/lbm °F)

Cold water temperatures were then interpolated from the performance curves.

Hot water temperatures were found from the following relationship:

Hot Water Temp= Cooling Range+ Cold Water Temp Values of hot water temperature calculated using the above methods are conservative, yielding results higher than expected actual temperatures. A cooling tower operating in a closed loop dissipates all the heat rejected to it by allowing hot water temperatures to rise or fall to an equilibrium point defined by the amount of heat the ambient air is capable of picking up. For conservatism, the analysis of cooling tower operation disregards the dampening effect the large volume of water stored in the basin has upon the system operating temperatures.

During operation, some portion of increasing or decreasing plant heat loads goes toward raising the basin water's sensible heat, while the remainder is discharged by the tower through forced evaporation. As a result, cold water temperatures tend to follow the changes in heat rejection rates, but reach the calculated values only in the long term. The calculated values of cold water temperatures, therefore, should be considered as conservative upper boundaries instead of actual temperatures.

During the first 1 hr after shutdown, all of the heat rejected from the station is assumed to go directly toward increasing the temperature of th water stored in the SCT basin During this time, S:J no credit is taken for heat removal by natural e poration from either the pool urface or in the tower fill. Based on the analysis, at shutdown th re is a total of approximately,

gal of water in the basin corresponding to a water level o

• (this includes water to an elevt ion of 65 ft O in, which is the minimum pump submergence level). From Table 9.2-10, 8.238 107 Btus are rejected to service water during the first 1 hr. This will raise the average temperature of the basin water by 1.55°F.~

~~

........... --~~

The anticipated maximum SCT basin temperature prio to shut wn i 8°F.

At 1 hr after shutdown, the average basin water temperature would be 8°F +.

or F. The first 1 hr represents all of the heat rejected to standby service water, which raises the sensible heat of the basin. The cooling tower fans may be started at 1 hr after shutdown without affecting the ability of the ultimate heat sink to remove plant heat.

For evaluating peak UHS water storage basin temperature, forced evaporation was calculated by the following relationship:

E = (TH) C Revision 27 9.2-21

RBS USAR (LH)p where:

E = Evaporation (gal)

TH = Total integrated heat (Btu)

LH = Latent heat of incoming water (Btu/lbm) p = Density of incoming water (lbm/ft3)

C = Conversion factor of 7.481 qal/ ft3 As stated previously, a fraction of the heat load goes to raising the sensible heat of the air. Actual forced evaporation is expected to be less than the calculated value.

The UHS water inventory loss due to evaporation for the 30-day period following the OBA is calculated using the computer program UHSSIM (Reference 4). The UHSSIM program provides a tool for predicting the transient temperature, mass, and dissolved solids content of power plant ultimate heat sinks that consist of a basin and cooling tower. The program performs an analysis of UHS cooling tower heat and mass transfer characteristics coupled with the mass and energy balance for the basin. It simulates the response of cooling towers and basins to varying weather conditions during and following a postulated accident.

The UHSSIM computer program methodology was originally developed by the University of Illinois, at Urbana-Champaign, under a contract with the NRC, specifically for evaluating UHS forced draft cooling tower designs for compliance with Regulatory Guide (RG) 1.27 (Reference 5). In the UHSSIM program, the algorithms in the original program methodology have been enhanced to provide more stringent convergence criteria, and to include additional physical phenomena and more modern methods of analysis.

RG 1.27, Rev. 2 states that, for evaluation of the UHS, the meteorological conditions resulting in the maximum evaporation and drift should be the worst 30-day average combination of controlling parameters based on regional climatological information. The weather search capabilities of UHSSIM were used to identify which 30-day summer period would produce the highest evaporation. The U.S. National Climatic Data Center (NCDC) of the National Oceanographic and Atmospheric Administration (NOAA) publishes historic hourly weather observations for the United States. River Bend Station is approximately 20 miles north of the Baton Rouge Metro Airport, for which the NCDC has digital hourly weather records back to July 2, 1948. The raw weather observations for the Baton Rouge Metro Airport were obtained from the NCDC for the time period of July 2, 1948 to November 29, 2014. The 30-day time period starting on June 6, 2009 was found to result in the highest evaporation from the UHS.

The following estimated maximum losses occur for the UHS during the 30-day period with the highest evaporation potential:

Revision 27 Loss up to 24 hr (gal) 9.2-22

The cooling tower storage facility has an initial inventory of approximately 6,778,000 Gal at the minimum basin water level of 114 5 (as mentioned earlier). In addition, a minimum of 2,512,800 Gal of inventory is credited as replenishment in less than 30 days for a total minimum credited inventory of 9,290,816 Gal.

xxxx xxxx Replace this Table with Insert A on the next page.

9.21x106 85,643 Replace this table with Insert AC1 Air Compressor (cooling water not recovered)

Leakage to N 20 minutes Ior to Isolation a 1 SWP*MOV96 RBS USAR A or B 1.00 X 1 1.00 X 105 Total whish is 6.12 x 106 gal ef water lost.

The quantity of water naturally evaporated from the surface of the UHS storage basin is minimal for a semi-enclosed basin such as this. For natural evaporation to occur, the vapor pressure of the ambient air must be lower than the vapor pressure of the water. During UHS operation, the air near the surface of the water is saturated at the temperature of the cold water leaving the fill material. Correspondingly, the water surface temperature is at or below this temperature, thus inhibiting natural evaporation.

A net solar and atmospheric heat load of 6.819x106 Btu/day was assumed to be impressed upon the water surface through the 54 ft x 54 ft center plenum and a corresponding natural evaporation rate to dissipate this heat added into the total integrated evaporation and drift values to determine the available basin volume shown in Table 9.2-12. Sun heat load is based conservatively on solar radiation incident to a horizontal surface at 30°-45' north latitude and assuming no cloud cover.

Maximum cooling tower drift loss is assumed to be 0.01 percent of the standby service water flow rate, based upon data furnished by the UHS supplier. Drift loss is a function of the internal tower design and is independent of ambient conditions (e.g., wind speed, temperature, humidity).

Cooling towers of similar design were tested at Oak Ridge National Laboratory by the Environmental Systems Company for the EPA. In their report Development and Demonstration of Low-Level Drift Instrumentation, October 1971, average drift losses of 0.005 percent were found.

The towers tested at Oak Ridge National Laboratory had two-pass wood slat drift eliminators. The towers described herein utilize three-pass, close space polyvinyl chloride drift eliminators with lower air velocities which should be more efficient.

Thus, basin capacity calculations, based upon 0.01 percent drift loss, conservatively predict tower drift loss.

The cooling tow&r &torag& facility has approximately 6,414,QQQ gal at the minim1:1m easin water le1.iel of 111 ft 1 Q in (as mentioned earlier). This excludes the approximate 70,000 gallons, which represents the water from the minimum pump submergence el. of 65 ft O in to the basin floor elevation of 64 ft 6 in. During the first 30 days of operation following a DBA, approximately 6

6.12 x 106 gal of water are lost due to non-returned cooling water supply to PVLCS, leakage to NSW, evaporation and drift. Based on the analysis, 297,900 gal remain available as a design safety margin (see Table 9.2-12).

~

The increase in water chemistry concentration due to the absence of blowdown from the system has no effect on the operation of the UHS or the standby service water system during 30 days of operation. However, the system is operated with a controlled makeup if the normal plant makeup wells are operable following an accident.

Revision 27 9.2-23

114 ft 5 in RBS USAR The makeup water required after 30 days of operation is a maximum of approximately 168,000 gal/day. Primary makeup water is provided by the normal plant makeup wells which are describe in Section 9.2.3. Makeup to the basin is manually controlled to maintain the water level above e

• which is the minimum basin operating level. Should the primary makeup water source become unavailable, this makeup can be supplied by any of the following alternate methods:

1.

Use temporary power to power the plant deep/shallow well pumps and provide makeup through the existing 4"-diameter pipeline into the SCT basin. Also, Fire Protection System can be used to provide make-up water into the SCT basin.

2.

Temporary diesel driven pump, hoses, and valves can be used to pump CWS flume basin water into the SCT basin.

3.

Temporary tank trucks, hoses and diesel driven pumps to transfer Mississippi River water into the SCT basin.

A hypochlorite feed system is provided to inhibit biological growth in the UHS water storage basin.

This system consists of a 1,000-gal. feed tank, a metering pump, a recirculation pump, and a network of distribution piping to allow treatment of separate compartments within the basin from the surface to the bottom elevation. A programmable controller sequences the opening and closing of solenoid valves on each branch of the piping network for a set amount of time to allow an adequate chemical dosage in each zone. The recirculation pump is a self-priming type which draws from the basin water surface and provides a medium for injection of the chemical and adequate dispersion through the diffuser pipes. An alternate means of adding chemicals can be achieved by using the systems tank drain valve, direct addition to the basin will allow for dispersion of the chemical through out the basin.

Sodium hypochlorite or alternative biocides or corrosion inhibitors may periodically be added to the UHS basin as needed, based on sampling and analysis performed by the chemistry department.

Failure of any portion of the hypochlorite feed system inside the UHS as a result of safe shutdown earthquake or other condition will not adversely affect the standby service water system. These components are plastic pipe and fittings routed in each of the basin compartments, except the one in which the standby service water pumps are located. Water velocity in the basin will be low when the pumps are operating, and sufficient forces will not be developed to draw failed components into the pumps.

The UHS can be used to dissipate residual heat produced when a reactor is shut down for refueling. During this period and during normal plant testing the cooling towers operate with a controlled blowdown and makeup.

Under normal operation, the fuel pool makeup is taken from the condensate storage tanks.

Should this source become unavailable, provision is made to draw necessary makeup from the standby cooling tower basin (Fig. 9.2-1).

Under normal operation, water for fire protection is supplied from the fire protection storage tanks.

Should this source become unavailable, 150 gpm of standby service water can be provided from the UHS for a maximum of 2 hr to hose stations in critical areas.

Revision 27 9.2-24

114 ft 5 in with makeup provided as previously discussed ooling tower storage facility is 95 ft. The minimum tower basin operating level is at el

• . After 30 days of operation

, the tower basin operating level is above 65 ft 0 in, the minimum pump submergence level.

The standby cooling tower consists of four equal area cells, each having an induced draft fan system. The cells are completely isolated from each other and have separate missile protected inlet distribution piping systems. Each cell has a design flow rate of 8,250 gpm. Two fully operating cells are required for safe shutdown.

The standby cooling tower is of counter flow induced mechanical draft design. The distribution system supplies the hot water evenly over the area of fill. The water flows through the multicell dense vitreous clay fill which is approximately 8 ft deep. By dividing the flow through the cells of the fill, enough water area is exposed to the air stream to provide sufficient evaporation for the removal of the required amount of heat. The induced draft fans draw air through the cells to aid the evaporation rate. Located above the distribution system and before the fans are the drift eliminators. Drift eliminators are a zigzag pattern of channels which prevent water carryover via the central discharge plenum.

The standby cooling tower is 158 ft 6 in inside diameter and is supported by a foundation above its storage basin. The storage basin has a normal water depth of 55 ft 6 in. The top of the tower is approximately 47 ft above the normal water level in the basins. The structure is tornado missile protected and designed to Seismic Category I requirements (Section 3.8.4). Sixty percent of the water storage basin is located below grade and is conservatively designed to prevent seepage.

The standby cooling tower basin utilizes watertight concrete in the construction of mat and walls.

The standby cooling tower uses five vaneaxial fans for each of four tower cells in an induced draft system arrangement. The fans and tower internals are located inside the tower structure and are protected by the walls and roof, which are designed to withstand both horizontal and vertical tornado missiles (Section 3.5.1).

Electric power to the four groups of five fans is supplied by two feeders from two standby 4.16-kV buses via two standby 4.16-kV - 480-V, 1-MVA transformer and two standby 480-V motor control centers in the cooling tower. The two standby 4.16-kV buses are those associated with the standby diesel generators A and B. Each feeder has the capability to provide electric power to only two groups of five fans of the cooling tower.

The cooling tower water storage facility is filled with well water, which is treated for bacteria control. A biocide additive is manually injected into the basins in quantities necessary to control seasonal variations in bacteria growth.

The drift eliminators are of the zigzag type (three pass close space) and have enough passes to ensure a maximum free water carryover of 0.01 percent. They are assembled in sections which are supported from the fan deck by steel rods. The drift eliminators are fire resistant polyvinyl chloride (PVC) with a flame spread rating below 25.

Fig. 9.2-11 gives further details of the cooling tower arrangement.

The standby service water pumps take suction from the cooling tower water storage facility. The pumps are located in fully missile protected Seismic Category I pump well structures. Pump well structures are designed such that sufficient net positive suction head (NPSH) is available for the standby service water pumps to drain the water to el 65 ft 0 in (Section 9.2.7). A minimum pump submergence of approximately 34 in is provided for vortex free operation.

Revision 27 9.2-25

Divisions RBS USAR 9.2.5.3 Safety Evaluation The ultimate heat sink consists of one 200 percent cooling tower and one 100 percent water storage basin.

The cooling tower water storage facility is a partially below grade, missile protected, Seismic Category I structure which can withstand each of the most severe natural phenomena expected, other site related events, and reasonable combinations of less severe natural phenomena and/or site related events. The method of analysis is similar to that used for other Seismic Category I structures.

The cooling tower structure is designed to withstand the safe shutdown earthquake (SSE). The fill, drift eliminators, fans, and piping are seismically analyzed. The seismic analysis of structures is discussed in Section 3.7.

The cooling tower structure is designed to withstand tornadoes and tornado missiles (Section 3.3 and Section 3.5, respectively). Tower internals are fully protected by the structure.

The cooling tower and the walls of the water storage facility are above the probable maximum flood level (el 95 ft 1 in) (Section 3.4).

Valves and other components essential to the operation of the system are located inside tunnels or inside the standby service water pumphouse. These structures prevent rainwater or snow from impinging on the components of the system, therefore protecting it from freezing or icing.

The water pump suction is more than 50 ft below the water level in the basin, therefore, even in extreme low ambient temperatures it does not experience a freezeup condition. The basin is partially below grade, hence ground temperatures contribute to maintain a water temperature above freezing.

The winter climate extreme minimum temperatures are of such rare occurrence and short-term duration that the plant operation of safety-related systems is not be adversely affected by icing (Section 2.3.1.2).

With the exception of the drift eliminators as described in Section 9.2.5.2, all materials in the UHS complex are designed to be nonflammable in order to negate the possibility of loss of sink function due to fire.

The failure of one diesel generator is considered to be an unlikely event. However, should this event occur, the safe operation of the UHS is not inhibited. Each diesel generator has the capacity required for operating two sets of five fans.

In determining the worst case post-LOCA SSW temperature, the worst single failure of one division of standby cooling tower fans with both i:HliHSteA-Of SSW otherwise responding to design basis event (i.e., LOP-LOCA). This is referred to as a Maximum Safeguard Loads (MSL) case.

In order for the standby cooling tower basin water temperature to be maintained at or below 95°F and to ensure the SSW System pumps provide sufficient flow to the safety related components during a LOP-LOCA, procedures require the following actions:

1.

Start SCT fans one hour into a LOP-LOCA.

Revision 27 9.2-26

Replace with Insert B on next page.

RBS USAR

2.

Throttle the SSW flow to the RHR Heat Exchangers from 5,800 gpm to approximately 3,000 gpm when the SCT water level drops to an elevation of 90 ft (conservatively).

3.

If one of the divisions of the SCT fans fails, at any time, operations may start equipment on affected division provided SCT basin temperature controlled< 95°F.

In deter

• ility oft S, with ay invento~ equirem e

analysis n 9.

appl' ision el). Th s

des*

ent wate s t inimu ed eq td act s w ed arios mini uir to the r DBA dies rater ation re th olled to ain inve The safety analysis of the standby service water system is described in Section 9.2.7.

9.2.5.4 Testing and Inspection Requirements The fans, pumps, and electrical apparatus serving the UHS are tested at regular intervals to ensure their availability.

Isolation valves are also tested on a regular basis to ensure their operability. Tests can be performed with either normal station power or standby power. Tests of the standby service water system pumps and valves are discussed in Section 9.2.7.

The UHS can be used to dissipate residual heat produced when a reactor is shut down for refueling. To demonstrate continued acceptable thermal performance of the UHS, surveillance tests are run on the active components (SSW pumps and fans).

Contribution to thermal performance by passive components such as the ceramic tile fill and spray nozzles is verified by periodic inspections.

9.2.5.5 Instrumentation Requirements Control switches are provided in the main control room for manual operation of the Division I and II standby cooling tower fans. Interlocks are provided to automatically start up a group of fans (one at a time in a timed sequence) when the respective Division I or II standby service water pump has been started. Interlocks are also provided to trip each running fan in the event of fan motor overload.

A Division I and II fan inoperative condition activates the respective standby service water system inoperative alarm in the main control room. An alarm is activated after a time delay in accordance with the system logic when loss of function occurs for any fan in a division when its associated standby service water pump is running.

The water levels in the standby cooling water basin is recorded in the main control room. High and low level alarms for the standby cooling tower basin are provided in the main control room.

The water temperature in the standby cooling water basin is measured at selected elevations throughout the basin, and a composite average is recorded in the control room.

Four wide range (0-100°F) and eight narrow range (70-85°F) RTD's are installed evenly around the center basin with sensors at various depths.

Revision 27 9.2-27

Initial Inventory 6,778,000 gal Credited Replenishment Inventory prior to 30 Days 2,512,800 gal Total credited Inventory 9,290,800 gal 1.Natural Evaporation 23,590 2.Forced Evaporation 7,373,341 3.Drift 47,426 4.PVLCS Air Compressor (cooling water not recovered) 64,800 5.Leakage to NSW from assumed SWP-MOV96A or B fail open prior to isolation 400,000

6. Constant assumed 30 gpm leakage to NSW from SWP-MOV96A or B.

1,296,000 Total 30 Day Losses (gal) 9,205,157 SCT Basin Inventory and Losses Losses for 30 Days (gal)

Insert A

The standby cooling tower is designed to provide sufficient cooling water to safely shut down and cool the unit following a design basis accident assuming the minimum required equipment is used to shut down the unit. However, in determining the basin capacity, all emergency diesel generators are assumed to operate following the DBA and the worst-case single failure of one of the SSW return header isolation valves (SWP-MOV96 A or B) is assumed to fail open immediately after the trip until it can be manually closed. Closure of the SSW return header isolation valves is a 20-minute time critical operator action. The UHS basin is sized in this case to provide a minimum of 21 days inventory without replenishment. For DBA scenarios where no diesel generator failure occurs, operation with more than the minimum equipment is controlled to maintain inventory.

To provide cooldown of the unit assuming no diesel generators fail and the worst-case single failure discussed above, replenishment of the SCT basin is required and credited by day 10 at a minimum flow rate of 87.25 GPM. The standby cooling tower can be replenished by day 10 by the circulating water flume which can transfer water to the standby cooling tower basin using a temporary diesel driven pump, hoses, and the fire protection piping. In addition, the deep well pumps can be powered if necessary, using a temporary diesel generator and used if available to inject water into the basin using the normal cooling tower makeup piping. Both the circulating water flume and deep well pumps can supply the required amount of water. Replenishment of the standby cooling tower basin after 30 days is discussed in section 9.2.5.2.

Insert B

RBG-48323 Technical Specification Page Markups

82.6%.

RBG-48323 Revised (Clean) Technical Specification Pages

SSW System and UHS 3.7.1 RIVER BEND 3.7-3 Amendment No. 81, 185, 196 ACTIONS (continued)

CONDITION REQUIRED ACTION COMPLETION TIME H.

Required Action and associated Completion Time of Condition A, E, or G not met.

H.1 ----------NOTE-----------

LCO 3.0.4.a is not applicable when entering MODE 3.

Be in MODE 3.

12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> I.

Required Action and associated Completion Time of Condition B, D or F not met.

OR Both SSW subsystems inoperable for reasons other than Condition F.

OR Three or four UHS cooling tower fan cells inoperable.

I.1 Be in MODE 3.

AND I.2 Be in MODE 4.

12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> 36 hours SURVEILLANCE REQUIREMENTS SURVEILLANCE FREQUENCY SR 3.7.1.1 Verify the water level of UHS cooling tower basin is 82.6%.

In accordance with the Surveillance Frequency Control Program SR 3.7.1.2 Verify the average water temperature of UHS is 88F.

In accordance with the Surveillance Frequency Control Program (continued)

RBG-48323 Technical Specification Bases Page Markups (Information Only)

21 This assumes system leakage, no emergency diesel generators fail and therefore all are assumed to operate following the DBA, and a single failure of one service water return header isolation valve (SWP-MOV96A or B) occurs which is the worst case single failure with respect to basin inventory.

Makeup water sources are available to replenish the UHS starting on day 10 to meet the 30 day post DBA period requirement (Regulatory Guide 1.27, Rev 2).

See

21

114 ft 5 inches 82.6%

21