NG-18-0066, Six-Month Status Report in Response to June 6, 2013 Commission Order Modifying Licenses with Regard to Reliable Hardened Containment Vents Capable of Operation Under Severe Accident Conditions

Six-Month Status Report in Response to June 6, 2013 Commission Order Modifying Licenses with Regard to Reliable Hardened Containment Vents Capable of Operation Under Severe Accident Conditions

ML18177A261
Person / Time
Site:	Duane Arnold
Issue date:	06/26/2018
From:	Dean Curtland NextEra Energy Duane Arnold
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
EA-13-109, NG-18-0066
Download: ML18177A261 (17)

Text

NEXTera.

EN E RGY~

DUANE June 26, 2018 ARNOLD NG-18-0066 U. S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555-0001 Duane Arnold Energy Center Docket No. 50-331 Renewed Facility Operating License No. DPR-49 NextEra Energy Duane Arnold. LLC's Six-Month Status Report in Response to June 6, 2013 Commission Order Modifying Licenses with Regard to Reliable Hardened Containment Vents Capable of Operation Under Severe Accident Conditions (Order Number EA-13-109)

References:

1. Order EA-13-109, "Order Modifying Licenses with Regard to Reliable Hardened Containment Vents Capable of Operation Under Severe Accident Conditions," dated June 6, 2013(ML13130A067)

2. NextEra Energy Duane Arnold LLC's Phase 1 Overall Integrated Plan in Response to June 6, 2013 Commission Order Modifying Licenses with Regard to Reliable Hardened Containment Vents Capable of Operation Under Severe Accident Conditions (Order Number EA-13-109, dated June 25, 2014(ML14182A423)

3. NextEra Energy Duane Arnold, LLC's Six-Month Status Report and Phase 1 and 2 Overall Integrated Plan in Response to June 6, 2013 Commission Order Modifying Licenses with Regard to Reliable Hardened Containment Vents Capable of Operation Under Severe Accident Conditions (Order Number EA-13-109) dated December 22, 2015 (ML15358A043)

On June 6, 2013, the Nuclear Regulatory Commission ("NRG" or "Commission") issued an Order (Reference 1) to NextEra Energy Duane Arnold, LLC. Reference 1 was immediately effective and directs NextEra Energy Duane Arnold, LLC (hereafter NextEra Energy Duane Arnold) to install a reliable hardened venting capability for pre-core damage and under severe accident conditions, including those involving a breach of the reactor vessel by molten core debris. Specific requirements are outlined in Attachment 2 of Reference 1.

NextEra Energy Duane Arnold, LLC, 3277 DAEC Road, Palo, IA 52324

Document Control Desk NG-18-0660 Page 2 of 2 Reference 1 required submission of a Phase 1 Overall Integrated Plan (OIP) pursuant to Section IV, Condition D, and status reports at six-month intervals thereafter. NextEra Energy Duane Arnold submitted the Phase 1 OIP by letter dated December 10, 2014 (Reference 2). Reference 3 included the required six-month status update, as well as the Phase 2 OIP submittal. The consolidated Phase 1 and 2 OIP document provided a list of the Phase 1 OIP open items, and addressed the NRC Interim Staff Evaluation open items for Phase 1. This letter is being submitted to satisfy the requirements for providing the six-month updates for Phases 1 and 2 of the Order in accordance with Section IV, Condition D.3, of Reference 1.

This letter contains no new regulatory commitments. If you have any questions regarding this submittal, please contact Michael Davis, Licensing Manager at 319-851-7032.

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

Executed on June 26, 2018.

Dean Curtland Site Director, Duane Arnold Energy Center NextEra Energy Duane Arnold, LLC Enclosure cc: Director, Office of Nuclear Reactor Regulation USNRC Regional Administrator Region Ill USN RC Project Manager, Duane Arnold Energy Center USNRC Resident Inspector, Duane Arnold Energy Center

Enclosure to NG-18-0066 NextEra Energy Duane Arnold, LLC's Six-Month Status Report in Response to June 6, 2013 Commission Order Modifying Licenses with Regard to Reliable Hardened Containment Vents Capable of Operation Under Severe Accident Conditions (Order Number EA-13-109) 15 pages follow

Enclosure to NG-18-0066 - NextEra Energy Duane Arnold, LLC's Six Month Status Report for the Implementation of Order EA-13-109,0rder Modifying Licenses with Regard to Reliable Hardened Containment Vents Capable of Operation under Severe Accident Conditions 1 Introduction NextEra Duane Arnold Energy Center, LLC developed an Overall Integrated Plan (Reference 1 in Section 8), documenting the planned installation of a Hardened Containment Vent System (HCVS) that provides reliable hardened venting capability for pre-core damage and under severe accident conditions, including those involving a breach of the reactor vessel by molten core debris, in response to Reference 2.

NextEra Duane Arnold Energy Center, LLC developed an updated and combined Phase 1 and 2 Overall Integrated Plan dated December 22, 2015 (Reference 7),

documenting:

1. The planned installation of a HCVS as described above; and

2. An alternative venting strategy that makes it unlikely that a drywell vent is needed to protect the containment from overpressure related failure under severe accident conditions, including those that involve a breach of the reactor vessel by molten core debris, in response to Reference 2.

This enclosure provides an update of milestone accomplishments since submittal of the combined Phase 1 and 2 Overall Integrated Plan, including any changes to the compliance method, schedule, or need for relief/relaxation and the basis, if any.

2 Milestone Accomplishments At the time of this update, all activities associated with implementation of Phase 1 have been completed. Refer to the Phase 1 Milestone Schedule and Phase 1 ISE Items status for details.

The following milestone(s) have been completed since the six-month update submitted on December 19, 2017 (Reference 9), and are current as of June 1, 2018.

• Submit 6 Month Status Report (Complete with this submittal)

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Enclosure to NG-18-0066 - NextEra Energy Duane Arnold, LLC's Six Month Status Report for the Implementation of Order EA-13-109,0rder Modifying Licenses with Regard to Reliable Hardened Containment Vents Capable of Operation under Severe Accident Conditions 3 Milestone Schedule Status The following provides an update to Part 5 of the combined Phase 1 and 2 Overall Integrated Plan. It provides the activity status of each item, and whether the expected completion date has changed. The dates are planning dates subject to change as design and implementation details are developed.

Phase 1 Milestone Schedule:

Issue preliminary/conceptual design report June 2014 Complete Submit Overall Integrated Implementation Plan June 2014 Complete Initial Outage for Phase 1 Planning Nov. 2014 Complete Submit 6 Month Status Report Dec. 2014 Complete Submit 6 Month Status Report June 2015 Complete Submit 6 Month Status Report Dec. 2015 Complete Design Complete Phase 1 Mar. 2016 Complete Submit 6 Month Status Report June 2016 Complete Operations Procedure Changes Developed Oct. 2016 Complete Site Specific Maintenance and Testing Oct. 2016 Complete Procedures Developed Training Complete Oct. 2016 Complete Implementation Outage End of Complete RF025 Procedure Changes Active End of Complete RF025 Walk Through Demonstration/Functional Test End of Complete RF025 Submit Completion Report 60 days Not Not required for after Required Phase 1 RF025 Page 2 of 15

Enclosure to NG-18-0066 - NextEra Energy Duane Arnold, LLC's Six Month Status Report for the Implementation of Order EA-13-109,0rder Modifying Licenses with Regard to Reliable Hardened Containment Vents Capable of Operation under Severe Accident Conditions Phase 2 Milestone Schedule Submit Overall Integrated Implementation Plan Dec.2015 Complete Hold preliminary/conceptual design meeting Feb 2017 Complete Submit 6 Month Status Report June 2016 Complete Submit 6 Month Status Report Dec.2016 Complete Submit 6 Month Status Report June 2017 Complete Submit 6 Month Status Report Dec.2017 Complete Design Engineering On-site/Complete Jan.2018 Complete Submit 6 Month Status Report June 2018 Complete with this submittal Operations Procedure Changes Developed Oct. 2018 Started Site Specific Maintenance Procedure Oct. 2018 Started Developed Training Complete Oct. 2018 Started Implementation Outage RF026 Not Started Procedure Changes Active RF026 Not Started Walk Through Demonstration/Functional Test RF026 Not Started Submit Completion Report RF026 Not Started Page 3of15

Enclosure to NG-18-0066 - NextEra Energy Duane Arnold, LLC's Six Month Status Report for the Implementation of Order EA-13-109,0rder Modifying Licenses with Regard to Reliable Hardened Containment Vents Capable of Operation under Severe Accident Conditions 4 Changes to Compliance Method There are no changes to the compliance method as documented in the combined Phase 1 and 2 Overall Integrated Plan (Reference 7). However, changes have been made to the design details which affect descriptions contained in Reference 7.

• The HCVS "Nitrogen Supply Isolation at 1A3 ROS" (V43-0642) will be normally closed and locked to prevent inadvertent vent operation. This valve will have to be manually opened at the Remote Operating Station (ROS) in the 1A3 Essential Switchgear Room to supply nitrogen for CV operation and purging.

• The HCVS nitrogen supply and purge pressure control valves (PCV4360 and PCV4361) will be normally closed to prevent inadvertent over pressurization. The PCVs are located at the ROS and will be manually adjusted to the prescribed setpoints after the main pneumatic supply valve is opened (V43-0642).

• The Uninterruptible Power Supply (UPS) originally had the normal power supply from 1832. Analysis identified that 1832 did not have adequate margin to add this load; therefore the normal power supply has been changed to 1815. A receptacle will be installed at the UPS for direct connection to the portable 480 VAC generator.

The power to 1815 will be lost during an ELAP. The UPS will provide power for 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />; the FLEX 480 VAC generator will provide power beyond 24 hrs.

5 Need for Relief/Relaxation and Basis for the Relief/Relaxation NextEra Duane Arnold Energy Center, LLC expects to comply with the order implementation date and no relief/relaxation is required at this time.

Page 4 of 15

Enclosure to NG-18-0066 - NextEra Energy Duane Arnold, LLC's Six Month Status Report for the Implementation of Order EA-13-109,0rder Modifying Licenses with Regard to Reliable Hardened Containment Vents Capable of Operation under Severe Accident Conditions 6 Open Items from Combined Phase 1 and 2 Overall Integrated Plan and Interim Staff Evaluations The following tables provide a summary of the open items documented in the combined Phase 1 and 2 Overall Integrated Plan or the Interim Staff Evaluation (ISE) and the status of each item.

Combined Phase 1 and 2 OIP Open Item Status Phase 1 Open Items

1. Confirm secondary containment bypass leakage is Completed. Appropriate rupture acceptable without an installed rupture disk or retain disk is included in design of an appropriate disk. modification.

2. Perform severe accident evaluation for FLEX DG and Completed. Actions to connect replacement gas to confirm accessibility for use for the FLEX DG and replace post 24 hour2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> actions. nitrogen bottles are performed in the Control Building battery room corridor and 1A3 essential switchgear room. DAEC has completed evaluations of temperature and radiological conditions to ensure that operators can safely access and operate controls and support equipment in these areas.

3. Evaluate tornado/missile effects on HCVS components Complete.

above the protected area of the Reactor Building.

4. Evaluate the system design for H2/CO measures to be Complete.

taken.

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Enclosure to NG-18-0066 - NextEra Energy Duane Arnold, LLC's Six Month Status Report for the Implementation of Order EA-13-109,0rder Modifying Licenses with Regard to Reliable Hardened Containment Vents Capable of Operation under Severe Accident Conditions Phase 1 Interim Staff Evaluation Status Open Items

1. Make available for NRC staff audit Complete.

documentation of licensee The DAEC final design of the HCVS confirmation that secondary utilizes an installed rupture disk.

containment leakage is Procedures for rupturing the disk have acceptable without an installed been developed for use during beyond rupture disk or that an appropriate design bases conditions.

rupture disk, including procedures for rupture during HCVS operation, is included in the HCVS design. (Section 3.1.2, Section 3.2.2.8)

2. Make available for NRC staff Complete.

audit analyses demonstrating DAEC has completed analysis that HCVS has the capacity to demonstrating the HCVS has the vent the steam/energy equivalent capacity to vent the steam/energy of one (1) percent of equivalent to one percent of licensed licensed/rated thermal power thermal power and that the suppression (unless a lower value is justified), pool and HCVS together are able to and that the suppression pool absorb and reject decay heat such that and the HCVS together are able following a reactor shutdown from full to absorb and reject decay heat, power containment pressure will be such that following a reactor maintained below the primary shutdown from full power containment design pressure limit of 53 containment pressure is restored PSIG.

and then maintained below the primary containment design pressure and the primary containment pressure limit.

(Section 3.2.2.1, Section 3.2.2.2)

3. Make available for NRC staff audit Complete.

evaluations of tornado missile DAEC has evaluated the potential effects on HCVS components effects of tornado missiles on HCVS above the protected area of the components above the protected area reactor building. (Section 3.2.2.3) of the reactor building and confirmed that HCVS function will not be impaired. HCVS components located above the protected area of the reactor building are limited to piping components and supports.

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Enclosure to NG-18-0066 - NextEra Energy Duane Arnold, LLC's Six Month Status Report for the Implementation of Order EA-13-109,0rder Modifying Licenses with Regard to Reliable Hardened Containment Vents Capable of Operation under Severe Accident Conditions

4. Make available for NRC staff audit Eliminated.

additional detail on the design features that minimize unintended The DAEC design has been modified cross flow of vented fluids within a since issuance of the ISE. The HCVS unit, including a one line diagram system utilizes a dedicated penetration containing sufficient detail to from the torus to HCVS piping with no confirm the description in the OIP. connecting systems eliminating the (Section 3.2.2.7) possibility of unintended cross flow.

5. Provide a description of the final Complete.

design of the HCVS to address The final DAEC design of the HCVS hydrogen detonation and addresses the potential for hydrogen deflagration. (Section 3.2.2.6) detonation and deflagration with the use of a nitrogen purge of the HCVS piping that ensures hydrogen and oxygen concentrations within the HCVS system are not susceptible to detonation or deflagration (Option 3 of Appendix H of NEI 13-02). The HCVS system isolation is performed by two primary containment isolation valves (PCIVs) to minimize any potential leakage. Prior to use of the system a partial purge of the system is performed to ensure no hydrogen is directly downstream of the PC IVs at the time of actuation. A full nitrogen purge is performed immediately following each period of venting the torus. Each purge is performed with nitrogen flow at sufficient velocity to limit stratification and ensure turbulent flow to preclude retaining hydrogen in the pipe. The piping is sloped upwards from the outboard PCIV to the atmospheric vent discharge to ensure hydrogen will exit the vent through buoyancy. No trapped high points are provided in the piping.

6. Provide a description of the Complete.

strategies for hydrogen control DAEC strategies for hydrogen control that minimizes the potential for are as noted above in response to hydrogen gas migration and Open Items 4 and 5. The HCVS ingress into the reactor building or system utilizes a dedicated penetration from the torus to HCVS piping with no Page 7 of 15

Enclosure to NG-18-0066 - NextEra Energy Duane Arnold, LLC's Six Month Status Report for the Implementation of Order EA-13-109,0rder Modifying Licenses with Regard to Reliable Hardened Containment Vents Capable of Operation under Severe Accident Conditions other buildings. (Section 3.2.2.6) connecting systems and the HCVS piping does not pass through other buildings thus eliminating the potential for migration of hydrogen gas from the HCVS into the reactor building or other buildings. Nitrogen purge of the system prior to use and immediately following isolation of the system prevents detonation or deflagration of hydrogen inside the HCVS (Option 3 of NEI 13-02 Appendix H).

7. Make available for NRC staff audit Complete.

documentation that demonstrates DAEC docketed an assessment of adequate communication between communications capabilities under the remote HCVS operation ELAP conditions in NG-12-0430 locations and HCVS decision "Response to NRC 10 CFR 50.54(f) makers during ELAP and severe Request for Information Regarding accident conditions. (Section Near-Term Task Force 3.2.2.5) Recommendation 9.3, Emergency Preparedness" (ADAMS Accession No. ML12307A120). NRC staff review of this assessment is documented in an NRC Letter dated June 6, 2013 "Duane Arnold Energy Center-Staff Assessment in Response to Recommendation 9.3 of the Near-Term Task Force Related to the Fukushima Dai-lchi Nuclear Power Plant Accident" (ADAMS Accession No. ML13142A320). The NRC staff concluded the communications assessment was reasonable to ensure communications were maintained during an ELAP. The HCVS operating locations are the main control room located in the control building and the Remote Operating Station in the 1A3 switchgear room also located in the control building.

Severe accident conditions do not have an impact on communications in the control building beyond those defined in the communications assessment for ELAP conditions. HCVS decision makers are located in the control room so communication with the operating location in the control room can be Page 8 of 15

Enclosure to NG-18-0066 - NextEra Energy Duane Arnold, LLC's Six Month Status Report for the Implementation of Order EA-13-109,0rder Modifying Licenses with Regard to Reliable Hardened Containment Vents Capable of Operation under Severe Accident Conditions made directly with no equipment requirements. Operators at the Remote Operating Station can communicate with HCVS decision makers via a variety of methods including sound powered phones, hand held radios, plant page, or telephone.

8. Make available for NRG staff audit Complete.

an evaluation of temperature and DAEC has completed evaluations of radiological conditions to ensure temperature and radiological conditions that operating personnel can to ensure that operators can safely safely access and operate access and operate controls and controls and support equipment. support equipment for the HCVS (Section 3.2.1, Section 3.2.2.3, system. HCVS controls and support Section 3.2.2.4, Section 3.2.2.5, equipment requiring access by Section 3.2.2.10, Section 3.2.4.1, operators are located within the control Section 3.2.4.2, Section 3.2.5.2 building to minimize radiological and and Section 3.2.6) temperature challenges.

9. Make available for NRG staff audit Complete.

the final sizing evaluation for DAEC has completed final sizing HCVS batteries/battery charger evaluations for HCVS batteries to including incorporation into FLEX ensure the batteries can power HCVS DG loading calculation. (Section equipment for a minimum of 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />.

3.2.2.4, Section 3.2.3.1, Section DAEC has completed an evaluation for 3.2.3.2, Section 3.2.4.1, Section the battery chargers to confirm they are 3.2.4.2, Section 3.2.5.1 and capable of recharging the HCVS Section 3.2.5.2) batteries while loaded. A review of the use of FLEX diesel generators to power the HCVS battery chargers has confirmed the load is within the capacity of the FLEX diesel generators.

The 480 VAC FLEX diesel generators are equipped with two 50A output breakers and four 125A output breakers. One of the 50A breakers will be connected to the HCVS UPS via a 200 foot length cable. The voltage drop across the cable for the assumed SA UPS load is 1.03 volt which is well within the +10/-12% allowable input voltage range specified by the UPS vendor, and is acceptable. The UPS batteries are adequate for the first 24 Page 9 of 15

Enclosure to NG-18-0066 - NextEra Energy Duane Arnold, LLC's Six Month Status Report for the Implementation of Order EA-13-109,0rder Modifying Licenses with Regard to Reliable Hardened Containment Vents Capable of Operation under Severe Accident Conditions hours of HCVS service. The addition of the small load of the HCVS UPS to the FLEX 480 VAC generator after 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> is acceptable.

10. Make available for NRG staff Complete.

audit the final sizing evaluation DAEC has completed the final sizing for pneumatic N2 supply. evaluation of pneumatic nitrogen (Section 3.2.2.4, Section 3.2.3.1, supply that demonstrates adequate Section 3.2.3.2, Section 3.2.4.1, capacity is installed for the first 24 Section 3.2.4.2, Section 3.2.5.1 hours of an ELAP event. After 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> and Section 3.2.5.2) replacement nitrogen bottles can be applied in an accessible location in the control building.

11. Make available for NRG staff Eliminated.

audit documentation of an evaluation verifying the existing As stated in NG-15-0169, Six Month containment isolation valves, Status Update, due to design changes relied upon for the HCVS, will in vent location and routing, existing open under the maximum containment isolation valves will no expected differential pressure longer be used for venting. New vent during BDBEE and severe design will utilize a spare torus accident wetwell venting. (Section penetration with two new primary 3.2.2.9) containment isolation valves and a rupture disk.

An evaluation has been done to ensure the two new containment isolation valves will open under the maximum expected differential pressure during BDBEE and severe accident wet well venting.

12. Make available for NRG staff Complete.

audit descriptions of all DAEC has completed evaluations of instrumentation and controls key instruments and controls necessary (existing and planned) necessary to implement NRG Order EA-13-109 to implement this order including including the qualification methods as qualification methods. (Section part of the engineering change 3.2.2.10) package for the HCVS system to ensure the instrumentation and controls are suitable for the application.

13. Make available for NRG staff Complete.

audit the descriptions of local DAEC has completed evaluations of conditions (temperature, radiation key components necessary for HCVS and humidity) anticipated during venting to ensure they are capable of ELAP and severe accident for the performing their intended function Page 10 of 15

Enclosure to NG-18-0066 - NextEra Energy Duane Arnold, LLC's Six Month Status Report for the Implementation of Order EA-13-109,0rder Modifying Licenses with Regard to Reliable Hardened Containment Vents Capable of Operation under Severe Accident Conditions components (valves, under ELAP and severe accident instrumentation, sensors, conditions including local temperature, transmitters, indicators, radiation and humidity as part of the electronics, control devices, and engineering change package for the etc.) required for HCVS venting HCVS system.

including confirmation that the components are capable of performing their functions during ELAP and severe accident conditions. (Section 3.2.2.3, Section 3.2.2.5, Section 3.2.2.9, Section 3.2.2.10)

14. Provide a justification for Eliminated.

deviating from the As stated in NG-15-0169, Six Month instrumentation seismic Status Update, the qualification method qualification guidance specified used for each HCVS instrument will be in NEI 13-02, endorsed, in part, to the IEEE 344-2004 standard or a by JLD-ISG-2013-02 as an substantially similar industrial standard acceptable means for and therefore will not be deviating from implementing applicable NEI 13-02 or JLD-ISG-2013-02.

requirements of Order EA 109. (Section 3.2.2.9)

Phase 2 Interim Staff Evaluation Status Open Items

1. Licensee to evaluate the SAWA Started.

equipment and controls, as well as The SAWA pump and manual ingress and egress paths for the controls will either be placed behind expected severe accident conditions the pump house or in the Turbine (temperature, humidity, radiation) for Building south rail bay. The the sustained operating period. temperature conditions in these locations will be at or near ambient conditions. Portable heaters are available for extreme cold conditions (SAMP-726). Proposed equipment locations are shielded by concrete walls.

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Enclosure to NG-18-0066 - NextEra Energy Duane Arnold, LLC's Six Month Status Report for the Implementation of Order EA-13-109,0rder Modifying Licenses with Regard to Reliable Hardened Containment Vents Capable of Operation under Severe Accident Conditions

5. Licensee to demonstrate that there Complete.

is adequate communication Communications between the MGR between the MGR and the operator and the operator at the FLEX pump at the FLEX pump during severe during severe accident conditions accident conditions. are described in Section 3.13 of the FLEX Final Integrated Plan (ML16347A010). 24 two-way radios are kept in the control room with chargers. These radios are capable of transmitting and receiving with or without a repeater to provide communications for plant operations.

6. Licensee to demonstrate the SAWM Complete.

flow instrumentation qualification for The evaluation of the operating the expected environmental design conditions and selection of conditions. the flowmeter has been completed.

Considerations of seismic, temperature rating as well as process conditions are evaluated.

All other instruments were evaluated as part of the FLEX project.

7 Interim Staff Evaluation Impacts The June 2015 six-month update (Reference 6) noted the following two potential impacts to the Interim Staff Evaluation.

1) One ISE Open Item will be eliminated because the Hardened Pipe Vent will no longer use existing containment isolation valves. The revised vent pipe routing will instead use an existing spare torus penetration and install two new containment isolation valves and a rupture disk. An evaluation will be done to ensure the two new containment isolation valves will open under the maximum expected differential pressure during BDBEE and severe accident wetwell venting.

2) The Interim Staff Evaluation (ISE) inadvertently listed a vent pipe process pressure indicator which will not be part of the Duane Arnold design.

Page 13of15

Enclosure to NG-18-0066 - NextEra Energy Duane Arnold, LLC's Six Month Status Report for the Implementation of Order EA-13-109,0rder Modifying Licenses with Regard to Reliable Hardened Containment Vents Capable of Operation under Severe Accident Conditions In addition, as discussed previously in Section 4:

The HCVS "Nitrogen Supply Isolation at 1A3 ROS" (V43-0642) will be normally closed and locked to prevent inadvertent vent operation. This valve will have to be manually opened at the Remote Operating Station (ROS) in the 1A3 Essential Switchgear Room to supply nitrogen for CV operation and purging.

The HCVS nitrogen supply and purge pressure control valves (PCV4360 and PCV4361) will be normally closed to prevent inadvertent over pressurization. The PCVs are located at the ROS and will be manually adjusted to the prescribed setpoints after the main pneumatic supply valve is opened (V43-0642).

The Uninterruptible Power Supply (UPS) originally had the normal power supply from 1832. Analysis identified that 1832 did not have adequate margin to add this load; therefore the normal power supply has been changed to 1815. A receptacle will be installed at the UPS for direct connection to the portable 480 VAC generator.

The power to 1815 will be lost during an ELAP. The UPS will provide power for 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />; the FLEX 480 VAC generator will provide power beyond 24 hrs.

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Enclosure to NG-18-0066 - NextEra Energy Duane Arnold, LLC's Six Month Status Report for the Implementation of Order EA-13-109,0rder Modifying Licenses with Regard to Reliable Hardened Containment Vents Capable of Operation under Severe Accident Conditions 8 References The following references support the updates to the combined Phase 1 and 2 Overall Integrated Plan described in this Enclosure.

1. NextEra Duane Arnold Energy Center, LLC Phase 1 Overall Integrated Plan in Response to June 6, 2013 Commission Order Modifying Licenses with Regard to Reliable Hardened Containment Vents Capable of Operation Under Severe Accident Conditions (Order Number EA-13-109)," dated June 25, 2014.

2. NRG Order Number EA-13-109, "Order Modifying Licenses with Regard to Reliable Hardened Containment Vents Capable of Operation Under Severe Accident Conditions" dated June 6, 2013.

3. NEI 13-02, "Industry Guidance for Compliance with NRG Order EA-13-109, 'To Modify Licenses with Regard to Reliable Hardened Containment Vents Capable of Operation Under Severe Accident Conditions," Revision 1, dated April 2015.

4. NRG Interim Staff Guidance JLD-ISG-2013-02, "Compliance with Order EA 109, Order Modifying Licenses with Regard to Reliable Hardened Containment Vents Capable of Operation Under Severe Accident Conditions," Revision 0, dated November 2013 (Accession No. ML133048836).

5. NRG Endorsement of Industry "Hardened Containment Venting System (HCVS)

Phase 1 Overall Integrated Plan Template (EA-13-109) Rev O" (Accession No. ML14128A219).

6. NextEra Energy Duane Arnold, LLC's Six-Month Status Report in Response to June 6, 2013 Commission Order Modifying Licenses with Regard to Reliable Hardened Containment Vents Capable of Operation Under Severe Accident Conditions (Order Number EA-13-109), dated June 18, 2015(ML15170A333)

7. NextEra Duane Arnold Energy Center, LLC Combined Phase 1 and 2 Overall Integrated Plan in Response to June 6, 2013 Commission Order Modifying Licenses with Regard to Reliable Hardened Containment Vents Capable of Operation Under Severe Accident Conditions (Order Number EA-13-109), dated December 22, 2015.

8. NRG Interim Staff Guidance JLD-ISG-2015-01, "Compliance with Phase 2 of Order EA-13-109, Order Modifying Licenses with Regard to Reliable Hardened Containment Vents Capable of Operation Under Severe Accident Conditions,"

Revision 0, dated April 2015 (Accession No. ML15104A118).

9. NextEra Energy Duane Arnold, LLC's Six-Month Status Report in Response to June 6, 2013 Commission Order Modifying Licenses with Regard to Reliable Hardened Containment Vents Capable of Operation Under Severe Accident Conditions (Order Number EA-13-109), dated December 19, 2017 (ML17353A668).

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