NG-17-0121, 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 EA-13-109)

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 EA-13-109)

ML17180A217
Person / Time
Site:	Duane Arnold
Issue date:	06/29/2017
From:	Dean Curtland NextEra Energy Duane Arnold
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
EA-13-109, NG-17-0121
Download: ML17180A217 (16)

Text

June 29, 2017 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 EN ERGY~

DUANE ARNOLD NG-17-0121 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 December 10, 2014(ML14349A324)

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 ("NRC" 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 of Reference 1.

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

Document Control Desk NG-17-0121 Page 2of2 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 NRG 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 at 319-851-7032.

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

Executed on June 29, 2017.

ean 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 USNRC Project Manager, Duane Arnold Energy Center USNRC Resident Inspector, Duane Arnold Energy Center

Enclosure to NG-17-0121 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) 13 pages follow

Enclosure to NG-17-0121 - 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 22, 2016 (Reference 9), and are current as of June 1, 2017.

Held Preliminary /Conceptual Design Meeting Page 1 of 13

Enclosure to NG-17-0121 - 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:

Milestone Target Adivity

_--_comments ce>mple~ion Status

-_ {lripludes date Date __.-*

cha!]ges}

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 2of13

Enclosure to NG-17-0121 - 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 Milesfone Target - -

1-Activity.<

• --- - Comments I

Status.. -_

• {lnctudedate

~C9mpletion

>Date changesill this

- c_

colurnnf 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 with this submittal Submit 6 Month Status Report Dec.2017 Not Started Design Engineering On-site/Complete Jan.2018 Started Submit 6 Month Status Report June 2018 Not Started Operations Procedure Changes Developed Oct. 2018 Not Started Site Specific Maintenance Procedure Oct. 2018 Not Developed Started Training Complete Oct. 2018 Not 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 3 of 13

Enclosure to NG-17-0121 - 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 13

1.

2.

3.

4.

Enclosure to NG-17-0121 - 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 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.

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 1 A3 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.

Evaluate tornado/missile effects on HCVS components Complete.

above the protected area of the Reactor Building.

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

taken.

Page 5 of 13

Enclosure to NG-17-0121 - NextEra Energy Duane Arnold, LLC's Six Month Status Report for the Implementation of Order EA-13-109,0rder Modifying Licenses with Re~ard to Rel!~ble Hardened Containment Vents Capable of Operation under Severe Accident Cond1t1ons Phase 1 Interim Staff Evaluation Open Items a e ava1 a e or sta au 1t documentation of licensee confirmation that secondary containment leakage is acceptable without an installed rupture disk or that an appropriate rupture disk, including proce.dure.s for ruptur~

during HCVS operation, 1s included 1n the KCVS design. (Section 3.1.2, Section 3.2.2.8) a e ava1 a e or sta au 1t analyses demonstrating that HCVS has the capacity to vent the steam/energy equivalent of one (1) percent of licensed/rated thermal power (unless a lower value is.

Justified), and that the suppression pool and the HCVS together are able to absorb and reject decay heat, such that following a reactor shutdown from full power containment pressure is restored 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)

4.

a e ava1 a e or sta au 1t additional detail on the design features that minimize unintended cross flow of vented fluids within a unit, including a one line diagram containing sufficient detail to confirm the description in the OIP. (Section 3.2.2.7)

Status omp ete.

The DAEC final design of the HCVS utilizes an installed rupture disk. Procedures for rupturing the disk have been developed for use during beyond design bases conditions.

Complete.

DAEC has completed analysis demonstrating the HCVS has the capacity to vent the steam/energy equivalent to one percent of licensed thermal power and that the suppression pool and HCVS together are able to absorb and reject decay heat such that following a reactor shutdown from full power containment pressure will be maintained below the primary containment design pressure limit of 53 PSIG.

Complete.

DAEC has evaluated the potential effects of tornado missiles on HCVS components above the protected area 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.

Eliminated.

The DAEC design has been modified since issuance of the ISE. The HCVS system utilizes a dedicated penetration from the torus to HCVS piping ~it~ nq connecting systems eliminating the possibility of unintended cross flow.

Page 6 of 13

Enclosure to NG-17-0121 - 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. Provide a description of the tinal design Complete.

of the HCVS to address hydro~en The final DAEC design of the detonation and deflagration. ( ection HCVS addresses the potential for 3.2.2.6) hydrogen detonation and deflagration with the use of a nitrogen purge of the HCVS piping that ensures hydrogen and o~gen concentrations within the HC S system are not susceptible to detonation or defla~ation (O~tion 3 of A~endix Hof El 13-0 ).

The H VS system isolation is performed by two primary containment isolation valves (PCIVs) to minimize an{i potential leakage. Prior to use o the system a partial purge of the system is performed to ensure no hydrogen 1s directly downstream of the PCIVs at the time of actuation. A full nitrogen J:>Urge is performed immediatelh followin~ each period of venting t e torus.

ach purge is performed with nitro]en flow at sufficient veloci~ to imit stratification an ensure turbulent flow to preclude retaining h(cdroaen in the pipe. The piping is s ope uftwards from the outboard PCIV to he 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 strategies Complete.

for hydro~en control that minimizes the DAEC strategies for hbdrogen potential or hydrogen gas migration control are as noted a ove in and ingress into the reactor building or response to Open Items 4 and 5.

other buildings. (Section 3.2.2.6)

The HCVS system utilizes a dedicated c.enetration from the torus to H VS piping with no 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 defla~ration of hydro~en inside the HGV dOption 3 of N I 13-02 Appen ix H).

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Enclosure to NG-17-0121 - 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

7. Ma e available for NRG statt audit documentation that demonstrates adequate communication between the remote HCVS operation locations and HCVS decision makers during ELAP and severe accident conditions.

(Section 3.2.2.5)

Complete.

DAEC docketed an assessment of communications capabilities under ELAP conditions in NG-12-0430 "Response to NRG 10 CFR 50.54(f) Request for Information Regarding Near-Term Task Force Recommendation 9.3, Emergency Preparedness" (ADAMS Accession No. ML12307A120).

NRG staff review of this assessment is documented in an NRG 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 NRG 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 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.

Page 8 of 13

Enclosure to NG-17-0121 - NextEra Energy Duane Arnold, LLC's Six Month Status Report for the Implementation of Order EA-13-109,0rder Modi~ing Licenses with Re~ard to Rel.i~ble Hardened Containment Vents Capable of Operation under Severe Accident Cond1t1ons

8. Make availab e or NR sta audit an evaluation of temperature and radiological conditions to ensure that operating personnel can safely access and operate controls and supp<?rt equipment. (Section 3.2.1, Section 3.2.2.3, Section 3.2.2.4, Section 3.2.2.5, Section 3.2.2.10, Section 3.2.4.1, Section 3.2.4.2, Section 3.2.5.2 and Section 3.2.6)

. a e ava1 a e or sta au 1~ t e final sizing evaluation for pneumatic N2 supply. (Section 3.2.2.4, Section 3.2.3.1, Section 3.2.3.2, Section 3.2.4.1, Section 3.2.4.2, Section 3.2.5.1 and Section 3.2.5.2)

Complete.

DAEC has completed evaluations of temperature and radiological conditions to ensure that operators can safely access and operate controls and support equipment for the HCVS system. HCVS controls and support equipment requiring access by operators are located within the control building to minimize radiological and temperature challenges.

Complete.

DAEC has completed final sizing evaluations for HCVS batteries to ensure the batteries can power HCVS 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 />. DAEC has completed an evaluation for the battery chargers to confirm they are capable of recharging the H<;;VS batteries while loadea. 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 witn 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 BA 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 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> 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.

Complete.

DAEC has completed the fin~I sizing evaluation of pneumatic nitrogen supply that demonstrates adeguate capacity is installed for the first 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> 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 /> replacement nitrogen bottles can be applied in an accessible location in the control building.

Page 9 of 13

Enclosure to NG-17-0121 - 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. Ma e ava1la le or NR sta au it documentation of an evaluation verifying the existing containment isolation valves, relied upon for the HCVS, will open under the maximum expected differential pressure during BDBEE and severe accident wetwell venting. (Section 3.2.2.9)

. a e ava1 a e or sta au 1t descriptions of all instrumentation and controls (existing and planned) necessary to implement this order including qualification methods.

(Section 3.2.2.10)

. a e ava1 a e or sta au 1t t e descriptions of local conditions (temperature, radiation and humidity) anticipated during ELAP and severe accident for the components (valves, instrumentation, sensors, transmitters, indicators, electronics, control devices, and etc.) required for HCVS venting 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)

4. rov1 e a JUst1 1cat1on or ev1atmg from the instrumentation seismic qualification guidance specified in NEI 13-02, endorsed, in part, by JLD-ISG-2013-02 as an acceptable means for implementing applicable requirements of Order EA-13-109.

(Section 3.2.2.9)

As stated in NG-15-0169, Six Month Status Update, due to design changes in vent location and routing, existing containment isolation valves will no longer be used for venting. New vent design will utilize a spare torus penetration with two new primary 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.

Complete.

DAEC has completed evaluations of key instruments and controls necessary to implement NRG Order EA-13-109 including the qualification methods as part of the engineering change package for the HCVS system to ensure the instrumentation and controls are suitable for the application.

Complete.

DAEC has completed evaluations of key components necessary for HCVS venting to ensure they are capable of performing their intended function under ELAP and severe accident conditions including local temperature, radiation and humidity as part of the engineering change package for the HCVS system.

As stated in NG-15-0169, Six Month Status Update, the qualification method used for each HCVS instrument will be to the IEEE 344-2004 standard or a substantially similar industrial standard and therefore will not be deviating from NEI 13-02 or JLD-ISG-20r3-02.

Page 10of13

Enclosure to NG-17-0121 - 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 Interim Staff Evaluation Open Items Status

1. Licensee to evaluate the SAWA equipment Started.

and controls, as well as ingress and egress paths for the expected severe accident conditions (temperature, humidity, radiation) for the sustained operating period.

2. Licensee to demonstrate that SAWA Started.

components and connections external to protected buildings have been protected against the screened-in hazards of Order EA-12-049 for the station.

3. Licensee to demonstrate that containment Complete.

failure as a result of overpressure can be prevented without a drywell vent during severe accident conditions.

4. Licensee to demonstrate how the plant is Started.

bounded by the reference plant analysis that shows the SAWM strategy is successful in making it unlikely that a drywell vent is needed.

5. Licensee to demonstrate that there is Complete.

adequate communication between the MGR and the operator at the FLEX pump during severe accident conditions.

6. Licensee to demonstrate the SAWM flow Not started.

instrumentation qualification for the expected environmental conditions.

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 11 of 13

Enclosure to NG-17-0121 - 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 1 A3 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.

Page 12 of 13

Enclosure to NG-17-0121 - 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 December 10, 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 22, 2016 (ML16362A211).

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