NL-08-0351, Request to Implement an Alternative Source Term Response to Request for Additional Information Regarding the Power Sources for the Turbine Building Ventilation System

Request to Implement an Alternative Source Term Response to Request for Additional Information Regarding the Power Sources for the Turbine Building Ventilation System

ML080740313
Person / Time
Site:	Hatch
Issue date:	03/13/2008
From:	Stinson L Southern Nuclear Operating Co
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
NL-08-0351
Download: ML080740313 (11)

Text

L M. Stinson (Mike) Southern Nuclear Vice President Operating Company, Inc.

Fleet Operations Support 40 Inverness Center Parkway Post Office Box 1295 Birmingham. Alabama 35201 Tel 205.992.5181 Fax 205.992.0341 SOUTHERN COMPANY A

March 13, 2008 Energy to Serve YtJur World'"

Docket Nos.: 50-321 NL-08-0351 50-366 U. S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, D. C. 20555-0001 Edwin I. Hatch Nuclear Plant Request to Implement an Alternative Source Term Response to Request for Additional Information Regarding the Power Sources for the Turbine Building Ventilation System Ladies and Gentlemen:

On August 29, 2006 Southern Nuclear Operating Company (SNC) submitted a request to revise the Edwin I. Hatch Nuclear Plant (HNP) licensing/design basis with a full scope implementation of an alternative source term (AST). By letters dated November 6, 2006, November 27, 2006, January 30, 2007, June 22, 2007, July 16, 2007, August 13,2007, October 18, 2007, December 11,2007,' January 24,2008, February 4,2008, February 25,2008, and February 27,2008 SNC has submitted further information to support the NRC review of the HNP AST submittal.

By letter dated February 13, 2008 the NRC requested additional information concerning the power sources for the HNP turbine building ventilation exhaust systems which are credited in the AST analysis with purging the area around the main control room beginning 9 hours1.041667e-4 days <br />0.0025 hours <br />1.488095e-5 weeks <br />3.4245e-6 months <br /> following the initiation of three of the four HNP design basis accidents. The enclosure to this letter contains the SNC response to the referenced NRC request for additional information (RAI).

The 10 CFR 50.92 evaluation and the justification for the categorical exclusion from performing an environmental assessment that were included in the August 29, 2006 submittal continue to remain valid.

(Affirmation and signature are prOVided on the following page.)

U. S. Nuclear Regulatory Commission NL-08-0351 Page 2 Mr. L. M. Stinson states he is a Vice President of Southern Nuclear Operating Company, is authorized to execute this oath on behalf of Southern Nuclear Operating Company and to the best of his knowledge 'and belief, the facts set forth in this letter are true.

This letter contains no NRC commitments. If you have any questions, please advise.

RespectfUlly submitted, SOUTHERN NUCLEAR OPERATING COMPANY L. M. Stinson Vice President Fleet Operations Support Sworn to and subscribed before me this /.J /Jl day of tJ7actLJ, , 2008.

!JJO. ~

Notary Public My commission expires: J""" '" ~,,/O/O LMS/CLT/daj

Enclosure:

1. Response to Request for Additional Information Regarding the Power Sources for the Turbine Building Ventilation System cc: Southern Nuclear Operating Company Mr. J. T. Gasser, Executive Vice President Mr. D. R. Madison, Vice President - Hatch Mr. D. H. Jones, Vice President - Engineering RType: CHA02.004 U. S. Nuclear Regulatory Commission Mr. V. M. McCree, Acting Regional Administrator Mr. R. E. Martin, NRR Project Manager - Hatch Mr. J. A. Hickey, Senior Resident Inspector - Hatch State of Georgia Mr. N. Holcomb, Commissioner - Department of Natural Resources

Edwin I. Hatch Nuclear Plant Request to Implement an Alternative Source Term Enclosure 1 Response to Request for Additional Information Regarding the Power Sources for the Turbine Building Ventilation System

Enclosure 1 Edwin I. Hatch Nuclear Plant Request to Implement an Alternative Source Term Response to Request for Additional Information Regarding the Power Sources for the Turbine Building Ventilation System BACKGROUND Southern Nuclear Operating Company (SNC) committed to provide an alternate safety related power supply to the Edwin I. Hatch Nuclear Plant (HNP) Units 1 and 2 turbine building (TB) ventilation exhaust systems with a manual switchover in the SNC letter to the NRC dated October 18, 2007 and stated:

There are a total of four turbine building ventilation exhaust fans, two for each HNP unit. Only one of the four fans is needed for the execution of the dose mitigation function. Any one of the four fans is capable of achieving the necessary minimum exhaust rate of 15,000 cfm. The power requirement for each fan is 40 hp for Unit 1 and 75 hp for Unit 2. This small load can be accommodated by the emergency diesel generators within the required time period post-design basis accident (DBA).

The referenced SNC letter provided additional details regarding the proposed modifications. Preparation of the design change packages to implement the proposed modifications is ongoing. As a result of this design work some minor changes have occurred in the conceptual design (as had been noted in the referenced SNC letter). Consequently reference the enclosed Figure 1 for the revised configuration. This figure supersedes Figure 1 of Enclosure 1 of the October 18, 2007 SNC response. These minor changes have no impact on the intent of the proposed modification as described in the referenced SNC letter and these changes do not impact the discussions of emergency diesel generator capacity, vital area operator actions, and procedure control provided in the referenced SNC letter.

SNC notes that certain additional minor details may change as the design change packages are completed and implemented. However, the breaker and fused manual transfer switch scheme, as discussed in detail in the response to NRC Question 3, will not change.

NRC QUESTION 1 Provide assurance that the emergency diesel generators are capable of supporting the electrical load being added as a result of supplying the turbine building exhaust fans from a Class 1E power source. Include a detailed summary of any analyses used to make this determination.

SNC RESPONSE Only one TB ventilation exhaust fan per unit is in operation at any given time and the fans are electrically interlocked on each unit such that the two TB exhaust fans cannot run simultaneously. To accomplish its credited dose mitigation NL-08-0351 E1-1 Edwin I. Hatch Nuclear Plant Request to Implement an Alternative Source Term Response to Request for Additional Information Regarding the Power Sources for the Turbine Building Ventilation System______

function in an AST DBA scenario, the TB ventilation exhaust system must be placed in service within 9 hours1.041667e-4 days <br />0.0025 hours <br />1.488095e-5 weeks <br />3.4245e-6 months <br /> of DBA occurrence, assuming TB exhaust fan power failure due to loss of offsite power (LOSP) concurrent with the DBA. The 10 - 60 minute expected diesel generator loading for a loss of coolant accident (LOCA) condition is therefore considered limiting. After one hour, loads on the diesel will decrease as plant operators de-energize unnecessary loads. As shown below, even if a fan is restarted within the 10 - 60 minute limiting case window, diesel loading for either unit will be less than the allowable loading such that all connected loads will be adequately powered.

HNP UNIT 1 The Unit 1 TB exhaust fans (1U41-C002A/B) are normally powered from non-Class 1E motor control center (MCC) 1R24-S016. Upon implementation of the proposed design change, power will also be available to the fans from Class 1E MCC 1R24-S011 via a manually operated transfer switch. Upstream of this MCC is 600V Bus 1C, 4160V Bus 1E, and diesel generator 1A (see Figure 1).

Diesel generator 1A has the following electrical load ratings:

168 Hour Rating (7 day): 3250 kW 1000 Hour Rating: 2850 kW The maximum allowable steady-state loading of diesel generator 1A for a LOCA with an LOSP event during the 10 - 60 minute time frame for all cases of single failure should not exceed 3250 kW. The current maximum expected steady state loading on diesel generator 1A during the 10 - 60 minute time frame for a LOCA/LOSP event under conditions when another diesel generator or diesel battery has failed is 3192 kW (reference HNP Unit 1 Final Safety Analysis Report (FSAR) table 8.4-15). The 40 hp TB exhaust fan motor will add 35 kW of load, considering fan motor efficiency, to this diesel. If this motor is started within the 10 - 60 minute window, the total load on diesel generator 1A will be 3227 kW (3192 kW plus 35 kW), which is less than the allowable loading of 3250 kW.

HNP UNIT 2 The Unit 2 TB exhaust fans (2U41-C002A/B) are normally powered from non-Class 1E MCC 2R24-S016. Upon implementation of the proposed design change, power will also be available to the fans from Class 1E MCC 2R24-S011 via a manually operated transfer switch. Upstream of this MCC is 600V Bus 2C, 4160V Bus 2E, and diesel generator 2A (see Figure 1).

NL-08-0351 E1-2 Edwin I. Hatch Nuclear Plant Request to Implement an Alternative Source Term Response to Request for Additional Information Regarding the Power Sources for the Turbine Building Ventilation System______

Diesel generator 2A has the following electrical load ratings:

30 Minute Rating: 3500 kW 300 Hour Rating (12.5 day): 3250 kW 2000 Hour Rating: 3100 kW Continuous Rating: 2850 kW The maximum allowable steady-state loading of diesel generator 2A for a LOCA with an LOSP event during the 10 - 60 minute time frame for all cases of single failure should not exceed 3250 kW. The current maximum expected steady state loading on diesel generator 2A during the 10 - 60 minute time frame for a LOCA/LOSP event under conditions when another diesel generator or diesel battery has failed is 3164 kW (reference HNP Unit 2 FSAR table 8.3-12). The 75 hp turbine building fan motor will add 62 kW of load, considering fan motor efficiency, to this diesel. If this motor is started within the 10 - 60 minute window, the total load on diesel generator 2A will be 3226 kW (3164 kW plus 62 kW),

which is less than the allowable loading of 3250 kW.

NL-08-0351 E1-3 Edwin I. Hatch Nuclear Plant Request to Implement an Alternative Source Term Response to Request for Additional Information Regarding the Power Sources for the Turbine Building Ventilation System______

NRC QUESTION 2 Discuss how the reliability and availability of the turbine building exhaust fans and the associated electrical circuits, including individual fans and transfer switches, will be monitored and maintained.

SNC RESPONSE The TB ventilation exhaust systems, specifically their AST credited function of purging the area around the main control room beginning 9 hours1.041667e-4 days <br />0.0025 hours <br />1.488095e-5 weeks <br />3.4245e-6 months <br /> following the initiation of three of the four HNP DBAs, are not currently incorporated into the HNP Maintenance Rule program. The TB HVAC exhaust systems will be added to and evaluated in the HNP Maintenance Rule program consistent with 10 CFR 50.65 to provide reasonable assurance that the systems will reliably perform their AST credited function. This HNP Maintenance Rule program evaluation will include consideration of the alternate safety related power supply and the associated manual transfer switches. The inclusion of TB HVAC exhaust systems in the HNP Maintenance Rule program will be complete in sufficient time to support final AST implementation once NRC approval is obtained.

The existing TB ventilation system preventative maintenance procedure requires inspection and testing annually of each TB exhaust fan and associated dampers to ensure acceptable operation and condition. The TB exhaust fans are vaneaxial direct drive fans so there are no belts or sheaves associated with these fans requiring adjustment or inspection. Such inspection includes the following:

• Fan motor running amps are recorded and verified to be within expected operating range

• Fan motor is meggered per appropriate plant procedures and verified to be within expected range

• Exhaust fan housing and blades which are accessible are inspected for cleanliness and integrity, and cleaned if required

• Fan motor bearings are greased via the grease fittings

• Dampers are lubricated via the grease fittings Any abnormal conditions noted during this annual inspection are corrected in accordance with plant corrective action programs. It should also be noted that one fan per HNP unit is in near-continuous operation so any failure would be recognized by plant operators such that corrective maintenance could be scheduled.

As part of the implementation of the design change to provide a source of Class 1E power to the TB exhaust fans, fan operation from the new power source will be verified. Preventive maintenance and inspection tasks will be revised as appropriate to periodically test operation of the fans from the Class 1E power source.

NL-08-0351 E1-4 Edwin I. Hatch Nuclear Plant Request to Implement an Alternative Source Term Response to Request for Additional Information Regarding the Power Sources for the Turbine Building Ventilation System______

NRC QUESTION 3 Describe how electrical isolation will be maintained between non-Class 1E and Class 1E circuits. If double isolation (e.g., two breakers in series, a breaker and a fuse, or a breaker supplied with a loss-of-offsite power signal) is not used, provide a detailed discussion on how a fault on the non-Class 1E electrical circuit will not propagate to the Class 1E electrical circuit.

SNC RESPONSE In the referenced SNC letter of October 18, 2007 discussed above, SNC stated that, as is typical for HNP systems powered from emergency power buses, the design for providing Class 1E power as an alternate source to the TB ventilation exhaust systems will require that the TB exhaust fans be connected to the emergency power source such that any TB ventilation exhaust system electrical fault will not impact the essential 600V bus and/or other equipment being supplied by the bus. The primary isolation device is the component supply breaker located in the associated switchgear cubicle. The circuit breaker not only provides a means of primary isolation, but also provides circuit protection. The protective device settings are chosen to open the circuit breaker during a fault closest to the affected loads and to significantly reduce or eliminate the adverse effects of the fault to the rest of the distribution system.

The above method of electrical isolation between non-Class 1E and Class 1E circuits is consistent with the HNP current licensing basis (CLB). Compliance with HNP regulatory design bases for electrical systems, as defined in HNP Unit 1 FSAR sections 8.3.2 and 8.4.2 and Unit 2 FSAR section 8.1.4, will be maintained. The HNP CLB does not require utilization of double isolation devices between non-Class 1E and Class 1E circuits. Appropriately coordinated circuit protection, which may be a single isolation device, is utilized to ensure protection of up-stream electrical systems.

With regards to the Class 1E alternate power source for the TB ventilation exhaust systems, the ongoing detailed design work has identified that the isolation device between the non-Class 1E TB exhaust fans and the Class 1E circuits will be a 150A safety related, environmentally and seismically qualified thermal-magnetic circuit breaker. For additional protection, fuses will be provided. These fuses will be located in the seismically qualified manual transfer switch housing as further described below. Finally, SNC notes that during normal plant operation the TB ventilation exhaust systems will not be connected to the Class 1E alternate power source. Only during post-DBA operation, if offsite power cannot be restored within the required 9 hours1.041667e-4 days <br />0.0025 hours <br />1.488095e-5 weeks <br />3.4245e-6 months <br />, would it be necessary to connect the non-Class 1E TB exhaust fans to the Class 1E alternate power source.

NL-08-0351 E1-5 Edwin I. Hatch Nuclear Plant Request to Implement an Alternative Source Term Response to Request for Additional Information Regarding the Power Sources for the Turbine Building Ventilation System______

Due to design implementation schedules, the HNP Unit 2 design is being developed first. The following detailed discussion is specific to Unit 2. The Unit 1 design change details are expected to be similar.

The alternate power to the Unit 2 TB exhaust fans will be provided from Class 1E MCC 2R24-S011 via a 150A thermal-magnetic circuit breaker. This new breaker will be safety related and qualified to seismic and environmental requirements as appropriate for the installed location. The 150A breaker performs as the power circuit isolation device to separate Class 1E circuits from non-Class 1E circuits (see Figure 1).

The manual transfer switches to be utilized are fusible, double throw, 3-pole switches (see Figure 2). This switch design allows the use of protective fuses on each 'side' of the switch. On the Class 1E power side of the switch, for HNP Unit 2, 150A fuses will be installed. Evaluation of the trip characteristics of the downstream protective devices (the new 150A breaker and fuses) shows that they are adequately coordinated with the upstream load center breaker over the entire range. Therefore all circuit faults in the downstream side will be cleared by the 150A breaker or fuses prior to the operation of the upstream load center breaker. The manual transfer switches will be seismically qualified and seismically mounted to ensure reliability. The manual transfer switches will be aligned to the normal (non-Class 1E) power source and locked in-position to prevent inadvertent switching.

NL-08-0351 E1-6 Edwin I. Hatch Nuclear Plant Request to Implement an Alternative Source Term Response to Request for Additional Information Regarding the Power Sources for the Turbine Building Ventilation System______

UNIT 1 TURBINE BUILDING EXHAUST FANS UNIT 2 TURBINE BUILDING EXHAUST FANS 1U41-C002A 1U41-C002B 2U41-C002A 2U41-C002B TB Fan 2A TB Fan 2B TB Fan 2A TB Fan 2B 1R24-S016 1R24-S016 2R27-S039 2R27-S040 FR-1C FR-2C (Local Starter) (Local Starter)

(modified motor (modified motor starter) starter) 600V FUSED 600V FUSED See Note MANUAL MANUAL TRANSFER TRANSFER SWITCH SWITCH 600V FUSED 600V FUSED MANUAL MANUAL TRANSFER TRANSFER 2R24-S016 2R24-S016 SWITCH SWITCH FR - 3AL FR - 3AR (Feeder Breaker) (Feeder Breaker) 1R24-S011 (Powered from 1C Essential 2R24-S011 Bus that is backed by Diesel (Powered from 2C Essential Generator 1A) Bus that is backed by Diesel Generator 2A)

Note: Manual transfer switch will be internally wired between starter breaker and contactor (Unit 1 only)

Figure 1 - Conceptual Design for Turbine Building Fan Power Supply Modification NL-08-0351 E1-7 Edwin I. Hatch Nuclear Plant Request to Implement an Alternative Source Term Response to Request for Additional Information Regarding the Power Sources for the Turbine Building Ventilation System______

Switch shown in the 'Off' position with no source connected OFF Alternate Normal 150 A 150 A 150 A 150 A 150 A 150 A From Class 1E From non-Class 1E To Fan Motor Power Source Power Source Starter Figure 2 - Manual Transfer Switch Representative Detail (HNP Unit 2)

NL-08-0351 E1-8