RBG-30553, Forwards Evaluation of Plant Compliance W/Requirements of Station Blackout Rule 10CFR50.63.Electrically-independent HPCS Sys Provides Alternate Method of Achieving Safe Shutdown Which Exceeds Station Blackout Rule Requirements

Forwards Evaluation of Plant Compliance W/Requirements of Station Blackout Rule 10CFR50.63.Electrically-independent HPCS Sys Provides Alternate Method of Achieving Safe Shutdown Which Exceeds Station Blackout Rule Requirements

ML20245A507
Person / Time
Site:	River Bend
Issue date:	04/17/1989
From:	Deddens J GULF STATES UTILITIES CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
RBG-30553, NUDOCS 8904250241
Download: ML20245A507 (7)

Text

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GULF STATES ' UTILITIES COMPANY P O S T. O F F I C E D O X 2 9 51'

• DEAUMONT, TEXAS 777o4 AREACODE409 838[6631

April 17,' 1989 RBG-30553 File Code C9.5, G9.23.2

-U.S. Nuclear. Regulatory Commission Document Control Desk Washington, DC 20555 Centlemen:

River Bend Station - Unit 1 Decket No. 50-458

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Gulf States Utilities has evaluated the River Bend Station against the requirements of the station blackout rule, 10CFR50.63. This evaluation was completed using the guidance provided in Nuclear Management'.'and ' Resources Council (NUMARC) 87-00, " Guidelines and Technical. Bases for NUMARC Initiative Addressing Station Blackout at Light Water Reactors" except where' Regulatory Guide 1.155 tak3s precedence. The results of this ev duation'are attached.

In demonstrating compliance with the requirements of the station blackout rule, an alternating current (AC) independent approach with reliance on the Reactor . Core Isolation Cooling (RCIC) system was se.1ected. The results of the River Bend 3tation evaluations demonstrate the ability to cope with a station blackout for the proposed four hour station blackout duration without reliance on AC power sources. In addition to this capability, the High Pressure Core Spray (HPCS) system would be available as backup to the RCIC system during a station blackout event. The HPCS system is a safety'related system which conforms to the alternate AC (AAC) criteria given- in Appendix B of NUMARC 87-00. As a result, the electrically independent HPCS system provides an alternate method of achieving safe shutdown which exceeds the requirements of the station blackout rule.

Sincere y, w$ V J. C. Deddens Senior Vice President hO River Bend Nuclear Group I

l 8904250241 890417 PDR ADOCK 05000458 P PDC i

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L cc: Director of the Office of Nuclear Reactor Regulation l U.S. Nuclear Regulatory Commission ]

l Washington, D.C. '20555 1 U.S. Nuclear Regulatory Commission Region IV 611 Ryan Plaza Drive, Suite 1000 Arlington, TX 76011 NRC Senior Resident Inspector Post Office Box 1051

-St. Francisville, LA 70775 1 i

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Attachment On July 21, 1988, the Nuclear Regulatory Commission (NRC) amended its regulations in 10CFR, Part 50. A new section, 50.63, was added which requires that each light-water-cooled nuclear power plant be l able to withstand and recover from a station blackout (SBO) of a specified duration. Utilities are expected to have the baseline assumptions, analyses and related information used in their coping evaluation available for NRC review. It also identifies the factors that must be considered in specifying the station blackout j duration. Section 50.63 requires that, for the station blackout l duration, the plant be capable of maintaining core cooling and appropriate containment integrity. Section 50.63 further requires  ;

l that each licensee submit the following information:

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1. A proposed station blackout duration including a 1

! I justification for the selection based on the redundancy f and reliability of the onsite emergency AC power sources, the expected frequency of loss of offsite power, and the j probable time needed to restore offsite power;

2. A description of the procedures that will be implemented for station blackout events for the duration (as determined in 1 above) and for recovery therefrom; and

3. A list and proposed schedule for any needed modifications to equipment and associated procedures necessary for the specified SB0 duration. i The NRC has issued Regulatory Guide 1.155 " Station Blackout" which describes a means acceptable to the NRC staff for meeting the requirements of 10CFR 50.63. Regulatory Guide (RG) 1.155 states that the NRC Staff has determined that NUMARC 87-00 " Guidelines and Technical Bases for NUMARC Initiatives Addressing Station Blackout At Light Water Reactors" also provides guidance that is in large part identical to the RG 1.155 guidance and is acceptable to the NRC Staff for meeting these requirements.

Table 1 to RG 1.155 provides a cross-reference between RG 1.155 and NUMARC 87-00 and notes where the regulatory guidance takes precedence. )

l Gulf Ste rs Utili'Tes has evaluated the River Bend Station against the requirements of the SB0 rule using guidance from NUMARC 87-00 except where RG 1.155 takes precedence. The results of this l evaluation are detailed below. 1 1 J 1 of 5

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l A. Proposed Station Blackout Duration NUMARC 87-00, Section 3 was used to determine a proposed SB0 duration of four hours. No modifications were required to attain this proposed coping duration category.

The following plant factors were identified in determining the proposed station blackout duration:

1. AC Power Design Characteristic Group is P1 based on:

a. Expected frequency of grid-related loss of offsite power (LOOP) does not exceed once per 20 years; l

b. Estimated frequency of LOOPS due to extremely severe )

weather (ESW) place the plant in ESW Group 1; j

c. Estimated frequency of' LOOPS due to severe weather (SW)-

place the plant in SW Group 1;

d. The offsite power system is in the 1 1/2 Group.

2. The emergency AC power configuration group is C based on:

a. Two emergency AC power supplies not credited as alternate AC power sources;

b. One emergency AC power supply is necessary to operate safe shutdown equipment following a loss of offsite power.

3. The target EDG reliability is 0.95.

A target emergency diesel generator (EDG) reliability of 0.95 was selected based on having a nuclear unit average EDG reliability for the last 50 demands greater than 0.94.

B. Procedure Description Plant procedures have been reviewed and modified, as necessary, to meet the guidlines in NUMARC 87-00, Section 4, in the following areas:

1. Offsite alternating power restoration: " System Dispaching and Switching Manual" (GSU Corporate Procedure).

2. Plant blackstart: " Procedure No. 10, Plant Blackstart Procedure", (GSU Corporate Procedure).

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l The following plant procedures have been reviewed and the changes necessary to meet NUMARC 87-00 will be implemented in the following areas:

1. Severe weather: " SOP-0029, Severe Weather Operation", (River Bend Station Procedure).

2. Station Blackout response: "AOP-0050, Station Blackout".

3. Condensate Storage Tank Inventory: "STP-000-0001, Daily l Operating Logs".

4. Containment Isolation: "A0P-0003, Automatic Isolations".

C. Proposed Modifications and Schedule The ability of the River Bend Station to cope with a station blackout for four hours in accordance with NUMARC 87-00, Section 3.2.5 and as determined in Section "A" above; was assessed using NUMARC 87-00, Section 2 and Section 7 with the following results:

1. Condensate Inventory For Decay Heat Removal (Section 7.2.1)

It has been determined the minimum available condensate inventory provides sufficient water inventory for 5.9 hours1.041667e-4 days <br />0.0025 hours <br />1.488095e-5 weeks <br />3.4245e-6 months <br /> operation during a station blackout. The minimum permissible condensate storage tank level provides 125,000 gallons of water, which exceeds the required quantity fc. coping with a four-hour station blackout. No plant modifications are needed to utilize this water source. Availability of the minimum condensate storage tank inventory will be ensured through procedural changes.

2. Class IE Battery (ies) Capacity (Section 7.2.2)

A battery capacity calculation has been performed pursuant to NUMARC 87-00, Section 7.2.2 to verify that the Class 1E batteries have sufficient capacity to meet station blackout loads for four hours without load stripping.

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3. Compressed Air (Section 7.2.3)

Air-operated valves relied upon to cope with a station blackout for .four hours can either be. operated manually or have

. sufficient backup sources independent of the preferred and blacked out unit's Class 1E power supply. Valves requiring manual operation or that need backup sources for operation are identified in plant procedures.

4. Effects of Loss of Ventilation (Section 7.2.4)

The assumption in NUMARC 87-00, Section 2.7.1 that the control room will not exceed 120 F during a station blackout has been assessed.

This temperature- limit is based on maintaining the control room equipment temperature at 120 F with the panel doors open. This is equivalent .to limiting'the' control room ambient air temperature at 104 F with a 15 F differential temperature within the equipment panels. The steady state ambient air temperature within the River l_ Bend Station control room has been calculated to exceed 104 F during a four hour station blackout duration. Therefore, additional measures must be taken to limit the temperature level in:

the control room.

Reasonable assurance of the operability of station blackout response equipment in the RCIC room and HPCS room has been assessed using plant specific equipment qualification data. Assurance of the operability of control room equipment required to cope with a station blackout has been addressed by maintaining the control room ambient air. temperature at or below 104 F during a four hour station blackout duration. It is anticipated that this will be accomplished by using the installed smoke removal fans or suitable alternatives to provide additional ventilation of the control room.

The main steam tur.nel ambient air temperature following a station blackout has not been evaluated because the River Bend Station procedure AOP-0050, " Station Blackout", will include instructions to bypass the leakage detection system high temperature RCIC trip.

The following procedure changes are required to provide reasonable assurance for equipment operability for the coping duration of four hours:

o Modification of A0P-0050, " Station Blackout" to provide alternate AC power to the control building smoke removal fan.

o Modification of A0P-0050, " Station Blackout" to include instructions to bypass the leakage detection system high temperature RCIC trip.

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5. Containment Isolation (Section 7.2.5)

The plant list of containment isolation valves has been-

-reviewed to verify that valves which must be capable of being closed or that must be operated (cycled) under station blackout conditions can be positioned (with indication) independent of the preferred and blacked-out unit's Class 1E power supplies.

The following procedure change is required to ensure that appropriate containment integrity can be provided under station blackout conditions; o Revise A0P-0003, " Automatic Isolutions" to include additional guidance on closing isolation valves which do not maet the NUMARC 87-00 exclusion criteria during a I

station blackout.

6. Reactor Coolant Inventory (Section 2.5)

The ability to maintain adequate reactor coolant system inventory to ensure that the core is cooled during a four hour  ;

station blackout has been assessed. A plant-specific analysis I was used for this assessment. The expected rates of reactor coolant inventory loss under station blsekout conditions do not result in any core uncovery in a station blackout of four hours. Therefore, makeup systems, in addition to those currently available under SB0 conditions, are not required to maintain core cooling.

The modifications and associated procedure changes identified in Parts A, B and C above will be completed within one year or by the next refueling outage (whichever is later) after the notification provided by the Director of the Office of Nuclear Reactor Regulation in accordance with 10CFR50.63(c)(3).

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