ML20042D835

Submits Supplemental Info Re Util Response to Station Blackout Rule & Advises That Results of Plant Evaluations Demonstrate Ability to Cope W/Station Blackout for Proposed 4 H Duration W/O Reliance on Ac Power Sources

ML20042D835
Person / Time
Site:	River Bend
Issue date:	03/30/1990
From:	Deddens J GULF STATES UTILITIES CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
RBG-32597, NUDOCS 9004100188
Download: ML20042D835 (11)

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OULF STATES UTILITIES COMPANY  ;

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t March 30, 1990 ,

RBG-32597  !

File No. G9.5, G9.21.2 i U. S. Nuclear Regulatory Comnission 1 Doc eent Control Desk washington, D. C. 20555 i l

Gentlemen:

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River Bend Station - Unit 1 Docket No. 50-458  :

Gulf States Utilities (GSU) -initially responded to the Nuclear l' Regulatory Cmmission's (NBC) station blackout rule, 10CFR50.63, April 17, 1989 (RBG-30553) . Subsequently, the Nuclear Management and Resources Council (NUMARC) requested that GSU (along 'with other ,

utilities) supplement that previous submittal with a letter to the NRC indicating that:

1) The previous subnittal was based on the use of NUMARC 87-00 ,

I guidance including the clarifications in the attachment,

2) Any deviations fr a the accepted NtNARC 87-00 methods have been or will be clearly indicated, t

3) The GSU selected diesel generator target reliability of 0.950 '

will be maintained.

This letter provides that supplemental response.

I Gulf States has examined our previous subnittal and verified that River l Bend Station was evaluated using the guidance provided in Nuclear i l Management and Resources Council (NUMARC) 87-00, " Guidelines and l Technical Bases for NLNARC Initiative Addressing Station Blackout at Light Water Reactors" except where Regulatory Guide 1.155 takes l precedence.

1 1 The River Bend Station evaluation uses the SBO evaluation process frm l NUMARC 87-00 which allows the use of River Bend specific analyses based l on detailed analytical models. In order to address NUMARC's request, -

l the enclosed attachment provides clarification where GSU has used plant specific analyses permitted by NUMARC 87-00 rather than generic values suggested by NlNARC 87-00.

0 9004100188 900330 h V PDR ADOCK 05000458 { j P PDC l  %.

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As stated in our previous sutunittal, GSU has selected a target EDG  :

reliability of 0.95. GSU will maintain that target reliability.

l The results of the River Bend Station evaluations dmonstrate the' ability to cope with a station blackout for the proposed four hour .

j station blackout duration without reliance on AC power sources.

Sincerel ,  ;

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, J. C. Doddens l Senior Vice President '

River Bend Nuclear Group At> t JCD/KES/TFP pg j t

cc Director of the Office of Nuclear Reactor Regulation i U. S. Nuclear Regulatory Cm mission Washington, D. C. 20555  ;

U. S. Nuclear Regulatory Camission Region IV 611 Ryan Plaza Drive, Suite 1000 .

Arlington, TX 76011

• NRC Senior Resident inspector "

l Post Office Box 1051 St. Francisville, IA 70775 4 Nuclear Management and Resources Council 1 1776 Eye St. N.W., Suite 300 Washington, DC 20006-2496 l

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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 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 i factors that must be considered in specifying the station blackout duration. Section 50.63 requires that, .for the station blackout duration, the plant be capable of maintaining core cooling and appropriate containment integrity. Section 50.63 further requires i that each licensee submit the following information:

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1. A proposed station blackout duration including a justification for the selection based on the redundancy and reliability of the onsite emergency AC power sources, the expected frequency of loss of offsite power, and the 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 I to equipment and associated procedures necessary for the specified SBO duration. ,

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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. -

Gulf States Utilities has evaluated the River Bend Station against the requirements of the SBO rule using guidance from NUMARC 87-00 excep.t where RG 1.155 takes precedence. The results of this evaluation are detailed below.

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A. Proposed Station Blackout Duration NUMARC 87-00, Section 3 was used to determine a proposed SBO 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 ont

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

b. Estimated frequency of LOOPS due to extremely severe weather (ESW) place the plant in ESW Group 13 LOOPS due to severe weather place '

c. Estimated frequency of the plant in SW Group 1; e

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

Discussion LOOP Frequency - Grid Loss i For classification of River Bend Station as a plant with expected frequency of grid related loss of offsite power less than once per 20 years, GSU conducted a review of USAR descriptions of transmission lines feeding the site, system stability studies, and outage histories of incoming power lines. In addition, available historical records indicate GSU has not experienced a system wide grid failure in the last 49 years of operation.

LOOP Frequency - Extremely Severe Weather GSU has determined the River Bend Station to be in ESW Group 1 based on a plant specific analysis for extremely severe weather for the River Bend Station area. The site specific analysis determined the ESW Group to be Group 1, using Table 3-1 in NUMARC 87-00.

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LOOP Frequency - Severe Weather GSU has determined River Bend Station to be in SW Group;l based on calculations using NUMARC 87-00 methodology. The source of various factors for this determination is as follows:

hy -

Snowfall -

NUMARC 87-00, Table 3-3 h -

Tornado Frequency -

Plant Specific Analysis h2 -

Storm - Plant Specific Analysis 3

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Salt Spray - NUMARC 87-00, Table 3-3 4

b -

Right of Ways -

NUMARC 87-00, p. 3-7 c -

Salt Spray -

NUMARC 87-00, p. 3-7 In addition, using data provided in NUMARC 87-00, Table 3-3 yields the same classification'of SW Group 1.

Offuite Power System -

I Group r

GSU determined River Bend Station to be in the I 1/2 Off-site Power System Group. GSU used the methodology described in NUMARC 87-00 to evaluate the Off-Site Power System Group Classification of I 1/2. The I 1/2 classification is based on:

a) Division I and Division II safe shutdown buses are normally supplied through physically separated and electrically independent preferred power sources, b) Loss of normal station service power does not affect availability of Division I or II buses.

2. The emergency AC power configuration group is C based on l a. Two emergency AC power supplies not credited as alternate AC power Sources; r

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

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Discussion:

Number of EAC Power Supplies Normally Available GSU used the methodology described in NUMARC 87-00, Section 3.2.2, to evaluate the AC Power Configuration Group. The River Bend Section design includes two independent and redundant standby power supplies which are dedicated to providing emergency AC power to the safe shutdown buses. These are the Division I and II emergency diesel generators (EDG's).

alternato AC power source. Neither of these EDG's is used as an Number of Necessary EAC Standby Power Supplies GSU used the methodology described in NUMARC 87-00, Section 3.2.2 to evaluate the number of necessary EAC standby power supplies.

GSU's evaluation concluded only one of two available EDG's is required to supply safe shutdown loads to their respective 4.16 KV ENS standby buses.

3. The target EDG reliability is 0.95.

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

Discussion:

EDG Target Reliability

• GSU selected a target EDG reliability based on an evaluation using the methodology of NUMARC 87-00, Section 3.2.3. This evaluation was done in accordance with NSAC-108.

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

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

2. Plant blackstart: " Procedure No. B-3, Plant Blackstart Procedures", (GSU Corporate Procedure).

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The following River Bend Station procedures have been reviewed and the changes necessar the following areas:y to meet NUMARC 67-00 will be implemented in

1. Severe weather: " SOP-0029, Severe Weather Operation".

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

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

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

niscussion:

Modifications to River Bend Station procedures are currently being evaluated. Final procedures will be in place by the commitment date previously submitted. scheduled Procedure changes will reflect the detailed SB0 position developed in response 87-00. to NUMARC 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 asses, sed using NUHARC B7-00, 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 inventory providos sufficient water inventory condensate hours for over four operation during a station permissible condensate storage tank blackout. The minimum le"el provides 125,000 gallons of water, which exceeds the coping with a four-hour required quantity for station modifications are needed to utilize this water- ciackout. No plant source.

Availability of the minimum condensate stora tank inventory will be ensured through procedural changes. ge Discussion:

GSU Stone conducted and Webstera plant specific analyses of RPV level control using Engineering Corporation's Analyses were conducted for a number of cases computer modes.

to investigati the appropriate SBO management conditions, and strategy, determine containment inventory.

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The case which determined that 5.9 hours1.041667e-4 days <br />0.0025 hours <br />1.488095e-5 weeks <br />3.4245e-6 months <br /> of inventory was available in the condensate storage tank at the minimum technical Specification value of 125,000 gal. did not consider reactor coolant system leakage. Consideration of reactor recirculation pump leakage and maximum allowed leakage by Technical Specifications will slightly reduce the amount of time that CST is available.

Additional analyses were conducted to confirm that CST inventory will not be exhausted before the required 4 hour4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br /> coping duration.

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 IE batteries have sufficient capacity to meet station blackout loads for four hours without load stripping.

Discussion:

GSU reviewed existing battery calculations for standby batteries and determined they met NUMARC 87-00 guidance. The batteries were sized using the lowest expected electrolyte temperature. Load stripping is not required to maintain the required 4 hour4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br /> coping duration for battery capacity.

3. Ccmpressed 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.

Discussion:

GSU has verified that our previous position was based on methodology in NUMARC 87-00, Section 7.2.3. .

In addition, GSU has performed an extensive Safety System Functional Inspection (SSFI) on the instrument air system. Results from this SSPI were incorporated into the GSU response to Generic Letter 88-14. Modifications to meet GL 88-14 included the installation of back-up air cylinders in the control and auxiliary buildings.

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4. Effects of Loss of Ventilation (Section 7.2.4[

TheassumptioninNUMARCSf-00,Section2.7.1thatthe control room will not exceed I?.0 F during a station blackout has been assessed. This temperature limit is based on " maintaining the  !

control room equipment temperature at 120 r with the panel doors open. the control room '

ambient air This is equivalent temperature at to,r11miting 104 with a 15n r differential temperatute within the equipment panels. The steady state ambient air temperature within the Rgver Bend Station control l room has been calculated to exceed 104 r during a four hour  ;

station blackout duration. Therefore, additional measures must  ;

be taken to limit the temperature level in the control room. i i

Discussion:

The control room temperature response was determined by performing  !

a plant specific transient temperature analysis and a steady state  !

temperature analysis with verstilation. l The transient analysis used a Stone & Webster computer code. Heat l sources in the control room were determined by a plant specific r analysis. Heat sinks used were concrete walls and control cabinet

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steel. The results of ghe transient analysis indicates the control room will exceed 104 r during a four hour station blackout

, duration.

The steady state analysis includes ventilation and used traditional  !

heat transfer methods, i 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 roon equipment required to cope with a stationblackouthasbeenaddressedbymaintagningthecontrolroom ambient air temperature at or below 104 F during a four hour station blackout duration, i i

GSU used plant specific methodology to determine the temperature {

response of the RCIC equipment room, HPCS equipment room, and RHR l equipment room. This included detailed evaluation of heat sources  !

and use of a Stone & Webster computer code to evaluate the transient temperature response. [

Alternatives for limiting the  !

control room temperature response are being evaluated.  !

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An evaluation was performed for the heatup of the main steam tunnel during an SB0 event. Based on this evaluation, a bypass of the leak detection system for RCIC isolation must be performed.

Procedure AOP-0050, " Station Blackout", will include instructions to bypass the leakage detection system high temperature RCIC trip.

5. containment Isolation (Section 7.2.5)_

The plant list of containment isolation valves has been reviewed to verify that valves which must be capnble 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 AOP-0003, " Automatic Isolations" to include additional guidance on closing isolation valves which do not meet the NUMARC 87-00 exclusion criteria during a station blackout.

Discussion:

GSU used the NUMARC 87-00 evaluation methodology described in Section 7.2.5. This evaluation was conducted considering that locked closed valves and closed valves were in the same category.

These valves were reviewed again considering the supplemental information in Enclosuro 1 to NUKARC's January 4, 1990 letter to Gulf States Utilities. The results of this review do not change the above position.

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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 was used for this assessment. The expecttd rates of reactor coolant inventory loss under station blackout 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 880 conditions, are not required to maintain core cooling.

Discussion:

This analysis has been updated to include additional leakage. It has been confirmed that additional makeup systems, other than the minimum CST inventory, are not required to maintain core cooling for the 4 hour4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br /> coping duration, schedule 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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