Text

Summarizes Util Supplemental Response & Plan of Action on Outstanding Issues Noted in Re Seismic & Svc Water Flow Concerns Per Safety Sys Functional Insp at Plant. Results & Conclusions & Nutech Evaluation Encl
	ML20237K162
Person / Time
Site:	Cooper
Issue date:	08/14/1987
From:	Trevors G; NEBRASKA PUBLIC POWER DISTRICT
To:	; NRC OFFICE OF ADMINISTRATION & RESOURCES MANAGEMENT (ARM)
References
	TAC-66723, NUDOCS 8708190114
	Download: ML20237K162 (35)
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GENERAL OFFICE Nebraska Public Power District

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August 14, 1987 U.S. Nuclear Regulatory Commission Attention:

Document Control Desk Washington, DC 20555

Subject:

Safety System Functional Inspection at Cooper Nuclear Station, Brownville, Nebraska

Reference:

A.

Docket 50-298 B.

NRC Region IV Division of Reactor Safety and Projects letter dated July 9, 1987 C.

Nebraska Public Power District's letter NLS700358 dated July 24, 1987 Gentlemen:

At a meeting held on June 30, 1987, at the Nuclear Regulatory Commission (NRC)

Region IV office at Arlington, Texas, Nebraska Public Power District (NPPD) outlined its action plan for the major issues emanating from the recent Safety System Functional Inspection at the Cooper Nuclear Station (CNS).

Reference B requested that NPPD document the completed actions and future plans in regard to the topics listed below:

o AC Voltage Studies / Sufficiency o

DC Voltage Studies / Sufficiency o

Seismic Concerns o

Ventilation / Temperature Problems o

Service Water System Flows NPPD responded to the Seismic and Service Water flow concerns and gave a partial response to the remaining items in Reference C.

The District's supplemental response and plan of action on the outstanding issues are summarized in this letter.

The calculations, studies, and evaluations described herein are available for review at NPPD Offices.

A.

AC Voltage Studies / Sufficiency 1.

The AC Voltage Drop Analyses have been performed by Burns and Roe and NPPD personnel.

The analysis covering the segment of the distribution system from the off-site power lines to the MCC terminals on the 480 VAC system has been performed using Burns and Roe's Computer Program ELO 110.

NPPD personnel are perforning the voltage drop analysis for the remainder of the AC Distrib tion

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August 14, 1987 a.

The Burns and Roe study indicates the following:

(1)

For the 161 kV line supplied via the 345/161 kV transformer at CNS, the electrical distribution system i

powered via the Start-up transformer can withstand a j

" block" start of Emergency Core Cooling System (ECCS) equipment with the normal auxiliaries (essential and non-essential) remaining energized.

1 (2)

For the 69 kV line supplied from the Omaha Public Power 1

District (0 PPD) system, the emergency off-site supply, the

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electrical distribution system powered via the amergency station transformer can withstand a sequential starting of ECCS equipment as well as a phased start of two Service Watei ' umps with all non-essential equipmen,t de-energized.

~,he above cases meet the design requirements of the off-site power supply criteria for CNS; two independent power supplies in addition to the emergency diesel generators.

Attachraent A gives a summary of the Voltage Drop Analysis to the 480 VAC MCC terminals.

b.

NPPD is performing a voltage drop study on the 480 VAC and 120 VAC systems, NPPD Calculation 87-132.

The complete and in-depth analysis of all circuits will not be complete for a considerable time due to the magnitude of the task.

However, the circuits analyzed to date are adequate to perform their j

safety related functions under postulated voltage conditions.

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Voltage and current measurements have been taken to establish the margin between the calculation and the field condition for 120 tIAC component already analyzed.

The readings taken indicated there was a considerable margin of conservatism in the calculation.

Additional readings will have been taken under Special Test Procedure 87-014 when the complete in-depth analysis has been completed.

2.

The 4160 V AC Momentary Fault Study commissioned by NPPD indicates that while performing the monthly surveillance test on the emergency diesel generator, a phase-to-phase momentary fault, if it occurred, could be as high as 63,800 A.

The switchgear is certified to withstand 60,000 A and the breakers 58,000 A faulted current.

The District has undertaken a study of the effects of such a faulted condition occurring.

Following consultations with the manufacturer of the switchgear, General Electric, and discussions with consultant agencies, NPPD has determined that the ability to perform and maintain a safe shutdown of CNS from 100 percent power is not jeopardized by a phase-to-phase momentary fault on the 4160 V system during the surveillance testing of one of the diesel generators.

Page 3 August 14, 1987 The bases for this statement are:

a.

Only one diesel generator is tested at a time up to eight hours per month.

There are two emergency diesel generators at CNS.

b.

The magnitude of the fault, only 61 percent above faulted capacity, is unlikely to cause damage to other equipment in the same division if the fault is associated with the breaker.

c.

The fault can only occur on one safety-related division since only one diesel is tested at a time.

Therefore, a fault would not damage the redundant safety-related division (G.E. concurs with this position),

d.

For a fault of such magnitude to be produced, the fault has be f

occur at a specific point in the AC cycle to give a 1.6 DC offset.

e.

The switchgear and breakers are inspected at regular intervals, and the condition of equipment is well documented.

CNS has not experienced any problems of degradation of equipment in the switchgear during 13 years of commercial operation.

f.

The probability of a phase-to-phase fault occurring unpr the conditions postulated above is remote, lower than 10-per reactor year.

g.

The faulted capacity of the equipment is adequate if the diesel generators are not being operated in the test configuration.

l Based on the above statements, it is considered that the probability of a fault of such magnitude occurring is extremely low, and if it did, it could not damage the redundant essential switchgear.

Thus, the ability to perform a safe shutdown in the event of a transient or design basis accident is assured.

l B.

DC Voltage Studies / Sufficiency The DC Voltage Drop Study and the CC Load Study have been completed. The studies were performed by CYGNA Energy Services.

NPPD has completed an initial review of both studies and a full review is currently in progress.

3 l.

The DC Load Study shows that the existing batteries and chargers are l

capable of supporting the system demand during accident conditions.

2.

The DC Voltage Drop Study was satisfactory with the exception of the voltage drop associated with the closing coil circuits in relation to the 4160 V Breakers IFS and 1GS (Start-up transformer breakers),

as well as EG1 and EG2 (diesel generator breakers). The study shows a calculat ad voltage of 78 V at the coils. The coil manufacturer's specification states a 90 V minimum operating voltage is required.

A Special Test Procedure (STP 87-013) was conducted to measure the 1

e--___-__---_--.

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August 14, 1987 minimum voltage required to operate the coil.

The results of the STP showed that depending upon the type of breaker (1200 A or 2000 A) the closing coils operated at voltages ranging between 40 V and 58 V.

Repeatability of results was proven for each of the four breakers, tested with less than five percent variance in readings.

Even assuming a 20 percent variance on the 58 V reading, the minimum voltage for operation was demonstrated to be below the calculated minimum voltage of 78 V.

The DC Study indicates that the DC electrical distribution system meets the design criteria for CNS.

The DC calculations are available for review at NPPD Offices.

C.

Control Building HVAC Study In response to the concerns expressed during the Safety System Functional Inspection to the adequacy of the HVAC system in the Control Building, an HVAC study was initiated.

NUTECH Engineers performed a thermal transient evaluation for:

AC Switchgear Rooms IF and 1G, DC Switc'hgear Rooms 1A and 18, and Battery Rooms 1A and IB.

The results of the study, given in Attachment B, show that should ventilation fail during an accident or normal operation, the temperatures in the rooms in question are maintained within equipment specifications; however, the use of portable HVAC equipment is required.

Station Operating Procedures state that should ventilation fail, the dedicated portable ventilation equipment will be made operational within one hour.

In addition, if at any time the temperatures in the switchgear rooms rise above 104*F, additional ventilation will be supplied using the portable dedicated equipment until the ambient temperatures can be maintained below 104*F.

In response to concerns about the ambient temperatures in the battery rooms during the winter, the calculations associated with the evaluation show the temperature would fall to to 71*F with a Control Building minimum design temperature of 65'F following a loss of Control Building

HVAC, i

Attachment B gives a summary of the results and conclusions from the evaluation in greater detail.

The NUTECH evaluation together with associated calculations are available for review at NPPD Offices.

l l

Page 5 August 14, 1987 NPPD is currently evaluating the undertaking of further studies and the l

possible modifications to further improve the margin of operability of essential systems at CNS.

Sincerely, j

or e A. Trevors Division Manager of Nuclear Support GAT /APH:cbil2/4(PPGCIS)

Attachments cc:

Regional Office USNRC - Region IV Resident Inspector Cooper Nuclear Station I

i I

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l

Attachment A to Nebraska Public Power District's Letter to the NRC dated August 14, 1987 q

l This Attachment is a synopsis of the A ' voltage drop study performed by Burns and Roe.

1.0 Background

Nuclear Regulatory Commission (NRC), in attachment to its letter dated August 8, 1979, stipulated certain guidelines regarding the adequacy of i

Station Electric Distribution System voltages (Ref. 2.4.1).

A voltage l

drop analysis computation (Ref. 2.1) was performed for Cooper Nuclear l

Station (CNS) in 1979 to verify the adequacy of system voltages to start I

and operate all safety-related loads.

i 1

During May and June 1987, the NRC performed a Safety System Functional l

Inspection (SSFI) of the CNS Emergency Electrical system.

As a part of the SSFI, the NRC investigated the prevailing voltage profile study. The l

NRC noted that several values used in the prevailing voltage profile study were slightly different when compared with the present plant i

conditions.

In response to NRC questions, NPPD committed to undertake a systematic reevaluation of all the factors that may affect the plant voltage profile during a postulated Loss of Coolant Accident.

NPPD reanalyzed the transmission line network data to determine the system parameters which should be used for the CNS licensing basis. This information is provided in the Reference 2.7.

A Special Test Procedure, STP-87-010 (Reference 2.2) was written to aid in the determination of CNS plant load data.

STP-87-010 was performed to I

f obtain the actual load data while CNS was operating near its rated capacity.

Based on these measured values and examination of the plant auxiliary system operational requirements, a conservative plant loading model was established which is documented in the NPPD load data calculation (Reference 2.3).

2.0 References 1

2.1 Burns and Roe " Voltage Drop Analysis Computations and Test Procedure to Verify Computed Values,", Rev. 1, December 18, 1979

)

(Calc. No. 2.15.01),

j 2.2 NPPD Special Test Procedure:

STP-87-010-Measurement of Plant Electrical Loads.

2.3 NPPD Load Data: NPPD Calculation No.87-104.

2.4 NRC Guide Lines & NPPD Response:

2.4.1 NRC Guidelines, attachment to NRC letter data August 8, 1979 "Ref: Adequacy of Station Electric Distribution l

Systems Voltages." l L..

2.4.2 NRC letter Docket No. 50-298 dated June 3, 1977, addressed to NPPD with attachments.

2,4.3 NPPD letter dated July 18, 1977, addressed to NRC.

l 2.5 BRC Computer Program ELO110 Rev. 4

" Electrical System Design for 1

Three-Phase Short Circuit, Voltage Drop and Transformer Impedance Sizing" (Attachment I).

2.6 B&R Drawings:

1.

Burns and Roe Drawing 3001, Rev. No. N3 - Main One Line Diagram.

2.

Burns and Roe Drawing 3002, Rev. No. N13 - Auxiliary One Lina Diagram, Sh. 1.

3.

Burns and Roe Drawing 3003, Rev. No. N13 - Auxiliary One Line Diagram, Sh. 3.

4.

Burns and Roe Drawing 3004, Rev. No. N9 - Auxiliary ' One Line Diagram, Sh. 3.

5.

Burns and Roe Drawing 3005, Rev. No. N10 - Auxiliary One Line Diagram, Sh. 4.

6.

Burns and Roe Drawing 3006, Rev. No. N23 - Auxiliary One Line Diagram, Sh. 5, 7.

Burns and Roe Drawing 3007, Rev. No. N18 - Auxiliary One Line Diagram, Sh. 6.

8.

Burns and Roe Drawing 3010, Rev. No. N25 - Vital One Line i

Diagram.

9.

Burns and Roe Drawing 3401, Rev. No. N7 - Auxiliary One Line Diagram.

10.

Burns and Roe Drawing 3412, Rev. No. N4 - Augmented Radwaste Bldg. and ACAD System-Lighting Panels and Fixture Schedules, i

11.

Burns and Roe Drawing 3012, Rev. N3 - Main Three Line Diagram, Sheet No. 3.

12.

Burns and Roe Drawing 3019, Rev. N10 - Switchgear Elementary Diagrams, Sheet No. 3.

13.

Burns and Roe Drawing E150, 2.7 NPPD Data:

2.7.1 System Impedance and Grid Voltage Data 69 kV line.

2.7.2 System Impedance and Grid Voltage Data 161 kV line..__ _ _____-_______________ _ -

I 2.7.3 Cable / Bus Impedance Data: NPPD Calculation No.87-103.

]

i 2.7.4 NPPD Correspondence i

1.

161 kV and 345 kV System Impedances Letter from R. Rahrs to R. Lindstrom dated July 17,

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1987.

2.

69 kV System Impedances Letter from Jim Hackney to W. Fischer dated l

August 4, 1987.

3.

161 kV Bus Voltages Letter from J. Doudna to J. Hackney dated July 21, 1987.

i 4,

69 kV Bus Voltage Letter from I. Goering to W. Fischer dated July 6, 1987.

2.8 Vendor Data:

2.8.1 Start-up Station Service Transformer Test Data.

2.8.2 Emergency Station Service Transformer Test Data.

2.8.3 4.16 kV/480 V Sub-Station Transformer Test Data.

2.8.4 4 kV Motor Data.

2.8.5 460 V Motor Starter Data.

2.9 Cooper Nuclear Station Updated Safety Analysis Report - May, 1985.

2.10 Cooper Bessemer Company to Burns and Roe - March 5, 1974.

Certified report of engine field tests.

2.11 General Electric Pub. 362A648-0, Fig. 2.

2.12 Burns and Roe Calc. No. 2.09.06, Sh. 19.

2.13 Telecon:

K. A. Bugenis (B&R) and A. Gelfen (Telemechanique).

2.14 ITE - Electrical Products catalog,' Magnetic Starter Data Section 6.1.1.2, Page 7 2.15 Westinghouse - Magnetic Starter Data Section 8220, page 59.

3.0 Discussion 3.1 Start-up A.C. Power Source.

During normal plant operation, the station auxiliaries are powered from the Normal Station Service Transformer, which is connected to i

the CNS generator output.

A unit trip results in the tripping of 345 kV breakers and the loss of feed to the Normal Station Service Transformer.

An automatic fast transfer takes place to connect the Start-up Station Service Transformer in under 8 cycles, and the station auxiliaries continue to operate without interruption of power.

The Start-up Station Service Transformer is connected to the grid via a 161 kV line.

If a Loss of Coolant Accident (LOCA) occurs, a CNS unit trip will take place, and as a result, the fast transfer will occur without interruption of power to the plant auxiliaries.

Beside providing power to the running plant auxiliaries, the Start-up' Station Service Transformer will also be subjected to an automatic block start of the safety loads such as:

two (2) Residual Heat Removal (RHR) pumps and one (1) Core Spray Pump on c;ach of the two 4160 V Emergency Power Buses IF and 1G.

In addition, certain other critical loads on the 480 V critical power buses will also be connected simultaneously.

3.2 Emergency A.C. Power Source Should the 161 kV Start-up A.C.

Power Source not be available in I

the event of a fast transfer, the 4160 V Critical Power Buses IF and 1G would automatically be isolated from the other plant auxiliaries and then be connected to the Emergency Station Service Transformer.

After securing the power on 4160 V Buses IF and 1G, the 4160 V safety related loads are automatically connected and powered in a predetermined' sequence.

The 480 V MCC critical loads stay connected, hence, receive power as soon as voltage is available on the 4160 V Buses IF and 1G.

The LOCA signal also initiates the start of the Emergency Diesel Generator Sets 1A and 1B and keeps them ready, in the event of loss of power from the Emergency Station Service Transformer, which is connected to the 69 kV transmission line operated by Omaha Public Power District (OPPD).

3.3 Under-voltage Protection Schemes Normally, the plant auxiliary power buses operate at a voltage range of 3950 to 4250 V corresponding to a nominal 345 kV grid system range of 345 to 365 kV (Ref. 2.9 section 3.6).

In order to preclude damage to motors on essential equipment due to L

under-voltage conditions, the emergency 4160 V Power Buses IF and 1G, are provided with two levels of undervoltage protection.

The first level of undervoltage protection at Buses IF and 1G is provided by relays (CE Type IAV54E) 27/1F and 27/1G.

Each relay initiates tripping of all motor breakers, isolates its respective bus and starts its associated Diesel Generator.

These relays are induction disc type rel ays and as part of their design are subjected to an inherent time delay.

The second level undervoltage scheme is designed to protect the critical electrical equipment from a sustained degraded voltage condition.

The second level undervoltage relays on Buses IF and 1G and are also GE Type IAV 54E.

Besides the inherent time delay associated with the GE-IAV54E relays, there is an intentional 10 second time delay in the associated control circuit after which load shedding takes place to guard against a sustained undervoltage condition.

3.4 Transformers Taps The Station Start-up Service Transformer-tap setting is presently 2 which corresponds to 165,025 V with the secondary rated at 4160 V.

The Emergency Station Service Transformer tap setting is presently 2, which corresponds to 68,800 V with the secondary side rated at 4160 V.

3.5 Grid Voltages Grid voltages associated with off-site electrical power supplies to CNS are given below.

The operating range for the 345 kV system is from 3'55 kV to 365 kV, The NPPD 161 kV Bus at CNS is supplied by two sources, one being via a NPPD 345/161 kV transformer and the other being from the OPPD system. 161/kV line from Auburn.

A separate NPPD study has analyzed the 161 kV grid conditions The minimum voltage for the 161 kV line from Auburn is estimated at 159.4 kV, For the 161 kV line st,; 'ied via 345:161 kV transformer the minimum voltage is estimated at 165.4 k7.

Both cases evaluated assume a loss of CNS generation.

The high and low voltages for the 69 kV line are calculated to be 72.08 kV and 65.55 kV.

In the analysis performed by Burns and Roe all the above cases up to the 480 V MCC terminals have been considered.

The results arc tabulated in this Attachment.

Plant Load Dat a:

I To reflect re alis tic loading conditions in the analysis which initially used nameplate data, a Special Test Procedure (STP 87-010) was written to determine the actual station electrical load while operating near 100 percent power.

The results of the test procedure were scrutinized and further analyses were performed to determine the maximum credible electrical loading criteria (NPPD Calculation 87-104). The load information was used in the Burns and Roe calculations.

i l

The voltage drop study was performed using Burns and Roe Computer Program ELO110 - Revision 4.

The program is QA certified for use in the nuclear industry.

Several cases were developed to represent plant parameters, and accordingly a number of computer iterations were performed for the different grid voltage conditions and plant loading criteria.

The cases developed were:

l a.

Block starting of Emergency Core Cooling System (ECCS) equipment with all other auxiliaries operational and with the power source being supplied from either the 345:161 kV j

transformer or via the 161 kV line from Auburn through the Start-up Transformer.

b.

Sequential starting of the ECCS equipment with all other auxiliaries operational and with the power source supplied from either 345:161 kV transformer or via the 161 kV line from Auburr through the Start-up Transformer.

c.

Sequential starting of the ECCS equipment plus the phased starting of two Service Water pumps with all non-essential equipment "off line" and with power supplied from the 69 kV line via the Emergency Station Service Transformer.

The Station Distribution Network was modeled within the constraints of the Burns and Roe program up to the MCC terminals.

Cable impedance values used in the study were computed on a percent basis of 100 MVA and are reflected in NPPD Calculation 87-103.

The limitations of the program resulted in a number of conservatism

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being adopted such as starting all 480 V machinery simultaneously.

j

" Dummy" transformers and buses was utilized to reflect the varying conditions of the plant.

A detailed account of the modeling procedure is given in the Burns and Roe Study 4107-013.

A detailed review of plant voltage profiles has been performed by NPPD for the worse cases, maximum and minimum supply voltage.

.Results The results of the Burns and Roe study are shown in tables at the hek of this Attachment.

The computer input, output, and records of all other calculations are available for review at the NPPD offices.

The results are summarized as follows:

a.

For power supplied via the 345:161 kV transformer at CNS the systems evaluated can withstand a block as well as sequential starting of the ECCS equipment.

b.

For power supplied from the 161 kV line from Auburn the essential bus bars will trip on undervoltage if the system is subjected to a block start of ECCS pumps.

If the system is subjected to a sequential start, the essmtial bus bars will remain energized, c.

For power supplied from the 69 kV line via the Emergency Station Transformer the system will sustain a sequential start of ECCS and service water equipment with all non-essential systems deenergized.

l 6-l

4 '

The tables attached give a summary of the results.

Conclusion The review of voltage profiles for CNS for the Offsite power supplies indicate that under nonal and emergency conditions the electrical distribution system to the 480V MCC terminals is adequate to withstand a block / sequential start powered via 161 kV line from the 345:161 kV transformer or a sequential start powered via the 69 kV line. l 1

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Attachment B to Nebraska Public Power District's Letter to the NRC Dated August 14, 1987 This attachment gives a summary of the results, assumptions, and methodology in regard to the Thermal Transient Evaluation for the Control Building at CNS performed by NUTECH Engineers.

1.

.In response to the NRC's concerns expressed during the recent Safety System Functional Inspection, NPPD initiated an evaluation of the ventilation systems associated with essential electrical equipment located in the Control Building at CNS.

The evaluation was performec' on Battery Rooms 1A and 1B, DC Switchgear Rooms lA and 1B, and AC Switchgear Rooms 1F and 1G to develop the bounding transient room temperature profiles, resulting from Loss of Coolant Accident (LOCA), Loss of Offsite Power (LOOP), High Energy Line Break (HELB), and Loss of Venti' ation (IAV) events.

2.

The arrangement and function of the essential Battery and Switchgear Rooms is described in the Updated Safety Analysis Report (USAR) for CNS.

3.

The Ventilation System for the Battery Rooms is provided by dedicated exhaust fans powered from the essential bus.

The air is drawn out of the rooms utilizing one fan with the other acting as the redundant component.

For the DC Switchgear Rooms, ventilation is provided by two supply fans (one for each room) powered from a non-essential bus which provide Control Building corridor air to these rooms.

Tae air is then exhausted out of the rooms through a louver in the access door.

For the AC Switchgear Rooms IF and 1G ventilation is provided by a pair of redundant supply fans which provide outdoor air to the rooms.

There are redundant discharge fans which draw air from the critical switchgear rooms and either recirculate or discharge the air outdoors.

The electrical supplies foi the supply and exhaust fans are non-essential.

The dedicated portable ventilation system for the D.C.

Switchgear Rooms consists of a 3,000 cfm fan drawing air from outside the Control Building and discharging through portable trunking into the rooms.

The dedicated portable system for the AC Switchgear Rooms consists of two sets of fans and portable trunking.

One fan rated at 4,000 cfm draws air through the north doors of Switchgear Room 1F and exhaust into Room 1G.

The second fan, rated at 8,000 cfm draws air from Room 1G and 1F exhausting to the outside via the south door from Room 1G.

Power for these units is essential.

4.

The analysis was conducted for a combination of accident scenarios to determ'ne ^he worst case.

HELB combined with loss of ventilation is considered to be the worst case.

The analysis for the summer condition

[

is based on the climatic data given in the ASHRAE Handbook, for Otaaha, Nebraska.

The initici room temperatures for the summer conditionn are assumed to be 104*F.

.)

For winter conditions, the worst case is air supplied at the minimum design basis temperature for the Control Building of 65'F, with an initial Battery Room temperature of 80'F.

5.

The normal air flow rates have been measured as 900 cfm supplied to DC Switchgear Rooms 1A and IB, 1250 cfm exhausted from the Battery Rooms 1A F

zad 1B, 3800 efm supplied to AC Switchgear Rooms, and 4200 cfm exhausted from the AC Switchgear Rooms.

6.

The analytical methods are based upon standard HVAC formulae and techniques and have been computed using the NUTECH Engineers HVAC Computer Program, which has been verified and validated for use in the nuclear industry.

The time steps in the computation were at 1-second inte rvals.

The heat input included input from equipment as well as lighting.

The heat loads from equipment were calculated assuming constant loading at nareplate parameter throughout the transient with the exception of the 4160 5 :480 V transformer in Rooms IF and 10 The heat 3

loads for the transformers was based on the maximum credit' s loads calculated from the results of STP 87-010.

7.

The rooms being analyzed contain 298 ossential devices representing 23 typss of equipment by 7 different manufacturers.

Correspondence from I

vendors, coupled with testing of components at Wyle Laboratories, gives a high degree of assurance that equipment will operate at the elevated temperatures of 140*F for the DC Switchgear Rooms and 150*F for the AC Switchgear Rooms for short durations during the postulated events.

8.

The results of the evaluation are tabulated in this Attachment.

9.

Die conservatism in the evaluation process are considered to give sufficient margin, so that in reality the peak of the temperature transients will be lower than calculated.

In addition, where portable ventilation is utilized during a Loss of Ventilation incident the air flos rate into the DC Switthgear Room is approximately 40 percent greater than in the normal operating condition.

This factor alone is considered to account for approximately a 9'F margin in conservatism.

Other I

conservatism in the calculation process are:

a)

In general, the heat loads for the equipment are based on the nameplate ratings of current: voltage, and power.

The transformer heat load used in the analysis for Critical Switchgear Room 1F is at least 30 percent greater ths.n the normal measured load on the transformer.

In addition, the equipment is assumed to instantaneously reject heat at its maximum rate for a conservatively specified duration or for the entire duration of the transient.

Minimal credit is taken for sequencing or tripping of loads which would actually occur during the postulated events, b)

The initial temperatures for the Battery and Switchgear Rooms, and the adjacent room spaces are conservatively assumed to be at 104*F, the maximum design temperatures from the start of the incident.

In addition, the maximum outdoor ambient temperature is assumed to --.__._.___.

_-_____-_.,____m__-

i exist throughout the duration of the transient.

In reality, the manimum ambient temperature for a design basis day can be expected to vary by an sverage of 24*F over a 24-hour period based on ASHRAE

~ figures.

c)

The iny heat sinks which exist in the battery and switchgear rooms 1

havt ieen neglected in the transient analysis.

These included the i

the a1 mass of equipment contained in the rooms and the energy I

transfer paths which occur at wall and floor penetrations for I

ducting, piping, and conduit. While these openings are well sealed, the higher - heat conduction rate at these locations to the surrounding ares has been neglected.

For the critical Switchgear Rooms, the heat absorption capacity of

)

the non-heat generating devices located in these rooms can be expected to slow the rate at which the air temperature rises in the room such that the maximum temperatures would be lowered by about 5'F.

d)

The equipment in the affected rooms would only be subjected to a high ambient air temperature for a short period of time until

,artable ventilation is made operational.

The active components for each essential device are not directly exposed to transient room temperature conditions but are enclosed within metal clad switchgear or are within an equipment case.

A thermal lag effect would occur such that the essential components would not be expected to reach the peak temperatures postulated, and would not be subjected to temperatures above 150*F for a significant length of time, i.e.,

on the order of minutes.

The short duration temperature effects should not prevent proper operation of the equf.pment.

These facts, coupled with the conservatism outlined in above, plus the margin inherent in components of this type, give a high degree of assurance that the equipment would function adequately during the postulated abnormal events.

10.

CNS has a very good record of operability of the Ventilation System associated with the Control Building.

There has not been a loss of ventilation in 13 years of commercial operation.

In addition, there have been no repeated failures of electrical equipment which may suggesc a high temperature degradation problem.

j In addition, the annunciators associated with the Control Building i

Ventilation Supply and' return fans are essential and, coupled with the redundancy plus annunciated ' failure to start' logic circuits, it is unlikely that a complete loss of ventilation would not be acted upon by the plant operators.

l 11.

The postulated events during which the essential equipment located in the Battery and Switchgear Rooms would be subjected to high temperatures requires the simultaneous occurrence of a design basis day maximum temperature, a loss of offsite power or loss of ventilation and, in some instances, a worst case LOCA or HELB event. The likelihood of this event scenario is remote. 'The electrical grid in the CNS service area has i

proven to be very stable and reliable such that a total loss of offsite power has not occurred in the thirteen-year operating history of CNS.

Also, CNS is equipped with two emergency diesel generators such that the likelihood of a complete station blackout for CNS is even more remote.

Thus, the probability of an event is low.

12.

Conclusion If a complete loss of ventilation was to occur for the DC Switchgear Rooms or for the Control Building Ventilation System, the temperature rise in the affected areas would be rapid.

However, with regular monitoring of room temperatures and the availability of dedicated portable equipment powered from essential buses, the transient would be Jess than 75 minutes.

Considering the conservatism and the resulting margins, the temperatures of the CNS Battery and DC Switchgear Rooms are expected to peak well below 140'F.

Similarly, the temperatures of the AC Switchgear Rooms IF and 1G are not expected to exceed 150'F for a period of time long enough for the equipment to be heated to 150'F.

(Even if the ambient temperature exceeds 150*F).

l 1

CNS System Operating Procedures, together with Abnormal Operating Procedures, give guidance as to the actions to take in the event of an LOV or in the event ambient temperatures exceed 104*F during norn.al operations.

13.

References a)

Updated Safety Analysis Report, Cooper Nuclear Station, P.evision 4, July 22, 1986.

b)

HVAC Drawing, CNS-CB-1, Control Building Duct.ing Layout Elevations 882'-6" and 903'-6", Revision 5, May 15, 1974, c)

General Arrange Drawing, 2061, General Arrangement Reactor Building Plan at Elevation 931'-6'", Revision 4, March 23, 1984.

d)

Flow-Diagram, 2018, Turbine Generator Building and Control Building Heating and Ventilating, Cooper Nuclear Station, Revision 6, September 16, 1986, e)

Auxiliary One Line Diagram, Sheet No. 4, 3005, Cooper Nuclear Station, Revision N10, June 13, 1986, f)

Auxiliary One Line Diagram, Sheet No. 5, 3006, Cooper Nuclear Station, Revision N23, May 7, 1987, g)

Cooper Nuclear Station, Technical Specifications, Section 3.12.D, Battery Room Ventilation, September 25, 1986 (for page 215C - Change No. 19, October 31, 1975).

h)

American Society of Heating, Refrigerating, and Air Conditioning Engineers, Inc., ASHRAE Handbook 1981 Fundamentals.

14.

The tables and graphs are taken from the Nutech evaluation which is available along with the calculation packages for review at NPPD Offices.

APH:rsl3/1(IS) l i

1

-S-

1-i l

\\

l s-I t

l BATTERY AND SWITCHGEAR ROO!1 u.

,!! AXIL 1Uf! HEAT LOADS i

(

LOV LOOP HELB+LOV HELB+ LOOP Heat Loads Heat Loads Heat Loads Heat Loads Room (Btu /hr)

(Btu /hr)

I2) l Battery Room 1A 6,570 12,744 6,570 12,744 Battery Room 1B(2,3) 5,544 27,613 5,544 27,613

~

DC Switchgear Room 1A 16,094 37,662 16,094 37,662 DC Switchgear Room IB 15,895 37,788 15,895 37,788 Critical Switchgear 55,619 55,619 17,588 48,979 Room 1-F Critical Switchgear 42,722 42,722 12,368 34,785 m.

Room 1-G flo te :

1.

The heat loads shown represent the maximum values applied for each event sequence.

The heat loads vary with time for some event u_

sequences, 2.

The minimum heat loads are used in the battery room evaluation for winter conditions.

t 3.

For LOOP and HCLB+ LOOP event sequences, the peak heat load is 57,847 Stu/hr from 3 to 4 minutes in the event.

v L

e

~

nutech L.

i

e S.

IL*

L l-ki LOSS OF VENTILATION TRAMSIENT ANALYSIS RESULTS

SUMMARY

L i

Maximum j

Initial

~ Transient Steady State

'~

Room Temperature Temperature Temperature

(*F)

!i Battery Room 1-A 104.

-105.

105.

l Battery Room 1-B 104.

105.

m DC Switchgear 104.

136.

109.

Room 1-A DC Switchgear 104.

135.

109.

R,oom 1-B C-Critical Switchgear 104.

161.

105.

Room 1-F Critical Switchgear 104.

151.

105.

Room 1-G i

~

Note

~i 1.

The temperatures shown are determined assuming auxiliary ventilation equipment in place and operating within one hour 1

u.

i 2.

The minimum calculated battery room temperature for this event

~

during winter conditions with the USAR ventilation air temperature of 65'F is 71*F without auxiliary room heaters.

\\

t w

l Im e

I t

.g

~

rititen(:l1 t_

i LOSS OF OFFSITE PO11ER TRANSIENT A@ LYSIS RESULTS SUf!!!ARY flaximum Initial Transient Steady State Room Temperature Temperature Temperature

(*F)

-i Battery, Room 1-A 104.

105.

104.

Battery Room 1-B 104.

116.

103.

~

DC Switchgear 104.

133.

112.

Room 1-A DC Switchgear 104.

133.

110.

Room 1-B Critic.1 Switchgear 104.

161.

105.

Root.. 1-F Critical Switchgear 104.

151.

105.

Room 1-G l

' flote 1.

The temperatures shown are determined assuming auxiliary l_

ventilation equipment in place and operating within one hour, p.

2.

The minimum calculated battery room temperature for this event during winter conditions with the USAR ventilation air temperature of 65'F is 71'F without auxiliary room heaters.

j- >>

4 I-L.

nutech L

r..

IIIGH E!!ERGY LIl1E BREAK UITH

'~

LOSS OF vet 1TILATIOt1 TRAt1SIEt1T At1ALYSIS RESULTS SUttMARY L.

flaximum Initial Transient Steady State 1

Room-Temperature Temperature Temperature

(*F)

'('F)

Battery Room 1-A 104.

105.

Battery Room.1-B 104.

105.

DC Switchgear 104.

136.

109.

Room 1-A i

DC Switchgear 104.

135.

109.

Room 1-B Critical Switchgear 104.

126.

101.

Room 1-F Critica1'Switchgear 104.

121.

100.

Room 1-G tio te s 1.

The temperatures shown are determined assuming auxiliary ventilation equipment in place and operating within one hour, l '!_

i

~

l O'.mp e

.g nutech L

'!L

[-'

i l

9 HIGH ENERGY LINE BREAK WITH LOSS OF OFFSITE POWER TRANSIENT ANALYSIS RESULTS SUf111ARY l

llaximum Initial Transient Steady State l

Room Temperature Temperature Temperature

(*F)

('F)

Battery Room 1-A 104.

105.

104.

}

Battery Room 1-B 104.

116.

103.

DC Switchgear 104.

133.

112.

Room 1-A DC Switchgear 104.

133.

110.

Room 1-B Critical Switchgear 104.

156.

100.

Room 1-F Critical Switchgear 104.

144.

100.

Room 1-G

'~

Note:

1.

The temperatures shown are determined assuming auxiliary ventilation equipment in place and operating within one hour, i

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v t e Letter Sequence Supplement
TAC:66723, (Open)
Initiation Request Acceptance... Supplement Administration Meeting, Meeting Questions Answers Results Approval... Other:
MONTHYEAR1987-07-24 [Table View]

ML20237K162

Text

Subject:

Reference:

1.0 Background

SUMMARY

=

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