ML20236X341

Forwards Response to 980513 RAI Re GL 96-06, Assurance of Equipment Operability & Containment Integrity During Design- Basis Accident Conditions. W/11 Oversize Drawings

ML20236X341
Person / Time
Site:	McGuire, Mcguire
Issue date:	07/30/1998
From:	Barron H DUKE POWER CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
Shared Package
ML20236X343	List: ML20236X341
References
GL-96-06, GL-96-6, NUDOCS 9808070308
Download: ML20236X341 (13)

Text

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Duke Power Company A f>u!,e Ency Gmpny

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McGui,r Nudrar Station N-'V MG0lVP 12700 Hager: Ferry Rd.

Huntersville, NC 28078-9340 Vice President, McGuire (704) 875-4800 oma

.Nudrar Generation Department (704) 875-4809 Mx 1

July 30, 1998 1

U.

S. Nuclear Regulatory Commission Document Control Desk Washington, D.C.

20555

Subject:

McGuire Nuclear Station Docket Nos. 50-369, 370 Request for Additional Information Related to Generic Letter 96-06 Generic Letter 96-06, " Assurance of Equipment Operability and Containment Integrity During Design-Basis Accident Conditions," dated September 30, 1996, requested licensees to evaluate cooling water systems that serve containment air coolers to assure that they are not vulnerable to waterhammer and two-phase flow conditions.

Duke Energy provided its assessment of the waterhammer and two-phase flow issues for McGuire Units 1 and 2 by letter dated September 28, 1997.

By letter dated May 13, 1998, the NRC requested additional information related to the subject Generic Letter.

Please find enclosed McGuire's response to the subject request.

Questions should be directed to Kay Crane, McGuire Regulatory Compliance at (704) 875-4306.

Very truly yours, lkhwa~

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B.

Barron, Vice President McGuire Nuclear Station

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U.

S. Nuclear Regulatory Commission Document Control Desk July 30, 1998 Page 2 I

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Rinaldi, Project Manager U.

S. Nuclear Regulatory Commission Office of Nuclear Reactor Regulation Washington, D.C.

20555 Mr. Luis A. Reyes U.

S. Nuclear Regulatory Commission, Region II Atlanta Federal Center 61 Forsyth St.,

SW, Suite 23T85 Atlanta, GA 30303 Mr. Scott Shaeffer Senior Resident Inspector McGuire Nuclear Station t

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S. Nuclear Regulatory Commission Document Control Desk July 30, 1998 l

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NRC Request for Additional Information Related to Generic Letter 96-06 for McGuire Nuclear Station, Units 1 & 2 Item #1:

Describe worst-case bounding scenarios for defining when water hammer and two-phase flow could occur in the service water cooling systems associated with the i

I containment ventilation systems (taking into consideration i

the complete range of event possibilities, system configurations, parameters, and component failures) and identify the specific time periods when steam formation could occur.

Response

For McGuire, two recognized accident scenarios will create conditions within Containment which could potentially lead to water hammer or two phase flow in the service water cooling systems associated with the containment ventilation systems. These two conditions are "Large Break Loss of Coolant Accident" and " Main Steam Line Break".

While both l

scenarios create high containment air temperatures, the "Large Break Loss of Coolant Accident" is the worst case bounding scenario due to its long term implications.

The immediate containment temperature excursion is greater l

in a " Main Steam Line Break". However, the resultant conditions are very short term (less than one hour).

Consequently, the short term duration of high containment temperature coupled with the automatic isolation of the service water cooling systems creates a very low probability of water hammer or two phase flow.

The "Large Ereak Loss of Coolant Accident" will create sustained high containment temperatures for a period exceeding twenty-four hours.

This specific scenario could potentially create conditiens favorable for producing water hammer or two phase ficw in the service water cooling systems associated with the containment ventilation systems if these service water systems were in operation.

None of the service water cooling systems and containment ventilation systems discussed in this analysis perform a nuclear safety related function.

During the designated worst case bounding scenario, the containment ventilation systems which provide a normal cooling function are terminated assuming a loss of off-site electrical power.

The essential service water cooling systems are automatically double isolated from the non-essential containment header supplying the affected ventilation systems.

In addition, the containment penetrations 1

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l associated with the non-essential service water supply and return lines are automatically double isolated during this worst case bounding scenario.

Operation of the non-i essential service water cooling systems associated with the I

containment cooling ventilation systems can only be restored following a reset of the Engineered Safety Features signal received during the this worst case bounding scenario.

Reset of this signal is strictly controlled by station emergency procedures, i

Since non-essential service water cooling systems and non-l essential containment ventilation systems are removed from i

service immediately following the generation of a Engineered Safety Feature signal, there is no short term potential for water hammer or two phase flow.

By station emergency procedure, reset of the Engineered Safety Feature signal can only be performed when containment pressure is lower than 2 psig.

The Containment Pressure Response Computer Code j

predicts containment pressure will be approximately 9 psig after twenty-four hours into the event (See FSAR Figure 6-8).

Containment temperature at this point in the event is predicted to be approximately 180 degrees Fahrenheit (See FSAR Figure 6-10). Consequently, steam formation is not I

possible at this point in the event since the containment l

temperature is below the necessary saturation temperature to promote the formation of steam pockets.

Both pressure and temperature parameters continue to trend lower beyond the l

L twenty-four hour interval so this analysis is conservative in basing conclusions on the predicted conditions after l

twenty-four hours.

Based on the predictions of the Containment Pressure Response Code, pressure and temperature conditions at I

twenty-four hours following the initiation of the event will not support the formation of steam voids upon re-start of l

the service water cooling systems.

Assuming steam pockets are formed at beginning of the event when the containment temperature is predicted to be approximately 235 degrees F, it is realistic to assume these same pockets are condensed prior to obtaining a containment pressure condition allowing the restart of the service water cooling system.

Additional information concerning the site emergency procedures is discussed in Item #2.

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Item #1a: Confirm that all' scenarios have been considered, including those where the affected containment penetrations are not isolated.

Response

'A review of plant equipment located inside the containment buildings that is served by the service water system determined that, with the exception of the two previously listed conditions, no other credible accident scenarios (or normal operational situations)can create sustained high containment temperatures which could potentially result in water hammer or two phase flow.

The affected service water system containment penetrations serving both the upper and lower containment ventilation systems are isolated upon receipt of a high-high containment pressure signal (3 psig).

Therefore, the service water systems will not be in

. operation during initial phases of either of the two mentioned scenarios.

Item #1b: Discuss how long it will take for steam pockets to condense after they have been formed during the event scenario, such that the' cooling water system is fully charged with liquid, and' explain what happens to any non-condensable gases.

Response

With regards to the service water cooling systems, the average piping size associated with main air handling units used for normal containment cooling is approximately six inches.

The configuration does not create a large volume of service water exposed to high containment temperatures.

Assuming the containment temperature exceeds the saturation temperature of the service water in the piping and steam pockets are formed, they would condense when the containment temperature drops below the saturation temperature of the service water.

As this carbon steel service water piping is not insulated, the actual time necessary to condense the postulated steam void would be dependent upon the differential temperature between containment and the service water. -Based on the significant piping surface area exposed to containment temperatures, engineering judgment would conclude that the condensation time would be short term (on the order.of minutes). Consequently, given the containment pressure and temperature responses shown on UFSAR Figures 6-8 and 6-10 and the procedural-restrictions against resetting of the Engineered Safety Feature signal before containment pressure is lower than 2 psig, any steam in the service I

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water piping should be condensed before the service water containment isolation valves are reopened.

Concerning the non-condensables, all service water systems contain a small portion of entrained gases due to contact with the environment.

These gases will proportionally be removed from the service water solution as a function of decreased fluid pressure or increased fluid temperature.

In the postulated accident scenarios, the service water fluid is potentially subject to off-gassing due to its higher temperature.

This postulated off-gassing does not create a water hammer or two phase flow condition.

The only consequence of this scenario is to form a compressible gas pocket which would help mitigate the impact of any water hammer event.

Item #1c: Describe and justify all assumptions and input parameters (including those used in any computer codes).

Response

The affected containment isolation valves (and other safety related service water valves) are assumed to function (go closed) in accordance with the Engineered Safeguards Features incorporated into the design of McGuire Nuclear Station.

The affected systems and valves are tested on a periodic basis to ensure acceptable and expected operation.

It is assumed that any steam pockets are formed at the beginning of the event when the containment temperature is predicted to be approximately.235 degrees F and these same l

pockets are condensed prior to obtaining a containment pressure condition allowing the restart of the service water i

cooling system. Finally, the containment temperature and pressure values twenty-four hours into an event were extrapolated from UFSAR Figures 6-8 and 6-10 assuming that the trends remained linear.

This analysis (water hammer and two phase flow) is an engineering " transient" analysis based upon the design and i

function of the service water and ventilation systems during l

the postulated accident scenarios.

The expec"ed conditions l

within containment during these postulated accidents are derived through the use of Duke Power's proprietary Containment Pressure Response Computer Code.

This code has been reviewed and approved for use by the NRC.

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Item #1d Discuss'the uncertainties inherent in the analysis and explain how the uncertainties were determined, and how they were accounted for in the analysis to assure i

conservative results.

Response.

.The uncertainties related to the postulated water hammer and two phase flow scenario are the " assumed" containment temperatures and pressures during the specific accident scenarios along with possibility of placing the containment ventilation systems back into service following a reset of the Engineered Safety Features signal.

The containment t

pressure and temperature data is taken directly from McGuire's UFSAR and are based on the output of the previously mentioned Containment Pressure Response Computer Code.

Placing the containment ventilation systems and service water cooling systems back into service following a Large Break Loss of Coolant Accident is strictly controlled' by station emergency procedures.

There are no direct actions in any related procedure which will place these systems back into operation until containment pressure and j

temperature conditions reach acceptably low levels.

j Item #1e: Confirm that a complete failure modes and effects analysis (FMEA) for all components (including electrical and pneumatic failures) that could impact the performance of the cooling water system was performed.as a part of this assessment and confirm that the FMEA is documented and 1

available for review, or explain why a complete and fully I

documented FMEA was not performed.

Response

A failure modes and effects analysis was not performed for j

this postulated water hammer and two phase flow scenario as none of the affected systems perform a nuclear safety related function.

The containment pressure response for McGuire under the worst case bounding accident scenario is l

controlled entirely through the use of the containment spray system.and ice condenser.

The containment ventilation systems used to provide routine and normal containment cooling are not utilized.under the postulated accident l

conditions.

It is beyond the design basis of the service water cooling systems and containment penetration isolation system to assume service water cooling systems remain in operation during the postulated accident conditions.

This

' condition could only result from the failure of multiple automatic safety actions on both safety related trains.

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Item #1f: Explain and justify all uses of engineering i

judgment.

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Response

The use of engineering judgment is minimized in this analysis whenever possible.

Actual system design and i

l operational information is used to assess the postulated L

water hammer and two phase flow conditions.

Expected l

containment temperatures and pressures are determined from l

the approved Containment Pressure Response Computer Code.

Actual time for steam condensation within the service water cooling systems is judged to be on the order of minutes based on very conservative engineering assumptions with L

regards to heat transfer. Consequently,,given the containment pressure and temperature responses shown on i

UFSAR Figures 6-8 and 6-10 and the procedural restrictions against resetting of the Engineered Safety Feature signal before containment pressure is lower than 2 psig, any steam in the service water piping should be condensed before the I

service water containment isolation valves are reopened.

Item #2: Describe in detail any measures that exist or will be.taken to assure that the service water cooling systems associated with the containment ventilation systems will not i

be used as an option during the time periods when water j

hammer and two phase flow could occur.

Response

As previously stated, the operation of the service water l.

cooling systems and containment ventilation systems are terminated at'the receipt of an Engineered Safeguards Feature signal (3 psig in containment).

All containment 1

isolation valves for the associated service water penetrations will automatically double isolate.

The non-essential service water header supplying the containment ventilation units are automatically' double isolated from the i

p essential service water system using this same signal.

The E

containment ventilation units are also removed from service by this~ signal.

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For the service water cooling systems to be re-started, the Engineered Safeguards Feature signal must be reset and the affected isolation valves manually re-positioned from the Control Room.

Per station emergency procedure EP/l or 2/A/5000/El, the safety signal cannot be reset prior.to achieving a containment pressure of 2_psig or less.

The 6

m-_--_--__--_-_-----_---__-

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predicted containment pressure after twenty-four hours into the event is still approximately 9 psig.

Based upon the above, Engineering concludes that there are effective barriers to prevent the re-start of the service water cooling systems during time periods when containment conditions are favorable for the creation of water hammer and two phase flow. These conditions have been identified elsewhere in this response. No other credible scenarios exist that could result in steam voiding and water hammer conditions.

Itam #3: Provide a simplified diagram of the affected cooling water systems, showing major components, relative elevations, lengths of piping runs, and the location of any orifices and flow restrictions.

Response

The " simplified" diagrams available at McGuire do not provide all of the requested information.

Consequently, the following detailed design drawings are attached along with UFSAR Figures 6-8 " Containment Pressure Transient" and 6-10

" Lower Compartment Temperature".

MCFD-1574-01.00

-- Service Water Flow Diagram (RN System)

MCFD-1574-01.01

-- Service Water Flow Diagram (RN System)

MCFD-1574-04.00

-- Service Water Flow Diagram (RN System)

MCFD-1604-03.00

-- Service Water Flow Diagram (RV System)

I MCFD-1604-03.02

-- Service Water Flow Diagram (RV System)

MCFD-1604-03.03

-- Service Water Flow Diagram (RV System) l MC-1418-22.20-00 --

Service Water Piping Layout (RV System)

MC-1418-22.20-01 --

Service Water Piping Layout (RV System)

MC-1418-22.21-00 --

Service Water Piping Layout (RV System) i MC-1418-22.21-01 --

Service Water Piping Layout (RV System) l MC-1418-22.22-00 --

Service Water Piping Layout (RV System) l 7

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