ML20031H467

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Testimony of Mk Mitchell Re Doherty Contention 38(b) on Cold Shutdown within 24 Hours.No NRC Requirements Specify Facility Be Designed to Be Capable of Being Brought to Cold Shutdown in 24 Hours
ML20031H467
Person / Time
Site: Allens Creek File:Houston Lighting and Power Company icon.png
Issue date: 09/18/1981
From: Matthew Mitchell
GENERAL ELECTRIC CO., HOUSTON LIGHTING & POWER CO.
To:
Shared Package
ML20031H319 List:
References
NUDOCS 8110270510
Download: ML20031H467 (6)
v • d • e


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September 18, 1981 UNITED SThTES OF AMERICA 1

NUCLEAR REGULATORY COMMISSION 2

BEFORE THE ATOMIC SAFETY AND LICENSING BOARD 3

In the Matter of S

4 5

HOUSTON LIGHTING & POWER COMPANY S

Docket No. 50-466 S

(Allens Creek Nuclear Generating S

6 Station, Unit 1)

S 7

DIRECT TESTIMONY OF MIKE K. MITCHELL 8

REGARDING DOHERTY CONTENTION NO. 38(b) -

COLD SHUTDOWN WITHIN 24 HOURS 9

10 Q.

Would yoa please ntate your name and your position, and deecribe your educational and professional background?

11 A.

My name is Mike K. Mitchell.

I am employed at 12 General Electric vmpany (GE) as Senior Engineer, Plant 3

Design and Analysis.

A statement o,i my educational and amployment history is attached as Attachment MKM-1.

Q.

What is the purpose of your testimony?

16 A.

The purpose of my. testimony is to address Doherty 17 Contention 38(b), which alleges that:

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" Contrary to NUREG-0578, the ACNGS reactor cannot be brought to ccid shutdown in 24 19 hours2.199074e-4 days <br />0.00528 hours <br />3.141534e-5 weeks <br />7.2295e-6 months <br />."

Q.

To your knowledge, is there any NRC requirement f

20 21 that specifies that Allens Creek must be designed to be 22 capable of being brought to cold shutdown in 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />?

23 A.

No.

Following the TMI accident, there was a 24, tentative proposal in NUREG-0578 for such a requirement.

o 8110270510 810918 PDR ADOCK 05000466 T

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However, no such requirement was imposed upon the near-term 2

CP plants in NUREG-0"il?.

3 Q.

What is " cold shutdown"?

A.

The phrase " cold shutdown" is defined in the BWR-6 4

standard technical specifications to mean that the reactor 5

temperature is below 200*F at atmospheric pressure and the 6

reactor mode switch is in the shutdown position.

7 Q.

How is a reactor such as Allens Creek normally 8

brought to cold shutdown?

9 A.

Normally, the initial phase of nuclear system 10 cooldown for ACNGS is accomplished by dumping steam from the 11 reactor vessel to the main condenser.

When nuclear system 12 pressure has decreased to a point where steam supply pressure 13 is not sufficient to maintain the turbine shaft seals, 14 vacuum in the main condenser cannot be =aintained and Shutdown 15 Cooling Mode of the Residual Heat Removal (RHR) System is 16 started to complete the task of placing the reactor in cold 17 shutdown.

13 The RHR System has several modes of operation, but t

the mode of concern to achieve cold shutdown is the Shutdown l

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20 Cooling mode.

In this mode, reactor coolant is pumped from the recirculation loops by one of the RHR pumps and is 21 discharged to one of the RHR heat exchanger loops where 22 cooling occurs by transferring heat to the essential survice 23 l

The RHR heat exchangers are sized for cooling water.

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1 operation in the RHR mode o'f Suppression Pool Cooling f 11 wir a Loss of Coolant Accident (LOCA).

Because the 2

heat loud is much greater for thte mode than for Shutdown 3

8; Cooling, the RHR System is considerably oversized for 4

acnieving a normal cold shutdown condition.

m Q.

How long will it take to bring Allens Creek to cold shutdown?

7 A.

To determine the effectiveness of the ACNGS design 8

to achieve cold shutdown, decay heat load must be determined.

9 The maximum decay heat load after reactor shutdown calculated 10 for ACNGS is derived from the 1971 American Nuclear Society 1/

11 formula as required by 10 CFR 50, Appendix K.

Using this 12 decay heat load, General Electric has determined that the 13 main condenser will cool the system to a temperature of 14 approximately 344* F at 110 psig in two hours.

The system' lL5 is maintained at this temperature and pressure for an j

16 additional two hours while the RHR System is f:ushed with 17 reactor grade water.

At this point, one loop of the RHR 18 System is placed in service.

At this time the heat load 6

19 is approximately 284.6 x 10 BTU /hr and decreasing.

'n'ith the temperature difference between reactor coolant and service 20 21 22 1/

As an extra measure of conservatism, Appencix K requires 23 that an additional 20% heat load ha added to the decay heat load determined by the ANS formula.

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_ __ s water that exists at this time,2/ one RER heat exchanger I

1 p is capable of removing approximately twice the amount 2

f heat being generated.

During the initial phaser of 3

shutdown cooling (to avoid cooling the Reactor Pre 3sure Vessel (RPV) down too rapidly), the heat exchangez discharge flow is usually throttled such that the cooldown rate does not exceed 100* F/hr.

Subsequent to this initial gross 7

overcapacity period, the second heat exchanger loop can be 8

brought on line if needed to continue the cooldown process.

9 Based on analysis which has been correlated with heat 10 exchanger systems used on operating BWRs, the normal shutdown 1

cooling rcde of the RHR System is fully capable of achieving 1

12 a reactor coolant temperature of less than 200' F in less 13 than seven hours with two hours conservatively allowed for 14 flushing of the RHR System.

15 If a single failure occurs during this normal 16 shutdown sequence of events, the alternate shutdown flow 17 path may be initiated such that suppression pool water is 18 inicated directly into the RPV.

The time to reach 200 F

using this alternate mode is significantly less than tne 19 n rmal m de because the water being returned to the RPV in 20 the alternate mode is the cooler pool water (% 150' F) rather 21 than the warmer heat exchanger discharge water (N 300* F).

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Essential service cooling water is assumed to be 95 F,

24 thereby making the difference in reactor coolant and service water temperatures equal to 249* F.

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Consequently the normal mode is the more limiting mode when considering time to reach cold shutdown.

Thus, even assuming 2

arf single failure, the ACNGS reactor can achieve cold shutdown in much less than 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />.

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Attachment MKM-1 MIKE K. MITCHELL Mr. Mi chell is a Senior Engineer in the Plant Design & Analysis Section working for the General Electric Company, Nuclear Engineering Division, in San Jose, California, U.S.A.

His employment with GE be'gan in 1975 in the Piping Design Section.

Subsequent assignments have been in the areas of Seismic & Dynamic Analys't. MK III Containment Technology & Heat Exchanger Design.

Immediately prior to his present position, Mr. Mitchell was the super-visor of the Division's Engineering Training Program, which included technical responsibility for training of entry level engineers in the areas of heat transfer, fluid flow, and computer methods.

As a Senior Lead System Engineer, Mr. Mitchell is the person in GE with the primary responsibility and authority for the correct and complete design of-the Residual Heat Removal System.

Mr. Mitchell is a member of the National Society of Civil Engineers and a registered Professional Engineer in i

the State of California.

Mr. Mitchell is a 1975 graduate of the University of Arizona with a B.S. Degree in Civil Engineering.

He is also'a 1977 graduate of GE's Advanced Engineering Program and a 1978 graduate of the University of California, Berkeley, with a M.S.

Degree in Engineering.

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