ML17334A407

Forwards Response to Request for Addl Info Re NUREG-0737, Item II.B.1, RCS Vents

ML17334A407
Person / Time
Site:	Cook
Issue date:	06/28/1982
From:	Hunter R INDIANA MICHIGAN POWER CO. (FORMERLY INDIANA & MICHIG
To:	Harold Denton Office of Nuclear Reactor Regulation
References
RTR-NUREG-0737, RTR-NUREG-737, TASK-2.B.1, TASK-TM AEP:NRC:0584A, AEP:NRC:584A, NUDOCS 8207070219
Download: ML17334A407 (20)

Text

"}'EGULATORY, ORMATION DISTRIBUTION SY 4 (RIDS)

'AOCBSSION NBR:8207070219 DOC SEDATE: 82/06/28 NOTARI'ZED:

NO FACIL:50<<31'5 Donald C.

Cook Nuclear Power Plantr Unit ir Indiana 50 316 Donald C,

Cook Nuclear Power Plantr "Unit 2r Indiana AUTH BYNAME AUTHOR 'AFFILIATION HUNTERrR ~ S ~

Indiana 8 Michigan Electr ic Co, RBCIP ~ NAME RECIPIENT AFFILIATION, DENTONgH ~ RE Office of Nuclear iReactor iRegulationg,Director D

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050003.16'g

SUBJECT:

Forwards response to request for addi info re NUREG 0737'tem II,B~ 1, "RCS Vents ~,"

DISTRIBUTION -CODE:

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~ENCL SIZE ~,

TITLE: Response to NUREG 0737/NUREG 0660 -TMI Action Plan Rgmts (OL's)

NOTES:

RECIPIENT ID CODE/NAME ORB 01 BC 01 INTERNAL+ ELD/HDS3 IE/DEP EPDS NRR/DE DIR 21 NRR/DE/ADMQE 23 NRR/DHFS/DEPY29 NRR/DL/ADL 16 NRR/DL/ADSA 17 NRR/DSI DIR 24 NRR/DSI/ADRP '26 NRR/DS I/AEB NRR/DSI/RA8 NR

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INDIANA gt MICHIGAN ELECTRIC COMPANY P. O. 8OX 18 8OWI ING GREEN STATION NEW YORK, N. Y. 10004 June 28, 1982 AEP:NRC:0584A Donald C, Cook Nuclear Plant Unit Nos.

1 and 2

Docket Nos. 50-315 and 50-316 License Nos.

DPR-58 and DPR-74 NUREG-0737, ITEM II.B.1, REACTOR COOLANT SYSTEM VENTS REQUEST FOR ADDITIONAL INFORMATION Mr. Harold R. Denton, Director Office of Nuclear Reactor Regulation U..S. Nuclear Regulatory Commission Washington, D. C.

20555

Dear Mr. Denton:

This letter and its attachments provide the response to the request for additional information on the Reactor Coolant System Vents contained in Mr. S. A. Vaxga's letter of February 24, 1982.

This document has been prepared following Corporate procedures which incorporate a reasonable set of controls to insure its accuracy and com-pleteness prior to signature by the undersigned.

Very truly yours,

/os R.

S. Hunter Vice President cc:

John E. Dolan Columbus R.

W. Jurgensen W. G. Smith, Jr.

Bridgman R.

C. Callen G. Charnoff Joe Williams, Jr.

NRC Resident Inspector at Cook Plant Bridgman I, sa070702<9 BZ06aa PDR ADOCK 05000315 P

PDR

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ADDITIONAL INFORMATION ON REACTOR 'COOLANT

'SYSTEM 'VENTS ATTACHMENT 1 TO AEP:NRC:0584A The following are the responses to the additional information on Reactor Coolant System Vents (RCSV) requested in Mr. Varga's letter of Pebruary 24, 1982.

Res onse to Item 1.

To effectively remove the decay heat from the Reactor Coolant System we have Emergency Operating Procedures for Natural Circulation, 1-OHP 4023.001.008 for Unit 1 and 2-OHP 4023.001.008 for Unit 2.

These procedures provide the Operator with guidelines and instructions on Reactor Temperature Pressure Control to prevent'ormation of voids in the upper reactor head level.

The procedures specify time intervals for reducing RCS and Steam Generator pressures during the Natural Circulation phase of the cooldown.

The operator can control the circulation flow, including flow through the Steam Generator U tubes by monitoring the provided instrumentation.

Res onse to Item 2 A (3/8) inch diameter flow restriction orifice is provided in both the Reactor Vessel Head Vent and the Pressurizer Head Vent.

As the calculation shows in Attachment 2, the maximum postulated flow through each of the orifices is 147.2 gpm.

Prom the centrifugal charging pump flow characteristic

curve, also attached, it can be seen that the pump flow is 250 gpm at the system operating pressure (approximately 5200 ft.

of water).

Thus, enough margin exists between the capacity of one charging pump and the maximum postulated leak rate through one orifice in each vent path.

'Res onse'to Item 3 (a)

The entire RCS Vent System is classified as Seismic Class I.

Figures 1 and 2 of this Attachment 1

show the location of the second normally closed valve.

(b)

The piping, valves and orifices in the RCS Vent System are designed to 2485 psig at 650 F.

(c)

The following are the materials of construction in the RCS Vent System:

Piping A376 Type 304 and/or Type,316, Stainless Steel Valves SA-182 Type 316 Stainless Steel.

As per the ASME Code,Section III, Appendix I, the above materials are acceptable, for use as part of the Reactor

I4

2 Coolant Pressure Boundary.

Fabrication and cleaning controls were in accordance with an approved specification.

The Vent System does not have, any insulation on it.

The Vent system piping thickness is 0.25 inch and thus does not require a C

test as per the ASME

Code,Section III, Subsection NB, Table NB-2332 (a)-1.

The RCS Vent Syst'm is fabricated and tested in accordance with SRP 5.2.3.

i The RCS vent system

,consists of two subsystems (Pressurizer Vent

& Reactor Head Vent) each of which consists of two parallel ',flow paths with redundant fail closed isolation valves in each flow path.

Isolation valves in one flow path are powered by train A and the valves in the second flow path are powered by train B.

The system is designed such that any single failure would not prevent the operation of the vent system.

The only piping on top of the Reactor Head is a 3/4" line to the reactor vessel level instrumentation.

Since this line is smaller in size than the reactor head vent, the dynamic effects associated with the postulated rupture of this line would not prevent the operation of the RCS head vent system.

The only potential missile from other sources in the reactor head area would be a control rod. If a control rod became a missile its energy would be dissipated by the missile blocks above the reactor vess'el head.

Furthermore, rupture. of a control rod drive mechanism would result in a loss of coolant accident far more serious than a break of the RCS vent system.

The piping to the Pressurizer Safety Valves and the Power Operated Relief Valves is the only piping in the vicinity of the Pressurizer Vent. If this piping ruptures, or a valve stem blows out, a high point pressurizer vent would not be required.

Any gases that would have been collected inside the top of the pressurizeri would be discharged through the break.

'es onse to Item 4 The D. C. Cook Reactor Coolant Vent system design is such that two valves connected in series must be opened to create a flow path.

Each vent valve is provided with its own position indication and its own two position control switch.

The prevention of inadvertent actuation was considered in the selection and location of these control switches.

The following Procedures and Administrative Controls are employed to prevent the inadvertent actuation of the RCS Vent system:

During the fill and vent operations, (OHP 4021.002.001),

for both Units 1 and 2, the following valves are required

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to be verified closed and their, respective breakers racked out: (1) NS0-061,

062, 063 and 064..These are the Post-accident, vent valves for the pressurizer vent system.

(2)

The Reactor Head Post Accident Vent Valves NS0-021,

022, 023 and 024 are verified closed and their respective breakers racked out.

In addition, all the above mentioned high point vent valves have a Shift Supervisors Red Tag Clearance placed on their racked out breakers.

The clearance states,"The power is being removed from these valves to prevent inadvertant actuation and will remain off until authorization is received from the NRC".

The Clearance tags were placed on Unit 1 on November 10, 1981 and Unit 2 on October 14, 1982.

Res onse to Item 5(a and 5 b The Reactor Vessel Head Vent and the Pressurizer Head Vent discharge into the upper volume of the containment at elevations 660.0 ft. and 673.0 ft, respectively.

This will insure adequate dilution of the combustible gases, if any, released during a design basis accident.

Since the vent discharge points are located in the upper volume of the containment, components essential to a safe shutdown of the Reactor will not be sub)ected to a direct jet due to a discharge from the Vent system.

Res anse to Item 6 All of the displays, alarms and controls added to the control room for the RCS Vent System will be considered in the human factors analysis required by NUREG-0737 Item I.D.1.,

"Control Room Design Review".

'Res onse to"Item 7 (a)

The entire RCS Vent system is designed to withstand a

safe shutdown earthquake.

'(b)

The only missiles.that can be postulated from the failure of an RCS vent system components are the valve stems from the solenoid operated isolation valves.

It is highly unlikely that these valves would fail in this manner.

These isolation valves are located inside the missile barrier in the containment.

The isolation valves on the reactor head vent are located on top of the reactor head with the valve stems pointed upward.

During normal plant operation, missile blocks are provided over the reactor head.

If a valve stem did become a missile it would hit the missile blocks and deflect.

Since the valve stems are small in size and most of the energy would dissipate when they hit the missile blocks, the valve stems would not cause damage to any components required for a safe shutdown.

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The isolation valves on the pressurizer vent are located inside the pressurizer enclosure near the top of the pressurizer.

The valve stems are pointed towards the'op of the pressurizer enclosure.

The valve stems are small in size in relation to other equipment at the top of the pressurizer enclosure and would not prevent the safe shutdown of the plant in the unlikely event that a valve stem becomes a missile.

(c)

All the piping used nominal size or less,

.with the postulated applicable.

in the RCS Vent System is one inch and thus dynamic effects associated rupture of RCS vent pipe is not (d)

The RCS vent system piping is one inch nominal size or less.

Piping one inch or less is excluded in our high energy line studies.

However, the possibility of damaging a

CRDM due to a jet from the vent has been reviewed.

In the event of a jet from a vent pipe that damages a

CRDM, causing the most reactive control rod assembly to eject from the reactor vessel, the reactor could still shut down safely.

Furthermore, all accident analyses which call for a reactor scram assume that the most reactive control rod assembly remains stuck completely out of the core.

Me do not have to consider fluid sprays from normally unpressurized portions of the RCS Vent System because we do have leak detection instrumentation downstream of the isolation valves.

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