ML20005A513

Forwards RCS Vent Design Description Per Section 2.c(21)(b) of License NPF-8.Also Forwards Westinghouse Owners Group Generic Guidelines Which Will Be Incorporated W/Specific Procedures Prior to Operation of Head Vent Sys

ML20005A513
Person / Time
Site:	Farley
Issue date:	06/25/1981
From:	Clayton F ALABAMA POWER CO.
To:	Youngblood B Office of Nuclear Reactor Regulation
References
NUDOCS 8106300413
Download: ML20005A513 (21)

Text

+ 4 Malling Addrese Alabama Power Company 600 North 18th Street Post Office Box 2641 Birmingnam Alabama 35291 .

Telephone 205 783-6081 F. L Clayton. Jr.

S;,";

, ,',;ce Prg nt Alabama Power the Southern VeC!nc System June 25, 1981 Docket No. 50-364 5 r&

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Director, Nuclear Reactor Regulation 8 1 U. S. Nuclear Regulatory Connission l9d jg3 3 31981* jy Washington, D. C. 20555 {p p. ucouxons /-'

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kttention: Mr. B. J. Youngblood '{,, ,G Gentlemen: Y#M Joseph M. Farley Nuclear Plant - Unit 2 NPF-8 License Condition 2.c.(21)(b)

In accordance with the Farley Nuclear Plant Unit 2 Operating License NPF-8 Section 2.c.(21)(b), Alabama Power Company hereby submits Attach-ment 1 which provides the reactor coolant system vent design description.

Attachment 2 is the Westinghouse Owners Group generic guidelines which will be incorporated into Farley Nuclear Plant specific procedures prior to cperation of the head vent system.

If you have any questions, please advise.

Yours very t y, fl Ib.L.Clayton,Jr.'

FLCJr/RWS:de Attachments cc: Mr. R. A. Thomas (w/ attachments)

Mr. G. F. Trowbridge (w/ attachments)

Mr. J. P. O'Reilly w/ attachments)

Mr. J. O. Thoma w/ attachments)

Mr. W. H. Bradford w/ attachments)

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Attachment 1 REACTOR VESSEL HEAD VENT SYSTEM DESIGN DESCRIPTION Design Basis The basic function of the Reactor Vessel Head Vent System (RVHVS) is to remove noncondensable gases or steam from the reactor vessel head and the reactor coolant system. This system is designed to mitigate a possible condition of inadequate core cooling, or impaired natural circulation, resulting from the accumulation of noncondensable gases in the RCS.

Venting capability of the RCS hot legs is not required since the hot legs are not a high point in the system. The design of the reactor coolant system satisfies the requirements of NUREG-0737.

Design Description and Evaluation General Description The RVHVS is designed to remove noncondensable gases or steam from the reactor vessel via remote manual operations from the control room. The system discharges into a well Ventilated area of the containment to insure optimum dilution of. combustible gases. The RVHVS is designed to vent a volume of hydrogen at system design pressure and temperature approximately equivalent to one-half of the reactor coolant system volume in one hour.

The flow diagram of the reactor head vent system is shown in Figure 1.

The RVHVS consists of two par-'lel flow paths with redundant isolation valves in each ficw path. The v* ing operation uses only one of these

-- flow paths at any one time. The equipment design parameters are listed in Table 1.

The active portion of the RVHVS consists of four one-inch open/close solenoid operated isolation valves. The reactor vessel head vent system is connected to the existing 3/4" vent pipe, which is located at the center of the reactor vessel head. The system design with two valves in series in each flow path minimizes the possibility of reactar coolant pressure boundary leakage. The isolation valves in one flow path are

. powered by one vital power supply ar.d the valves in the second flow path are powered by a second vital power supply. The isolation valves are fail closed, normally closed active valves. The isolation valves are also included in the Westinghouse valve operability program which is an acceptable alternative to Regulatory Guide 1.48. These valves will be qualified to IEEE-323-1974, IEEE-344-1975, and TEEE-382-1972.

_. . -i l

REACTOR VESSEL HEAD VENT SYSTEM (cont'd) Page 2 DESIGN DESCRIPTION Design. Description and Evaluation (cont'd)

General Description (cont'd)

If one single active failure prevents a venting operation through one flow path, the redundant path is available for venting. Similarly, the two isolation valves in each flow path provide a single failure method of isolating each of the venting subsystems. With two valves in series the failure of any cne valve or power supply will not inadvertently opra a vent path. Thus, the combination of safety grade train assignu.ents and valve failure modes will not prevent vessel head venting nor venting isolation with any single active failure.

The RVHVS has two normally de-energized valves in series in each flow path. This arrangement eliminates the possibility of a er nriously opened flow path due to the spurious movement of one vahe. As such, power lockout to any valve is not considered necessary.

The RVHVS are operated from the control room. The isolation valves have stem position switches. The position indication from each valve is monitored in the control room by status lights.

The reactor vent piping branches into two redundant flow paths through

"~ 3/8-inch orifices. These orifices form the Safety Class 1 to Safety Class 2 transition. The system is orificed to limit the blowdown from o a break downstream of either of the orifices to within the capacity of .

one of the centrifugal charging pumps.

A break of the Reacter Vessel head vent line upstream of the orifices

- would result in a small LOCA of not greater than one-inch diameter.

This break is similar to those analyzed in WCAP-9600 (Reference 1).

Since this break would behave in a manner similar to the hot leg break case presented in WCAP-9600, the results presented therein are applicable.

This postulated vent line break would therefore result in no calculated core uncovery.

All piping and equipment used in the reactor head vent system from the connection to the existing vent pipa to the orifices is designed and fabricated in accordance wi',n ASME,Section III, Class 1 requirements.

From the orifices up to a.d including the second isolation valves, all equipment is designed ar.d fabricated in accordance with ASME,Section III, Class 2 requirements. The piping downstream of the second isolation valves is non-nuclear safety.

The system provides for venting the reactor vessel head by using only safety grade equipment. The RVHVS satisfie: applicable requirements and industry standards including ASME Code classification, safety classifi-cation, single-failure criteria, and environmental qualification.

i REACTOR VESSEL HEAD VENT SYSTEM (cont'd) Page 3 DESIGN DESCRIPTION Design ~ Description and Evaluation (cont'd)

Supports The vent system piping is supported to ensure that the resulting loads and stresses on the piping and on the vent connection to the part-length control rod drive mechanism housing are acceptable.

The support design for attaching the head vent system piping to the CRDM Seismic Support Platform is shown in Figure 2. This support is a two-part clamp configuration, called a double bolt clamp bracket. This clamp support is used to rigidly support the piping in the radial direc-tion. The clamp and asscciated bolts, nuts, spacers, and washers are made of stainless steel, with high strength hold down bolts threaded into the deck ~of the CPJM Seismic Support Platform. A gap exists between the one inch head vent pipe and the support clamp to allow for thermal expansion in axial direction.

The support design for attaching the head vent piping syste.n to the reactor vessel lifting leg in the vertical direction. Is shown in figure 3.

~

Analytical Considerations The analysis of'the reactor vessel head vent piping is based on the following plant operating conditions defined in ASME Code, Section III:

1. Normal Condition:

Pressure, deadweight, and thermal expansion analysis of the vent pipe during a) normal reactor operation with the vent isolation valves closed and b) post-refueling venting.

2. Upset Condition:

l-l Loads generated by the Operating Basis Earthquake (OBE)

3. Faulted Condition:

Loads generated by the Safe Shutdown Earthquake (SSE).

Loads generated by valve thrust during venting. In ac-cordance with ASME III, faulted conditions are not included in fatigue evaluations. '

r:-

REACTOR' VESSEL' HEAD VENT SYSTEM (cont'd). Page 4 DESIGN DESCRIPTION Design ~DescriptionandEvalu$ tion (cont'd)

Analytical Consideration 3 (cont'd)

The Class 1 piping used for the reactor vessel head vent is one inch schedule-160, and is analyzed following the procedures of NC-3600 for Class 2 piping.

For all plant operating conditions listed above, the piping stresses are shown to meet the requirements of equations (8), (9), and (10) or (11) of ASME III, NC-3600, with a maximum normal operating temperature of 620 F and a design pressure of 2485 psig.

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REFERENCES Page 5

1. WCAP-9600, " Report on Small Break Accidents for Westinghouse NSSS System," June,1979, (specifically Case F, Section 3.2).

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Page 6 TABLE.1

. REACTOR VESSEL HEAD VENT SYSTEM E0VIPMENT DESIGN PARAMETERS Reactor Vessel Head Vent Subsystem' Valves 6

Number (includes two manual valve)

Design pressure, psig 2485 Design temperatures, *F 650 Piping'

. Vent line, nominal diameter, in. 3/4 and 1 Design pressure, psig 2485 Design temperature, F 650 Maximum nonmal. operating temperature, F 620 .

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i ATTACHMENT 2 REACTOR VESSEL HEAD VENT OPERATION e-REVISION 0 FEBRUARY ,1981

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REACTOR VESSEL HEAD VENT OPERATION A. PURPOSE The objective of these instructions is to specify required operator actions and precautions necessary to remove gases from the reactor vessel head by operation of the Reactor Vessel Head Vent.

CAUTION: This venting guideline should not be used as the primary means to mitigate an Inadequate Core Cooling event.

Refer to Inadequate Core Cooling Guidelines for appropriate operator actions and precautions.

CAUTION: This venting guideline assumes that the reactor containment conditions are near normal conditions aqd that any venting operation is performed prior to throttling safety injection flow during a POST-LOCA cooldown and dearessurization operation.

. B. ' SYMPTOMS For plants with a RV level indication

1. Reactor vessel level is less than (insert plant specific value which includes an allowance for normal channel accuracy) percent of span.

For plants with/without a RV level indication

2. Abnormal reactor coolant system conditions such as large variations in pressurizer level during normal charging of spraying operations have occurred.

3. If. available, reactor vessel head temperatures equal to or greater ,

)

" than saturation temperature.

Page 1 February, 1981 Revision 0

4. Plant events have occurred (such as accumulator tank discharge, rapid RCS cooldown, or core uncovery events) that may result in the presence of a gaseous void in the vessel head.

C. IMMEDIATE ACTIONS None D. SUBSEQUENT ACTIONS CAUTION: Do not trip any running or start any non-operating reactor coolant pumps during the performance of the following actions.

NOTE- If the safety injection system is in operation, then the actions of steps marked by an asterisk will not be applicable.

1. Terminate any changes to the reactor coolant system that may be in progress and bring the RCS to as close to a steady-state condition as possible.

• 2. Attempt Oc recembine any condensible gases by increasing RCS pressure through the use of the pressurizer backup heaters and increased charging flow. If this step is successful in condensing the gas volums in the vessel head (as indicated by a return to normal readings in those parameters used to determine the presence of the gases) than return to the appropriate operating instruction.

CAUTION: Increased charging flow with condensible gases in the RCS may result in a decreasing pressurizer level. If pressurizer level decreases to less than 20% of span, then j attempt to restore level by continuing the charging flow or manually starting safety injection pumps. If level cannot be restored, then manually initiate safety injection and proceed to E0I-0, Immediate Actions and Diagnostics.

February,1981 Revision 0 Page 2 i

3. In preparation for venting, isolate the containment purge and exhaust system and the pressure vacuum relief line and start all available containment air circulation equipment.

4. Increase the RCS sub-cooling to (insert plant specific value

~

which is 50*F aba a the value which is the sum of the errors for the temperature measurement system used, and for the pressure measurement system translated into temperature using the saturation tables) by either initiating an RCS pressurizaticn or by dumping steam from the non-faulted steam generators.

5. If required, perform the actions of Appendix B to determine the maximum allowable time period for venting.(only for plants which vent directly to containment).

• 6. Isolate letdown and initiate an RCS makeup by the chemical volume and control system to increase pressurizer level to greater than

• ~~

50% of span. *

• 7. If not already performed, manually block the low pressure SI initiation if the permissive is energized.

CAUTION: The venting operation may result in pressure decreasing below the SI setpoint. Action should be taken to manually block the automatic SI signal when the permissive is energized.

• 8. Increase charging flow to maximum to limit the pressurizer pressure and level decrease during the venting period.

NOTE: Observe the pressurizer level trend during the venting and, from the following conditions, determine the probable status of the reactor coolant system.

February,1981 REVISION O Page 3

~

a) Increasing pressurizer level - Gaseous voids exist in the RCS other than the reactor vessel head or pressurizer.

b) Constant pressurizer level - No significant gaseous voids exist in the reactor coolant system.

c) Decreasing pressurizer level - Gaseous void exists in the reactor vessel head.

9. 0 pen the vent isolation valves in one head vent flow path.

NOTE: If one or both valves fail to open, close both valves and open the isolation valves'in the parallel flow path.

10. Close both vent isolation valves when:

a) Reactor vessel level indication stabilizes, g -

b) The time period determined in Step 5 is met, E .

c) Pressuri:er pressure decreases by 200 psi, E

d) Pressuri:er level decreases below 20 percent of span E

e) Reactor coolant sub-cooling decreases below (insert plant specific value which is the sum of the errors for the temperature measurement system used, and for the pressure measurement system translated into temperature using the saturation tables).

E f) The reactor vessel head is refilled as indicated by a decrease in the rate of a depressurization or a change in the rate of the pressurizer level trend.

February,1981 Revision 0 page 4

CAUTION: If during the venting period, a loss of reactor coolant pump operation occurs, continue the venting and allow natural circulation to establish itself. -

• 11. Re-establish normal charging and letdown to maintain the pressurizer

-. -water level in the operating range.

• 12. Evaluate the response of the pressurizer level trend to determine if a gas bubble existed in the vessel head. If a gas bubble-existed and the venting was terminated prior to the vessel head being completely refilled, then return to Step 4.

NOTE: If multiple venting operations are required and the con-tainment hydrogen concentration is equal to or greater than 3 volume percent, then provisions must be made to remove or reduce the volume of hydrogen from the containment prior to re-opening the reactor vessel

-- head vent. .

13. Return to'the appropriate operating instruction following the successful ccmpletion of the venting of the reactor vessel head.

February,1981 Revision 0 Page 5 4

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APPENDIX "A" RV HEAD VENT GUIDELINE RCS GASEOUS V0ID DETECTION AND SIZING

1. Achieve a constant pressurizer level and pressure condition.

2. Place the RCS wide range or pressurizer pressure and the pressurizer level on trend recorders. The scale should be 150 psig pressure and 10% of span for level.

3. Record the following parameters.

RCS Pressure = PSI

=  %

PZR Level Charging Rate = GPM Seal Injection Flow = GPM Seal

• Leakoff Low = GPM

=

Time

4. Isolate the RCS letdown flow, turn off all pressurizer heaters, and terminate the pressurizer spray by placing the spray control in manual and zeroing the demand signal.

5. Allow the RCS charging flow to either increase RCS pressure 100 psi or increase pressurizer level 5% of span.

6. Record the RCS pressure, pressurizer level and time, i

RCS Pressure = PSI

=  !

PZR Level  %

Time =

1 1

7. Reinitiate RCS letdown flow and restore normal pressurizer pressure and level control.

P00R ORIGINAL Februa ry, 1981 Revision 0 Page 6

8. Calculate the initial and final pressurizer vapor space volumes.

3 Initial Vapor Volume = (1-PZR Level % X Total Cylindrical PZR Volume FT ) ,

(Upper Spherical Volume FT3 )

= FT3 Final Vapor Volume = (Initial Volume) - (a PZR Level X Total Cylindrical Volume) 3

= FT ,

9. Determine the total charged volume into the RCS.

Charged Volume = (Charging + Seal Injection - Seal Leakoff GPM) X ,

1 (Time) X (7.45 GAL)FT7 3

= FT ,

10. Determine the expected pressurizer level change.

3 Expected a level = (Charging Vo'tume FT ) X (Total P Volume FT 3 )

=  %

11. If the actual pressurizer level change is less than the xpected level change then a gaseous void exists in the reactor coolant system. Perform the following step to determine the volume of the RCS void.

12. The initial and final RCS gaseous void volumes can be calculated from the following equations, f

Revision 0 Page 7 February,1981

4. ' .

Initial RCS Void = (Initial Vapor Volume) - (Final Vaoor Volume) -(Charged Volur (7 _ Final PressureInitial Pressure) J

=

3 FT Final RCS Void = (Initial RCS Void) X (Initial Pressure)

(Final Pressure)

= 3 FT i

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February,1981 Revision 0 Page 8

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,. . l APPENDIX "B".

RV HEAD VENT GUIDELINE i

VENTING TIME PERIOD

1. Convert the containment free-volume to containment volume at standard

-temperature and pressure conditions.

3 Cont. Volume (STP) = (Cont. Volume FT ) X (Co Prmure**)X( )

=

3 FT

• Temperature in degrees Rankine (*F + 460)

• • If containment pressure has increased above 14.7 psia then use 14.7 psig as pressure for conservatism.

2. Determine the containment hydrogen concentration in volume percent units.

~

NOTE: The containment hydrogen concentration will be insigificant if there has been no leakage from the RCS to the containment.

3.. Calculate the maximum hydrogen volume that can be vented to the containment which will result in a containment hydrogen concentration of less than or equal to 3 volume percent.

Maximum H2 Volume = (3.0%-Cont. Hp Concentra on %) X (Cont. Volume [STP])

to be Vented 3

= FT I

4. From Curve #1 (RCS Pressure vs. H2 FlowRate)determinetheallowable venting period which will limit the containment hydrogen concentration f to 3 volume percent.

I Venting Period = Max. Hp Vented (From Step 3)

H2 Flow Rate

= Mins.

1 February,.1981 Revision 0 Page 9

• - ~~

CURVE #1 APPENDIX B

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