ML20037D461
| ML20037D461 | |
| Person / Time | |
|---|---|
| Site: | Prairie Island  |
| Issue date: | 02/28/1981 |
| From: | NORTHERN STATES POWER CO. |
| To: | |
| Shared Package | |
| ML20037D432 | List: |
| References | |
| RTR-NUREG-0737, RTR-NUREG-737, TASK-2.B.1, TASK-2.D.1, TASK-TM PROC-810228-01, TAC-12428, TAC-12429, NUDOCS 8107100263 | |
| Download: ML20037D461 (11) | |
Text
..~e REACTOR VESSEL HEAD VENT OPERATIO" l
l REVISICN 0 l
l FEBRUARY,1981 l
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8107100263 810706 DR ADOCK 05000282 PDR I
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REACTOR VESSEL HEAD VENT OPERATIOM A.
PURPOSE l
The objective of thc e instructions is to specify required operator actions and precautions necessary to remove gases from tne reacter vessel head by operation of the Reactor Vessel Head Vent.
CAUTI0ti:
This venting guideline should not be used as the primary means to mitigate an Inadecuate Core Ccoling event, j
Refer to Inadequate Core Coolinc Guidelines for appropriate operator actions and precautions.
CAUTIg: This venting guideline assumes that the reactor containrent conditions are near normal conditions and that any venting oceration is performed prior to throttling safety injection fic.w during a POST-LOCA cooldown and depressurizatien operation.
B.
SYftPT0ftS 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 durir.] r.ormal charging oY sprayir.g operations have occurred.
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3.
If available, reactor vessel head temperatures equal to or greater than saturation temperature.
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l February, 1981 Revision 0 Page i
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.
SUBSEOUENT 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 esterisk 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 to recombine 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 l
the gas voltme in the vessel head (as indicated by a return to l
normal readings in those pa'ameters used to determine the presence f
i of the gases) then return to the appropriate operating instruction.
l CAUTION:
Increased charging flow with condensible gases in the RCS may result in a decreasing pressurizer level.
If pressurizer level decreases to less than 205 of span, then attempt to restore level by continuing the charging ficw or nanually starting safety injection pumps.
If level cannot be restored, then manually initiate safety injection and proceed to E01-0, Inmediate Actions and Diagnostics.
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February,1981 Revisior. O Page 2
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3.
In preparation for venting, isolate the containment purge and exhaust system and the pressure vacuum relief line and start all evailable containment air circulation equipment.
4 Increase the RCS sub-cooling to (insert plant specific value which is 50 F above the value which is the sun of the errors for the temperature measurement system used, and for the pressure measurement system translated into terrperature using the saturation tables) by either initiating im RCS pressurization 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.
I CAUTI0ft: The venting operation may result in pressure decreasing below the SI setpoint. Action should be taken to j
manually block the automatic SI signal when the j
permissive is energized, i
- 8.
Increase charging flow to maximum to limit the pressurizer pressure and level decrease during the venting period.
fiOTE: Observe the pressurizer level trend during the venting j
and, from the following conditions, determine the probable i
status of the reactor coolant system.
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a) Increasing pressurizer level - Gaseous voids exist in the RCS other than the reactor vessel head or pressurizer.
b) Constant pressurizer level - fio significant gaseous voids exist in the reactor coolant system.
c) Decreasing pressurizer level - 2: seous ~ void exists in the reactor vessel head.
9.
Open the vent isolation valves in one head vent flow patn.
0TE:
If one or both valves fail to open, close both valves and open the isolation valves'in the parallel flow sath.
- 10. Close both vent isolation valves when:
a) Reactor vessel level indication stabilizes, E
b) The time period determined in Step 5 is met, E
c) Pressurizer pressure decreases by 200 psi, E
d) Pressurizer level decreases below 20 percent of span E
e) Reactor coolant sub-cooling decreases below (insert plant l
specific value which is the sum of the errors for the temperature measurement system used, and for the pressure 1
measurement system translated into temperature using the j
saturation tables).
OR 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.
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b CAUTION:
If during the venting period, a loss of reactor coolant pump operation occurs, continue the venting and allov, natural circulation to establish itself.
- ll.
Re-establish normal charging and 'letdow-to maintain the pressurizer water level in the operating range.
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- 12.
Evaluate the response of the pressurizer level trend to determine if a gas bubble exis".cu in the vessel head.
If a gas bubble existed and the venting was terminated prior to tne 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-openinc.he reactor vessel head vent.
- 13. Return to the appropriate operating instruction following the successful completion of the venting of the reactor vessel head.
February,1981 Revision 0 Page 5
APPENDIX "A" RV HEAD VENT GUIDELINE RCS GASE0US VOID 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.
5.
Record the following parameters.
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PZR Level 5
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Charging Rate GPM
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Seal Injection Flow =
GPM Seal Leakoff Low GPM
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Time
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4.
Isolate the RCS letdown flow, turn off all pressurizer heaters, anc terminate the pressurizer spray by placing the spray control in manual and zeroing the demand signal.
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5.
Allow the RCS charging flow to either increase RCS pressure 100 psi or increase pressurizer level 5% of span.
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6.
Record the RCS pressure, pressurizer level and time.
RCS Pressure =
PSI l
PZR Level
=
i Time
=
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7.
Reinitiate RCS letdown flow and restore normal pressurizer pressure and level control.
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8.
Calculate the initial and final pressurizer vapor space volumes.
3 Initial Vapor Volume = (1-PZR Level % X Total Cylindrical PZR Volume FT ) _
3 (Upper Spherical Volume FT )
FT3
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(Initial Volume) - (t PZR Level X Total Cylindrical Final Vapor Volume
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Volume) 3 FT
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9.
Determine the total charged volume into the RCS.
i Charced Volume = (Charging + Seal Injection - Seal Leakoff Gp!') "
1 (Time) X (7.45 N )
ria 3
FT
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- 10. Determine the expected pressurizer level change.
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Expected a level = (Charging Volume FT ) X (Total P olume Fic)
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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 ecuations.
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.q g-
--on
.,,, -g-,.v-,-,-- -, -,,, ~ -
,,m.
,,, - - -. ~., -,
,,,,,,----s,,----.
., - -,-a e
n..
-.,, ~~-,-
a e,e
o Initial RCS Void = (Initial Vaccr Volume) - (Final Vapor Volume) -(Charged Volume
(), Initial Pressure) tinal Pressure 3
FT
=
Final RCS Void = (Initial RCS Void) X (Initial Pressure)
(Final Pressure) 3 FT
=
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APPEf4 DIX "B" RV HEAD VEtr' GUIDELIf1E VEtiTIf!G TIME PERIOD 1.
Convert the containment free-volume to containment volume at standard temperature and pressure conditions.
Cont. Volume (STP) = (Cont. Volume FT ) y [ Cont. Pressure **)yf 492 R 3
l 14.7 PSIs
' Cont. 4emp.")
3 FT
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- 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.
1 fiOTE: 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 s?,1ttd to the containment which will result in a containment hyd, ogen concentration of less than or equal to 3 volume percent.
Volume = (3.0%-Cont. Ho Concentration #) X (Cont. Volume [STP3)
Maximum H2 100#,
to be Vented
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4.
From Curve #1 (RCS Pressure vs. H Flow Rate) determine the allowable 2
venting period which will limit the containment hydrogen concentration to 3 volume percent.
Venting Period = f4ax. Hp Vented (From Step 3)
H2 Flow Rate Mins.
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CURVE =1 AF?Et; DIX B 2000
/
1500
'^'
'C S tessure
' PSI) 1000 500 r-i 1000 2000 3000 4000 5000 HYDROCEN FLOW RATE (SCFM)
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