ML20058B607
| ML20058B607 | |
| Person / Time | |
|---|---|
| Site: | Maine Yankee |
| Issue date: | 10/15/1990 |
| From: | Maine Yankee |
| To: | |
| Shared Package | |
| ML20058B597 | List: |
| References | |
| NUDOCS 9010300333 | |
| Download: ML20058B607 (2) | |
Text
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3,22 FEEDWATER TRIP SYSTEM Acolicability:
Applies to the operating status of the feedwater trip system.
Ob.iective:
To specify conditions of the feedwater trip system necessary to ensure steam generator cooldown potential remains acceptable in the event of a main steam line break.
Specification:
The feedwater trip system shall be operable to perform the following functions i
whenever the reactor coolant boron concentration is less than that required for hot shutdown.
1.
Automatic shutdown of all main feedwater, condensate and heater drain pumps which are operating or set for automatic start.
2.
Automatic closure of all main feedwater regulating valves and main feedwater regulating bypass valves which are open or set to open automatically in the line to the low pressure SG(s).
[ 3.
Automatic closure of the emergency feedwater control and isolation valves in
[
the EfW lines which are open or set to open automatically to the low pressure Steam Generator (s),
t heeotion:
1.
Specifications 1 and 2 do not apply when the main feedwater lines are I
isolated from the steam generators.
2.
While in the hot standby condition, only one means for isolating l
auxil'.ary feedwater flow is required to be operable.
Remedial Action:
If the feedwater trip system is found to be inoperable, it must be restored to an operable status within.the next two hours, or else the reactor must be shut down within the next six hours and the reactor coolant i
system borated to hot shutdown concentration within an additional six hours.
L l
Basis:
The feedwater trip system limits the cooldown of the reactor coolant system in the event.of a main steam line break by limiting the flow of cold feedwater into the steam generators.
Limiting the reactor coolant system cooldown limits reactivity insertion associated with a negative reactivity temperature coefficient during a cooldown.
The feedwater trip system is actuated by signals generated by safety related circuitry associated with the reactor protective system and safety injection system. This safety related circuitry is not itself part of the feedwater trip system. The system provides signals to the controls of feedwater system pumps (main feedwater pumps, condensate pumps, and heater drain pumps), and to the controls of the feedwater regulating valves, feedwater regulating valve bypass
[ valves, and emergency feedwater control and isolation valves.
Amendment 67. 76
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9010300333 901015 3.22-1 DR ADOCK O g9, '
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%e systea valves are aligned to provide flow to each steam generator following system actuation upon low steam generator water level signal from any one of the
.o three steam generators. However, for a steam generator depressurization event, such as a steam line break, receipt of a low steam generator pressure signal initiates closure of the control and isolation valve (s) feeding the depressurized steamgenerator(s). This limits excessive reactor coolant system cooldown and the resultant reactivity insertion produced by excessive feedwater flow to a depressurized steam generator.
Flow will continue to steam generators remaining pressurized.
Flow to a depressurized steam generator will be reestablished by reopening the control and isolation valves after repressurization e.g., by isolation from the steam line break.
Operability of the system assures that the reactivity attributable to reactor coolant system cooldown due to feedwater addition to steam generators after a main steam line break is within the limits established in the steam line break safety analysis.
If the feedwater trip system is discovered to be inoperable, the best course of action is to restore its operability promptly, thus avoiding challenges to plant systems that result from perturbing steady state o)eration. A two-hour time period presents low risk of a main steam line brea( yet allows enough time for deliberate restoration of system operability through maintenance actions.
If operability cannot be restored the reactor must be shut down.
Six hours provides ample time for an orderly controlled shutdown.
'.f operability cannot be restored by that time, the reactor coolant system must bt, borated to hot shutdown concentration within an additional six hours. Twelve hoirs permits an orderly shutdown while assuring that the risk of a main steam line break during the period is very low.
The intended function of the feedwater trip system can be accomplished under conditions of partial system inoperability arovided all main feedwater system pumps and valves tripped by the system whic1 are operating can be tri) ped by the operable portions of the trip system.
Pumps which cannot be tripped ay the trip system due-to partial trip system inoperability can be shut down to assure functional capability.
When the reactor coolant system is at hot shutdown boron concentration, the steam line break cooldown cannot cause sufficient reactivity insertion to cause a return to critical, so the feed trip system is not required to function.
L During plant operation in the hot standby condition, emergency feedwater flow may be warmed by aligning flow to the first stage feedwater 3 reheaters, through the main feedwater regulating valve bypass valves and to eac1 of the steam generators.
Analysis has shown that in the hot standby condition, a single failure of a bypass valve to close during a steam line break meets applicable acceptance criteria.
Amendment No Fi, 79, 91 3.22-2
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