ML20197A661
| ML20197A661 | |
| Person / Time | |
|---|---|
| Site: | Millstone  |
| Issue date: | 12/17/1997 |
| From: | NORTHEAST NUCLEAR ENERGY CO. |
| To: | |
| Shared Package | |
| ML20197A653 | List: |
| References | |
| NUDOCS 9712230118 | |
| Download: ML20197A661 (3) | |
Text
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Docket No. 50-423 B16892 t
1 Millstone Nuclear Power Station Unit No. 3 Proposed Revision to Technical Specification Pressurizer Level (PTSCR 3-31-97)
Revised Bases Section 3/4.4.3 Pace
,g
g BASES 3/4.4.2 SAFETY VALVES The pressurizer Code safety valves operate to prevent the RCS from being pressurized above its Safety Limit of 2750 psia.
Each safety valve is designed to relieve 420,000 lbs per hour of saturated steam at the valve Setpoint. The relief capacity of a single safety valve is adequate to relieve any overpressure condition which could occur during shutdown.
In the event that no safety valves are OPERABLE, an operating RHR loop, connected to the RCS, provides overpressure relief capability and will prevent RCS overpressurization.
In addition, the Cold Overpressure Protection System provides a diverse means of protection against RCS overpressurization at low temperatures.
During operation, all pressurizer Code safety valves must be OPERABLE to prevent the RCS from being pressurized above its Safety Limit of 2750 psia. The combined relief capacity of all of these valves is greater than the maximum surge rate resulting from a complete loss-of-load assuming no Reactor trip until the first Reactor Trip System Trip Setpoint is reached (i.e., no credit is taken for a direct Reactor trip on the loss-of-load) and also assuming no operation of the power-operated relief valves or steam dump valves.
Demonstration of the safety valves' lift settings will occur only during shutdown and will be performed in accordance with the provisions of Section XI of the ASME Boiler and Pressure Code, 3/4.4.3 PRESSURIZER In MODES 1, 2 and 3, the LC0 requirement for the pressurizer to be OPERABLE with a level less than or equal to 89% ensures that a steam bubble exists which is reflected implicitly in various accident analyses.
All analyses aerformed from a critical reactor condition assume the existence of a steam buable and saturated conditions in the pressurizer.
In making this assumption, the analyses neglect the small fraction of noncondensible gases normally present.
The maximum pressurizer water level limit, which ensures that a steam bubble exists in the pressurizer, satisfies Criterion 2 of the NRC Policy Statement.
Other pressurizer level assumptions used in accident analyses are adequately maintained with automatic and procedural controls.
Accident analyses do not take credit for pressurizer heater operation, however, an implicit initial assumption of the safety analyses is that the RCS is operating at normal pressure.
The 12 hour1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> periodic suroeillance requires that during steady state operation, pressurizer level it maintained below the nominal upper limit to provide a minimum space for a steam bubble. The Surveillance is performed by observing the indicated level. The 12 hour1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> interval has been shown by operating practice to be sufficient to regularly assess level for any deviation and to ensure that a steam bubble exists in the pressurizer.
Alarms are also available for' early detection of abnormal level indications.
The requirement that a minimum number of pressurizer heaters be OPERABLE enhances the capability of the plant to control Reactor Coolant System pressure
_and establish natural circulation.
l MILLSTONE - UNIT 3 B 3/4 4-2 Amendment No.
0556 l
l 1
..R.EMTOR COOLANT SYSTEN -
BASES-
-3/4.4.4 REllEF VALVES The power operated relief valves.(PORVs) and steam bubble function to
- relieve RCS pressure during all design transients up to and including the design step load decrease with steam dump. Operation of the PORVs minimizes the undesirable opening of the spring-loaded pressurizer Code safety valves.
Each PORV has-a remotely operated block valve to provide a positive shutoff capability should a relief valve become inoperable.
Requiring the PORVs to be OPERABLE ensures that the capability.for depressurization during safety grade cold shutdown is met.
Action statements a, b, and c distinguishes the inoperability of the power operated relief valves (PORV).
Specifically, a PORY may be designated inoperable but it may be able to manually open and close and therefore, able to perform its function.
PORV inoperability may be.due to seat leakage, instrumentation problems, automatic control problems, or other causes that do not prevent manual use and do not create a possibility for a small-break LOCA.
For these reasons, the block valve may be closed but the action requires power to be maintained to the valve. This allows quick-access to the PORV for pressure control.
On the other hand if a PORV is inoperable and not capable of being manually cycled, it must be either restored or isolated by closing the associated block valve and removing power.
The prime importance for the capability to close the block valve is to isolate a stuck-open PORV. Therefore, if the block valve (s) cannot be restored to operable status within 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br />, the remedial action is to place the PORV in manual control (i.e. the control switch in the "CLOSE" position) to preclude its automatic opening for an overpressure event and to avoid the potential of a stuck-open PORV at a time that the block valve is inoperable. The time allowed to restore the block valve (s) to operable status is based upon the remedial action time limits for inoperable PORV per ACTION requirements b and c.
These actions do not specify closure of the block valves because such action would not likely be possible when the block valve is inoperable.
NILLSTONE - UNIT 3 B 3/4 4-2a Amendment No pp.
0560
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