ML13331A898
| ML13331A898 | |
| Person / Time | |
|---|---|
| Site: | San Onofre  |
| Issue date: | 11/12/1986 |
| From: | SOUTHERN CALIFORNIA EDISON CO. |
| To: | |
| Shared Package | |
| ML13331A896 | List: |
| References | |
| TAC-62164, NUDOCS 8611140384 | |
| Download: ML13331A898 (6) | |
Text
2.1 REACTOR CORE -
Limiting Combination of Power, Pressure, and Temperature APPLICABILITY:
Applies to reactor power, system pressure, coolant temperature, and flow during operation of the plant.
OBJECTIVE:
To maintain the integrity of the reactor coolant system and to prevent the release of excessive amounts of fission product activity to the coolant.
SPECIFICATION:
Safety Limits (1) The reactor coolant system pressure shall not exceed 2735 psig with fuel assemblies in the reactor.
(2) The combination of reactor power and coolant temperature shall not exceed the locus of points established for the RCS pressure in Figure 2.1.1.
If the actual power and temperature is above the locus of points for the appropriate RCS pressure, the safety limit is exceeded.
Maximum Safety System Settings The maximum safety system trip settings shall be as stated in Table 2.1 TABLE 2.1 Three Reactor Coolant Pumps Operating
- 1. Pressurizer
< 27.3 ft. above bottom High Level of pressurizer
- 2. Pressurizer
< 2220 psig Pressure:
High
- 3.
Nuclear Overpower
< 109% of indicated full power
- 4 Variable Low Pressure
> 26.15 (0.894 AT+T avg.) -
14341
- 5. Coolant Flow
> 85% of indicated full loop flow
- May be bypassed at power levels below 10% of full power.
- The nuclear overpower trip is based upon a symmetrical power distribution. If an asymmetric power distribution greater than 10% should occur, the nuclear overpower trip on all channels shall be reduced one percent for each percent above 10%.
8611140384 861112 PDR ADOCK 05000206 P
PDR 2-1
BASIS:
Safety Limits
- 1.
Reacor-Coolant System Pressure The Reactor Coolant System serves as a barrier which prevents release of radionuclides contained in the reactor Coolant to the containment atmosphere.
In addition, the failure of components of the Reactor Coolant System could result in damage to the fuel and pressurization of the containment.
A safety limit of 2735 psig (110% of design pressure) has been established which represents the maximum transient pressure allowable in the Reactor Coolant System under the ASME Code,Section VIII.
- 2. Plant Operatingransit In order to prevent any significant amount of fission products from being released from the fuel to the reactor coolant, it is necessary to prevent clad overheating both during normal operation and while undergoing system transients.
Clad overheating and potential failure could occur if the heat transfer mechanism at the clad surface departs from nucleate boiling.
System parameters which affect this departure from nucleate boiling (DNB) have been correlated with experimental data to provide a means of determining the probability of DNB occurrence.
The ratio of the heat flux at which DNB is expected to occur for a given set of conditions to the actual heat flux experienced at a point is the DNB ratio and reflects the probability that DNB will actually occur.
It has been determined that under the most unfavorable conditions of power distribution expected during core lifetime and if a DNB ratio of 1.44 should exist, not more than 7 out of the total of 28,260 fuel rods would be expected to experience DNB.
These conditions correspond to a reactor power of 125% of rated power.
Thus, with the expected power distribution and peaking factors, no significant release of fission products to the reactor coolant system should occur at DNB ratios greater than 1.30.(1)
The DNB ratio, although fundamental, is not an observable variable. 'For this reason, limits have been placed on reactor coolant temperature, flow, pressure, and power level, these being the observable process variables related to determination of the DNB ratio.
The curves presented in Figure 2. 1. 1 represent loci of conditions at which a minimum DNB ratio of 1.30 or greater would occur.
(1) (2) (3) 2-2(
Maximum Safety System Settings
- 1.
Pressurizer High Level and High Pressure In the event of loss of load, the temperature and pressureof the Reactor Coolant System wouldeincereatseure haneres su be a large and rapid reduction in th heasextrce frou e Reactor Coolant System through the steam generato.
he maximum settings of the pressurizer high level trip and the pressurizer high pressure trip are established to maintain the DNB ratio above 1.30 and to prevent the loss of the cushioning effect of the steam volume in the pressurizer (recsulting(i solid hydraulic system) during a loss-of-load transient.
)
- 2.
Variable Low Pressure Loss of Flow and Nuclear Ove Trips These settings are established to accommodate the most severe transients upon which the design is based, e.g., loss of coolant flow, rod withdrawal at power, inadvertent boron dilution and large load increase without exceeding the safety limits.
The settings have been derived in consideration of instrument errors and response times of all necessary equipment. Thus, these settings should prevent the release of any significant quantities Sonprdcstthcoln as a result of transients.
on products to the coolant In order to prevent significant fuel damage in the event of increased peaking factors due to an asymmetric power distribution in the core, the nuclear overpower trip setting on all channels is reduced by one percent for each percent that the asymmetry in power distribution exceeds 10%.
This provision should maintain the DNB ratio above a value of 1.30 throughout design transients mentioned above.
The response of the plant to a reduction in coolant flow while the reactor is at substantial power is a corresponding increase in reactor coolant temperature If the increase in temperature is large enough, DNB could occur, following loss of flow.
The low flow sinal is set high enough to actuate a trip in time to prevent excessively high temperatures and low enough to reflect that a loss of flow conditions exists.
Since coolant loop flow is either full on or full off, any loss of flow '4) mean a reduction of the initial flow (10) to zero.
2-3
ATTACHMENT 3 Proposed Change No. 165 Technical Specifications San Onofre Nuclear Generating Station Unit 1
2.1 REACTOR CORE wimiting Combination of Power, ossure, and Temperature APPLICABILITY: Applies to reactor power, system pressure, coolant temperature, and flow during operation of the plant.
OBJECTIVE:
To maintain the integrity of the reactor coolant system and to prevent the release of excessive amounts of fission product activity to the coolant.
SPECIFICATION: Safety Limits (1) The reactor coolant system pressure shall not exceed 2735 psig with fuel assemblies in the reactor.
(2) The combination of reactor power and coolant temperature shall not exceed the locus of points established for the RCS pressure in Figure 2.1.1. If the actual power and temperature is above the locus of points for the appropriate RCS pressure, the safety limit is exceeded.
MAXIMUM SAFETY SYSTEM SETTINGS The maximum safety system trip settings shall be as stated in Table 2.1 TABLE 2.1 Three Reactor Coolant Pumps Operating
- 1. Pressurizer
< 20.8 ft. above bottom of High Level pressurizer when steam/feedflow mismatch trip isnot credited, or
( 27.3 ft. above bottom of pressurizer when steam/feedflow mismatch trip is credi ted
- 2. Pressurizer
< 2220 psig Pressure:
High
- 3.
Nuclear Overpower
< 109. of indicated full power
- 4.
Variable Low Pressure
> 26.15 (0.894 A avg.) -
14341
- 5.
Coolant Flow
> 85% of indicated full loop flow Credit can be taken for the steam/feedflow mismatch trip when this system is modified such that a single failure will not prevent the system from performing its safety function (PT-459 Modification).
The nuclear overpower trip is based upon a symmetrical power distribution. If an asymmetric power distribution greater than 10%
should occur, the nuclear overpower trip on all channels shall be reduced one percent for each percent above 10%.
May be bypassed at power levels below 10% of full power,
Maximum Safety emhSettings Pressurzerih Level and High Pressur In the event of loss of load, the temperature and pressure of the Reactor Coolant System would increase since there would be a large and rapid reduction in the heat extracted from the Reactor Coolant System through the steam generators.
The maximumsetnsothprsuir high level trip and the pressurizer high pressure of t
he r es surized to maintain the DNB ratio above 1.30 and to prevent the losstablhe cushioning effect of the steam volume in the pressurizer (resulting in a solid hydraulic system) during a loss-of-load transient. (3) (4)
In the event that steam/feedflow mismatch trip cannot be credited due to single failure considerations, the pressurizer high level trip is provided. In order to meet acceptance criteria for the Loss of Main Feedwater transient the pressurizer high level trip must be set at 20.8 ft. (50%) or less.
- 2.
Variab ss o low ucl verpower Trips These settings are established to accommodate the most severe transients upon which the design is based, e.g., loss of coolant flow, rod withdrawal at power, inadvertent boron dilution and large load increase without exceeding the safety limits.
The settings have been derived in consideration of instrument errors and response times of all necessary equipment. Thus, these settings should prevent the release of any significant quantities of fission products to the coolant as a result of transients. (3) (4) (5)
In order to prevent significant fuel damage in the event of increased peaking factors due to an asymmetric power distribution in the core, the nuclear overpower trip setting on all channels is reduced by one percent for each percent that the asymmetry in power distribution exceeds 10%.
This provision should maintain the DNB ratio above a value of 1.30 throughout design transients mentioned above.
The response of the plant to a reduction in coolant flow while the reactor is at substantial power is a corresponding increase in reactor coolant temperature. If the increase in temperature is large enough, DNB could occur, following loss of flow.
The low flow signal is set high enough to actuate a trip in time to prevent excessively high temperatures and low enough to reflect that a loss of flow condition exists.
Since coolant loop flow is either full on or full off, any loss of flow would mean a reduction of the initial flow (100%) to zero. (3) (6)