ML033100404

Technical Specification Bases (TSB) Change

ML033100404
Person / Time
Site:	Oconee
Issue date:	10/29/2003
From:	Rosalyn Jones Duke Power Co
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
Download: ML033100404 (30)

Text

Duke c Power, A Duke Energy Company R. A. JONES Vice President Duke Power 29672 / Oconee Nuclear Site 7800 Rochester Highway Seneca, SC 29672 864 885 3158 864 885 3564 fax October 29, 2003 U. S. Nuclear Regulatory Commission Washington, D. C. 20555 Attention: Document Control Desk

Subject:

Oconee Nuclear Station Docket Numbers 50-269, 270, and 287 Technical Specification Bases (TSB) Change Please see attached revisions to Tech Spec Bases 3.3.1, Reactor Protective System (RPS) Instrumentation, were implemented'on October 23, 2003.

Attachment contains the new TSB pages and Attachment 2 contains the markup version of the Bases pages.

If any additional information is needed, please contact Larry E. Nicholson, at (864-885-3292).

Very r

yours, R.

ones, Vice President Oc n Nuclear Site A O'D www. duke-energy. corn

U. S. Nuclear Regulatory Commission October 29, 2003 Page 2 cc:

Mr. L. N. Olshan Office of Nuclear Reactor Regulation U. S. Nuclear Regulatory Commission Washington, D. C.

20555 Mr. L. A. Reyes, Regional Administrator U. S. Nuclear Regulatory Commission -

Region II Atlanta Federal Center 61 Forsyth St., SW, Suite 23T85 Atlanta, Georgia 30303 Mel Shannon Senior Resident Inspector Oconee Nuclear Station Mr. Henry Porter Director Division of Radioactive Waste Management Bureau of Land and Waste Management Department of Health & Environmental Control 2600 Bull Street Columbia, SC 29201

RPS Instrumentation B 3.3.1 B 3.3 INSTRUMENTATION B 3.3.1 Reactor Protective System (RPS) Instrumentation BASES BACKGROUND The RPS initiates a reactor trip to protect against violating the core fuel design limits and the Reactor Coolant System (RCS) pressure boundary during anticipated transients. By tripping the reactor, the RPS also assists the Engineered Safeguards (ES) Systems in mitigating accidents.

The protective and monitoring systems have been designed to assure safe operation of the reactor. This is achieved by specifying limiting safety system settings (LSSS) in terms of parameters directly monitored by the RPS, as well as the LCOs on other reactor system parameters and equipment performance.

The LSSS, defined in this Specification as the Allowable Value, in conjunction with the LCOs, establishes the threshold for protective system action to prevent exceeding acceptable limits during accidents or transients.

During anticipated transients, which are those events expected to occur one or more times during the unit's life, the acceptable limit is:

a.

The departure from nucleate boiling ratio (DNBR) shall be maintained above the Safety Limit (SL) value;

b.

Fuel centerline melt shall not occur; and

c.

The RCS pressure SL of 2750 psia shall not be exceeded.

Maintaining the parameters within the above values ensures that the offsite dose will be within the 10 CFR 20 and 10 CFR 100 criteria during anticipated transients.

Accidents are events that are analyzed even though they are not expected to occur during the unit's life. The acceptable limit during accidents is that the offsite dose shall be maintained within reference 10 CFR 100 limits.

Meeting the acceptable dose limit for an accident category is considered having acceptable consequences for that event.

OCONEE UNITS 1, 2, & 3 B 3.3.1 -1 BASES REVISION DATED 10/23/03

RPS Instrumentation B 3.3.1 BASES BACKGROUND RPS Overview (continued)

The RPS consists of four separate redundant protective channels that receive inputs of neutron flux, RCS pressure, RCS flow, RCS temperature, RCS pump status, reactor building (RB) pressure, main feedwater (MFW) pump status, and turbine status.

Figure 7.1, UFSAR, Chapter 7 (Ref. 1), shows the arrangement of a typical RPS protective channel. A protective channel is composed of measurement channels, a manual trip channel, a reactor trip module (RTM), and control rod drive (CRD) trip devices. LCO 3.3.1 provides requirements for the individual measurement channels. These channels encompass all equipment and electronics from the point at which the measured parameter is sensed through the bistable relay contacts in the trip string. LCO 3.3.2, "Reactor Protective System (RPS) Manual Reactor Trip," LCO 3.3.3, "Reactor Protective System (RPS) - Reactor Trip Module (RTM),' and LCO 3.3.4, "control rod Drive (CRD) Trip Devices," discuss the remaining RPS elements.

The RPS instrumentation measures critical unit parameters and compares these to predetermined setpoints. If the setpoint is exceeded, a channel trip signal is generated. The generation of any two trip signals in any of the four RPS channels will result in the trip of the reactor.

The Reactor Trip System (RTS) contains multiple CRD trip devices; two AC trip breakers, two DC trip breaker pairs, and eight electronic trip assembly (ETA) relays. The system has two separate paths (or channels), with each path having one AC breaker in series with a pair of DC breakers and functionally in series with four ETA relays in parallel. Each path provides independent power to the CRDs. Either path can provide sufficient power to operate all CRDs. Two separate power paths to the CRDs ensure that a single failure that opens one path will not cause an unwanted reactor trip.

The RPS consists of four independent protective channels, each containing an RTM. The RTM receives signals from its own measurement channels that indicate a protective channel trip is required. The RTM transmits this signal to its own two-out-of-four trip logic and to the two-out-of-four logic of the RTMs in the other three RPS channels. Whenever any two RPS channels transmit channel trip signals, the RTM logic in each channel actuates to remove 120 VAC power from its associated CRD trip device.

OCONEE UNITS 1 2 3

B 3.3.1-2 BASES REVISION DATED 10/23/03 l

RPS Instrumentation B 3.3.1 BASES BACKGROUND RPS Overview (continued)

The reactor is tripped by opening circuit breakers and ETA relays that interrupt the control power supply to the CRDs. Six breakers are installed to increase reliability and allow testing of the trip system. A one-out-of-two taken twice logic is used to interrupt power to the rods.

The RPS has three bypasses: a shutdown bypass, a dummy bistable and an RPS channel bypass. Shutdown bypass allows the withdrawal of safety rods for SDM availability and rapid negative reactivity insertion during unit cooldowns or heatups. The dummy bistable is used to bypass one or more functions (bistable trips) associated with one RPS Channel. The RPS Channel bypass allows one entire RPS channel to be taken out of service for maintenance and testing. Test circuits in the trip strings allow complete testing of all RPS trip Functions.

The RPS operates from the instrumentation channels discussed next. The specific relationship between measurement channels and protective channels differs from parameter to parameter. Three basic configurations are used:

a.

Four completely redundant measurements (e.g., reactor coolant flow) with one channel input to each protective channel;

b.

Four channels that provide similar, but not identical, measurements (e.g., power range nuclear instrumentation where each RPS channel monitors a different quadrant), with one channel input to each protective channel; and

c.

Redundant measurements with combinational trip logic outside of the protective channels and the combined output provided to each protective channel (e.g., main feedwater pump trip instrumentation).

These arrangements and the relationship of instrumentation channels to trip Functions are discussed next to assist in understanding the overall effect of instrumentation channel failure.

Power Range Nuclear Instrumentation Power Range Nuclear Instrumentation channels provide inputs to the following trip Functions:

1.

Nuclear Overpower OCONEE UNITS 1, 2, & 3 B 3.3.1-3 BASES REVISION DATED 10/23/03

RPS Instrumentation B 3.3.1 BASES BACKGROUND Power Range Nuclear Instrumentation (continued)

a.

Nuclear Overpower - High Setpoint;

b.

Nuclear Overpower - Low Setpoint;

7.

Reactor Coolant Pump to Power;

8.

Nuclear Overpower Flux/Flow Imbalance;

9.

Main Turbine Trip (Hydraulic Fluid Pressure); and

10.

Loss of Main Feedwater (LOMFW) Pumps (Hydraulic Oil Pressure).

The power range instrumentation has four linear level channels, one for each core quadrant. Each channel feeds one RPS protective channel.

Each channel originates in a detector assembly containing two uncompensated ion chambers. The ion chambers are positioned to represent the top half and bottom half of the core. The individual currents from the chambers are fed to individual linear amplifiers. The summation of the top and bottom is the total reactor power. The difference of the top minus the bottom neutron signal is the measured AXIAL POWER IMBALANCE for the associated core quadrant.

Reactor Coolant System Outlet Temperature The Reactor Coolant System Outlet Temperature provides input to the following Functions:

2.

RCS High Outlet Temperature; and

5.

RCS Variable Low Pressure.

The RCS Outlet Temperature is measured by two resistance elements in each hot leg, for a total of four. One temperature detector is associated with each protective channel.

OCONEE UNITS 1, 2, & 3 B 3.3.1-4 BASES REVISION DATED 10/23/03

RPS Instrumentation B 3.3.1 BASES BACKGROUND Reactor Coolant System Pressure (continued)

The Reactor Coolant System Pressure provides input to the following Functions:

3.

RCS High Pressure;

4.

RCS Low Pressure;

5.

RCS Variable Low Pressure; and

11.

Shutdown Bypass RCS High Pressure.

The RPS inputs of reactor coolant pressure are provided by two pressure transmitters in each hot leg, for a total of four. One sensor is associated with each protective channel.

Reactor Buildinq Pressure The Reactor Building Pressure measurements provide input only to the Reactor Building High Pressure trip, Function 6. There are four RB High Pressure sensors, one associated with each protective channel.

Reactor Coolant Pump Power Monitoring Reactor coolant pump power monitors are inputs to the Reactor Coolant Pump to Power trip, Function 7. Each RCP, operating current, and voltage is measured by four current transformers and four potential transformers driving four underpower relays. Each power monitoring channel consists of an underpower relay. One channel for each pump is associated with each protective channel.

Reactor Coolant System Flow The Reactor Coolant System Flow measurements are an input to the Nuclear Overpower Flux/Flow Imbalance trip, Function 8. The reactor coolant flow inputs to the RPS are provided by eight high accuracy differential pressure transmitters, four on each loop, which measure flow through calibrated flow tubes. One flow input in each loop is associated with each protective channel.

OCONEE UNITS 1, 2, & 3 B 3.3.1-5 BASES REVISION DATED 10/23/03

RPS Instrumentation B 3.3.1 BASES BACKGROUND Main Turbine Automatic Stop Oil Pressure (continued)

Main Turbine Automatic Stop Oil Pressure is an input to the Main Turbine Trip (Hydraulic Fluid Pressure) reactor trip, Function 9. Each of the four protective channels receives turbine status information from one of the four pressure switches monitoring main turbine automatic stop oil pressure. An open indication will be provided to the RPS on a turbine trip. Contact buffers in each protective channel continuously monitor the status of the contact inputs and initiate an RPS trip when a main turbine trip is indicated.

Feedwater Pump Hydraulic Oil Pressure Feedwater Pump Hydraulic Oil Pressure is an input to the Loss of Main Feedwater Pumps (Hydraulic Oil Pressure) trip, Function 10. Hydraulic Oil pressure is measured by four switches on each feedwater pump. One switch on each pump, connected in series with a switch on the other MFW pump, is associated with each protective channel.

RPS Bypasses The RPS is designed with three types of bypasses: dummy bistable, channel bypass and shutdown bypass.

The dummy bistable provides a method of placing one or more functions in a RPS protective channel in a bypassed condition, the channel bypass provides a method of placing all Functions in one RPS protective channel in a bypassed condition, and shutdown bypass provides a method of leaving the safety rods withdrawn during cooldown and depressurization of the RCS. Each bypass is discussed next.

Dummy Bistable The dummy bistable is used to bypass one or more functions (bistable trips) associated with one RPS Channel. A dummy bistable is used if a parameter in an RPS channel fails and causes that channel to trip. Dummy bistables may be used in only one RPS channel at a time. Also, if an RPS channel is bypassed, no other RPS channel may contain a dummy bistable. Inserting a dummy bistable in the place of a failed (tripped) bistable allows the RPS channels to be reset, thus allowing the remainder of the functions in that RPS channel to be returned to service. This is more OCONEE UNITS 1, 2, & 3 B 3.3.1-6 BASES REVISION DATED 10/23/03

RPS Instrumentation B 3.3.1 BASES BACKGROUND Dummy Bistable (continued) conservative than manually bypassing the entire RPS channel. For an RPS channel with a dummy bistable installed, only the affected function(s) is inoperable. The installation of the STAR hardware in the nuclear overpower flux/flow imbalance trip string requires the use of jumpers to bypass the trip string. The installation of these jumpers does not require the removal of the STAR processor module, therefore, the protective channel is not forced into a tripped condition.

Channel Bypass A channel bypass provision is provided to allow for maintenance and testing of the RPS. The use of channel bypass keeps the protective channel trip relay energized regardless of the status of the instrumentation channel of the bistable relay contacts. To place a protective channel in channel bypass, the other three channels must not be in channel bypass or otherwise inoperable (e.g., a dummy bistable installed). This can be verified by observing alarms/indicator lights. This is administratively*

controlled by having only one manual bypass key available for each unit.

All RPS trips are reduced to a two-out-of-three logic in channel bypass.

Shutdown Bypass During unit cooldown and heatup, it is desirable to leave the safety rods at least partially withdrawn to provide shutdown capabilities in the event of unusual positive reactivity additions (moderator dilution, etc.).

However, the unit is also depressurized as coolant temperature is decreased. If the safety rods are withdrawn and coolant pressure is decreased, an RCS Low Pressure trip will occur at 1800 psig and the rods will fall into the core. To avoid this, the protective system allows the operator to bypass the low pressure trip and maintain shutdown capabilities. During the cooldown and depressurization, the safety rods are inserted prior to the low pressure trip of 1800 psig. The RCS pressure is decreased to less than 1720 psig, then each RPS channel is placed in shutdown bypass.

In shutdown bypass, a normally closed contact opens when the operator closes the shutdown bypass key switch (status shall be indicated by a light). This action bypasses the RCS Low Pressure trip, Nuclear Overpower Flux/Flow Imbalance trip, Reactor Coolant Pump to Power trip, OCONEE UNITS 1,2, &3 B 3.3.1-7 BASES REVISION DATED 10/23/03

RPS Instrumentation B 3.3.1 BASES BACKGROUND Shutdown Bypass (continued) and the RCS Variable Low Pressure trip, and inserts a new RCS High Pressure, 1720 psig trip. The operator can now withdraw the safety rods for additional rapidly insertable negative reactivity.

The insertion of the new high pressure trip performs two functions.. First, with a trip setpoint of 1720 psig, the bistable prevents operation at normal system pressure, 2155 psig, with a portion of the RPS bypassed. The second function is to ensure that the bypass is removed prior to normal operation. When the RCS pressure is increased during a unit heatup, the safety rods are inserted prior to reaching 1720 psig. The shutdown bypass is removed, which returns the RPS to normal, and system pressure is increased to greater than 1800 psig. The safety rods are then withdrawn and remain at the full out condition for the rest of the heatup.

In addition to the Shutdown Bypass RCS High Pressure trip, the high flux trip setpoint is administratively reduced to < 5% RTP prior to placing the RPS in shutdown bypass. This provides a backup to the Shutdown Bypass RCS High Pressure trip and allows low power physics testing while preventing the generation of any significant amount of power.

Module Interlock and Test Trip Relay Each channel and each trip module is capable of being individually tested.

When a module is placed into the test mode, it causes the test trip relay to open and to indicate an RPS channel trip. Under normal conditions, the channel to be tested is placed in bypass before a module is tested. Each trip module is electrically interlocked to the other three trip modules.

Removal of a trip module will indicate a tripped channel in the remaining trip modules.

Trip Setpoints/Allowable Value The Allowable Value and trip setpoint are based on the analytical limits stated in UFSAR, Chapter 15 (Ref. 2). The selection of the Allowable Value and associated trip setpoint is such that adequate protection is provided when all sensor and processing time delays are taken into account. To allow for calibration tolerances, instrumentation uncertainties, instrument drift, and severe environment errors for those RPS channels that must function in harsh environments as defined by 10 CFR 50.49 OCONEE UNITS 1,2, &3 B 3.3.1 -8 BASES REVISION DATED 10/23/03

RPS Instrumentation B 3.3.1 BASES BACKGROUND Trip Setpoints/Allowable Value (continued)

(Ref. 3), the Allowable Values specified in Table 3.3.1-1 in the accompanying LCO are conservative with respect to the analytical limits to account for all known uncertainties for each channel. The actual trip setpoint entered into the bistable is more conservative than that specified by the Allowable Value to account for changes in random measurement errors detectable by a CHANNEL FUNCTIONAL TEST. One example of such a change in measurement error is drift during the Surveillance Frequency. A channel is inoperable if its actual trip setpoint is not within its required Allowable Value. All field sensors and signal processing equipment for these channels are assumed to operate within the allowances of these uncertainty magnitudes. The trip setpoints are the nominal values at which the bistables are set. Any bistable is considered to be properly adjusted when the as left" value is within the band for CHANNEL CALIBRATION accuracy. A detailed description of the methodology used to determine the Allowable Value, trip setpoints, and associated uncertainties is provided in Reference 4.

Setpoints in accordance with the Allowable Value ensure that the limits of Chapter 2.0, Safety Limits," in the Technical Specifications are not violated during anticipated transients and that the consequences of accidents will be acceptable, providing the unit is operated from within the LCOs at the onset of the anticipated transient or accident and the equipment functions as designed. Note that in LCO 3.3.1 the Allowable Values listed in Table 3.3.1-1 for Functions 1 through 8 and 11 are the LSSS.

Each channel can be tested online to verify that the setpoint accuracy is within the specified allowance requirements. Once a designated channel is taken out of service for testing, a simulated signal is injected in place of the field instrument signal. Surveillances for the channels are specified in the SR section.

APPLICABLE Each of the analyzed accidents and transients that require a reactor trip to SAFETY ANALYSES, meet the acceptance criteria can be detected by one or more RPS LCO, and Functions. The accident analysis contained in the UFSAR, Chapter 15 APPLICABILITY (Ref. 2), takes credit for most RPS trip Functions. Functions not specifically credited in the accident analysis were qualitatively credited in the safety analysis and the NRC staff approved licensing basis for the unit.

These Functions are high RB pressure, high RCS temperature, turbine trip, and loss of main feedwater. These Functions may provide protection for conditions that do not require dynamic transient analysis to demonstrate Function performance. These Functions also serve as backups to Functions that were credited in the safety analysis.

OCONEE UNITS 1, 2, & 3 B 3.3.1-9 BASES REVISION DATED 10/23/03

RPS Instrumentation B 3.3.1 BASES APPLICABLE The LCO requires all instrumentation performing an RPS Function to be SAFETY ANALYSES, OPERABLE. Failure of any instrument renders the affected channel(s)

LCO, and inoperable and reduces the reliability of the affected Functions. The three APPLICABILITY channels of each Function in Table 3.3.1 -1 of the RPS instrumentation (continued) shall be OPERABLE during its specified Applicability to ensure that a reactor trip will be actuated if needed. Additionally, during shutdown bypass with any CRD trip breaker closed, the applicable RPS Functions must also be available. This ensures the capability to trip the withdrawn CONTROL RODS exists at all times that rod motion is possible. The trip Function channels specified in Table 3.3.1 -1 are considered OPERABLE when all channel components necessary to provide a reactor trip are functional and in service for the required MODE or Other Specified Condition listed in Table 3.3.1-1.

Only the Allowable Values are specified for each RPS trip Function in the LCO. Nominal trip setpoints are specified in the setpoint calculations. The nominal setpoints are selected to ensure that the setpoint measured by CHANNEL FUNCTIONAL TESTS does not exceed the Allowable Value if the bistable is performing as required. A trip setpoint found less conservative than the nominal trip setpoint, but within its Allowable Value, is considered OPERABLE with respect to the uncertainty allowances assumed for the applicable surveillance interval provided that operation, testing and subsequent calibration are consistent with the assumptions of

.the setpoint calculations. Each Allowable Value specified is more conservative than instrument uncertainties appropriate to the trip Function.

These uncertainties are defined in Reference 4.

For most RPS Functions, the Allowable Value in conjunction with the nominal trip setpoint ensure that the departure from nucleate boiling (DNB),

center line fuel melt, or RCS pressure SLs are not challenged. Cycle specific values for use during operation are contained in the COLR.

Certain RPS trips function to indirectly protect the SLs by detecting specific conditions that do not immediately challenge SLs but will eventually lead to challenge if no action is taken. These trips function to minimize the unit transients caused by the specific conditions. The Allowable Value for these Functions is selected at the minimum deviation from normal values that will indicate the condition, without risking spurious trips due to normal fluctuations in the measured parameter.

The Allowable Values for bypass removal Functions are stated in the Applicable MODE or Other Specified Condition column of Table 3.3.1 -1.

The safety analyses applicable to each RPS Function are discussed next.

OCONEE UNITS 1, 2, & 3 B 3.3.1 -1 0 BASES REVISION DATED 10/23/03

RPS Instrumentation B 3.3.1 BASES APPLICABLE

1.

Nuclear Overpower SAFETY ANALYSES, LCO, and

a.

Nuclear Overpower -

High Setpoint APPLICABILITY (continued)

The Nuclear Overpower - High Setpoint trip provides protection for the design thermal overpower condition based on the measured out of core neutron leakage flux.

The Nuclear Overpower - High Setpoint trip initiates a reactor trip when the neutron power reaches a predefined setpoint at the design overpower limit. Because THERMAL POWER lags the neutron power, tripping when the neutron power reaches the design overpower will limit THERMAL POWER to prevent exceeding acceptable fuel damage limits.

Thus, the Nuclear Overpower - High Setpoint trip protects against violation of the DNBR and fuel centerline melt SLs.

However, the RCS Variable Low Pressure, and Nuclear Overpower Flux/Flow Imbalance, provide more direct protection. The role of the Nuclear Overpower - High Setpoint trip is to limit reactor THERMAL POWER below the highest power at which the other two trips are known to provide protection.

The Nuclear Overpower - High Setpoint trip also provides transient protection for rapid positive reactivity excursions during power operations. These events include the rod withdrawal accident and the rod ejection accident. By providing a trip during these events, the Nuclear Overpower -

High Setpoint trip protects the unit from excessive power levels and also serves to limit reactor power to prevent violation of the RCS pressure SL.

Rod withdrawal accident analyses cover a large spectrum of reactivity insertion rates (rod worths), which exhibit slow and rapid rates of power increases. At high reactivity insertion rates, the Nuclear Overpower - High Setpoint trip provides the primary protection. At low reactivity insertion rates, the high pressure trip provides primary protection.

OCONEE UNITS 1, 2, & 3 B 3.3.1 -1 BASES REVISION DATED 10/23/03

RPS Instrumentation B 3.3.1 BASES APPLICABLE

b.

Nuclear Overpower - Low Setpoint SAFETY ANALYSES, LCO, and Prior to initiating shutdown bypass, the Nuclear APPLICABILITY Overpower - Low Setpoint trip must be reduced to

• 5% RTP.

(continued)

The low power setpoint, in conjunction with the lower Shutdown Bypass RCS High Pressure setpoint, ensure that the unit is protected from excessive power conditions when other RPS trips are bypassed.

The setpoint Allowable Value was chosen to be as low as practical and still lie within the range of the out of core instrumentation.

2.

RCS Hich Outlet Temperature The RCS High Outlet Temperature trip, in conjunction with the RCS Low Pressure and RCS Variable Low Pressure trips, provides protection for the DNBR SL. A trip is initiated whenever the reactor vessel outlet temperature approaches the conditions necessary for DNB. Portions of each RCS High Outlet Temperature trip channel are common with the RCS Variable Low Pressure trip. The RCS High Outlet Temperature trip provides steady state protection for the DNBR SL.

The RCS High Outlet Temperature trip limits the maximum RCS temperature to below the highest value for which DNB protection by the Variable Low Pressure trip is ensured. The trip setpoint Allowable Value is selected to ensure that a trip occurs before hot leg temperatures reach the point beyond which the RCS Low Pressure and Variable Low Pressure trips are analyzed. Above the high temperature trip, the variable low pressure trip need not provide protection, because the unit would have tripped already. The setpoint Allowable Value does not reflect errors induced by harsh environmental conditions that the equipment is expected to experience because the trip is not required to mitigate accidents that create harsh conditions in the RB.

3.

RCS High Pressure The RCS High Pressure trip works in conjunction with the pressurizer and main steam relief valves to prevent RCS overpressurization, thereby protecting the RCS High Pressure SL.

OCONEE UNITS 1, 2, & 3 B 3.3.1-12 BASES REVISION DATED 10/23/03

RPS Instrumentation B 3.3.1 BASES APPLICABLE

3.

RCS HIGH PRESSURE (continued)

SAFETY ANALYSES, LCO, and The RCS High Pressure trip has been credited in the transient APPLICABILITY analysis calculations for slow positive reactivity insertion transients (rod withdrawal transients and moderator dilution). The rod withdrawal transient covers a large spectrum of reactivity insertion rates and rod worths that exhibit slow and rapid rates of power increases. At high reactivity insertion rates, the Nuclear Overpower

- High Setpoint trip provides the primary protection. At low reactivity insertion rates, the RCS High Pressure trip provides the primary protection.

The setpoint Allowable Value is selected to ensure that the RCS High Pressure SL is not challenged during steady state operation or slow power increasing transients. The setpoint Allowable Value does not reflect errors induced by harsh environmental conditions because the equipment is not required to mitigate accidents that create harsh conditions in the RB.

4.

RCS Low Pressure The RCS Low Pressure trip, in conjunction with the RCS High Outlet Temperature and Variable Low Pressure trips, provides protection for the DNBR SL. A trip is initiated whenever the system pressure approaches the conditions necessary for DNB. The RCS Low Pressure trip provides DNB low pressure limit for the RCS Variable Low Pressure trip.

The RCS Low Pressure setpoint Allowable Value is selected to ensure that a reactor trip occurs before RCS pressure is reduced below the lowest point at which the RCS Variable Low Pressure trip is analyzed. The RCS Low Pressure trip provides protection for primary system depressurization events and has been credited in the accident analysis calculations for small break loss of coolant accidents (LOCAs). Harsh RB conditions created by small break LOCAs cannot affect performance of the RCS pressure sensors and transmitters within the time frame for a reactor trip. Therefore, degraded environmental conditions are not considered in the Allowable Value determination.

OCONEE UNITS 1, 2, & 3 B 3.3.1-13 BASES REVISION DATED 10/23/03

RPS Instrumentation B 3.3.1 BASES APPLICABLE

5.

RCS Variable Low Pressure SAFETY ANALYSES, LCO, and The RCS Variable Low Pressure trip, in conjunction with the RCS APPLICABILITY High Outlet Temperature and RCS Low Pressure trips, provides (continued) protection for the DNBR SL. A trip is initiated whenever the system parameters of pressure and temperature approach the conditions necessary for DNB. The RCS Variable Low Pressure trip provides a floating low pressure trip based on the RCS High Outlet Temperature within the range specified by the RCS High Outlet Temperature and RCS Low Pressure trips.

The RCS Variable Low Pressure setpoint Allowable Value is selected to ensure that a trip occurs when temperature and pressure approach the conditions necessary for DNB while operating in a temperature pressure region constrained by the low pressure and high temperature trips. The RCS Variable Low Pressure trip is assumed for transient protection in the main steam line break analysis. The setpoint allowable value does not include errors induced by the harsh environment, because the trip actuates prior to the harsh environment.

6.

Reactor Building High Pressure The Reactor Building High Pressure trip provides an early indication of a high energy line break (HELB) inside the RB. By detecting changes in the RB pressure, the RPS can provide a reactor trip before the other system parameters have varied significantly. Thus, this trip acts to minimize accident consequences. It also provides a backup for RPS trip instruments exposed to an RB HELB environment..

The Allowable Value for RB High Pressure trip is set at the lowest value consistent with avoiding spurious trips during normal operation.

The electronic components of the RB High Pressure trip are located in an area that is not exposed to high temperature steam environments during HELB transients inside containment. The components are exposed to high radiation conditions. Therefore, the determination of the setpoint Allowable Value accounts for errors induced by the high radiation.

OCONEE UNITS 1, 2, & 3 B 3.3.1-1 4 BASES REVISION DATED 10/23/03

RPS Instrumentation B 3.3.1 BASES APPLICABLE

7.

Reactor Coolant Pump to Power SAFETY ANALYSES, LCO, and The Reactor Coolant Pump to Power trip provides protection for APPLICABILITY changes in the reactor coolant flow due to the loss of multiple RCPs.

(continued)

Because the flow reduction lags loss of power indications due to the inertia of the RCPs, the trip initiates protective action earlier than a trip based on a measured flow signal.

The Reactor Coolant Pump to Power trip has been credited in the accident analysis calculations for the loss of more than two RCPs.

The Allowable Value for the Reactor Coolant Pump to Power trip setpoint is selected to prevent normal power operation unless at least three RCPs are operating. RCP status is monitored by power transducers on each pump. These relays indicate a loss of an RCP on underpower. The underpower setpoint is selected to reliably trip on loss of voltage to the RCPs. Neither the reactor power nor the pump power setpoint account for instrumentation errors caused by harsh environments because the trip Function is not required to respond to events that could create harsh environments around the equipment.

8.

Nuclear Overpower Flux/Flow Imbalance The Nuclear Overpower Flux/Flow Imbalance trip provides steady state protection for the power imbalance SLs. A reactor trip is initiated prior to the core power, AXIAL POWER IMBALANCE, and reactor coolant flow conditions exceeding the DNB or fuel centerline temperature limits.

This trip supplements the protection provided by the Reactor Coolant Pump to Power trip, through the power to flow ratio, for loss of reactor coolant flow events. The power to flow ratio provides direct protection for the DNBR SL for the loss of one or more RCPs and for locked RCP rotor accidents.

The power to flow ratio of the Nuclear Overpower Flux/Flow Imbalance trip also provides steady state protection to prevent reactor power from exceeding the allowable power when the primary system flow rate is less than full four pump flow. Thus, the power to flow ratio prevents overpower conditions similar to the Nuclear Overpower trip. This protection ensures that during reduced flow conditions the core power is maintained below that required to begin DNB.

OCONEE UNITS 1, 2, & 3 B 3.3.1-15 BASES REVISION DATED 10/23/03

RPS Instrumentation B 3.3.1 BASES APPLICABLE SAFETY ANALYSES, LCO, and APPLICABILITY

8.

Nuclear Overpower Flux/Flow Imbalance (continued)

The Allowable Value is selected to ensure that a trip occurs when the core power, axial power peaking, and reactor coolant flow conditions indicate an approach to DNB or fuel centerline temperature limits.

By measuring reactor coolant flow and by tripping only when conditions approach an SL, the unit can operate with the loss of one pump from a four pump initial condition at power levels at least as low as approximately 80% RTP. The Allowable Value for the Function is given in the unit COLR because the cycle specific core peaking changes affect the Allowable Value.

9.

Main Turbine Trip (Hydraulic Fluid Pressure)

The Main Turbine Trip Function trips the reactor when the main turbine is lost at high power levels. The Main Turbine Trip Function provides an early reactor trip in anticipation of the loss of heat sink associated with a turbine trip. The Main Turbine Trip Function was added to the B&W designed units in accordance with NUREG-0737 (Ref. 5) following the Three Mile Island Unit 2 accident. The trip lowers the probability of an RCS power operated relief valve (PORV) actuation for turbine trip cases. This trip is activated at higher power levels, thereby limiting the range through which the Integrated Control System must provide an automatic runback on a turbine trip.

Each of the four turbine hydraulic fluid pressure switches feeds one protective channel through buffers that continuously monitor the status of the contacts.

For the Main Turbine Trip (Hydraulic Fluid Pressure) bistable, the Allowable Value of 800 psig is selected to provide a trip whenever main turbine hydraulic fluid pressure drops below the normal operating range. To ensure that the trip is enabled as required by the LCO, the reactor power bypass is set with an Allowable Value of 30% RTP. The turbine trip is not required to protect against events that can create a harsh environment in the turbine building.

Therefore, errors induced by harsh environments are not included in the determination of the setpoint Allowable Value.

OCONEE UNITS 1, 2, & 3 B 3.3.1-16 BASES REVISION DATED 10/23/03

RPS Instrumentation B 3.3.1 BASES APPLICABLE

10.

Loss of Main Feedwater Pumps (Hydraulic Oil Pressure)

SAFETY ANALYSES, LCO, and The Loss of Main Feedwater Pumps (Hydraulic Oil APPLICABILITY Pressure) trip provides a reactor trip at high power (continued) levels when both MFW pumps are lost. The trip provides an early reactor trip in anticipation of the loss of heat sink associated with the LOMF. This trip was added in accordance with NUREG-0737 (Ref.

5) following the Three Mile Island Unit 2 accident. This trip provides a reactor trip at high power levels for a LOMF to minimize challenges to the PORV.

For the feedwater pump hydraulic oil pressure bistables, the Allowable Value of 75 psig is selected to provide a trip whenever feedwater pump hydraulic oil pressure drops below the normal operating range. To ensure that the trip is enabled as required by the LCO, the reactor power bypass is set with an Allowable Value of 2% RTP. The Loss of Main Feedwater Pumps (Hydraulic Oil Pressure) trip-is not required to protect against events that can create a harsh environment in the turbine building. Therefore, errors caused by harsh environments are not included in the determination of the setpoint Allowable Value.

11.

Shutdown Bypass RCS HiQh Pressure The RPS Shutdown Bypass RCS High Pressure is provided to allow for withdrawing the CONTROL RODS prior to reaching the normal RCS Low Pressure trip setpoint. The shutdown bypass provides trip protection during deboration and RCS heatup by allowing the operator to at least partially withdraw the safety groups of CONTROL RODS. This makes their negative reactivity available to terminate inadvertent reactivity excursions. Use of the shutdown bypass trip requires that the neutron power trip setpoint be reduced to 5% of full power or less. The Shutdown Bypass RCS High Pressure trip forces a reactor trip to occur whenever the unit switches from power operation to shutdown bypass or vice versa. This ensures that the CONTROL RODS are all inserted before power operation can begin.

The operator is required to remove the shutdown bypass, reset the Nuclear Overpower - High Power trip setpoint, and again withdraw the safety group rods before proceeding with startup.

Accidents analyzed in the UFSAR, Chapter 15 (Ref. 2), do not describe events that occur during shutdown bypass operation, because the consequences of these events are enveloped by the events presented in the UFSAR.

OCONEE UNITS 1, 2, & 3 B 3.3.1-1 7 BASES REVISION DATED 10/23/03

RPS Instrumentation B 3.3.1 BASES APPLICABLE

11.

Shutdown Bypass RCS High Pressure (continued)

SAFETY ANALYSES, LCO, and During shutdown bypass operation with the Shutdown Bypass RCS APPLICABILITY High Pressure trip active with a setpoint of < 1720 psig and the Nuclear Overpower - Low Setpoint set at or below 5% RTP, the trips listed below can be bypassed. Under these conditions, the Shutdown Bypass RCS High Pressure trip and the Nuclear Overpower - Low Setpoint trip act to prevent unit conditions from reaching a point where actuation of these Functions is necessary.

l.a Nuclear Overpower - High Setpoint;

3.

RCS High Pressure;

4.

RCS Low Pressure;

5.

RCS Variable Low Pressure;

7.

Reactor Coolant Pump to Power; and

8.

Nuclear Overpower Flux/Flow Imbalance.

The Shutdown Bypass RCS High Pressure Function's Allowable Value is selected to ensure a trip occurs before producing THERMAL POWER.

General Discussion The RPS satisfies Criterion 3 of 10 CFR 50.36 (Ref. 8). In MODES 1 and 2, the following trips shall be OPERABLE because the reactor can be critical in these MODES. These trips are designed to take the reactor subcritical to maintain the SLs during anticipated transients and to assist the ESPS in providing acceptable consequences during accidents.

1 a.

Nuclear Overpower - High Setpoint;

2.

RCS High Outlet Temperature;

3.

RCS High Pressure;

4.

RCS Low Pressure; OCONEE UNITS 1, 2, & 3 B 3.3.1-18 BASES REVISION DATED 10/23/03

RPS Instrumentation B 3.3.1 BASES APPLICABLE General Discussion (continued)

SAFETY ANALYSES, LCO, and

5.

RCS Variable Low Pressure; APPLICABILITY

6.

Reactor Building High Pressure;

7.

Reactor Coolant Pump to Power; and

8.

Nuclear Overpower Flux/Flow Imbalance.

Functions 1, 3, 4, 5, 7, and 8 just listed may be bypassed in MODE 2 when RCS pressure is below 1720 psig, provided the Shutdown Bypass RCS High Pressure and the Nuclear Overpower - Low setpoint trip are placed in operation. Under these conditions, the Shutdown Bypass RCS High Pressure trip and the Nuclear Overpower-Low setpoint trip act to prevent unit conditions from reaching a point where actuation of these Functions is necessary.

The Main Turbine Trip (Hydraulic Fluid Pressure) Function is required to be OPERABLE in MODE 1 at 2 30% RTP. The Loss of Main Feedwater Pumps (Hydraulic Oil Pressure) Function is required to be OPERABLE in MODE 1 and in MODE 2 at 2 2% RTP. Analyses presented in BAW-1 893 (Ref. 6) have shown that for operation below these power levels, these trips are not necessary to minimize challenges to the PORVs as required by NUREG-0737 (Ref. 5).

Because the safety function of the RPS is to trip the CONTROL RODS, the RPS is not required to be OPERABLE in MODE 3, 4, or 5 if either the reactor trip breakers are open, or the CRD System is incapable of rod withdrawal. Similarly, the RPS is not required to be OPERABLE in MODE 6 because the CONTROL RODS are normally decoupled from the CRDs.

However, in MODE 2, 3, 4, or 5, the Shutdown Bypass RCS High Pressure and Nuclear Overpower - Low setpoint trips are required to be OPERABLE if the CRD trip breakers are closed and the CRD System is capable of rod withdrawal. Under these conditions, the Shutdown Bypass RCS High Pressure and Nuclear Overpower - Low setpoint trips are sufficient to prevent an approach to conditions that could challenge SLs.

ACTIONS Conditions A and B are applicable to all RPS protective Functions. If a channel's trip setpoint is found nonconservative with respect to the required Allowable Value in Table 3.3.1-1, or the transmitter, instrument loop, signal processing electronics or bistable is found inoperable, the channel must be declared inoperable and Condition A entered immediately.

OCONEE UNITS 1, 2, & 3 B 3.3.1-1 9 BASES REVISION DATED 10/23/03

RPS Instrumentation B 3.3.1 BASES ACTIONS When an RPS channel is manually tripped, the functions that were (continued) inoperable prior to tripping remain inoperable. Other functions in the same channel that were OPERABLE prior to tripping remain OPERABLE.

A.1 For Required Action A.1, if one or more Functions in a required protective channel becomes inoperable, the affected protective channel must be placed in trip. This Required Action places all RPS Functions in a one-out-of-two logic configuration. The non-required" channel is placed in bypass when the required inoperable channel is placed in trip to prevent bypass of a second required channel. In this configuration, the RPS can still perform its safety functions in the presence of a random failure of any single Channel. The 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> Completion Time is sufficient time to perform Required Action A.1.

B.1 Required Action B.1 directs entry into the appropriate Condition referenced in Table 3.3.1-1. The applicable Condition referenced in the table is Function dependent. If the Required Action and the associated Completion Time of Condition A are not met or if more than two channels are inoperable, Condition B is entered to provide for transfer to the appropriate subsequent Condition.

C.1 and C.2 If the Required Action and associated Completion Time of Condition A are not met and Table 3.3.1-1 directs entry into Condition C, the unit must be brought to a MODE in which the specified RPS trip Functions are not required to be OPERABLE. The allowed Completion Time of 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> is reasonable, based on operating experience, to reach MODE 3 from full power conditions in an orderly manner and to open all CRD trip breakers without challenging unit systems.

D.1 If the Required Action and associated Completion Time of Condition A are not met and Table 3.3.1-1 directs entry into Condition D, the unit must be brought to a MODE in which the specified RPS trip Functions are not OCONEE UNITS 1, 2, & 3 B 3.3.1-20 BASES REVISION DATED 10/23/03

RPS Instrumentation B 3.3.1 BASES ACTIONS D.1 (continued) required to be OPERABLE. To achieve this status, all CRD trip breakers must be opened. The allowed Completion Time of 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> is reasonable, based on operating experience, to open CRD trip breakers without challenging unit systems.

E.1 If the Required Action and associated Completion Time of Condition A are not met and Table 3.3.1-1 directs entry into Condition E, the unit must be brought to a MODE in which the specified RPS trip Function is not required to be OPERABLE. To achieve this status, THERMAL POWER must be reduced < 30% RTP. The allowed Completion Time of 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> is reasonable, based on operating experience, to reach 30% RTP from full power conditions in an orderly manner without challenging unit systems.

F.1 If the Required Action and associated Completion Time of Condition A are not met and Table 3.3.1-1 directs entry into Condition F, the unit must be brought to a MODE in which the specified RPS trip Function is not required to be OPERABLE. To achieve this status, THERMAL POWER must be reduced < 2% RTP. The allowed Completion Time of 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> is reasonable, based on operating experience, to reach 2% RTP from full power conditions in an orderly manner without challenging unit systems.

SURVEILLANCE The SRs for each RPS Function are identified by the SRs REQUIREMENTS column of Table 3.3.1-1 for that Function. Most Functions are subject to CHANNEL CHECK, CHANNEL FUNCTIONAL TEST, and CHANNEL CALIBRATION testing.

The SRs are modified by a Note. The Note directs the reader to Table 3.3.1-1 to determine the correct SRs to perform for each RPS Function.

SR 3.3.1.1 Performance of the CHANNEL CHECK once every 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> ensures that a gross failure of instrumentation has not occurred. A CHANNEL CHECK is normally a comparison of the parameter indicated on one channel to a OCONEE UNITS 1, 2, & 3 B 3.3.1-21 BASES REVISION DATED 10/23/03

RPS Instrumentation B 3.3.1 BASES SURVEILLANCE SR 3.3.1.1 (continued)

REQUIREMENTS similar parameter on other channels. It is based on the assumption that instrument channels monitoring the same parameter should read approximately the same value. Significant deviations between two instrument channels could be an indication of excessive instrument drift in one of the channels or of something even more serious. CHANNEL CHECK will detect gross channel failure; therefore, it is key in verifying that the instrumentation continues to operate properly between each CHANNEL CALIBRATION.

Agreement criteria are determined based on a combination of the channel instrument uncertainties, including isolation, indication, and readability. If a channel is outside the criteria, it may be an indication that the transmitter or the signal processing equipment has drifted outside its limit. If the channels are within the criteria, it is an indication that the channels are OPERABLE. If the channels are normally off scale during times when surveillance is required, the CHANNEL CHECK will only verify that they are off scale in the same direction. Off scale low current loop channels are verified to be reading at the bottom of the range and not failed downscale.

The Frequency, equivalent to once every shift, is based on operating experience that demonstrates channel failure is rare. Since the probability of two random.failures in redundant channels in any 12 hour1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> period is extremely low, the CHANNEL CHECK minimizes the chance of loss of protective function due to failure of redundant channels. The CHANNEL CHECK supplements less formal but more frequent checks of channel OPERABILITY during normal operational use of the displays associated with the LCO's required channels.

For Functions that trip on a combination of several measurements, such as the Nuclear Overpower Flux/Flow Imbalance Function, the CHANNEL CHECK must be performed on each input.

SR 3.3.1.2 This SR is the performance of a heat balance calibration for the power range channels every 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> when reactor power is > 15% RTP. The heat balance calibration consists of a comparison of the results of the calorimetric with the power range channel output. The outputs of the power range channels are normalized to the calorimetric. If the calorimetric exceeds the Nuclear Instrumentation System (NIS) channel output by 2%

RTP, the NIS is not declared inoperable but must be adjusted. If the NIS OCONEE UNITS 1, 2, & 3 B 3.3.1-22 BASES REVISION DATED 10/23/03

RPS Instrumentation B 3.3.1 BASES SURVEILLANCE SR 3.3.1.2 (continued)

REQUIREMENTS channel cannot be properly adjusted, the channel is declared inoperable. A Note clarifies that this Surveillance is required to be performed only if reactor power is > 15% RTP and that 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> is allowed for performing the first Surveillance after reaching 15% RTP. At lower power levels, calorimetric data are less accurate.

The power range channel's output shall be adjusted consistent with the calorimetric results if the calorimetric exceeds the power range channel's output by 2 2% RTP. The value of 2% is adequate because this value is assumed in the safety analyses of UFSAR, Chapter 15 (Ref. 2). These checks and, if necessary, the adjustment of the power range channels ensure that channel accuracy is maintained within the analyzed error margins. The 24 hour2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> Frequency'is adequate, based on unit operating experience, which demonstrates the change in the difference between the power range indication and the calorimetric results rarely exceeds a small fraction of 2% in any 24 hour2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> period. Furthermore, the control room operators monitor redundant indications and alarms to detect deviations in channel outputs.

SR 3.3.1.3 A comparison of power range nuclear instrumentation channels against incore detectors shall be performed at a 31 day Frequency when reactor power is 2 15% RTP. A Note clarifies that 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> is allowed for performing the first Surveillance after reaching 15% RTP. If the absolute difference between the power range and incore measurements is 2%

RTP, the power range channel is not inoperable, but an adjustment of the measured imbalance to agree with the incore measurements is necessary.

If the power range channel cannot be properly recalibrated, the channel is declared inoperable. The calculation of the Allowable Value envelope assumes a difference in out of core to incore measurements of 2.5%.

Additional inaccuracies beyond those that are measured are also included in the setpoint envelope calculation. The 31 day Frequency is adequate, considering that long term drift of the excore linear amplifiers is small and burnup of the detectors is slow. Also, the excore readings are a strong function of the power produced in the peripheral fuel bundles, and do not represent an integrated reading across the core. The slow changes in neutron flux during the fuel cycle can also be detected at this interval.

OCONEE UNITS 1, 2, & 3 B 3.3.1-23 BASES REVISION DATED 10/23/03

RPS Instrumentation B 3.3.1 BASES SURVEILLANCE SR 3.3.1.4 REQUIREMENTS (continued)

A CHANNEL FUNCTIONAL TEST is performed on each required RPS channel to ensure that the entire channel will perform the intended function.

Setpoints must be found within the Allowable Values specified in Table 3.3.1-1. Any setpoint adjustment shall be consistent with the assumptions of the current setpoint analysis.

The as found and as left values must also be recorded and reviewed for consistency with the assumptions of the surveillance interval extension analysis. The requirements for this review are outlined in BAW-1 01 67 (Ref. 7).

The Frequency of 45 days on a STAGGERED TEST BASIS is consistent with the calculations of Reference 7 that indicate the RPS retains a high level of reliability for this test interval.

SR 3.3.1.5 A Note to the Surveillance indicates that neutron detectors are excluded from CHANNEL CALIBRATION. This Note is necessary because of the difficulty in generating an appropriate detector input signal. Excluding the detectors is acceptable because the principles of detector operation ensure virtually instantaneous response.

A CHANNEL CALIBRATION is a complete check of the instrument channel, including the sensor. The test verifies that the channel responds to the measured parameter within the necessary range and accuracy.

CHANNEL CALIBRATION leaves the channel adjusted to account for instrument drift to ensure that the instrument channel remains operational between successive tests. CHANNEL CALIBRATION shall find that measurement errors and bistable setpoint errors are within the assumptions of the setpoint analysis. CHANNEL CALIBRATIONS must be performed consistent with the assumptions of the setpoint analysis.

Whenever a sensing element is replaced, the next required CHANNEL CALIBRATION of the resistance temperature detectors (RTD)sensors is accomplished by an inplace cross calibration that compares the other sensing elements with the recently installed sensing element.

The Frequency is justified by the assumption of an 18 month calibration interval in the determination of the magnitude of equipment drift in the setpoint analysis.

OCONEE UNITS 1, 2, & 3 B 3.3.1-24 BASES REVISION DATED 10/23/03

RPS Instrumentation B 3.3.1 BASES (continued)

REFERENCES I

1.

UFSAR, Chapter 7.

2.

UFSAR, Chapter 15.

3.

10 CFR 50.49.

4.

EDM-1 02, Instrument Setpoint/Uncertainty Calculations."

5.

NUREG-0737, "Clarification of TMI Action Plan Requirements,"

November 1979.

6.

BAW-1 893, 'Basis for Raising Arming Threshold for Anticipating Reactor Trip on Turbine Trip,' October 1985.

7.

BAW-1 0167, May 1986.

8.

10 CFR 50.36.

OCONEE UNITS 1, 2, & 3 B 3.3.1-25 BASES REVISION DATED 10/23/03

RPS Instrumentation B 3.3.1 BASES APPLICABLE General Discussion (continued)

SAFETY ANALYSES, LCO, and

5.

RCS Variable Low Pressure; APPLICABILITY

6.

Reactor Building High Pressure;

7.

Reactor Coolant Pump to Power; and

8.

Nuclear Overpower Flux/Flow Imbalance.

Functions 1, 3, 4, 5, 7, and 8 just listed may be bypassed in MODE 2 when RCS pressure is below 1720 psig, provided the Shutdown Bypass RCS High Pressure and the Nuclear Overpower - Low setpoint trip are placed in operation. Under these conditions, the Shutdown Bypass RCS High Pressure trip and the Nuclear Overpower - Low setpoint trip act to prevent unit conditions from reaching a point where actuation of these Functions is necessary.

The Main Turbine Trip (Hydraulic Fluid Pressure) Function is required to be OPERABLE in MODE 1 at Ž 30% RTP. The Loss of Main Feedwater Pumps (Hydraulic Oil Pressure) Function is required to be OPERABLE in MODE 1 and in MODE 2 at 2 2% RTP. Analyses presented in BAW-1 893 (Ref. 6) have shown that for operation below these power levels, these trips are not necessary to minimize challenges to the PORVs as required by NUREG-0737 (Ref. 5).

Because the safety function of the RPS is to trip the CONTROL RODS, the RPS is not required to be OPERABLE in MODE 3, 4, or 5 if either the reactor trip breakers are open, or the CRD System is incapable of rod withdrawal. Similarly, the RPS is not required to be OPERABLE in MODE 6 because the CONTROL RODS are normally decoupled from the CRDs.

However, in MODE 2, 3, 4, or 5, the Shutdown Bypass RCS High Pressure and Nuclear Overpower - Low setpoint trips are required to be OPERABLE if the CRD trip breakers are closed and the CRD System is capable of rod withdrawal. Under these conditions, the Shutdown Bypass RCS High Pressure and Nuclear Overpower - Low setpoint trips are sufficient to prevent an approach to conditions that could challenge SLs.

ACTIONS Conditions A and B are applicable to all RPS protective Functions. If a channel's trip setpoint is found nonconservative with respect to the required Allowable Value in Table 3.3.1-1, or the transmitter, instrument loop, signal procesming elonic or bistable is found inoperablA the channe mlust be 1~pP declared inoperable and Condition A entered immediately.

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