RA-18-0281, Technical Specification Bases Changes

Technical Specification Bases Changes

ML19184A605
Person / Time
Site:	Oconee
Issue date:	06/25/2019
From:	Dalton S Duke Energy Carolinas
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
RA-18-0281
Download: ML19184A605 (41)

Text

OCONEE UNITS 1, 2, & 3 B 3.7.9-1 Rev. 001 CRVS Booster Fans B 3.7.9 B 3.7 PLANT SYSTEMS

B 3.7.9 Control Room Ventilation System (CRVS) Booster Fans

BASES BACKGROUND The CRVS Booster Fan trains provide a protected environment from which occupants can control the unit following an uncontrolled release of radioactivity, hazardous chemicals, or smoke.

The CRVS consists of two Booster Fan trains that draw outside air and filter the air in the control room envelope (CRE) and a CRE boundary that limits the inleakage of unfiltered air (Ref. 1). Each CRVS Booster F an train consists of a pre

-filter, a high efficiency particulate air (HEPA) filter, and a charcoal filter for removal of gaseous activity (principally iodines), and a 100% capacity fan. Ductwork, valves or dampers, doors, barriers, and instrumentation also form part of the system.

The CRE is the area within the confines of the CRE boundary that contains the spaces that control room occupants inhabit to control the unit during normal and accident conditions. This area encompasses the control room, and may encompass other non

-critical areas to which frequent personnel access or continuous occupancy is not necessary in the event of an accident. The CRE is protected during normal operation, natural events, and accident conditions. The CRE boundary is the combination of walls, floor, roof, ducting, doors, penetrations and equipment that physically form the CRE. The OPERABILITY of the CRE boundary must be maintained to ensure that the inleakage of unfiltered air into the CRE will not exceed the inleakage assumed in the licensing basis analysis of the design basis accident (DBA) consequences to CRE occupants. The CRE and its boundary are defined in the Control Room Envelope Habitability Program.

The CRVS is an emergency system. Upon receipt of a radiation alarm from the Control Room air radiation monitor, the CRVS Booster Fan trains are started manually to minimize unfiltered air from entering the control room. Upon starting the fans, dampers are automatically positioned to isolate the control room. The pre

-filters remove any large particles in the air, and any entrained water droplets present, to prevent excessive loading of the HEPA and carbon filters.

Each CRVS Booster Fan train , is capable of CRE unfiltered air infiltration below analyzed limits. Both CRVS Booster Fan trains operating simultaneously are capable of positively pressurizing the associated

CRE. The CRVS operation is discussed in the UFSAR, Section 9.4 (Ref. 1). The CRVS is designed to maintain a habitable environment in the CRE for 30

-days of continuous occupancy after a Design Basis Accident (DBA), without exceeding a 5 rem total effective dose equivalent (TEDE).

CRVS Booster Fans B 3.7.9 BASES (continued)

OCONEE UNITS 1, 2, & 3 B 3.7.9-2 Rev. 001 APPLICABLE The CRVS components are arranged in two ventilation trains. The SAFETY ANALYSIS location of components and ducting within the CRE ensures an adequate supply of filtered air to all areas requiring access. The CRVS provides airborne radiological protection for the CRE occupants as demonstrated by the CRE occupant dose analyses for the most limiting design basis accident fission product release presented in the UFSAR, Chapter 15 (Ref. 2). The CRVS Booster Fan trains provide protection from smoke and hazardous chemical s to the CRE occupants. The analysis of hazardous chemical releases demonstrates that the toxicity limits are not exceeded in the CRE following a hazardous chemical release (Ref. 3). The evaluation of a smoke challenge demonstrates that it will not result in the inability of the CRE occupants to control the reactor either from the control room or from the Standby Shutdown Facility (Ref.

6). The CRVS Booster Fan trains satisfy Criterion 3 of 10 CFR 50.36(c)(2)(ii)

(Ref. 4). LCO Two CRVS train s are required to be OPERABLE to ensure that at least one is available if a single active failure disables the other train.

Total system failure, such as from a loss of both ventilation trains or from an

inoperable CRE boundary, could result in exceeding a dose of 5 rem TEDE to the CRE occupants in the event of a large radioactive release.

Each CRVS Booster Fan train is considered OPERABLE when the individual components necessary to limit CRE occupant exposure are OPERABLE. A CRVS Booster Fan train is considered OPERABLE when the associated:

a. Booster Fan is OPERABLE;

b. HEPA filter and carbon absorber are not excessively restricting flow, and are capable of performing their filtration functions; and

c. Ductwork, valves, and flowpath dampers are OPERABLE, and control room unfiltered inleakage can be maintained within limits.

CRVS Booster Fans B 3.7.9 BASES OCONEE UNITS 1, 2, & 3 B 3.7.9-3 Rev. 001 LCO In order for the CRVS Booster Fan trains to be considered OPERABLE, (continued) the CRE boundary must be maintained such that the CRE occupant dose from a large radioactive release does not exceed the calculated dose in the licensing basis consequences analyses for DBAs and that CRE occupants are protected from hazardous chemicals and smoke.

The LCO is modified by a Note allowing the CRE boundary to be opened intermittently under administrative controls. This Note only applies to openings in the CRE boundary that can be rapidly restored to the design condition, such as doors, hatches, floor plugs, and access panels , so that the CRE boundary can be restored and the CRE pressurized within 30 minutes to minimize inleakage as assumed in the station's Alternate Source Term (AST) accident analysis

. For entry and exit through doors, the administrative control of the opening is performed by the person(s) entering or exiting the area. For other openings, these controls should be proceduralized and consist of stationing a dedicated individual at the opening who is in continuous communication with the operators in the CRE. This individual will have a method to rapidly close the opening and to restore the CRE boundary to a condition equivalent to the design condition when a need for CRE isolation is indicated. APPLICABILITY In MODES 1, 2, 3, 4, 5, and 6, and during movement of recently irradiated fuel assembles for any unit, the CRVS must be OPERABLE to ensure that the CRE will remain habitable during and following a DBA. During movement of recently irradiated fuel assemblies by any unit, the CRVS Booster Fan trains must be OPERABLE to cope with a release due to a fuel handling accident involving handling recently irradiated fuel. Due to radioactive decay, the CRVS is only required to mitigate fuel handling accidents involving handling recently irradiated fuel (i.e., fuel that has occupied part of a critical reactor core within the previous 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />).

ACTIONS A.1 With one CRVS Booster Fan train inoperable for reasons other than an inoperable CRE boundary, action must be taken to restore OPERABLE status within 7 day s. In this Condition, the remaining OPERABLE CRVS Booster Fan train is adequate to perform the CRE occupant protection function. However, the overall reliability is reduced because a failure in the OPERABLE CRVS Booster Fan train could result in loss of CRVS function. The 7 day Completion Time is based on the low probability of a DBA occurring during this time period and ability of the remaining booster fan train to provide the required capability

.

CRVS Booster Fans B 3.7.9 BASES OCONEE UNITS 1, 2, & 3 B 3.7.9-4 Rev. 001 ACTIONS B.1, B.2, and B.3 (continued)

If the unfiltered inleakage of potentially contaminated air past the CRE boundary and into the CRE can result in CRE occupant radiological dose greater than the calculated dose of the licensing basis analyses of consequences (allowed to be up to 5 rem TEDE), or inadequate protection of CRE occupants from hazardous chemicals or smoke, the CRE boundary is inoperable. Actions must be taken to restore an OPERABLE CRE boundary within 90 days.

During the period that the CRE boundary is considered inoperable, action must be initiated to implement mitigating actions to lessen the effect on CRE occupants from the potential hazards of a radiological or chemical event or a challenge from smoke. Actions must be taken with 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> to verify that in the event of a DBA, the mitigating actions will ensure that CRE occupant radiological exposures will not exceed limits and that CRE occupants are protected from hazardous chemicals and smoke.

These mitigating actions (i.e., actions that are taken to offset the consequences of the inoperable CRE boundary) should be preplanned for implementation upon entry into the condition, regardless of whether entry is intentional or unintentional. The 24 hour2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> Completion Time is reasonable based on the low probability of a DBA occurring during this time period, and the use of mitigating actions. The 90 day Completion Time is reasonable based on the determination that the mitigating actions will ensure protection of CRE occupants within analyzed limits while limiting the probability that CRE occupants will have to implement protective measures that may adversely affect their ability to control the reactor and maintain it in a safe shutdown condition in the event of a DBA. In addition, the 90 day Completion Time is a reasonable time to diagnose, plan and possibly repair, and test most problems with the CRE boundary. C.1 and C.2 In MODE 1, 2, 3, or 4, if the inoperable CRVS Booster Fan train or the CRE boundary cannot be restored to OPERABLE status within the required Completion Time, the unit must be placed in a MODE that minimizes accident risk. To achieve this status, the unit must be placed in at least MODE 3 within 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br />, and in MODE 5 within 36 hours4.166667e-4 days <br />0.01 hours <br />5.952381e-5 weeks <br />1.3698e-5 months <br />. The allowed Completion Times are reasonable, based on operating experience, to reach the required unit conditions from full power conditions in an orderly manner and without challenging the systems.

CRVS Booster Fans B 3.7.9 BASES OCONEE UNITS 1, 2, & 3 B 3.7.9-5 Rev. 001 ACTIONS D.1 and D.2 (continued)

In MODE 5 or 6, or during movement of recently irradiated fuel assemblies, if the inoperable CRVS Booster Fan train cannot be restor ed to OPERABLE status within the required Completion Time, the OPERABLE CRVS Booster Fan train must be started. This action ensures that the remaining train is OPERABLE, and that any active failure will be readily detected. An alternative to Required Action D.1 is to immediately suspend activities that could release radioactivity that might require isolation of the CRE. This places the unit in a condition that minimizes the accident risk. This does not preclude the movement of fuel to a safe position.

E.1 In MODE 5 or 6, or during movement of recently irradiated fuel assembles, when two CRVS Booster Fan trains are inoperable, or with one or more CRVS Booster Fan trains inoperable due to an inoperable CRE boundary, action must be taken immediately to suspend activities that could result in a release of radioactivity that might require isolation of the CRE. This places the unit in a condition that minimized the accident risk. This does not preclude the movement of fuel to a safe position.

F.1 If both CRVS trains are inoperable in MODE 1, 2, 3, or 4 for reasons other than an inoperable CRE boundary (i.e., Condition B), one train must be restored to OPERABLE status within 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />. In this Condition, the capability to minimize the radiation dose personnel located in the Control Room during and after an accident is unavailable. The 24 hour2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> Completion Time is based on the low probability of an accident occurring during this time period.

G.1 If the Required Action and associated Completion Time of Condition F is not met, LCO 3.0.3 must be entered immediately.

SURVEILLANCE SR 3.7.9.1 REQUIREMENTS Standby systems should be checked periodically to ensure that they function properly. As the environment and normal operating conditions on this system are not severe, testing each train adequately checks this system. The trains need only be operated for one hour and all dampers verified to be OPERABLE to demonstrate

CRVS Booster Fans B 3.7.9 BASES OCONEE UNITS 1, 2, & 3 B 3.7.9-6 Rev. 001 SURVEILLANCE SR 3.7.9.1 (continued)

REQUIREMENTS the function of the system. This test includes an external visual inspection of the CRVS Booster Fan trains. The Surveillance Frequency is based on operating experience, equipment reliability, and plant risk and is controlled under the Surveillance Frequency Control Program.

SR 3.7.9.2

This SR verifies that the required CRVS Booster Fan train testing is performed in accordance with the Ventilation Filter Testing Program (VFTP). The VFTP includes testing H E PA filter performance , carbon absorber efficiency, minimum system flow rate, and the physical properties of the activated carbon. Specific test frequencies and additional information are discussed in detail in the VFTP.

SR 3.7.9.3 This SR verifies that the CRE isolates and operates on a manual actuation signal. The Frequency is based on industry operating experience and is consistent with the typical refueling cycle and will be managed in accordance with the Surveillance Frequency Control Program. SR 3.7.9.4 The Surveillance Frequency verifies the OPERABILITY of the CRE boundary by testing for unfiltered air inleakage past the CRE boundary and into the CRE. The details of the testing are specified in the Control Room Envelope Habitability Program. The CRE is considered habitable when the radiological dose to CRE occupants calculated in the licensing basis analyses of DBA consequences is no more than 5 rem TEDE and the CRE occupants are protected from hazardous chemicals and smoke. This SR verifies that the unfiltered air inleakage into the CRE is no greater than the flow rate assumed in the licensing basis analyses of DBA consequences. When unfiltered air inleakage is greater than the assumed flow rate, Condition B must be entered. Required Action B.3 allows time to restore the CRE boundary to OPERABLE status provided mitigating actions can ensure that the CRE remains within the licensing basis habitability limits for the occupants following an accident. Compensatory measures are discussed in Regulatory Guide 1.196, Section C.2.7.3, (Ref. 6) which endorses, with exceptions, NEI 99

-03, Section 8.4 and Appendix F (Ref. 7). These compensatory measures may also be used as mitigating actions as CRVS Booster Fans B 3.7.9 BASES OCONEE UNITS 1, 2, & 3 B 3.7.9-7 Rev. 001 SURVEILLANCE SR 3.7.9.4 (continued)

REQUIREMENTS required by Required Action B.2. Temporary analytical methods may also be used as compensatory measures to restore OPERABILITY (Ref. 8).

Options for restoring the CRE boundary to OPERABLE status include changing the licensing basis DBA consequence analysis, repairing the CRE boundary, or a combination of these actions. Depending upon the nature of the problem and the corrective action, a full scope inleakage test may not be necessary to establish that the CRE boundary has been restored to OPERABLE status.

SR 3.7.9.5 This SR verifies the CRVS can supply the CRE with outside air to meet the design requirement. The design flowrate of each booster fan is 1350 cfm +/-10% (i.e., 1215 cfm to 1485 cfm). This lower limit ensures each train is capable of supplying enough air to meet the minimum total system flowrate requirement of 1215 cfm. The 1485 cfm upper limit is required to meet the carbon filter residence time limit of each individual booster fan train (Ref. 5). The frequency is consistent with industry practice and other filtration SRs, and will be managed in accordance with the Surveillance Frequency Control Program.

REFERENCES

1. UFSAR, Section 9.4.

2. UFSAR, Chapter 15.

3. UFSAR, Section 6.4.2.5 4. 10 CFR 50.36.

5. Regulatory Guide 1.52, Rev. 4.

6. Regulatory Guide 1.196, Rev. 1.

7. NEI 99-03, "Control Room Habitability Assessment," June 2001.

8. Letter from Eric J. Leeds (NRC) to James W. Davis (NEI) dated January 30, 2004, "NEI Draft White Paper, Use of Generic Letter 91-18 Process and Alternative Source Terms in the Context of Control Room Habitability."

OCONEE UNITS 1, 2, & 3 B 3.2.3-1 Rev. 001 QPT B 3.2.3 B 3.2 POWER DISTRIBUTION LIMITS B 3.2.3 QUADRANT POWER TILT (QPT)

BASES BACKGROUND This LCO is required to limit the core power distribution based on accident initial condition criteria.

The power density at any point in the core must be limited to maintain specified acceptable fuel design limits, including limits that preserve the criteria specified in 10 CFR 50.46 (Ref. 1). Together, LCO 3.2.1, "Regulating Rod Position Limits," LCO 3.2.2, "AXIAL POWER IMBALANCE Operating Limits," and LCO 3.2.3, "QUADRANT POWER TILT (QPT)," provide limits on control component operation and on monitored process variables to ensure that the core operates within the F Q(Z) and F NH limits. F Q(Z) is the maximum local linear power density in the core divided by the core average fuel rod linear power density, assuming nominal fuel pellet and fuel rod dimensions. Operation within the F Q(Z) limits prevents power peaks that exceed the loss of coolant accident (LOCA) limits. F NH is the ratio of the integral of linear power along the fuel rod on which minimum departure from nucleate boiling ratio occurs, to the average fuel rod power. Operation within the F NH limits prevents departure from nucleate boiling (DNB) during an anticipated transient.

This LCO is required to limit fuel cladding failures that breach the primary fission product barrier and release fission products to the reactor coolant in the event of a LOCA, loss of forced reactor coolant flow, or other accident requiring termination by a Reactor Protection System trip function. This LCO limits the amount of damage to the fuel cladding during an accident by maintaining the validity of the assumptions used in the safety analysis related to the initial power distribution and reactivity.

Fuel cladding failure during a postulated LOCA is limited by restricting the maximum linear heat rate (LHR) so that the peak cladding temperature does not exceed 2200F (Ref. 1). Peak cladding temperatures > 2200 F cause severe cladding failure by oxidation due to a Zircaloy water reaction. Other criteria must also be met (e.g., maximum cladding oxidation, maximum hydrogen generation, coolable geometry, and long term cooling). However, peak cladding temperature is usually most limiting.

QPT B 3.2.3 BASES OCONEE UNITS 1, 2, & 3 B 3.2.3-2 Rev. 001 BACKGROUND Proximity to the DNB condition is expressed by the departure from (continued) nucleate boiling ratio (DNBR), defined as the ratio of the cladding surface heat flux required to cause DNB to the actual cladding surface heat flux. The minimum DNBR value during both normal operation and anticipated transients is limited to the DNBR correlation limit for the particular fuel design in use, and is accepted as an appropriate margin to DNB. The DNBR correlation limit ensures that there is at least 95% probability at the 95% confidence level (the 95/95 DNB criterion) that the hot fuel rod in the core does not experience DNB.

The measurement system independent limits on QPT are determined analytically by the reload safety evaluation analysis without adjustment for measurement system error and uncertainty. Operation beyond these limits could invalidate core power distribution assumptions used in the accident analysis. The error adjusted maximum allowable limits (measurement system dependent limits) for QPT are specified in the COLR.

APPLICABLE The fuel cladding must not sustain damage as a result of normal operation SAFETY ANALYSES and anticipated transients. The LCOs based on power distribution (LCO 3.2.1, LCO 3.2.2, and LCO 3.2.3) preclude core power distributions that violate the following fuel design criteria:

a. During a large break LOCA, the peak cladding temperature must not exceed 2200F (Ref. 1).

b. During anticipated transients, there must be at least 95% probability at the 95% confidence level (the 95/95 DNB criterion) that the hot fuel rod in the core does not experience a DNB condition.

QPT is one of the process variables that characterize and control the three dimensional power distribution of the reactor core.

Fuel cladding damage could result if an anticipated transient occurs with simultaneous violation of one or more of the LCOs governing the core power distribution. Changes in the power distribution can cause increased power peaking and correspondingly increased local LHRs.

The dependence of the core power distribution on burnup, regulating rod insertion, and spatial xenon distribution is taken into account during the reload safety evaluation analysis. An allowance for QPT is accommodated in the analysis and resultant LCO limits.

The QPT power peaking factors (percent increase in power peak per percent increase in QPT) are usually determined for each symmetric fuel assembly on a fuel cycle

-specific basis (Ref. 5) and used to set the QPT setpoints in the COLR.

Reference 5 also allows a conservative increase of 1.5 % peak power per 1% QPT to be used in lieu of the cycle

-specific factors.

QPT B 3.2.3 BASES OCONEE UNITS 1, 2, & 3 B 3.2.3-3 Rev. 001 APPLICABLE The bounding increase in peaking taken for QPT was developed from a SAFETY ANALYSES database of full core power distribution calculations (Ref. 2).

These (continued) calculations consisted of simulations of many power distributions with til t causing mechanisms (e.g., dropped or misaligned CONTROL RODS, misloaded assemblies, and burnup gradients).

An increase of < 2% peak power per 1% QPT was supported by this analysis; therefore, a value of 2% peak power increase per 1% QPT is used to bound peak power increases due to QPT.

Operation at the AXIAL POWER IMBALANCE or rod position limits must be interpreted as operating the core at the maximum allowable F Q(Z) or F NH peaking factors for accident initial conditions with the allowed QPT present.

QPT satisfies Criterion 2 of 10 CFR 50.36 (Ref. 3).

LCO The power distribution LCO limits have been established based on correlations between power peaking and easily measured process variables: regulating rod position, AXIAL POWER IMBALANCE, and QPT. The regulating rod position limits and the AXIAL POWER IMBALANCE boundaries contained in the COLR represent the measurement system independent limits. These are the limits at which the core power distribution either exceeds the LOCA LHR limits or causes a reduction in DNBR below the safety limit during anticipated transients with the allowable QPT present and with regulating rod position consistent with the limitations on regulating rod positions determined by the fuel cycle design an d specified by LCO 3.2.1.

The allowable limits and maximum limits for QPT applicable for the full symmetrical Incore Detector System, Backup Incore Detector System, and Excore Detector System are provided; the limits are given in the COLR. The limits for the three systems are derived by adjustment of the measurement system independent QPT limits to allow for system observability and instrumentation errors.

APPLICABILITY In MODE 1, the limits on QPT must be maintained when THERMAL POWER is > 20% RTP to prevent the core power distribution from exceeding the design limits. The minimum power level of 20% RTP is large enough to obtain meaningful QPT indications without compromising safety. Operation at or below 20% RTP with QPT up to the maximum limit specified in the COLR is acceptable because the resulting maximum LHR is not high enough to cause violation of the LOCA LHR limit (F Q(Z) limit) or the initial condition DNB allowable peaking limit (F NH limit) during accidents initiated from this power level.

QPT B 3.2.3 BASES OCONEE UNITS 1, 2, & 3 B 3.2.3-4 Rev. 001 APPLICABILITY In MODE 2, the combination of QPT with maximum ALLOWABLE (continued)

THERMAL POWER level does not result in LHRs sufficiently large to violate the fuel design limits, and therefore, applicability in this MODE is not required. Although not specifically addressed in the LCO, QPTs greater than the maximum limit specified in the COLR in MODE 1 with THERMAL POWER < 20% RTP are allowed for the same reason.

In MODES 3, 4, 5, and 6, this LCO is not applicable, because the reactor is not generating significant THERMAL POWER and QPT is indeterminate.

ACTIONS A.1 The steady state limit specified in the COLR provides an allowance for QPT that may occur during normal operation. A peaking increase to accommodate QPTs up to the steady state limit is allowed by the regulating rod position limits of LCO 3.2.1 and the AXIAL POWER IMBALANCE limits of LCO 3.2.2.

The safety analysis has shown that a conservative corrective action is to reduce THERMAL POWER by 2% RTP or more from the ALLOWABLE THERMAL POWER for each 1% of QPT in excess of the steady state limit. This action limits the local LHR to a value corresponding to steady state operation, thereby reducing it to a value within the assumed accident initial condition limits. The required Completion Time of 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br /> is reasonable, based on limiting the potential for xenon redistribution, the low probability of an accident occurring, and the steps required to complete the Required Action.

If QPT can be reduced to less than or equal to the steady state limit in < 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br />, the reactor may return to normal operation without undergoing a power reduction. Significant radial xenon redistribution does not occur within this amount of time.

A.2 Power operation is allowed to continue if THERMAL POWER is reduced in accordance with Required Action A.1. The same reduction (i.e., 2% RTP or more) is also applicable to the nuclear overpower trip setpoints (flux and flux/flow imbalance), for each 1% of QPT in excess of the steady state limit. This reduction maintains both core protection and thermal margins at the

QPT B 3.2.3 BASES OCONEE UNITS 1, 2, & 3 B 3.2.3-5 Rev. 001 ACTIONS A.2 (continued) reduced THERMAL POWER level similar to that at RTP. The required Completion Time of 10 hours1.157407e-4 days <br />0.00278 hours <br />1.653439e-5 weeks <br />3.805e-6 months <br /> is reasonable based on the need to limit the potentially adverse xenon redistribution, the low probability of an accident occurring while operating out of specification, and the number of steps required to complete the Required Action.

A.3 Although the actions directed by Required Action A.1 restore margins, if the source of the QPT is not determined and corrected, it is prudent to establish increased margins. A required Completion Time of 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> to reduce QPT to less than the steady state limit is a reasonable time for investigation and corrective measures.

B.1 If QPT exceeds the transient limit but is equal to or less than the maximum limit due to a misaligned CONTROL ROD or APSR, then power operation is allowed to continue if the THERMAL POWER is reduced 2% RTP or more from the ALLOWABLE THERMAL POWER for each 1% of QPT in excess of the steady state limit. Thus, the transient limit is the upper bound within which the 2% for 1% power reduction rule may be applied, but only for QPTs caused by CONTROL ROD or APSR misalignment. The required Completion Time of 30 minutes ensures that the operator completes the THERMAL POWER reduction before significant xenon redistribution occurs.

B.2 When a misaligned CONTROL ROD or APSR occurs, a local xenon redistribution may occur. The required Completion Time of 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br /> allows the operator sufficient time to relatch or realign a CONTROL ROD or APSR, but is short enough to limit xenon redistribution so that large increases in the local LHR do not occur due to xenon redistribution resulting from the QPT.

QPT B 3.2.3 BASES OCONEE UNITS 1, 2, & 3 B 3.2.3-6 Rev. 001 ACTIONS C.1 (continued)

If the Required Action and associated Completion Time of Condition A or B are not met, a further power reduction is required. Power reduction to < 60% RTP provides conservative protection from increased peaking due to xenon redistribution. The required Completion Time of 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br /> is reasonable to allow the operator to reduce THERMAL POWER to < 60% of ALLOWABLE THERMAL POWER without challenging unit systems.

C.2 Reduction of the nuclear overpower trip setpoints, based on flux and flux/flow imbalance, to 65.5% of ALLOWABLE THERMAL POWER after THERMAL POWER has been reduced to < 60% of ALLOWABLE THERMAL POWER maintains both core protection and thermal margin at reduced power similar to that at full power. The required Completion Time of 10 hours1.157407e-4 days <br />0.00278 hours <br />1.653439e-5 weeks <br />3.805e-6 months <br /> allows the operator sufficient time to reset the trip setpoint and is reasonable based on operating experience.

D.1 Power reduction to 60% of the ALLOWABLE THERMAL POWER is a conservative method of limiting the maximum core LHR for QPTs up to the maximum limit specified by the COLR. Although the power reduction is based on the correlation used in Required Actions A.1 and B.1, the database for a power peaking increase as a function of QPT is less extensive for tilt mechanisms other than misaligned CONTROL RODS and APSRs. Because greater uncertainty in the potential power peaking increase exists with the less extensive database, a more conservative action is taken when the tilt is caused by a mechanism other than a misaligned CONTROL ROD or APSR. The required Completion Time of 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br /> allows the operator to reduce THERMAL POWER to < 60% of the ALLOWABLE THERMAL POWER without challenging unit systems.

D.2 Reduction of the nuclear overpower trip setpoints, based on flux and flux/flow imbalance, to 65.5% of the ALLOWABLE THERMAL POWER after THERMAL POWER has been reduced to < 60% of the ALLOWABLE THERMAL POWER maintains both core protection and an operating margin at reduced power similar to that at full power. The required Completion Time of 10 hours1.157407e-4 days <br />0.00278 hours <br />1.653439e-5 weeks <br />3.805e-6 months <br /> allows the operator sufficient time to reset the trip setpoint and is reasonable based on operating experience.

QPT B 3.2.3 BASES OCONEE UNITS 1, 2, & 3 B 3.2.3-7 Rev. 001 ACTIONS E.1 (continued)

If the Required Action and associated Completion Time for Condition C or D are not met, then the reactor will continue in power operation with significant QPT. Either the power level has not been reduced to comply with the Required Action or the nuclear overpower trip setpoints (flux and flux/flow imbalance) have not been reduced within the required Completion Time. To preclude risk of fuel damage in any of these conditions, THERMAL POWER is reduced further. Operation at 20% RTP allows the operator to investigate the cause of the QPT and to correct it. Local LHRs with a large QPT do not violate the fuel design limits at or below 20% RTP. The required Completion Time of 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br /> is acceptable based on limiting the potential increase in local LHRs that could occur due to xenon redistribution with the QPT out of specification.

F.1 QPT in excess of the maximum limit specified in the COLR can be an indication of a severe power distribution anomaly, and a power reduction to at most 20% RTP ensures local LHRs do not exceed allowable limits while the cause is being determined and corrected.

The required Completion Time of 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br /> is reasonable to allow the operator to reduce THERMAL POWER to 20% RTP without challenging unit systems.

SURVEILLANCE QPT can be monitored by both the Incore and Excore Detector Systems. REQUIREMENTS If the Full Incore Detector System is available, this system shall be used for QPT monitoring. (The Full Incore Detector System is not available when the OAC is not available or the NAS computer is in alarm.) The Full Incore Detector System is preferred due to Excore Detector System tilts potentially being affected (i.e., normalized to zero) anytime an Excore Detector calibration is performed. Reasonable completion times exist to allow the use of the Incore Detector System for QPT monitoring. If the Full Incore Detector System is not available, the Excore Detector System should be the basis for QPT monitoring. If the Full Incore Detector System is not available and 1 or more Excore Detectors are not OPERABLE (NI NI-8), then the Backup Incore Detector System should be the basis for QPT monitoring. The QPT limits are derived from their corresponding measurement system independent limits by adjustment for system observability errors and instrumentation errors. Although they may be based on the same measurement system independent limit, the limits for the different systems are not identical because of differences in the errors applicable for these systems. QPT measurements using the

QPT B 3.2.3 BASES OCONEE UNITS 1, 2, & 3 B 3.2.3-8 Rev. 001 SURVEILLANCE Backup Detector System consist of OPERABLE (Reference 4) Incore REQUIREMENTS detectors configured as follows: (continued)

a. Two sets of four detectors shall lie in each core half. Each set of detectors shall lie in the same axial plane.

The two sets in the same core half may lie in the same axial plane.

b. Detectors in the same plane shall have quarter core radial symmetry. Figure B 3.2.3

-1 (Backup Incore Detector System for QPT Measurement) depicts an example of this configuration.

The Excore Detector System consists of four detectors (one located outside each quadrant of the core). Each detector consists functionally of two six-foot uncompensated ion chambers adjacent to the top and bottom halves of the core.

SR 3.2.3.1

The Surveillance Frequency is based on operating experience, equipment reliability, and plant risk and is controlled under the Surveillance Frequency Control Program.

Following restoration of the QPT to within the steady state limit, operation at 95% RTP may proceed provided the QPT is determined to remain within the steady state limit at the increased THERMAL POWER level. In case QPT exceeds the steady state limit for more than 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> or exceeds the transient limit (Condition A, B, or D), the potential for xenon redistribution is greater. Therefore, the QPT is monitored for 12 consecutive hourly intervals to determine whether the period of any oscillation due to xenon redistribution causes the QPT to exceed the steady state limit again.

REFERENCES

1. 10 CFR 50.46.

2. BAW 10122A, "Normal Operating Controls," Rev. 1, May 1984. 3. 10 CFR 50.36.

4. SLC 16.7.8, Incore Instrumentation 5. DPND-NFS-1001A, Oconee Nuclear Station Reload Design Methodology, Revision 7a, NRC Safety Evaluation dated July 21, 2011.

OCONEE UNITS 1, 2, & 3 B 3.2.3-9 Rev. 001 QPT B 3.2.3 Figure B 3.2.3

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Backup Incore Detector System for QUADRANT POWER TILT Measurement