ML060590026

Technical Specifications, Eliminate Power Range Neutron High-Flux Negative Rate Reactor Trip Function. Enclosure 1

ML060590026
Person / Time
Site:	Farley
Issue date:	02/27/2006
From:	Martin R E Plant Licensing Branch III-2
To:	Stinson L M Southern Nuclear Operating Co
References
TAC MC8525
Download: ML060590026 (5)

Text

RTS Instrumentation

3.3.1 Table

3.3.1-1 (page 1 of 8)Reactor Trip System Instrumentation APPLICABLE MODES OR OTHER SPECIFIED REQUIRED SURVEILLANCE ALLOWABLE TRIP FUNCTION CONDITIONS CHANNELS CONDITIONS REQUIREMENTS VALUE SETPOINT 1. Manual Reactor 1,2 2 B SR 3.3.1.12 NA NA Trip 3 (a), 4 (a), 5 (a) 2 C SR 3.3.1.12 NA NA 2. Power Range Neutron Flux a. High 1,2 4 D SR 3.3.1.1 S 109.4% RTP s 109%SR 3.3.1.2 RTP SR 3.3.1.7 SR 3.3.1.10 SR 3.3.1.14 b. Low 1 (b), 2 4 E SR 3.3.1.1 S 25.495, RTP S 25% RTP SR 3.3.1.8 SR 3.3.1.10 SR 3.3.1.14 3. Power Range 1,2 4 D SR 3.3.1.7 S 5.4% RTP S 5% RTP Neutron Flux High SR 3.3.1.10 with time with time Positive Rate constant constant a2sec 22sec 4. Intermediate 1 (b), 2 (c) 2 FG SR 3.3.1.1 S 40% RTP S 35% RTP Range Neutron SR 3.3.1.8 Flux SR 3.3.1.10 2 (d) 2 H SR 3.3.1.1 s 40% RTP s 35% RTP SR 3.3.1.8 SR 3.3.1.10 (a) With Reactor Trip Breakers (RTSs) closed and Rod Control System capable of rod withdrawal.(b) Below the P-10 (Power Range Neutron Flux) interlocks.(c) Above the P-6 (Intermediate Range Neutron Flux) interlocks.(d) Below the P46 (intermediate Range Neutron Flux) Interlocks.

Farley Units 1 and 2 3.3.1-14 Amendment No. 171 (Unit 1)Amendment No. 164 (Unit 2)

RTS Instrumentation B 3.3.1 BASES APPLICABLE

b. Power Range Neutron Flux-Low SAFETY ANALYSES, LCO, and The LCO requirement for the Power Range Neutron Flux -APPLICABILITY Low trip Function ensures that protection is provided against (continued) a positive reactivity excursion from low power or subcritical conditions.

The LCO requires all four of the Power Range Neutron Flux -Low channels to be OPERABLE.

The channels are combined in a 2-out-of-4 trip Logic.In MODE 1, below the Power Range Neutron FlUx (P-10 setpoint), and in MODE 2, the Power Range Neutron Flux -Low trip must be OPERABLE.

This Function may be manually blocked by the operator when two out of four power range channels are greater than approximately 10% RTP (P-1 0 setpoint).

This Function is automatically unblocked when three out of four power range channels are below the P-1 0 setpoint.

Above the P-10 setpoint, positive reactivity additions are mitigated by the Power Range Neutron Flux --High trip Function.In MODE 3, 4, 5, or 6, the Power Range Neutron Flux -Low trip Function does not have to be OPERABLE because the reactor is shut down. Other RTS trip Functions and administrative controls provide protection against positive reactivity additions or power excursions in MODE 3, 4, 5, or 6.3. Power Ranae Neutron Flux -High Positive Rate The Power Range Neutron Flux -High Positive Rate trip uses the same NIS detectors as discussed for Function 2 above.The Power Range Neutron Flux -High Positive Rate trip Function ensures that protection is provided against rapid increases in neutron flux that are characteristic of an RCCA drive rod housing rupture and the accompanying ejection of the RCCA. In certain cases, this Function compliments the Power Range Neutron (continued)

Farley Units I and 2 B 3.3.11-110 Revision RTS Instrumentation B 3.3.1 BASES APPLICABLE SAFETY ANALYSES, LCO, and APPLICABILITY

3. Power Range Neutron Flux-High Positive Rate (continued)

Flux- High and Low Setpoint trip Functions to ensure that the criteria are met for a rod ejection event.I The LCO requires all four of the Power Range Neutron Flux -High Positive Rate channels to be OPERABLE.

The channels are combined in a 2-out-of-4 trip Logic.In MODE 1 or 2, when there is a potential to add a large amount of positive reactivity from a rod ejection accident (REA), the Power Range Neutron Flux-High Positive Rate trip must be OPERABLE.In MODE 3, 4, 5, or 6, the Power Range Neutron Flux -High Positive Rate trip Function does not have to be OPERABLE because other RTS trip Functions and administrative controls will provide protection against positive reactivity additions.

Also, since only the shutdown banks may be withdrawn in MODE 3, 4, or 5, the remaining complement of control bank worth ensures a sufficient degree of SDM in the event of an REA. In MODE 6, no rods are withdrawn and the SDM is increased during refueling operations.

The reactor vessel head is also removed or the closures bolts are detensioned preventing any pressure buildup.(continued)

Farley Units 1 and 2 B 3.3.1-11 Revision RTS Instrumentation B 3.3.1 BASES APPLICABLE SAFETY ANALYSES, LCO, and APPLICABILITY

4. Intermediate Range Neutron Flux.The Internediate Range Neutron Flux trip Function ensures that protection is provided against an uncontrolled RCCA bank rod withdrawal accident from a subcritical condition during startup. This trip Function provides diverse protection to the Power Range Neutron Flux--Low Setpoint trip Function.

The NIS intermediate range detectors are located external to the reactor vessel and measure neutrons leaking from the core. The NIS intermediate range channels also provide a control interlock signal to prevent automatic and manual rod withdrawal prior to initiating a reactor trip.Limiting further rod withdrawal may terminate the transient and eliminate the need to trip the reactor. No credit is taken in the safety analyses for this trip function.The LCO requires two channels of Intermediate Range Neutron Flux to be OPERABLE.

Two OPERABLE channels are sufficient to ensure no single random failure will disable this trip Function.

The trip function is accomplished by a 1-out-of-2 trip Logic.Because this trip Function is important only during startup, there is generally no need to disable channels for on-line testing while the Function is required to be OPERABLE.

Therefore, a third channel is unnecessary.

In MODE 1 below the P-1 0 setpoint, and in MODE 2, vwhen there is a potential for an uncontrolled RCCA bank rod withdrawal accident during reactor startup, the Intermediate Range Neutron Flux trip must be OPERABLE.

Above the P-1 0 setpoint, the Power Range Neutron Flux-High Setpoint trip and the Power Range Neutron Flux -High Positive Rate trip provide core protection for a rod (continued)

Farley Units I and 2 B 3.3.1-12 Revision RTS Instrumentation B 3.3.1 BASES ACTIONS C.1 and C.2 (continued) within the allowed 48 hour5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br /> Completion Time, the unit must be placed in a MODE in which the requirement does not apply. To achieve this status, the RTBs must be opened within the next hour. The additional hour provides sufficient time to accomplish the action in an orderly manner. With the RTBs open, these Functions are no longer required.The Completion Time is reasonable considering that in this Condition, the remaining OPERABLE train is adequate to perform the safety function, and giver the low probability of an event occurring during this interval.D.1.1. D.1.2, D.2.1. D.2.2, and D.3 Condition D applies to the Power Range Neutron Flux -High and Power Range Neutron Flux -High Positive Rate Functions.

The Nl44 power range detector provides input to the CRD System therefore, the NIS has a two-out-of-four trip logic. A known inoperable channel must be placed in the tripped condition.

This results in a partial trip condition requiring only one-out-of-three logic for actuation.

The 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> allowed to place the inoperable channel in the tripped condition is justified in WCAP-1 0271 -P-A (Ref. 7).In addition to placing the inoperable channel in the tripped condition, THERMAL POWER must be reduced to < 75% RTP within 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br />.Reducing the power level prevents operation of the core with radial power distributions beyond the design limits. With one of the NIS power range detectors inoperable, 1/4 of the radial power distribution monitoring capabilily is lost.As an alternative to the above actions, the inoperable channel can be placed in the tripped condition within 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> and the QPTR monitored once every 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> as per SR 3.2.4.2, QPTR verification.

Calculating QPTR every 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> compensates for the lost monitoring capability due to the inoperable NIS power range channel and allows continued unit operation at power levels > 75% RTP. The 6 hour6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> Completion Time and the 12 hour1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> Frequency are consistent with LCO :3.2.4,"QUADRANT POWER TILT RATIO (QPTR)." (continued)

Farley Units 1 and 2 B 3.3.1-38 Revision