ML12065A171

B 3.1 Reactivity Control Systems, B 3.1.5 Shutdown Bank Insertion Limits, Bases, Background

ML12065A171
Person / Time
Site:	Callaway
Issue date:	03/01/2012
From:	NRC Region 4
To:
References
FOIA/PA-2012-0110
Download: ML12065A171 (4)

Text

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Shutdown Bank inse-t-on  ; l-e .1.5 B3.1 REACTIVITY CONTROL SYSTEMS B 1 i.5 Shutdown RBank 'ns-^^i-" Limits BASES m- ACK RCI- UIIL. M1 IItUUVVI I ;g110 I :'W

... U ,Ji Ui * :I assumptions in all,-," a-alyses that assume rod inserfi-n u on..reactor trip. The insertion limits directly affect core power and fuel burnup distributions and assumptions of available ejected rod worth, SDMand initial reactivity insertion rate.

The applicable criteria for these reactivity and power distribution design requirements are 10 CFR 50, Appendix A, GDC 10, "Reactor Design,"

GDC 26. "Reactivity Control System Redundancy and Capability, ".GDC __

28, "Reactivity Limits" (Ref. 1), and 10 CFR 50.46, "Acceptance Criteria for Emergency Core Cooling Systems for Light Water Nuclear Power Reactors" (Ref. 2). Limits on rod insertion have been established, and all rod positions are monitored and controlled during power operation to ensure that the power distribution and reactivity limits defined by the design power peaking and SDM limits are preserved.

The rod cluster control assemblies (RCAs) are divided among four control banks and five shutdown banks. Each bank may be further subdivided into two groups to provide for precise reactivity control. A group consists of two or more RCCAs that are electrically paralleled to step simultaneously. If a bank of RCCAs consists of two groups, the groups are moved in a staggered fashion, but always within one step of each other. Three shutdown banks (C, D, and E) consist of a single group. See LCO 3.1.4, "Rod Group Alignment Limits," for control and shutdown rod OPERABILITY and alignment requirements, and LCO 3.1.7, "Rod Position Indication," for position indication requirements.

.......... . .- The control banksareused for precise reactivity control. of the reactor.

The positions of the control banks are controlled manually using the Rod Control System. Automatic rod control is available for insertion only.

They are capable of adding negative reactivity very quickly (compared to borating). The control banks must be maintained above designed insertion limits and ate typically near the fully withdrawn position during noW2na full power operations.

Hence, they are not capable of adding a large amount of positive reactivity Rnrntion or dilution of the Reactor Coolant Svstem (RCS) compensates for the reactivity changes associated with large changes in RS Itemperature. The design calculations are performed with the assumption that the shutdown banks are withdrawn first. The shutd,.,,,n, banks can be fully withdrawn without the core going critical. This (continu ed,

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Shutdown Bank insertion Limits BASES

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on errors. *n BACKGRONTD provides availablNe negative reciiyin heevent of borato errs h (continued) shutdown banks are controlled manually by the control room operator.

During nomnal unit operation, the shutdown banks are either fully withdrawn or fully inserted. The shutdown banks must be completely withdrawn from the core, prior to withdrawing any control banks dr-ing an approach to criticality. The shutdown banks are then left in this position until the reactor is shut down. They affect core power and burnup distribution, and add negative reactivity to shut down the reactor upon receipt of a reactor trip signal.

APPLICABLE On a reactor trip, all RCCAs (shutdown banks and control banks), except SAFETY the most reactive RCCA, are assumed to insert into the core. The

-ANA*YSES-..... -sh-utdW-ib-a*nkssh Frb a-&Vor--bov-e h-eiir inserrtio n lim-itvs-an ilabl-lto insert the maximum amount of negative reactivity on a reactor trip signai.

The control banks may be partially inserted in the core, as allowed by LCO 3.1.6, "Control Bank Insertion Limits." The shutdown bank and control bank insertion limits are established to ensure that a sufficient amount of negative reactivity is available to shut down the reactor and maintain the required SDM (see LCO 3.1.1, "SHUTDOWN MARGIN (SDM)") following a reactor trip from full power. The combination of control banks and shutdown banks (less the most reactive RCCA, which is assumed to be fully withdrawn) is sufficient to take the reactor from full power conditions at rated temperature to zero power, and to maintain the required SDM at rated no load temperature (Ref. 3). The shutdown bank insertion limit also limits the reactivity worth of an ejected shutdown rod.

The acceptance criteria for addressing shutdown and control rod bank insertion limits and inoperability or misalignment is that:

a. There be no violations of:

1. specified acceptable fuel design limits, or

2. RCS pressure boundary integrity; and

b. The core remains subcritical after accident transients.

As such, the shutdown bank insertion limits affect safety analysis involving core reactivity and SDM (Ref. 3).

The shutdown bank insertion limits preserve an initial condition assumed in the safety analyses and, as such, satisfy- Criterion 2 of i 0CFR5U.36c)(2)Aii).

(continued)

CALLAWAY PLANT B 3.1 .5-2

Shutdown Bank insertion Limits BASES (continued)

L._,_,,_, The i.,=*'-shutdown banks must -bewithin their insertion limits any time the reactor is critical or approaching criticality. This ensures that a sufficient amount of negative reactivity is avaiiabie to shut down the reactor and maintain the required SDM following a reactor trip.

The shutdown bank insertion limits are defined in the COLR.

APPLICABILITY The shutdown banks must be within their insertion limits, with the reactor in MODE 1 and in MODE 2 with any control bank not fully inserted. The applicability in MODE 2 begins at initial control bank withdrawal, during an approach to criticality, and continues throughout MODE 2, until all control bank rods are again fully inserted by reactor trip or by shutdown. This ensures that a sufficient amount of negative reactivity is available to shut:

down the reactor and maintain the required SDM following a reactor trip.

The shutdown banks do not have to be within their insertion limits in MODE 3, unless an approach to criticality is being made. In MODE 3, 4, 5, or 6, the shutdown banks are typically fully inserted in the core and contribute to the SDM. Refer to LCO 3.1.1 for SDM requirements in MODES 2 with kff < 1.0, 3, 4, and 5. LCO 3.9.1, "Boron Concentration,"

ensures adequate SDM in MODE 6.

The Applicability requirements have been modified by a Note indicating the LCO requirement is suspended during SR 3.1.4.2. This SR verifies the freedom of the rods to move, and requires the shutdown bank to move below the LCO limits, which would normally violate the LCO.

ACTIONS A.1.11 A.1.2 and A.2 When one or more shutdown banks is not within insertion limits, 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br /> is allowed to restore the shutdown banks.to within the insertion limits.__..

This is necessary because the available SDM may be significantly reduced, with one or more of the shutdown banks not within their insertion limits. Also, verification of SDM or initiation of boration within 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> is required, since the SDM in MODES 1 and 2 is ensured by adhering to the control and shutdown bank insertion limits (see LCO 3.1.1). If shutdown banks are not within their insertion limits, then SDM will be verified by performing a reactivity balance calculation, considering the effects listed in the BASES for SR 3.1.1.1.

The allowed Completion Time of 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br /> provides an acceptable time for evaluating and repairing minor problems without allowing the plant to remain in an unacceptable condition for an extended period of time.

(continued)

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• CALLAIW~Y PLAMIT D n.

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Shutdown Bank insertion Limits B 3.1.5 BASES ACTIONS B.1 (continued-If ,theshutdown banks cannot be restored to within their insertion limits within 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br />, the unit must be brought to MODE 3 where the LCO is not applicable. 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 conditions in an orderly manner and without challenging plant sye,-,ms.

SURVEILLANCE SR 3.1.5. 1 REQUIREMENTS Verification that the shutdown banks are within their insertion limits prior to an approach to criticality ensures that when the reactor is critical, or being taken critical, the shutdown banks will be available to shut down the reactradthe-rcquired SDM-will be maintained following a reactor trip.

This SR and Frequency ensure that the shutdown banks are withdrawn before the. control banks are withdrawn during a unit startup.

Since the shutdown banks are positioned manually by the control room operator, a verification of shutdown. bank position at a Frequency of 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br />, after the reactor is taken critical, is adequate to ensure that they are within their insertion limits. Also, the 12 hour1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> Frequency takes into account other information available in the control room for the purpose of monitoring the status of shutdown rods.

REFERENCES 1. 10 CFR 50, AppendixA, GDC 10, GDC 26, and GDC 28.

2. 10 CFR 50.46.

3. FSAR, Chapter 15, Section 15.1.5.

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