ML12065A172

B 3.1 Reactivity Control Systems, B 3.1.6 Control Bank Insertion Limits, Bases, Background

ML12065A172
Person / Time
Site:	Callaway
Issue date:	03/01/2012
From:	NRC Region 4
To:
References
FOIA/PA-2012-0110
Download: ML12065A172 (5)

Text

Limits 1,_,ontrol Bank Inserion-,n B 3.1.

-B 3.1 REACTIV!"ITY CONTROL SYSTEMS B83.1!.6 Control Bank insertion Lrimit BASES BACKGROUND The insertion limits of the shutdown and control rods are initial assumptions in all safety analyses that assume rod insertion upon reactor trip. The insertion limits directly affect core power and fuel bumup distributions and assumptions of available SDM, and 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,"

G-DC-26. "Rea-ct ivity -Cb-rrdt-Sys~teRddu.d ny dn-Cppbi GDC 28, "Reactivity Limits" (Ref. 1), and iu0 CFuR 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 (RCCAs) 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 bank insertion limits are specified in the COLR. The control banks are required to be at or above the insertion limit lines.

The COLR also indicates how the control banks are moved in an overlap pattern. Overlap is the distance travelled together by two control banks.

The control banks are used 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 reactivity very quickly (compared to borating or diluting).

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CALLAWAY P LANIT R I..6-!1 Revision !

7 Control Bank Insertion Limits B 3.1.6 BASES The power density at any point in the core must be limited, so that the fuel (continued) design criteria are maintained. Together, LOG 3.1.4, "Rod Group Alignment Limits," LCO 3.1.5, "Shutdown Bank insertion Limits,"

LCO 3.1.6, "Control Bank Insertion Limits," LCO 3.2.3, "AXIAL FLUX DIFFERENCE !AFD)," and LCO 3-2.4, "QUADRANT POWER TILT RATIO (QPTR)," provide limits on control component operation and on monitored process variables, which ensure that the core operates within the fuel design criteria.

The shutdown and control bank insertion and alignment limits, AFD, and QPTR are process variables that together characterize and control the three dimensional power distribution of the reactor core. Additionally, the control bank insertion limits control the reactivity that could be~added in the e-vent o-fa rod ejec-tion accident, and the shutdown and control bank insertion iiits ensure the required SOM is maintained.

Operation within the subject LCO limits will prevent fuel cladding failures

. ... ...J4. I 04 -n

...Vn _ a , .._K. _ *-dre ea1 fissio products to the reactor coolant in the event of a loss of coolant accident (LOCA), loss of flow, ejected rod, or other accident requiring termination by a Reactor Trip System (RTS) trip function.

APPLICABLE The shutdown and control bank insertion limits, AFD, and QPTR LCOs SAFETY. are required to prevent power distributions that could result in fuel ANALYSES cladding failures in the event of a LOCA, loss of flow, ejected rod, or other accident requiring termination by an RTS trip function.

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

a..... There be.no violations of:

1. specified acceptable fuel design limits, or

2. Reactor Coolant System pressure boundary integrity; and

b. The core remains subcritical -after accident transients.

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

(continued) 10 A 1-LAM.IAY PLANT Revision 0

Control Bank, inserion I imit BASES APPLIC ttABLE The SDM --, ir,-,n- is ensured by ilmiting t'he control'. and i*-*"utown SAFETY bank insertion limits so that allowable inserted worth of the RCCAs is ANAtiSES suich hat sso sufficient 1 - -- U"' . =.. :,_=., L 1.0 11 t ,- ....

(continued) reactor to hot zero power with a reactivity margin that assumes the maximum worth RCCA remains fully withdrawn upon trip (Ref. 4).

Operation at the insertion limits or AFD limits may approach the maximum allowable linear heat generation rate or peaking factor with the allowed QPTR present. Operation at the insertion limit may also indicate the maximum ejected RCCA worth could be equal to the limiting value in fuel cycles that have sufficiently high ejected RCCA worths.

The control and shutdown bank insertion limits ensure that safety

-an-aly-se5- ass-um ption-sfor-SDM-,-ejecte-d--rod-wo rth.l-a nd-pow--rdistribution--

peaking factors are preserved (Ref. 5).

The insertion limits satisfy Criterion 2 of IOCFR50.36(c)(2)(ii), in that they are initial conditions assumed in the safety analysis.

LCO The limits on control banks sequence, overlap, and physical insertion, as defined in the COLR, must be maintained because they serve the function of preserving power distribution, ensuring that the SDM is maintained, ensuring that ejected rod worth is maintained, and ensuring adequate negative reactivity insertion is available on trip. The overlap between control banks provides more uniform rates of reactivity insertion and withdrawal and is imposed to maintain acceptable power peaking during control bank motion.

APPLICABILITY The control bank sequence, overlap, and physical insertion limits shall be maintained with the reactor in MODES 1 and 2 with "k - 1.0. These limits must be maintained, since they preserve the assumed power .

distribution, ejected rod worth, SDM, and reactivity rate insertion assumptions. Applicability in MODES 3, 4, and 5 is not required, since neither the power distribution nor ejected rod worth assumptions would be exceeded in these MODES.

The applicability requirements have been modified by a Note indicating the LCO requirements are suspended during the performance of SR 3.1.4.2. This SR verifies the freedom of the rods to move, and requires the control bank to move below the LCO limits, which would violate the LCO.

(continued)

CALLAWAY PLANT B ".1.6-3 Revision 0

Control Bank insertion Limits BASES (continued)

SA.i.iA.!.2. A.2, .1.i, 8.1.2, and M.2 hen th~e controi ~anks are outside the acceptab'e insertion ,imits, thI must be restored to within those limits. This restoration can occur in two

a. Reducing power to be consistent with rod position; or

b. Moving rods to be consistent with power.

Also, verification of SDM or initiation of boration to regain SDM is required within 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br />, since the SDM in MODES I and 2 normally ensured by adhering to the control and shutdown bank insertion limits (see

... ..LCO-3.I-,-"S

---

TOWN-MARGIN-(SDM)")-h Deen upse ifT.-oft-rc- --

banks are not within their insertion limits, then SDM wili be verified by performing a reactivity balance calculation, considering the effects listed in the BASES for SR 3.1.1.1.

Similarly, if the control banks are found to be out of sequence or in the wrong overlap configuration, they must be restored to meet the limits.

Operation beyond the LCO limits is allowed for a short time period in order to take conservative action because the simultaneous occurrence of either a LOCA, loss of flow accident, ejected rod accident, or other accident, during this short time period, together with an inadequate power distribution or reactivity capability, has an acceptably low probability.

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 /> for restoring the banks to within the insertion, sequence, and overlap limits 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.

Failure of overlap or sequence support equipment does not require ..

entering the ACTIONS as long as sequence and overlap limits are maintained.

C.1 If Required Actions A.1 and A.2, or B.1 and B.2 cannot be completed within the associated Completion Times, the plant 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 on operating experience, for reaching the required MODE from full power conditions in an orderly manner and without challenging piant systems.

(continued)

CrAI!_I-A DI KLAT

Control Sank insertion Limits BASES (continued)

REQUIREMENTS This Sur.eillance iSr-q-iredl to ensure that the-..... , . n" .

s*. ,

criticality with the control banks below their insertion limits.

The estimated critical position (ECP) depends upon a number of factors, one of which is xenon concentration. Ifthe ECP was calculated long before criticality, xenon concentration could change to make the ECP substantially in error. Conversely, determining the ECP immediately before criticality could be an unnecessary burden. There are a number of unit parameters requiring operator attention at that point. Performing the ECP calculation within 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br /> prior to criticality avoids a large error from changes in xenon concentration, but allows the operator some flexibility to s*chedulethe-ECP-c-atculationwtith -other-tartupactivities_-.........

SR 3.1.6.2 Verification of the control bank insertion limits at a Frequency of 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> is sufficient to detect control banks that may be approaching the insertion limits since, normally, very little rod motion occurs in 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br />.

SR 3.1.6.3 When control banks are maintained within their insertion limits as checked by SR 3.1.6.2 above, it is unlikely that their sequence and overlap will not be in accordance with requirements provided in the COLR. The verification of compliance with the sequence and overlap limits specified in the COLR consists of an observation that the static rod positions of those control banks not fully withdrawn from the core are within the limits

.. specified in the COLR. Bank sequence and overlap must also be maintained during rod movement, implicit within the LCO. A Frequency of 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> is consistent with the insertion limit check above in SR 3.1.6.2.

REFERENCES 1. 10 CFR 50, Appendix A, GDC 10, GDC 26, GDC 28.

2. 10 CFR 50.46.

3. FSAR, Chapter 15.

4. FSAR, Chapter 15, Section 15.1.5.

5. WCAP-9272-P-A, "Westinghouse Reload Safety Evaluation Methodology," July 1985.

CALLAWVAY PLANT IB3.i .6-5 Revision %j