Section 3.1 Reactivity Control

Question 1

What is LCO 3.1.1 SHUTDOWN MARGIN (SDM) and its applicability?

Answer 1

LCO 3.1.1 SHUTDOWN MARGIN (SDM)

SDM shall be within the limits specified in the COLR.

APPLICABILITY: MODE 3, 4, and 5.

Question 2

What do you do if LCO 3.1.1 SHUTDOWN MARGIN (SDM) is not met?

Answer 2

Within 15 minutes, borate and restore SDM to within limit.

Condition: A. SDM not within limit.

Required Action: A.1 Initiate boration to restore SDM to within limit.

Completion Time: 15 minutes

LCO 3.1.1
SDM shall be within the limits specified in the COLR.

Question 3

What is LCO 3.1.2 Reactivity Balance and its applicability?

Answer 3

LCO 3.1.2 Reactivity Balance

The core reactivity balance shall be within ± 1% Δρ of predicted values.

APPLICABILITY: MODE 1.

Question 4

What is and when do you perform a Reactivity Balance?

Answer 4

When the reactor core is critical, a reactivity balance exists and the net reactivity is zero.

The positive reactivity inherent in the core design is balanced by the negative reactivity of the control components, thermal feedback, neutron leakage, and materials in the core that absorb neutrons such as
burnable absorbers.

Excess reactivity can be inferred from the critical
boron curve, which provides an indication of the soluble boron concentration in the Primary Coolant System (PCS) versus cycle burnup.

Periodic measurement of the PCS boron concentration for comparison with the predicted value with other variables fixed (such as control rod height, temperature, pressure, and power) provides a convenient method of ensuring that core reactivity is within design expectations, and that the calculational models used to generate the safety analysis are adequate.

LCO 3.1.2 Reactivity Balance
The core reactivity balance shall be within ± 1% Δρ of predicted values.

Question 5

What is the critical boron curve based upon?

Answer 5

The critical boron curve is based on steady state operation at RTP. Therefore, deviations from the
predicted critical boron curve may indicate deficiencies in the design analysis, deficiencies in the calculational models, or abnormal core conditions, and must be evaluated.

Question 6

What is LCO 3.1.3 Moderator Temperature Coefficient (MTC) and its applicability?

Answer 6

LCO 3.1.3 Moderator Temperature Coefficient (MTC)

Moderator Temperature Coefficient (MTC). The MTC shall be maintained less positive than 0.5 E-4 Δρ/°F at ≤ 2% RATED THERMAL POWER (RTP).

APPLICABILITY: MODES 1 and 2.

Question 7

What is the most limiting event for the technical basis of LCO 3.1.3 Moderator Temperature Coefficient (MTC)?

Answer 7

The event that produces the most rapid cooldown of the PCS, and is therefore the most limiting event with respect to the negative MTC, is a Main Steam Line Break (MSLB) event.

Following the reactor trip for the postulated EOC MSLB event, the large moderator temperature reduction combined with the large negative MTC may produce reactivity increases that are as much as the shutdown reactivity. When this occurs, a substantial fraction of core power (approximately 12% RTP) is produced.

LCO 3.1.3 Moderator Temperature Coefficient (MTC)

Moderator Temperature Coefficient (MTC). The MTC shall be maintained less positive than 0.5 E-4 Δρ/°F at ≤ 2% RATED THERMAL POWER (RTP).

Question 8

What is LCO 3.1.4 Control Rod Alignment and its applicability?

Answer 8

LCO 3.1.4 Control Rod Alignment

All control rods, including their position indication channels, shall be OPERABLE and aligned to within 8 inches of all other rods in their respective group, and the control rod position deviation alarm shall be OPERABLE.

APPLICABILITY: MODES 1 and 2.

Question 9

What do you do if LCO 3.1.4 Control Rod Alignment is not met for rod position indication?

Answer 9

If one channel of rod position indication inoperable for one or more control rods. You must perform rod position verification within 15 minutes of any rod motion in that group.

Question 10

What do you do if LCO 3.1.4 Control Rod Alignment is not met for the rod position deviation alarm?

Answer 10

If the rod position deviation alarm is inoperable, then perform rod position verification within 15 minutes of movement of any control rod.

Question 11

What do you do if LCO 3.1.4 Control Rod Alignment is not met for control rod alignment?

Answer 11

If one control rod misaligned by > 8 inches, perform peaking factor verification within 2 hours or reduce power to less than 75% RTP within 2 hours.

Question 12

What do you do if LCO 3.1.4 Control Rod Alignment is not met for a full-length control rod immovable but trippable?

Answer 12

If one full-length control rod immovable, but trippable, then restore the control rod to operable status prior to entering Mode 2 from any Mode 3 entry.

If its part-length or more than one, then LCO 3.0.3

Question 13

What is LCO 3.1.4 Control Rod Alignment based upon?

Answer 13

LCO 3.1.4 Control Rod Alignment

Limits on control rod alignment and OPERABILITY have been established, and all control 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.

Question 14

What is LCO 3.1.5 Shutdown and Part-Length Rod Group Insertion Limits and its applicability?

Answer 14

LCO 3.1.5 Shutdown and Part-Length Rod Group Insertion Limits

All shutdown and part-length rod groups shall be withdrawn to ≥ 128 inches.

APPLICABILITY:
MODE 1,
MODE 2 with any regulating rod withdrawn above 5 inches.

Question 15

What must be done if LCO 3.1.5 Shutdown and Part-Length Rod Group Insertion Limits is not met?

Answer 15

If one or more shutdown or part-length rods not within limit, then IMMEDIATELY declare affected control rod(s) inoperable and enter the applicable Conditions and Required Actions of LCO 3.1.4.

COMPLETION TIME: Immediately

LCO 3.1.5
All shutdown and part-length rod groups shall be withdrawn to ≥ 128 inches.

Question 16

What is the technical basis of LCO 3.1.5 Shutdown and Part-Length Rod Group Insertion Limits?

Answer 16

The shutdown rod group insertion limit is established to ensure that a sufficient amount of negative reactivity is available to shut down the reactor and maintain the required SDM following a reactor trip from full power.

The combination of regulating rod and shutdown rods 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. The shutdown rod group insertion limit also limits the reactivity worth of an ejected shutdown rod.

LCO 3.1.5
All shutdown and part-length rod groups shall be withdrawn to ≥ 128 inches.

Question 17

What is LCO 3.1.6 Regulating Rod Group Position Limits and its applicability?

Answer 17

LCO 3.1.6: Regulating Rod Group Position Limits

The Power Dependent Insertion Limit (PDIL) alarm circuit and the Control Rod Out Of Sequence (CROOS) alarm circuit shall be OPERABLE, and the regulating rod groups shall be limited to the withdrawal sequence, overlap, and insertion limits specified in the COLR.

APPLICABILITY: MODES 1 and 2.

Question 18

What do you do if LCO 3.1.6 Regulating Rod Group Position Limits is not met for PDIL or CROOS alarm circuit inoperable?

Answer 18

With the PDIL or CROOS alarm circuit inoperable, perform a group position verification within 15 minutes of any rod motion.

LCO 3.1.6: The Power Dependent Insertion Limit (PDIL) alarm circuit and the Control Rod Out Of Sequence (CROOS) alarm circuit shall be OPERABLE, and the regulating rod groups shall be limited to the withdrawal sequence, overlap, and insertion limits specified in the COLR.

Question 19

What do the insertion limits for regulating rods directly impact?

Answer 19

The insertion limits directly affect core power distributions, assumptions of available SDM, and initial reactivity insertion rate.

LCO 3.1.6: The Power Dependent Insertion Limit (PDIL) alarm circuit and the Control Rod Out Of Sequence (CROOS) alarm circuit shall be OPERABLE, and the regulating rod groups shall be limited to the withdrawal sequence, overlap, and insertion limits specified in the COLR.

Question 20

Why do regulating rod groups operate with a predetermined amount of position overlap?

Answer 20

The regulating rod groups operate with a predetermined amount of position overlap, in order to approximate a linear relation between rod worth and rod position (integral rod worth). The regulating rod groups are withdrawn and operate in a predetermined sequence. The group sequence and overlap limits are specified in the COLR.

LCO 3.1.6: The Power Dependent Insertion Limit (PDIL) alarm circuit and the Control Rod Out Of Sequence (CROOS) alarm circuit shall be OPERABLE, and the regulating rod groups shall be limited to the withdrawal sequence, overlap, and insertion limits specified in the COLR.

Question 21

What does the behavior of the total radial peaking factor relate to?

Answer 21

The long term behavior relates to the variation of the
steady state (FrT) with core burnup and is affected by the amount of rod insertion assumed, the portion of a burnup cycle over which such insertion is assumed, and the expected power level variation throughout the cycle. 
The short term behavior relates to transient perturbations to the steady state radial peaks, due to radial xenon redistribution.

Question 22

What is LCO 3.1.7 Special Test Exceptions (STE) and its applicability?

Answer 22

LCO 3.1.7 During the performance of PHYSICS TESTS, the requirements of: LCO 3.1.4, “Control Rod Alignment”;
LCO 3.1.5, “Shutdown and Part-Length Rod Group Insertion Limits”; LCO 3.1.6, “Regulating Rod Group Position Limits”; and LCO 3.4.2, “PCS Minimum Temperature for Criticality” may be suspended, provided:
a. THERMAL POWER is ≤ 2% RTP;
b. ≥ 1% shutdown reactivity, based on predicted control rod worth, is available for trip insertion; and
c. Tave is ≥ 500°F.

APPLICABILITY: MODE 2 during PHYSICS TESTS.

Question 23

What do you do if Thermal Power is not within its limit of

Answer 23

CONDITION: A. THERMAL POWER not within limit.

REQUIRED ACTION: A.1 Reduce THERMAL POWER to within limit.

COMPLETION TIME: 15 minutes

LCO 3.1.7 During the performance of PHYSICS TESTS, the requirements of: LCO 3.1.4, “Control Rod Alignment”;
LCO 3.1.5, “Shutdown and Part-Length Rod Group Insertion Limits”; LCO 3.1.6, “Regulating Rod Group Position Limits”; and LCO 3.4.2, “PCS Minimum Temperature for Criticality” may be suspended, provided:
a. THERMAL POWER is ≤ 2% RTP;
b. ≥ 1% shutdown reactivity, based on predicted control rod worth, is available for trip insertion; and
c. Tave is ≥ 500°F.

Question 24

What do you do if Shutdown reactivity is not within its limit of >- 1% during LCO 3.1.7 Special Test Exemption?

Answer 24

CONDITION: B. Shutdown reactivity not within limit.

REQUIRED ACTION: B.1 Initiate boration to restore shutdown reactivity to within limit.

COMPLETION TIME: 15 minutes

LCO 3.1.7 During the performance of PHYSICS TESTS, the requirements of: LCO 3.1.4, “Control Rod Alignment”;
LCO 3.1.5, “Shutdown and Part-Length Rod Group Insertion Limits”; LCO 3.1.6, “Regulating Rod Group Position Limits”; and LCO 3.4.2, “PCS Minimum Temperature for Criticality” may be suspended, provided:
a. THERMAL POWER is ≤ 2% RTP;
b. ≥ 1% shutdown reactivity, based on predicted control rod worth, is available for trip insertion; and
c. Tave is ≥ 500°F.

Question 25

What do you do if Tave is not within its limit of >=500F during LCO 3.1.7 Special Test Exemption?

Answer 25

CONDITION: C. Tave not within limit.

REQUIRED ACTION: C.1 Restore Tave to within limit.

COMPLETION TIME: 15 minutes

LCO 3.1.7 During the performance of PHYSICS TESTS, the requirements of: LCO 3.1.4, “Control Rod Alignment”;
LCO 3.1.5, “Shutdown and Part-Length Rod Group Insertion Limits”; LCO 3.1.6, “Regulating Rod Group Position Limits”; and LCO 3.4.2, “PCS Minimum Temperature for Criticality” may be suspended, provided:
a. THERMAL POWER is ≤ 2% RTP;
b. ≥ 1% shutdown reactivity, based on predicted control rod worth, is available for trip insertion; and
c. Tave is ≥ 500°F.

Question 26

What requires suspension of physics testing within 1 hour?

Answer 26

Required Action and associated Completion Times (15 min to restore) not met. for

LCO 3.1.7: During the performance of PHYSICS TESTS, the requirements of: LCO 3.1.4, “Control Rod Alignment”;
LCO 3.1.5, “Shutdown and Part-Length Rod Group Insertion Limits”; LCO 3.1.6, “Regulating Rod Group Position Limits”; and LCO 3.4.2, “PCS Minimum Temperature for Criticality” may be suspended, provided:
a. THERMAL POWER is ≤ 2% RTP;
b. ≥ 1% shutdown reactivity, based on predicted control rod worth, is available for trip insertion; and
c. Tave is ≥ 500°F.