Section 3.2 POWER DISTRIBUTION LIMITS

Question 1

What is T.S. 3.2.1 Linear Heat Rate (LHR) and its applicability?

Answer 1

3.2.1 Linear Heat Rate (LHR)

LHR shall be within the limits specified in the COLR, and the Incore Alarm
System or Excore Monitoring System shall be OPERABLE to monitor
LHR.

MODE 1 with THERMAL POWER > 25% RTP.

Question 2

What do you do if the LHR is not within limits of the COLR?

Answer 2

3.2.1 Linear Heat Rate (LHR)

LHR, as determined by the automatic Incore Alarm System, not within limits specified in the COLR, as indicated by FOUR or more coincident incore channels

LHR, as determined by the Excore Monitoring System, not within limits specified in
the COLR.

LHR, as determined by manual incore detector readings, not within limits
specified in the COLR.

THEN: Within 1 hour, Restore LHR to within limits.

Question 3

What is the purpose of T.S. 3.2.1 Linear Heat Rate?

Answer 3

T.S. 3.2.1 Linear Heat Rate

To limit the core power distribution to the initial values assumed in the accident analyses.

Operation within the limits imposed by this LCO either limits or prevents potential fuel cladding failures that could breach the primary fission product barrier and release fission products to the primary coolant in the event of a Loss Of Coolant Accident (LOCA), loss of flow accident, ejected control rod accident, or other postulated accident requiring termination by a Reactor Protection System trip function.

The limitation on the LHR in the peak power fuel rod at the peak power elevation Z ensures that, in the event of a LOCA, the peak temperature of the fuel cladding does not exceed 2200°F.

Question 4

How does the Incore System monitor for LHR?

Answer 4

The Incore Alarm System performs this function by continuously monitoring the
local power at many points throughout the core and comparing the
measurements to predetermined setpoints above which the limit on LHR could be exceeded.

Incore output monitored by PPC via SPI. Loss of Y-40 results in loss of SPI.

Question 5

How does the Excore System monitor for LHR?

Answer 5

By providing comparison of the measured core ASI with predetermined ASI limits based on incore measurements.

An Excore Monitoring System Allowable Power Level (APL), which may be less
than RATED THERMAL POWER, and an additional restriction on Quadrant Power Tilt (Tq), are applied when using the Excore Monitoring System to ensure that the ASI limits adequately restrict the LHR to less than the limiting values.

Excore monitoring of LHR via PR 5, 6, 7 & 8. Ion Chambers.

Question 6

What makes the Incore Alarm System for LHR Operable?

Answer 6

Incore Alarm System for LHR Operable

must have at least 90 of the 180 incore detectors OPERABLE and 2 incore detectors
per axial level per core quadrant OPERABLE. In addition, the plant process computer must be OPERABLE and the required alarm setpoints entered into the plant computer.

Only 36 of the 45 instrument locations are included in the Incore Alarm System Uncertainty Analysis (180 of the possible 215 detectors).

Question 7

What makes the Excore System for monitoring LHR Operable?

Answer 7

Excore System for monitoring LHR Operable

must have been calibrated with OPERABLE incore detectors, the ASI must
not have been out of limits for the last 24 hours, and THERMAL POWER must be less than the APL.

Question 8

Does fuel damage occuring when operating outside the LHR limits?

Answer 8

Fuel cladding damage does not necessarily occur while the plant is
operating at conditions outside the limits of these LCOs during normal
operation. Fuel cladding damage could result, however, if an accident
occurs from initial conditions outside the limits of these LCOs. The
potential for fuel cladding damage exists because changes in the power
distribution can cause increased power peaking and can
correspondingly increase local LHR.

Question 9

What is T.S. 3.2.2 Total Radial Peaking Factor (F_R^T) and its applicability?

Answer 9

3.2.2 TOTAL RADIAL PEAKING FACTOR (F_R^T)

(F_R^T) shall be within the limits specified in the COLR.

MODE 1 with THERMAL POWER > 25% RTP

Question 10

How is F_R^T Monitored?

Answer 10

Data from the incore detectors are used for determining the measured F_R^T.

Question 11

Why do we have F_R^T Limits?

Answer 11

F_R^T Limits

The limitations on F_R^T are provided to ensure that assumptions used in
the analysis for establishing DNB margin, LHR limit and the thermal
margin/low pressure and variable high power trip setpoints remain valid
during operation.

In MODE 1 with THERMAL POWER > 25% RTP, power distribution
must be maintained within the limits assumed in the accident analyses
to ensure that fuel damage does not result following an AOO.

Question 12

What is T.S. 3.2.3 QUADRANT POWER TILT (T_q) and its applicability?

Answer 12

3.2.3 QUADRANT POWER TILT (T_q)

T_q shall be ≤ 0.05.

MODE 1 with THERMAL POWER > 25% RTP.

Question 13

What is Quadrant Power Tilt (T_q)?

Answer 13

Quadrant Power Tilt (T_q)

The maximum positive ratio of the power generated in any quadrant minus the average quadrant power, to the average quadrant power.

Question 14

How is Quadrant Power Tilt (T_q) monitored?

Answer 14

The power range monitoring system provides alarms when T<sub>q</sub> exceeds
predetermined values (5% and 10%).

The average of the four power range signals is developed by a single “Comparitor Averager.”

Each power range channel compares its output signal to this average signal. Two channel deviation alarm bistables, set at different levels, are provided in each
power range channel.

The deviation alarms will annunciate when the associated channel signal is either above or below the average, however, only a signal above the average is of concern with regard to Tq.

Question 15

What is T.S. 3.2.4 AXIAL SHAPE INDEX (ASI) and its applicability?

Answer 15

3.2.4 AXIAL SHAPE INDEX (ASI)

The ASI shall be within the limits specified in the COLR.

MODE 1 with THERMAL POWER > 25% RTP

Question 16

How is the ASI Alarm Generated?

Answer 16

ASI Alarm Generation

Provided by Thermal Margin Monitor.

Ye = ASI as calculated from the output of the Power Range NIs upper (U) and lower (L) detector outputs.

Yi is based upon the average ASI of the entire quadrant as measured by the incores.

The ASI Function Generator takes Ye, Yi and the Shape Annealing Factor for each Excore to generate the relationship between Ye and Yi. This signal is sent to the ASI Comparator.

The Local Power Density Function takes the max of Delta-T or NI power and develops an upper and lower ASI level (Yp and Yn) for that power level. This output is sent to the ASI Comparator which generates the ASI Alarm.

Question 17

When is the ASI Alarm active and what controls its status?

Answer 17

ASI Alarm Active

Active at 15% ascending power

Inactive at 14.5 descending power

Controlled by 15% Bistable via LPD Block

Question 18

What does the limitation on ASI, along with the limitations of LCO 3.3.1, “Reactor
Protective System Instrumentation,” provide.

Answer 18

ASI Purpose

Represents a conservative envelope of operating conditions consistent with the assumptions that have been analytically demonstrated adequate for maintaining an
acceptable minimum DNBR throughout all AOOs.