Reactivity Control

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Author:
heidin
ID:
141733
Filename:
Reactivity Control
Updated:
2012-03-15 10:37:35
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THERMAL LIMITS CORE MON READINGS THEORY POISONS MAP ILC
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  1. During performance of 2PT-01.11, the operator observes the following values from the Core Performance Edit:

    CMFLCPR is 1.05
    CMAPRAT is 0.95

    Which thermal limit is in excess of Technical Specification limits, and what is the potential consequence of this limit being exceeded?


    A. CMAPRAT. Departure from nucleate boiling may occur during a transient.
    B. CMFLCPR. Departure from nucleate boiling may occur during a transient.
    C. CMAPRAT. Peak fuel clad temperature may exceed 2200°F during a LOCA.
    D. CMFLCPR. Peak fuel clad temperature may exceed 2200°F during a LOCA.
    B. CMFLCPR. Departure from nucleate boiling may occur during a transient.


    Both CMFLCPR and CMAPRAT are normally less than or equal to one. CMAPRAT is core max APRAT. APRAT is actual APLHGR divided by APLHGR limit. CMFLCPR is core max fractional limiting CPR. CPR operating limit is greater than one (as is the safety limit). The fractional limiting CPR is CPR limit divided by actual CPR (opposite than for APRAT). CMFLCPR is kept within limits to prevent transition boiling during anticipated operational occurrences. CMAPRAT is kept within limits to prevent exceeding 10CFR50.46 criteria on a LOCA.
  2. Unit 1 is starting up and is currently at 24.6%.

    Using the attached Core Mon edit and 1PT-01.11, Core Performance Paramenter Check, determine if any thermal limit has bee exceeded.


    A. CMFLPD has been exceeded.
    B. CMAPRAT has been exceeded.
    C. CMFLCPR has been exceeded.
    D. No thermal limit has been exceeded.
    D. No thermal limit has been exceeded.
  3. While at 100%, CWIPs 2C and 2D tripped due to severe grass impingement on the traveling screens. The operating crew has entered the applicable procedures and rapidly reduced reactor power.

    Plant status is as follows:
    Rx power: 50%
    CWIP 2A: Running
    CWIP 2B: Not Available
    CWIP 2C: TRIPPED, will not restart
    CWIP 2D: TRIPPED, will not restart

    Considering only the effects of Xenon and assuming no further operator action, which one of the following describes reactor power 3 hours after reaching 50% power?

    A. Greater than 50% and decreasing.
    B. Less than 50% and decreasing.
    C. Greater than 50% and increasing.
    D. Less than 50% and increasing.
    B. Less than 50% and decreasing.


    The reduction in power causes a reduction in Xe-135 production (due to less Xe-135 being produced directly from fission), and a very large reduction in Xe-135 burnout (due to the decreased neutron flux. A relatively high inventory of I-135 still exists, and Xe-135 production remains relatively high. This effect causes Xe-135 concentration to increase and power will start decreasing. This increase in Xe-135 concentration causes more Xe-135 decay to start occurring, and in about 4-6 hours, the I-135 concentration will have decayed sufficiently low enough to cause Xe-135 concentration to stop increasing with power now lower that the iniial 80%. In the 30 to 40 hours, Xe-135 concentration will decrease until a lower equilibrium level is reached and power will again rise and stop at a level slightly above 80% power. The total time of the Xe-135 transient is 40 to 50 hours, probably closer to 40 hours due to the small (20%) change in power. (At t=10, the peak xenon transient has passed and xenon is starting to rapidly decay and will continue to decay for the next 30 hours.) the final steady-state Xenon concentration will be less than the 100% power concentration and less than the initial Xenon level experienced at 80% power. Hence, if left long inough, final steady state reactor power would be greater than 80% at t= 40 or 45.
  4. The plant is at 94% power with the OPRM system INOPERABLE. The A recirc pump trips. Plant conditions are:

    - Reactor power = 62%
    - Core flow = 37.73 Mlbs/hr (computer point U1CPWTCF)

    The CO scans the RTGB and sees the following annuciators in alarm” A5 4-8, OPRM ENABLED.

    The required action is to:


    A. Immediately insert a manual scram.
    B. Raise core flow or insert control rods to adjust reactor power.
    C. Increase monitoring for Instability. Adjusting reactor power is not required.
    D. Raise core flow since rod insertion is only permitted with two loop operation.
    B. Raise core flow or insert control rods to adjust reactor power.


    Region B of the OPRM INOPERABLE – TWO LOOP OPERATION power/flow map is entered. With the OPRM system inoperable, AOP-4.0 requires the region be exited by raising core flow or by inserting control rods. A reactor scram is only required if region A is entered or if power oscillations are observed. If in the budder region or if using the power/flow map and AOP actoins for the OPRM system OPERABLE, then a power adjustment is not necessary.

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