TAA-MCD Flashcards
Define undermoderated
MTC is negative
resonance escape probability is dominate over thermal utilization factor
Define overmoderated
MTC is positive
Thermal utilization factor is dominate over resonance escape probability
Describe core power effects of FTC
At higher fuel temps doppler broadening lessens per degree F
Why does FTC become more negative over core life
build in of Pu-240
State ECCS acceptance criteria
Cladding temp <2200F Cladding oxidation <17% of thickness Hydrogen generation <1% Coolable geometry Long-term cooling
what is Critical Heat flux
the heat transfer per unit area to cause DNB
discuss how CHF change over core height
CHF decreases from the bottom to the top of the core
Define departure from nucleate boiling ratio
CHF divided by AHF at any point along a fuel rod
T.S. limit >/= 1.14
Discuss what the concern is with RCS hot leg becoming saturated
Delta-T is no longer representative of reactor power output
State the basis for heat flux hot channel factor
Fuel temp <4700F
Maintain cladding temp <2200F
Maintain DNBR >/=1.14
Define FqZ (Heat flux Hot Channel Factor)
the ratio of highest linear power density at core height Z along any fuel rod to the core average fuel rod linear power density
State the Kw/ft that would cause fuel melt and cladding ocidation
21 Kw/Ft = 4700F (fuel melt)
18 Kw/Ft = 2200F (cladding Oxidation)
Define FnDelta-H (Nuclear Enthalpy rise Hot Channel Factor)
Ratio of the total power produced by the highest power fuel rod to the total power produced by the average fuel rod power
- is a measure of a maximum total power produced in a fuel rod
- basis: DNBR
Define Axial Flux DIfference
AFD = Ptop - Pbottom
Define Axial Offset
Ptop-Pbottom/Ptop+Pbottom
State the T.S. for AFD
If unacceptable:
restore to within limits within 15 min
OR
restore power to <50% within 30 min
Summarize guidance for AFD control
Inside admin band: do NOTHING Outside band (ARO): push-pull-drift Outside band: push-pull
State acceptance criteria for rod control
+/- 10% load change
+/- 5% per minute load ramp rate
50% step load rejection with auto steam dumps
State the function of the Setpoint Study
A setpoint study which defines NSSS control system setpoints and time constants to be used for initial plant start up and subsequent operation as verified by startup testing
State Reactor response to a SLOW reactivity addition accident
No power overshoot before RPS trip
Core protected by OTDT trip
State Reactor response to a FAST reactivity addition accident
power overshoots before rods insert
Core protected by FTC
- High Flux/ high rate trips
State Reactor response to a PROMPT reactivity addition accident
Large power overshoot
FTC limits power rise
RX eventually trips from PR flux trip
State why single rod withdrawal is worse than a bank withdrawal
A single rod withdrawal causes significant localized hot channel factor peeking
State RCS response to a Rod drop accident with rods in manual
Tave decreases adding negative reactivity
Decrease is not enough to restore power to original level
State plant response to a Rod drop accident with rods in AUTO
Rods withdraw due to PMM (if no C-11)
slight power overshoot causing rods to drive back in
Describe the analyzed rod ejection accident
LOCA and reactivity addition accident
FTC required to terminate power rise
RX trip on high flux rate
BOL full power would result in 10% fuel melt
During an increased Secondary Heat removal accident why is BOL with auto rods is most limiting
Less negative MTC
Temp and pressure are more stable
power is higher and dominant so DNBR decreases
State design features that minimize the consequences of steam line breaks
Flow restrictor in outlet of SG nozzle MSI actuation SI actuation ASME class 1 piping Various RX trips
State most limiting factor in MSLB accident
Most reactive RCCA is assumed to be stuck fully withdrawn after reactor trip
- allows possible re-criticality
- results in higher peaking factors
Explain why HZP and EOL for MSLB is severe
HZP: maximum SG water inventory
EOL: MTC is most negative
State DNB parameters of concern
Tave = 595.1F
PZR press >/= 2185#
- restore within 2hrs
For a Decreased Secondary heat load removal accident state why a low-low SG water level with a LOP is severe
Minimizes the SG heat transfer capability and increase the amount of RCS stored energy at the time of RX trip
State how RCS Bleed and Feed is accomplished
Used during loss of all feed event (loss of heat sink)
- Both PORVs and one CCP + SI
Explain why it is important that the initiation of bleed and feed be delayed criteria is met
WR level in and 3 SG < 30% PZR pressure > 2385# - SG mass still available for cooling - Cooling helps repressurization - lower RCS pressure allows more ECCS flow
List stages for Large Break LOCA
Blowdown
Refill
Reflood
Recirculation
Discuss SBLOCA worse case and location
Cold leg 4” SBLOCA is the worse case due to loop seal and that steam is prevented from being vented from the core
State the UFSAR worse case LBLOCA
Loss of one train of ECCS
Both trains of CBS work
Explain why for SBLOCAs the core can become uncovered
A loop seal forms in the intermediate leg which slowly depletes inventory and causes core uncovery
- once level is low enough the loop seal is broken and reflood can commence
Describe how to determine a SGTR from a LOCA
an uncontrolled SG NR level increase
Describe major actions in E-3 that are required to recover from a SGTR
Identify and Isolate the ruptured SG
Cooldown RCS
Depressurize RCS
Terminate SI
Explain my stopping an RCP is not desirable during a SGTR
CDR for natural circ is slower
normal sprays are not available for depressurization
For a SGTR state the UFSAR major assumptions
1 intact ASDV fails to open
Ruptured SG ASDV fails open
LOP
Normal plant parameters
For a SGTR state the consequences for not meeting the TCAs
Water may relieve out of the SG safeties, radiological mess
For loss of flow accidents that the core safety limit of concern
DNBR >/= 1.14
Explain RCP under voltage trip reasoning
this is an anticipatory trip that senses flow maybe too low
Explain RCP under frequency trip reasoning
The RCP flywheel won’t have enough inertia for adequate coast down
State relationship between loss of flow and OTDT trips
OTDT is a DNB trip
OTDT assumes nominal flow
Explain why a seized RCP rotor is the most severe low flow accident
There is no flywheel coast down
significant DNB occurs
State the most significant post-LOCA H2 contributor
zirc water reaction
State why transfer to hot leg recirc is desired
Prevents boron precipitation
condenses any steam in the outlet plenum
List the 5 indications of natural circulation
Subcooling >40f Hot leg temps - stable or decreasing Core exit thermocouples - stable or decreasing SG pressures - stable or decreasing Cold leg temps - at Tsat for SG pressure
Discuss why Delta-T can not be relied upon in natural circulation
Delta-T is only valid for forced flow
State limits on subcooling if natural circ is being used
this allows vessel head to cooldown
- > 50F with 2 CRDMs running
- 100 and 130F if CRDMs fans are not funning
State how to enhance natural circ
PZR level at 25% RCS subcooling at 50f SG NR at 50% CDR at 50F/hr ALL CRDM fans on
State the two factors that determine the severity of a SBO
Duration of the event
Response of the RCP seals
Discuss why the RCP seals are the most susceptible in a SBO
If cooling is lost then seals will degrade >550F
This will cause a LOCA and core uncovery if power is not restored
Describe two corrective measures that must be taken to minimize a SBO
Cool down RCS
Depressurize the RCP
Describe UFSAR SBO conclusions
4 HR duration
4 HR battery capacity
CST required volume: 137,000gallon
Core is not expected to become uncovered
State worse case ATWS event
Loss of secondary heat sink
- loss of load (2959#) RCS pressure
State assumed RX power after ATWS
after 10 min RX power is 5% due to steam demand and EFW capacity
Discuss how to limit an ATWS event
Trip the turbine w/in 30 seconds (preserves SG inventory)
Initiate SG flow w/in 60 second
List the operator actions to mitigate ATWS event
Insert negative reactivity
trip turbine w/in 30 seconds
EFW actuation within 60 seconds
Verify PORVS and safeties open when required
State the temp for inadequate core cooling
CETC >1100F, assumes core damage will happen
State conditions for inadequate core cooling
No CCPs or SIPs
State in order of preference inadequate core cooling recovery methods
ECCS actuation
Secondary Depressurization
RCP restart
RCS depressurization
Explain response of normal response of NI following a reactor trip
Prompt drop to 6%
stable -1/3 SUR
SR detectors should reenergize at 5e-11 about 15 to 20 min
Explain what determines equilibrium fission rate in a shut down RX
Directly proportional to source strength (higher at EOL)
Inversely proportional to SDM
Why does SR counts increase as voiding increases with RCPs running
RCS is saturated and progressively voiding
Indicated SR level rises as a much larger fraction of the neutron population reaches the NIs (less shielding from coolant)
Why does SR counts change as voiding increases without RCPs
SR counts increases as core uncovers and downcomer empties
SR counts then decrease as level drops further and source strength drops
Explain the response of incore NI as the core is uncoverd
During uncovery the outputs above the water level rise significantly
The outputs below the water level will read lower and show more variation
State how to calculate Subcooling margin
Use WR RCS pressure (PT-403,405)
Determine Tsat for pressure
Subtract highest average CETC quadrant temperature
What does a negative subcooling margin mean
Indication of superheat at core exit
What does 40F subcooling margin mean
Saturation temperatures at core exit
Discuss why CDR is more restrictive
CDR is more restrictive due to the tensile stress on the inner vessel wall causing the vessel to be closer to max allowed stress
State the four conditions that must be present for Pressurized thermal shock
Severe cooling and high rate
High internal pressure
High NDT
Critical flaw
State the three things as an operator that can be done to reduce PTS
Stop the cooldown
Terminate SI
Soak the RCS
State the Containment design basis for a LBLOCA
LBLOCA in the intermediate leg
Combines effect of high core reflood rate plus SG heat addition
State issue with FR-Z.1 versus other FRPs
FR-Z.1 there is no alternate recovery actions can be provided because CBS is the only ESF system that will mitigate a rise in containment pressure
State parameters for entry into Containment status tree
pressure >52#
OR
Pressure >18# and Phase A and B isolations not isolated
List the four major classifications on post accident fuel conditions
Undamaged fuel
Failed cladding
Overheated fuel
Core Melt
Describe the fission products unique to each type of post accident fuel conditions
Failed cladding - Xenon, Krypton, Iodine
Overheated Fuel - Xenon, Krypton, Iodine and CESIUM
Core Melt - Strontium and Barium
State auxiliary parameters to asses core damage
Containment H2
CETCs
RVLIS
Containment radiation level
Describe how Iodine spiking occurs
Iodine transfuses through a cladding defect into the RCS
Describe where Post accident samples can be drawn from
Chemistry samples from Loops 1 or 3 OR RHR pump discharge all through the PASS System Radiation on sample can be very high
State which Radiation monitor is most useful to the plant to determine containment rad levels
Post LOCA Containment area radiation monitors
State how to estimate radiation doses in containment
Take external dose rates at the hatch and solve for internal dose
Describe how the operator determines the dose to the public
Raddose V is used to calculate
State what must be done to use CSF for EAL entry
Conditions must be evaluated and verified via hardwire indications
