Week 6: Simulator Morning Questions

Question 1

Plant is at 100% power. Turbine trips. What are your immediate actions? What if the trip is from 40% power?

Answer 1

After a turbine trip at 100% power, operators will enter E-0, as a Rx trip will have also occurred due to P-9.

After a turbine trip at 40% power, operators will enter into the associated Off-Normal procedure for a turbine trip, as the Rx will not have automatically tripped.

Question 2

While at 100% power, rods unexpectedly begin stepping in at high speed. What are your actions?

Answer 2

RO will verify with BOP whether or not a load rejection is occurring; if not, the RO will take manual control of the rods to halt the spurious motion.

Question 3

Draw Pressurizer Pressure Channel 1 High pressure trip from transmitter to Rx trip breaker.

Answer 3

The pressure transmitter feeds process control instrumentation, ultimately ending up with an associated bistable for the High Pressure Rx trip. This bistable compares the current value of the transmitter to the trip setpoint and determines if the trip criteria is met. If so, that bistable deenergizes its line to the SSPS. The both trains of the SSPS receive the output of the CH1 bistable and compares it to the trip coincidence logic associated with that particular trip. If the criteria is met, each SSPS train will open its associated Rx trip breaker, deenergizing the CRDMs and dropping the rods into the core.

Question 4

Plant is in Mode 3. PZR spray valve sticks open. Describe plant response and immediate operator actions.

Answer 4

PZR pressure will begin to fall, all heaters will energize. Rx trip is blocked as we are below the P-7 setpoint; instead, SI setpoint of 1849 will be reached, tripping the reactor. E-0 will be entered.

Question 5

Describe the configuration of the RCCAs into banks and groups.

Answer 5

Control Banks:
A - 4, 2 groups of 2
B - 8, 2 groups of 4
C - 8, 2 groups of 4
D - 5, 2 RCCAs in Group 1, 3 RCCAs in Group 2

SD Banks:
SA - 8, 2 groups of 4
SB - 8, 2 groups of 4
SC - 4, 1 group
SD - 4, 1 group
SE - 4, 1 group

Question 6

What is SI termination?

Answer 6

SI termination is halting the operation of the SI system as actuated by the ESFAS, specifically securing Charging, SI, and RHR pumps

Question 7

What conditions must be met to Reset SI?

Answer 7

P-4, 60 second timer (See Drawing #008)

Question 8

What gives Phase A isolation? Phase B isolation?

Answer 8

SI, CTMT Hi-3 at 27 psig, manual for both

Question 9

List 5 possible causes of a Load Rejection.

Answer 9

Offsite Load Transient
Generator Breakers TRIPPED
Exciter Field Breaker TRIPPED
Malfunction of Turbine EHC
Turbine Runback/Setback
Turbine TRIP when less than 50% power

Question 10

List 10 indications of a Load Rejection.

Answer 10

Control Rods AUTOMATICALLY inserting if in AUTO
Increased Tavg
Condenser Steam Dump Valves OPEN
Increased Pressurizer Level
Increased Steam Header Pressure
Atmospheric Steam Relief Valves OPEN
Decreased Steam Generator Level
Decreased Turbine Impulse Pressure
Pressurizer Power-Operated Relief Valves OPEN
Decreased Steam Flow indication

Question 11

Explain the response of the following to a load rejection:
1. Rod Control
2. PZR Pressure Control
3. PZR Level Control
4. SG Level Control
5. Steam Dumps

Answer 11

1. Rods step in
2. Will increase, Sprays and PORVs will actuate in response
3. Will increase, charging flow will reduce in response
4. Will decrease, FW increases in response
5. Opens with a C-7 in conjunction with a C-9 to control Tavg to program

Question 12

Rods are below the RIL. What are your actions? When do you stop this action?

Answer 12

Emergency borate until the Lo-Lo RIL alarm clears, then terminate emergency boration.

Question 13

Plant is at 100%, all systems in auto. PT506 (Impulse Pressure) fails low. What happens?

Answer 13

Rod control thinks that Rx power is higher than Turbine power and begins to insert rods, reducing Tavg. Rods will continue to insert until the power term in Rod Control decays.

Question 14

Draw the Reactor Control Unit (Rod Control Logic).

Answer 14

Inputs: Thot, Tcold, Tref, PR NI Power, Turbine Impulse Pressure

Question 15

List the first 4 steps of E-0 and explain why they are required.

Answer 15

Verify Rx trip; all emergency systems are designed for decay heat only, so if we aren’t tripped yet nothing else matters
Verify Turbine trip; otherwise we are excessively cooling down the Rx
Verify power to NB buses; need this to power safety-related systems
Verify SI actuation; procedure handles both Rx trip and SI

Question 16

List the SI termination criteria.

Answer 16

PZR level greater than 4% NR
PZR pressure stable
30 degrees of subcooling margin
260,000 lbm/hr of AFW flow or >4% NR level in 1 intact SG

Question 17

Explain how the pressurizer works thermodynamically.

Answer 17

As RCS temperature increases, the RCS coolant becomes less dense, and therefore expands. This additional volume goes to the PZR, increasing level. As the coolant level in the PZR rises, the steam bubble at the top of the PZR is compressed, raising RCS pressure.

Question 18

What are the entry conditions for emergency boration?
When can each condition be terminated?

Answer 18

Control rod bank below the RIL with reactor; Rods Bank Lo-Lo alarm cleared
Failure of two or more RCCAs to fully insert following Rx trip; when 100ppm/stuck rod has been added to RCS.
Unexplained/Uncontrolled reactivity increase; 100 ppm past the point of observed reactivity decrease
Reactor makeup control system failure; when desired RCS boron concentration reached or operator judgement

Question 19

What are the emergency boration pathways?

Answer 19

Through BG HIS-8104
Through BG HIS-110A and -110B
Through V-177
Using RWST

Question 20

Describe subcritical multiplication.

Answer 20

The presence of a neutron source in a fissile material will produce a steady-state neutron population greater than that of the source via fission reactions; however, the fission neutrons produced cannot support a self-sustaining chain reaction.

Question 21

List all protective functions produced by Tavg and dT.

Answer 21

OTDT
OPDT
P-4
P-12
C-3
C-4

Question 22

What is (1+tau_1 * s)/(1+tau_2 * s)? Draw response to step input.

What is (tau * s)/(1+tau * s)? Draw response to step input.

Answer 22

Lead-Lag; rises to a point above the initial input and then decays to match the initial input.

Rate Lag; initially matches the initial input, then decays away to 0.

Question 23

List the 6 preemptive actions.

Answer 23

Reduction of AFW flow
Isolation of a faulted SG
Mitigate Thot/Tcold increase after SG dryout
Isolation of a ruptured SG
Transfer steam dump control to Pressure mode
Stopping RCPs for failed-open pressurizer spray valve

Question 24

What is the purpose of the delay tank in the CVCS?

Answer 24

To allow for N-16 decay.

Question 25

What is the purpose of the preemptive action to reduce AFW flow?

Answer 25

To prevent an uncontrolled cooldown of the RCS below 557F.

Question 26

What is the purpose of the preemptive action to isolate a faulted SG?

Answer 26

If the break is downstream of the MSIVs, the closure stops the leak and protects personnel and equipment.
If the break is upstream of the MSIVs, the closure isolates the intact SGs from the faulted one, reducing break flow.

Question 27

What is the purpose of the preemptive action to mitigate Thot/Tcold increase after SG dryout?

Answer 27

During the blowdown of a faulted SG, the ECCS adds water to the RCS. When blowdown ends, the RCS cooldown ends as well. Decay heat then starts a RCS heatup, raising PZR level. This plus the additional mass added by SI can lead to a solid plant condition unless the heatup is controlled.

Question 28

What is the purpose of the preemptive action to isolate a ruptured SG?

Answer 28

Isolating the ruptured SG accomplishes 2 things: first, isolating the steam from the ruptured SG stops the flow of contaminated steam into the environment, reducing dose to the public. Second, trapping the steam in the ruptured SG increases pressure in said SG, reducing the dP between the RCS and the SG at the U-Tube rupture, slowing the flow of primary coolant into the SG.

Question 29

What is the purpose of the preemptive action to transfer steam dump control to Pressure mode?

Answer 29

Post-trip, the steam dumps will be in Rx trip Tavg mode, controlling Tavg to 557F. Accurate indication of Tavg depends on forced flow in the RCS; therefore, if RCPs trip, accurate Tavg indication will be lost. Switching to Pressure mode for the steam dumps will allow for more accurate temperature control in that condition.

Question 30

What is the purpose of the preemptive action to stop RCPs for failed-open pressurizer spray valve?

Answer 30

If a PZR spray valve is stuck open, RCS pressure will continue to decrease post-trip to the point where SI will be initiated. In order to prevent an unnecessary SI, the RCPs supplying the spray and surge lines for the impacted spray valve (either loops 1 and 4 or 2 and 4) should be tripped to slow spray flow.

Question 31

List all control functions produced by Tavg and dT.

Answer 31

Auctioneered Hi Tavg; Rod Control, PZR Level Control, Steam Dumps, RIL
Auctioneered Hi dT; RIL

Question 32

What are critical safety functions?

Answer 32

Subcriticality (S)
Core Cooling (C)
Heat Sink (H)
Integrity (P)
Containment (Z)
Inventory (I)

Question 33

What 5 things are verified by the RO to determine if SI is not required?

Answer 33

SL pressure greater than 615
Subcooling greater than 30
CTMT pressure less than 3.5
PZR level greater than 4% level
PZR pressure greater than 1849

Question 34

What are indications of being at the Point of Adding Heat?

Answer 34

Steam dumps opening, Tavg changing, PZR Level, SUR begins decreasing

Question 35

What 3 things are verified by the RO to determine if the reactor is tripped?

Answer 35

All DRPI lights on bottom
Rx trip breakers open
Power on IR dectectors decreasing