KB_OAT_Time_Constrained_Input.txt

Purpose

The KB_OAT_Time_Constrained_Input.txt input file defines the Time Constraint Load PIF for the operator. This PIF represents the time pressure experienced by the operator when key plant parameters are approaching critical threshold values.

Two threshold levels are used for each monitored parameter:

• Normal operation threshold — applied when the operator's high-level goal is maintaining normal operation or troubleshooting an abnormal condition.
• Accident threshold — applied when the operator switches to the goal of mitigating an accident condition.

This dual-threshold approach captures the operator's changing sensitivity to key parameters depending on perceived plant condition. For example:

• During normal operation with a decreasing steam generator level, the operator focuses on the time available until the reactor trip setpoint is reached (normal threshold).
• After reactor trip, the operator's focus shifts to maintaining adequate decay heat removal from the steam generator; a much lower level may suffice (accident threshold).

The Time Constraint Load PIF is based on perceived information rather than direct thermal-hydraulic model data. Perceived data may differ from actual values due to scan time lags and perception filter distortion.

PIF Calculation Equations

Step 1: Time Available Until Threshold (Equation 5)

t_i,available = (P_i - P_i,Threshold) / dP_i/dt

Where:

• P_i — current perceived value of parameter i
• P_i,Threshold — applicable threshold value (normal or accident, depending on crew goal)
• dP_i/dt — perceived rate of change of parameter i

Step 2: PIF Value from Time Available (Equation 6)

PIF_TimeConstraint,i = 10 × [1 - (t_min,i - t_Lower) / (t_Upper - t_Lower)]

• If t_min,i > t_Upper: PIF = 0 (no time pressure)
• If t_min,i < t_Lower: PIF = 10 (maximum time pressure, saturated)

Where t_Lower and t_Upper are the tuning constants Lower_Threshold and Upper_Threshold respectively (in minutes).

Step 3: Buildup Lag Filter (Equation 7)

Before the parameter crosses the accident threshold, the PIF update is passed through a buildup lag filter to model the gradual onset of time-pressure stress:

PIF_TCL,Updated = PIF_TCL,Old + (PIF_TCL,New - PIF_TCL,Old) × (t_lapse / tau_buildup)

Where:

• PIF_TCL,Old — last updated PIF value
• PIF_TCL,New — unfiltered PIF value from Equation 6
• PIF_TCL,Updated — lag-filtered output
• t_lapse — update period in seconds (time_lapse)
• tau_buildup — buildup time constant in seconds (Buildup_Time_Constant)

Step 4: Decay After Accident Threshold is Crossed (Equation 8)

Once the parameter exceeds the accident threshold, the PIF decays according to:

PIF_TCL,Updated = 10 × (1 - exp(-(t_current - t_threshold) / tau_decay))

Where:

• t_current — current simulation time
• t_threshold — time at which the parameter exceeded the accident threshold
• tau_decay — decay time constant (Decay_Time_Constant)

The overall Time Constraint Load PIF for the operator is the maximum of all individual parameter PIF values (i.e., the most limiting parameter governs).

Input File Format

Num_of_Time_Constrained_Parameters   number_of_parameters
Time_Lapse_For_Update                time_lapse
Lower_Threshold_(minutes)            lower_threshold
Upper_Threshold_(minutes)            upper_threshold
Decay_Time_Constant_(sec)            decay_time_constant
Buildup_Time_Constant_(time_steps)   buildup_time_constant

time_constrained_parameter_1         parameter_name_1
nominal_value_1
normal_threshold_1                   accident_threshold_1
.
time_constrained_parameter_n         parameter_name_n
nominal_value_n
normal_threshold_n                   accident_threshold_n

Global Parameters

Parameter	Type	Description	Example Value
number_of_parameters	Integer	Number of time-constrained parameters. Must match the count of entries in the file. Range: > 0.	3
time_lapse	Double	Time increment (seconds) between successive updates of time-constrained parameter values. Updates use the operator's currently memorized perceived value. Range: > 0.0.	30.0
lower_threshold	Double	Lower time threshold (minutes). If the time to reach the applicable threshold is less than this value, the parameter PIF is set to 10.0. Range: > 0.	5.0
upper_threshold	Double	Upper time threshold (minutes). If the time to reach the applicable threshold exceeds this value, the parameter PIF is set to 0.0. Range: > 0.	25.0
decay_time_constant	Double	Decay time constant (seconds) applied to the PIF once a parameter exceeds the accident threshold (τ_decay in Equation 8). Range: > 0.	100.0
buildup_time_constant	Double	Buildup time constant (time steps) applied to PIF buildup before the accident threshold is reached (τ_buildup in Equation 7). Range: > 0.	50.0

Per-Parameter Fields

Parameter	Type	Description	Example Value
time_constrained_parameter	String	Descriptive name for the time-constrained parameter. No spaces; use _. Recommended prefix: TCL_.	TCL_PZR_Pressure
parameter_name	String	Must match a parameter in ControlPanel.txt. The monitored control panel indicator.	PZR_Pressure
nominal_value	Double	Nominal value for the parameter. Used to determine whether the parameter is trending toward the threshold from above or below.	2250.0
normal_threshold	Double	Threshold value used during normal operation (crew goal is normal operation or troubleshooting with reactor at power).	2000.0
accident_threshold	Double	Threshold value used during emergency operation (crew goal is maintaining global safety margin or troubleshooting with reactor tripped).	750.0

Sample Input

Num_of_Time_Constrained_Parameters   3
Time_Lapse_For_Update                30.0
Lower_Threshold_(minutes)            5.0
Upper_Threshold_(minutes)            25.0
Decay_Time_Constant_(sec)            100.0
Buildup_Time_Constant_(time_steps)   50.0

TCL_PZR_Pressure
PZR_Pressure
2250.
2000.   750.

TCL_PZR_Level
PZR_Level
0.50
.20    .10

TCL_SG_A_NR_Level
SG_A_NR_Level
0.44
.25    .10

Sample Explanation

Three parameters are monitored for time constraint loading:

TCL_PZR_Pressure (Pressurizer Pressure)

• Nominal: 2250 psia
• Normal threshold: 2000 psia — just above the reactor trip setpoint
• Accident threshold: 750 psia — just above the pressure at which safety injection accumulators passively inject cooling water

TCL_PZR_Level (Pressurizer Level)

• Nominal: 0.50 (50% water level)
• Normal threshold: 20% — just below the lower end of the controller range
• Accident threshold: 10% — crew should initiate safety injection at approximately 12%

TCL_SG_A_NR_Level (Steam Generator A Narrow Range Level)

• Nominal: 0.44 (44%)
• Normal threshold: 25% — just below the lower end of the normal controller range
• Accident threshold: 10% — minimum level required for the SG to be credited as a heat sink

Parameter values are updated every 30 seconds. If the time to reach any threshold is less than 5 minutes, the PIF is set to 10.0 (lower_threshold). If the time to reach any threshold exceeds 25 minutes, the PIF is set to 0 (upper_threshold).