KB_OAT_Safety_Parameters.txt

Purpose

The KB_OAT_Safety_Parameters.txt input file supports calculation of the System Criticality Performance Influencing Factor (PIF). This PIF represents the operator's perception of the level of degradation of key safety functions. It is loosely based on the Safety Parameter Display System (SPDS) used in U.S. nuclear plant control rooms.

The value of the System Criticality PIF corresponds to the aggregate deviation of key safety parameters from their nominal values. Typical parameters include:

• Reactor coolant system subcooling margin
• Wide range steam generator water levels
• Pressurizer water level
• Reactor vessel water level

The contribution from each parameter to the overall PIF is the Parameter Criticality (PIF_ParameterCriticality). Given a set of high and low threshold limits, the parameter criticality corresponds to the magnitude of the parameter's deviation from a nominal "safe" condition (see Figure 16 in the manual).

PIF_SystemCriticality Formula

The overall System Criticality PIF is based on a normalized weighted sum of the individual parameter criticality values (Equation 3):

PIF_SystemCriticality = SUM(omega_i * PIF_ParameterCriticality_i) / SUM(omega_i)

Where omega_i is the weighting factor for parameter i. A higher value of the System Criticality PIF indicates a more adverse overall plant condition. The rate of change of the PIF value indicates whether overall plant health is improving or worsening.

Parameter criticality behavior at the threshold limits:

Condition	PIF_ParameterCriticality
Parameter value < lo_lo_level	10.0 (maximum)
Parameter value between lo_lo_level and lo_level	Linear interpolation between 10.0 and 0.0
Parameter value between lo_level and hi_level	0.0 (nominal safe range)
Parameter value between hi_level and hi_hi_level	Linear interpolation between 0.0 and 10.0
Parameter value > hi_hi_level	10.0 (maximum)

Figure 16 Reference

Figure 16 in the ADS-IDAC manual ("Parameter Criticality PIF") graphically illustrates this piecewise-linear relationship. Both high and low deviations from the nominal safe state contribute to the PIF value.

Input File Format

SPDS_Input number_of_parameters
Time_Lapse time_lapse
SPDS_parameter_1 parameter_name_1
lo_lo_level_1
lo_level_1 hi_level_1 hi_hi_level_1
weighting_factor_1

.
.
SPDS_parameter_n parameter_name_n
lo_lo_level_n
lo_level_n hi_level_n hi_hi_level_n
weighting_factor_n

Global Parameters

Parameter	Type	Description	Example Value
number_of_parameters	Integer	Number of SPDS safety parameters. Range: ≥ 0. If 0, no further data should be entered.	6
time_lapse	Double	Time interval (seconds) between successive safety parameter PIF updates. Must not be set less than the scan period in KB_OAT_Scanned_Parameters.txt.	1.0

Per-Parameter Fields

Parameter	Type	Description	Example Value
SPDS_parameter	String	Unique identifying name for the safety parameter. Recommended prefix: SPDS_. No spaces; use _.	SPDS_PZR_Level
parameter_name	String	Must match a control panel parameter in ControlPanel.txt. The indicator used to calculate the individual PIF value. No spaces; use _.	PZR_Level
lo_lo_level	Double	Lower low level limit. If the parameter falls below this value, the parameter PIF is set to 10.0.	0.10
lo_level	Double	Upper low level limit. Parameter values between lo_level and hi_level yield a PIF of 0.0. Values between lo_lo_level and lo_level are linearly interpolated.	0.40
hi_level	Double	Lower high level limit. Values between lo_level and hi_level yield a PIF of 0.0. Values between hi_level and hi_hi_level are linearly interpolated.	0.70
hi_hi_level	Double	Upper high level limit. If the parameter exceeds this value, the parameter PIF is set to 10.0.	0.95
weighting_factor	Double	Individual weight for the parameter in the normalized sum. Recommended range: 0.0–1.0. Only the relative ratios between weights matter due to normalization.	0.75

Weighting Factor Normalization

Because the aggregation formula normalizes by the sum of all weighting factors, only the relative ratios among the weighting_factor values affect the result. Setting values in the range 0.0–1.0 is recommended for readability, but any consistent scaling may be used.

Sample Input

The following example defines six SPDS parameters. Only the first three are shown in full in the manual sample.

SPDS_Input 6
Time_Lapse
1.0
SPDS_Min_Sub_Cooling
Min_Sub_Cooling
5.0
25.0 75.0 100.0
1.0
SPDS_SG_A_WR_Level
SG_A_WR_Level
0.10 0.60 0.85 0.99
0.5
SPDS_PZR_Level
PZR_Level
0.10 0.40 0.70 0.95
0.75

Worked Calculation

Given the three parameters above, with:

• Subcooling margin = 10 °F
• SG A wide range level = 0.05
• Pressurizer level = 0.55

Individual parameter PIF values:

PIF_subcooling      = 10.0 × (25.0 − 10.0) / (25.0 − 5.0)  = 7.5
PIF_SG_A_WR_Level   = 10.0   (below lo_lo_level of 0.10)
PIF_PZR_Level       = 0.0    (within nominal range 0.40–0.70)

Overall System Criticality PIF:

PIF_SystemCriticality = [(1.0 × 7.5) + (0.5 × 10.0) + (0.75 × 0.0)] / (1.0 + 0.5 + 0.75)
                      = 12.5 / 2.25
                      = 5.56

In this configuration, subcooling margin is the dominant safety parameter. SG A wide range level is assigned half the weight of subcooling margin, and pressurizer level is assigned 25% less weight than subcooling margin.