Goal Selection Process: Decision Maker (ODM)
This page describes Figure 5 of the ADS-IDAC manual: the Goal Selection Process for the Decision Maker. During each simulation time step, the Decision Maker (ODM) re-evaluates its high-level goal based on perceived plant information and operator performance influencing factors (PIFs).
Figure 5 from original manual: "Goal Selection Process (Decision Maker)"
Overview
Action Taker Goal Selection
A separate goal selection flowchart is provided only for the Decision Maker. The Action Taker does not perform independent goal selection. The OAT simply compares its current goal to the ODM's goal and initiates a goal update if they differ. See Block 10 of the Decision-Making Process (Action Taker).
The four high-level goals in ADS-IDAC, in order of escalating response level, are:
| Goal | Identifier | Description |
|---|---|---|
| Normal Operation | VGNOP | Plant is in a normal full-power operating state |
| Troubleshooting | VGTS | Plant deviates from normal but no reactor trip has been detected |
| Maintain Global Safety Margin | VGMGSM | Reactor has tripped; emergency procedures are initiated |
| Monitoring | VGMON | Plant is off-normal but no specific abnormal condition has been diagnosed |
Flowchart
Block Descriptions
Block 1 — Start (Dead-Time Gate)
Small errors in the RELAP input deck initial conditions may cause minor plant transients not indicative of an actual abnormal condition. These transients can actuate spurious alarms or other abnormal indications but usually decay within the first several minutes of a simulation run.
To prevent these artificial perturbations from influencing operator decision-making, goal selection is blocked for a dead-time of 60 seconds after the start of the simulation (hard-coded as dead_time in OperatorDM.cpp), allowing the RELAP thermal-hydraulic model to reach a steady-state condition.
Block 2 — Key Parameters in Expected State? (Normal Operation Mental Belief)
The operator knowledge base includes a "Normal Operation" mental belief that describes the plant parameters associated with a normal full-power operating condition. A typical description for a pressurized water reactor includes:
- Reactor Coolant System Temperature
- Reactor Coolant System Pressure
- Pressurizer Level
- Steam Generator Water Levels
The analyst specifies the expected values (and trends, if applicable) for these parameters. A threshold parameter establishes how many specified conditions must be satisfied for the operator to conclude the plant is in a normal operating state. If a sufficient number of conditions are satisfied, the Normal Operation mental belief is activated (or maintained).
Block 3 — Goal: Normal Operation (VGNOP)
If the Normal Operation mental belief is active, the goal is set to Normal Operation. This goal drives the following operator behaviors:
- Passive information gathering
- Control panel scanning
- Rule-based memorized mental procedures
Blocked Activities under Normal Operation
Knowledge-based problem solving and procedure following strategies are blocked when the goal is Normal Operation.
Block 4 — PIF: Enable Troubleshooting?
The operator profile includes a static Performance Influencing Factor (PIF) that reflects the operator's tendency to delay initiation of the emergency operating procedures in order to troubleshoot the perceived abnormal condition. This PIF is set in the range 0.0–1.0:
| PIF Value | Effect |
|---|---|
0.0 | Troubleshooting is blocked; operator proceeds directly to Monitoring goal |
1.0 | Troubleshooting is always enabled; Monitoring goal is blocked |
0.0 < PIF < 1.0 | A branching point is generated to simulate either option; branching probability equals the PIF value |
Block 5 — Goal: Monitoring (VGMON)
The Monitoring goal is entered when the operator perceives the plant is no longer in a normal operating state but a specific abnormal condition has not yet been detected. This goal serves two main functions:
- Enables later activation of the Maintain Global Safety Margin goal
- Permits active and passive information gathering to diagnose the abnormal condition
Should plant parameters return to normal values, the operator may return to the Normal Operation goal.
Block 6 — Abnormal Condition Detected?
Based on perceived information, the operator's fuzzy logic diagnostic engine generates a spectrum of possible abnormal and emergency conditions. When the membership values from the diagnosis process exceed a predetermined threshold (set in the operator profile), the operator concludes an abnormal condition has occurred.
In addition to the diagnostic engine output, detection of a reactor trip condition also activates an abnormal condition operator belief.
Block 7 — Goal: Troubleshooting (VGTS)
Activation of the Troubleshooting goal enables the knowledge-based "Knowledge-Based Problem Solving" strategy. Should the reactor plant return to a normal operating state, the operator may return to the Normal Operation goal.
Diagnostic Engine Suspended at VGTS
Once the Troubleshooting goal is activated, the fuzzy logic diagnostic engine no longer influences operator behavior. Only two conditions can cause a transition away from the Troubleshooting goal:
- Restoration of normal plant operation
- A reactor shutdown (triggering transition to VGMGSM)
Block 8 — PIF: Enable Procedure Usage?
The operator profile includes a static PIF factor that reflects the operator's tendency to transition from knowledge-based reasoning to the written procedure following strategy. This PIF ranges from 0.0 to 1.0:
| PIF Value | Effect |
|---|---|
0.0 | Transition to procedure following is blocked; operator continues troubleshooting strategy |
1.0 | Once reactor trip is perceived, troubleshooting is abandoned in favor of written procedures |
0.0 < PIF < 1.0 | A branching point is generated; branching probability equals the enable procedure usage PIF value |
Block 9 — Goal: Maintain Global Safety Margin (VGMGSM)
Activation of the Maintain Global Safety Margin goal:
- Blocks further implementation of knowledge-based actions (if Troubleshooting was previously active)
- Allows execution of the "Follow Written Procedure" problem-solving strategy
Terminal Goal State
Once the Maintain Global Safety Margin goal is activated, transitions to other goal states are prohibited. The operator may not return to the Normal Operation, Monitoring, or Troubleshooting goals.
Block 10 — Reactor Trip?
Prior to activating the Maintain Global Safety Margin goal, the process verifies that a reactor trip has actually been perceived. If a reactor trip has been detected, the operator transitions to the VGMGSM goal. If not, the operator remains in the Troubleshooting goal.
Goal Transition Summary
Relationship Between Goals and Problem-Solving Strategies
| Goal | Passive Info Gathering & Panel Scanning | Skill-Based Memorized Actions | Written Procedure Following | Knowledge-Based Problem Solving |
|---|---|---|---|---|
| Normal Operation (VGNOP) | Yes | Yes | No | No |
| Monitoring (VGMON) | Yes | Yes | No | No |
| Troubleshooting (VGTS) | Yes | Yes | No | Yes |
| Maintain Global Safety Margin (VGMGSM) | Yes | Yes | Yes | No |