Decision-Making Process: Action Taker (OAT)
This page describes Figure 3 of the ADS-IDAC manual: the Decision-Making Process for the Action Taker (OAT). The decision-making process immediately follows information processing. During this process, the OAT evaluates the current goal and strategy, identifies actions in accordance with the selected problem-solving strategy, and implements memorized mental procedures.
Figure 3 from original manual: "Decision-Making Process (Action Taker)"
Key Characteristics of the Action Taker
OAT vs. ODM Capabilities
The Action Taker (OAT) is the only crew member permitted to directly manipulate reactor plant controls. However, unlike the Decision Maker (ODM), the OAT does not have knowledge-based reasoning capability. The OAT cannot perform the "Knowledge-Based Reasoning" strategy; that strategy is exclusive to the ODM. The OAT's strategies are limited to:
- Wait and Monitor — passive information gathering and mental procedure execution
- Follow Instruction — execution of actions ordered by the Decision Maker
The OAT relies on the ODM to identify corrective actions through knowledge-based diagnosis; the ODM then issues those actions to the OAT as ordered activities via the blackboard.
Flowchart
Block Descriptions
Block 1 — Start Decision-Making Process
The decision-making process immediately follows information processing. During this process, the operator:
- Evaluates the current goal and strategy
- Identifies actions in accordance with the selected problem-solving strategy
- Implements memorized mental procedures
Block 2 — Abnormal Signal Detected?
An abnormal signal indicates a condition incompatible with continued power operation. Either of two conditions triggers this detection:
- Activation of the
Reactor_Trippedmental belief (seeKB_OAT(ODM)_HardWired_Diagnosis.txt) - The fuzzy logic diagnostic engine accident relationship value exceeding a preset threshold (see
Action_Taker.txtandKB_OAT_Event_Matrix.txt)
Detection of an abnormal condition shifts the control room crew into an accident response mode that can lead (depending on operator preferences and tendencies in Action_Taker.txt and Decision_Maker.txt) to implementation of the emergency operating procedures.
Block 3 — Interrupt Low Priority Mental Procedures
Certain memorized mental procedures are incompatible with a post-trip reactor plant condition and are permanently suspended once an abnormal condition is detected. For example, a mental procedure to reduce turbine load is no longer appropriate once the reactor and turbine have tripped.
One-Time Interruption
The interruption of low-priority mental procedures can occur only once during a simulation. Once the abnormal signal has been detected, newly identified low-priority mental procedures can still be added to the operator queue and implemented.
The low-priority procedure threshold is specified in the Action_Taker.txt input file. Priority levels for mental procedures are defined in KB_OAT_HardWired_Diagnosis.txt (lower priority values indicate higher priority procedures).
Block 4 — Pause Activity Flag Active?
Each operator has two separate Boolean pause activity flags:
| Pause Flag | Suspends |
|---|---|
| Mental procedure flag | Activities associated with mental procedure execution |
| General activity flag | All other operator activities |
An active pause flag (set to true) indicates the operator is already performing an activity. Further decision-making activities are bypassed until the flag is cleared during a subsequent information processing step.
Block 5 — Ordered Activity in Queue?
If the Decision Maker has assigned an ordered activity to the Action Taker, execution of memorized mental procedures is bypassed. This allows actions ordered by the Decision Maker to take priority over memorized actions self-identified by the Action Taker.
Block 6 — Mental Procedure in Queue?
If there are no waiting ordered activities, the mental procedure queue is checked. Additionally, a check is made to ensure the Decision Maker is not simultaneously performing the same mental procedure (because two operators cannot perform the same procedure step at the same time).
If a waiting mental procedure exists (and is not being performed by a different operator), execution of the mental procedure takes priority over goal and strategy selection.
Block 7 — Perform Mental Procedure Step
The operator executes the mental procedure actions.
Block 8 — New Branch Generated?
Some mental procedure actions require interaction with the reactor plant or crew coordination (e.g., checking equipment status, manipulating a control, verifying a parameter value). These tasks require time to complete, so further decision-making is suspended until they are done.
Branches vs. DDET Branching Events
A branch is a discrete event or information chunk created during a simulation sequence. Most branches do not cause multiple accident sequences to be generated. A DDET branching event (i.e., sequence splitting) only occurs when two or more branches of the same type are generated in a single time step.
Block 9 — Activate Pause Activity Flag
If a new branch is generated, the appropriate pause activity flag is set to true. Further decision-making is suspended until the flag is reset during later information processing. This models the time required to perform tasks and prevents overloading the operator with multiple simultaneous tasks.
Block 10 — Evaluate Goal
The Action Taker's high-level goal is compared to the Decision Maker's goal. If the two goals do not match, the Action Taker's goal is updated to mirror the Decision Maker's goal.
Action Taker Goal Selection
A separate Goal Selection flowchart (Figure 5) is provided only for the Decision Maker. The Action Taker does not perform independent goal selection — it simply mirrors the ODM's current goal.
Block 11 — New Goal Selected?
If the goal evaluation indicates the current goal must change, further decision-making is suspended and the goal is updated.
Block 16 — Activate Pause Activity Flag (Goal Update)
If the goal is to be updated, a new goal branch is generated and the pause activity flag is activated to prevent further decision-making. When the new goal is perceived during subsequent information processing, the pause flag is cleared and decision-making resumes.
Block 12 — Evaluate Strategy
The appropriateness of the current problem-solving strategy is evaluated. See the Strategy Selection Process (Action Taker) flowchart.
Block 13 — New Strategy Selected?
If the strategy evaluation indicates the current strategy must change, further decision-making is suspended and the strategy is updated.
Block 17 — Activate Pause Activity Flag (Strategy Update)
If the strategy is to be updated, a new strategy branch is generated and the pause activity flag is activated. When the new strategy is perceived during subsequent information processing, the pause flag is cleared and decision-making resumes.
Block 14 — Ordered Activity in Queue?
The ordered action queue is checked for activities previously ordered by the Decision Maker that are awaiting execution. The ordered action queue is a first-in, first-out (FIFO) queue — the oldest ordered action is performed first.
Block 18 — Perform Ordered Activity
If a previously ordered activity is found, the Action Taker performs the requested action.
Block 19 — New Branch Generated?
Execution of certain ordered actions requires generation of a new branch. Examples include actions associated with a time delay, or actions that require interaction with the control panel or another operator.
Block 20 — Activate Pause Activity Flag (Ordered Activity)
If the ordered activity generates a new branch, the pause activity flag is activated. When the operator receives confirmation from the control panel that the ordered action has been completed (during a subsequent information processing step), the pause flag is cleared and decision-making resumes.
Block 15 — End Decision-Making Process
The Action Taker's decision-making process is complete for this time step.