Overview

ADS-IDAC Overview

Dynamic PRA and Human Error Prediction

Situational context and event dynamics are important considerations when assessing the potential for human errors during nuclear power plant accidents. Static probabilistic risk assessment methods often cannot adequately capture the rich contextual information that influences operator behavior. Dynamic PRA methods address this by providing an explicit treatment of feedback arising from man-machine interactions.

ADS-IDAC is built on the recognition that operator error likelihood depends strongly on the evolving plant state. By coupling a thermalhydraulic plant model with an operations crew cognitive model, ADS-IDAC permits the dynamic simulation of operator performance throughout the full duration of an accident transient. A major goal of the ADS-IDAC project is the prediction of situational contexts that might lead to human error events, particularly knowledge-driven errors of commission — cases where operators take actions that worsen the plant state based on an incorrect situational assessment.

The Discrete Dynamic Event Tree

ADS-IDAC generates a discrete dynamic event tree (DDET) using simple branching rules. Each branch point represents a discrete decision, event, or performance variation, such as:

• whether an operator follows procedures immediately or first attempts knowledge-based reasoning,
• the time at which an operator executes a specific action,
• whether a hardware component fails on demand, and
• whether a procedure step is skipped.

A significant advantage of this approach is the ability to directly assess the impact of operator actions on key plant parameters. By simulating many DDET paths, ADS-IDAC can more realistically determine the safety significance of human errors than methods that treat operator performance independently of plant dynamics.

Coupling with RELAP5

The thermalhydraulic component of ADS-IDAC is based on the RELAP5 thermal hydraulic code. RELAP5 provides the plant model simulation — tracking reactor coolant system conditions, safety system actuations, and mitigating system responses. The ADS-IDAC cognitive model receives plant parameter values from RELAP5 at each time step and, in turn, feeds operator actions (valve positions, pump states, etc.) back into the RELAP5 simulation.

Programming Languages

ADS-IDAC is written in two main programming languages. The RELAP5 thermal hydraulic code and related interface infrastructure are written in Fortran. The remainder of the ADS-IDAC code — including the cognitive model and simulation scheduler — is written in C++.

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Input Manual Description

This manual is the reference document for analysts using the ADS-IDAC simulation code. It provides a general overview of major modeling elements contained in ADS-IDAC, but this overview does not replace the detailed information available in the technical references listed in Section 6.

Manual Organization

Section	Title	Contents
1	Introduction	General overview of ADS-IDAC modeling elements; simplified process flowcharts for key cognitive processes; general user notes
2	General Modeling Guidance	Guidance for modeling potential error events and sources of crew-to-crew variability; guidance for developing a RELAP5 reactor plant model suitable for use with ADS-IDAC
3	ADS-IDAC File Structure	Overview of the data files that support ADS-IDAC execution; detailed description of code output files
4	Input File Format	Detailed guidance on content and format of all input files required to run ADS-IDAC; for each file: purpose, file format, input option descriptions, and a sample input
5	Term Conversions	Complete listing of integer term conversions relating descriptive variable names to integer code values (range 3000–3165)
6	References	Comprehensive reference list for background information and detailed model documentation

Section 5: Term Conversions

The ADS-IDAC source code uses a set of integer constants to identify key data attributes. For example, the Decision Making Operator has the integer value 3043. This coding scheme allows key data descriptors to be represented as a single integer while still permitting meaningful names in the source code.

The constants are defined in src/ADSIDAC/Global/SimConstants.h as enum class types and sim:: namespace constants (for example sim::Operator::ODM). The 2009 manual writes the same constants as names that begin with the letter V (for example VODM); the Term Conversions page lists both. Several input files require the user to enter the integer value; the input file descriptions in Section 4 identify the allowable integer values in each case.

Use Integers, Not Variable Names

When an input file requires a term conversion code, you must enter the integer value (e.g., 3043), not the variable name (e.g., VODM). Entering the variable name as a string will cause an input processing error.

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Naming Conventions

The following conventions are used throughout this manual to improve consistency and readability.

Document Notation

Notation	Meaning
Bold italics	An input variable that must be provided by the analyst. The detailed input description for each file specifies the data type (integer, double, or string), the allowable data range, and other options.
"quoted name"	An input file name.
[bracketed item]	An optional or conditional input parameter. These are only required when the associated input option has been selected; the input file descriptions provide additional detail.
. (three dot lines following an example)	Indicates that multiple data entries of the same type are permitted in the input file. The sample provided is representative only.

Input Variable Data Types

Data Type	Description	Example
double	Real-valued numbers	3.14, 0.001
integer	Integer numbers	1, 0, -12
string	Word comprised of character elements	Reactor_Trip

File Name Prefixes

ADS-IDAC uses a structured file naming scheme. The prefixes below are used consistently across all input files.

Crew Member Prefixes

ADS-IDAC models two active crew members. Input files are differentiated by a crew member prefix embedded in the file name:

Prefix	Crew Role	Represents
OAT	Action Taker	Reactor Operator
ODM	Decision Maker	Shift Supervisor / Senior Reactor Operator

A third role, the Consultant (OCT, e.g. Shift Technical Advisor), is defined in the IDAC architecture and present in the code and input layout (Input/Crew/Consultant/), but no Consultant operator is instantiated in current simulations: the role's input file is not read at runtime. Keep the directory in place.

For example: KB_ODM_Event_Matrix.txt is the event matrix for the Decision Maker, while KB_OAT_Event_Matrix.txt is the corresponding file for the Action Taker.

File Category Prefixes

Prefix	Applies To	Description
KB_	File names	Files associated with the operator knowledge base
ZProcedure_	File names	Files describing the content of individual procedure steps
ZProcedure_MPBG_	File names	Mental procedure files (belief-generated; see General Note 4)
ZProcedure_FRG_	File names	Functional recovery guideline files (trigger a temporary procedure transfer)

Control and Alarm Naming

Prefix	Applies To	Description
X_	Control variable names	Controls that can be manipulated by the operators. This convention is consistent with customary PRA practice.
A_	Alarm names	Alarm identifiers. This convention is recommended but not mandatory; its use improves readability of the input files.

String Formatting

All strings entered in ADS-IDAC input files must be entered without spaces. Use the underscore character (_) to separate words where needed. For example, Reactor Trip must be entered as Reactor_Trip. The only exception is when the string is enclosed in quotation marks. Refer to General Note 2 for full details.