Presentation Transcript
PRA and CAFTA Training : PRA and CAFTA Training Objectives
Review basic PRA concepts
Review CAFTA components and functionality
Create a complete fault tree
What is PRA? : What is PRA? Probabilistic Risk Assessment (PRA) is an organized method of determining the likelihood that combinations of events lead to an unacceptable situation.
Risk is defined as the product of expected frequency of occurrence and anticipated consequence for an accident or activity.
PRA can be used to ensure cost effective, safe operation/use of facilities.
PRA is also used to allocate limited resources among competing needs.
What is a Fault Tree : What is a Fault Tree Fault Tree model
Models component / support system interdependencies. Used to generate minimal cutsets.
Provides for a logical display of intra-system interactions and component interrelationships
Describes ways system can fail
Uses AND, OR and other gate types
Can be linked together to explicitly model design dependencies
Includes Common cause failures and operator errors
Developing Fault Trees : Developing Fault Trees Development of System Fault Trees
Basic Logic of Fault Tree Models
Component Failure Characteristics
Testing and Maintenance
Human Errors
Dependent Failures
PRA Terms : PRA Terms Top Event Frequency is the estimated likelihood of the top event, per year.
Top Event Frequency is expressed in units of: “expected events per year”
A basic event is the lowest level in a fault tree
Cutsets are the minimum combination of basic events required to occur in order to cause the top event. When sorted by probability, cutsets reveal most likely sequences of events, leading to a better understanding of vulnerabilities.
CAFTA : CAFTA
CAFTA is:
Database Editor
Fault Tree Editor
Cutset Editor
CAFTA Topics :
Software Overview
Reliability Database Editor
Fault Tree Editor
Model Quantification
Cutset Editor
General Information
Case Study
CAFTA Topics
CAFTA For Windows : CAFTA For Windows Software Overview
CAFTA For Windows : CAFTA For Windows Four Steps to Construct System Model
Define Fault Tree Logic
Build Reliability Database
Evaluate Fault Tree to Obtain Cutsets
Review and Analyze Cutset Results
CAFTA For Windows : CAFTA For Windows Fault Tree Model and Databases
Database Editor-- RDED : CAFTA Database Structures
Basic Event database
Failure Rate (Type Code) database
Gate database
Three databases work together to define the attributes of all events
Database Editor-- RDED
BE Naming Conventions : Basic Event Naming Conventions:
(Example) BE Naming Conventions
Calculation Formulas : Calculation Formulas Calculation Formulas
Fault Tree Editor-- FTED : Movement Commands Fault Tree Editor-- FTED
Navigating Through a Fault Tree : Navigation
by Dragging Gates
by searching Parents of a event/gate
by viewing Top events
Find Gate/Event by FIND menu function
Jump to the Gate/Event if found
View and Select Fault Tree Tops
Navigating Through a Fault Tree
Gate Types : Gate and Basic Event Types ---Text Form
Gate Types
Fault Tree Editor-- FTED : Gate and Basic Event Types ---Graphic Form
Fault Tree Editor-- FTED
Fault Tree Editor-- FTED : Examples: Combination gate:
G COM3 A B C D
Indicates a 3-out-4 combination gate, while
F COM3 A B C D E
Indicates a 3-out-5 combination gate
Fault Tree Editor-- FTED
Example : Example System B Failure is the top event in the fault tree.
Valve failure and Operator failure are basic events. A cutset can consist of a single basic event.
Pump failure occurs if Test & Maintenance make it unavailable OR if it fails to start OR if it fails to run.
There are five possible combinations of these failures, or cutsets, that can lead to system B failing.
Failure of System B results in the accident sequences TAB SAFE or TAB FAIL.
Example
Fault Tree Editor-- FTED : FTED Editing Features
Loading Existing Fault Tree File
Connect to Different Databases
Editing Database Records
Text and Graphical Input
Extract Subtree
Delete event locally and/or globally
Changing Gate Type
Prune Gate: Gate -> Event
Merging Files
Drag-Drop Editing
“Undo” to reverse the previous editing
Fault Tree Editor-- FTED
Fault Tree Editor-- FTED : FTED Logic Modeling Features
Circular Logic Checking
A AND B C D
B OR E F G
G OR X A Z
Compressing Equivalence and True/False Values: to make fault tree size smaller
Prune Modules: Change all Modules to basic events;
Module = Independent Subtree
Fault Tree Editor-- FTED
Fault Tree Editor-- FTED : FTED Logic Modeling Features
Check Gate Independence
To produce list of events which prevent the gate from being independent
Check Module Independence
To produce list of events which prevent the module from being independent
Define physical and logical links Fault Tree Editor-- FTED
Model Evaluation : Model Evaluation: Quantification Process Model Evaluation
Quantification : Quantification Setup:
Quantification
Quantification : Four Parameters need to be set for Quantification:
Quantification Method: Cutset generation or gate probability calculation; or other user-defined quantification
Truncation Probability: decide how many cutsets are generated and how long it takes to generate
Truncation order: remove any cutsets which has higher order than specified
Module Operation: this is additional processing option, if any module exists.
Quantification
Fault Tree Editor-- FTED : Options of Module Operations:
Expand Module: module cutsets are included in the final cutsets of the fault tree top
Prune Modules: Module is declared as a basic event and its probability is used rather than module cutsets
Only Module: cutset generation is for all modules, rather than for all tops of the fault tree.
Fault Tree Editor-- FTED
Printing : Printing Fault Trees
Use Properties -> Group Pages menu function to turn on/off of group of page
Printing
Printing : Printing Fault Trees
Use Properties->Auto Page Breaks menu function to decide appearance of each page
Printing
Cutset Editor-- CSED : CSED Provides Cutset Review Functions
Do the cutsets make any sense?
Are there single and double, and higher order cutsets?
What are the dominant cutsets?
What do you think should be the dominant cutsets?
What recovery actions should be added to some of cutsets?
Cutset Editor-- CSED
Cutset Editor-- CSED : Cutset Editor Screen:
Class Name: enabled by the display option
Top Event and Probability
Cutset Properties: (In different font and colors)
Generated : original
Deleted: not counted for module probability
Added: added by user; not generated
Recovery : added by user
Cutset Editor-- CSED
Cutset Editor-- CSED : Cutset Editor Screen:
Cutset Properties: (In different font and colors)
True: prob. = 1
False: Prob. = 0
Subsumed: no longer contribute to top probability
Truncated: cutset probability below the cutoff
Delete-term: cutset not count to top probability
Cutset Editor-- CSED
Cutset Editor-- CSED : Reporting Cutsets Results Cutset Editor-- CSED
CAFTA Files : CAFTA Files
.CAF - Fault Tree Files
.RR - Basic Event Database, Gate Description Data, Failure Rate (Type Code) Database
.CUT - Cutset File
.RAW - Temporary output from cutset generator
.FTP - Temporary input to cutset generator
CAFTA Files
CAFTA Data Flow : CAFTA Data Flow: CAFTA Data Flow
Advanced Features : Fault Tree Editor
Drag a .caf file from explorer and drop it in FTED will open the file in the FTED window
Copy and Paste a gate logic between different fault tree files
Drag&Drop gate logic between different fault tree files
Could open many windows to view different parts of one fault tree file
Ctrl+DlbClick between events(gates) will automatically add new event to the gate logic
Advanced Features
Advanced Features : Fault Tree Editor
Can set some event as Flag and use the event string in sequence quantification
Seven types of links to other PSA project files, and go to those file directly from FTED
Can load different formats of fault tree files, as long as filters for those files are supplied and specified in the CAFTA configuration
Advanced Features
Begin Using FTED : Begin Using FTED
Begin Using FTED : Begin Using FTED Choose a standard template and standard Access database.
Name your database. The database will have an extension .rr It will contain a basic event table, a gate table, and type code table.FTED will display one basic event as shown below.
Input Fault Tree Logic : Input Fault Tree Logic Next, Click and hold the left mouse button on the basic event symbol (the circle). A palette of gate types will pop up, as shown below As you drag the cursor across each button in the pallette, the gate type label will appear in the lower left of your screen (on the status line). Choose the “OR” gate symbol
Input Fault Tree Logic : Input Fault Tree Logic This will put two basic events below the new “OR” gate.
Input Fault Tree Logic : Input Fault Tree Logic While the top gate is highlighted (surrounded by a dashed box), choose Edit and then Add Event to place the third event under this gate
Input Fault Tree Logic : Input Fault Tree Logic Fault tree logic may also be entered using the following input methods:
In the toolbar click on the yellow down arrow key (with plus sign) to convert an event to a gate
Press the Ctrl key and double click between two existing gates (be careful not to click in a description box).
A quick way to add a large number of gates is to use the Edit, Input option.
After events are added, they can also be changed to gates by clicking on basic event circle to pull down the palette of gates and events.
Input Event Data : Input Event Data Double click on a basic event to enter event data
Input Event Data : Input Event Data Select the appropriate calculation method
Merging Two Fault Trees : Merging Two Fault Trees If two fault trees share the same database (*.rr), then merging the two fault trees will include all of the basic event, gate, and type code data.
If you are merging two fault trees with separate databases, then you must open the database editor and import the basic event, gate and type code data for the second tree.
Merging two fault trees : Merging two fault trees Open tree1.rr
Select File, Import
In the file name box type “*.rr” this will show you all files with the extension .rr
Merging two fault trees : Merging two fault trees Find the database for the second tree and click ok. This will allow you to choose field within that database to import.
Merging two fault trees : Merging two fault trees Select the double arrows to import all fields.
Click Ok
To import Gate data, select Window, GATE DATA. Repeat the import process for the gate data
To import Type Code data, select Window, TYPECODE DATA. Repeat the import process for the type code data
Failure Modes : Failure Modes Example of failure modes:
Fail to Run
Fail to Start
Fail to Open
Transfers Open
Transfers Closed
Common Cause Failure
Operator Error
Test & Maintenance
Catch the
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