Reliability Engineering and System Safety 30 (1990) 313-322

PC Workstation-Based Level 1 PRA Code Package KIRAP

S. H. Han, T. W. Kim, K. S. Jeong & K. J. Yoo

Korea Advanced Energy Research Institute, Reactor Safety Department, PO Box 7, Daeduk-danji, Daejeon, Korea

A B S T R A C T

The fault tree construction and analysis code package KIRAP is developed, which includes a character-based graphic fault tree editor, cutset generation capability, and a full screen cutset editor. Its structure and functions are briefly presented. Future implementation plans .for its improvement are also discussed.

1 INTRODUCTION

Currently, the capability of a PC (Personal Computer) is being enhanced rapidly and PC-based PSA (Probabilistic Safety Analysis) computer codes L2 have been widely developed. Some integrated PSA codes such as IRRAS 1 contain fault tree editors which enable the fault tree to be constructed interactively on the PC graphic screen, event data management capability, cutset generation capability and reporting capability. These capabilities are more convenient for constructing fault trees and for managing event data than old computer codes, and can greatly reduce effort and time for fault tree preparation and analysis.

KIRAP is developed to perform the construction of fault trees and calculation of cutsets interactively on PCs. Since KIRAP has the capability to insert fault trees interactively on PC graphic screens with menus or hot key operation, to manage event data, and to calculate cutsets, it helps the user to perform fault tree operations easier and faster.

313 Reliabili O' Engineering and System S~[eO' 0951-8320/90/$03"50 ~ 1990 Elsevier Science Publishers Ltd, England. Printed in Great Britain

314 S. H. Han, T. W. Kim, K. S. Jeong, K. J. Yoo

2 DESCRIPTION OF KIRAP

An overall computat ion scheme for KIRAP is shown in Fig. 1. KIRAP is composed of three computer codes; TREE (the fault tree editor), CUT (cutset generation code, batch mode), and RESULT (cutset generation code, interactive mode).

After the user constructs a fault tree using TREE, TREE generates the fault tree in the form of Boolean equations, which are contained in the CUT file. These CUT files are transferred to CUT or RESULT. C U T is run in the batch mode like the old computer codes and is used for only cutset calculation. It can treat larger fault trees or larger event sequences than RESULT can. CUT can run on IBM-PC, mainframe computers and workstations. RESULT can calculate cutsets and edit cutsets in the interactive mode. Intermediate results of cutsets generated by CUT and RESULT are stored in LNK files and are reused at another run. If necessary, Boolean equations for event sequences are written by hand and cutsets for event sequences can be calculated.

Characteristic features of KIRAP are a character based graphic fault tree

*.GDB File

Generic Data

KII~P-TREE

Generic Data Logic Check Editor Fault Tree

Modularization

Fault Tree Event Data Editor Editor

Event Tree Equations

(By User)

KI~P-CUT

[[ Cut Set Generation

I Results ]

I [ - -

*.CUT File

CUT Input Form ]

1 KIP~P-RESULT

- - Cut Set Editor

I Results

Overview of KIRAP.

*.FTD File

Fault Tree

*.LNK File

Cut Sets

Fig. 1.

*.EBB File

Event Data

Cut Set Generation

PC workstation-based level 1 PRA code package KIRA P 315

editor, use of a generic data base, a cutset generation program and a full screen cutset editor.

2.1 Data files

K I R A P uses following types of data files.

- -Fau l t tree file ( , . FTD) It contains fault tree logic.

- -Gener ic data file ( , . GDB) It contains a generic data base. Generic data are composed of failure data for a given component type and failure mode. Event data come from the generic data base at the creation of the event.

- -Even t data file ( , . EDB) An event is a basic event or a gate defined in a fault tree. An event data file contains failure data for events.

- - C U T input file ( , . CUT) It contains a fault tree in the form of Boolean equations and event failure data. It is used as input of CUT and RESULT codes.

- - L N K file ( , . LNK) It contains information of intermediate and final cutsets for fault trees, and those of event sequences in the form of Boolean equations.

2.2 TREE: The fault tree editor

T R E E is used for generating fault trees interactively on a character based graphic screen. In the TREE, it is important to manage a generic data base. Generic data are composed of failure data for a given component type and failure mode. If an event is added to a fault tree with a component type and a failure mode, TREE searches the generic data and assigns the corresponding data to the event automatically. If the generic data base is well defined, effort and time for preparing event data will be greatly reduced.

T R E E contains a fault tree modularization module and fault tree logic checking module. TREE can handle OR, AND, N out of M gates, and up to 1000 events. T R E E is composed of the following five modules.

2.2.1 Fault tree editor module

The user can generate and modify a fault tree using this module. Figure 2 shows an example screen of the fault tree editor. The main working window appears on the left side, the menu window appears on the right side, and information about the current event is displayed on the lower side. The main window is composed of 6 • 6 event meshes. To insert an event, locate the cursor on a gate, press the menu key, and insert an event (see Fig. 2). If the

316 S. H. Han, T. W. Kim, K. S. Jeong, K. J. Yoo

FAULT TREE EDITOR Copyright by S.H. Han, KAERI

GA

GPA

FILE : S.FTD TOP EVENT : TOP

TOP 2

i I i GB GC

+ + +

I , I , t - - 1 GTK GPB GTK GPC GTK

T + T T + T

X X T ~ I - ~ - - ~ O I XXPPRO~3C XXCV~57C XXPPAO~3C B B B B B

TDDEVENT DEL EVENT MOD EVENT SELECT TOP LOAD TREE SAVE TREE TOG TRANS LIST EVENT MOVE EVENT QUIT

ESC-Toggle Main/Menu

3, 3> XXPPO93RC <2.40e-004 , 10.0> <i, :l.OOe-O05, : 24.0> M:PUMP C FAILS TO RUN

RETURN:Modify INS:Insert ALT-T:Tog Transfer ALT-F:Tog Fail Fig. 2. An example work screen of the fault tree editor.

user wants to add an event XXPPR093C to the gate GPC, locate the cursor on the GPC and press the INS key. After an event appears below GPC, insert the name XXPPR093C. If the name XXPPR093C is inserted, TREE searches the generic data ... P P R . . . and assigns the data to XXPPR093C. To delete or modify an event, locate the cursor on an event and press the menu key.

GENERIC DATA EDITOR Copyright by S.H. Hart, KAERI

FILE : S.GDB SELECT : PP

PPS <2.0e-003 , I0.0> <0, 2.0e-003 PUMP FAILS TO START PPA <1.0e-001 , 10.0> <0, 1.0e-001

OPERATOR FAILS TO START PUMP PPR <2.4e-004 , i0.0> <I, l.Oe-O05

PUMP FAILS TO RUN PPZ <2.0e-003 , 10.0> <0, 2.0e-003

PUMP FAILURE

, 0.0>

, 0.0>

, 24.0>

, O.O>

INS DATA ADD DATA MOD DATA DEL DATA GOAD FILE SAVE FILE SELECT PRINT SORT OFF QUIT

ESC-Toggle Main/Menu

O> Name <Mean, Ef> <Class, Lamda, Tan> Class- O:Q=LA~A I:Q=LA~A*TAU 3:Q=LA~A*TAU/2 RETURN-Modify INS-Insert

Fig. 3. An example work screen of the generic data editor.

PC workstation-based level 1 PRA code package KIRAP 317

The fault tree editor contains the following features.

- - A d d an event to a gate. - -Dele te an event from a gate. - - M o d i f y data for an event. - -Select a top gate. - - C h a n g e a gate to a transfer gate.

2.2.2 Generic data editor module Using this module, the user can generate, modify and delete generic data. The work screen is shown in Fig. 3.

2.2.3 Event data editor module The user can modify and check event data using this module. The work screen is similar to that of the generic data editor module.

2.2.4 Fault tree modularization module The user can modularize a fault tree or expand module events in reverse. The user can select a method from the following three methods.

- -Level 1: An independent subtree is replaced by a module. - -Level 2: Independent events among events which belong to a gate are

replaced by a module. - -Level 3: Independent events including events contained in lower level

gates are modularized.

Comparison of the three methods is illustrated in Fig. 4. The fault tree modularization module and the fault tree logic check

module have the same type of working window as the fault tree editor module.

2.2.5 Fault tree logic check module The user can check fault tree logic using this module. After some selected events are designated as failed states by the user, this module determines the state of each gate, whether it is failed or not, and displays the fault tree with failed events blinking. It helps the user to trace how a cutset is generated.

2.3 CUT: The cutset generation program

C U T is a computer code to generate minimal cutsets by expanding a given Boolean equation and using absorption rules. A fault tree is inserted in the form of Boolean equations, which uses + (OR), • (AND),/(NOT), and so on. To calculate cutsets, C U T uses a user program like SETS. 3 Using the user

318 S. H. Han, T. W. Kim, K. S. Jeong, K. J. Yoo

Level-1

j ~ el --> G1 A B

A, B and C are independent events. The gate 61 becomes a module.

l, evel-2

i i ill i i A B C M D

A, B, and C are independent events and become a module H. D appears more than one t i~e,

i t is not included in the module.

Level-3

i i

C l D E l D r - - -

A, B, and C are independent events and become a module H

Fig. 4. M o d u l a r i z a t i o n examples .

program, the user can reduce equations, merge equations, delete terms from the equations, and so on. The execution of CUT code is operated in a batch mode. CUT is run on an IBM-PC and workstations without modifying input files. Figure 5 shows the diagram of CUT.

CUT has the following features:

--Generates minimal cut sets. --Handles complement events. --Merges equations into one equation. --Prevents merging for selected equations. --Sets events to TRUE (OMEGA) or FALSE (PHI). --Stores the results on a file and can reuse it at another run. --Truncates cutsets by a cutoff value. --Deletes terms containing selected terms. - -Reads inputs from several files. --Calculates importance measures (Fussel-Vesely, Risk Reduction

Worth, Risk Achievement Worth). --Generates cutsets by bottom-up or top-down algorithm. GENPRG

PC workstation-based level 1 PRA code package KIRAP 319

Input File - User Program - Equations - Data

I I

Commands Interpreter

I

READ

Another Input File

I

I VALUE ] Read Data

DELTRM I eql - eq2 -> Result

I i ~RGE Option - PHI, O~GA

STOP top = gl * g2 g l = a * b g 2 = e + d

top = (a+b) * (c+d)

~ZO~ Read Equation

Equation File

II

READ from Other Files

J PRTEOfl

V Print Out

Write Equations on a File

REDUCE Option - PROBA, EEEPT

REPORT Operation

X * X -->X X + X * Y - - > X X + /X --> PHI etc.

GENPRG Generate User Program • TOP-DOWN • BOITOM-UP

I [ User Progr~ on File ]

Fig. 5. Computation procedures in CUT code.

command generates a user program according to the logic of the bottom-up or top-down algorithm and executes the program to determine minimal cutsets.

--Handles 5000 events and 8000 cutsets.

2.4 R E S U L T : The cutset generation program

RESULT has two routines: the cutset generation routine and the cutset editing routine. The cutset generation routine enables the user to calculate

320 S. H. Han, 7". W. Kim, K. S. Jeong, K. J. Yoo

KIRAP : CUT SET EDITOR Version 0.9 PROBA : 3.3e-02 Copyright by Han, Sang Hoon, I~ERI SELECT :

1.Oe-02 XXPPA093C XXPPAO91A l.Oe-02 XXPPA093C XXPPAO92B 1.Oe-02 XXPPAO9ZB XXPPAO91A 3.0e-03 XXI~/O001 Z.4e-05 XXPPAO92B XXPPR091/~ 2.4e-05 XXPPA093C XXPPRO91A 2.4e-05 XXPPR093C XXPPAO9ZB 2.4e-05 XXPPA093C XXPPROgZB 2.4e-05 XXPPRO92B XXPPAO91A 2.4e-05 XXPPR093C XXPPAO91A 1.Oe-05 XXCVO05?C XXPPAO92B 1.Oe-05 XXPPAOgZB XXCVOO55A 1.Oe-05 XXPPA093C XXCVOO55A 1.Oe-05 XXCVOO56B XXPPAO91A 1.Oe-05 XXCVO057C XXPPAO91A 1.Oe-05 XXPPA093C XXCVOO56B 1.Oe-06 XXTKFO01 5.8e-08 XXPPRO92B XXPPRO91A

DELETE SET INSERT SET SELECT DEL A EVEN ADD A EVEN QUIT

<9> XXPPR093C (2.4e-04) : PUMP C FAILS TO RUN ESC:Toggle Window/Menu INS:Add Event DEL:Del Event

Fig. 6. An example work screen of the cutset editor.

cutsets interactively using the capability of the CUT code. After cutsets are generated, the user can edit, add and delete cutsets on a full screen cutset editor with menu or function keys. Figure 6 is a working screen of the cutset editor. RESULT can handle 4000 events and 5000 cutsets.

3 EXAMPLES OF APPLICATION

KIRAP is used to carry out fault tree and event tree analysis o fYGN 3 and 4 (Young Gwang Nuclear Unit). In KIRAP, PSA operation can be performed in the following order.

(a) Generation of generic data base (TREE). (b) Construction and modularization of fault trees (TREE). (c) Cutset generation for support and system fault trees (CUT/RESULT). (d) Cutset generation for event sequences (CUT/RESULT).

Figure 7 shows an example file structure of the work. The LIB directory contains a generic data base. Fault trees for EP, AFWS and HPSI are constructed and modularized by each fault tree constructor using the TREE code. Cutsets for support systems such as EP are generated using CUT/RESULT. Cutsets for front line systems such as AFWS and HPSI are generated, which include cutsets of support systems. Cutset calculation for each system requires about 5-30 min computation time on 386-PCs. Next.

PC workstation-based level 1 PRA code package KIRAP 321

- - \ L I B - - AL~.GDB

- - \ E P - - E P . F T D , EP.EDB EP.CUT , EP.LNE

--\HPSI -- HPSI.FTD , HPSI.EDB

HPSI.CUT , HPSI.LNE

--\AFWS - - AFWS,FTD , AFWS.EDB AFWS.ClJT , AFWS.~E

--\S-LOCA - - S-LOCA.USR , S-LOCA.LNK

- - \LOP - - LOP.USR , LOP.LNK

--\TOTAL - - TOTAL.USR , TOTAL.LNK

- AL~.GDB : Generic Data Base - * . ~ D , *.EDB : Generated By TREE - *.CUT : Boolean Equat ions f o r each System F a n l t Tree - *.LNK : I n t e rmed ia t e Cut Se t s f o r each System and Event Tree - *.USR : Boolean Equat ions f o r Event Sequences prepared by User - EP , HPSI , /LI~S : S y s t e m - S-L0CA , h0P : Event Trees - TOTAL : To ta l Core Melt Equation

F ig . 7. D i r e c t o r i e s / f i l e s f o r Y G N 3 a n d 4 P S A .

Boolean equations for event tree sequences are prepared by hand and cutsets for each sequence are calculated. Each event tree analysis requires about lO-16min.

To calculate cutsets for front-line systems and event sequences, trans- ferring and linking data files is treated manually and carefully. The user has to keep in mind which data files are linked.

4 REMARKS

KIRAP is developed to carry out reliability analysis on PCs. It is composed of TREE, C U T and RESULT. TREE is for fault tree construction, and C U T and RESULT are for cutset generation. At present, we have not met any difficulties in constructing fault trees and generating cutsets for them, but as far as data transfers for analyses of event sequences are concerned we have had some difficulties, that is, they are not carried out automatically but manually. The user must keep in mind which fault trees are needed, which data files are needed, and which cutset files are linked for event sequences.

322 s. H. Han, T. W. Kim, K. S. Jeong, K. J. Yoo

KIRAP is still in the development stage and the following features will be implemented.

- -uncer ta in ty analysis, ---event tree editor, - - d a t a management and linkage for cutsets, intermediate cutsets, and

event data.

R E F E R E N C E S

1. USNRC, Integrated Reliability and Risk Analysis System (IRRAS) User's Guide, Version 2.0 (Draft). NUREG/CR-5111, EG&G Idaho, Inc., 1988.

2. Gubler, R. & Lederman, L. Computer software for PSA Level I analysis used and developed within the framework of the IAEA's inter-regional PSA programme. Probabilistic Safety Assessment and Risk Management PSA '87, Vol. I, Zurich, 30 August-4 September, 1987, pp. 43-7.

3. Worrell, R. B., SETS Reference Manual. NUREG/CR-4213, Sandia National Laboratory, 1985.