Transactions of the Korean Nuclear Society Virtual Spring Meeting July 9-10, 2020 Development of Level-2 PSA Software AIMS-L2 Sang Hoon HAN and Jaehyun Cho Korea Atomic Energy Research Institute, 111, Daedeok-daero 989Beon-gil, Yuseong-gu, Daejeon, 305-353, Korea * Corresponding author: shhan2@kaeri.re.kr 1. Introduction 2. Basic Features of AIMS-L2 1. Level-1 ET (CD) 2. PDS ET System for PDS KAERI has been developing software for PSA analysis, such as AIMS-PSA and FTREX for Level 1 Low Pressure Loss of Long Term Containment Contt' Isolation Aux Feedwater Feed & Bleed Safety Loss of Long Term Feedwater DHR Spray Aux Feedwater Feed & Bleed Injection Seq# State Feedwater DHR PSA, CONPAS for Level 2 PSA. We have been using Seq# State LOFW CIS AFWS F&B LTDHR LPI/LPR CSI LOFW AFWS F&B LTDHR 1 ok 2 1 3 2 MACCS for Level 3 PSA, and we are developing a new 4 3 1 ok 5 4 6 ok 2 cd 7 5 RCAP now. 8 6 3 ok 9 7 10 8 4 cd 11 9 12 10 CONPAS [1, 2] is software developed to analyze 5 cd 13 11 14 12 15 Level 2 PSA, and its methodology is based on the 3. PDS Logic Diagram NUREG-1150 [3]. In CONPAS method, the Level 2 PSA is analyzed by receiving only the accident ENTRY SBO. CONTAINMENT FROM CONTAINMENT TRANSIENT ISOLATION LEVEL1 BYPASS OR STATUS Seq# State sequence frequency from the Level 1 PSA. Therefore, it If-Then-Else rule PDS ET LOCA TYPE CRITERIA CONBYPASS CONISOLAT TRANLOCA IF A:GISLOCA= FAILURE; is difficult to fully combine the Level 1 PSA and Level NOT ISOLATED 1 THEN EVENT V; SLOW SBO 2 2 PSA models. In addition, CONPAS software was IF A:GSGTR = FAILURE; FAST SBO 3 GP-NO_BYPASS ISOLATED TRANSIENT THEN SGTR; 4 developed with the outdated Visual Basic 6, so it can no LLOCA DEFAULT NO BYPASS; 5 M/S LOCA 6 G-CDF-LOGIC longer be updated. RBCM 7 GP-EVENT_V 8 GP-SGTR 9 KAERI decided to develop a new Level 2 PSA DET 4. CET Status of RCS Pressure Debris Cooled In- software AIMS-L2 that includes the following features MeltStop DET Status of In- Vessel Injection In_Cavity before Vessel Containment Heat Removal Vessel, No Vessel Injection Breach Rupture Seq# State D-MeltStop INVESSINJ CAVCOND RCSPRESS CSRCOOL MELTSTOP D-MS-MELTSTOP1 D-CSR-YES 1 Mode of Induced Core Melt Alpha Mode D-IVI-On D-MS-RV_Rupture1 2 RCS Pressure Status of Mode of Induced D-MS-CMT_FAIL1 RCS Pressure Alpha Mode Amount of RCS Fail Criteria during Core Melt In_Cavity Primary System D-CSR-NO 3 Primary System Progressin Containment Alpha DET D-MS-RV_Rupture1 before Vessel 4 Containment CET Logic Corium Ejected Progression Injection Failure Seq# State D-RCS-P-NotLow D-MS-RV_Rupture to solve these shortcomings; Breach 5 Failure Seq# State Failure at RV Stopped Before Failure (Steam D-CAV-FLOOD D-CSR-YES D-MS-MELTSTOP1 6 out of Cavity Seq# State D-RCSFail P-RCS CAVCOND RCSFAIL D-MS-RV_Rupture1 Failure RV Failure Explosion) D-RCS-P-Low 7 D-MS-CMT_FAIL1 8 D-IVI-LPI-DeadHeaded D-Alpha D-CSR-NO D-MS-RV_Rupture1 RCSPRESS ALPHA D-RCS-P-NotHigh No RCS Failure 9 %CRITERIA 1 D-RCS-P-NotLow RV RUPTURE 10 CET-ET RCSFAIL MELTSTOP ALPHA CR_EJECT D-MS-MELTSTOP2 D-NoRCSFail-Flood 2 D-CAV-NOTFLOOD D-CSR-YES 11 D-MS-RV_Rupture2 12 D-NoAlpha-P_NotLow %CRITERIA D-CAV-Flood D-HLB-Flood D-RCS-P-Low D-MS-CMT_FAIL2 1 - Develop with the latest VB.net 3 D-CSR-NO D-RCS-P-NotLow 13 D-MS-RV_Rupture2 14 D-Alpha-P_NotLow D-SGTR-Flood D-RCS-P-NotLow D-MS-RV_Rupture C-MS-MELTSTOP D-RCS-P-High 4 %CRITERIA 15 2 1 D-NoRCSFail-NotFlood D-CAV-FLOOD D-MS-MELTSTOP2 16 5 D-CSR-YES D-MS-RV_Rupture2 D-NoAlpha-P_Low D-RCS-P-Low 17 3 D-CAV-NotFlood D-HLB-NotFlood D-IVI-Failed D-MS-CMT_FAIL2 D-RCS-P-Low 18 C-CR-HIGH 6 D-CSR-NO D-MS-RV_Rupture2 D-Alpha-P_Low 2 D-SGTR-NotFlood 19 4 7 D-CAV-NOTFLOOD D-MS-RV_Rupture 20 - Management of Level 2 PSA using a project C-AP-NOALPHA C-CR-MEDIUM C-RF-NoRCSFail 3 C-MS-RV_RUPTURE C-CR-LOW 4 C-AP-ALPHA If-Then-Else rule explorer 5 C-MS-CMT_FAIL 6 C-MS-MELTSTOP G-PDS-Logic 7 IF P:RCSPRESS=HIGH; - Ability to convert Level 2 PSA model into a fault C-AP-NOALPHA Low C-RF-HLB C-MS-RV_RUPTURE 8 THEN HIGH; C-AP-ALPHA 9 C-MS-CMT_FAIL 10 IF P:RCSPRESS !=HIGH; tree, which is required for combining Level 1 & C-RF-SGTR 11 THEN NOT HIGH; 2 PSA models 5. STC - Ability to perform easy sensitivity analysis Source Term Core Melt Stop Contt' Isolation - Uncertainty analysis based on the distribution of Catagorization Contt' Bypass before RV If-Then-Else rule State Seq# State Logic Diagram Rupture STC CONBYPASS CONISOLAT MELTSTOP each variable IF C:ALPHA = NO ALPHA; S-MS-MetlStop THEN NO ALPHA CF; 1 S-CI-Isolated S-MS-RV_Rupture IF C:ALPHA = ALPHA; 2 S-MS-CB_Fail 3 THEN ALPHA CF; S-CB-NoBypass AIMS-L2 introduces the concept of project explorer, S-CI-NotIso_CSR-Yes 4 S-CI-NotIso_CSR-No 5 which provides an easy interface for analyzing the Level S-CB-V 6 S-CB-SGTR 7 2 PSA. The basic function of AIMS-L2 is presented in Fig 1. Level 2 PSA Procedure in CONPAS section 2. Meanwhile, various approaches for integrating Level In CONPAS, a Level-2 PSA is performed in the 1 and 2 PSAs have been developed [4, 5]. AIMS-L2 following steps (see Fig. 1); provides the basis for combining Level 1 and 2 PSA models by converting the existing Level 2 PSA model - Extend the core damage event tree (CD ET) by of CONPAS into a fault tree without modifying the incorporating the systems related to PDS (Plant Level 2 PSA model. That is, as in a typical Level 1 PSA, Damage State), which is the starting point for we can generate a model in the form of a fault tree and Level-2 PSAs. calculate minimal cut sets. It is described in section 3. - Classify the state of the extended CD ET using In addition, by introducing a feature to input relations PDS LD (Plant damage state logic diagram). between DET events, it provides a basis that can easily - Evaluate probabilities of containment event tree analyze sensitivity and uncertainty. The features are (CET) sequences for each PDS. A CET is a described in section 4. model to describe a severe accident phenomenon in a containment and a decomposition event tree (DET) is a model to describe the probability of each phenomenon.
Transactions of the Korean Nuclear Society Virtual Spring Meeting July 9-10, 2020 - Classify the source term category for each CET the left side is the project explorer that manages the sequence using the source term category logic input models by KET, PDS LD, CET, DET, and STC, diagram (STC LD). and the right side is a window where you can open and edit each event tree. AIMS-L2 can perform Level 2 PSA analysis using A basic Level 2 analysis can be done by simply the input of CONPAS as it is. The concept of project executing the analysis menu. Sequence frequencies of has been introduced to enhance the usability. In Fig. 2, CET and STC are calculated for each PDS. Fig 2. Example Screen of AIMS-L2 (with Project Explorer) 3. Converting a Level 2 PSA Model into a Fault Tree - The branch probability for EXVCOOL can be calculated using DET for EXVCOOL. In order to combine Level 1 PSA and Level 2 PSA - According to the If-Then-Else Rule in DET, models, it is necessary to convert a Level 2 PSA model CRM-EJECT proceeds to MEDIUM, and CVT- into a fault tree. WATER proceeds to FLOODED. In a Level 2 PSA model, each branch probability of - The branch probability of DET can be calculated CET is determined by a DET. A branch of a DET as follows; • ‘1. COOLED’ = 9.9e -1 consists of 2 types. One is a branch with probability, the • ‘2. NOT COOLED’= 0 other is a branch represented by If-Then-Else rule. If- • ‘3. COOLED’= 1e -2 x 5e-1 Then-Else rule determines which scenario each branch • ‘4. NOT COOLED’ = 1e -2 x 5e-1 proceeds to. Therefore, by converting the DET model for each branch of CET into a fault tree, the Level 2 - In DET, a branch with probability is treated as a PSA model can be converted into a fault tree. basic event, and converted into a fault tree. Fig. 3 shows how DET determines the branch - By linking these fault trees and CET, we can probability of CET for EXVCOOL, and shows how to convert a CET into a fault tree model. convert them to a fault tree and connect to CET;
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