CHERNE intensive course:Probabilistic Risk Assessment (PRA)

for PWR nuclear power plantMartorell S.1, Keshav C.2

1 Universitat Politècnica de València (SPAIN)2 Haute Ecole Spaak, rue Royale 150, B-1000 Brussels,

Belgium

Background

Objective?Give an introduction of the fundamentals and procedures of a probabilistic risk assessment and develop a practical case for a PWR nuclear power plant.

Advantages?• PRA is a systematic and comprehensive methodology

to evaluate risks associated with every life-cycle aspectof a complex engineered technological entity, fromconcept definition, through design, construction andoperation, and up to removal from service

• PRA has become a standard tool that helps risk informed decision making

Content & Logistic

1. Development of the course- Introduction to fundamentals and procedures - Lessons

- Practical application – Computers room

2. Introduction to fundamentals and procedures to develop a PRA

- Introduction to LWR technology (Elements, PWR, BWR)

- Overview of the PRA

- Accident identification

- Accident sequence modeling

- Data assessment

- Accident sequence quantification

Content & Logistic

1. Practical application to a PWR Nuclear Power Plant-Large Break Loss of Coolant Accident (LBLOCA) – Level 1 PRA

-Use of Software tools

2. Application tools-Level 1 PRA - LBLOCA documentation

-FaultTree+ , IAEA Database,…

3. Evaluation of the course-Case Study (portfolio)

4. ReferenceProcedures for conducting PSA of NPP (Level 1). Safety Series Nº 50-

P-4. International Atomic Energy Agency. Vienna. 1992.

Overview

24h IC given in January 2011 at UPV for the first time and attended by students from Brussels and Jülich.

Introduction to fundamentals and procedures to develop a PRA

PRA: Risk Concept

SAFETY PRINCIPLES AND SYSTEMS

HAZARD RISKACCIDENT SEQUENCES

Reliability, Maintainability,

Availability (RAM) of

Safety Related Equipment (SRE)

INITIATING

EVENTHAZARD

INTERMEDIATE EVENTS

CONSE-

QUENCE

FREQUENCY

DAMAGE

(SEVERITY)

CAUSES

(FAILURES,

ERRORS, …)

RISK

SAFETY

PREVENTION

PROTECTION

DECISION

MAKING

PRA: 3 levels!

In international practice three levels of PRA evolved

Level 1:

The assessment of plant failures leading to the determination of core damage frequency

Level 2:

The assessment of containment response leading, together with Level 1 results, to the determination of containment release frequencies

Level 3:

The assessment of off-site consequences leading, together with the results of Level 2 analysis, to estimate public risks

PRA: Steps & tasks

Management and

organization

1

Identification of hazards& accidentinitiators

Accidentsequencemodeling

3

Data assessment

4

Accident

sequence

quantification

5

Reportof the

analysis

6

Procedures for conducting PRA of NPP (Level 1). Safety Series Nº 50-P-4. International Atomic Energy Agency. Vienna. 1992.

2

Practical application to a PWR Nuclear Power Plant:

LBLOCA

Introduction

1. PWR Nuclear Power Plant

LBLOCA – PRA level 1

2. Analysing ToolsFaultTree+

IAEA Database

3. Steps

Accident sequence modelling

Data assessment

Accident sequence quantification

Identification of hazards & Accident initiator

1. Familiarization with the plant

2. Identification of hazards (sources of radioactive release)

3. Selection of plant operational states

4. Definition of consequences and damage states

5. Identification of accident initiators

6. Determination of safety functions and plant systems

Identification of hazards & Accident initiator

1. Familiarization with the plant

2. Identification of hazards (sources of radioactive release)

3. Selection of plant operational states

4. Definition of consequences and damage states

5. Identification of accident initiators

6. Determination of safety functions and plant systems

CONSEQUENCE:

Core damage

HAZARD:

Core as the onlysource of radioactive

release

Event Sequence Modelingusing FaultTree+ (Reliability Workbench)

GIATOP

FALLO DE LA INYECCION

DE DOS O MAS

ACUMULADORES

GIA4

DESCARGA INEFICAZ DEL

ACUMULADOR 15T01A

GMIA001

MODULO FALLOS

BASICOS DE VALVULAS

DE DESCARGA DEL

ACUMULADOR 15T01A

GIA5

DESCARGA INEFICAZ DEL

ACUMULADOR 15T01B

GMIA002

MODULO FALLOS

BASICOS DE VALVULAS

DESCARGA DE

ACUMULADOR 15T01B

GIA6

DESCARGA INEFICAZ DEL

ACUMULADOR 15T01C

GMIA003

MODULO FALLOS

BASICOS DE VALVULAS

DE DESCARGA DE

ACUMULADOR 15T01C

CASA-XR1

INOPERABILIDAD DEL

ACUMULADOR

GIA7

LOCA GRANDE O LOCA

INTERMEDIO NO INDUCIDO

POR ATWS

1TU10LRF1B

LOCA EN RAMA FRIA DEL

LAZO 1 DEL PRIMARIO

GIA7

LOCA GRANDE O LOCA

INTERMEDIO NO INDUCIDO

POR ATWS

1TU10LRF2B

LOCA EN RAMA FRIA DEL

LAZO 2 DEL PRIMARIO

GIA7

LOCA GRANDE O LOCA

INTERMEDIO NO INDUCIDO

POR ATWS

1TU10LRF3B

LOCA EN RAMA FRIA DEL

LAZO 3 DEL PRIMARIO

GIA1

FALLO DE LA INYECCION

DEL ACUMULADOR

15T01A

GIA2

FALLO DE LA INYECCION

DEL ACUMULADOR

15T01B

GIA3

FALLO DE LA INYECCION

DEL ACUMULADOR

15T01C

GIA8

PRESION INSUFICIENTE EN

ACUMULADORES POR

ERRORES DE

CALIBRACION

GIAO

FALLOS INDEPENDIENTES

DE ACUMULADORES

>_ 2

Data Assessment

• Assessment of the frequency of initiating events

• Assessment of RAM of components

• Databases

• Assessment of human error probabilities

Accident sequence quantification

• Qualitative analysis (Boolean equations)

• Quantitative analysis of frequencies of accident sequences

• Importance and sensitivity analysis

• Uncertainty analysis

Overview by students

• Very interesting (new or complementary, used for thesis, apply the software to any technical risk analysis : Japan!)

• Theory vs. Practical? “Good distribution between both”, “theory well detailed and organized for short time”, “practical case help to understand some of the theoretical aspects”

• Improvements? Maybe make the course longer

• Recommended? Yes by all the students! It was a good experience…

Thank you for your attention