[Safety Analysis of the Proposed Nuclear System in Nigeria]

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ABSTRACT

The dependability of critical safety systems needs to be quantitatively determined in order to verify their effectiveness, e.g. with regard to regulatory requirements. Since modular redundant safety systems are not required for normal operation, their reliability is strongly dependent on periodic inspection. Several modeling methods for the quantitative assessment of dependability are described in the literature, with a broad variation in complexity and modeling power. Static modeling techniques such as fault tree analysis (FTA) or reliability block diagrams (RBD) are not capable of capturing redundancy and repair or test activities. Dynamic state space based models such as continuous time Markov chains (CTMC) are more powerful but often result in very large, intractable models. Moreover, exponentially distributed state residence times are not a correct representation of actual residence times associated with repair activities or periodic inspection. In this study, a hybrid model combines a system level RBD with a CTMC to describe the dynamics. The effects of periodic testing are modeled by redistributing state probabilities at deterministic test times. Applying the method to the primary safety shutdown system of the BR2(Belgian Reactor 2)—nuclear research reactor, resulted in a quantitative as well as a qualitative assessment of its reliability.

Keywords

Hybrid reliability model;

Markov process;

Reliability block diagram;

Shutdown system;

Belgian reactor 2

Nomenclature

C: Set of components

Pi(t): State residence probability function for state i (a function of time).

: Column vector (n×1) with elements Pi(t)

: dPi(t)/dt, Time derivative of Pi(t)

: Column vector (n×1) with elements

PFDS(t): Probability of failure on demand at time t for the overall system

PFDavg: Average probability of failure on demand for a specified period of time

Pr{A}: Probability of A

PscramS(t): Probability of spurious scram in time interval [0,t]

qij(t): Transition rate from state j to state i

qij: Constant transition rate from state j to state i

Q: State transition matrix (n×n) with elements qij for i?j and

RA(t): (Unconditional) reliability function for component A

RA|B(t): Reliability function for component A, conditional on component B being functional at time t

: Reliability function for component A, conditional on component B not being functional at time t

RS(t): Reliability function for the overall system

S: System state space

TI: Length of the surveillance test interval for the case of a fixed test frequency

wij(tk): transition probability from state j to state i at time tk

W(tk): redistribution matrix (n×n) with elements wij(tk)

X(t): System state at time t

: System state just before an instantaneous transition (due to test) at time tk

: System state just after an instantaneous transition (due to test) at time tk

?A: Total failure rate for component A

?A,D: Dangerous failure rate for component A

?A,S: Safe failure rate for component A

µS: Equivalent constant repair rate associated to recovery from safe failure of a measurement/comparator (MC) module

µD: Equivalent constant repair rate associated to recovery from dangerous failure of a measurement/comparator (MC) module

TABLE OF CONTENTS

ABSTRACT2

Keywords2

Nomenclature3

CHAPTER 1: INTRODUCTION6

1.1 Background and Theortical Framework6

1.2 Research Objective and Significance of the Study10

CHAPTER 2: LITERATURE REVIEW11

2.1 Review Of The Present Energy Infrastructure In Nigeria11

2.2 The Safety Implication Of The Proposed Plant Base On ...