ALEXANDRIA UNIVERSITY FACULTY OF ENGINEERING NUCLEAR & RADIATION ...

111 Pages·2013·3.98 MB·English

ALEXANDRIA UNIVERSITY
FACULTY OF ENGINEERING
NUCLEAR & RADIATION ENGINEERING DEPARTMENT

Analysis of Reactivity Accidents in MTR for Various Protection System
Parameters and Core Conditions

A Thesis
Presented to the Graduate School
Faculty of Engineering, Alexandria University
In Partial Fulfillment of the
Requirements for the Degree

Of

Master of Science

In

Nuclear Engineering
By

ENG/ Fergany Mahmoud Mohamed

2011
Abstract

Egypt Second Research Reactor (ETRR-2) core was modified to irradiate LEU (Low Enriched
Uranium) plates in two irradiation boxes for fission 99Mo production. The old core
comprising 29 fuel elements and one Co Irradiation Device and the new core comprising 27
fuel elements, one Co Irradiation Device, and two 99Mo production boxes. The in core
irradiation has the advantage of no special cooling or irradiation loop is required. The purpose
of the present work is the analysis of reactivity accidents in ETRR-2 cores. The analysis was
done to evaluate the accidents from different point of view:
- Analysis of the modified core for various Reactor Protection System (RPS) parameters
- Comparison between the two cores
- Analysis of the 99Mo production boxes

PARET computer code and standard correlations were employed to compute various
parameters. Initiating events in reactivity-induced accidents involve various modes of
reactivity insertion, namely, prompt critical condition (ρ=1$), accidental ejection of partial and
complete cobalt irradiation Device, uncontrolled withdrawal of a control rod accident, and
sudden cooling of the reactor core. The time histories of reactor power, energy released, and
maximum clad temperature of fuel and uranium plate were calculated for each of these
accidents. The results show that the maximum clad temperatures remain well below the clad
melting in both fuel and uranium plates during almost all of these accidents. It is concluded
that for the proposed irradiation the reactivity accidents with shutdown system enables will not
result in fuel or uranium plate failure.

I
TABBLE OF CONTENTS
Abstract………………………………………………………………………………………....Ι
TABBLE OF CONTENTS…………………………………………………………………ΙΙ
Chapter 1 INTRODUCTION ………………………………………………………………1
Chapter 2 REVIEW OF LITERATURE…………………………………………………..4
Chapter 3 ETRR-2 REACTOR DESCRIPTION……………………………………….15
Chapter 4 MODELING AND METHODOLOGY ……………………………………28
4.1. PARET Code………………………………………………………………………..29
4.2. Methodology ………………………………………………………………………..35
4.3. Modeling of Reactivity Insertions……………………………………………..37
4.4. Comparison with NRI Experiment……………………………………………42
Chapter 5 RESULTS AND DISCUSSION……………………………………………...45
5.1. PART ONE: Analysis of the new core for various RPS parameters….46
5.1.1 Variation of scram setting (power setting) ……………………………………46
5.1.2 Variation of I&C (instrumentation and control) delay time……………..…..49
5.1.3 Variation of dropping time…………………………………………………….51
5.1.4 Variation of shut down margin………………………………………………...54
5.2. PART TWO: Analysis of Accidents for old and new cores……………..57
5.2.1. Transients with scram…………………………………………………………...57
5.2.1. 1. Prompt critical condition accident (ρ=1$)…………………………………..58
5.2.1.2. Accidental ejection of a cobalt irradiation box………………………………60
5.2.1.2.1. Accidental ejection of partial cobalt irradiation box……….…………60
5.2.1.2.2. Accidental ejection of complete cobalt irradiation box…………….....60
5.2.1. 3. Uncontrolled withdrawal of a control rod…………………………………..63
5.2.2. Self-Limiting Transients………………………………………………………..66
5.2.2. 1. Prompt critical condition accident (ρ=1$)…………………………………..66
5.2.2.2. Accidental ejection of a cobalt irradiation box………………………………68
5.2.2.2.1. Accidental ejection of partial cobalt irradiation box……………….68
5.2.2.2.2. Accidental ejection of complete cobalt irradiation box…………….68
5.2.2. 3. Uncontrolled withdrawal of a control rod…………………………………..70
5.2.2.4. Sudden cooling of the core inlet water……………………………....70
5.2.2.4.1. The transition from power regime zero to power regime one…….70
5.2.2.4.2. The transition from power regime one to power regime two……..73
5.3. PART THREE: Analysis of Molybdenum production box ....…………..78
5.3.1 Prompt critical condition accident (ρ=1$)………………………………………...79
5.3.2 Accidental ejection of complete cobalt irradiation box…………………………...80
5.3.3 Uncontrolled withdrawal of a control rod…………………………………………81
Chapter 6 CONCLUSIONS………………………………………………………………..83
APPENDIX ………………………………………………………………………………….85
REFERENCES……………………………………………………………………………..105
CHAPTER 1
Introduction
1.1 General
The analysis of reactivity accident is an important part of safety study in every nuclear reactor.
By means of it, the maximum power and total energy released, the maximum fuel, clad and
coolant temperatures, and eventually partial core melting (and consequently, the fission
product release), may be predicted for every probable case considered [1]. Almost all the
analysis of reactivity accident is carried out with the help of validated codes that simulate the
coupled kinetics and thermal-hydraulics of reactor core. A simpler code should be sufficient
for most calculation and analysis purposes of research reactors [2, 3].

The objective of the analysis of reactivity induced accidents is to ensure that the clad
temperature of the fuel is kept below the melting temperature in all postulated accidents.
Analysis of Reactivity insertion accident is not only required in the safety study of new
reactors but also when replacement of reactivity control devices, removal or insertion of
experimental apparatus, and installation of new core components with new characteristics [4]
as will be seen in the present work. The analysis should take into account conservative
characteristics of reactor protection system (RPS) and error in measurements of power and
shutdown margin.

1.2 Main objectives
Egypt Second Research Reactor (ETRR-2) core was modified to irradiate LEU (Low Enriched
Uranium) plates in two irradiation boxes for fission 99Mo production. The old core
comprising 29 fuel elements and one Cobalt Irradiation Device (CID) and the new core
comprising 27 fuel elements, one CID, and two 99Mo production boxes.
The intent of this work is to perform analysis for the both ETRR-2 cores with validated and
simple code. The validated code should be accurate enough and capable of simulating the
reactivity accident applicable to the ETRR-2 new core configuration with 99Mo production
boxes.
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The application includes (1) analysis of the new core for various RPS main parameters (scram
setting, delay time in instrumentation, and control plate drop time, and shutdown margin), (2)
comparison with the old core (licensed core) for conservative characteristics of RPS, and (3)
analysis of the 99Mo Production boxes.

PARET code was selected for performing the analysis which is designed for use in predicting
the course and consequences of non-destructive transients in small rector cores [5]. The
analyzed postulated accidents are:
1. Prompt critical condition accident as generic accident;
2. Accidental ejection of Co Irradiation Device (partial and complete ejection);
3. Uncontrolled withdrawal of control plate;
4. Sudden cooling of the reactor core.

1.3 Thesis organization
The thesis fall in six chapters including this introduction
• Chapter two: literature review of the needs for the analysis of reactivity
insertion accidents for various material testing reactors.
• Chapter three: describe ETRR-2 core components (fuel elements, control plates, and
99Mo production boxes…), core modifications, reactor protection systems, and
operational regimes.
• Chapter four: describes the PARET code model and methodology of analysis, and
comparison between PARET and RELAP code for SPERT IV experimental data.
• Chapter five: discusses the obtain results.
• Chapter six: present the conclusions and recommendation for future work.

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CHAPTER 2
Literature Review
Analysis of reactivity insertion accidents is a very important from safety point view. It is a
part of Safety Analysis Report of new nuclear reactor, core conversion from HEU to LEU, and
core modification /upgrading.
In the present review, six MTR research reactors and ETRR-2 similar system are
involved:
- RA-2 Research reactor
- Massachusetts Institute of Technology Research Reactor (MITR)
- McMaster Nuclear Reactor (MNR)
- Pakistan Research Reactor-1 (PARR-1)
- Greek Research Reactor (GRR-1)
- IAEA 10 MW benchmark research reactor

R. Waldman and A. Vertullo (1987) analyzed the reactivity transients in MTR cores with
LEU (Low Enriched Uranium), and HEU (Highly Enriched Uranium) fuels. The analysis
includes:
1. The description of the reactivity accident that happened in the RA-2 critical facility in 1983.
2. The evaluation of the accident from different point of view: Theoretical and qualitative
analysis, PARET code calculations, and comparison with experiments.
3. Differences between LEU and HEU RA-2 cores [1].

Hernan G. Trosman (1994) developed a simulation model for transient analysis of
Massachusetts Institute of Technology Research Reactor (MITR) loop components. A
simulation model (TAMLOC) has been developed to simulate several transients for the MIT
Nuclear Research Reactor. The transients include slow to moderate reactivity insertion, loss of
heat sink, pump cost down with attendant natural convection, and small loss of coolant
accidents. The simulation model can be used to analyze operational transients such as power
maneuvering, start up, and shutdown. The intent of this research is to aid in the studies of an
upgraded design of the MITR-II reactor Fig (2.1). The simulated results have been validated
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compared to the available data of a reactor startup, a shutdown, and pump cast down. The
simulations and results of TAMLOC have been used as a part of a proposed MITR-III design
[6].

Figure2.1. MITR-II core

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