Core Loading Requirements In Converting Heu Mnsr Core To Leu Using Wims And Citation Codes.
ABSTRACT
The world over research reactors are being converted from highly enriched uranium(HEU) to low enriched uranium (LEU). The NIRR-1 falls in the category of HEUs,being 90% enriched in the fissile U-235.
It is therefore desirable to convert it fromthis enrichment to about 20% in conformity with this global trend.
The reason forthis general trend is to make research reactor fuel as unattractive as possible togroups that may be interested in using such highly enriched reactor cores for non peaceful purposes.
In this work, we have developed a computational scheme thatwould theoretically achieve this objective as easily as possible.
The schemesystematically reduces the enrichment from 90% (or any other initial values) to 20%and even below, in steps of 5% or any desired percentage variation.
At each step,important neutronics parameters, especially safety related parameters are computed.Two fuel types are considered – UAl4 and UO2 – and the variation of safetyreactivity factor (SRF) with enrichment is also discussed for each fuel type.
It isshown that between 90% and 10% inclusive, the value of this parameter remainshigher than 1.5.
TABLE OF CONTENTS
Title page – – – – – – – – – i
Declaration- – – – – – – – – ii
Certification – – – – – – – – – iii
Dedication – – – – – – – – iv
Acknowledgement – – – – – – – – v
Abstract- – – – – – – – – vi
Table of contents – – – – – – – – – vii
List of tables – – – – – – – – xi
List of graphs – – – – – – – – – xii
List of figures – – – – – – – – – xiii
CHAPTER ONE: BACKGROUND TO THE STUDY
1.1 Introduction – – – – – – – – 1
1.2 Research Reactors – – – – – – – – 4
1.3 Nigeria Research Reactor (NIRR-1) – – – – – 5
1.3 WIMS – – – – – – – – -10
1.4 CITATION – – – – – – – -12
1.5 Statement of Problem – – – – – – -13
1.6 Justification – – – – – – – -14
1.7 Objectives of the Study – – – – – -15
1.8 Research Question – – – – – – -15
CHAPTER TWO: REVIEW OF RELATED LITERATURE
2.0 Introduction – – – – – – – – 16
2.1 Uranium enrichment – – – – – – – 16
2.2 High-enriched uranium verses low-enriched uranium – – – 17
2.3 Fertile material and fission chain reaction – – – – 20
2.4 Neutron moderation and moderator properties- – – – 23
2.5 Cross section – – – – – – – 28
2.6 Multi-group energy scheme – – – – – – 30
2.7 Critical mass, criticality and reactivity – – – – 31
2.8 Nuclear fuel assemblies – – – – – – 34
2.9 Classes of nuclear fuel – – – – – 38
a. Ceramic fuel – – – – – – 38
b. Dispersion-type fuel – – – – – – 39
c. Monolithic fuels – – – – – – 41
2.10 Control rod worth and S-shape curve – – – – 42
2.11 Control rod and reactivity regulation – – – – 44
2.12 WIMS and CITATION codes- – – – – – 51
CHAPTER THREE: THEORITICAL CONSIDERATION AND CALCULATIONS
3.10 Introduction – – – – – – – 54
3.11 Homogeneous resonance theory- – – – – 55
3.12 Nuclear data library – – – – – – 60
3.13 Equivalence theory – – – – – – 63
3.14 Infinite cell arrays – – – – – – 67
3.15 Sub-group theory – – – – – – 71
3.16 Reactor design and core models – – – – 71
3.17 Materials and implementation – – – – 73
3.18 Enrichment – – – – – – 80
3.19 Test mockup – – – – – 82
3.20 Rod worth – – – – – – 83
3.21 Excess rho and Critical depth – – – – – 83
3.22 Rod curve – – – – – – – 84
3.23 Be shim data – – – – – – 84
3.24 Temp. coef – – – – – – 85
3.25 Safety criteria – – – – – – 87
CHAPTER FOUR
Results and Discussions- – – – – – – 88
CHAPTER FIVE: CONCLUSION AND RECOMMENDATIONS
5.1 Conclusions – – – – – – – 99
5.2 Recommendations – – – – – – 100
References – – – – – – 102
INTRODUCTION
BACKGROUND TO THE STUDY
The world over, research reactors are being converted from highly enricheduranium (HEU) to low enriched uranium (LEU). The NIRR-1 falls in the categoryof HEUs, being 90% enriched in the fissile U-235.
It is therefore desirable toconvert it from this enrichment to about 20% in conformity with this global trend.
The reason for this general trend is to make research reactor fuel as unattractive aspossible to groups that may be interested in using such highly enriched reactor coresfor non-peaceful applications.
In this work, we have developed a computationalscheme that would theoretically achieve this objective. The scheme systematicallyreduces the enrichment from 90% (or any other initial values) to 20% and evenbelow, in steps of 5% or any desired percentage variation.
At each step, importantneutronics parameters, especially safety related parameters are computed.
Two fueltypes are considered – UAl4 and UO2 – and the variation of safety reactivity factor(SRF) with enrichment is also discussed for each fuel type.
REFERENCES
Ahmed, Y.A.; Ewa, I.O.B.; Umar, I.M. (2002). Effective resonance energy and non-idealityof epithermal neutron flux distribution in neutron activation analysis. Nigerian Journal ofPhysics 14 (1), 82–85.
Albarhoum M. (2008). Automation of the modeling and some neutronics calculations of theSyrian miniature neutron source reactors. Annals of Nuclear Energy 35, 1760–1763
Albarhoum M. (2004). Core Configuration of the Syrian reduced enrichment fuel MNSR.Proceedings of the 2004 International Meeting on Reduced Enrichment for Research andTest Reactors, Vienna, Austria, November 7-12.
Albarhoum M. (2005a). The use of UAlx-Al reduced enrichment fuel in a well reflectedMNSR. Proceedings of the 2005 International Meeting on Reduced Enrichment for Researchand Test Reactors, Boston, USA, November 6-11.
Albarhoum M. (2005b): A 3-D Neutronics Model for the Calibration of the Control Rod ofthe Syrian MNSR. Progress in Nuclear Energy, 46, No. 2, pp. 159-164.
Albarhoum M. (2006). Mixed Fuel versus Low Enriched Fuel in the Syrian MNSR.Proceedings of the 2006 International Meeting on Reduced Enrichment for Research andTest Reactors, Cape Town, South Africa, October 29- November 2.
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