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Optimized Control Rod of the Research Reactor BR2

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Optimized Control Rod of the Research Reactor BR2 BNEN Belgian Nuclear Higher Education Network BNEN Vrije Universiteit Brussel • Universiteit Gent • Katholieke Universiteit Leuven • Université de Liège • Université Catholique de Louvain • Studiecentrum voor Kernenergie – Centre d’Étude de l’Énergie Nucléaire●Université Libre de Bruxelles CONFIDENTIAL Optimized Control Rod of the Research Reactor BR2 BNEN/2006-2007 Xingmin Liu Promotor: Prof. Dr. Ir. Jean-Marie NOTERDAEME, UGent Academic year 2006-2007 Thesis submitted in partial fulfilment of the requirements for the degree of Master of Science in Nuclear Engineering Belgian Nuclear Higher Education Network, c/o SCK•CEN, Boeretang 200, BE-2400 Mol, Belgium BNEN Belgian Nuclear Higher Education Network BNEN Vrije Universiteit Brussel • Universiteit Gent • Katholieke Universiteit Leuven • Université de Liège • Université Catholique de Louvain • Studiecentrum voor Kernenergie – Centre d’Étude de l’Énergie Nucléaire●Université Libre de Bruxelles All property right and copy right are reserved. Any communication or reproduction of this document and any communication or use of its contents without explicit authorisation is pro- hibited. Any infringement to this rule is illegal and entitles to claim damages from the infringer, without prejudice to any other right in case of granting a patent of registration in the field or intellectual property. 1 © BNEN, Belgian Nuclear Education Network ii Master of Science in Nuclear Engineering Thesis Summary Page Name of the student: Xingmin Liu Title: Optimized nuclear control of the research reactor BR2 Abstract: At the present time the BR2 reactor uses Control Rods with cadmium as neutron absorbing part. The lower section of the Control Rod is a beryllium assembly cooled by light water. A capsule containing about 190 grams of cobalt granules is inserted between the lower part of the cadmium section and the upper part of the beryllium follower. Due to the burn up of the lower end of the cadmium section during the reactor operation, the presently used rods for reactivity control of the BR2 reactor have to be replaced by new ones. Considered are various types Control Rods with full active part of the following materials: cadmium (Cd), hafnium (Hf), europium oxide (Eu2O3) and gadolinium oxide (Gd2O3). Options for decrease of the burn up of the control rod material in the hot spot, such as use of stainless steel in the lower active part of the Control Rod are discussed. Comparison with the characteristics of the presently used Control Rods types is performed. The changing of the characteristics of different types Control Rods and the perturbation effects on the reactor neutronics during the BR2 fuel cycle are investigated. The burn up of the Control Rod absorbing material, total and differential control rods worth, macroscopic and effective microscopic absorption cross sections, fuel and reactivity evolution are evaluated during ~ 30 operating cycles, which is equivalent to ~ 1000 EFPD of reactor operation. The calculations are performed for the full scale 3-D heterogeneous geometry model of BR2 using MCNP&ORIGEN-S combined method. A criterion for choice of the new control rod types is presented. The main procedures for control of the BR2 reactor are revisited and modified to satisfy the new irradiation conditions. Promotor: Prof. Dr. Ir. Jean-Marie Noterdaeme Approval for submission by promotor: Mentors: Ir. Edgar Koonen Dr. Silva Kalcheva Assessors: Prof. Dr. Ir. Pierre-Etienne Labeau Prof. Dr. Ir.Greet Janssens-Maenhout Academic Year 2006-2007 Belgian Nuclear Higher Education Network, c/o SCK•CEN, Boeretang 200, BE-2400 Mol, Belgium Acknowledgement I would like to express my gratitude to all those who gave me the possibility to complete this thesis. I want to thank the department of BR2 of SCKyCEN for providing me such a good thesis and a very comfortable office to do this thesis. I would like to express my sincere gratitude to my promoter Prof. Dr. Ir. Jean-Marie Noterdaeme who kept an eye on the progress of my work. I am very grateful to my mentor Edgar Koonen for his important support, help and for all his kindness. It is difficult to overstate my gratitude to another mentor Dr. Silva Kalcheva. With her patience, she taught me the using of code, gave me a lot of good advices at the beginning and helped me solve all the questions throughout the thesis. Without her help, I could not finish my thesis in time. Finally, I would like to give special thanks to my wife. During the study, she took on all family affairs alone, I owe her too much. iv Summary At the present, the BR2 reactor uses Control Rods with cadmium as neutron absorbing part. The lower section of the Control Rod is a beryllium assembly cooled by light water. A capsule containing about 190 grams of cobalt granules is inserted between the lower part of the cadmium section and the upper part of the beryllium follower. Due to the burn up of the lower end of the cadmium section during the reactor operation, the presently used rods for reactivity control of the BR2 reactor have to be replaced by new ones. A modification design for the control rod will be developed. Chapter 1 mainly introduces the importance of control reactivity for a reactor, and then gives a general idea of how to choose a kind of control rod material with good characteristics; finally, according to historical experiences of BR2 operation, shows the importance and the aim of this thesis. The choice of control rod materials is related to the characteristics of BR2, therefore, in Chapter 2 the main description of BR2 reactor will be introduced, which can help us to know how to choose an appropriate control rod type among those candidate materials for BR2. The central topic in the Chapter 3 is the choice of control rod material. Firstly, the general condition of research reactors in the world will be introduced and the basic parameters including control rod material will be listed. Secondly, Chapter 3 describes the detailed characteristics from macroscopic to microscopic of several important absorbing materials such as cadmium (Cd), hafnium (Hf), europium oxide (Eu2O3), gadolinium oxide(Gd2O3) and stellite. The characteristics of these candidate materials will determine the behavior of the rod in the core during irradiation. The calculation methodologies will be given in Chapter 4. The methods of completing the thesis are chiefly numerical methods (application of appropriate computational tools) complemented with analytical considerations (based on reactor kinetics theory) and experimental methods (measurement of the reactor period). The behavior of the control rod is time-dependent, so the reactor kinetics theory is the main principle, which lies in the basis for determination of the reactor period. Therefore, the first part Chapter 4.1 gives some theoretical aspects of the processes of reactor kinetics for the case of a slab reactor combined with the real parameters of BR2. The aim of this chapter is: starting from the one-speed diffusion equation and through the equations of the reactor kinetics to deduce step by step the formula for the reactor period. Several numerical solutions of the kinetics equations are given in Appendices. The reactor period is the main parameter to be measured and to be used in the experimental technique for determination of control rod worth. Therefore, in the second part Chapter 4.2 the experimental method will be also introduced as a kind of validation and certification method to theory analysis and calculation. The basic computational tools used in this thesis for determination of the control rod characteristics are MCNP, SCALE4.4a and MCNP&ORIGEN-S method. The functions of these codes and how to use them to solve the task of the thesis will be discussed in Chapter 4.3. v The first several chapters mostly introduce some knowledge related to the optimal design. With the theoretical support of these chapters, Chapter 5 mainly discusses what should be calculated, that means, we must know what are the factors affecting the behavior of the control rod in the BR2 and what is the criterion of the optimal design. On the basis of those, the calculation will be started. At first, choosing several ideal CR types with different absorbing material, and then modeling using the MCNP Monte Carlo code complemented with time-dependent evaluations by SCALE4.4a, finally, the process of calculation will be given. The content of Chapter 6 is analysis of calculation results which is the most important section in the thesis. The analysis method is the comparison. We can proceed from three main aspects: comparison of CR material characteristics during irradiation, comparison of the reactor neutronics characteristics of BR2 with different type of CR, and comparison of neutron flux distribution with different type of CR. For the first aspect, the comparison includes five terms: macroscopic absorption cross sections, activity, nuclear heating in the lower active part of the control rods, total control rods worth’s and differential control rod worth; for the second aspect, we do the comparison for the keff and reactivity variations during the operating cycle; for the third aspect, we compare the axial distribution of the neutron flux for both the various types of CR at same position and the same type of CR at the different position of the control rod. The final conclusion is given in Chapter 7. The conclusion of each section in the last chapter will be summarized, according to which, a most optimal CR type is chosen as the new control rod type and the detailed reasons are presented. Although the material has been chosen, the ideal dimension of CR has not yet been decided, therefore, the final step is to compare the different dimensions so as to get a most optimal design. vi Contents CHAPTER 1 INTRODUCTION........................................................................................................................ 1 CHAPTER 2 THE OVERVIEW OF BR2.........................................................................................................
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