Developing a fresh core neutronic model at 300K for a VVER-1000 reactor type using MCNP6 GP Nyalunga 25449753 Dissertation submitted in partial fulfilment of the requirements for the degree Magister Scientiae in Nuclear Engineering at the Potchefstroom Campus of the North-West University Supervisor : Dr VV Naicker Co-supervisor: Miss MH du Toit May 2016 [Type text] Page 1 Developing a fresh core neutronic model at 300K for a VVER-1000 reactor type using MCNP6 Declaration of Author I, Gezekile Nyalunga, declare that the work provided in the following dissertation is my own work. I hereby confirm that where I have consulted the published work of others, this is always clearly acknowledged, and where I have quoted from the work of others, the source is always given. ______________ Gezekile Portia Nyalunga Date: 13 November 2015 NWU - Potchefstroom i North-West University Developing a fresh core neutronic model at 300K for a VVER-1000 reactor type using MCNP6 Abstract A steady state neutronics model for a fresh core Voda Voda Energo Reaktor (VVER)-1000 reactor type is developed using an internationally recognised code, Monte Carlo N-Particle, version 6 (MCNP6). This research study is based on a VVER type of pressurized water reactor (PWR), which is of Russian design. The neutronics model is done at 300 K, assuming the use of fresh fuel. Major core operational parameters including the 푘푒푓푓 , power profiles, reactivity coefficients and control rod worth were evaluated for the reactor core. The present study looks at the ability of the VVER-1000 reactor system to provide appropriate neutronics behaviour of the fresh core at the start of the initial cycle from cold zero power. A convergence study on the MCNP6 results is the most crucial part of MCNP6 simulation in the study, hence a convergence study of the MCNP6 results was initially done to ensure accuracy. The primary objective of the study is to develop an MCNP input model for the VVER-1000 reactor core using the North-West University Reactor Code suite (NWURCS) developed at the North-West University, School of Mechanical and Nuclear Engineering. The verification of the NWURCS code also forms part of the study. The steady state results obtained from the different models for all the investigated cases are presented and compared to previous research. The calculated values support safe start-up of a reactor and also assist in predicting the behaviour of the system. Keywords: MCNP6, Neutronics, Convergence, Criticality, Reactivity coefficients, Verification, NWURCS ii North-West University Developing a fresh core neutronic model at 300K for a VVER-1000 reactor type using MCNP6 Acknowledgements . To the SARChi Chair in Nuclear Engineering, I would love to show my appreciation for financially supporting my studies for the two years of the programme. A million times thank you would go to my two supervisors, Dr Naicker and Miss du Toit for their massive assistance and the guidance they provided me throughout the study. To my parents (Mr TK and Mrs DK Nyalunga), son Khayalethu, and siblings (Nomcebo, Fortune, and Nontokozo), I would love to show my appreciation for the support I received from all of you when I decided to pursue master’s studies. Without your support and patience, I could not have done it. A special thanks to my half-sister (Zakhele Nyalunga) for looking after my son when my mom was at work; for the love, she gave my son while I was not there. To my colleagues, Tannie Francina and the professors at the department, a special thank you goes to all of you for the nice times we had together when we were taking a break from studying and the catching up we used to do during birthday celebration. I would like to give gratitude to the HPC at the NWU for allowing me to use their cluster computers for the MCNP calculations. I would like to give a special thanks to Mr Eric Chinaka for assisting me with the MCNP6 code. Last but not least, I would like to thank my God, the Almighty for giving me strength and always holding my head high. iii North-West University Developing a fresh core neutronic model at 300K for a VVER-1000 reactor type using MCNP6 Table of Contents Declaration of Author ..................................................................................................................................... i Abstract ........................................................................................................................................................ ii Acknowledgements ..................................................................................................................................... iii List of Tables .............................................................................................................................................. vii List of figures ..............................................................................................................................................viii List of Acronyms ........................................................................................................................................... x 1. Background and Overview ........................................................................................................................ 1 1.1. Introduction ........................................................................................................................................ 1 1.1.1. Motivation for Research ............................................................................................................... 2 1.1.2. VVER-1000 type Reactor ............................................................................................................. 2 1.2. Background ........................................................................................................................................ 3 1.3. Problem Statement ............................................................................................................................ 5 1.4. Aims ................................................................................................................................................... 5 1.5. Outline of the Dissertation .................................................................................................................. 6 2. Theory and Literature Review ................................................................................................................... 7 2.1. Reactor Physics Calculations ............................................................................................................. 7 2.2. Monte Carlo Techniques .................................................................................................................... 7 2.2.1. Description of Monte Carlo Methods ............................................................................................ 7 2.2.2. Probability Density Function ........................................................................................................ 9 2.2.3. Criticality Calculations .................................................................................................................. 9 2.2.4. Tally Definition ........................................................................................................................... 10 2.3. Convergence Study of MCNP6 Problem .......................................................................................... 12 2.3.1. Shannon Entropy of the Fission Source Spatial Distribution ...................................................... 13 2.3.2. Tally Convergence of the Monte Carlo Problem ......................................................................... 14 2.4. Neutronics Code .............................................................................................................................. 19 2.5. VVER-1000 model definition ............................................................................................................ 20 2.5.1. VVER-1000 Reactor Core Configuration .................................................................................... 20 2.5.2. VVER-1000 Core Symmetry ...................................................................................................... 27 2.6. Reactivity Coefficients ...................................................................................................................... 27 2.6.1. Doppler Coefficient .................................................................................................................... 28 2.6.2. Moderator Temperature and Density Coefficient ........................................................................ 30 2.7. Critical Boron Concentration ............................................................................................................ 31 2.8. Control Rod Worth ........................................................................................................................... 32 2.9. Delayed Neutrons ............................................................................................................................ 35 2.10. Verification ..................................................................................................................................... 35 iv North-West University Developing a fresh core neutronic model at 300K for a VVER-1000 reactor type using MCNP6 3. Methodology ..........................................................................................................................................