**Acknowledgements**

I want to express my appreciation to Prof. Univ. Dr. Octavian Sima from University of Bucharest and Dr. Doru Stanga, Head of the Radiological Characterization Laboratory from Horia Hulubei National Institute for R&D in Physics and Nuclear Engineering for their constant support which they have given to me over the years. Each of them represents a rigorous scientific model for me which I hope will be reflected in my work. Also, I want to show my gratitude to Dr. Radu Deju, Head of the Reactor Decommissioning Department and Dr. Mitica Dragusin, Nuclear Safety Director from Horia Hulubei National Institute for R&D in Physics and Nuclear Engineering for their confidence and work appreciation.
