Radiation Detection Techniques for the Enhancement of Nuclear Safety

Abstract: The hazard originating from the use of nuclear materials in various areas of the society necessitates a number of experimental techniques for controlling and increasing the safety connected to radioactive substances. The following thesis is divided into two parts, representing different aspects to the detection of radiation effects. The first part aims at investigating radiation-induced material damage of steel alloys that may potentially be used in future Generation IV systems. Concepts like the LFR or SFR will operate under higher temperature and radiation levels than present LWR and detailed knowledge on the material integrity under high level conditions is important for the performance of the major safety barrier and thus the safety of a nuclear power plant. Ion-irradiation is used to simulate neutron-induced damage and the microstructure of the samples is investigated with the help of Positron Annihilation Lifetime Spectroscopy with the Chalmers Pulsed Positron Beam. A study regarding problems and challenges of ion-irradiation experiments is included. Additionally, depth profiling for the calibration of the measurement setup is performed. The second part aims at experimental and computational methods for purposes of Nuclear Safeguards and Emergency Preparedness, respectively. The chapter on safeguards measurements treats two of the major issues within the field, namely spent fuel and nuclear forensics. Firstly, an independent method for investigations of the boron content in a PWR fuel pool is presented, demonstrating how liquid scintillator detectors can be applied for estimations of the relative amount of neutrons absorbed in H and B. Secondly, HPGe measurements on strong Am-sources are performed for a qualitative analysis of inherent impurities to be used as signatures for the identification of unknown sources, helpful to forensic investigations. The chapter on Emergency Preparedness summarizes the computational work that was performed for simulations of source distributions in human phantoms. The IRINA voxel phantom is presented and Monte Carlo simulations for comparisons to the IGOR voxel phantom and the ICRP reference adult male voxel phantom are made for different distributions of Co and La in the human body.