The Transmutation Of Tc-99in Thermal Reactors

With the rapid development of nuclear power in China, the issue of disposal of nuclear spent fuel attracts the attention of nuclear industrial society. Especially for the disposal of the high level radioactive waste in the spent fuel, the high level radioactive waste affects not only the sustainable development of nuclear power, but also the safety of the human environment. As one of major long-lived fission products, Tc-99has the characteristics of long half life, well soluble in the groundwater and low mineral absorption, result in high geochemical mobility, which could lead to its release in the environment during long term storage. Therefore, the study of the proper disposition of Tc-99is important for long term and health development of nuclear power.The partitioning and transmutation (P&T) technology can solve the problem of the disposal of Tc-99effectively. Nuclear transmutation is the conversion of one chemical element or isotope into another. Through neutron transmutation technology, Tc-99can convert to stable isotope Ru-100by capturing a neutron. As a dominating type of commercial reactors in the world, thermal reactor technology is pretty mature after decades of development and has the potential in large-scale transmutation applications.I conducted a systematic study on neutronic characteristics of Tc-99transmutation in thermal reactor in this thesis. I simulated the model of pressurized water reactor by MCNP code and introduced the Tc-99metal to the reactor by thin layer coating on fuel rods, then I studied the effects on keff of the PWR after coating Tc-99on fuel rods. My simulation results shows that if I just coat0.2λc (0.0065mm) thickness Tc-99on PWR fuel rods, the system keff merely decrease to0.98530. As the thickness increase, the decreasing of keff expands.As loading the Tc-99to the PWR is equivalent to introducing extra poisons to PWR system to control excess reactivity, I need to remove some control poisons like boric acid concentration from primary coolant or burnable poison rods from fuel assemblies to keep the reactor in criticality. After coating0.2λc thickness on the fuel rods, for example, I may reduce the boric acid concentration by149ppm or remove48burnable poison rods to keep criticality.I also calculated the transmutation rate in this paper. The results showed that with the thickness increasing, the loading amount of Tc-99also increases, while the transmutation rate has a downward trend. The transmutation rate of Tc-99decreases from7.656%to7.109%when the thickness increases from0.05λc to0.2λc. For the case of0.2λc thickness, the total Tc-99coating amount is291.37kg and the transmutation amount is19.340kg, which is equal to the Tc-99generation amount of the core, the Tc-99production and consumption in the PWR reach an equilibrium.