A Preliminary Study On The Neutronics And The Heat Releasing Rate Characteristics Of ~99(Tc) Transmutation Target

In the development of nuclear energy, the accommodate of nuclear fuel, the construction of nuclear power stations, the spent fuel treatment and disposal of the entire nuclear fuel cycle chain must be well considered. The government has established the “Nuclear Fuel Cycle and Nuclear Safety Technology”, a key sub topic belong to“863project”, aiming at the advanced nuclear fuel cycle to carry out a large number of research studies, including the evolution of transmutation for the long lived fission products and the high radioactive nuclear wastes in fast and thermal reactors, has already solved the problem of basic feasibility of transmutation for long lived fissions products using thermal reactors. The project has very important significance for the development of suitable mode of thermal reactor transmutation for China’s national conditions, a lot of implications for realizing the advanced closed fuel cycle route and the sustainable development strategy of nuclear energy.99Tc is one of the most important long life fission products, and is very suitable to be transmutated in thermal reactor because of its high cross section for thermal neutron absorption. Supported by the “863” project, this paper refers to 17 x 17 PWR assembly model, chooses the 99 Tc transmutation target mixing with the inert matrix Zr H2 and Al2O3 in which the volume fractions of 99 Tc are 40%~60%, puts them in the assembly where the fuel cells are replaced by 99 Tc transmutation targets. In this paper, the neutronics parameters of assembly with 99 Tc transmutation targets and the heat releasing of 99 Tc targets is calculated, the influence on the power factor distribution of PWR assembly by 99 Tc transmutation targets is estimate.Calculation of the neutronics parameters before and after putting 99 Tc transmutation targets in assembly shows that due to a large thermal neutron absorption cross section of 99 Tc, it brings shorter cycle life and more negative temperature coefficient of the PWR assembly. Besides, the targets with Zr H2 affect more on the neutronics parameters than those with Al2O3 as they moderate neutrons better than Al2O3.The paper has calculated the specific heat releasing rate distribution in axial of the 99 Tc targets with MCNP, and the power distribution in assembly after adding 99 Tc targets. The results show that the 99 Tc transmutation targets can smooth the assembly power distribution. The more 99 Tc volume fractions, the smoother it becomes. Compared the matrix of Zr H2 with Al2O3, it is found that Al2O3 brings better power distribution than the other one.According to the conclusions of this paper, transmutation for 99 Tc in PWR is feasible. The conclusions provide reference for the research of 99 Tc neutronics characteristics and the simulation specimens which are used for the thermal hydraulic experimental outside the reactor.