Compact neutron generator as external neutron source of subcritical assembly for Mo-99 production (SAMOP)

摘要

Subcritical assembly for Mo-99 production (SAMOP) has been developed at The Center for Accelerator Science and Technology (CAST), National Nuclear Energy Agency (SATAN). The objective of the SAMOP development is to provide a prototype of a subcritical assembly which produces Mo-99 isotope. In the nuclear medical application, Mo-99 plays an important role as a generator of isotope Tc-99m which is the most widely used radioisotope for diagnostic purposes. SAMOP use uranyl nitrate solution UO_2(NO_3)_2 as fuel as well as target material for the process of Mo-99 production. This process is based on the fission reaction of uranium U-235 contained in the uranyl nitrate solution. The U-235 fission reactions occur as long as there are still neutrons from external neutron source and it will stop whenever the external neutron source is removed. Presently SAMOP uses external neutron source from the radial beam port of the Kartini research reactor which emerges thermal neutrons in the order of 10~8 n/cm~2s. For further development, SAMOP will be equipped with a compact neutron generator as an external neutron source. Compact neutron generator is a neutron source device that contains a compact ion accelerator and that produces neutrons by fusing isotopes of hydrogen. The fusion reactions take place in the device by accelerating either deuteron, triton, or a mixture of these two isotopes into a metal hydride target which also contains deuterium, tritium or a mixture of these isotopes. The fusion of deuterium atoms (D + D) results in the formation of a He-3 ion and a neutron with a kinetic energy of approximately 2.5 MeV. The fusion of a deuterium and a tritium atom (D + T) results in the formation of a He-4 ion and a neutron with a kinetic energy of approximately 14.1 MeV. SAMOP needs an external neutron source which can provide neutrons with an average neutron flux of 10~8 n/cm~2s for maintaining the sustainability of U-235 fission reactions. The results of the study on compact neutron generator as an external neutron source of SAMOP show that a compact neutron generator has a chance to substitute a nuclear reactor as external neutron source of SAMOP. A compact neutron generator can produce fast neutrons which neutron yield is sufficient to meet the need of neutron for SAMOP. It depends on the type of the compact neutron generator, one of which is the compact neutron generator produced by LSNL i.e. the axial compact neutron generator which can produce neutron yield up to 10~9 n/s. The benefit of using a compact neutron generator as an external neutron source of SAMOP is that the operational cost will reduce since the neutron production cost using a compact neutron generator is cheaper than a nuclear reactor. In addition, the operational procedure of a compact neutron generator is simpler than a nuclear reactor.