**6. Conclusion**

336 Nuclear Reactors

the coating layer is Si eluted from the tube. This Si coating layer might inhibit the corrosion of the specimens. In any case, the progress of the corrosion was not observed in the SUS304 specimens, and SUS304 has good compatibility with a flowing aqueous K2MoO4 solution.

Fig. 9. SEM photograph of specimen 2 cross-section surface immersed in flowing aqueous

Fig. 10. EPMA color map of specimen 2 cross-section surface immersed in flowing aqueous

During the test term, the aqueous K2MoO4 solution was chemically stable, and the precipitation or the deposit was not generated in the solution. Then the molybdenum concentration of the solution was almost constant before and after the test, and the concentrations before and after the test were 396.2 mg/mℓ and 384.0 mg/mℓ respectively. The concentrations were measured with an Inductively Coupled Plasma Atomic Emission Spectrometer (ICP-AES). The pH of the solution was also almost constant at pH9.5-9.7.

**5.3.2 Chemical stability of flowing aqueous K2MoO4 solution** 

K2MoO4 solution for 84.5 days

K2MoO4 solution for 84.5 days

In the 99Mo production system with the solution irradiation method, a static or flowing aqueous molybdenum solution in a capsule is irradiated with neutrons in a testing reactor, and 99Mo is produced by the 98Mo (n, γ) 99Mo reaction. The system aims to provide 100% of the 99Mo imported into Japan. As a part of the technology development, aqueous (NH4)6Mo7O24·4H2O and K2MoO4 solutions were selected as candidates for the irradiation target of the system, and compatibility between the static two solutions and the structural materials of the capsule and pipes in the system, the chemical stability, the radiolysis and the γ heating of the solutions were investigated. As a result, it was found that the solutions are promising as the target. In addition, compatibility between a flowing aqueous K2MoO4 solution, which was the first candidate for the irradiation target in terms of a 99Mo production rate, and the structural material and the chemical stability of the flowing solution were investigated. As a result, it was found that stainless steel SUS304 has good compatibility with a flowing aqueous K2MoO4 solution and that the solution is chemically stable. The fundamental characteristics of the selected aqueous molybdate solutions became clear, and SUS304 can be used as the structural material of the capsule and the pipes.

In the future, a neutron irradiation test will be carried out as an overall test of 99Mo production system with the solution irradiation method, and 99Mo production, the separation of activation by-products, the quantity of radiolysis gas, nuclear heating and so on will be investigated.

Aiming at the domestic production of 99Mo in Japan, the development of 99Mo production with the solution irradiation method is kept going.
