**3.1 Structure of 99Mo production system with solution irradiation method**

The schematic diagram of the 99Mo production system with the solution irradiation method is shown in Fig. 1. The system consists of an irradiation system, a supply and circulation system, and a collection and subdivision system. In the irradiation system, an aqueous molybdenum solution in a capsule installed in a reactor core is irradiated with neutrons under static or circulation condition, and 99Mo is generated. In the supply and circulation system, the solution is supplied to the capsule through pipes and is circulated by a circulator in irradiation operation. A gas disposal device and a heat exchanger are installed in order to take measures against the radiolysis gas and heat generated from the solution by irradiation. The system is designed so as to minimize unirradiated solution. In the collection and subdivision system, after the solution including the generated 99Mo is collected from the capsule through pipes, it is treated so as to be products such as PZC-99Mo columns or 99Mo transport containers.

Fig. 1. Schematic diagram of 99Mo production system with solution irradiation method

The detailed design of the 99Mo production system is carried out based on the results of future investigations and tests.

#### **3.2 Progress of the development made thus far**

The most important element of the solution irradiation method is the aqueous molybdenum solution as the irradiation target. The solution with a high concentration near the saturation is used for efficient 99Mo production, and the solution always is in contact with the structural materials of the capsule and the pipes in the 99Mo production system under irradiation. Aqueous molybdate solutions are promising candidates for the irradiation target. The effect of the solutions on metals such as the structural materials has been researched, and molybdates are known as corrosion inhibitors (Kurosawa & Fukushima, 1987; Lu et al, 1989; McCune et al, 1982; Saremi et al, 2006). However, the behavior of aqueous molybdenum solutions including the aqueous molybdate solutions under such the conditions is not well understood. Therefore, the following subjects about the fundamental characteristics of the solutions should be investigated:


326 Nuclear Reactors

In this new method, efficient and low-cost 99Mo production compared with the conventional 99Mo production can be realized by using the (n, γ) reaction and PZC. This new method

The schematic diagram of the 99Mo production system with the solution irradiation method is shown in Fig. 1. The system consists of an irradiation system, a supply and circulation system, and a collection and subdivision system. In the irradiation system, an aqueous molybdenum solution in a capsule installed in a reactor core is irradiated with neutrons under static or circulation condition, and 99Mo is generated. In the supply and circulation system, the solution is supplied to the capsule through pipes and is circulated by a circulator in irradiation operation. A gas disposal device and a heat exchanger are installed in order to take measures against the radiolysis gas and heat generated from the solution by irradiation. The system is designed so as to minimize unirradiated solution. In the collection and subdivision system, after the solution including the generated 99Mo is collected from the capsule through pipes, it is treated so as to be products such as PZC-99Mo columns or 99Mo

Fig. 1. Schematic diagram of 99Mo production system with solution irradiation method

The detailed design of the 99Mo production system is carried out based on the results of

The most important element of the solution irradiation method is the aqueous molybdenum solution as the irradiation target. The solution with a high concentration near the saturation

**3.1 Structure of 99Mo production system with solution irradiation method** 

aims to provide 100% of the 99Mo imported into Japan.

**3. Overview of solution irradiation method** 

transport containers.

future investigations and tests.

**3.2 Progress of the development made thus far** 

4. Effect of γ ray and neutron irradiation on the solutions such as the radiolysis, the γ heating and the activation by-products.

The some subjects described above had already investigated (Inaba et al., 2009), and the progress of the development made thus far is explained as below:
