**2.2.2 Solution irradiation method**

324 Nuclear Reactors

In this paper, a comparison between 99Mo production methods, an overview of the solution irradiation method containing the structure of 99Mo production system with the method and the progress of the development made thus far, estimates of 99Mo production with the

A comparison between the three 99Mo production methods (the fission method, the solid irradiation method and the solution irradiation method) is shown in Table 1, assuming the

In the conventional fission method ((n, f) method), high-enriched uranium targets are irradiated with neutrons in a testing reactor, and 99Mo is produced by the 235U (n, f) 99Mo reaction. Most of the world supply of 99Mo is produced by the (n, f) method since 99Mo with a high-level specific activity of 370 TBq/g-Mo is obtained. However, the method has problems about the nuclear nonproliferation and the generation of a significant amount of radioactive waste including Fission Products (FPs) and Pu. Caused by the radioactive waste, the separation process of 99Mo is too complex, and 99Mo production with the (n, f) method needs expensive facilities and extreme care to avoid contamination with FPs. The 99Mo production cost by this method achieves 57 US\$/37 GBq (Boyd, 1997), and it is too

In the conventional solid irradiation method, solid targets including natural molybdenum such as MoO3 pellets are irradiated with neutrons in a testing reactor, and 99Mo is produced by the 98Mo (n, γ) 99Mo reaction. The post-irradiation process is only dissolution of the irradiated solid targets with an alkaline solution, and only a small amount of radioactive waste is generated in the process compared with the (n, f) method. The 99Mo production cost

However, the (n, γ) method has the disadvantage of producing 99Mo with a low-level specific activity of 37-74 GBq/g-Mo and therefore the method has not had practical application in earnest. In order to utilize 99Mo with the low-level specific activity, a highperformance adsorbent for (n, γ) 99Mo is needed. The Japan Atomic Energy Research Institute (the present organization: JAEA) and KAKEN Inc. had developed the highperformance molybdenum adsorbent of Poly-Zirconium Compound (PZC) in 1995 (Hasegawa et al., 1996) and improved PZC (Hasegawa et al., 1999), and then the practical application of the (n, γ) method is just in sight. The molybdenum adsorbent performance of PZC is over 100 times compared with the conventional molybdenum adsorbent of alumina. 99Mo production in JMTR will start by using the solid irradiation method. JMTR aims to provide 99Mo of 37 TBq/w (1,000 Ci/w), and it will cover about 20% of the 99Mo imported

of this method or the (n, γ) method is only 0.83 US\$/37 GBq (Boyd, 1997).

method, and the results of a newly conducted test are described.

**2. Comparison between 99Mo production methods** 

99Mo production in JMTR, which is a tank-type reactor.

**2.1 Fission method ((n, f) method)** 

**2.2 Neutron capture method ((n, γ) method)** 

**2.2.1 Solid irradiation method** 

into Japan (Inaba et al., 2011).

expensive.

In the new solution irradiation method, a solution target including natural molybdenum such as an aqueous solution of a molybdenum compound (aqueous molybdenum solution) is irradiated with neutrons in a testing reactor, and 99Mo is produced by the 98Mo (n, γ) 99Mo reaction. This new method is the improved type of the solid irradiation method, and it is possible to enhance the 99Mo production compared with the solid irradiation method. The solution irradiation method has the following advantages compared with the solid irradiation method:



Table 1. Comparison between three 99Mo production methods

Development of 99Mo Production Technology with Solution Irradiation Method 327

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

1. Selection of the aqueous molybdenum solutions as candidates for the irradiation target

4. Effect of γ ray and neutron irradiation on the solutions such as the radiolysis, the γ

The some subjects described above had already investigated (Inaba et al., 2009), and the

The selection of candidates for the irradiation target was carried out. The conditions

1. The irradiation target solution has the high molybdenum content for the efficient

2. Few activation by-products are generated by target solution irradiation for the

3. The solution has good compatibility with the structural materials of the capsule and the

4. The solution is chemically stable and has no generation of precipitation for the

Based on the conditions (1) and (2), two aqueous molybdate solutions (aqueous ammonium molybdate and potassium molybdate solutions) were selected as the candidates for the irradiation target among the aqueous solutions of general molybdenum

The solubilities of ammonium molybdate ((NH4)6Mo7O24·4H2O) and potassium molybdate (K2MoO4) for pure water are 44 g/100 g-H2O and 182.4 g/100 g-H2O respectively, and the molybdenum contents in the solubilities of (NH4)6Mo7O24·4H2O and K2MoO4 are 23.9 g and

The activation by-product of (NH4)6Mo7O24·4H2O is only 92mNb. The activation by-products of K2MoO4 are 42K and 92mNb. The γ-ray energy emitted from 42K is high. However, by using PZC, it is possible to remove 42K and 92mNb from the two aqueous molybdate solutions

The conditions (3) and (4) were confirmed by tests with the two solutions.

characteristics of the solutions should be investigated:

heating and the activation by-products.

**3.2.1 Selection of candidates for irradiation target** 

prevention of radioactive contamination.

pipes for the prevention of corrosion.

required for the irradiation target solution are as follows:

prevention of an obstruction to the solution's flow.

3. Chemical stability of the solutions

production of 99Mo.

compounds.

73.5 g respectively.

irradiated with neutrons.

2. Compatibility between the solutions and the structural materials

progress of the development made thus far is explained as below:

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