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

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

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

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 expensive.

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

## **2.2.1 Solid irradiation method**

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

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 into Japan (Inaba et al., 2011).
