**3.2.1 Selection of candidates for irradiation target**

The selection of candidates for the irradiation target was carried out. The conditions required for the irradiation target solution are as follows:


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 compounds.

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 73.5 g respectively.

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 irradiated with neutrons.

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

Development of 99Mo Production Technology with Solution Irradiation Method 329

ABCDEFGH I J K LMNOPQR

SH2 SH3 SR1

SH1

OSF SR2 1

HR

Size and material of capsule

OSF 1

M-9

Be frame

Oarai shroud facility-1

Gamma-ray shield plate

Dissolved molybdenum in each irradiation target

Table 2. Conditions of capsule and two irradiation targets of aqueous (NH4)6Mo7O24· 4H2O

The disintegration rates of 98Mo (isotopic ratio: 24.138%) and 99Mo are shown as following

*dN <sup>N</sup> dt* = −

φσ

98 98

(1)

98

• Aqueous (NH4)6Mo7O24・4H2O solution (concentration: 90% of saturation):

• Aqueous K2MoO4 solution (concentration: 90% of saturation):

**4.2 Basic equations for estimates of 99Mo production rates** 

Outer tube: outer diameter of 65 mm, inner diameter of 61 mm Inner tube: outer diameter of 59 mm, inner diameter of 55 mm

Fig. 2. JMTR core arrangement

372.8 g/1,663 cm3

702.7 g/1,663 cm3

and K2MoO4 solutions

equations:

Irradiation height: 700 mm Irradiation volume: 1,663 cm3

Material: Stainless steel

Fuel element

Control rod with fuel follower Al reflector element

Be reflector element

### **3.2.2 Unirradiation and γ-ray irradiation tests**

Unirradiation and γ-ray irradiation tests were carried out by using the selected two aqueous molybdate solutions (aqueous (NH4)6Mo7O24·4H2O and K2MoO4 solutions), and compatibility between the two solutions and the structural materials of stainless steel and aluminum, the chemical stability, the circulation characteristics, the radiolysis and the γ heating of the two solutions were investigated. In addition, the integrity of PZC was investigated under γ-ray irradiation. As a result, the following were found:


However, the pH of the aqueous (NH4)6Mo7O24·4H2O solution needs to be adjusted from weak alkaline to weak acid for the prevention of precipitation. This is a disadvantage as one of the candidates for the irradiation target.

At present, the aqueous K2MoO4 solution, which has no pH adjustment and has higher molybdenum content than that of the aqueous (NH4)6Mo7O24·4H2O solution, is investigated as the first candidate of the irradiation target.
