**5.3.1 Corrosivity of flowing aqueous K2MoO4 solution for SUS304**

The surface states of the two SUS304 specimens before and after the immersion in the flowing aqueous K2MoO4 solution for a total of 84.5 days are shown in the Fig. 6, and the relationships between the immersion time and corrosion rates of the specimens are shown in Fig. 7. The corrosion rates were estimated by the following equation:

Fig. 6. Surface states of SUS304 specimens before and after compatibility test

The equation (6) shows the wastage thickness per unit time. In the visual observation and comparison of the two specimens' surfaces before and after the compatibility test, whereas streamlined patterns, partly slight tarnish and the partly slight loss of metallic luster were found on the surfaces, obvious corrosion such as corrosion products was not found. The corrosion rate of the specimen 1 increased temporarily to 0.10 mm/y in the initial stage of the test (an immersion time of 21 days) and decreased finally to 0.02 mm/y. On the other hand, the corrosion rate of the specimen 2 was 0 mm/y at the beginning and end of the test. There was no change in the state of the specimen 1 surface in the initial stage of the test, and the temporary increase of the specimen 1 corrosion rate might be affected by taking out from the immersion container.

C Si Mn P S Ni Cr Fe 0.06 0.51 0.73 0.026 0.002 8.03 18.07 Balance

The average temperature and flow rate of the aqueous K2MoO4 solution used in the test were 81C for a total immersion time of 112.7 days and 123 cm3/min for a total immersion

The surface states of the two SUS304 specimens before and after the immersion in the flowing aqueous K2MoO4 solution for a total of 84.5 days are shown in the Fig. 6, and the relationships between the immersion time and corrosion rates of the specimens are shown in

*Surface area Immersion time Density*

<sup>×</sup> <sup>×</sup> <sup>=</sup> (6)

**5.3.1 Corrosivity of flowing aqueous K2MoO4 solution for SUS304** 

Fig. 7. The corrosion rates were estimated by the following equation:

*Weight change Corrosion rate*

Fig. 6. Surface states of SUS304 specimens before and after compatibility test

The equation (6) shows the wastage thickness per unit time. In the visual observation and comparison of the two specimens' surfaces before and after the compatibility test, whereas streamlined patterns, partly slight tarnish and the partly slight loss of metallic luster were found on the surfaces, obvious corrosion such as corrosion products was not found. The corrosion rate of the specimen 1 increased temporarily to 0.10 mm/y in the initial stage of the test (an immersion time of 21 days) and decreased finally to 0.02 mm/y. On the other hand, the corrosion rate of the specimen 2 was 0 mm/y at the beginning and end of the test. There was no change in the state of the specimen 1 surface in the initial stage of the test, and the temporary increase of the specimen 1 corrosion rate might be affected by taking out

Table 3. Chemical composition of SUS304 specimen

**5.3 Results and discussions** 

from the immersion container.

time under flow of 85.5 days respectively.

(Unit: wt%)

Fig. 8. Inverted materials microscope photograph of specimen 2 surface immersed in flowing aqueous K2MoO4 solution for 84.5 days

For the confirmation of the detailed surface states, the specimen 2 as the representative of the two specimens were observed and analyzed with an inverted materials microscope and a field emission Electron Probe Micro Analyzer (EPMA). Fig. 8 shows the inverted materials microscope photograph of the specimen 2 surface. The black lines and dots in Fig. 8 are preexistent scratches and hollows. Tarnish is recognized on the surface. Fig. 9 shows the Scanning Electron Microscope (SEM) photograph of the specimen 2 cross-section surface taken with the EPMA, and Fig. 10 shows the color map of the specimen 2 cross-section surface analyzed with the EPMA. The cross-section surface was prepared by cutting the center of the specimen 2, mounting in a resin and polishing. A thin coating layer, which is thought to be the cause of the tarnish, is found on the surface as shown in Fig. 9. To see Fig. 10, K and Mo, which are the main components of K2MoO4, are not detected and a relativelyhigh level of Si is detected on the surface. After the test, the corrosion of the glass outer tube in the immersion container was found, and then it is considered that the main component of

Development of 99Mo Production Technology with Solution Irradiation Method 337

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

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

Aiming at the domestic production of 99Mo in Japan, the development of 99Mo production

The author would like to thank Dr. Tsuchiya, K. and Mr. Ishida, T. of JAEA and Mr.

AECL (December 2007). AECL Provides Status Report on NRU Reactor, In: *AECL Web Page,*

AECL (May 2008). AECL to Discontinue Development of the MAPLE Reactors, In: *AECL* 

Inaba, Y.; Ishikawa, K.; Tatenuma, K. & Ishitsuka, E. (2009). Development of 99Mo

*Energy Society of Japan,* Vol. 8, No. 2, (June 2009), pp. 142-153 (in Japanese) Inaba, Y.; Iimura, K.; Hosokawa, J.; Izumo, H.; Hori, N. & Ishitsuka, E. (2011). Status of

*Nuclear Science,* Vol. 58, No. 3-3, (June 2011), pp. 1151-1158, ISSN 0018-9499 Ishitsuka, E. & Tatenuma, K. (2008). Manufacturing Method of Radioactive Molybdenum,

Production Technique by Solution Irradiation Method, *Transactions of the Atomic* 

Development on 99Mo Production Technologies in JMTR, *IEEE Transactions on* 

Manufacturing Apparatus and Radioactive Molybdenum Manufactured Thereby,

http://www.aecl.ca/NewsRoom/News/Press-2007/071204.htm

http://www.aecl.ca/NewsRoom/News/Press-2008/080516.htm

used as the structural material of the capsule and the pipes.

with the solution irradiation method is kept going.

27.06.2011, Available from

*Japanese Patent*, 2008-102078

Ishikawa, K. of KAKEN. Inc. for their valuable comments.

*Web Page,* 27.06.2011, Available from

**6. Conclusion** 

on will be investigated.

**7. Acknowledgment** 

**8. References** 

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 K2MoO4 solution for 84.5 days

Fig. 10. EPMA color map of specimen 2 cross-section surface immersed in flowing aqueous K2MoO4 solution for 84.5 days

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

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.
