**5.2 Test method and conditions**

332 Nuclear Reactors

Fig. 4 shows the schematic diagram of a test apparatus, which was used in order to investigate compatibility between a flowing aqueous K2MoO4 solution and a structural material and the chemical stability of the solution. The test apparatus consists of a immersion container for immersing specimens under flow, a glass storage tank with a volume of about 700 cm3, a thermocouple inside the storage tank for solution temperature measurement, a feed pump to circulate the solution, a flowmeter, Teflon tubes with an inner diameter of 7.5 mm to connect each component, two syringes, which were used for depressurization, solution supply, air purge and solution sampling, a data logger to collect temperature data and to monitor the temperature and so on. Some components such as the immersion container and the storage tank were installed into a heating chamber to heat the

Syringe

Luer lock

Flowmeter

Immersion container

Looped Teflon tube

Specimens

Draw line of test solution

Data logger

Fig. 4. Schematic diagram of test apparatus for compatibility test

Feed pump

Glass storage tank

Heating chamber

Teflon tube

Thermocouple

Stainless pad

circulating solution was about 300 cm3 except the volume of the storage tank.

The immersion container consists of a glass outer tube with an outer diameter of 22 mm and a height of 62.5 mm and a Teflon inner holder with an inner diameter of 13 mm and a height of 60 mm, and two specimens (specimen 1 and 2) were fixed in the center of the container by the holder as shown in Fig. 5 and they were arranged one above the other in the container. The storage tank was located upstream of the immersion container to keep the solution temperature constant and to prevent the solution from pulsating by the feed pump. In addition to the storage tank, a looped long Teflon tube connected between the pump and the storage tank was used to keep the solution temperature in the heating chamber. The total length of the circulation route of the solution was about 6.8 m, and the total quantity of

1 2

**5.1 Test apparatus** 

solution.

The compatibility test was carried out by using the test apparatus with a closed loop shown in Fig. 4. After the specimens were set in the immersion container, aqueous K2MoO4 solution was injected in the closed loop, and the solution was circulated at a constant flow rate. The flow rate was set at about 120 cm3/min, considering the flow velocity assumed in an actual 99Mo production system. The concentration of the solution was adjusted to about 90% of the saturation for the prevention of crystallization, and the temperature of the solution was maintained at about 80C for the prevention of boiling. As the specimens immersed in the solution, stainless steel SUS304 was used based on the results of the previous immersion tests (Inaba et al., 2009). SUS304 has been used as the structural material of capsules and pipes in JMTR. The size of the specimens was 10W×30L×1.5T mm. Table 3 shows the chemical composition of a SUS304 specimen. The total immersion time of the specimens was 112.7 days, and the immersion time under flow was 84.5 days out of a total of 112.7 days. The total immersion time was longer than the immersion time under flow because the feed pump was temporarily stopped by the planned blackouts and the pump troubles.

During the test, at regular intervals, the specimen 1 was taken from the immersion container, and the specimen's weight was measured after washing by pure water and drying, and its surface state was observed. In addition, the aqueous solution was sampled from the closed loop by using one of the syringes, and the pH and molybdenum concentration of the solution were measured, and the solution state was observed.

After the test, the specimen 1 and 2 were taken from the immersion container, and the specimens' weight was measured, and their surface states were observed. In addition, the aqueous solution was sampled from the closed loop, and the pH and molybdenum concentration of the solution were measured, and the solution state was observed.

Development of 99Mo Production Technology with Solution Irradiation Method 335

Solution conditions Temp. : 81ºC (average) Conc. : 57 wt% (initial stage) Flow rate : 123 cm3/min (average)

Fig. 7. Relationships between immersion time and corrosion rates of SUS304 specimens

● Specimen 1 ○ Specimen 2

0 20 40 60 80 100 120

Immersion time (d)

Fig. 8. Inverted materials microscope photograph of specimen 2 surface immersed in

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

immersed in flowing aqueous K2MoO4 solution for 84.5 days


0

0.05

Corrosion rate

 (mm/y) 0.1

0.15

flowing aqueous K2MoO4 solution for 84.5 days


Table 3. Chemical composition of SUS304 specimen

### **5.3 Results and discussions**

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 time under flow of 85.5 days respectively.
