Development of Experimental Techniques/Facilities at JAEA R&D Centers

Oarai Research and Development Center

13-6 Development of Domestic 99Mo Production by (n, ) Method－ Fabrication Technology for High-Density MoO3 Pellet －Pressure㺃Pulse current

Graphite punch

Graphite mold
Thermocouple

Molybdenum trioxide
powderGraphitespacerElectrode (–)

Sintering density (%T.D.)

Electrode (+)
Graphitespacer10095

Atmosphere: Air
Pellet size:φ20 × 10 mm

90

1 μm

85
1 μm

80
75
70

1 μm

400

450

500

550600Sintering temperature (℃)

Pressure
Fig.13-11 Schematic diagram of spark plasma sintering
methodStarting powder is installed in graphite mold. Sintering andmolding are simultaneously performed by pulse electricity
under pressure. During this operation, powder surfaces
are cleaned and activated, and local temperature increase
produces high-density pellet under lower temperature.

Fig.13-12 Relationship between sintering temperature andsintering density of MoO3 pellet
The sintering density increases with increasing sintering
temperature. The target density (90%T.D., T.D.: theoreticaldensity) was attained by sintering at about 500 °C. On theother hand, changes in grain growth were not observed below
a sintering temperature of 550 °C.

In Japan, about 1400000 cases are diagnosed using nuclear
medicine every year. About 900000 of these nuclear medicine
diagnoses use technetium-99m (99mTc), whose half-life is 6 h.
99mTc is produced as a daughter nuclide from molybdenum-99( 99Mo), whose half-life is 66 h. The quantity of 99mTc
demanded in Japan is ranked as second in the world, after
only the U.S.A., but all of the 99mTc is imported from abroad.
A stable supply of 99Mo in Japan might be difficult to obtainbecause of troubles with transportation and other problems.
Therefore, the establishment of domestic production of 99Mo
is an important issue for Japan. Two methods are used toproduce 99Mo by nuclear reactors, the nuclear fission method
and the neutron activation method [(n, γ) method]. The Japan
Materials Testing Reactor (JMTR) is developing the (n, γ)
method for 99Mo production from the viewpoints of physicalprotection of nuclear materials and the reduction of highly
radioactive waste.
99 Mo is produced in molybdenum trioxide (MoO ,3sublimation temperature: 795 °C) by the (n, γ) method in
nuclear reactors. Next, irradiated MoO 3 is resolved into
6M sodium hydroxide (NaOH), and then 99mTc is extracted
from the solution. The technical issues in this method are
the establishment of a high production rate of 99Mo andthe extraction of 99mTc with a high purity and radioactivity
concentration. For that purpose, a fabrication method forhigh-density MoO3 pellets was also developed in this study toincrease the amount of 98Mo per unit volume and to optimize

the characteristics such as solubility.
As the first step, fabrication tests of high-density MoO3
pellets were conducted using the spark plasma sintering
method, as shown in Fig.13-11.
This method results in a high-purity pellet because no binder
is added, and the sintering temperature is low. The pellet
properties were measured for various sintering temperaturesand sintering densities. In this result, the target density wasattained by sintering at a temperature above 500 °C, as shownin Fig.13-12. Scanning electron microscopy observation ofthe MoO3 pellet revealed that grain growth did not occur
below a sintering temperature of 550 °C, and the grain sizeof the MoO3 pellet was almost the same as that of the starting
powder. Next, MoO3 pellets were oxidized in atmosphere asan oxidization treatment, and the solubility into 6M NaOH
was measured. The result confirmed that the MoO3 pellet
dissolved within the target time, and the obtained solution wasclear and exhibited high purity.
The above results demonstrate that a technique forfabricating high-density MoO3 pellets from an irradiated target
was established, and the prospects are bright for domestic99Mo production by the (n,γ) method.
The present study was performed as part of the program“Technology development of domestic 99Mo/99mTc productionby (n, γ) method in JMTR” commissioned by the Ministry ofEducation, Culture, Sports, Science and Technology of Japan(MEXT).

Reference
Nishikata, K. et al., Fabrication and Characterization of High-Density MoO3 Pellets, Proceedings of the 2012 Powder Metallurgy World Congress &Exhibition (PM 2012), Yokohama, Japan, 2012, 8p., in CD-ROM.
JAEA R&D Review 2013115