Research and Development of Advanced Nuclear System

2-6

Toward Highly Efficient Production of MOX Fuel
=Confirmed Feasibility of Production from Agitated Granular Powder=

13wt%H2O

raw powder

14wt%H2O

15wt%H2O

Fig.2-11 SEM photomicrograph of MOX powder obtained using agitating granulation
Granulation was initiated when the added water fraction exceeded 10wt%. Addition of 13〜17wt% water resulted in goodflowability.
1.950 1.958 1.966 1.974 1.982 1.990

pelletejectionO/M ratio

2.00

core rodgreen pellet obtainedby die-wall lubrication
method

1.99O/M ratio

54

average for sintering tray 1 㨪 8
calculation (1973 K)
calculation (2023 K)

die50

1.98

Sintering
tray 14h8h12 h18 h㨪Density (㧑T.D.)

58

1.97
side vent

46
0200

400

600

Pelletizing pressure (MPa)

1.96lubricantlower punch

Sintering
tray 801015
5holding time(h)20

Fig.2-12 Relationship between pelletizing pressure anddensity
47〜55% of theoretical density (T.D.) was obtained by 220〜
550 MPa of pelletizing pressure. 93〜96%T.D. was obtained
after sintering.

Fig.2-13 O/M ratio control of MOX pellet in a small-scale
test
An O/M ratio of approximately 1.97 was obtained after heat
treatment at 2023 K under a control of PH2/PH2O ratio.

Low decontamination fuel has been developed for FBRs. A
highly efficient and simplified fuel production process has
been developed that requires one-third as many steps as theconventional process. The core techniques include agitating
granulation, die-wall lubrication, and control of the oxygen tometal (O/M) ratio.
Agitating granulation leads to the formation of a goodflowable powder that can be smoothly poured into a metallic
die. Water is added to a uranium-plutonium mixed oxide(MOX) powder obtained using the microwave de-nitration
method. With agitating granulation, the conventional
granulation process can be omitted. Investigation of therelationship between the granulation conditions and thepowder characteristics revealed that a large diameter
granulated powder with good flowability can be obtained byadding 13〜17wt% water (Fig.2-11).
The die-wall lubrication method involves the application ofa lubricant on the die-wall in order to decrease the friction
between the MOX powder and die wall. With this technique,conventional processes, such as the addition and mixing of
lubricant and presintering, can be omitted. As shown in
Fig.2-12, the density can be controlled without a nonuniform

compressive load, by applying the lubricant in a spiralmanner from the bottom up. The amount of lubricant can bedecreased from 0.2wt% to 0.017wt% using this method.
The O/M ratio can be adjusted to 1.97 during sintering inorder to prevent chemical reactions between the fuel andcladding. The O/M ratio depends on the oxygen potential,
which is affected by the PH2/PH2O in the H2/Ar gas used forsintering. With a conventional sintering furnace, a lack of
uniformity of the O/M ratio among different pellets is arecognized problem. It has been suggested that the H2 gas
remaining between the sintering plates cannot react
uniformly with the pellets. Therefore, a mesh plate wasdeveloped. In a small-scale (a few kilogram scale) test usingmesh plates, it was confirmed that the gas was equallysupplied to all of the pellets. The temperature andatmospheric conditions for control of the O/M ratio were thendetermined on the basis of the laboratory-scale test results.
As can be seen in Fig.2-13, the O/M ratio can be accuratelycontrolled.
Based on the results of this investigation, an efficient
production process was confirmed that involves agitating
granulation, die-wall lubrication, and heat treatment.

Reference
Hirooka, S. et al., Oxide Fuel Fabrication Technology Development of the FaCT Project(3) - Analysis of Sintering Behavior for MOX Pellet Production,
Proceedings of GLOBAL 2011, Makuhari, Japan, 2011, paper no.445139, 6p., in CD-ROM.

42 JAEA R&D Review 2012