Research and Development of Advanced Nuclear System

1-10 Toward Innovative MOX Fuel Production by Simplified Process–Developing a Unified Process Combining
Microwave Heating with Granulation–
Present Process

Recovered MOX

UO2 powder

De-Nitration

bySimplified Pellet Fuel Process

Pu/U Solution

Pu EAS*M㧴 conversion

M㧴 conversion/Binder-less Granulation

Calcination / Reduction

Calcination / Reduction

MOX powder (50%Pu)

MOX powder

Refill*Pu EAS
Pu Enrichment
Adjustment
in Solution

RefillLot Blending

Weighing

Cross Blending

Ball Milling
Binder Mixing

Reduction of powder
treatment processes etc

Granulation
DissolutionLubricant Mix.

Effect of Pu EAS

Pressing
Pre-waxing
Sintering
Crashing / Milling

De-gassing

Effect of Binder-less Granulation

MOX hollow pellet
Pressing

Recovered MOX

Effect of Die-lubrication pressing

Sintering

Grinding

Grinding

Density and Appearance Inspection

Density and Appearance Inspection

Inspection by Gov.

Inspection by Gov.

Product Pellet

Product Pellet

Lot Mixing

ǩ-Auto radio

Fig.1-30 Simplified pellet fuel production process
Simplified pellet fuel making process (right) compared with present process (left)

The key for the industrial production of MOX fuel to beburned in the FBR is the reduction of its manufacturing cost.
The most promising method for meeting this requirement is thesimplified technology shown in Fig.1-30. The key ideas behind
this method are (1) adjustment of mixing rate of PuO2/UO2 inthe liquid state, (2) combining de-nitration with granulation,and (3) fabricating a hollow-pellet with a lubricated die. Thedetails are as follows.
Apart from its simplicity, the distinctive characteristic of thesimplified technology is its accuracy in adjustment of mixing
rate of PuO2/UO2, since the job is carried out in the liquid state.
By this means, complicated powder mixing processes neededin the conventional solid state mechanical mixing systemwere greatly improved. In simulation experiments employing
a mockup system and typical liquids, a mixing accuracy of±2.5% was attained. The overflow type fixed quantity service
cylinder and an air lift separator which supplies air freeliquid into the service cylinder played important roles in thissuccess. In laboratory experiments employing real fuel liquids(Pu/U=3/7), we observed the mixing state of the powder
products which were de-nitrated by microwave heating, andconfirmed that non uniform distribution of Pu was not appearedin the hollow-pellet. The results clearly show that the uniformityof MOX powder products obtained by the liquid phase mixing
method is better than that by the conventional method.
Another distinctive characteristic of the simplified technology
is the granulation done in process of adjusting the U/Pu mixing
rate. In this method, high speed agitation with rotating blades isefficiently employed, and not an organic binder but rather wateris sprayed, resulting in slippery particles. Thus, the flowabilityof particles is improved (over 60 in Carr coefficient), a great
benefit. The density of MOX hollow-pellets, which were filledwith these particles and compressed by the usual press in a die,reached over 95% TD after sintering.
Further, a hollow-pellet was fabricated utilizing the same
MOX particles as above, and compressed in a die which
was lubricated. These results demonstrated the feasibility ofthis simplified technology for MOX fuel production on thelaboratory scale.
Hereafter, we would like to carry out larger scale experimentsto attain the target production rate by 2010 when the adoptionof innovative technology will be made. The improvement ofproduction efficiency is the key for this innovative technology,we believe.

Reference
Suzuki, M. et al., Development of FR Fuel Cycle in Japan(3) -Current State on Unified Technology of Denitration Conversion and Granulation for
Simplified Pellet Fuel Fabrication Based on Microwave Heating- , Proceedings of 2008 International Congress on Advances in Nuclear Power Plants(ICAPP '08), Anaheim, CA, USA, 2008, p.2036-2045, in CD-ROM.
JAEA R&D Review 200819