PLENTIFUL ENERGY

During casting, a partial vacuum (10-25 torr) was drawn above the melt for
approximately twenty minutes. From data on evaporation rates of tungsten under
increased pressure, it was estimated that the evaporation rate of americium could be
reduced two hundred times by casting under a pressure of about 800 torr.
Furthermore, based on experience with U-Zr injection casting, the vacuum level in
the molds could be as high as 150 torr and the molds would still fill. (The filling
technique starts at partial vacuum in the space above the melt and then pressurizes
it, drawing the melt up into the glass tubes.) A judicious choice of casting
parameters combined with feed stocks free of volatile impurities should make
fabrication of minor actinide containing fuels quite viable.
The minor-actinide-containing test pin (U-20Pu-1.3Np-1.2Am) was irradiated in
EBR-II to 6% burnup, but this test too was prematurely terminated when EBR-II
was shut down in 1994. The post-irradiation examinations showed very satisfactory
irradiation performance. The micrograph shown in Figure 6-7 does not exhibit any
features not seen in other fuels. The radial distribution of the fuel constituents is
also shown in Figure 6-7. The uranium, plutonium, and zirconium distribution is
very similar to that in the standard U-Pu-Zr fuel. Neptunium does not migrate; it
stays put. Americium generally follows zirconium, precipitates in pores, and tends
to migrate more in porous fuel. Although this was a limited test, the information it
gave was positive, indicating that recycle in IFR all-actinide fuel should raise no
new difficulties from spent fuel with only the major isotopes in it.
(a)
(b)
U
Pu
Zr
Am
Np
1 mm
0 1
2
Fuel radius from center (mm)
Figure 6-7. Post irradiation examinations for minor-actinide-containing fuel
at 6% burnup (U-20Pu-1.3Np-1.2Am)
6.10 Other Characteristics
Metal fuel greatly eases the requirements placed on the non-reactor portion of
the fuel cycle. Fabrication is simple, easy and cheap, processing is done in only a
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