Page 280 - 00. Complete Version - Progress Report IPEN 2014-2016

280 Nuclear Reactors and Fuel Cycle | Progress Report

imum uranium density is 4.8 gU/cm3 and for 6 to 10%. Erbium oxide is used with mass con-
U3O8-Al the maximum is 3.2 gU/cm3. centration between 1 and 2.5%. These differ-
ences in proportion are due to higher absorp-
From the important parameters for fuel plate tion cross section of Erbium.
qualification, it was found that the length and
width of the meat of all produced fuel plates The study of densification using these two ma-
met the specification. Also, the microstruc- terials followed the same route. The powders
ture of the dispersions showed good appear- were mixed mechanically and pressed in or-
ance, as showed in Figure2. der to their green density reach 50% of theo-
retical density of the mixture.
Fuel plates with high uranium concentration
were successful fabricated. U3Si2-Al fuel plates Experimentally, it was found that additions of
reached uranium density of 4.7 gU/cm3. U3O8- up to 4% of Er2O3 increase shrinkage to high-
Al fuel plates reached uranium density of 3.05 er values than for pure UO2, showing that er-
gU/cm3. bium acts as a sintering aid agent and allows
its use without the need of additives. On the
Studies on densification of UO2 in other hand, Gadolinium Oxide, when added
LWR type fuels with burnable poison to 7% in proportion by mass, causes a signifi-
cant drop in shrinkage. It was possible to get
Light Water Reactors (LWR) use enriched ura- best results using nano-gadolínia, increasing
nium to increase the reactivity of nuclear fuel, the shrinkage and also allowing to use it for
but this would have no use if it wasn’t possible the manufacture of nuclear fuels without the
to extend nuclear reactions over time, allow- need of additives.
ing the nuclear fuel useful life to be extended.
Quantification of crystalline

Burnable poison is first of all a tool for long- phases of uranium silicide
term control of a nuclear reactor. Its function is
basically to control the neutron population. For To synthesize of uranium silicide intermetal-
this purpose, the chemical element employed lic at the Nuclear Fuel Center, metallic ura-
should react with neutrons arising from nucle- nium and silicon are melted in an induction
ar fission of the uranium atom and besides, the furnace at vacuum atmosphere. Even though
isotope formed (son of nuclear reaction) should appropriate precautions are taken, due to the
be unable to perform this function. Because of considerable different vapor pressure of the
this feature, the term burnable is established, elements, a perfect stoichiometry of U3Si2 is
as this material will lose the ability to absorb virtually impossible. Considering that the di-
neutrons, while the fuel reactivity decreases. verse compositions of this material have dif-
ferent behavior under radiation, the control
For this purpose, the two burnable poisons of the formed compounds is vital for the re-
commercially used with the nuclear fuels are actor performance and security. In this sense,
Gadolinium and Erbium. Both burnable poi- a method is being developed for quantifica-
sons belongs to rare earths family. They are tion of crystalline phases of uranium silicide
added to fuel in powder form as oxides, with using X-ray diffraction and data refinement
chemical formula Gd2O3 and Er2O3. The first using the Rietveld method. Initial results are
one is used with mass concentration between promising, however, attention must be tak-

Instituto de Pesquisas Energéticas e Nucleares