AB INITIO STUDY OF ADVANCED METALLIC NUCLEAR FUELS FOR FAST BREEDER REACTORS Page: 4 of 14
This article is part of the collection entitled: Office of Scientific & Technical Information Technical Reports and was provided to Digital Library by the UNT Libraries Government Documents Department.
The following text was automatically extracted from the image on this page using optical character recognition software:
of a-U phase. In other words, each of these high-melting temperature elements plays a role of '-
stabilizer' helping to keep uranium in the metastable bcc phase upon cooling.
Zirconium metal possesses a unique capability to suppress interdiffusion between the
nuclear fuel and stainless-steel cladding and this makes Zr a good candidate as a solver to
nuclear fuels for fast breeder reactors. The Zr-based actinide alloys, particularly U-Pu-Zr, proved
to be very promising fuels for liquid metal fast breeder reactors because of their advantage in
view of superior performance, reactor safety, and fuel cycle economics . It was established 
that the U-Zr system is characterized by the complete solubility of the body centered cubic high-
temperature phases, y-U and f-Zr, that is usually referred to in phase diagrams by '-phase' solid
solutions. Below T ~ 722 0C, these solutions separate into a relatively flat miscibility gap.
The intermediate UZr2 phase with C32 (AlB2)-type structure is formed on cooling from
the y-phase with the homogeneity range from 63 to 82 at. % Zr . It is well known that the
high-temperature Zr-based solid solutions may transform into the so-called metastable ow-phase
at low temperatures, which can also be stabilized from the a (hcp) phase of Zr under
compression . Ogawa et al.  suggested that the 8-UZr2 phase could be regarded as the cw-
phase solid solution that is stabilized against the a-Zr (hcp) structure by addition of U due to
increase of Zr d-band occupancy.
Recently Kim et al.  suggested some advantages of U-TRU-Mo fuels over U-TRU-Zr
in TRU-burning advanced fast nuclear reactors: U-Pu-Mo fuels have higher thermal
conductivity, lower thermal expansion, and higher melting points than U-Pu-Zr fuels resulting in
better safety. However, the main advantages of U-TRU-Mo fuels lies in a much lower
constituent redistribution, including migration of minor actinides (MA) and lanthanides (LA)
toward the cladding due to the existence of a single y-phase over typical fuel operation
temperatures. Contrary to U-Pu-Mo fuels, in U-Pu-Zr fuels MA Am redistribution is similar to
that of Zr with tendency to precipitate to the center and near the fuel surface .
Low-enriched uranium alloys with 6 to 12 wt. % of Mo are under consideration by the
GTRI program as very high density fuels (8-9 gU/cm3 and 15-17 gU/cm3 for dispersion-type and
monolithic-type, respectively) that allow nuclear research and test reactors conversion from use
of HEU to LEU fuels . According to the U-Mo phase diagram , Mo exhibits a high
solubility (- 35 at. %) in y-U (bcc) but below 560 0C the equilibrium state corresponds to a
mixture of a-U (orthorhombic) and so-called Y-phase, which is the U2Mo compound with the
C 11b (MoSi2 prototype) structure. However, by rapid cooling from the y-phase a metastable y-
state can be retained up to room temperature.
Semi-empirical model calculations , supported by experimental observations, indicate
that the excess enthalpy of solution of the y-U-Zr phase controls the constituent redistribution
process in the U-Zr fuels. This statement encouraged us to perform ab initio calculations of the
heat of formation of the y-U-Zr solid solutions [14, 15]. We later expanded our study to the
ternary U-Pu-Zr system  as well as to the bcc alloys that plutonium forms with MA . In
our recent paper  we presented results of ab initio calculations of the heat of formation of the
y-U-Mo solid solutions. In this study we summarize results published in Ref. [14-18] and present
results of ab initio calculation of the decomposition curve for the y-U-Mo alloys. We also present
results of ab initio calculations of the heat of formation of Am with Zr and Mo and discuss a
possible mechanism of Am redistribution in the y-U-Zr and y-U-Mo.
Here’s what’s next.
This article can be searched. Note: Results may vary based on the legibility of text within the document.
Tools / Downloads
Get a copy of this page or view the extracted text.
Citing and Sharing
Basic information for referencing this web page. We also provide extended guidance on usage rights, references, copying or embedding.
Reference the current page of this Article.
Landa, A; Soderlind, P; Grabowski, B; Turchi, P A; Ruban, A V & Vitos, L. AB INITIO STUDY OF ADVANCED METALLIC NUCLEAR FUELS FOR FAST BREEDER REACTORS, article, April 23, 2012; Livermore, California. (digital.library.unt.edu/ark:/67531/metadc831967/m1/4/: accessed September 25, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.