English version

Phase stability and oxidation behavior of high plutonium content fast reactor MOX Fuel

(Ref. BAP-2017-93)

Tewerkstelling : Voltijds
Duur : Bepaalde duur
Plaats : Leuven
Solliciteren tot en met : 24/03/2017
For future fast reactors, like the lead-bismuth-cooled reactor MYRRHA, hypo-stoichiometric uranium-plutonium oxides (mixed oxides=MOX) (O/(U/Pu)=O/M<2.0) with Pu content up to 30% are envisaged. For Pu level above 20%, it is known [1-3] that phase separation into two face centered cubic phases with different oxygen content is likely to occur during cooling after sintering. Recent studies [4] revealed that depending on cooling rate and final O/M ratio, phase separation can induce severe macroscopic cracks that can potentially impact fuel properties and cause in-pile safety issues (e.g. decrease in thermal conductivity). This calls for a careful re-appraisal of conditions used for high plutonium MOX fabrication, in particular on the determination and control of oxygen stoichiometry and cooling rate. A correlated issue is the spontaneous oxidation of MOX pellets at room temperature, even if subjected to very low oxygen and moisture contents as it is the case during their stay in glove boxes. Using XRD measurements, it has been recently shown [5] that spontaneous oxidation was mostly dictated by the variation in stoichiometry of the low-oxygen phase, coupled to the decrease in its fraction in bi-phasic MOX. The knowledge of the extent and kinetics of the oxidation process is therefore crucial when fabricating and/or handling hypo-stoichiometric uranium–plutonium mixed oxides with high plutonium content. Low temperature oxidation is influenced by temperature, initial stoichiometry, presence of one or several phases, oxygen and humidity content of atmosphere. Some basis knowledge on the respective influence of these parameters exists, also from MOX manufacturers such as Belgonucléaire, but a detailed study of the mechanisms at play is still needed. From a broader perspective it is also of relevance for spent fuel storage studies and can be connected to a more fundamental study on phase equilibria in the complex U-Pu-O system.[1] R. Vauchy, A.-C. Robisson, F. Audubert, F. Hodaj, Ceram. Int., 40 (2014) 10991-10999.[2] R. Böhler, et al., J. Nucl. Mater., 448 (2014) 330-339.[3] C. Sari, U. Benedict, H. Blank, J. Nucl. Mater., 35 (1970) 267-277.[4] R. Vauchy, R.C. Belin, A.-C. Robisson, F. Hodaj, J. Eur. Ceram. Soc., 34 (2014) 2543-2551.[5] R. Vauchy, et al., J. Nucl. Mater., 465 (2015) 349-357.

Phase stability and oxidation behavior of high plutonium content fast reactor MOX Fuel

The researcher will be active in the Fuel Materials expert group at SCK•CEN in Mol (https://www.sckcen.be/en).

The daily supervision of the PhD will be done by SCK•CEN Mentor Dr. Delville Rémi, rdelvill@sckcen.be, +32 (0)14 333165 and SCK•CEN Co-mentor Dr. Tyrpekl Václav, vtyrpekl@sckcen.be, +32 (0)14 333261. The University promotor will be Prof. dr. ir. Jozef (Jef) Vleugels, jozef.vleugels@kuleuven.be, +32 (0)16 321244 from the Department of Materials Engineering of KU Leuven (http://www.mtm.kuleuven.be/English/).

The candidate will obtain a Ph.D. in Engineering: Materials Engineering at the Faculty of Engineering (http://eng.kuleuven.be/english) of KU Leuven (http://www.kuleuven.be/kuleuven/).


SCK•CEN is currently setting up a brand new line ofglove boxes for MOX production and characterization, building up on theexperience acquired in the UO2 lab and from Belgonucléaire. The newline will allow the fabrication UO2/PuO2 powder via wetroutes, the mixing and co-milling of powders, pressing of pellets and sinteringunder perfectly controlled conditions (T, p(O2)) in a hightemperature furnace in order to control fuel stoichiometry. A low temperaturefurnace with controlled atmosphere may be used for oxidation studies. High-endcharacterization technique (BET surface area analysis, thermogravimetry, XRD)will be available for characterizing powder characteristics, stoichiometry andphase in powder/pellets.  This will allow performing a set of parametricstudies to study the phase stability and oxidation behavior of high Pu contentMOX in the framework of the PhD. 


Master of Sciences, Master of Sciences in Engineering, Master in NuclearEngineering, Master in Materials Engineering, or an equivalent master degree.


Ph.D.fellowship for the duration of a maximum of 4 years


For more information please contact Prof. dr. ir. Jef Vleugels, tel.: +32 16 32 12 44, mail: jozef.vleugels@kuleuven.be or Dr. Delville Rémi (rdelvill@sckcen.be) or SCK•CEN Co-mentor Dr. Tyrpekl Vaclav (vtyrpekl@sckcen.be)

The candidate will have to pass the selection campaign of the Scientific Council of SCK-CEN, by an oral defence of the research theme on May 20-22 2015. The full procedure is explained at: http://academy.sckcen.be/en/Your_thesis_internship/PhD_thesis

Before applying, please consult the guidelines for application for PhD

Deadline for application: March 24, 2017
Notification of selection for first round: April 28, 2017
Second round - oral presentations: May 23 and 24, 2017
Notification of final result: June 30, 2017
Anticipated starting date of the PhD research (subject to university administrative issues): October 1, 2017

You can apply for this job no later than March 24, 2017 via the

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