UNIVERSITY OF CAMBRIDGE Department of Materials Science & Metallurgy Structural and Thermodynamic Properties of Sodium Actinide Ternary Oxides Anna Louise Smith Churchill College May 2015 A dissertation submitted for the degree of Doctor of Philosophy iii Declaration ThepresentdissertationissubmittedforthedegreeofDoctorofPhilosophyattheUniversity ofCambridge(UnitedKingdom). Theworkdescribedhereinwascarriedbytheauthorduring the period October 15th 2011 to May 1st 2015 as part of a PhD program at the Department of Materials Science and Metallurgy, University of Cambridge. The research project was supervised by Prof. Anthony K. Cheetham, Goldsmiths’ Professor of Materials Science, University of Cambridge. This dissertation is the result of my own work and includes nothing which is the outcome of work done in collaboration except as declared in the Preface and speci(cid:28)ed in the text. It is not substantially the same as any that I have submitted, or, is being concurrently submitted for a degree or diploma or other quali(cid:28)cation at the University of Cambridge or any other University or similar institution. I further state that no substantial part of my dissertation has already been submitted, or, is being concurrently submitted for any such degree, diploma or other quali(cid:28)cation at the University of Cambridge or any other University or similar institution. This dissertation is less than 60,000 words in length. Anna Louise Smith Cambridge, April 2015 v Abstract I n the potential event of a clad breach in a Sodium-cooled Fast Reactor (SFR), the sodium metallic coolant could come into contact with the (U,Pu,Np)O nuclear fuel. The reaction 2 products are numerous, but there is little knowledge of their structural and thermodynamic properties. Under the oxygen potential conditions of the reactor, pentavalent Na AnO 3 4 (An=U,Pu,Np) is expected to form, but its structure was the subject of controversy un- til now. We showed that α-Na3UO4 adopts a monoclinic symmetry in space group P2/c. Neutron di(cid:27)raction combined with X-ray Absorption Near Edge Structure (XANES) spec- troscopy at the U-M edge also revealed that this phase could accommodate excess sodium 4 on the uranium site, with subsequent charge compensation of the uranium cation from U(V) to U(VI), which was not previously foreseen. The corresponding mixed valence state compo- sition is written Na (U ,Na )O with 0<x<0.16(2). To complete the data on the Na-U-O 3 1−x x 4 system, the thermodynamic functions of Na U O and Na UO were evaluated using Knud- 2 2 7 4 5 sen e(cid:27)usion mass spectrometry (KEMS) and thermal-relaxation calorimetry. In addition, the oxygen content required at 900 K within liquid sodium to form pentavalent Na UO and 3 4 hexavalent Na UO were calculated to be 0.7 and 1.5 wppm, respectively, which are levels 4 5 typically encountered in SFRs. A thermodynamic model for the Np-O system was then developed using the CALPHAD method. This is particularly relevant since it is envisaged to incorporate minor actinides into the fuel to minimize the nuclear waste inventory. The poorly known structures of the Na- Np-O and Na-Pu-O phases diagrams, i.e., tetravalent Na AnO (An=Np,Pu), pentavalent 2 3 Na AnO , hexavalent Na AnO and α-Na NpO , and heptavalent Na AnO , were also re- 3 4 4 5 2 4 5 6 (cid:28)ned by the Rietveld method. The structures of Na NpO and Na PuO were determined ab 3 4 3 4 initio from powder X-ray di(cid:27)raction data, and found to be orthorhombic in the space group Fmmm. The valence states of the neptunium cations were con(cid:28)rmed from the isomer shift values of their M(cid:246)ssbauer spectra. Having established the charge states without ambiguity, XANES spectra were collected at the Np-L and Pu-L edges to serve as reference data for 3 3 An(V), An(VI), and An(VII) oxide phases in the solid state. Finally, KEMS studies of α- Na NpO showed very promising results for the determination of the enthalpies of formation 2 4 of the sodium neptunates and plutonates, for which there is almost no data available. The heat capacities and entropies at 298.15 K of α-Na NpO , Na NpO , Na NpO , and Na PuO 2 4 4 5 5 6 5 6 were also determined. Comparing their Gibbs energy values, the sodium neptunates were found to be slightly more stable than their isostructural uranium analogues. vi Supervision, Funding The PhD studies presented in this manuscript have been supervised by Prof. Anthony K. Cheetham,Goldsmiths’ProfessorofMaterialsScienceattheDepartmentofMaterialsScience and Metallurgy (University of Cambridge), Prof. Rudy J.M. Konings, and Dr. Philippe E. Raison from the Joint Research Centre-Institute for Transuranium Elements (JRC-ITU, Karlsruhe). The research was carried out for 1 year at the Department of Materials Science and Metallurgy, and for 2 years and 7 months at the Institute for Transuranium Elements in the Materials Research Unit. Funding for the PhD studentship was provided by the 7th Framework Program of the Eu- ropean Commission, the Joint Advanced Severe Accidents Modelling and Integration for Na- cooled neutron reactors (JASMIN) programme (N○295803 in FP7), and the Ras al Khaimah Centre for Advanced Materials. Collaborations This PhD work has involved many collaborations initiated by the author with the following research groups and laboratories: 1. Materials Research Unit (JRC-ITU, Karlsruhe, Germany): The solid state syntheses of the sodium uranate, neptunate, and plutonate samples, as well as their encapsulation for speci(cid:28)c measurements, were carried out solely by the author using the glove box facilities of the Materials Research Unit at the JRC-ITU. Jean-Yves Colle and Dr. Ond(cid:176)ej Bene† trained the author to perform the Knuden e(cid:27)usion mass spectrometry measurements, and these were then carried out under their assistance. 2. Laboratoire de ModØlisation, de Thermodynamique et de Thermochimie, DEN, DANS, DPC, SCCME (CEA Saclay, France): Dr. ChristineGuØneautrainedtheauthortousetheCALPHADmethodandtheThermocalc software. The thermodynamic model for the Np-O system was developed by the author following her recommendations. 3. Actinide Research Unit (JRC-ITU, Karlsruhe, Germany): Amir Hen performed the M(cid:246)ssbauer spectroscopy measurements and (cid:28)tted the M(cid:246)ssbauer spectra presented in this manuscript. The interpretation of the (cid:28)tted parameters was done solely by the author. Dr. Eric Colineau and Dr. Jean-Christophe Griveau carried out the magnetic susceptibility and low temperature heat capacity measurements. The author performed the corresponding data treatment and interpretation of the results. Amir Hen, Dr. Eric Colineau, Dr. Jean-Christophe Griveau, Dr. Nicola Magnani, and Dr. Roberto Caciu(cid:27)o provided sound advice regarding the interpretation of the M(cid:246)ssbauer spectroscopy, magnetic susceptibility, and low temperature heat capacity data. vii Dr. Philippe Raison trained the author to perform the X-ray di(cid:27)raction measurements, and these were then carried out under the assistance of Daniel BouºxiŁre. Giorgio Pagliosa performed the high temperature X-ray di(cid:27)raction measurements. The structural re(cid:28)nements and interpretation of the room temperature and high temperature X-ray data were done by the author. The ab-initio structure determinations were realised with the help of Dr. Philippe Raison. 4. CEA, UniversitØ de Grenoble Alpes, INAC-SPSMS (Grenoble, France): Dr. Jean-Pierre Sanchez provided a very fruitful input to the (cid:28)tting and interpretation of the M(cid:246)ssbauer and magnetic susceptibility data. 5. Nuclear Fuel Unit (JRC-ITU, Karlsruhe, Germany), CEA, DEN, DEC, CEN (Cadarache, France), European Synchrotron Radiation Facility, BM20, (Grenoble,France): Dr. Damien Prieur (JRC-ITU), Dr. Philippe Martin (CEA), Dr. Christoph Hennig (ESRF), and Dr Andreas Scheinost (ESRF) trained the author to perform the X-ray Absorption Spectroscopy (XAS) measurements at the ESRF on the beamline BM20, and these were then carried out by the author under their assistance. Dr. Damien Prieur (ITU) and Dr. Philippe Martin (CEA) also trained the author for the use of the ATHENA and ARTEMIS softwares. The treatment of the collected XAS data was done by the author. 6. European Synchrotron Radiation Facility, ID26, (Grenoble, France): Dr. Kristina Kvashnina carried out the X-ray Absorption Near Edge Structure spectroscopy measurements at the beamline ID26. The treatment of the data was done by the author. 7. PSL Research University, Chimie ParisTech-CNRS, Institut de Recherche de Chimie Paris, (Paris, France): Dr. Gilles Wallez provided very fruitful advice regarding the structure determination of the trisodium uranate phase. 8. Institut Laue Langevin, D2B, (ILL, Grenoble, France): Dr. Emmanuelle Suard provided assistance with the neutron di(cid:27)raction measurement of the trisodium uranate sample. The data treatment was performed by the author. 9. Nuclear Chemistry Unit (JRC-ITU, Karlsruhe, Germany): The ICP-MS measurements were performed by the Analytical Service of the JRC-ITU. 10. Nuclear Fuel Unit (JRC-ITU, Karlsruhe, Germany), UMR CEA/CNRS 3685-NIMBE (Gif-sur-Yvette, France): Dr. Laura Martel (JRC-ITU) and Dr. Thibault Charpentier (CEA) performed 23Na Nuclear Magnetic Resonance measurements on various sodium uranate phases. These data are not presented in this manuscript. viii List of publications Some of the results reported in this thesis have been published in the following peer reviewed scienti(cid:28)c journals: ● A.L. Smith, J.-Y. Colle, O. Bene†, A. KovÆcs, P.E. Raison, R.J.M. Konings, Mass spec- trometric study of the vaporization behaviour of α-Na NpO : Thermodynamic investigation 2 4 of the enthalpy of formation, Journal of Chemical Thermodynamics 60 (2013) 132-141 ● A.L. Smith, P.E. Raison, L. Martel, T. Charpentier, I. Farnan, D. Prieur, C. Hennig, A.C. Scheinost, R.J.M. Konings, A.K. Cheetham, A 23Na Magic-Angle Spinning Nuclear Magnetic Resonance, XANES, and High-Temperature X-ray Di(cid:27)raction Study of NaUO , 3 Na UO , and Na U O , Inorganic Chemistry 53 (2014) 375-382 4 5 2 2 7 ● A.L. Smith, P.E. Raison, L. Martel, D. Prieur, T. Charpentier, G. Wallez, E. Suard, A.C. Scheinost, C. Hennig, P. Martin, K.O. Kvashnina, A.K. Cheetham, R.J.M. Konings, A New Look at the Structural Properties of Trisodium Uranate Na UO , Inorganic Chemistry 3 4 54(7) (2015) 3552-3561 ●A.L.Smith,A.Hen,P.E.Raison,E.Colineau,J.-C.Griveau,N.Magnani,J.-P.Sanchez, R.J.M. Konings, R. Caciu(cid:27)o, A.K. Cheetham, X-ray di(cid:27)raction, M(cid:246)ssbauer spectroscopy, magnetic susceptibility, and speci(cid:28)c heat investigations of Na NpO and Na NpO , Inorganic 4 5 5 6 Chemistry 54(9) (2015) 4556-4564 ● A.L. Smith, P.E. Raison, A. Hen, D. Bykov, E. Colineau, R.J.M. Konings, A.K. Cheetham, Structural investigations of Na NpO and Na PuO using X-ray di(cid:27)raction and 3 4 3 4 M(cid:246)ssbauer spectroscopy, submitted to Dalton Transactions (2015) ● A.L. Smith, J.-Y. Colle, P.E. Raison, O. Bene†, R.J.M. Konings, Thermodynamic inves- tigation of Na U O using Knudsen e(cid:27)usion mass spectrometry and high temperature X-ray 2 2 7 di(cid:27)raction, Journal of Chemical Thermodynamics (2015), accepted for publication ● A.L. Smith, J.-C. Griveau, E. Colineau, P.E. Raison, R.J.M. Konings, Low temperature heat capacity of Na UO and Na NpO , submitted to Journal of Chemical Thermodynamics 4 5 4 5 (2015) ● A.L. Smith, J.-C. Griveau, E. Colineau, P.E. Raison, R.J.M. Konings, Low temperature heat capacity of α-Na NpO , submitted to Thermochimica Acta (2015) 2 4 ix Acknowledgements M y time as a PhD student has been a wonderful experience and I am very grateful to all the people around me who have contributed to making it an unforgettable period. I (cid:28)rstly wish to thank Tony Cheetham for welcoming me in his research group, for his great enthusiasm in this rather uncommon project -the study of the solid state chemistry of actinide materials-, for his continuous support, his excellent advice regarding the paper writingprocess,andforgivingmethefreedomandmeanstopursuethiswork. Iwasdelighted to bene(cid:28)t from his knowledge and to spend some time in his group. I am also very grateful to Rudy Konings and Philippe Raison for their friendliness, strong support, high availability, continuous enthusiasm, and sound advice. It has been a real pleasure to work with them, and I have learned a lot from their experience in the (cid:28)eld of the uranium and transuranium elements’ chemistry. I furthermore acknowledge the European Commission and the Ras al Khaimah Centre for Advanced Materials for funding my PhD studentship. I had the chance during my studies to collaborate with scientists from various labo- ratories and research groups, and I am very thankful for their time, friendliness, and for sharing with me their expertise: Christine GuØneau, Jean-Yves Colle, Ond(cid:176)ej Bene†, Gilles Wallez, Jean-Christophe Griveau, Eric Colineau, Amir Hen, Roberto Caciu(cid:27)o, Nicola Mag- nani, Philippe Martin, Damien Prieur, Laura Martel, Thibault Charpentier, Ian Farnan, Joe Somers, KristinaKvashnina, Jean-PierreSanchez, AndreasScheinost, ChristophHennig, and Emmanuelle Suard. Working in a (cid:16)hot(cid:17) laboratory with radioactive materials is very constraining, and I could not have gathered all these results without the technical help of Daniel BouºxiŁre, Giorgio Pagliosa, Mark Sierig, and FrØdØric Naisse. Among other things, they had to endure an amazing number of (cid:16)bag-ins(cid:17) and (cid:16)bag-outs(cid:17) with me! I also wish to thank Anita Bailey and Petra Strube for their great kindness, for the help with the administrative procedures, and for facilitating the organization of my visits to Cambridge. A very special thank you note should also go to Shakiba, Emma, Patrick, Sebastien, Ali, Hamish, Paul, Wei, Naoyuki, and Ryan for their friendliness during my time in Cambridge, around a cup of tea or co(cid:27)ee, in the laboratory, during our Wednesdays lunches outside, or evenings at formal dinners. I also keep an unforgettable memory of our conference trips! On the other side of the English Channel, I also address a big thank you to Laura, Emily, Beno(cid:238)t, Sylvain, Philippe, Alexandra, Marie-Claire, Mohamed, Jean-Francois, Vaclav, Fidelma, Luca, Tsveti, Elisa, Fabiola, Octavian for a great time spent together during our lunchesatthe(cid:16)cantine(cid:17), parties, eveningsatthetheatre, and(cid:16)pique-niques(cid:17) attheBaggersee. Finally, this thesis is dedicated to my mother AgnŁs, my father David, Fiona, Gavin, and Robert for their unconditional support and love.