Dario Manara, Rudy Konings, Philippe Raison

LFR fuel overview and perspectives Dario Manara, Rudy Konings, Philippe Raison European Commission Joint Research Centre Institute for transuranium materials (ITU) P.O. Box 2340 76125 Karlsruhe Germany

Generation IV overall mission Significant advances in: Sustainability Safety and reliability Proliferation and physical protection Economics Competitive in various markets Designed for different applications: Electricity, Hydrogen, Clean water, Heat US Argentina Brazil Switzerland UK Generation IV International Forum (GIF) Canada Euratom S. Africa France Korea Japan

Low neutron capture cross section of non-fissile elements + good irradiation behaviour High fissile density Criteria for fuel materials No chemical reaction with cladding or coolant Favorable physical properties, especially thermal conductivity and melting point (together give the margin to melting) High mechanical stability (isotropic expansion, stable against radiation) High thermal stability (no phase transitions, no dissociation) Compatibility with reprocessing methods.

NUCLEAR FUEL OPTIONS MOX Metal fuel Nitride fuel Carbide fuel INCLUDING INERT MATRIX fuel and minor actinide-containing containing fuel. Coated particle fuel for high temperature reactors Molten salt fuel

Oxide and Advanced Nuclear Fuels OXIDES: MORE STABLE AT ROOM T; EASIER TO PREPARE METALS, CARBIDES, NITRIDES: POSSIBLE OPTION AS GEN IV NUCLEAR FUEL THANKS TO: HIGHER FUEL DENSITY HIGHER MARGIN-TO-MELTING INTEGRAL 50 Melting Density U-density point (K) (g cm -3 ) (g cm -3 ) U 1388 19.05 19.05 UO 2 3130 10.95 9.6 UC 2780 13.63 12.97 UN 3123 14.32 13.53 T melt CIM = λ( T ) dt T op Î/W m -1 K -1 40 30 20 UN U UC 10 UO 2 0 300 500 700 900 1100 1300 T/K

GIV - MATERIALS

Fuel performance indicators

SSTAR LFR SYSTEMS CONSIDERED ELSY MYRRHA Nitrides, metals MOX, (nitrides) MOX (30-35% 35% PuO 2 )

Schematic Diagram of The Laser Flash Measurements of Irradiated Fuels Fiber Optic 1. Step: HF induction furnace is heating up the sample. Mirror With Field Stop Diaphragm Glove BOX Water Cooled Vacuum Chamber Telescope Manipulators 4. Step: the temperature wave reaches the back sample surface generating a temperature increase. Sample 2. Step: laser shot is fired towards the sample front face. Support Plate HF-Heater γ-shielding HF-Power Supply 5. Step: the increasing temperature thermogram is measured by the highly sensitive fast pyrometer. Laser power monitor 3. Step: the temperature wave generated by the laser pulse is moving through the sample towards the back surface. u Pulsed Nd-YAG Laser (0.1-1.0 ms, 10J) Fiber Optic Motorized Filter Wheel System Personal Computer Dichroic Mirror Si PD InGaAs PD Logarithmic Amplifiers CW Nd-YAG Laser Data processing according to the general integral of the heat transport equation DTmax Beam Mixer Transient Recorder (14bit, 1MHz)

Thermal conductivity of irradiated UO 2 102 GWd/t LWR UO 2 (x 10-6 Thermal diffusivity at 490K, m 2 s -1 ) 2.0 1.8 1.0 degradation by out-of-pile auto-irradiation 0.8 At end of life (no out-of pile auto-irradiation) Fresh fuel Degradation by in-pile burn-up end of life (model prediction) After storage Annealed at 590 K recovery by out-of-pile 0.6 Annealed at 725 K annealing 0.0 0.2 0.4 0.6 0.8 1.0 Radial position (r/r 0 ) The white circles along the radius indicate the spots for thermal diffusivity measurements by Laser flash. Predicted and measured thermal diffusivity. After annealing the diffusivity converges to the predicted values.

OXIDE FUEL Rather low thermal conductivity, high emissivity High vapour pressure. Non- stoichiometry. Well established U(Pu)O 2 UO 2+x UNCERTAIN 2+x OBSCURE D.Manara et al., J. Nucl. Mater. 342 (2005), 148. After: C. Guéneau et al., J. Nucl. Mater. 304 (2002), 161. After: Kato et al., JNM 2008

Oxygen potential of (U,Pu)O 2 U 4+ U 6+ Pu 4+ U 4+ U 3+ Pu 4+ Pu 3+ The situation is even more complex in the presence of MA: NpO 2, AmO 2-x and CmO 2-x have even higher oxygen potential.

Experimental data + CALPHAD UO 2±x and PuO 2-x Guéneau et al. JNM 2011 High oxygen potential O 2 losses before melting Cf. well known systems like CeO 2!!! THE EXPERIMENTALIST S STRUGGLE FOR EQUILIBRIUM... N. Dupin In F. De Bruycker et al. JNM 2011 UO 2 melts quasi- congruently under an inert atmosphere, PuO2 melts the closest to congruently under an oxidising atmosphere.

The U-Pu-O system At 3000 K Experimental data with HUGE uncertainty 350 K O 2 losses very important! FUNDAMENTAL FOR THE COMPREHENSION OF IN-PILE NUCLEAR FUEL BEHAVIOUR!!! More research ongoing on chemical analysis of melted MOX samples: O, Pu distribution Similar research on (U, Th), (U, Am) MOX + minor actinide fuel F. De Bruycker et al. JNM 2011, C. Guéneau et al. JNM 2011

Fast Reactor (U,Pu)O 2 fuel Source: Olander

Mixed oxide (MOX) fuel fabrication methods Source: IAEA-Technical Report Series 415

NITRIDES P N2 extremely high. Metal de-mixing under irradiation (NIMPHE2 experience)? Quasi-metallic behaviour: low emissivity, high conductivity. Melting point: few experimental data, not always accurate. Melting point UN measured under at least 2.5 bar N 2 : at 1atm, decomposition around 3000 K. Melting behaviour: almost unknown. After: Tagawa, JNM 51 (1974), 78.

Phase diagrams Nitrides Source: Massalski

(U,Pu)N fuel PuO 2 UO 2 Graphite Blending Compaction MO 2 (cr) + 2C(cr) M(cr) + CO(g) M(cr cr) + ½N 2 (g) MN(cr) Carbothermic Reduction Milling Pressing Additives Sintering Grinding

Fast Reactor (U, Pu)N fuel Porosity 40% 4 at% burnup 710 W/m He- or Na- bonded 85% TD (initial) No restructuring at same linear heat as oxides (not true in NIMPHE 2) Porosity 10% Source: Tanaka et al.

Fast reactor metallic fuel Alpha-Uranium is not suited (swelling) Stabilisation with Zr (cf. EBR II experience). Lower smeared density (< 80% TD) and larger pellet-cladding gap to accommodate swelling (about 30% volume increase). Na-bonded Pseudo-binary U 0.8 Pu 0.2 -Zr U-15Pu-12Zr12Zr Source: Kittel et al. 2.4 at% burnup 460 W/m Na-bonded

Fast reactor fuels: overview Oxide fuel Low thermal conductivity, high fuel temperature, restructuring, Pu redistribution. Extensively studied. Nitride fuel Decomposition before melting; phase diagram poorly known. Am vaporisation 15 N enrichment to avoid 14 C production Metal fuel Pyrophoric, needs purified atmosphere Low melting T; huge expansion Am vaporisation Carbide fuel Pyrophoric, needs purified atmosphere Not compatible with aqueous reprocessing Metastability

Fast reactor fuels: perspectives Oxide fuel Rich experience. Nitride fuel Excellent CIM and fissile nuclide density. Need to be better studied. Optimize fabrication. Metal fuel Maximum fissile nuclide density and efficiency. Carbide fuel Fair experience Oxidation issue Difficult recycling: more suited for VHTR fuel.

THANKS: - EC FP7 EUROTRANS + F-BRIDGE + SEARCH - Prof. L. LUZZI (POLITECNICO DI MILANO) - Dr. M. TARANTINO and N. FORGIONE (Università di Pisa) THANK YOU FOR YOUR ATTENTION

Mixed oxide (MOX) fuel fabrication methods OCOM (Siemens) Optimised Comilling COCA (COGEMA) Cogranulation Cadarache MIMAS (BN, COGEMA) Micronised Master Blend SBR (BNFL) Short Binderless Route