The 10 th OECD/NEA Information Exchange Meeting on Actinide and Fission Product Partitioning and Transmutation October 6-10, 2008 Mito, Japan Development of Nitride Fuel and Pyrochemical Process for Transmutation of Minor Actinides Y. Arai 1) , M. Akabori 1) , K. Minato 1) and M. Uno 2) 1) Japan Atomic Energy Agency (JAEA) 2) Osaka University 1 10-IEMPT Mito, Japan
Content of Presentation (1) Introduction of nitride fuel cycle development for transmutation of minor actinides (MA) (2) Progress of thermal property measurements on nitride fuel • Thermal expansion, thermal conductivity, and so on • MA nitrides and their solid solutions • Burnup simulated nitrides • ZrN or TiN-containing nitrides (3) Progress of pyrochemical process for treatment of spent nitride fuel • Electrochemical behavior of nitrides in LiCl-KCl melt • Formation of nitrides from electrodeposits in cathode (4) Summary 2 10-IEMPT Mito, Japan
Double-Strata Cycle Concept and Nitride Fuel � Double-strata fuel cycle concept LWR/FBR U, Pu • Each fuel cycle pursues safety Fuel Fabrication and economy of the fuel cycle independently. 1st Strata Commercial Cycle U, Pu • Performance of the commercial MA , FP power-generation fuel cycle is Reprocessing U, Pu not disturbed by MA. • Hazardous MA are confined in the dedicated transmutation MA , FP fuel cycle with a small throughput. 2nd Strata Transmutation � Nitride fuel for MA transmutation Cycle • High thermal conductivity, high melting point and high Short-lived FP heavy metal density • Mutual solubility among Repository actinide mononitrides 3 10-IEMPT Mito, Japan
R&D Activities on Nitride Fuel and Pyrochemical Process � Preparation of MA bearing HLLW from Commercial Fuel Cycle nitrides by carbothermic reduction N-15 Partitioning � Measurement of thermal MA(+Pu) Nitride properties on MA nitrides and burnup simulated nitrides Transmuter (ADS) � Molten salt electrolysis for Spent Fuel treatment of spent nitride fuel N-15 Molten Salt Electrorefining � Formation of nitrides from electrodeposits in cathode MA(+Pu) Electrodeposits � Irradiation behavior of U-free Nitride Formation in liq. Cd nitride fuel � N-15 related issues Flowsheet for MA transmutation fuel cycle 4 10-IEMPT Mito, Japan
Preparation of Nitride Fuel for ADS � Nitride fuel for ADS is a so-called U-free fuel. In this case, MA are contained as a principal component and a diluent material such as ZrN is added in place of U. A composition of nitride fuel proposed by JAEA is (MA 0.24 Pu 0.16 Zr 0.6 )N. � There are two routes for preparation of nitride fuel for ADS. One is the carbothermic reduction of MA oxides partitioned from HLLW, and the other is the nitride formation of MA and Pu recovered in liquid Cd cathode by pyrochemical reprocessing. 1) MA partitioned from HLLW 2) (MA + Pu) in liquid Cd cathode Nitridation/distillation Sol-gel method combined reduction (MA oxide + carbon) sphere (MA + Pu) nitride powder Carbothermic reduction MA nitride sphere (MA,Pu,Zr)N fuel for ADS ZrN 5 10-IEMPT Mito, Japan
Thermal Expansion of MA Nitrides and Their Solid Solutions • Thermal expansions of MA nitrides and their solid solutions were measured from room temperature to 1478K by high temperature X-ray diffractometry. • Average thermal expansion coefficients of the solid solutions could be approximated by the linear mixture rule of respective mononitrides. 6 10-IEMPT Mito, Japan Ref. M. Takano, et al (2008)
Heat Capacity of NpN and AmN • Heat capacities of NpN and AmN were measured from 374 to 1071K by drop calorimetry and compared with literature values for UN and PuN. • Heat capacities of actinide mononitrides had similar temperature dependence, although that of AmN was slightly smaller than those of UN, NpN and PuN. 7 10-IEMPT Mito, Japan Ref. T. Nishi, et al (2008)
Thermal Conductivity of NpN and AmN 30 6 UN (Arai et al.) -1 ) 25 -1 ) -1 K 2 s Thermal conducticvity (Wm -6 m 20 Thermal diffusivity (10 4 NpN PuN (Arai et al.) 15 2 NpN AmN 10 AmN : on heating : on heating : on cooling : on cooling UO 2 (Ronchi et al.) 5 0 500 1000 1500 0 Temperature (K) 500 1000 1500 Temperature (K) • Thermal diffusivities of NpN and AmN were measured from 473 to 1473K by laser flash method, from which thermal conductivities were derived. • Thermal conductivities of actinide mononitrides decreased with the atomic number of actinides, although they had similar temperature dependence. 8 10-IEMPT Mito, Japan Ref. T. Nishi, et al (2008)
Thermal Conductivity of Burnup Simulated Nitrides 150 -1 ) 120 K -1 UN [ Thi s wor k] m UN+M o 7. 1 m ol % [ Thi s wor k] W 30 ( UN+M o 1. 6m ol % [ Thi s wor k] κ 0 U 0. 973 Nd 0. 027 N [ Thi s wor k] y, t vi U 0. 878 Nd 0. 122 N [ Thi s wor k] i 20 conduct M o( Handbook) ( U, Nd) N+M o ( L) [ Thi s wor k] m al 10 ( U, Nd) N+M o ( H) [ Thi s wor k] Ther 0 200 600 1000 1400 1800 Tem pr atur e, T ( K) • Thermal conductivity of UN+Mo : Almost independent of Mo content • Thermal conductivity of (U,Nd)N : Decrease with Nd content • Thermal conductivity of (U,Nd)N+Mo : Decrease with Nd content but independent of Mo content 9 10-IEMPT Mito, Japan Ref. M. Uno, et al (2007)
Thermal Conductivity of Nitrides with Diluent Materials UN [ Thi s w ork] 80 80 -1 ) U 0. 4 Zr 6 N [ Thi s w ork] K 70 70 -1 0. Zr N ( 100 % T. D. ) [ Basi ni ] m W Zr N ( 70 % T. D . ) [ Basi ni ] 60 60 ( κ 0 Zr N ( 89. 2 % T. D. ) [ Hedge] ty, 50 50 vi Ti N [ l i terature] i conduct 40 40 UN+Ti N [ Thi s wor k] UN+Ti N [ Thi s wor k] 30 30 UN+Ti N [ Schul z Eq. ] Therm al 20 20 • Thermal conductivity of (U 0.4 Zr 0.6 )N 10 10 : ≅ UN 0 0 • Thermal conductivity of 0.4UN+0.6TiN 250 250 650 650 1050 1050 1450 1450 1850 1850 : >UN Tem pr at ur e, T ( K) 10 10-IEMPT Mito, Japan Ref. M. Uno, et al (2007)
Molten Salt Electrolysis of Burnup Simulated Nitrides � Electrochemical measurement in LiCl-KCl-UCl 3 : CV and EMF � Potential-controlled electrolysis using liquid Cd cathode � UN in UN+Mo and (U,Nd)N: Dissolution in LiCl-KCl at the similar potential as pure UN and recovery of U in liquid Cd cathode � Mo in UN+Mo: Remain in anode undissoved � NdN in (U,Nd)N: Dissolution but Nd almost stay in the salt phase UN+Mo (U,Nd)N Current / mA Comparison of CV before and after the electrolysis for UN+Mo and (U,Nd)N 11 10-IEMPT Mito, Japan Ref. T. Satoh, et al (2007)
Molten Salt Electrolysis of Nitrides with Diluent Materials � Electrochemical measurement in LiCl-KCl-UCl 3 : CV and EMF � Potential-controlled electrolysis using liquid Cd cathode � UN in (U,Zr)N: Dissolution in LiCl-KCl at more positive potential (~by 1V) than pure UN and recovery of U in liquid Cd cathode � UN in UN+TiN: Dissolution in LiCl-KCl at the similar potential as pure UN and recovery of U in liquid Cd cathode 100 120 (U 0.4 Zr 0.6 )N (U 0.4 Zr 0.6 )N (U 0.4 Zr 0.6 )N ZrN 80 Current / mA Current / mA 50 (B) Before 40 UN After 0 0 (A) -40 -50 -1.2 -0.8 -0.4 0.0 0.4 0.8 -1.2 -0.8 -0.4 0.0 0.4 Potential / V vs. Ag/AgCl Potential / V vs. Ag/AgCl Comparison of CV between Comparison of CV before and after UN, (U 0.4 Zr 0.6 )N and ZrN the electrolysis for (U 0.4 Zr 0.6 )N 12 10-IEMPT Mito, Japan Ref. T. Satoh, et al (2008)
AmN Formation Behavior in Molten Cd Prepared by carbothermic reduction of AmO 2 Prepared by solid-solid reaction of AmN and CdCl 2 (1) Electrolysis of AmN in LiCl-KCl-AmCl 3 melt with liquid Cd cathode (2) Nitridation/distillation combined reaction of the electrodeposits in N 2 stream at 973K (3) Vacuum heating at 723K for removal of residual Cd Constituted by Cd and AmCd 6 Reference AmN ▼： Cd ＊： Pt holder □： Am 2 O 3 ×： W holder (by carbothermic reduction) Intensity (arb. unit) ＊ ＊ × × Products of reaction ▼ ▼ ▼ ▼ □ □ □ ▼ □ × Am-Cd alloy × ▼ (Cd+AmCd 6 ) ▼▼ ▼ ▼ ▼ Appearance of AmN powder after heating the product in vacuum at 723K 10 30 20 2θ (deg.) 13 10-IEMPT Mito, Japan Ref. H. Hayashi, et al (2008)
Nitride Pellet Preparation from Pyrochemical Process U-Pu-Cd in Y 2 O 3 crucible (U,Pu)N pellet in Mo Liquid Cd cathode in Al 2 O 3 before nitridation/distillation crucible before electrolysis crucible after electrolysis combined reaction (U,Pu)N powder obtained (U,Pu)N pellet prepared by by nitridation/distillation sintering in flowing Ar-H 2 � Single phase of (U,Pu)N � Density: ~84%TD combined reaction atmosphere at 2023K � O 2 impurity: 0.1~0.2wt% 14 10-IEMPT Mito, Japan Ref. Y. Arai, et al (2008)
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