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The 3rd Japanese-Russian Seminar on Technetium Dubna, Russia, June 23 – July 01, 2002

The 3rd Japanese-Russian Seminar on Technetium Dubna, Russia, June 23 – July 01, 2002. Behavior and Structures of 99 Tc-Species in Solvent Extraction Systems of The Nuclear Fuel Cycle S. Tachimori, T. Yaita, S. Suzuki Japan Atomic Energy Research Institute.

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The 3rd Japanese-Russian Seminar on Technetium Dubna, Russia, June 23 – July 01, 2002

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  1. The 3rd Japanese-Russian Seminar on Technetium Dubna, Russia, June 23 – July 01, 2002 Behavior and Structures of 99Tc-Species in Solvent Extraction Systems of The Nuclear Fuel Cycle S. Tachimori, T. Yaita, S. Suzuki Japan Atomic Energy Research Institute

  2. OUTLINE OF OUR STUDY ON Tc IN THE PUREX PROCESS 1. Extraction behavior of 99Tc in the 30 vol% TBP-n-dodecane-HNO3 system. Almost clarified. 2. Study of chemical form of 99Tc extracted by the 30 vol% TBP-n-dodecane. Just started at the Synchrotron Radiation Facilities (PF, Spring 8) by EXAFS MAIN ITEMS OF THE PRESENTATION 1. Distribution model of Tc(VII) in the 30 vol% TBP-n-dodecane-HNO3 system Control of Tc(VII) in the Purex process; Decontamination & Recovery 2. Determination of the structure of Tc(VII)-TBP complexes HTcO4-HNO3-TBP, UO2-HNO3-HTcO4-TBP

  3. Chemical forms of the extracted Tc(VII) in the TBP-HNO3 system (Suggested until now) 1.HTcO4 System (HTcO4)・3TBP, (HTcO4)・4TBP 2.HTcO4–HNO3－U(VI) System UO2(NO3-)( TcO4-)・2TBP, UO2(TcO4-)2・2TBP, (UO2)2(NO3-)2( TcO4-)2・3TBP 3.HTcO4–HNO3－An(IV) System An(NO3-)3( TcO4-)・2TBP 4.HTcO4–HNO3-Zr(IV) System Zr(NO3-)3( TcO4-)・2TBP This Presentation

  4. Noncentrosymmetric tetrahedral TcO4:1s -> 4d ns -> np rTc-O TcO4 in 3M HNO3 1.73 Å TcO4–Zr - TBP in DD 1.70 Å 1.73 Å TcO4– TBP in DD 1.71 Å TcO4– Th - TBP in DD 1.73 Å TcO4– U - CMPO in DD TcO4– U - TBP in DD 1.74 Å Figure Radial structural function of Tc K-EXAFS Figure Normalized Tc K-XANES

  5. TcO4- Tc-O: R=1.74 Å N=4 s2=0.002 UO22+ TcO4—UO22+ Figure Curve fitting of Tc K-EXAFS Spectra on the basis of UO2-TcO4-NO3-TBP system Tc-U: R=3.59 Å s2=0.005

  6. TcO4- NO3- NO3- UO2-TcO4-NO3-TBP UO22+ NO3- TBP UO2(TcO4)(NO3)(TBP)2 (Candidate) UO22+ UO2-NO3-TBP TBP UO2 (NO3)2(TBP)2 UO2-NO3-H2O UO22+ H2O UO2 (NO3)2(H2O)2 Figure Comparison of Radial structural functions

  7. U=Oax U-Oeq UO2(TcO4)(NO3)(TBP)2 U--Tc Fitting parameters (tentative) U=Oax: R=1.77 Å (1.76Å) N=2;s2=0.002 U-Oeq1: R=2.31 Å (2.38Å) N=2;s2=0.005 U-Oeq2: R=2.51 Å (2.51Å) s2=0.006 U-Oeq3: R=2.97 Å s2=0.008 U---Tc: R=3.6 Å s2=0.006 Figure Curve fitting of EXAFS Spectra on the basis of UO2(TcO4)(NO3)(TBP)2 model. *fit residual={S|yexp-ytheo|/S|yexp|}=0.19

  8. Table Comparison of bond length in several uranyl nitrate complexes U-Oax U-O(NO3) U-N(NO3) U-Oligand U-O(TcO4) U-Tc bidentate bidentate r = 1.75A 2.51 2.95 H2O : 2.51 N = 2 4 2 2 UO2(NO3)2・2H2O r = 1.77A 2.52 2.90 TBP: 2.39 N = 2 4 2 2 UO2(NO3)2・2TBP r = 1.77A 2.51 2.95 TBP: 2.312.95 3.59 N = 2 2 1 UO2(NO3)(TcO4)・2TBP

  9. Coordination structure of TcO4- toward Uranium

  10. CONCLUSION • Behavior of 99Tc in the Purex reprocessing process • Control of Tc(VII) in the process and its recovery are feasible. • 2. Structure of 99Tc in the [HNO3-TBP] system • 1)Tc-99 takes a form of distorted tetrahedral TcO4-, and Tc-O • bond length changes slightly depending on the environment. • 2) When NO3- of [uranyl nitrate-TBP] complex is replaced • by TcO4-ion, bonding of TBP to U(VI) is strengthened. • 3) Coordination of TcO4- to U(VI) is bidentate. • 4) Bond distance between U(VI) and ligand in [U-NO3-TcO4-TBP] • complex is, • TBP (2.31Å) < NO3- (2.51Å) < TcO4- (2.95Å)

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