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

OUTLINE OF OUR STUDY ON Tc IN THE PUREX PROCESS 1. Extraction behavior of 99 Tc in the 30 vol% TBP-n-dodecane-HNO 3 system. Almost clarified. 2. Study of chemical form of 99 Tc 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-HNO 3 system Control of Tc(VII) in the Purex process; Decontamination & Recovery 2. Determination of the structure of Tc(VII)-TBP complexes HTcO 4 -HNO 3 -TBP, UO 2 -HNO 3 -HTcO 4 -TBP

Chemical forms of the extracted Tc(VII) in the TBP-HNO 3 system (Suggested until now) 1. HTcO 4 System (HTcO 4 ) ・ 3TBP, (HTcO 4 ) ・ 4TBP 2. HTcO 4 –HNO 3 － U(VI) System UO 2 (NO 3 - )( TcO 4 - ) ・ 2TBP, UO 2 (TcO 4 - ) 2 ・ 2TBP, (UO 2 ) 2 (NO 3 - ) 2 ( TcO 4 - ) 2 ・ 3TBP 3. HTcO 4 –HNO 3 － An(IV) System An(NO 3 - ) 3 ( TcO 4 - ) ・ 2TBP 4. HTcO 4 –HNO 3 -Zr(IV) System Zr(NO 3 - ) 3 ( TcO 4 - ) ・ 2TBP This Presentation

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

TcO 4 - TcO 4 — UO 2 2+ Figure Curve fitting of Tc K-EXAFS Spectra on the basis of UO 2 -TcO 4 -NO 3 -TBP system Tc-O: R=1.74 Å N=4  2 =0.002 Tc-U: R=3.59 Å  2 =0.005 UO 2 2+

Figure Comparison of Radial structural functions UO 2 -TcO 4 -NO 3 -TBP UO 2 -NO 3 -TBP UO 2 -NO 3 -H 2 O TcO 4 - UO 2 (TcO 4 )(NO 3 )(TBP) 2 (Candidate) UO 2 (NO 3 ) 2 (TBP) 2 NO 3 - UO 2 (NO 3 ) 2 (H 2 O) 2 H2OH2O TBP UO 2 2+ TBP UO 2 2+ NO 3 -

Figure Curve fitting of EXAFS Spectra on the basis of UO 2 (TcO 4 )(NO 3 )(TBP) 2 model. *fit residual={S|y exp -y theo |/S|y exp |}=0.19 U=Oax: R=1.77 Å (1.76Å) N=2;  2 =0.002 U-Oeq 1 : R=2.31 Å (2.38Å) N=2;  2 =0.005 U-Oeq 2 : R=2.51 Å (2.51Å)  2 =0.006 U-Oeq 3 : R=2.97 Å  2 =0.008 U---Tc: R=3.6 Å  2 =0.006 UO 2 (TcO 4 )(NO 3 )(TBP) 2 Fitting parameters (tentative) U--Tc U=O ax U-O eq

U-O ax U-O(NO 3 ) U-N(NO 3 ) U-O ligand U-O(TcO 4 ) U-Tc UO 2 (NO 3 ) 2 ・ 2H 2 O UO 2 (NO 3 ) 2 ・ 2TBP UO 2 (NO 3 )(TcO 4 ) ・ 2TBP r = 1.75A H 2 O : 2.51 N = r = 1.77A TBP : 2.39 N = r = 1.77A TBP : N = Table Comparison of bond length in several uranyl nitrate complexes bidentate

Coordination structure of TcO 4 - toward Uranium

CONCLUSION 1.Behavior of 99 Tc in the Purex reprocessing process Control of Tc(VII) in the process and its recovery are feasible. 2. Structure of 99 Tc in the [HNO 3 -TBP] system 1) Tc-99 takes a form of distorted tetrahedral TcO 4 -, and Tc-O bond length changes slightly depending on the environment. 2) When NO 3 - of [uranyl nitrate-TBP] complex is replaced by TcO 4 - ion, bonding of TBP to U(VI) is strengthened. 3) Coordination of TcO 4 - to U(VI) is bidentate. 4) Bond distance between U(VI) and ligand in [U-NO 3 -TcO 4 -TBP] complex is, TBP (2.31Å) < NO 3 - (2.51Å) < TcO 4 - (2.95Å)