The 3rd Japanese-Russian Seminaron Technetium

Dubna, Russia, June 23 – July 01, 2002

Behavior and Structures of 99Tc-Species inSolvent 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 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

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

21 21.05 21.1 21.15

E / keV0 1 2 3 4 5 6

|FT

|

R / Å

Tc-O

Tc-U

Tc-U

Tc-Th

Tc-Zr

TcO4 in 3M HNO3

TcO4–Zr - TBP in DD

TcO4– TBP in DD

TcO4– Th - TBP in DD

TcO4– U - CMPO in DD

TcO4– U - TBP in DD

1.73 Å

1.70 Å

1.73 Å

1.71 Å

1.73 Å

1.74 Å

FigureNormalized Tc K-XANES

FigureRadial structural function ofTc K-EXAFS

Noncentrosymmetric tetrahedral TcO4:1s -> 4d ns -> np

rTc-O

0 1 2 3 4

RawFit1Fit2

|FT|

R / Å

Tc-O

Tc-U

TcO4-

TcO4—UO2

2+

FigureCurve fitting of Tc K-EXAFS Spectra on the basis of UO2-TcO4-NO3-TBP system

Tc-O: R=1.74 Å N=4 2=0.002

Tc-U: R=3.59 Å2=0.005

UO22+

FigureComparison of Radial structural functions

0 1 2 3 4

|FT

|

U--Tc

U--P

U=O

U=O

U=O

U-Oeq

U-Oeq

U-Oeq

R / Å

UO2-TcO4-NO3-TBP

UO2-NO3-TBP

UO2-NO3-H2O

TcO4-

UO2(TcO4)(NO3)(TBP)2 (Candidate)

UO2 (NO3)2(TBP)2

NO3-

UO2 (NO3)2(H2O)2

H2O

TBP

UO22+

UO22+

TBP

UO22+

NO3-

NO3-

0 1 2 3 4

RawFit

|FT|

R / Å

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

U=Oax: R=1.77 Å (1.76Å) N=2;2=0.002U-Oeq1: R=2.31 Å (2.38Å) N=2;2=0.005U-Oeq2: R=2.51 Å (2.51Å)2=0.006U-Oeq3: R=2.97 Å2=0.008U---Tc: R=3.6 Å2=0.006

UO2(TcO4)(NO3)(TBP)2

Fitting parameters (tentative)Fitting parameters (tentative)U--Tc

U=Oax

U-Oeq

U-Oax U-O(NO3) U-N(NO3) U-Oligand U-O(TcO4) U-Tc

UO2(NO3)2・2H2O

UO2(NO3)2・ 2TBP

UO2(NO3)(TcO4)・ 2TBP

r = 1.75A 2.51 2.95 H2O : 2.51N = 2 4 2 2

r = 1.77A 2.52 2.90 TBP : 2.39N = 2 4 2 2

r = 1.77A 2.51 2.95 TBP : 2.31 2.95 3.59N = 2 2 1

Table Comparison of bond length in several uranyl nitrate complexes

bidentate bidentate

Tc

O

U

O

1.74 Å2.95 Å

3.6 Å

102º

100º

Coordination structure of TcO4- toward Uranium

CONCLUSION

1. 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)