Journal of Nuclear and Radiochemical Sciences, Vol. 6, No. 3, pp. 271-274, 2005

Technetium Separation for Future Reprocessing
T. Asakura,* S. Hotoku, Y. Ban, M. Matsumura, and Y. Morita
Department of Fuel Cycle Safety Research, Japan Atomic Energy Research Institute Tokai-mura, Ibaraki
319-1195, Japan
Received: July 31, 2005; In Final Form: September 30, 2005
Tc extraction and separation experiments were performed basing on PUREX technique with using spent UO2 fuelwith burn-up of 44 GWd t −1. The experimental results were examined with performing calculations by a simulation code ESSCAR (Extraction System Simulation Code for Advanced Reprocessing). It was demonstrated thatTc can be extracted almost quantitatively from a dissolver solution and that extracted Tc also can be recovered
almost quantitatively by scrubbing. Further, it is clearly presented with the calculation results of ESSCAR that Tc
extraction mechanism is dominated by the synergistic effect of Zr and U.

1. Introduction
In JAERI (Japan Atomic Energy Research Institute), PARC
(Partitioning Conundrum-key) process,1 a PUREX techniquebased separation process concept has been proposed and studied as the basis for future development in reprocessing, as apart of safety research to improve safety by simplifying
PUREX process. The separation scheme of nuclides in theprocess concept is illustrated in Figure 1. In the solvent extractive separation scheme, U and Pu are recovered as productswith sufficient decontamination factor within a single extraction cycle for recycle use, with controlling the extractive
behavior of long-lived nuclides such as Np and Tc. It is significantly important to sufficiently restrict the transfer of Tc into
U products and Pu products to obtain high decontamination
factor, because Tc easily contaminates the products. Further,
restriction of Tc-99 transfer into highly active wastes andrecovery of it for transmutation into non-radioactive nuclide,Ru-100 for example, reduces long-term radiation toxicity of thewaste.
In the literature, 2 Tc was extracted almost quantitatively
from a dissolver solution at U-Pu co-extraction (co-decontamination) part, passed through scrub part and reached at U/Pu
partition part. In this report, Tc behavior in the co-decontamination part is mainly explained by the effect of synergistic
extraction with Zr, and Tc passes through the scrubbing part,
where Zr is back-extracted into scrubbing solution, by theeffect of synergistic extraction with U. As for Tc back-extrac-

tion from the extractive solvent, the authors have alreadyshown that it can be possible by utilizing a high-acid scrubbing
method.1
Under these backgrounds, the authors have conducted extractive separation experiments using actual spent UO2 fuel solutions, and examined the feasibility of Tc separation and recovery
with utilizing PUREX techniques. We also tried to explain themechanism, which dominates Tc behaviors in extraction process, with utilizing a simulation code.
2. Experimental
The spent fuel used for experiments were UO2 fuels whichwere burnt in a commercial light water reactor up to 44 GWd
t −1. The spent fuels were treated inside of an alpha-gamma(air-tight, sufficiently shielded) cell in NUCEF (Nuclear Fuel
Cycle Safety Engineering Facility) of JAERI, and a test line
composed of a dissolver, extractors etc. in the cell 3 was used
for experiments.
For respective extraction run, 1.5 to 2 litters of dissolver
solutions were used to perform a chemical engineering test on
counter-current contact with miniature mixer-settler type liquid-liquid extractors. Three extractive runs, Run No. 1, 2 and3, were performed. In Table 1, the composition of a dissolver
solution for respective extraction run was summarized. The
flow-sheet composed from mixer-settler contactors for experimental Run No. 1 and No. 2 is shown in Figure 2. U-Pu coextraction (co-decontamination) part was composed of 8 stagesof extraction banks (banks No. 1–8). A dissolver solution (A1)was supplied at the bank No. 8 and a main extraction solvent(30 vol% TBP in dodecane) was supplied at the bank No. 1.
At the bank No. 16, a scrubbing solution was supplied and a
scrubbing part of 8 stages (banks No. 9–16) was composed.
As already reported in the literature,2 Tc is expected to passthrough this scrubbing part. Thus, Tc separation part of 7
TABLE 1: Composition of Dissolver Solution Used forExperimental Run No. 1, 2, and 3

Figure 1. Separation process concept “PARC (Partitioning Conundrum-key)”.
*Corresponding author. E-mail: asakura.toshihide@jaea.go.jp.
FAX: +81-29-282-6677.

Run No.

[HNO3]/mol l−1

1
2
3

3.2
3.0
3.1

Concentration in dissolver solution
[U]
[Pu]
[Zr]
[Tc]
/g l−1/g l−1/g l−1/g l−1200
196
214© 2005 The Japan Society of Nuclear and Radiochemical Sciences
Published on Web 12/28/2005

2.25
1.86
2.03

0.682
0.639
0.700

0.368
0.188
0.206

272 J. Nucl. Radiochem. Sci., Vol. 6, No. 3, 2005

Asakuramined by the emission strength of Tc in ICP-AES (InductionCoupled Plasma Atomic Emission Spectroscopy) compared toa calibration line for concentration standards. The detection
limit for this method was 2 × 10−3 g l−1.
3. Simulation Code

Figure 2. Experimental flow-sheet for Run No. 1 and No. 2.

stages of extraction banks (banks No. 20–26) was composed.
To recover U and Pu, which are expected to leak into a Tc
product solution, three stages of extraction banks (banks No.
17–19) were used. In Table 2, the flow rates of the solutions,A1–A4, O1, O2, for Run No. 1 and No. 2, respectively, weresummarized.

TABLE 2: Flow Rate of Respective Solution in Each Experimental Run

Run 1
Run 2

A1
193
201

A2
94
91

Flow rate / ml h−1
A3
A4
40
82
42
83

O1
480
487

O2
120
121

In Figure 3, the flow-sheet for the experiment Run No. 3 isshown. The number of extraction banks for the U-Pu co-extraction part or the scrub part was the same as Run No. 1 or 2.
Organic to aqueous flow rate ratio was increased, and the HNO3
concentration of the scrubbing solution was altered to 4 mol l −1
(M). The aim of these alterations was to accelerate Np extraction from a dissolver solution. In this flow-sheet for Run No.
3, 7 stages of a Np separation part (banks No. 20–26) was also
composed. Tc separation part was composed of 10 stages ofthe banks (No. 27–36), and Tc scrubbing solution (A4) was
simplified as single solution of 6 M HNO3.
After 10 hours operation with active feed, those extractors
were shut down and analytical samples of an organic solution
and an aqueous solution were collected from every extraction
banks to analyze Tc concentrations. If Tc-95m, which wasadded to the dissolver solution as a RI tracer, was detected, Tc
concentration was determined by the concentration of gamma
radioactivity of the tracer. The detection limit for the measurement was 9 × 10−3 g l −1 in the case of Run No. 1 and 2, or 9
× 10−4 g l −1 in the case of Run No. 3, respectively. If it was notpossible to determine the Tc concentration with this methodwith interferences by other radio-nuclides, the value was deter-

For simulation calculation of extraction experiments,
ESSCAR (extraction system simulation code for advanced
reprocessing) 4 was used. This code can treat TBP-HNO3
extraction system composed of a desired number of pulsedcolumn type extractors and mixer-settler type extractors. A
pulsed-column type extractor is imaginarily divided into
desired number of calculation units (meshes) with arbitraryheights. In the case of mixer-settler type extractor, respective
extraction bank is the calculation unit. The code numericallysolves differential equations, which express material balanceof chemical species (HNO3, metal ions etc.) in respective calculation unit, by Newton’s method. To describe material balance, mass transfer between organic solution and aqueous
solution phase basing on distribution coefficient, and rates ofchemical reactions, reduction-oxidation reaction, for example,
in respective phase. The code gives us the numeric solutions
for steady-state or transient-state.
Tc distribution coefficient is mathematically expressed as
empirical equations proposed by Kolarik et al. 5 with slight
modification to enable to treat Pu effect on Tc distribution as
follows,
D Tc = D Tc, 0 + D Tc, Zr + D Tc, U + D Tc, Pu(1)τ)
D Tc, 0 = 0.845C 1.92exp(3300
free-TBP, org
0.848 exp(230 τ )2.324C NO−3, aq
4.69 exp(410 τ )1+0.157C NO−3, aq

D Tc, U = 0.331(2)

exp(8070τ)
1.95 exp(160 τ )exp(324τ)+01.72C NO−3, aq

exp(3150τ)

exp(–350τ)

2 2+
C UO
−1.3432 , org{1+4.87C NO−3, aq exp(980τ)}exp(–1060τ) (3)C UO2+2 , org + C Pu4+, org–0.707

D Tc, Zr = 1670C Zr, org C NO−3, aq exp(2810τ)–0.707

D Tc, Pu = 3.31C NO−3, aq C

τ=

2
4+
C Pu
, org
+
C Pu4+, org exp(–1060τ)
UO2+
,
org
2

1
1
–
298
T

(4)
(5)
(6)

Here, D Tc : overall distribution ratio of Tc; D Tc, 0 : distribution
coefficient of HTcO4 itself; D Tc, U, D Tc, Zr or D Tc, Pu: contributionof synergistic effect of U, Zr or Pu to the distribution of TcO4−,
respectively; Cfree-TBP, org, CUO22+, org, CZr, org or CPu4+, org : concentration (M) of free-TBP, UO22+, Zr or Pu4+, respectively, in theorganic phase; CNO −3, ap: concentration (M) of NO3− in the aqueous phase; T: temperature (K).
In the current cases, however, the contribution of Pu effectto Tc distribution is almost negligible because of its small concentration.
4. Results and Discussion

Figure 3. Experimental flow-sheet for Run No. 3.

4.1. Tc Extraction. In Figure 4, the Tc concentration profiles at the U, Pu co-extraction part (the extraction banks No.
1 to 8) and the scrub part (the extraction banks No. 9 to 16)
obtained from two experimental runs are summarized as Figure
4a for Run No. 1 and Figure 4b for Run No. 2. The Tc concentration values are represented by plot symbols, the squares forTechnetium Separation for Future Reprocessing

J. Nucl. Radiochem. Sci., Vol. 6, No. 3, 2005 273

Figure 4. Tc concentration in the extraction banks No. 1–16, U, Pu
co-extraction part and scrub part. Experimental values expressed asplot symbols, and calculated values expressed as lines. a) Run No. 1
and b) Run No. 2.

the organic solutions and the circles for the aqueous solutions, inthese figures. The open plots represent the values under detection limit. The analytical methods utilized to determine thesevalues are also shown in the figures. As shown in the figures,
Tc concentration in the aqueous solution at the respective extraction bank steadily decreased according to the aqueous flow
direction in the U-Pu co-extraction part, from the bank No. 8,
the feed point of the dissolver solution, toward the bank No. 1 inboth runs. These results clearly imply that the majority of Tc
was extracted into the solvent. The percentage of Tc remaining
in the raffinate is calculated to be 1.0% for Run No. 1 or under
1.5% for Run No. 2, respectively, assuming that the aqueousconcentration value at the bank No. 1 obtained in the respective
experiment, 2.49 × 10−3 g l −1 for Run No. 1 or under the detection limit (2 × 10−3 g l−1) for Run No. 2, is equal to the concentration in raffinate constantly flowing out, and using the flow rate
values in Table 1 and the concentration values in the feed inTable 2. It should be noted that the Tc concentration in the raffinate was not directly determined. As described in the experimental section, the analytical samples were collected from allbanks after shut down operation of the mixers-settlers extractors
and the influence of such operation on the concentration profiles
in the extractors was not clarified. In the scrub part, the extraction banks No. 9 to 16, the Tc concentrations in the organic solutions maintained roughly constant values at the banks No. 9 toNo. 14. Although the values decrease at the banks No. 15 andNo. 16, the differences from the former banks are not substantial. Therefore, it is clear that the extracted Tc passed throughthe scrub part.
In these figures, the calculation results by ESSCAR are also
shown as the lines. Although the calculated values do notcompletely agree with the experimental values in each figure,but the calculation results successfully represent the essential
phenomena, Tc extraction in the co-extraction part and passing
through the scrubbing part.
Further, we succeeded to clearly present the extraction
mechanism of Tc by utilizing ESSCAR. Two calculations for
Run No. 2 were performed as an example. In the first calculation, the distribution of Tc was described as D Tc = D Tc, Zr + D Tc,
0 , thus, only the synergistic extraction effect of Zr together
with the intrinsic Tc extraction was considered (refer to eq 1).
The results are represented as the lines noted as “Zr-effect” inFigure 5. In the second, only the synergistic extraction effectof U was considered, namely D Tc = D Tc, U + D Tc, 0, and theresults are similarly noted as “U-effect” in the figure. Thelines for “Zr-effect” show that Tc will be extracted in the decontamination part with. On the other hand, the lines for “Ueffect” show that Tc will not be extracted. In the scub part, thelines for “Zr-effect” shows that Tc will be back-extracted andbe restricted to flow out as an organic solution. The lines for

Figure 5. Tc concentration calculated by ESSCAR code.
Zr-effect: Tc distribution coefficient calculated from synergistic effect of Zr only.
U-effect: Tc distribution coefficient calculated from synergistic effect of U only.

Figure 6. Tc concentration in the extraction banks No. 17–26, U, Pu
recovery part and Tc back-extraction part. Experimental values
expressed as plot symbols, and calculated values expressed as lines.
a) Run No. 1 and b) Run No. 2.

“U-effect” show that the Tc concentration in organic solution
does not significantly decrease. Therefore, ESSCAR calculation results clearly present that;
1. The phenomenon of Tc extraction in the co-decontamination part is dominated by the synergistic extraction effect ofZr, not that of U;
2. The phenomenon of extracted Tc passing through the scrubpart is dominated by the synergistic extraction effect of U,
not that of Zr.
4.2. Tc Separation. In Figure 6, the Tc concentration profiles at the U, Pu recovery part (the extraction banks No. 17 to19) and the Tc back-extraction part (the extraction banks No.
20 to 26) obtained from two experimental runs are summarized as Figure 6a for Run No. 1 and Figure 6b for Run No. 2.
The Tc concentration values are respectively expressed as theplot symbols in the figures, the squares for organic solutions andthe circles for the aqueous solutions. The open plots, again, represent the values under detection limit. It is clear from thesefigures that the Tc concentration in the organic solution steadilydecreases in the Tc back-extraction part as the bank number
increases from No. 20 to 26, but that Tc still flows out as theorganic solution especially in the case of Run No. 1. In the U,
Pu recovery part, the extraction banks No. 17–19, the Tc concentration in the aqueous solution maintains almost constant value
and Tc flows out as the aqueous solution, too. The recovery of274 J. Nucl. Radiochem. Sci., Vol. 6, No. 3, 2005

Asakura5. Conclusion
We performed Tc extraction-separation experiments, basingon PUREX techniques, using spent UO2 fuel with burn-up of
44 GWd t −1. We performed simulation calculations by
ESSCAR, too, and the results can be summarized as follows.
1. Tc is extracted by TBP with significant efficiency from adissolver solution. Quantitative extraction of Tc is feasible.
2. Tc is extracted in a co-decontamination part by the synergistic extraction effect of Zr. Tc passes through a scrub partby the synergistic extraction effect of U.
3. Extracted Tc is separated from U and Pu as a product byadditional scrub. Quantitative recovery of Tc is feasible, too.
Here, because of low Pu concentration, (only 1% of U), thesynergistic effect with Pu was not discussed. Scoping for the
future when MOX fuel is widely utilized with innovative lightwater reactors or fast breeding reactors as nuclear power
plants, the synergistic effect of Pu will be a quite importantfactor to describe Tc extraction behavior.

Figure 7. Tc concentration in the extraction banks No. 17–36, U, Pu
recovery part, Np separation part and Tc back-extraction part, in Run
No. 3. Experimental values expressed as plot symbols, and calculated
values expressed as lines.

Tc in the product solution is calculated to be 68.7% for Run No.1
or 54.2% for Run No. 2, respectively, in the same manner as sect4.1, and is not sufficiently high. The calculated concentration
values agree fairly well with the experimental ones, except thosefor the organic solutions at U, Pu recovery part. Therefore, it isconfidently said that Tc can be separated from U and Pu and berecovered as Tc product and the recovery can be increased byadding more extraction bank for Tc back-extraction.
Figure 7 shows the concentration profile of Tc in bank No. 17
to No. 36 in Run No. 3. From this figure, it can be noted thatsignificant amount of Tc was back-extracted in the Np separation part (banks No. 19 to No. 26) and flowed out as Np product.
It is expected that such undesirable Tc loss in the Np product can
be avoided by exchanging the order of the two separation parts,a Tc separation part before a Np separation part. Although theagreement of calculation results with experimental ones is notvery well, the trend is represented. In extraction banks No. 27
to 36, Tc separation part, the concentration of Tc in aqueous
solution significantly decreased and the remaining Tc in organic
solution was under detection limit (9 × 10−4 g l −1). Thus, it canbe said that Tc is sufficiently back-extracted. The experimental
results in Tc separation part, only those for aqueous solution
being available here, agree very well with the calculated ones.
The back-extraction in this part seems to be more efficient thanthat for Run No. 1 or No. 2 shown in Figure 5a or 5b. This difference can be explained by the lower U load in the solvent in
the case of Run No. 3 (approximately 50 g l −1) than that in thecase of Run No. 1 or No. 2 (approximately 65 g l −1).

Acknowledgement. This work was carried out under the
auspices of the Ministry of Education, Culture, Sports, Scienceand Technology (MEXT) of Japan. The authors greatly thankto the financial support given form the MEXT, and the every
member of the laboratory and NUCEF who contribute to perform the spent fuel tests.
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