Journal of Nuclear and Radiochemical Sciences, Vol. 6, No. 3, pp. 275-278, 2005

Separation and Utilization of Tc and Other Rare Metal Fission Products by an Extended
Aqueous Reprocessing
Masaki Ozawa,*, a, b Shinichi Koyama,a Tatsuya Suzuki,b and Yasuhiko FujiibaO-arai Engineering Center, Japan Nuclear Cycle Development Institute, Oarai-machi, Higahiibaraki-gun,Ibaraki 311-1393, Japanb
Research Laboratory for Nuclear Reactors, Tokyo Institute of Technology, O-okayama, Meguro-ku, Tokyo,
Japan
Received: July 31, 2005; In Final Form: September 30, 2005
A novel reprocessing system with recovery of actinides, long-lived fission products (LLFP) and valuable rare
metal fission products (RMFP) has been proposed. This process is based on ion exchange (IX) and catalyticelectrolytic extraction (CEE). The pre-filtration step using tertiary pyridine-type anion-exchange resin is set prior
to the main actinide recovery steps in this system. The perfect isolation of platinum group elements (Pt-G) suchas 106Ru from fuel dissolver solution was successfully demonstrated for irradiated mixed oxide (MOX) fuel. The
CEE method, being set as a post-pre-filtration process, was applicable to separation of RMFP including TcO4 − andReO 4 − by selective and accelerative deposition with Pd 2+ as a catalyst. Quaternary Pd-Ru-Rh-Re deposited Pt
electrodes showed the highest cathodic current. The catalytic ability is about twice superior to that of the base Pt
electrode when used for artificial sea water as well as alkaline solution.
The recovery and separation of actinides and RMFP by a multi-functional reprocessing system consisting of IX
and CEE will minimize the quantity and improve the quality of high level liquid waste (HLLW). The recovered
RMFP will be used as a “FP-catalyst” for hydrogen production in water electrolysis.

1. Introduction
In order to optimize the radioactive waste treatment in the
nuclear fuel cycle, partitioning and transmutation (i.e. P&T) of
actinides (An) and fission products (FP) have been considered.
Actinides are α radioactive, and their half-lives are long; e.g.
2.4 × 10 4, 4.3 × 10 2 and 2.1 × 10 6 years for 239Pu, 241Am and
237
Np, respectively. Among FPs concerned, Tc, Pd, Se and Te
are long-lived fission products (LLFP), and Ru, Rh, Pd, Tc, Se
and Te are precious and rare metal fission products (RMFP).
The half-life of 99Tc is as long as 2.1 × 105 years. By considering its fate, utilization with and without transmutation ( 99Tc(n,γ)100 Tc → β − → 100Ru(stable)) are pictured in the future.
Typical amounts of FP estimated by calculations with the
ORIGEN-II code are shown in Table 1. Amounts of RMFP
generated are proportional to burnup of the fuel, and spent
mixed oxide (MOX) fuel, highly irradiated in fast reactor (burnup: 150 GWd/t, cooling time: 4 years), will contain morethan 30 kg of RMFP per metric ton.

delicate processes as recovery and separation of LLFP and
RMFP. We propose a new reprocessing system based on ion
exchange (IX) and catalytic electrolytic extraction (CEE)
methods. The state-of-the-arts of separation technology on
RMFP and minor actinides (MA) from spent fuel by the IX
method and utilization technology of RMFP (including Tc)
and Re (as hydrogen generation catalysts) by the CEE method
are described.
2. Novel Reprocessing System Provided with Separation
Function of LLFP and RMFPAn innovative reprocessing system is newly proposed. A
schematic diagram of the process is shown in Figure 1. The
process is based on IX chromatography using pyridine resin.
SF*Dissolver
Solution
diluted HCl solution

TABLE 1: Typical Amount of RMFP Per Ton of Fast-reactor Spent Fuel
Pure metal
Amount(kg/HMt)

Ru
12.5

Rh
3.6

Pd
11.1

Tc
3.3

Te

Se

Note

2.7

FBR-SF; 150 GWd/t,
0.2
Cooled 4 years.

Diluted HCl
EluteTertiary Pyridine
Resin Filter

Alkali-Rinsing
NaOH

PreFiltration of
RMFP byIX

Dissolver solution

Step I-A

Re-Dissolution
conc.HCl)

Concentrated HCl
Elute

It is, therefore, indispensable to establish effective separation methods and a way of utilization as the concept of P&T,U(Partitioning, Transmutation and Utilization) by using innovative technologies.1, 2 Thereby, the HLLW containing non-α,
non-LLFP and non-RMFP nuclides would be preferably produced for a non-deep disposal.
The current fuel reprocessing system cannot respond to such
*Corresponding author. E-mail: ozawa.masaki@jaea.go.jp.
FAX: +81-29-267-1676.

Slica-supported
Tertiary Pyridine Resin
Diluted HCl
Elute III

Catalytic
Electrolytic
Extractionof RMFPPtG(Ru106,etc) &Tc99-Product

Advanced
Reprocessing
by IX

Step II

Step I-B
Evaporaion /Solidification

Ln FP(Cs137, etc) Waste
MA

U Pu Np-Product

Re-Dissolution HNO3)
Addition of CH3OH

HNO3 +CH3OH
Elute

Slica-supported
Tertiary Pyridine Resin
Diluted HNO3
EluteUtilization
Utilization

Am / Cm
Separation
by IX

Evaporaion /Solidification

Total
Actinides
Recycling

Cm-Product
Cm-Product

Am-Product
Am-Product

Step III

Figure 1. Reprocessing flow sheet provided with multi-functional
separation ability.

© 2005 The Japan Society of Nuclear and Radiochemical Sciences
Published on Web 12/28/2005

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

-CH 2-CH-CH2-CH-

N-CH-CH2-

Figure 2. Chemical form of tertiary pyridine-type anion exchange
resin.

Tertiary pyridine resin has functions of a weakly basic anion
exchanger and a soft donor extractant. As shown in Figure 1,
the reprocessing system mainly consists of three processes; thefirst step (Step I-A) consists of a pre-filtration process prior tomain reprocessing of Step II and a recovery process of RMFP
by CEE (Step I-B). Step II is the main process for separationof spent fuel, i.e. spent fuel is separated into 3 groups such as
FPs with Ln (III), MA (III), and Pu with U, Np. The fractionof FPs with Ln(III) will be HLLW. The third step (Step III) isa mutual separation process of MA(III) to Am and Cm products.
On Step I-A, technetium and Pt-G elements are expected toadsorb on the gelated tertiary pyridine resin in the dilutedhydrochloric acid medium referring to the basic adsorption
property on anion exchange resin. The adsorbed elements are
rinsed out by alkaline elution from the resin. Technetium and
Pt-G elements in this effluent are recovered again on an electrode by CEE.
On Step II, the column packed with a high-porous type oftertiary pyridine resin embedded in silica beads is used forhydrochloric acid-based reprocessing. The resin was produced
by Research Laboratory for Nuclear Reactors, Tokyo Instituteof Technology.3−5 The chemical structure of this resin is presented in Figure 2. The resin has high radiation resistance inhydrochloric acid solution. The average diameter of the resinis 60 µm. The total exchange capacity is 1.94 meq/g (dry) in
Cl−form and the cross-linkage is 20%. While multivalent
U(VI), Np(VI) and Pu(IV) are strongly adsorbed on anion
exchange resin in highly concentrated hydrochloric acid solution,6 the distribution of trivalent MA(III) and Ln(III) arelower than the multivalent Ans in such a medium. Moreover,the distribution coefficient of Ce(III) was about 4 times lower
than those of Am(III) in a pure hydrochloric acid. Therefore,groups of Ln(III) with other FPs like Cs and Sr, trivalent
MA(III) and multivalent U(VI), Np(VI) and Pu(IV) are individually separated in this order.
The mutual separation of Am and Cm at Step III is alreadyconfirmed by trace experiments.4 In this process, the same
resin as on Step II was used, while nitric acid solution wasused instead of hydrochloric acid solution.
3. Separation and Recovery of RMFP
Separation of RMFP by tertiary pyridine resin (Step I-A).
Mixed oxide (MOX) fuel, 21.0-wt% Pu in 18.0-wt% enricheduranium, was irradiated from the 16th to 35th cycle at the 3rd
row in the experimental fast reactor JOYO. The effective fullpower days were 1019.33, and the peak burnup was 143.8 GWd/t.
A total of 1560 days have passed from the reactor shut down toanalysis.
A chopped irradiated fuel pin was transported to AlphaGamma Facility (AGF) of the Japan Nuclear Cycle Development
Institute. The irradiated fuel was further sliced into pieces of 5
mm in length at AGF.
The sliced specimen was then placed in a flask mountedwith reflux condenser, and dissolved in 28 mL of 8 mol/dm3
nitric acid solution by heating for 6 h at boiling temperature.

Ozawa
(%)
Am 241100

Eu 155100

Ce 144100

Sb 125100

Ru 106100

Cs 137100

SF Dissolver
Solution
0.5 mol/dm3 HCl

PreFiltration

H2O Rinsing

1 mol/dm3 NaOH Rinsing

Resin Rinsed by
Alkaline soln.
Am 2410.19

Eu 155

N.D

Ce 144N.D

Sb 12578.9

Ru 106

94.9

Cs 137<0.01

Tertiary
Pyridine
Resin
FilterEluate by H 2O
Am 2410.21

Eu 1550.21

Ce 1440.23

Sb 12517.0

Ru 106

5.14

Cs 1370.42

Eluate by NaOH
Am 241<0.01

Eu 155<0.01

Ru106- free Feed D.S

Ce 144

N.D.

Am 241>99.5

Sb 1254.08

Eu 155>99.7

Ru 106

N.D.

Ce 144>99.7

Cs 137<0.01

Sb 125N.D.

Ru 106

N.D.

Cs 137>99.5

Eluate by 0.5 mol/dm3 HCl

Figure 3. Material balance of 106Ru and Other FP on pre-filtration(STEP I-A).

After several drops of concentrated hydrofluoric acid wereadded, the solution was again heated for 6 h in order to minimize amounts of insoluble residue. The weight of dissolved
fuel was estimated to be 1.27 g.
The fundamental flow sheet is based on a concept shown in
Figure 1. The separation on Step I-A was employed to remove
RMFP (106Ru, 99Tc, etc). On this step, gamma spectrometry
was applied to identify gamma nuclides like 106Ru, 125Sb, 144Ce,
155
Eu, 241Am and so on.
A 0.1 mL aliquot of the dissolved spent fuel solution was
diluted by adding 50 mL of pure water. The sample solution
was heated and dried, and was dissolved again in 3 mL of 0.5
mol/dm 3 hydrochloric acid. The resulted hydrochloric dissolver solution was loaded onto resin (8 mL column volume).
Tertiary pyridine resin of a non-support type was used as prefilter anion exchange resin. After sample loading, the column
was fed with 4 column volumes of 0.5 mol/dm3 hydrochloric
acid solution. The resin was rinsed by pure water of 4 column
volumes. Then, 1 mL of resin was taken from the column andrinsed again by pure water. After the rinse, the rinsing waterand resin were encapsulated in a plastic vial. Furthermore, 3
column volumes of 1 mol/dm3 sodium hydroxide solution were
fed to the resin. After the alkali rinse, the resin and eluted
sodium hydroxide solution were analyzed by γ-ray spectrometry to confirm the adsorbed nuclides.
Strong γ -ray peaks of 106Ru and 125Sb were observed in theresin rinsed by pure water after anion-exchange. Other
nuclides, such as 241Am and 137Cs were scarce. Figure 3 shows
the material balance of main nuclides before and after the prefiltration. A weight ratio of nuclide was assumed 100% at the
inlet. Ruthenium-106 and 125Sb were not detected in the eluate
by elution with 0.5 mol/dm3 hydrochloric acid solution. Whileother nuclides, 241Am, 155Eu and 137Cs, were scarcely detectedin the outlet of rinsing water and alkaline solution, the amountsof each nuclide were less than 0.5%. It is concluded that 106Ru
and 125Sb can be isolated perfectly from the spent fuel and the αcontamination is very small. Noticeable FP (106Ru and 125Sb) free dissolver solution is preferable to increase the decontamination factor in the whole reprocessing process.
Since the tertiary pyridine is a soft donor ligand and the ionsof Pt-G elements are soft acid, they are strongly bonded by coordination. Technetium (99Tc) was not detected by γ-spectrometry.
Although absorption of Tc(VII), Ru(IV) and Pd(II) on Dowex 1
resin in hydrochloric acid decreases with increasing acidity,

Separation and Utilization of Tc and Other Rare Metal Fission Products

these species have rather high distribution coefficients (logD >1) in the region 0.1 mol/dm3 < [HCl] < 12 mol/dm3.6 The logD
values of actinide ions increase with increasing acidity, but thevalues are smaller than 0 for [HCl] < 1 mol/dm 3. Therefore,
anionic TcO4− and other Pt-G elements are considered to be welladsorbed on tertiary pyridine resin and separated from actinides
in the same manner as Dowex 1 resin of a weakly basic anion
exchanger.
Recovery of RMFP by catalytic electrolytic extraction(Step I-B). Details of the CEE method applied here to Step I-B
to recover and purify RMFP obtained from Step 1A were discussed elsewhere.7 In principle, Pd2+ (or Fe2+) would accelerate
electro-deposition of the other ions as a promoter (i.e. Pdadatom)
at the electrode surface or as a mediator in the bulk solution. As
for a typical example of CEE of RMFP from simulated HLLW,
the galvanostatic electrolysis resulted in the quantitative deposition, where metal ions with E0 > 0.7V tended to deposit on thecathode, and the deposition ratio seemed to be proportional tothe order of the redox potential; Pd > Te > Se > Rh > Ru > Re.
Molybdenum and Zr can be recovered as co-precipitation at H+< 1.5 mol/dm3.
An interaction between Pd2+ and TcO4 − during CEE was also
confirmed.2 The working Pt electrode was polarized fromnoble to base potential side, every 30 min step by step. The
amount of deposition was measured by a radiometric method
at each polarized potential. While the deposition of Tc wassignificantly suppressed with an increase of the nitric acidconcentration, addition of Pd2+ (Pd / Tc = 5) enhanced its electro-deposition expectedly even though nitric acid concentration was 2 mol/dm 3. Namely, the Pd 2+ effect can conquer anegative nitric acid effect causing the redissolution of Tc
deposit. The Tc deposit was brownish in color and apparently
not dendritic. The deposition ratio was, however, as low as 2%
at maximum, and the deposition amount of Tc was larger thanthat of Ru under almost the same nitric acid concentration. An
observed potential region of TcO 4 − for quantitative electrodeposition was 0.4 V– 0.05 V (V vs. NHE), agreeing with thehydrogen adsorption-desorption potential region of a Pt electrode. The maximum deposition was observed near the hydrogen evolution potential. Thus, H ad likely participates in theelectro-deposition of TcO4 − in the system
TcO4 − + 3Had + H+ → TcO2 ⋅ 2H2O.
In the extremely negative conditions (i.e. < – 0.3V), however,hydrogen evolution occurred simultaneously and disturbed
again the Tc deposition reaction. In the case of a carbon electrode which had no H ad region in 3 mol/dm3 nitric acid solution, reduction of TcO 4 − to TcO2+ was the most significant in
the potentiostatic electrolysis at φ E = – 0.3 V or – 1.0 V (V vs.
Ag/AgCl).8
4. Utilization of RMFPThe hydrogen overpotential of metals periodically changes,
and specifically Pt-G elements, Re and Tc show lower overpotentials. One can explain those in referring to d-hole characteristics based on the band theory. For utilization of RMFP,
hydrogen evolution characteristic of the RMFP-deposit on Pt
electrodes was investigated for electrolysis in alkaline solution.
RMFP-deposited electrodes were fabricated based on the
CEE method. Details of electrolysis conditions are described
elsewhere.2, 9 Results of electrochemical reduction are summarized in Table 2, where “Pd-Ru-Rh-Re (3.5:4:1:1)” means thequaternary Pd-Ru-Rh-Re deposited Pt electrode obtained fromelectrolyte containing Pd, Ru, Rh and Re (Tc) ions in the ratio of
3.5:4:1:1, which corresponds to the composition of the fast-reactor MOX spent fuel listed in the Table 1. The deposition ratios
of RMFP were estimated from the reduction ratios calculated

J. Nucl. Radiochem. Sci., Vol. 6, No. 3, 2005 277

Pd
20 µm

µm
20 µm

IMG1

Rh
µm
20 µm

Pd L

Ru
µm
20 µm

Rh L

Ru L

Re
Re
20 µm

Re M

Figure 4. EDS(EPMA) of the deposits on the Pt electrode from
nitric acid solution ; Solution composition : Pd-Ru-Rh-Re(3.5:4:1:1),
divided addition of Pd2+.

from the balance of ionic concentration during the electrolysis.
The highest reduction ratio of 95–99% was obtained for Pd bydischarging from Pd2+ to metallic Pd, and the deposit tended toform dendrites which were easily detached by simultaneoushydrogen evolution. The reduction manner of Rh was similar tothat of Pd; a 1 step reduction of Rh3+ to metallic Rh. On thecontrary, reduction of Ru might proceed by 2 steps, i.e. RuNO3+→ Ru 2+ and Ru 2+ → Ru (metal), with the reduction ratio ofaround 14%. The reduction ratio was 16% for ReO4 − and only
1.7% for TcO4−. As reported previously,1, 2, 7 the presence of Pd2+
accelerated deposition of Rh as well as Ru, and the co-existenceof Rh3+ also accelerated the reduction of ReO4 − in the present
experiment (16% → 43.0%). Specifically, in CEE with a low
cathode current density, e.g. 2.5 mA/cm2, compulsory stirring
was necessary to get a minute and stable deposit of Pd layers.
This procedure was very essential to obtain larger amounts ofco-deposit with other ions. Figure 4 shows an element map of
the surface deposit observed with EPMA (electron probe micro
analyzer) for the final run (*2 ) in Table 2. In this run, Pd2+ wasadded to catholyte divided by 5 times to allow Pd to exist constantly in the bulk solution (as Pd2+) and at the electrode surface(as Pdadatom). The shape of deposit was not dendritic but rather
spherical and homogeneous, likely cohered with fine particles.
TABLE 2: Reduction Ratios of RMFP by Catalytic Electrolytic Extraction
System

Pd
Pd
> 99
Ru
Rh
Re
Tc
Pd-Ru
99.3
Pd-Rh
99.0
Pd-Re
99.4
Ru-Rh
Ru-Re
Rh-Re
Pd-Ru-Rh-Re(1:1:1:1) 95.7
Pd-Ru-Rh-Re(3.5:4:1:1)*1 99.0
Pd-Ru-Rh-Re(3.5:4:1:1)*2 94.7
*1: Pd block addition.
*2: Pd 5divided addition.

Reduction ratio / %
Ru
14
60.9
58.2
14.5
46.0
11.8
16.5

Rh
> 99
84.7
32.5
10.0
14.5
2.10
26.6

Composition of
Re Tc Electrode Surface
16
- 1.7
Pd Ru
Pd Rh
10.0 Pd Re
Ru Rh
13.5 Ru Re
43.0 Rh Re
19.0 - Pd Ru Rh Re
33.4 - Pd Ru Rh Re
55.3 - Pd Ru Rh Re

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

Ozawa
5. Conclusions

Cathode Current, I (mA) at ψ E = -1.25 V

200

Pd -Ru-Rh-Re(3.5:4:1:1)
Ru
Pd -Ru -Rh -Re(3.5:4:1:1)
Ru-Rh

Rh -RePd -Ru -Rh-Re(1:1:1:1)
Pd -Ru-Rh-Tc

Pd -Ru(1:1:1:0.5)

100

Ru-Re
Pd -RePt

Pd -Rh
Tc

Pd
Re

0
-1.3

Rh

-1.2

-1.1

-1

-0.9

ψ Hinit. (V vs. Ag/AgCL)

Figure 5. Relation between cathodic current corresponds to hydrogen
evolution at –1.25 V (vs. Ag/AgCl) and initial hydrogen evolution
potential on each deposit electrode in 1 mol/dm 3 sodium hydroxide
solution.

In the quaternary ionic solution system, an excess and divided
addition of Pd2+ resulted in the deposit with almost equal atomcomposition of Pt-G metals (Pd-Ru-Rh). However, the number
of Re atoms at the surface of deposit was smaller than those ofothers despite the rather higher reduction ratio.
The cathodic currents corresponding to hydrogen evolution at
the given polarized potential vs. initial hydrogen evolution
potential for various RMFP-deposited electrodes are shown in
Figure 5. The cathode currents decreased for the Pd, Rh and Re
deposited Pt electrodes in 1 mol/dm3 sodium hydroxide solution,
but increased only for the Ru deposited Pt electrode. The current of the quaternary Pd-Ru-Rh-Re (3.5:4:1:1) deposited Pt
electrode was the highest, exceeding that of the Pt electrode byfactor 2 in 1 mol/dm3 sodium hydroxide solution and artificial
sea water. Among RMFPs, Ru seems to be responsible for highreactivity on hydrogen evolution. As for the apparent relative
reactivity of RMFP estimated from the currents per mg of
deposit, however, binary deposits of Ru-Re and Rh-Re showed
the highest reactivity. The cathode current of the quaternary
Pd-Ru-Rh-Re deposited Pt electrode in artificial sea water
decreased about a half to a third of that in 1 mol/dm3 sodiumhydroxide solution. The reactivities were still comparable tothat of Pt in 1 mol/dm3 sodium hydroxide solution. The roles ofRe and Tc in this system are still unclear, and we are planning
further parametrical experiments.

A novel reprocessing system for recovery of LLFP and RMFP
as well as actinides using IX and CEE methods is proposed.
The process can directly separate Pt-G elements with Tc as wellas Am and Cm from the spent fuel in the minimum number ofreprocessing steps. The perfect isolation of 106Ru and 125Sb fromfuel dissolver solution by IX at the pre-filtration step was successfully demonstrated for irradiated MOX fuel. The CEE,
being set in the post-IX process, was applicable to recover
RMFP including TcO4− and ReO4− through unique and accelerative deposition by adding Pd2+ as a catalyst. The quaternary PdRu-Rh-Re deposited Pt electrodes showed the highest cathodic
current corresponding to the hydrogen evolution reaction. The
current was about twice higher than that of the base Pt electrodein the use for artificial sea water as well as alkaline solution.
The recovery and separation of actinides, LLFP and RMFP
by the multi-functional reprocessing system consisting of IX andCEE processes are relevant to minimize the quantity andimprove the quality of HLLW. The promising utilization fieldof recovered RMFP will be a “FP-catalyst” for hydrogen production in water electrolysis. RMFP (including Tc) and Re will
be highly expected to be flow material to bridge nuclear andhydrogen energy systems.
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(6) K. A. Kraus and F. Nelson, Proc. Intern. Conf. Peaceful Uses
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