Development of the MAREC Process for HLLW Partitioning Using a ...

Journal of NUCLEAR SCIENCE and TECHNOLOGY, Vol. 41, No. 3, p. 315–322 (March 2004)

ORIGINAL PAPER

Development of the MAREC Process for HLLW Partitioning Using a Novel Silica-Based CMPO Extraction Resin Yuezhou WEI1;
, Anyun ZHANG1 , Mikio KUMAGAI1 , Masayuki WATANABE2; y and Naoto HAYASHI2 2

1 Institute of Research and Innovation, Takada, Kashiwa-shi, Chiba 277-0861 Tokai Works, Japan Nuclear Cycle Development Institute, Tokai-mura, Naka-gun, Ibaraki 319-1194

(Received July 18, 2003 and accepted in revised form November 11, 2003) A new partitioning technology named ‘‘MAREC’’ process has been proposed for the separation of minor actinides (MA=Am, Cm) from high level liquid waste (HLLW) by extraction chromatography using a novel porous silica-based CMPO extraction resin. Separation experiments for simulated HLLW solutions containing typical fission product (FP) elements were carried out by a column packed with the CMPO/SiO2 –P extraction resin. The experimental results showed that MA as a mixture with some heavy rare earths can be effectively separated from other FP elements by using two chromatographic columns. Furthermore, some specific FP elements such as Pd, Zr and Mo were also efficiently separated from the simulated HLLW. The separation behavior of the elements are considered to result from the difference of their adsorption and elution selectivity based on the complex formation with CMPO and the eluents such as DTPA and H2 C2 O4 . These results revealed that the proposed MAREC process for HLLW partitioning is essentially feasible. KEYWORDS: high level liquid waste, minor actinide, lanthanide, partitioning, extraction chromatography, silica-based CMPO extraction resin, DTPA, oxalic acid

I. Introduction As a final disposal method for the high level liquid waste (HLLW) generated by spent fuel reprocessing, the geologic disposal concept of vitrified HLLW has been proposed and investigated worldwide. On the other hand, from the viewpoints of minimizing the long-term radiological risk and facilitating the management of HLLW, a partitioning of the long-lived minor actinides (MA=Am, Cm) and some specific fission products (FP) such as Cs, Sr, Tc and the platinum group metals from HLLW is much more desirable. Since the late 1980s, the so-called Partitioning/Transmutation (P/T) waste management strategy has been proposed to establish a closed nuclear fuel cycle in some countries such as Japan, EU and USA.1,2) For this purpose, a number of partitioning processes (e.g., TALSPEAK, TRUEX, DIAMEX, TRPO, DIDPA, ALINA, CSEX and SREX) based on liquid-liquid extraction method using various conventional and newly developed extractants have been developed.1–8) Among the extractants used in these processes, a neutral chelating reagent named octyl(phenyl)-N,N-diisobutylcarbamoylmethylphosphine oxide (CMPO), a bifunctional organophosphours compound, is well known to be able to extract effectively many kinds of the actinide and FP ions from an aqueous solution containing concentrated nitric acid. Furthermore, since CMPO shows fairly excellent chemical-stability in nitric acid solution and is a commercially available product, it has been extensively studied for the actinides partitioning from HLLW.1–3,6,9,10) However, because the trivalent actinides and rare earth elements (RE) exhibit almost the same




Corresponding author, Tel. +81-4-7144-8865, Fax. +81-4-71447602, E-mail: [email protected] y Present address: Japan Nuclear Fuel Ltd., Rokkasho-mura, Kamikita-gun, Aomori 039-3212

extractability with CMPO and the separation between MA and RE is difficult. In recent years, an improved TRUEX process called SETFICS process which uses the TRUEXsolvent (the mixture of CMPO/TBP and n-dodecane) as extractant and the complexing reagent, diethylenetriaminepentaacetic acid (DTPA) as a stripping reagent was developed by Japan Nuclear Cycle Development Institute (JNC).6) In this process, the trivalent MA and RE in HLLW are co-extracted into the organic phase by TRUEX-solvent, and then MA is selectively stripped into aqueous phase by the solution containing DTPA and NaNO3 (salting-out reagent). Since Am and Cm can form more stable complexes with DTPA than the RE especially the light RE (lRE) such as La, Ce, Pr, Nd, Pm and Sm,11,12) the MA is preferentially stripped from the organic phase and effectively separated from the light RE, which shears more than 95 mass% of the total fission product RE. On the other hand, as similarly to all of the liquid–liquid extraction processes, the SETFICS process will generate a great amount of organic waste resulted from the hydrolytic and radiolytic degradation of the solvent. In addition, a large number of equipment is required for the multi-stage extraction, stripping and solvent-washing processes. These will affect the economic performance of the process. Compared to uranium and plutonium, the minor actinides are significantly less abundant in the spent fuel, so the scale of the separation process for minor actinides from HLLW should be considerably smaller than that of a main separation process such as PUREX. In our previous works,13–17) it is evaluated that as a partitioning process of MA from HLLW, extraction chromatography which utilizes a minimal organic solvent and compact equipment is a promising technology since it can overcome the above backdrops of the liquid-liquid extraction.

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In this work, to develop an alternative technology of the SETFICS process, we have proposed a new partitioning process named MAREC process (Minor Actinides Recovery from HLLW by Extraction Chromatography) which uses the separation columns packed with a novel silica-based CMPO impregnated adsorbent as extraction resin and DTPA as an elution reagent. The separation experiments using the CMPO adsorbent packed column for some simulated HLLW solutions containing fission product RE and other typical FP elements were carried out to evaluate the separation behavior of the elements. Since Y reportedly exhibits similar behavior with Am and Cm in the adsorption onto CMPO and elution with DTPA,6,12) it was used as the mimic element of Am and Cm in this work.

II. Outline of the MAREC Process The flow sheet of the MAREC process for the recovery of MA from HLLW is shown in Fig. 1. The process consists of two separation columns both packed with the CMPO/SiO2 – P adsorbent. In the step (1), the HLLW solution containing about 3 M (M=mol/dm3 ) HNO3 is applied to the first column, and the adsorptive elements including Am(III), Cm(III), RE(III), Zr(IV), Mo(VI) and Pd(II) are adsorbed by the adsorbent mostly as their neutral nitrato-complexes.18–20) In the step (2), the non-adsorptive or weakly adsorptive FPs such as Cs(I), Sr(II), Rh(III) and Ru(III) are washed off by concentrated HNO3 resulting in the non-adsorptive FP effluent, while leaving the adsorptive elements High Level Liquid Waste (3M HNO3) Washing (3M HNO3 ) MA-hRE elution (0.05M DTPA-pH2)

CMPO adsorbent column-1

Cs, Sr, Rh, Ru, etc. (3M HNO3)

lRE elution (H2O)

MA-hRE-Zr-Mo (0.05M DTPA-pH2)

lRE (pH3-4)

Nitric acid concentration adjustment

HNO3(to 3M)

Washing (3M HNO3 )

MA: Am, Cm lRE: La, Ce, Pr, Nd, Pm, Sm hRE: Eu, Gd,Tb-Lu, Y CMPO adsorbent column-2

Pd, DTPA (3M HNO3)

MA-hRE (pH2-3)

MA-hRE elution (H2O) Zr, Mo elution (0.5M (COOH)2 or 0.05M DTPA-pH2)

Zr, Mo (0.5M (COOH)2) or (0.05M DTPA-pH2)

To MA/hRE separation

Fig. 1 Flow sheet of the MAREC process for minor actinides partitioning from HLLW

in the column. In the step (3), the adsorbed MA, heavy RE (hRE) including Eu(III)–Lu(III) and Y(III), Zr(IV), Mo(VI) and Pd(II) are selectively eluted off the column by a DTPA containing acidic solution (Am & Cm containing effluent), because these elements can strongly react with DTPA and form highly stable complexes.11,12) In the step (4), the adsorbed light RE(III) elements are eluted out by a diluted HNO3 or water (lRE effluent) resulting from the destruction of their nitrato-complexes. In the step (5), the nitric acid concentration in the Am & Cm containing effluent is adjusted to 1–3 M by the addition of a concentrated HNO3 . In this step, most complexes of the metals with DTPA are destroyed and form nitrato-complexes due to the low dissociation of DTPA at high proton concentration. Subsequently, the resulting solution is introduced into the second column packed with the CMPO adsorbent (step (6)). In the step (7), with the supply of 1–3 M HNO3 , the Pd(II) complexing with DTPA and the free DTPA molecule are washed out, leaving the adsorptive elements in the column. In the step (8), the MA and hRE are eluted off the column selectively by a dilute HNO3 or water, resulting in the Am & Cm product solution with pH value of about 2–3. In the final step, the Zr(VI) and Mo(VI) remained in the column are eluted off by using a solution containing oxalic acid or DTPA which are strong complexing reagent of these elements. Since Np, a long-lived minor actinide, is recovered in the main process, i.e. simplified PUREXprocess developed by JNC,21) its treatment is not considered in this process. Compared to a liquid-liquid extraction partitioning process, the MAREC process should have the following advantages: (1) a minimal organic solvent utilization and less waste accumulation, (2) compact equipment, and (3) efficient recovery of the target components from their dilute solution. In addition, besides the MA, the Pd and Zr together with Mo can be also recovered by the MAREC process and this will facilitate the HLLW management since these metals reportedly interfere with the vitrification process. Moreover, since no any metal salts are introduced to the MAREC process, it is a completely ‘‘salt-free’’ process. Both CMPO and DTPA reagents have been extensively studied and successfully applied to quite large-scale extraction processes till now.

III. Experimental 1. Materials RE(NO3 )3 xH2 O (RE=La, Ce, Nd, Sm, Eu, Gd and Y) and nitrate of other FP (Cs(I), Sr(II), Pd(II), Mo(VI), Zr(IV) and Ru(III)) were of commercial reagents of analytical grade. The concentrations of all metal ions were about 5103 M except that Mo(VI) was 2103 M. Yttrium(III) as a heavy rare earth was used to simulate the behavior of Am and Cm due to their similar adsorption-elution performance with CMPO and DTPA.6,12) The acidity of the feed solution as a simulated HLLW was adjusted to 3 M HNO3 . The eluent solutions such as 0.05 M DTPA-pH 2.0 and 0.5 M H2 C2 O4 were prepared temporarily before use. Other reagents were also of analytical grade and were used without further purification. JOURNAL OF NUCLEAR SCIENCE AND TECHNOLOGY

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Development of the MAREC Process for HLLW Partitioning Using a Novel Silica-Based CMPO Extraction Resin Polymer immobilized in silica Particles size: 40-60 µm Polymer content: 17-18 wt% (Methanol)

SiO2-P particles Washing

O C8H17

Vacuum filtration Vacuum drying

Impregnation in rotary evaporator

Removing diluent

Vacuum drying Extraction resin (CMPO/SiO2-P)

O

P CH2 C N

CH2CH(CH3)2 CH2CH(CH3)2

(333K, 24h) Extractant: CMPO Diluent: dichloromethane (298K, 1h) (Evacuation, 298-323K, 1-2h) (298-323K, 24h)

SiO2-P

Composition (wt%) CMPO: 33 Polymer: 11-12 SiO2: 55-56

0.5g-CMPO/SiO2-P

Fig. 2 Preparatory procedures of the silica-based CMPO extraction resin

The CMPO/SiO2 –P extraction resin was prepared by impregnating CMPO into the porous silica/polymer composite support (SiO2 –P) developed in our previous work.14) SiO2 –P support contains a macroreticular styrene-divinylbenzene copolymer which is immobilized in porous silica particles with a pore size of 0.6 mm and mean diameter of 50 mm. A commercially available CMPO reagent with the purity of 98.3% was impregnated into the SiO2 –P support by the procedures given in Fig. 2. Firstly the SiO2 –P (polymer immobilized in silica) particles were washed with methanol three times and dried in vacuo at 333 K overnight. Five grams of CMPO reagent was placed in a conical flask and dissolved using 60 cm3 of dichloromethane as a diluent. Subsequently, 10 g of the dried SiO2 –P particles was added to the solution and the mixture was rotated vigorously for 2 h at 298 K. Then the diluent was removed under reduced pressure at 323 K by rotary evaporator. The remainder was dried in vacuo overnight at 323 K and the silica-based extraction resin, CMPO/SiO2 –P, was obtained. Since there was no loss of CMPO during impregnation, the resultant extraction resin contains 0.5 g of CMPO in 1.0 g of SiO2 –P (33 wt%). Figure 3 shows the photos of the silica-based CMPO extraction resin. This novel CMPO extraction resin immobilized in the fine silica particles shows much faster adsorption kinetics as compared to a conventional CMPO extraction resin supported on polymer beads.16) 2. Separation Experiment Figure 4 shows the schematic diagram of the column apparatus for chromatographic separation experiments. About 24 g of the dry CMPO/SiO2 –P was packed to the glass column with 1 cm inner diameter and 50 cm length. The extraction resin was immersed into distilled water for 24 h and then equilibrated with 3 M HNO3 before use. The operating temperature in loading and elution cycles was kept at a constant temperature (298 K or 323 K) by a thermostated circulating VOL. 41, NO. 3, MARCH 2004

25 µm

0.5g-CMPO/SiO2-P

Fig. 3 Photos of the silica-based CMPO extraction resin

3 way valve Drain

CMPO adsorbent Pyrex glass

To water bath

Pressure gauge

PI PIA Pressure limiter

Drain

From water bath

Metering pump Drain

Fraction collector Feed solutions

Fig. 4 Schematic diagram of the column apparatus for chromatographic experiments

water bath. The flow rate was controlled to 1 cm3 /min by metering pump. Following the supply of the feed solution (simulated HLLW) to the column, given volumes of the washing and eluent solutions were passed through the column successively in terms of the schematic flow sheet shown in Fig. 1. During the passage of all the solutions through the

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Y. WEI et al. DV Feed 3MHNO3

0.05M DTPA – pH2

dil. HNO3 (pH3.5)

3

8 Sr(II) La(III)

6

Pd

Ce(III)

Sr

2

Nd(III)

lRE

Sm(III)

hRE

4

pH

Concentration (10-3 mol/dm3)

Zr

Eu(III) Gd(III)

Mo

Y(III)

1

Zr(IV)

2

Mo(VI)

Ru

Ru(III) Pd(II)

0 0

100

200

300

0 500

400

Weight of effluent (g)

Fig. 5 Results of separation experiment for a simulated HLLW at 298 K (Column:
10 mmh500 mm, Flow rate: 0.76 m/h)

DV

Feed 3MHNO3

dil. HNO3 (pH3.5)

3

Zr Sr(II) La(III) Ce(III)

8

Nd(III)

Pd

Sm(III)

lRE Sr

2

pH

Concentration (10-3 mol/dm3)

12

0.05M DTPA – pH2

Eu(III)

hRE

Gd(III) Y(III)

4

Zr(IV)

1

Mo(VI)

Ru

Ru(III) Pd(II)

0 0

100

200

300

400

0 500

Weight of effluent (g)

Fig. 6 Results of separation experiment for a simulated HLLW at 323 K (Column:
10 mmh500 mm, Flow rate: 0.76 m/h)

column, the pressure drop was detected to be less than 0.1 MPa. The effluents from the column were collected by an automatic fraction collector in 10-cm3 aliquots. The weight and pH value of each fraction solution were measured. The concentrations of the metal ions in the collected solutions were quantitatively analyzed by ICP-AES.

IV. Results and Discussion 1. Separation Behavior in the First Column To examine the separation behavior of the heavy RE(III), light RE(III) and other FP elements, a separation experiment for a simulated HLLW solution containing about 5103 M of 12 typical FP elements and 3 M HNO3 was carried out us-

ing the CMPO/SiO2 –P packed column at 298 K. The elution curves of various FP elements and the pH values in the column chromatography are shown in Fig. 5. As can be seen, Sr(II) and most portion of Ru(III) showed no adsorption. These elements leaked out with the feed solution and the 3 M HNO3 washing solution. On the other hand, all of the RE(III), Pd(II), Zr(IV) and Mo(VI) strongly adsorbed onto the extraction resin. With the supply of 0.05 M DTPA-pH 2.0 solution to the column, Pd(II), Zr(IV), Mo(VI) and the heavy RE(III) were eluted off efficiently, showing an elution order as: Pd(II), Zr(IV), Mo(VI), Y(III), Gd(III), Eu(III), Sm(III), Nd(III). The light RE(III), i.e. La(III), Ce(III) and a part of Nd(III) were finally eluted out by the diluted HNO3 solution with pH 3.5. JOURNAL OF NUCLEAR SCIENCE AND TECHNOLOGY

Development of the MAREC Process for HLLW Partitioning Using a Novel Silica-Based CMPO Extraction Resin

23

Am

Cm

Bk Cf

Es

Fm

22

21

HOOCH2C – HOOCH2C –

CH2COOH N – CH2CH2 – N – CH2CH2 – N –– CH2COOH CH2COOH –

Stability constant, log Ks

319

(DTPA)

20

Am Cm Bk

Cf

Es

Fm

Eu

Dy

Ho

Er

19 La Ce

Pr

Nd

Pm

Sm

Gd

Tb

Tm Yb Lu

Atomic number Fig. 7 The stability constants of the complexes of trivalent lanthanides and actinides with DTPA at 298 K11,12)

As illustrated in Fig. 5, the elution curves of the adsorbed elements showed quite long tails, indicating that the elution kinetics was fairly slow. To examine the effect of temperature on the elution kinetics, a separation experiment was conducted at the temperature of 323 K and the other conditions were identical with those of the experiment at 298 K. Figure 6 shows the results of this chromatographic experiment. Compared to the elution curves shown in Fig. 5, all the elements presented sharper elution peaks with very slight tailing. This means that the elution kinetics was significantly promoted by raising the temperature from 298 to 323 K. All the elements except Ru contained in the feed solution were eluted and separated more effectively from each other. Ruthenium presented a complicate elution behavior and interfered with the separation of other elements. This is considered to result from the complicated chemical properties of Ru in HNO3 medium22) and its behavior needs to be investigated further. From the above experimental results, it was found that the elements containing in the simulated HLLW could be separated to the three groups: (1) Non-adsorptive FP elements such as Sr, Ru; (2) heavy RE such as Y, Gd, Eu, Sm mixed with Pd, Zr and Mo; (3) light RE such as La, Ce, Nd. In addition, since Am(III) and Cm(III) were reported to have very close adsorption-elution behavior with the heavy RE for CMPO and DTPA,6,12,16) they are expected to be separated together with the heavy RE. It is well known that CMPO can extract almost all of trivalent actinides and lanthanides effectively from HNO3 solution by Eq. (1):18–20) M3þ þ 3CMPO þ 3NO3  ¼ M(NO3 )3 3CMPO ðM: RE, Am, Cm, etc.Þ:

ð1Þ

Similarly, DTPA, a multi-dentate acidic chelating agent containing five carboxyl and three amine groups capable of being protonated, can also form a series of 1:1 type of stable coordination compounds with many metal ions in a weakly acidic solution according to the following equation:11,12) VOL. 41, NO. 3, MARCH 2004

M3þ þ H5 DTPA ¼ MH2 DTPA þ 3Hþ :

ð2Þ

Therefore, the adsorbed metal ions on CMPO/SiO2 –P can be eluted out by DTPA through the equation: M(NO3 )3 3CMPO/SiO2 {P(re) þ H5 DTPA(aq) ¼ 3(HNO3 CMPO/SiO2 {P(re) ) þ MH2 DTPA(aq) : ð3Þ where subscripts ‘‘re’’ and ‘‘aq’’ denote the resin phase and aqueous phase, respectively. The elution order of the adsorbed elements from CMPO/SiO2 –P depends on the ability of complex formation between the metal ions and the ligand (DTPA). Figure 7 illustrates the stability constants of the complexes of trivalent lanthanides and actinides with DTPA at 298 K, which are cited from the data reported by Moeller et al.11) and Baybarz.12) As can be seen, Am(III), Cm(III) and the heavy RE(III) can form more stable complexes with DTPA than the light RE(III). It was found that the experimental results illustrated in Figs. 5 and 6 show a good agreement with the complex formation ability. On the other hand, the elution effect of the light RE(III) from CMPO/SiO2 –P by a dilute nitric acid solution can be explained by Eq. (1). With supplying dilute HNO3 to the column, the NO3  concentration in the resin bed will be decreased and this results in the decomposition of the metal complexes as shown in Eq. (1). 2. Separation Behavior in the Second Column From the experimental results shown in Figs. 5 and 6, it is evident that the MA effluent which contains Am(III), Cm(III), heavy RE(III), Pd(II), Zr(IV), Mo(VI) can be effectively separated from other FP elements in the HLLW. In the MAREC process (Fig. 1), the MA effluent is applied to the second CMPO/SiO2 –P packed column to achieve a further separation of MA from the mixed FP elements, especially Pd, Zr and Mo. To investigate the separation behavior of these elements, a separation experiment for a simulated MA effluent containing about 5103 M of the heavy RE(III) (Y, Gd, Eu, Sm), Pd(II), Zr(IV) and Mo(VI), 0.05 M DTPA and 3 M HNO3 was performed using water

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Feed 3M HNO3

H2O

0.5M H2H2O4

3

8 hRE Sm(III) Eu(III)

Pd

6

Gd(III)

Mo

2

Y(III) Zr(IV)

pH

Concentration (10-3 mol/dm3)

Zr

Mo(VI)

4

Pd(II)

1 2

0

0 0

100

200

300

400

Weight of effluent (g)

Fig. 8 Results of separation experiment for a simulated MA-effluent at 323 K (Column:
10 mmh500 mm, Flow rate: 0.76 m/h)

1.0

Concentration of TOC (mol/dm3)

DTPA 0.8

80 TOC conc.

0.6

60

0.4

40

0.2

20 H2C2O4

0

0

100

200

300

400

Percentage of eluted DTPA or H2C2O4 (%)

100

0

Weight of effluent (g)

Fig. 9 Elution profiles of DTPA and H2 C2 O4 in the separation experiment for a simulated MA-effluent at 323 K (Column:
10 mmh500 mm, Flow rate: 0.76 m/h)

and 0.5 M oxalic acid (H2 C2 O4 ) as eluents at 323 K. The results of this experiment are shown in Fig. 8. Pd(II) showed no adsorption and leaked the column firstly. It is presumed that Pd(II) can still form stable complexes with DTPA even at concentrated HNO3 , although the complex formation for other metal ions at high Hþ concentration would be difficult as indicated by Eq. (2). The adsorbed heavy RE(III), i.e. Y(III), Gd(III), Eu(III) and Sm(III) were efficiently eluted off by supplying H2 O to the column corresponding to the decrease of NO3  concentration. As Am(III) and Cm(III) present very similar adsorption-elution behavior with RE(III) for CMPO and H2 O,14,16) they are expected to behave similarly to the RE(III). The Zr(IV) and Mo(VI) contained in the feed solution were strongly adsorbed by the CMPO/SiO2 –P and finally eluted out effectively by 0.5 M H2 C2 O4 solution.

The properties and mechanism of Zr(IV) and Mo(VI) adsorption by the CMPO/SiO2 –P have been reported in our previous article.23) The elution effect by H2 C2 O4 is considered to result from the complex formation between these metals and H2 C2 O4 , while the complexes are not adsorbed by CMPO/SiO2 –P.16) This experiment demonstrated that the elements in the simulated MA effluent were successfully separated to the three groups: (1) Pd; (2) MA-heavy RE; (3) Zr–Mo. The occurrence behavior of the eluents, DTPA and H2 C2 O4 in the above separation experiment was examined by the measurement of TOC (total organic carbon) concentrations in the effluent solutions and the results are presented in Fig. 9. From the first occurrence peak of TOC, it was found that DTPA showed almost the same elution behavior JOURNAL OF NUCLEAR SCIENCE AND TECHNOLOGY

Development of the MAREC Process for HLLW Partitioning Using a Novel Silica-Based CMPO Extraction Resin Table 1 The estimated distribution behavior of typical elements in HLLW in the MAREC process Elements

The 1st column

The 2nd column

Am, Cm, Y, Gd–Lu

To Am & Cm effluent

To Am & Cm effluent

La–Nd

To RE effluent

Sm

30% to Am & Cm effluent, 70% to RE effluent

30% to Am & Cm effluent

Eu

70% to Am & Cm effluent, 30% to RE effluent

70% to Am & Cm effluent

Zr, Mo

To Am & Cm effluent

To Zr & Mo effluent (10% to Am & Cm effluent)

Ru

60% to non-adsorptive FP effluent, 20% to Am & Cm effluent, 20% to RE effluent

20% to Am & Cm effluent

Pd

To Am & Cm effluent

To Pd effluent

Other FPs

To non-adsorptive FP effluent

—

—

with the non-adsorptive Pd as shown in Fig. 8. This means that DTPA simply passed trough the column without adsorption on the extraction resin. Similarly, from the second peak of TOC, it is evident that the H2 C2 O4 supplied to the column as the eluent of Zr and Mo was not retained by the extraction resin and left the column immediately together with these elements. These results indicate that the use of both DTPA and H2 C2 O4 as eluents do not interfere with the chromatographic separation process. Furthermore, these reagents are easily decomposed after use up since they consist of C, H, O or N atoms only.24) From the experimental results of Figs. 5, 6 and 8, the separation performance of the typical elements contained in the HLLW is summarized in Table 1 (some elements behavior was predicted). The values given in the table were calculated from the analytical results of the FP elements concentration in each fractional eluates obtained in the column experiments of Figs. 6 and 8. Since Am and Cm were not used in these experiments, the values for Am and Cm were estimated according to their adsorption/extraction and elution/stripping behavior reported in the literatures6,16) as well as the complexes formation performance shown in Fig. 7. The separation performances of the elements illustrated in Table 1 are almost the same with those obtained in the SETFICS process.25) These results reveal that the proposed MAREC process for HLLW partitioning is essentially feasible, although further experiments to examine the behavior of some actinides such as U, Pu and Np and ‘‘hot tests’’ using practical HLLW are needed. In addition, investigation and evaluation for the chemical stability and radiolytic behavior of the CMPO/SiO2 –P extraction resin are under the way. VOL. 41, NO. 3, MARCH 2004

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V. Conclusions A new partitioning technology named ‘‘MAREC’’ process has been proposed for the separation of minor actinides from HLLW by extraction chromatography using a novel silicabased CMPO extraction resin. Separation experiments for simulated HLLW containing typical FP elements were carried out by using two chromatographic columns using DTPA and H2 C2 O4 solutions as eluents, respectively. In the first column, the elements contained in the simulated HLLW could be separated to: (1) Non-adsorptive FP elements; (2) heavy RE such as Y, Gd, Eu, Sm mixed with Pd, Zr and Mo; and (3) light RE such as La, Ce, Nd. Since Am(III) and Cm(III) reportedly show very similar adsorption–elution behavior with the heavy RE for CMPO and DTPA, they are expected to be separated together with the heavy RE. In the second column, the elements in the simulated MA effluent were successfully separated to: (1) Pd; (2) MA–heavy RE; and (3) Zr–Mo. The separation effects of the elements are considered to result from their different ability of complex formation with the eluents of DTPA and H2 C2 O4 . The experimental results demonstrated that the proposed MAREC process for HLLW partitioning is essentially feasible, although further investigation to examine the behavior of some actinides such as U, Pu and Np and ‘‘hot tests’’ using practical HLLW are necessary. In addition, radiation resistance of the CMPO/SiO2 –P extraction resin needs to be investigated. References 1) Z. Kolarik, ‘‘Current european research on the separation of actinides from high-level radioactive wastes,’’ J. Nucl. Fuel Cycle Envion., 5[1], 21 (1998). 2) C. Madic, ‘‘Overview of the hydrometallurgical and pyrometallurgical processes studied on world-wide for the partitioning of high active nuclear wastes,’’ Proc. NUCEF 2001, Tokai, Japan, Oct. 31–Nov. 2, 2001, p. 27 (2001). 3) E. P. Horwitz, H. Diamond, R. C. Gatrone, et al., ‘‘A new class of aqueous complexing agents for use in solvent extraction processes,’’ Solvent Extraction 1990, T. Sekine, Ed., Elsevier Sci. Publ., 357 (1990). 4) E. P. Horwitz, L. D. Mark, D. E. Fisher, ‘‘SREX: A new process for the extraction and recovery of strontium from acidic nuclear waste stream,’’ Solvent Extr. Ion Exch., 9[1], 1 (1991). 5) Y. Zhu, R. Jiao, ‘‘Chinese experience in the removal of actinides from highly active waste by trialkylphosphine–oxide extraction,’’ Nucl. Technol., 108, 361 (1994). 6) Y. Koma, M. Watanabe, S. Nemoto, et al., ‘‘Trivalent f-element intra-group separation by solvent extraction with CMPO-complexant system,’’ J. Nucl. Sci. Technol., 35, 130 (1998). 7) Y. Morita, I. Yamaguchi, T. Fujiwara, et al., ‘‘The first test of 4-group partitioning process with real high-level liquid waste at NUCEF,’’ Proc. NUCEF’98, Hitachinaka, Japan, Nov. 16–17, 1998, p. 491 (1999). 8) H. Eccles, ‘‘Nuclear fuel cycle technologies-sustainable in the twenty first century,’’ Solvent Extr. Ion Exch., 18, 633 (2000). 9) J. N. Mathur, M. S. Murali, P. R. Natarajan, et al., ‘‘Extraction of actinides and fission products by octyl(phenyl)-N,N-diisobutylcarbamoylmethylphoshine oxide from nitric acid media,’’ Talanta, 39, 493 (1992).

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