**8. Conclusion of nitrogen isotope separation by ion exchange method and the comparison with NITROX separation method**

Long chromatographic operations were studied to nitrogen isotope separation by using 80% enriched 15N-NH4Cl. The main purpose was to get very highly enriched 15N isotope and to study how the flow rate and column diameter affect to nitrogen isotope separation. From the results obtained by each runs, it was confirmed that front and rear boundary could enrich 14N and 15N steadily to very high percentage. Since the feeding and elution solution are same for Run 1, Run 2 and Run 3, the same separation coefficients should be obtained no matter the migration distance. Due to the small amount of ammonium remained on the column, separation effect became slightly decrease with long chromatographic migration distance, especially by large diameter columns. When compared with the results of Run 2 and Run 3, the HETP value of Run 3 is smaller than Run2.

During the long operation, 15N can be steadily enriched to very high purity. Because the remixing phenomena take place, the highly enriched 15N will penetrated into the middle band, it decreased the maximum enrichment percentage of 15N, but the highly enriched zones became broadened with long migration distance. The maximum percentage of enriched 15N was 99.859% and 4.6 gram of highly enriched 15N (99.82%) were successfully obtained by fifty meter's operation.

Chemical exchange of nitrogen oxide system has been discussed for nitrogen isotope separation deeply in early times. Fifty years ago, W.Spindel and T. Taylor performed nitrogen isotope separation by chemical exchange (NITROX) with the condition of 15 ml/min of 10 mol/dm3 nitric acid, containing the natural 15N abundance [7]. They produced material containing 6.0 g of nitrogen analyzing 99% 15N by twenty-five days continuously columns operation. Because of the large separation factor (1.055) by using NITROX method, most of industrial scale plants in the world are adopted with this method to produce nitrogen isotopes. As mentioned above, ion exchange method has the advantage of very small HETP, it can obtain very highly enriched nitrogen isotopes and no large amount of waste gas and liquid occurred, it can be widely used if combined with NITROX method when 15N has been enriched to the percentage of, for example, 80%. One problem come from ion exchange method is the capacity of resin. The ion exchange NH4-R/NH3aq on cation exchange resin being inefficient for large scale production, according to the small flow rate accepted in the separation columns. That involves utilization of too large diameter separation columns with prohibitive amount of cation exchange resin.

Taking into account that the world market is about 20 to 40 Kg 15N annually, the supply of that isotope for nitride fuel production for nuclear power reactors (NPR) and accelerator driven system (ADS) would therefore demand an increase in production capacity by a factor of 1000. For an industrial plant producing 100 t/y 15N, using present technology of isotopic exchange in NITROX system, the first separation stage of the cascade would be feed with 10M HNO3 solution of 600 ml/h flow rate. If conversion of HNO3 into NO, NO2, at the enriching end of the columns, would be done with gaseous SO2, for a production plant of 100 t/y 15N, a consumption of 4 million ton SO2/y and a production of 70% H2SO4 waste solution of 4.5 million ml/y are estimated. The reconversion of H2SO4 into SO2 in order to recycle of SO2 is a problem to be solved to compensate the cost of SO2, and to diminish the amount of H2SO4 waste solution. If it's considered that all ADS installations for minor actinides transmutation utilize nitride fuel with 15N, the need of that isotope is about 4 t/y, with a cost of 400 million USD (the price of 15N was considered 100 USD). It should be taken into consideration an important price reduction of 15N in order to make possible its utilization for large scale production of nitride fuel for NPRs and ADSs.

### **Author details**

362 Ion Exchange Technologies

Adsorption band length cm

chromatography

is a large amount of highly enriched 15N and the slope coefficient of isotopic distribution curve becomes flat. This is the evidence that by long chromatographic operation, highly enriched 15N was remixing again with the middle level enriched 15N in the middle position of ammonium adsorption band. The percentage and gram distribution of enriched 15N which along with ammonium adsorption band were listed in Table 4. 15N was mainly concentrated in the adsorption band which range from 64.5-152.03 cm in the adsorption

> Percentage distribution of 15N %

0~28.5 <4.118 0.0566 28.5~ 33 4.118 ~ 35.32 0.3539 33 ~ 46.5 35.32 ~ 80.39 2.2598 46.5 ~ 64.5 80.39 ~91.81 3.2737 64.5 ~ 82.5 91.81 ~ 98.73 3.5679 82.5~ 123 98.73~ 99.79 8.1944 123 ~147.3 99.79 ~99.86 4.6148 147.3~ 152.03 99.86 ~ 99.69 0.8185 **Table 4.** Percentage and gram distribution of enriched 15N along ammonium adsorption band by 50 m

**8. Conclusion of nitrogen isotope separation by ion exchange method** 

Long chromatographic operations were studied to nitrogen isotope separation by using 80% enriched 15N-NH4Cl. The main purpose was to get very highly enriched 15N isotope and to study how the flow rate and column diameter affect to nitrogen isotope separation. From the results obtained by each runs, it was confirmed that front and rear boundary could enrich 14N and 15N steadily to very high percentage. Since the feeding and elution solution are same for Run 1, Run 2 and Run 3, the same separation coefficients should be obtained no matter the migration distance. Due to the small amount of ammonium remained on the column, separation effect became slightly decrease with long chromatographic migration distance, especially by large diameter columns. When compared with the results of Run 2

During the long operation, 15N can be steadily enriched to very high purity. Because the remixing phenomena take place, the highly enriched 15N will penetrated into the middle band, it decreased the maximum enrichment percentage of 15N, but the highly enriched zones became broadened with long migration distance. The maximum percentage of enriched 15N was 99.859% and 4.6 gram of highly enriched 15N (99.82%) were successfully

**and the comparison with NITROX separation method** 

and Run 3, the HETP value of Run 3 is smaller than Run2.

obtained by fifty meter's operation.

15N g

band and 4.6 gram of highly enriched 15N(>99.82%) were successfully obtained.

Xingcheng Ding\* and Xunyue Liu *Institute of Nuclear Agricultural Science, Zhejiang University, Hangzhou, P.R.China* 
