**7. Uranium recovery and effluent treatment**

A great variety of uranium residues must be recovered by chemicals means. A major source of such residues is uranium remaining in crucibles after melting and pouring. The recovery of solid or liquid uranium residues is vital because quantities are generated in every step of the process and this is a valuable material that must be recovered for reuse. Figure 17 displays a schematic diagram of the process showing the flow of products and residues.

The first step of the chemical recovery process is usually acid leaching to solubilize the uranium content. Any of several purification steps may then be employed to separate impurities such as iron, chromium, nickel, silicon, boron, etc. The end product of chemical recovery process is UF4 which can be reduced to metal and then recycled. A typical sequence of chemical processing steps to recover uranium compounds from leach liquor is solvent extraction with tributyl phosphate, dinitration of purified uranyl nitrate solution to produce uranium trioxide (UO3), and hydrogen reduction and hydrofluorination of UO2 to UF4. The technology of these operations is similar to that used in processing normal uranium.

Since chemical recovery will usually involve aqueous mixtures of uranium compounds, nuclear safety limits the critical dimensions of process equipment and imposes bath quantities within safe limits. If these factors are properly provided for chemical recovery unit design, the process operating costs will not be substantially raised by nuclear safety requirements.

Fig. 16. Schematic illustration of the fuel element produced at IPEN.

element is transferred to the reactor.

requirements.

**7. Uranium recovery and effluent treatment** 

Once qualified, the fuel element is washed in a bath of ethyl alcohol and dried manually with the aid of a jet of hot air. After this cleaning, a visual inspection is conducted, especially inside the cooling channels (the channels between the fuel plates), trying to detect possible obstructions caused by chips or foreign material. After washing and inspection, the fuel

A great variety of uranium residues must be recovered by chemicals means. A major source of such residues is uranium remaining in crucibles after melting and pouring. The recovery of solid or liquid uranium residues is vital because quantities are generated in every step of the process and this is a valuable material that must be recovered for reuse. Figure 17 displays a schematic diagram of the process showing the flow of products and residues. The first step of the chemical recovery process is usually acid leaching to solubilize the uranium content. Any of several purification steps may then be employed to separate impurities such as iron, chromium, nickel, silicon, boron, etc. The end product of chemical recovery process is UF4 which can be reduced to metal and then recycled. A typical sequence of chemical processing steps to recover uranium compounds from leach liquor is solvent extraction with tributyl phosphate, dinitration of purified uranyl nitrate solution to produce uranium trioxide (UO3), and hydrogen reduction and hydrofluorination of UO2 to UF4. The

technology of these operations is similar to that used in processing normal uranium.

Since chemical recovery will usually involve aqueous mixtures of uranium compounds, nuclear safety limits the critical dimensions of process equipment and imposes bath quantities within safe limits. If these factors are properly provided for chemical recovery unit design, the process operating costs will not be substantially raised by nuclear safety The aggregate amount of scrap recycled via chemical recovery may reach 10% or more of finished fuel material weight. Chemical recovery is naturally more costly than direct recycle of metallic scrap to remelt. These considerations justify various expedients to by-pass chemical recovery by recycling metallic scrap. However, particular emphasis is given to the recovery of all residues solids and liquids because of the higher intrinsic value of the enriched material.

As an example, the IPEN process to produce U3Si2 involves metallic uranium as an intermediate product, through magnesiothermic reduction which produces slags containing uranium. The recovery process consists on slag lixivium of calcined by-products from metallic uranium reduction. The results from researching this process confirmed that this method could be integrated in treatment and recovery routines of uranium. The chemical route avoids dealing with metallic uranium since this material is unstable, pyroforic and extremely reactive. On the other hand, U3O8 is a stable oxide with low chemical reactivity, and it justifies the slags calcination of metallic uranium reduction by-products. This calcination occurs under oxidizing atmosphere and transforms the metallic uranium into U3O8. Some experiments have been carried out using diferente nitric molar concentrations, acid excess contents and temperature control of the lixivium process. The nitric lixivium main chemical reaction for calcined metallic uranium slags is represented by the equation:

$$\text{U}\_{\text{5O}}\text{s} \text{(s)} + 8\text{ HNO}\_{3}\text{(l)} \rightarrow 3\text{ UO}\_{2}\text{(NO}\_{3}\text{)}\_{2}\text{(l)} + 2\text{ N}\text{O}\_{2}\text{(g)} + 4\text{H}\_{2}\text{O(l)}\tag{26}$$

The adopted process has the following parameters:


As results, the full lixivium took 9 hours; the fluoride concentration in lixivium was 0,002g/L. Lixivium made at lower temperatures and lower nitric concentrations reduced both the magnesium and calcium fluorides solubility and the corrosion effect caused bifluoride ions was not prominent. This ensured a stable and secure lixivium from the operational point of view. The nitric dissolution of metallic uranium slags produced uranyl nitrate solution, which has been reused as a feed-in compound for uranium purification system made by solvent extraction method, using diluted n-tributhylphospate. The purified uranium product was then precipitated as ammonium diuranate (ADU) at 60°C, by injecting ammonium gas diluted with air. Aiming at returning the recovered product to the fuel fabrication cycle with nuclear quality level, the purified ADU was converted into uranium tetrafluoride (UF4) by U3O8 route. The final yield in U content was 94%, proving the viability of IPEN´s slag recovering from uranium magnesiothermic reduction.

#### **8. Acknowledgements**

Thanks are due to IPEN for providing generously the technology of Nuclear Fuel Center, fully exemplified in this chapter, providing so nuclear know-how to a more peaceful, safer and healthy world. We are especially thankful to our colleagues who provided lots of information shown here, mainly Mr. Davilson Gomes da Silva who made many of the illustrations to qualify better this text.

Fig. 17. Flowsheet MTR fuel processing (products and residues solid, liquids) (55; 54)

This chapter gave a general idea of the MTR fuel elements production for multipurpose and researching reactors that are producing radioisotopes throughout the world. Nowadays, the level of uranium enrichment is envisaged to be 20% (LEU), according to ruling requests of RERTR program. The given example of this production derived from IPEN/CNEN-São Paulo-Brazil, which produces through a well stablished routine to fabricate its own MTR fuel elements. Nevertheless, the technique to produce such elements has many variants,

As a final consideration, the future of fuel elements material, based on RERTR request, should also supply many high performance research reactors needing higher core densities of 6 to 9 gU/cm3. This demand is not possible with U3Si2 elements, since its operational upper limit is less than 5 gU/cm3. So, the presently envisaged product to reach this request is based on U-Mo alloy. Nevertheless, this product is not ready yet. Future prognosis are very confident that alloys U + 7 to 10wt%Mo should meet up this ability. This alloy production is still in experimental-pilot level, by this moment (2011), but with very consistent and pertinent results. For those willing to follow the development of this research, we indicate the transaction pages of RERTR and RRFM2, where all papers and

[1] Cunningham, J. E. and Boyle, E. J. MTR-Type fuel elements. International Conference on Peaceful uses atomic energy. [ed.] United Nations. 1955, Vol. 9, pp. 203-7. [2] Kaufman, A.R. *Nuclear reactor fuel elements, metallurgy and fabrication.* New York, NY,

[4] Cunningham, J.E., et al. Fuel Dispersions in Aluminium-Base Elements for research

[5] Saller, H.A. Reaction Technology and Chemical Processing - Preparation, Properties and

[6] Thurber, W.C. And Beaver, R.J. Segregation in Uranium-Aluminum Alloys and its Effect

[7] Lennox, D.H. And Kelber, C.N. *Summary Report on the Hazards of the Argonaut Reactor.* 

[8] Kucera, W.J., Leitten, C.F. And Beaver, R.J. Specifications and Procedures Used in

[9] Knight, R.W., Binns, J. And Adamson Jr, G.M. Fabrication Procedures for Manufacturing High Flux Isotope Reactor Fuel Elements. *Oak Ridge National Lab.* Jun 1968. [10] R.I., Beaver, Adamson Jr, G.M. And Patriarca, P. Procedures for Fabricating

2RERTR – Reduced Enrichment for Research and Test Reactors Program]: http://www.rertr.anl.gov/ RRFM – http://www.euronuclear.org/meetings/rrfm2011/transactions/RRFM2011-transactions.pdf

Cladding of Aluminum-Uranium Alloys. [ed.] United Nations. 1956, Vol. 9, pp.

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Manufacturing U3O8-Aluminium Dispersion Fuel Elements for Core I of the

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**9. Conclusions** 

results are displayed freely.

214-20.

June, 1964.

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Lemont, Mi : s.n., 1956. ANL – 5647.

**10. References** 

which are applied diversely from plant to plant.

#### **9. Conclusions**

50 Radioisotopes – Applications in Physical Sciences

Fig. 17. Flowsheet MTR fuel processing (products and residues solid, liquids) (55; 54)

This chapter gave a general idea of the MTR fuel elements production for multipurpose and researching reactors that are producing radioisotopes throughout the world. Nowadays, the level of uranium enrichment is envisaged to be 20% (LEU), according to ruling requests of RERTR program. The given example of this production derived from IPEN/CNEN-São Paulo-Brazil, which produces through a well stablished routine to fabricate its own MTR fuel elements. Nevertheless, the technique to produce such elements has many variants, which are applied diversely from plant to plant.

As a final consideration, the future of fuel elements material, based on RERTR request, should also supply many high performance research reactors needing higher core densities of 6 to 9 gU/cm3. This demand is not possible with U3Si2 elements, since its operational upper limit is less than 5 gU/cm3. So, the presently envisaged product to reach this request is based on U-Mo alloy. Nevertheless, this product is not ready yet. Future prognosis are very confident that alloys U + 7 to 10wt%Mo should meet up this ability. This alloy production is still in experimental-pilot level, by this moment (2011), but with very consistent and pertinent results. For those willing to follow the development of this research, we indicate the transaction pages of RERTR and RRFM2, where all papers and results are displayed freely.

#### **10. References**


<sup>2</sup>RERTR – Reduced Enrichment for Research and Test Reactors Program]: http://www.rertr.anl.gov/ RRFM – http://www.euronuclear.org/meetings/rrfm2011/transactions/RRFM2011-transactions.pdf

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*Application of Reduced-Enriched Fuels for Research and Test Reactor: Proceedings Held in* 

Low-Enriched Uranium Silicide-Aluminum Dispersion Fuel for Use in Non-Power


**3** 

*Japan* 

**Application of Enriched Stable Isotopes in** 

**Element Uptake and Translocation in Plant** 

*1NARO Western Region Agricultural Research Center 2National Institute for Agro-Environmental Sciences* 

Shinsuke Mori1, Akira Kawasaki2, Satoru Ishikawa2 and Tomohito Arao2

Isotope technique including radioisotopes and stable isotopes is useful and potent tool for various scientific areas. Especially, enriched stable isotopes are indispensable tools for

 Stable isotope ratios are usually used in examining the biogeochemical cycling of light elements such as carbon(C), oxygen (O), nitrogen (N) and sulphur (S) in the environment. Thermal ionization mass spectrometry (TIMS) for the isotope analysis has been the most standard technique for many years. However, for TIMS analysis, time for sample preparation is needed because sample need to ensure efficient ionization. On the other hand, ICP-MS analysis has some advantages that sample preparation is simple and high sample throughput for isotope experiments where a large amount of samples need to be analyzed (Stürup et al. 2008). The disadvantage to resolve in isotope analysis using ICP-MS is spectroscopic interferences in the process of analysis. It is therefore needed to be resolved

When plant physiologists investigate mineral absorption mechanisms in roots of plant, evaluation of symplastic mineral absorption capacity in roots cell in kinetics and time course experiments is very important because mineral translocation in shoots is mainly contributed to capacity of symplastic absorption in roots. In these experiments, radioisotopes methods are mainly used for element uptake in plants. Radioisotopes in solute were the most useful markers used in nutrient uptake and translocation in plants because they are chemically similar to the solute and can be distinguished from non-labeled solutes already contained in the roots (Davenport 2007). However, there are limitations to this method, including radioisotope administrative restriction and the restricted half-life of the radioisotope. Isotope tracer experiments, using a stable isotope, are very similar to those using a radioisotope on element to analyse plant mechanisms (Stürup et al. 2008). Accurate and precise determination of mineral isotope ratios is required for analysis of enriched stable isotopes. Inductive coupled plasma mass spectrometry (ICP-MS) has now become the effective and potent technique for enriched stable isotope tracer experiments due to increased availability. Therefore, the application of enriched stable isotopes in various

**1. Introduction** 

these interferences.

biological systems increased rapidly.

researchers in biological systems (Stürup et al. 2008).


http://www.ibilabs.com/Ammonium%20Urany%20Carbonate%20MSDS.htm.

