Uranium Conversion Facilities and Enrichment Plants

Nuclear forensics also plays a role with regard to the processing of uranium ore concentrates in the UCF and fabrication of uraninm oxide for fueling nuclear reactors or of uranium hexafluoride for isotope enrichment facilities. Characterization of the nuclear materials can detect unauthorized operations and partially ascertain that no undeclared activities are taking place but one shonld always bear in mind that absence of evidence is not evidence of absence. In some cases, relevant information may be obtained from bulk samples but highly significant details may be found in analysis of single particles. Some examples will be presented here, but more details are discussed in Section 5.4. 

The production of UFg at the UCF and, more importantly, the isotope enrichment process, are inevitably accompanied by some release of gaseous UFg. Once UFg is released into the atmosphere, it will react with moisture to form aerosols of uranyl fluoride and HF (Equation 5.1)  

This would probably be a sequential reaction with one water molecule at a time, but for the present discnssion this is not relevant. Formally, uranyl fluoride may be in a cluster with HF and water molecules [UO2F2 HF HjO ] and the hydrogen fluoride may also be clustered with other HF and water molecules [HF HjOJ. 

For safeguards purposes, swipe samples are collected from different surfaces inside the enrichment facility. These could include operational equipment like pipes, cylinders, and machinery or even surfaces from the walls and floor. Bulk isotopic analysis of these swipe samples would give the average enrichment of the released particles. However, for a complete understanding of the operations carried out in the facility, single particle analysis is more revealing, as discussed and demonstrated here. 

FIGURE 5.5 The particle size distribution of spherical uranium particles produced at a relative humidity of 68%. (From Kips, R. et al., Microsc. Microanal., 13, 156, 2007. With permission.) 

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