Highly enriched uranium particles

Indonesia Research center May 1994 Low levels of fission and activation products were seen in water and vegetation. Swipe samples taken in buildings showed low and high-enriched uranium particles from research and medical isotope production activities... 

FIGURE 20.14 Secondary ion mass spectrum of counts per second (logarithmic scale) versus m/z value (10-140 Th) for the analysis of a highly enriched uranium particle. Source Betti, M.,Tamborini, G., Koch, L. (1999), Use of secondary ion mass spectrometry in nuclear forensic analysis for the characterization of plutonium and highly enriched uranium particles. Analytical Chemistry, 7i (14), 2616-2622. 

Betti, M., et al. (1999) Use of secondary ion mass spectrometry in nuclear forensic analysis for the characterization of plutonium and highly enriched uranium particles. Analytical Chemistry, 71,2616-2622. 

Because particles containing insoluble uranium compounds can reside in the lung for years, it is likely that radiotoxicity as well as chemical toxicity can result from inhalation exposure to highly enriched uranium compounds. Radiation effects on tissues from the alveolar regions of the lungs were examined in Albino HMT (Fischer 344) male rats exposed, nose-only, for 100 minutes to an aerosol of to 92.8% U-enriched uranium dioxide with a concentration of 2,273 nCi/m (84.1 kBq/m ) to 5,458 nCi/m ... 

Early in the environmental sampling program of the IAEA it was recognized that the analysis of individual micrometer-sized particles was a source of unique information about nuclear materials and activities. O Table 63.17 shows the calculated composition of 1 pm diameter particles coming from various nuclear processes. Thus, it can be seen that a pure particle of natural U oxide ( NU ) contains about 10 U atoms in total and that when this particle is irradiated in a reactor, approximately 5 million atoms of Pu would be created. Furthermore, a particle of high-enriched uranium ( HEU ) would produce only small numbers of Pa and Th daughter atoms in 10 years of decay. To be able to age-date such a particle would involve measurement of these small components, something which is currently not possible with the most sensitive techniques. 

This fuel cycle is based upon FSV-type fuel, which operated from 1976 through 1989. Fuel composition consists again of two separate TRISO particles, 93% highly enriched uranium (HEU) particles and fertile Th-232 particles to achieve maximum U-233 conversion ratios and therefore limit the amount of plutonium produced. Although HEU-fueled reactors would not be considered for commercial use in the United States, the interest here is historical in nature. This design also uses a once-through fuel cycle, refueling half of the core at every reload interval. 

The high-temperature gas-cooled reactor (HTGR) is a thermal reactor that produces desired steam conditions. Helium is used as the coolam. Graphite, with its superior high temperature properties, is used as the moderator and structural material. The fuel is a mixture of enriched uranium and thorium in the form of carbide particles clad with ceramic coatings. 

Fresh fuel of the GTHTR300 consists of coated fuel particles with low enriched uranium that is on itself unattractive for weapon programmes. The radiation dose of spent fuel is too high... 

While nuclear power plants use multiple layers of protection from the radioactive particles inside the reactor core, a serious accident can cause the release of radioactive material into the environment. It is not a nuclear explosion, because the uranium fuel used in a nuclear power plant does not contain a high enough concentration of U-235. For an explosion to occur, the uranium fuel inside the reactor would have to be enriched to about 90% U-235, but it is only enriched to about 3.5%. 

Preparative centrifugal separations are often classified according to the phases of the media and the material to be purified, e.g., gas-gas, liquid-liquid, or liquid-solid. Gas-phase separations are very important in certain applications, e.g., uranium-isotope enrichment, but are highly specialized and not widely used. Liquid-liquid or even liquid-liquid-solid separations, on the other hand, are much more common. However, the majority of preparative separations involve the sedimentation of solid particles in a liquid medium. 

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. 

---