Depleted uranium levels

An example of a common situation that leads to greater radiation exposure levels than would be expected occurs with some uranium compounds. Depleted uranium is an a-emitting isotope with an extremely long half-hfe, 4 billion years. As a result of this long half-life, is generally not considered to present a significant radiation hazard. However, uranium fluorides, a typical synthetic starting material, can... 

Sansone, U., Stellate, L., Jia, G., Rosamilia, S., Gaudino, S., Barbizzi, S., Belli, M. (2001). Levels of depleted uranium in Kosovo soils. Radiat. Prot. Dosimetry 91 317-20. 

Table 2-8 shows the mass equivalents for natural and depleted uranium for radiation levels that caused potential radiological effects in rats exposed once for 100 minutes to airborne 92.8% enriched uranium with an estimated specific activity of 51.6 pCi/g (Morris et al. 1989). These mass equivalent values for natural and depleted uranium for the minimal concentration of radioactivity that is expected to induce potential radiological effects are well above levels that would be expected to be inhaled or ingested. In addition, the mass equivalents for natural and depleted uranium for potential radiological effects are 3,600 and 76,500 times higher, respectively, than the occupational exposure limits (short-term exposure) recommended by the National Institute for Occupational Safety and Health (NIOSH 1997). Therefore, MRLs for uranium based on studies that used enriched uranium are inappropriate. 

A. TB 9-1300-278 details the safe response to accidents involving army tank munitions that contain depleted uranium. CTT Task 031-503-1017, Respond to Depleted Uranium/Low Level Radioactive Materials (DULLRAM) Hazards (draft) details the response of individual soldiers to these hazards. 

Because in the LWR fuel cycle most of the uranium in the ore appears in the depleted uranium from isotope separation, this depleted uranium if not used as breeder fuel, will slowly buUd up its decay daughters and Ra toxicity. Ultimately, a toxicity level within a few percent of that of the original ore will be reached. 

Process knowledge and samples taken of the solidified waste material from the processing of unirradiated depleted uranium dioxide targets with simulated materials have indicated that no RCRA regulated hazardous constituents are present above applicable regulatory levels. Based on this information, it is concluded that after the high activity waste is neutralized, it is radioactive waste that no longer exhibits any hazardous characteristics. 

Articles manufactured from natural or depleted uranium are by definition LSA-I and hence would normally have to be transported in an Industrial package lype 1 (IP-1). However, provided the materials are contained in an inactive sheath made of metal or other substantial material they may be transported in excepted packages. The sheath is expected to prevent oxidation or abrasion, absorb all alpha radiation, reduce the beta radiation levels and reduce the potential risk of contamination. 

The experience of the analyst needs to be taken into account when interpreting the results. One may interpret a corrected isotope ratio that is within one standard deviation of the natural uranium isotopic signature as consistent with natural uranium. Two standard deviations may be the preference of others. In our experience, the majority of natural uranium-containing samples produced results that were within one standard deviation of the natural 23Su/238 j isotope j-gtio since the level of confidence in the results has often been a critical factor, we have typically repeated analysis of the small minority of samples that have had ratio results that have fallen below one deviation from natural uranium to eliminate doubt as to whether a small amount of depleted uranium may have contributed to the total uranium content. More often than not, results that were within two standard deviations of the natural uranium isotope ratio were very low-concentration samples. 

Depleted uranium foils (0.2% enrichment, S-mils thick by l-ln. diam) and foils (93% enrichment, 4.5-mils thick by i-in. diam) were placed at corresponding locations about the center of the two halves of the llPR-6 machine. Foils were placed among the adjoining surfaces of the plates. In another experiments a 2- >< 2- x -in. plate of 93% enriched uranium and a 2- x 2- X -in. plate of depleted uranium (0.2% enriched) that are normally in the core were replaced by packets of foils equivalent in weight and enrichment to the two plates. All foils were irradiated for one hour at a power level of about 50 W and, subsequently counted for fissiim fragments. jbi the case of the packets, only l-in.-diam foils punched out from the... 

Some DU is drawn from these stockpiles to dilute high-eruiched (approximately 90%) uranium released from weapons programs, particularly in Russia, and destined for use in civil reactors. This weapons-grade material is diluted to about 25 1 with depleted uranium, or 29 1 with depleted uranium that has been enriched slightly (to 1.5% U-235) to minimize levels of (natural) U-234 in the product. 

Additionally, there are secondary processes, like production of depleted uranium (DU) for commercial purposes or synthesis of fine chemicals that use the waste (or tails) of uranium isotope enrichment plants. When discussing the analytical chemistry of these applications, the emphasis is placed on determining the impurities in materials where uranium is the major component, while in the other chapters of this book, the analytical objective is usually the detection of trace levels of uranium and their characterization. 

For mill tailings and depleted uranium, currently stored primarily as UF, two different approaches will be taken. Mill tailings are too voluminous, too low a near term threat and too stable a chemical form to warrant more than cover and monitor operations to be sure that the mobility is limited. Depleted uranium, however, is different. These wastes must be put into a more stable chemical form and container to limit their mobility. These wastes, as is well known, will eventually, after 10 -10 years, approach the toxiciQr of high level waste at that period of time, i.e., eating either would produce the same health effects. 

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