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DOE-STD-1136-2004
Guide of Good Practices for Occupational Radiation Protection in Uranium Facilities
air and saline solutions, can accelerate the corrosion of the material over time and produce greater
possibility for generating airbor ne radioactive material. Stored in a dry environment or coated with an
anti-corrosion surface treatment, the metal may show no visible signs of corrosion for many years.
Uranium metal may be dissolved using nitric acid, which is also used to passivate ("p ickle") the
metal to inhibit oxidation.
2.3 RADIOLOGICAL CHARACTERISTICS AND EFFECTS
Uranium isotopes decay by alpha particle emission and some also emit low-energy gamma rays. For
Classes W and Y material (See last paragraph of Section 2.5 for discussio n of Class D, W and Y), the
inhalation hazard from alpha particle release in the respiratory tract is the predominant radiological hazard
associated with the alpha-emitting uranium isotopes. The primary uranium decay products, listed in Table 2-
2, decay by beta particle emission, most with a small yield of gamma emissions as well. These decay
products increase the shallow dose equivalent and lens of the eye dose equivalent resulting from external
radiation exposures, due mainly to the 2.29 MeV (Emax) beta from 234mPa.The surface exposure rates shown
in Table 2-7 result primarily from beta radiation from decay products. The exposure rates decrease quickly
with distance because of the attenuation of the beta radiation and the small yield of the gamma radiatio n.
Table 2 -7. Beta Surface Exposure Rates from Equilibrium Thickness of Uranium Metal and
Compounds
Beta Surface Exposure
Source
Rate, mrad/h
U-Nat metal slab
233
UO2
207
UF4
179
UO2 (NO3)2 6H20
111
UO3
204
U3O8
203
UO2 F2
176
Na2U2 O7
167
Beta surface exposure rate in air through a polystyrene filter 7
mg/cm2 thick.
Because some uranium decay products have short half-lives (on the order of days), those decay
products will usually be present with uranium during processing. Figure 2-5 illustrates the ingrowth of the
238
U decay products. An assumption of secular equilibrium should not be made until processing is complete
because many routine chemical processing steps separate uranium from its decay products. Both the
inhalation and external exposure hazards associated with the decay products are increased in areas where
the decay products are concentrated. The overall inhalation hazard will typically decrease in those areas as
the uranium is removed. In the case of cast uranium metal, the exposure rates from high
2-18


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