Table 2 -11. Inhalation Classification for Some Uranium Compounds

DOE-STD-1136-2004

Guide of Good Practices for Occupational Radiological Protection in Uranium Facilities

The relative activities of the primary uranium isotopes are also significantly affected by the degree of

enrichment (see Figure 2-2). The figure shows that total activity is due chiefly to 238U for depleted and 234U

for enriched uranium, while 235U accounts for little of the total activity, even at very high enrichments.

Chemical form determines solubility and consequent transportability in body fluids. ICRP

Publication 30 classifies all materials into three inhalation classes--D, W, and Y (soon to be Types F for

fast, M for moderate, and S for slow). Class D is most transportable (pulmonary removal half-time of

days), Class Y the least transportable (removal half-time of years), and Class W an intermediate category

(removal half-time of weeks). The transportability of an inhaled or ingested material determines its fate

within the body and, therefore, the resulting radiation dose or chemical effect. Table 2-11 lists several

common uranium compounds and their assigned transportability classes.

Table 2 -11. Inhalation Classification for Some Uranium Compounds

Uranium hexafluoride

UF6

Class "D"(a)

Uranyl fluoride

UO2F2

Class "D"(a)

Uranyl nitrate

UO2(NO3)2

Class "D"

Uranyl acetate

UO2(C2H3O2)2

Class "D"

Uranyl chloride

UO2Cl2

Class "D"

Uranyl sulfate

UO2SO4

Class "D"

Uranium trioxide

UO3

Class "W"

Uranium tetrafluoride

UF4

Class "W"(a)

Uranium oxide

U3O8

Class "Y"(b)

Uranium dioxide

UO2

Class "Y"(b)

Uranium tetroxide

UO4

Class "W"

Ammonium diuranate

(NH4)2 + U2O7

Class "W"(b)

Uranium aluminide

UAlx

Class "Y"(a)

Uranium carbide

UC2

Class "Y"

Uranium- zirconium alloy

UZr

Class "Y"

High-fired uranium dioxide

UO2

Class "Y"(b)

(a) "D" and "W" and "Y" are inhalation solubility classes established by the ICRP: "D" class

material is very soluble, with lung retention time in days; "W" class material is moderately soluble,

with lung retention time in weeks; "Y" class material is relatively insoluble, with lung retention

time in years.

(b) Ammonium diuranate is known to contain uranium as UO3, and should not be assigned to a

single inhalation class. The solubility of uranium oxides is very dependent on heat treatment. The

rate of oxidation may also affect the solubility. Although references assign inhalation classes to

various uranium compounds, it is recommended that solubility studies be performed to characterize

the actual materials present.

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