Occupational Intakes of Radionuclides Part 1 - ICRP

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DRAFT REPORT FOR CONSULTATION
characteristic of the element. Thus element-specific values of sr, were not assessed for
Type M and S materials. Taking account of these factors and the overall large
variation in estimated values of sr, the updated default values for Types M and S were
taken to be the same and rounded up to 3 d –1 . It is assumed here that the default sr
value of 3 d –1 for Type M and S materials applies to all elements, unless the Type F
element-specific value is itself less than 3 d –1 , in which case the Type F elementspecific
value is also applied to Types M and S. For example, for silver, default
values are used for all three Types, as in Table 7; for barium, the element-specific
value of sr is 20 d –1 for Type F, but the default value of 3 d –1 is used for Types M and
S; for yttrium, the element-specific value of sr is 1 d –1 for Type F, and so 1 d –1 is also
used for Types M and S.
Slow dissolution rate, ss:
(153) For Types M and S, median values are 0.003 d –1 and 0.00018 d –1 , similar to
the current default values of 0.005 d –1 and 0.0001 d –1 . The default values remain
0.005 d –1 and 0.0001 d –1 , respectively.
(154) Thus the data currently available suggest larger typical rapid fractions for
Types M and S materials, but with lower rapid dissolution rates than original default
values for all three Types. This has the effect of reducing rapid absorption in the
extrathoracic airways and increasing it in the lungs.
Table 7. Updated default absorption parameter values for Type F, M, and S
materials a,b
Type F(fast) M (moderate) S (slow)
Fraction dissolved rapidly fr 1 0.2 0.01
Dissolution rates:
Rapid (d -1 ) sr 30 c 3 d
Slow (d -1 ) ss - 0.005 0.0001
a
Reference values (see footnote to Table 3).
b
The bound state is also used for default Types of some elements.
c
Element-specific rapid dissolution rates are adopted for Type F forms of many
elements
d -1
The element-specific value for Type F is used if it is less than 3 d
(155) The default absorption rates, expressed as approximate half-times, and the
corresponding amounts of material deposited in each region that reach body fluids
(from the respiratory tract) can be summarised as follows:
Type V: 100% absorbed instantaneously. Regional deposition does not need to
be assessed for such materials, because in dose calculations they can be
treated as if they were injected directly into body fluids.
Type F: 100% absorbed with a half-time of ~30 minutes. There is rapid
absorption of almost all material deposited in bb and AI, ~80% of
material deposited in BB, and ~25% of material deposited in ET2. The
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3 d