Occupational Intakes of Radionuclides Part 1 - ICRP

DRAFT REPORT FOR CONSULTATION
2376 Table 6 Central values of dissolution parameters for Type F, M, and S material from a review
of experimental data a
2377
Type F(fast) M (moderate) S (slow)
Fraction dissolved rapidly
Dissolution rates:
fr 0.95 (0.84) [1.4] 0.20 (0.18) [4] 0.007 (0.003) [9]
Rapid (d-1) sr 12 (9) [8] 1.7 (1.5) [9] 2.0 (3.8) [14]
Slow (d-1) ss 0.02 (0.02) [8] 0.003 (0.003) [4] 0.00018 (0.00008) [9]
2378
2379
a
Median value, with geometric mean in parentheses, and geometric standard deviation in
2380
2381
brackets.
2382 (149) Updated default values, given in Table 7, were based mainly on the following
2383 considerations, but also take account of the large uncertainties in the central values
2384
2385
and the need for simple rounded numbers.
2386 Rapid fraction fr:
2387 (150) For Type F, the median value (0.95) is close to the current default value of
2388 1.0. For simplicity in implementation it is preferable not to change to two-phase
2389 dissolution. The default value remains 1.0.
2390 For Type M, the median value is higher (0.20) than the current default (0.1). The
2391 updated default value is taken to be 0.2.
2392 For Type S, the median value is higher (0.007) than the current default (0.001).
2393
2394
The updated default value is rounded to 0.01.
2395 Rapid dissolution rate, sr:
2396 (151) Type F: the median of values of sr estimated from experimental data for
materials that would be assigned to Type F, is 12 d –1 2397
(Table 5), (much lower than the
original HRTM default value of 100 d –1 2398
). However, this outcome is heavily
2399 influenced by results for a few elements: about half of the results are from only four
2400 elements. To include information from a wider range of elements in choosing the
2401 default value, consideration was also given to the element-specific values of sr for
2402 soluble (Type F) forms of the element, which were assessed where suitable
2403 experimental information was available (see above). There are element-specific
2404 values for several elements for which no material-specific values were assessed.
2405 Hence the distribution of element-specific values covers a wider range of elements,
2406 and in it each element makes the same contribution (one entry): its median value is 50
d –1 2407 . Taking both medians into account, the updated default value of sr for Type F is
taken to be 30 d –1 2408
.
2409 (152) Types M and Type S: The medians of estimated values of sr for materials that
would be assigned to Types M and S, are 1.7 d –1 , and 2 d –1 2410
, respectively (Table 5),
(very much lower than the original HRTM default of 100 d –1 2411
). As for Type F, the
2412 distributions are heavily influenced by results for a few elements. For Type F,
2413 consideration of element-specific values of sr involved a wider range of elements, and
2414 led to the choice of a somewhat higher value than the material-specific values.
2415 However, whereas for Type F materials the rapid dissolution rate, sr, represents
2416 overall absorption, and is assumed to be element-specific, for Type M and S materials
2417
sr is more likely to be determined by dissolution of the particle matrix, and so less
68