2 Deposition Data Analysis
4.8 Worst-Case Collective Dose Commitments
4.8.1 Worst-Case Collective Dose Commitments for the PRS
The effective, maximum collective dose commitments corresponding to the adjusted total depositions for Cs-137, Sr-90, and I-131 in Table 83, Table 84, and Table 85, respectively, were computed for the
PRS. For Cs-137, Figure 85(a) illustrates the frequency and cumulative percentages for the maximum collective dose commitments for the region of study assuming no threshold. Table 105 and Table 106 provide the maximum collective dose commitment for the region as well as each country in the region as a function of the assumed threshold value. Note that the maximum collective dose commitments (for the PRS no threshold case) are again rank-ordered as follows:
PRS Cs-137: Regional > Japan > Russia > China > Alaska (U.S.) > S. Korea > N. Korea > Aleutians (U.S.)
> Mongolia
Therefore, even though the maximum dose commitment was found in Russia, the maximum collective dose is found in Japan (which is not surprising based upon its high population density and relative proximity to the PRS). Using a mortality risk factor of 5x10-5 per mSv for all ages [19], these results would indicate that there might be up to 355 additional, eventual mortalities in the region based upon the “no threshold” results in Table 105; Japan might have as many as 329 additional mortalities while Russia and China might have as many as 103 and 83, respectively. North and South Korea and Alaska are the other areas with a significant impact of between 10 and 18 additional, eventual mortalities.
However, it should be noted that even the mortality impact on Japan is one person out of
approximately 300 000 persons impacted by the maximum deposition and dose from the PRS. For comparison, the mortality impact on Russia is one person out of fewer than 10 000 persons impacted by the deposition. Figure 85(b) illustrates the results for the transboundary conditions; note there is a significant impact on the magnitude of the collective dose commitments versus those for the overall region in Figure 85(a).
0 Collective dose commitment (person-Sv)
Frequency Collective dose commitment (person-Sv)
Frequency
Figure 85. Frequency histogram and cumulative percentages for the PRS Cs-137 effective population dose commitments for the (a) Regional and (b) Transboundary areas for CY2000. No Threshold Basis. The corresponding population information is presented in Figure 37 and Figure 38.
Table 105 and Table 106 can also be used to evaluate the impact that small doses in concert with large populations have on the worst-case collective dose estimates. If a value of 0.1 mSv (or 10 mrem) per person is used as a threshold for the collective dose computation, then Japan, which had the highest collective dose commitment (and a possibility of up to 329 additional mortalities), has a collective dose approximately 40% lower than that without a threshold imposed. When a threshold of 0.15 mSv (or 15 mrem) is imposed, the collective dose decreases by approximately 65%. It requires a threshold of 1.0 mSv (or 100 mrem) to result in a collective dose of zero, or, in other words, to have the same impact as a 0.1 mSv threshold on the original UNSCEAR values. Again the impact of such thresholds
Frequency, Number of Days Frequency, Number of Days
For Sr-90, Figure 86(a) illustrates the frequency and cumulative percentages for the maximum collective dose commitments for the region of study from the PRS assuming no threshold. Table 107 and Table 108 provide the maximum collective dose commitment for the region as well as each country in the region as a function of the assumed threshold level. Note that the maximum collective PRS dose commitments (for the no threshold hypothesis) have the same ordering as those for the Cs-137. Again, even though the maximum dose commitment was found in Russia, the maximum collective dose is found in Japan (which translates into 17 additional mortalities). The results in Table 107 and Table 108 confirm the potential impacts of small doses in concert with large populations on the collective dose estimates discussed above for Cs-137. With a relatively low threshold of 0.1 mSv (or 10 mrem), the collective dose commitment and potential additional mortalities in Japan become zero, and, other than Russia, only the US territories have non-zero collective dose commitments.
Figure 86(b) illustrates the transboundary results for the PRS Sr-90 collective dose commitments; note that these results are necessarily consistent with those for Cs-137 above.
0 50 100 150 200 250 300
9.88E -04 4.11E+0
1 8.21E+01
1.23E+02 1.64E+0
2 2.05E+0
2 2.46E+02
2.87E+0 2 3.28E+02
More Collective dose commitment (person-Sv)
Frequency
0 20 40 60 80 100 120
Cumulative(%)
(a) Regional
0 50 100 150 200 250 300 350
0.00E+0 0 3.83E+01
7.66E+0 1 1.15E+02
1.53E+02 1.92E+0
2 2.30E+02
2.68E+0 2 3.07E+02
More Collective dose commitment (person-Sv)
Frequency
0 20 40 60 80 100 120
Cumulative(%)
(b) Transboundary
Figure 86. Frequency histogram and cumulative percentages for the PRS Sr-90 effective population dose commitments for the (a) Regional and (b) Transboundary areas for CY2000. No Threshold Basis. The corresponding population information is presented in Figure 39 and Figure 40.
For I-131, Figure 87(a) illustrates the frequency and cumulative percentages for the maximum collective dose commitments for the region of study assuming no threshold. Table 109 and Table 110 provide the maximum collective dose commitment for the region as well as each country as a function of the assumed threshold level. Note that the maximum collective PRS dose commitments (for the no threshold hypothesis) are rank-ordered as follows:
PRS I-131: Regional > Russia > Japan > Aleutians (U.S.) > Alaska (U.S.) > China
Thus for I-131, the maximum dose commitment and collective dose are found in Russia (which is unlike the results for Cs-137 and Sr-90). This is not surprising based upon the higher deposition velocity of I-131. As a matter of fact, the results in Table 109 and Table 110 indicate that little I-131 from PRS impacts any country including Russia. (Even in Russia, there is not enough of a collective dose to translate into a single, additional mortality.) Furthermore, the impact is much smaller than that for either Cs-137 or Sr-90 releases from the PRS. Figure 87(b) illustrates the transboundary results for I-131 from the PRS, which are also negligible for all the countries studied.
Frequency, Number of Days Frequency, Number of Days
0 Collective dose commitment (person-Sv)
Frequency Collective dose commitment (person-Sv)
Frequency
Figure 87. Frequency histogram and cumulative percentages for the PRS I-131 effective population dose commitments for the (a) Regional and (b) Transboundary areas for CY2000. No Threshold Basis. The corresponding population information is presented in Figure 41 and Figure 42.
4.8.1.1 Specific Case Examples: Japan and U.S. Collective Dose Commitments from the PRS
Because it is apparent that air masses from the Asian continent can move rapidly and only slightly diluted across the Pacific Ocean [14,15], it has been decided to examine these areas for possible impacts from the nuclear risk sites. Furthermore, because the Sr-90 depositions necessarily follow those for Cs-137 and the I-131 depositions are smaller and will have significantly less impact on the transboundary region (which includes both Japan and the U.S.), it was decided to examine only Cs-137 for these specific examples.
Figure 88 illustrates the collective dose results for Japan from the PRS releases for CY2000. Using a mortality risk factor of 5x10-5 per mSv for all ages [19], almost 97% of all maximum collective dose commitments will result in fewer than 18 additional, eventual mortalities from the PRS releases. As mentioned above, the maximum collective dose commitment of 6570 person-Sv, which appears from Figure 88 to be very much an isolated case, would result in as many as 329 additional eventual mortalities. Collective dose commitment (person-Sv)
Frequency
Figure 88. Japan Results: Frequency histogram and cumulative percentages for the weighted PRS Cs-137
Frequency, Number of Days Frequency, Number of Days
Frequency, Number of Days
The results for the weighted collective dose commitments from the PRS for the U.S. territories considered in this report are illustrated in Figure 89. Note that, when a mortality risk factor of 5x10-5 per mSv for all ages [19] is employed, approximately 94% of the maximum collective doses for Alaska would result in fewer than one additional mortality and none of the maximum collective dose commitments for the Aleutian Islands would translate into a single, additional mortality from the adjusted PRS releases for CY2000.
0 50 100 150 200 250
0.00E+00 3.92E+01
7.84E+0 1 1.18E+
02 1.57E+0
2 1.96E+0
2 2.35E+02
2.75E+0 2 3.14E+02
More Collective dose commitment (person-Sv)
Frequency
0 20 40 60 80 100 120
Cumulative(%)
(a) Alaska (U.S.)
0 20 40 60 80 100 120 140 160 180 200
0.00E+00 5.85E
-01 1.17E+0
0 1.75E+
00 2.34E+0
0 2.92E+0
0 3.51E+00
4.09E+0 0 4.68E+00
More Collective dose commitment (person-Sv)
Frequency
0 20 40 60 80 100 120
Cumulative(%)
(b) Aleutian Islands (U.S.)
Figure 89. Alaska (U.S.) Results: Frequency histogram and cumulative percentages for the PRS Cs-137 effective collective dose commitments for (a) Alaska and (b) the Aleutian Islands for CY2000.
No Threshold Basis. The corresponding population information is found in Figure 44 and Figure 45.