Maximum Effective Dose Commitments for the VRS

Using the transfer factors described above, the effective dose commitments for the maximum total depositions for Cs-137, Sr-90, and I-131 corresponding to the values in Table 18, Table 22, and Table 26, respectively, were computed for the VRS. For Cs-137, Table 36 provides the total, maximum effective dose commitment for the region and each country as well as the components of the total by type (i.e., ingestion, inhalation, and external exposure). Note that the maximum, non-zero total dose commitments for the VRS are ordered as follows:

VRS Cs-137: Region = Russia > China > N. Korea > Japan > Taiwan > Alaska (U.S.) > Mongolia

> Aleutians (U.S.) > Hong Kong > Vietnam

Therefore, even though the maximum dose commitment resides in Russia (as found for the PRS results), the values for other surrounding countries (e.g., China, N. Korea, and Japan) are not orders of magnitude lower than that for Russia, but approximately four to eight times lower. This will be significant if the dose commitments are large enough to be of concern.

Figure 29 illustrates the frequency and cumulative percentages for the Cs-137 maximum effective dose commitments for the region of study. The maximum total Cs-137 deposition of 2.64x10⁴ Bq m^-2 from Table 18 translates into an effective dose commitment of approximately 4 mSv (or 0.4 rem) per person as indicated in Table 36, which is less than twice the average annual background dose of 2.4 mSv [13] and thus within what could be considered normal variation of the background dose. It should also be noted that 95% of the maximum dose commitments are less than 1.35 mSv or 0.13 rem per person, which indicate that most of the dose commitments are much less than the maximum (as illustrated in Figure 29). Furthermore, 85% of the maximum dose commitments are less than 0.68 mSv (or 0.07 rem) per person. Finally, over 98% of all maximum dose commitments for CY2000 are less than the average annual background dose.

0 Dose commitment (mSv per person)

Frequency

Figure 29. Frequency histogram and cumulative percentages for the VRS Cs-137 maximum effective dose commitments (left) and corresponding populations (right).

Figure 30 illustrates the results for the transboundary conditions provided in Table 36. There are less significant impacts on the maximum dose commitment (i.e., by about a factor of four) or population than for the PRS. This is because of the proximity of China to the VRS as illustrated in Figure 1. For these conditions, N. Korea will have the next highest (to China) dose commitment of 0.65 mSv per person, which is considerably smaller than the average annual background dose.

0 Dose commitment (mSv per person)

Frequency

Figure 30. Transboundary frequency histogram and cumulative percentages for the VRS Cs-137 maximum effective dose commitments (left) and corresponding populations (right).

For the Sr-90 values computed from the VRS Cs-137 results as described above, Table 37 provides the total, maximum effective dose commitment for the region and each country as well as the components of the total by type (i.e., ingestion, inhalation, and external exposure which are zero for Sr-90). Note that the dose commitment ordering is the same as that for the VRS Cs-137 results.

Figure 31 illustrates the frequency and cumulative percentages for the Sr-90 maximum effective dose commitments for the region of study. The maximum total Sr-90 deposition of 3.26x10⁴ Bq m^-2 from Table 22 translates into a maximum, committed dose of 1.69 mSv (or 0.17 rem) per person (as indicated in Table 37), which is significantly less than the average annual background dose of 2.4 mSv. It should be noted that 95% of the maximum dose commitments are less than 0.57 mSv (or 0.06 rem) per person and 85% of the maximum dose commitments are less than 0.29 mSv (or 0.03 rem) per person. This indicates that the majority of dose commitments are much less than the maximum (as

Frequency, Number of Days Frequency, Number of Days

Frequency, Number of Days Frequency, Number of Days

illustrated in Figure 31). Figure 32 illustrates the transboundary results, which necessarily follow those for Cs-137 above.

0 Dose commitment (mSv per person)

Frequency

Figure 31. Frequency histogram and cumulative percentages for the VRS Sr-90 maximum effective dose commitments (left) and corresponding populations (right).

0 Dose commitment (mSv per person)

Frequency

Figure 32. Transboundary frequency histogram and cumulative percentages for the VRS Sr-90 maximum effective dose commitments (left) and corresponding populations (right).

For the I-131 values computed from the VRS Cs-137 results as described above, Table 38 provides the total, maximum effective dose commitment for the region and each country as well as the components of the total by type (i.e., ingestion, inhalation, and external exposure). The ordering of the VRS I-131 results generally agrees with that for the Cs-137 and Sr-90 except for those additional countries that have no dose commitments.

Figure 33 illustrates the frequency and cumulative percentages for the I-131 maximum effective dose commitments for the region of study. The maximum total deposition of 5.28x10⁴ Bq m^-2 from Table 26 translates into a committed dose of 0.25 mSv (or 0.03 rem) per person as illustrated in Table 38, which is almost an order of magnitude lower than the average annual background dose of 2.4 mSv [13]. It should be noted that 95% of the maximum dose commitments are less than 0.08 mSv (or 0.01 rem) per person. As illustrated in Figure 33, this indicates that many of the dose commitments from I-131 are significantly lower than the maximum. Figure 34 illustrates the transboundary results for

Frequency, Number of Days Frequency, Number of Days

Frequency, Number of Days Frequency, Number of Days

0 Dose commitment (mSv per person)

Frequency

Figure 33. Frequency histogram and cumulative percentages for the VRS I-131 maximum effective dose commitments (left) and corresponding populations (right).

0 Dose commitment (mSv per person)

Frequency

Figure 34. Transboundary frequency histogram and cumulative percentages for the VRS I-131 maximum effective dose commitments (left) and corresponding populations (right).

3.2.3.1 Specific Case Examples: Japan and U.S. Dose Commitments from the VRS As explained above, the Cs-137 results for Japan and the U.S. territories considered in this study are provided. Figure 35 illustrates the maximum dose commitments from the VRS for Japan. The dose commitment frequency and magnitudes for the VRS are very different than those from the PRS. There are dose commitments on more than 96% of CY2000 days and the maximum dose of 0.6 mSv per person in December 2000 is more than an order of magnitude higher than that from the PRS. Also there are maximum dose commitments over 0.15 mSv per person on approximately 10% of all CY2000 days. Therefore, the impact from the VRS on Japan is greater than that from the PRS;

however, all such dose commitments are significantly less than the average annual background dose of 2.4 mSv [13].

Frequency, Number of Days Frequency, Number of Days

Frequency, Number of Days Frequency, Number of Days

0 Dose commitment (mSv per person)

Frequency

Figure 35. Japan Results: Frequency histogram and cumulative percentages for the VRS Cs-137 maximum effective dose commitments (left) and corresponding populations (right).

The dose commitment histograms for the U.S. territories considered in this study are provided in Figure 36. Note that the dose commitments are approximately an order of magnitude less than those in Japan. There is also a much lower frequency of dose commitments from the VRS for both Alaska in Figure 36(a) and the Aleutian Islands in Figure 36(b) than in Japan. Again the maximum doses of 2x10^-2 and 9x10^-3 mSv per person for Alaska and the Aleutian Islands, respectively, appear to be isolated cases and occur within approximately one month of each other. The maximum deposition in Japan, on the other hand, occurred in December 2000. All such dose commitments are within the normal variation for the background dose.

0 Dose commitment (mSv per person)

Frequency Dose commitment (mSv per person)

Frequency

(b) Aleutian Islands (U.S.)

Figure 36. U.S. Results: Frequency histogram and cumulative percentages for the VRS Cs-137 maximum effective dose commitments for Alaska (left) and the Aleutian Islands (right).

3.2.4 Maximum Effective Dose Commitments Summarized and Compared to