Summary of the Effective UNSCEAR Collective Dose Commitments

UNSCEAR 1993 Report methodology and assuming no threshold) for both the PRS and VRS is presented in Exhibit 10. Therefore, even though the maximum effective dose commitments from the PRS and VRS were reasonably similar (as illustrated above), the higher populations impacted from the VRS releases generally resulted in significantly larger collective dose commitments. It also appears that the Cs-137 dose commitments will be of primary concern for either site.

Exhibit 10. Summary of Maximum (Non-Zero) Effective Collective Dose Commitments Using the UNSCEAR 1993 Report Methodology

PRS VRS Maximum Effective Collective

Dose Commitment (person-Sv)* Maximum Effective Collective Dose Commitment (person-Sv)*

Region Cs-137 Sr-90 I-131 Region Cs-137 Sr-90 I-131 Regional 2.98E+02 1.27E+02 3.78E+00 Regional 8.23E+03 3.33E+03 2.06E+02 Transboundary** 2.76E+02 1.19E+02 7.46E-02 Transboundary** 8.22E+03 3.32E+03 2.06E+02 China 6.96E+01 2.78E+01 4.08E-08 China 7.21E+03 2.93E+03 1.76E+02

Hong Kong Hong Kong 1.59E+00 3.72E-04

Japan 2.76E+02 1.19E+02 7.46E-02 Japan 7.99E+03 3.28E+03 2.06E+02 Mongolia 1.59E-01 5.98E-02 Mongolia 1.35E+00 4.74E-01 1.13E-07 N. Korea 8.47E+00 3.38E+00 N. Korea 2.09E+03 8.68E+02 9.12E+01 Russia 8.63E+01 3.76E+01 3.78E+00 Russia 1.36E+03 5.63E+02 6.68E+01 S. Korea 9.75E+00 1.78E+00 S. Korea 2.05E+03 8.53E+02 9.82E+01

Taiwan Taiwan 2.67E+02 1.13E+02

Aleutians (U.S.) 2.21E-01 8.15E-02 2.49E-03 Aleutians (U.S.) 1.39E-02 3.29E-03 4.74E-07 Alaska (U.S.) 1.48E+01 5.20E+00 7.10E-05 Alaska (U.S.) 1.54E+00 8.66E-02 4.95E-18

Vietnam Vietnam 6.07E-09 3.46E-13

* The effective collective dose commitments are comprised of the following components (based upon the UNSCEAR 1993 Report [13] methodology):

Cs-137: Ingestion 36.2%, Inhalation 0.1%, External Exposure 63.8%

Sr-90: Ingestion 91.9%, Inhalation 8.1%, External Exposure 0%

I-131: Ingestion 93.5%, Inhalation 3.8%, External Exposure 2.7%.

** The transboundary region includes only land areas outside of Russia.

A study of the impact of imposing threshold values on the various collective dose commitments was also undertaken. Figure 55 illustrates the impact of such thresholds on the maximum collective Cs-137

Frequency, Number of Days Frequency, Number of Days

dose commitments for those areas where the impact would be at least one additional mortality (using a mortality risk factor of 5x10^-5 per mSv for all ages [19]). Note that only the collective doses for the entire region and Russia do not fall to zero using a threshold value of 0.10 mSv per person. Therefore, there would be a significant impact on collective doses if even a relatively small threshold (i.e., 0.10 mSv) were imposed on the calculation.

0 50 100 150 200 250 300 350

0 0.2 0.4 0.6 0.8 1

Threshold (mSv)

CollectiveDoseCommitment(person-Sv)

Regional Transboundary China Japan Russia

Figure 55. Impact of Imposing Hypothetical Threshold Values on the UNSCEAR Maximum Effective Collective Cs-137 Dose Commitments for the PRS. Only those values are shown where at least one additional mortality would result for the no threshold case.

The corresponding relationship between the maximum collective dose commitments and threshold for the VRS is provided in Figure 56. Notice that the impact of thresholds on the VRS collective dose commitments is much smaller than that for the corresponding PRS doses; however, they still appear to be significant for most countries impacted by the PRS releases.

0 1000 2000 3000 4000 5000 6000 7000 8000 9000

0 0.2 0.4 0.6 0.8 1

Threshold (mSv)

CollectiveDoseCommitment(person-Sv) Regional Transboundary China Japan N. Korea Russia S. Korea Taiwan

Figure 56. Impact of Imposing Hypothetical Threshold Values on the UNSCEAR Maximum Effective Collective Cs-137 Dose Commitments for the VRS. Only those values are shown where at least one additional mortality would result for the no threshold case.

4 Parameter Variation Study

There are three major sources of potential “error” or uncertainty in the dose calculations provided in this report. The first is the deposition values [6] provided as the input to said calculations. The deposition data provided are based upon data for approximately 90% of the days in a single calendar year (i.e., CY2000) and, as was stated by Mahura [6], a multi-year approach would be best for statistical analysis of the deposition data. Furthermore, because wet deposition is related to rainfall, these deposition data can be highly variable as are the dry deposition velocities (whose effects were indicated by the differences found between Cs-137, Sr-90, and I-131 depositions for the five specific case studies used to generate the relationship between Cs-137 and the other radionuclides of interest).

Thus the possible input data to this study would have had a great deal more variation if the resources were available to examine the possible effects such as year-to-year variation or variation in deposition velocities. It is thought that by examining the range of conceivable release values (as they compare to the “unit hypothetical release” of 8.64x10¹⁴ Bq used to generate the data [6]) and the maximum values on a day-to-day basis for the given time-slice represented by the CY2000 results, that a reasonable set of conclusions can be drawn concerning future releases from the two risk sites studied in this report.

A second source of potential variation present in the dose calculations in this report are the UNSCEAR 1993 Report deposition-to-dose transfer factors (i.e., P2345, P245, and P25) described above. Given a total deposition at a specific location, these provide an estimate of the dose commitment that would be imparted to an adult (except for the case of I-131 where a weighted value is instead used) under average or nominal conditions using information that is often decades old and not necessarily concerning the region of interest. The UNSCEAR methodology is sound; however, little account was taken for the countries of interest in this study. In this section, the parameters that constitute the various deposition-to-dose transfer factors will be examined to provide a more reasonable range of values for the region of interest.

The third source of error applies to computing collective doses, and that is the population data used in this study. These data are from 1995 [7] and, therefore, are somewhat out of date. However, these data are used “as-is” as any adjustment of the data would be arbitrary and likely to introduce more error than warranted especially when considering the other sources of error that are examined below.

There are a number of different techniques that can be used to examine such variations in the factors comprising the deposition-to-dose coefficients defined above. One could set up a number of scenarios where the doses will be computed for each individual (i.e., infant, child, adult, etc.) of interest for each of the 13 countries represented in the region of interest. This would also entail defining the various parameters for ingestion, inhalation, and external exposure representing each selected region and individual. However, such a technique appears unwarranted when considering the variation inherent in the input data. The approach taken in this study is to define reasonable ranges for the source term and the various parameters used in computing the deposition-to-dose coefficients and then, using said ranges, compute the resulting ranges of the transfer factors and the resulting maximum dose commitments for both the maximum individual and adult cases. These results will be analyzed to determine whether accounting for reasonable variation in the source term and the parameters used to develop the deposition-to-dose transfer coefficients would alter the conclusions drawn from

examination of the dose commitments computed using the UNSCEAR values for the “unit hypothetical release.”