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Waste Generation by Decontamination

Model and Data

As Fig. 4.5 shows, artificial decontamination generates waste materials containing radioactive cesium. From the observation in the previous section, we consider that artificial decontamination should be applied only in the region with the initial contamination of 300 kBq/m2 or greater. The area roughly corresponds to that shown in the expanded map in Fig. 4.3. In Table 4.2, the area for each contamination level is shown in the second column from the left. The total area subject to artificial decontamination is approximately 1,500 km2.

According to in-situ measurements for soil contamination [9], cesium has migrated into the soil to a depth of about 5 cm. Assuming that the contaminated materials are removed from the area to a depth of 5 cm, we can estimate the volume and mass of the radioactive waste to be generated by artificial decontamination activities (see Appendix for mathematical formulation).

Results

The third and fourth columns of Table 4.2 show results of the waste volume estimate for the cases of fast and slow natural dispersion by the model shown in the Appendix. Depending on the speed of natural dispersion, 16 or 24 million m3 of waste will be generated from decontamination for regions with 1,000 kBq/m2 or greater (the yellow and red regions in Fig. 4.3), respectively. But if artifi decontamination is applied to regions with lower contamination levels, the total volume of radioactive waste generated could be as large as 37 or 58 million cubic meters, respectively. The total volume of waste and, as discussed below, the cost are dependent on how decontamination is applied in the two low-contamination regions.

Radioactive waste from artificial decontamination will be characterized by huge volumes of low and heterogeneous radioactivity concentrations. Average concentrations of radioactivity that would be included in the waste from artificial decontamination are shown in Fig. 4.9. Those wastes have similar levels of radioactivity concentrations to those generated from hospitals, research laboratories, and nuclear-facility decommissioning, which are categorized as “very low-level waste (VLLW)” in Japanese regulations (Chap. 15). The results of previous studies [10] on cost estimates for disposal of Very Low Level Waste indicate that the least expensive option, called trench disposal, was estimated to be 650,000 yen/m3, or

$25 per gallon of waste.

Table 4.2 Evaluation of volume and cost of disposal for radioactive waste arising from decontamination

Initial soil contamination, β (kBq/m2)

Area, A, included in Fig. 4.3 (km2)

Waste volume (million m3)

Estimated cost (trillion yen)

Fast dispersion

Slow dispersion

Fast dispersion

Slow dispersion

>3,000

183

5.60

8.13

3.64

5.28

1,000–3,000

368

10.5

15.7

6.83

10.2

Subtotal

551

16.1

23.8

10.5

15.5

600–1,000

282

6.60

10.5

4.29

6.83

300–600

721

14.1

23.2

9.17

15.1

Subtotal

1,003

20.7

33.7

13.5

21.9

Total

1,554

36.8

57.5

23.9

37.4

Fig. 4.9 Average radioactivity concentration in Bq/g of waste generated from decontamination of areas with initial contamination of >1,000 kBq/m2 for fast or slow natural dispersion. Average density of 1,600 kg/m3 is assumed. For waste with concentrations in the hatched region, disposal in controlled landfill sites is required by Japanese law (see Chap. 15)

The two rightmost columns in Table 4.2 show the estimated cost. Depending on the area targeted for decontamination, the cost of decontamination varies greatly. Even if decontamination is limited to highly contaminated areas where the dose rate is above 20 mSv/year, the cost is likely to be on the order of ten trillion yen.

 
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