Marco conceptual para preparación y presentación de Estados Financieros

areas (e.g., evacuation zones), only one to three samples were taken to avoid prolonged exposure of sampling workers to radiation” [8.20].

8.2.3. Protocol for assessing radionuclide contamination in soil samples

3) Measure the ambient equivalent dose rate (µSv/h) using a portable dosimeter at a height of 1 m. At all locations, slowly move the survey meter 3 m in all directions from the center to confirm the absence of any singular points with sudden spikes in air-dose rates.

4) Try to locate sites with open space, and if possible, areas not covered by vegetation. Do not remove small fragments of leaves and organic layers because they may contain ¹³⁷Cs and ¹³⁴Cs. ...

5) Soil samples can be collected using one of two methods:

1) ...Each U-8 measurement container should be weighed before sampling and clearly marked. Insert the U-8 container gently into the soil and use it as a scoop. Cut the surface with a disposable plastic knife and mix well in the plastic bag before sealing.

2) Using a core sampler for hard soil...50 mm in diameter.... The samples should be placed in plastic bags, and then mixed well by shaking the outside of the plastic bag and packed into U-8 containers (when using a 100-mL core sampler). Metal samplers can be used at the same sampling site after cleaning with alcohol in situ, but never use the same sampler for different locations to prevent cross-contamination. Samplers should be cleaned after returning to the lab.

Source: Figure 6 of Ref. [8.20].

FIG. 8.19. Emergency procedure for the investigation of radioactive contamination of the soil using the U-8 container.

3) Soil water content may be measured in the field using a portable time-domain reflectometer (TDR). This procedure is optional if oven-drying is impossible due to the need to avoid iodine sublimation at higher temperatures.

4) Because of the possible spatial variability, all five soil samples should be measured. All sampling containers should be properly labeled with weight, soil depth, GPS reference number, and land-use type, and hermetically sealed. Wipe the outside of the container with alcohol-impregnated tissue paper to decontaminate and take a photograph to distinguish the soil color and type.

5) Each sample should be placed inside a new plastic bag and zip-locked by a person who has not touched the soil (expected to be uncontaminated).

The five samples from each location should also be zip-locked in a larger bag and transported to a laboratory in secured containers labeled with radioactive signs.

6) The national radiation safety regulations should be observed at all times (i.e., do not exceed 5 μSv/h at the surface of the transportation container as proposed in the Japanese L package standard).

Source: Figure 7 of Ref. [8.20].

FIG. 8.20. Emergency procedure for the investigation of radioactive contamination of compacted soil using the 100 mL soil core sampler.

7) In the laboratory, information regarding GPS coordinates (region, latitude, and longitude), land use, soil types, digital photographs, sampling dates, and other relevant comments should be entered into a computer database.

8) The U-8 soil containers should be sealed again in zip-lock bags or plastic film by two persons (one person to touch the container, and another to cover the container without touching its surface), to avoid contamination of the Ge-detector.

9) The bulk density should be calculated using net sample weights and field soil moisture contents. If oven-drying is possible (i.e., ¹³¹I level is low), soil can be dried and the bulk density can be calculated.

10) To convert the amount of radioactive contamination per kilogram of soil to the amount of radioactive contamination per 1 m² of land (Bq/m²), average the radioactive contamination (Bq/kg soil) and the bulk density values of the five subsamples.

11) Before measurement, the sample container should again be shaken well to mix the large amounts of ¹³⁷Cs in the surface soil. ...

12) Given the expected high concentrations of radionuclides, the counting time will be limited by the counting statistics error of ¹³⁷Cs, ¹³⁴Cs, and

131I, which should be a maximum of 5% (ideally 3%).”

8.2.3.3. Results of preliminary sampling

The spatial pattern of the ¹³⁷Cs inventory after the Fukushima Daiichi accident (see Fig. 8.21) is based on the emergency soil sampling protocol. Onda et al. [8.20] propose the following:

“Five soil samples (No. 1–No. 5) were collected within a 3 m × 3-m area at each sampling site (56 sites in total). The influence of the number and combination of samples at each site in the ¹³⁷Cs inventory mapping results are discussed below.

“Our map shows unfavorable variation in the ¹³⁷Cs inventory when a single soil sample is selected from the five. In maps based on soil samples No. 1 and No. 3, an area with a relatively high ¹³⁷Cs inventory, appearing northwest of the reactor in the soil sample No. 5 map, is missing. Using multiple samples reduces the differences in ¹³⁷Cs inventory patterns among maps, but large inconsistencies still exist among maps based on combinations of three regularly selected soil samples. Finally, the ¹³⁷Cs inventories of the five soil samples were averaged and used to produce an inventory map. The spotlike distribution of the ¹³⁷Cs inventory was

Source: Figure 9 of Ref. [8.20].

FIG. 8.21. Influence of the number of samples at each sampling site on the ¹³⁷Cs inventory mapping results.

averaged when the five samples were combined and the resulting map is largely consistent with the results of the Third Airborne Monitoring Survey of Radioactivity (MEXT [8.25]).

“The results of this study indicate that collecting and combining at least five soil samples within a 3 m × 3-m area is the minimum number required to produce a precise fallout inventory map of radionuclides from the FDNPP accident. The emergency sampling protocol proposed in this study should be considered in case of emergency situations following nuclear hazards.”