Cloud shine

The 95 Quantile X/Q at 3000 m for a ground release with wake as calculated by the MACCS2 code is 5.16E-05 sec/m at 3000 m and 1.16E-03 secern at a distance of 300 m, yielding a X/Q ratio of. 044. Thus, the calculated bounding dose at 3000 meters is. 044 (1 rem) or 44 mrem. The DOE calculated dose and this dose that is derived from it include dose contributions from committed effective dose for 50 years (CEDE) and immersion in the radioactive plume (cloud shine). This potential dose consequence represents a conservative upper bound on the public dose since the maximum radiological inventory corresponding to HC2 levels was used in the analysis, and no mitigation of the release was taken into account. 

External gamma radiation from the plume, called cloud shine... 

During a release, the dose from cloud shine, ground shine, skin contamination, and inhalation is predominant. After the plume has passed, the dose from ground shine and ingestion of contaminated food and milk becomes predominant. 

Protective action Cloud shine Ground shine... 

Sheltering. As discussed above under Public Protective Actions, sheltering can be effective protection from exposure from the cloud shine, ground shine, and inhalation dose resulting from a plume. The degree of effectiveness depends on the building type. 

Noble gases (gamma 1 emitters Xe, Kr) Cloud shine 1,500,000... 

The PWR 4 example assumes a catastrophic failure of the containment. As a result, a large part of the radioactive material in the containment atmosphere would be released in a short period (a puff release). Such a puff release could expose people near the plant to substantial cloud shine and inhalation doses within an hour or so of the release. 

The top right figure shows the contributions to the 24-hr whole body dose. The inhalation pathway would contribute the least to projected whole body dose the cloud shine dose would be sublethal, but the additional 24-hr ground shine contribution would lead to projected doses in excess of the early injury threshold (50 to 100 rem) out to 7 miles or so and the early fatality threshold (250 rem) out to about 3 miles. 

In this example, the early doses (cloud shine and inhalation) are not sufficient to cause early injuries, but they do exceed Environmental Protection Agency protective action guides. Other source terms have been postulated (no matter how unlikely) that could cause early injuries close to the plant resulting from cloud shine and inhalation. This shows the importance of early protective actions. For large source terms like PWR 4 involving a puff release of... 

Most of the total dose increase between 4 hr and 7 days (shown in the top left part of Figure 5.2-8) results from ground contamination deposited by the passing plume. This shows the importance of ground contamination. In this example, the direct dose from the plume (cloud shine and inhalation) is not sufficient to result in early deaths or injuries but if people remain on contaminated ground, their dose will increase until, at about 6 hr, the dose could result in injuries and, at 12 hr, cause death. Obviously, after a major release, areas of substantial ground contamination must be identified, and the population must be evacuated. 

From the bottom figures, it can be seen that projected thyroid doses are dominated by inhalation doses. The ground and cloud shine contributions increase the thyroid dose only marginally within 24 hr. Thyroid ablation would occur at thyroid doses abovfc about 1000 rem. This would not be expected beyond about 3 miles for the postulated (PWR 4) source term and weather conditions. Whole-body dose (not thyroid dose) would be the most important dose for most accidents in terms of early fatalities and injuries. 

Cloud shine dose from all or at least part of the plume can be avoided (if the evacuation begins before or shortly after the release). 

Improvised respiratory protection, such as placing a towel over the mouth and nose, reduces only the inhalation exposure, not the exposure to cloud shine or the exposure to contaminated ground and other surfaces. Since, for most severe accidents, inhalation dose would... 

Type of shelter Cloud shine Ground shine Inhalation... 

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