a range of reactor to base separation distances of 20-100 m and a range of reactor powers from 333 kWt to 2.5 MWt. The doses represent a total exposure to both natural (uncontrollable) and man-made (controllable) radiation sources. Currently, guidelines have been established, allowing a 5 rem dose from controllable radiation sources with a 25 rem total dose from controllable plus uncontrollable radiation sources for a 30 day exposure period. Manned truncated conical shadow shield masses for a 500 kWt reactor and a 5 m high shielded area are shown in Fig. 8 for shielded area widths of 40 m and 160 m using dose extremes of 5 and 25 rem/30 days. The shielded area that can be used for manned operations can be enlarged by extending the shield into a 360° ring. Due to the much higher masses as compared to shielding a more limited area, longer separation distances were studied for the same doses. Figure
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