An aerial radiological survey of the Pilgrim Station Nuclear Power Plant and surrounding area, Plymouth, Massachusetts

Terrestrial radioactivity surrounding the Pilgrim Station Nuclear Power Plant was measured using aerial radiolog- ical survey techniques. The purpose of this survey was to document exposure rates near the plant and to identify unexpected, man-made radiation sources within the survey area. The surveyed area included land areas within a three-mile radius of the plant site. Data were acquired using an airborne detection system that employs sodium iodide, thallium-activated detectors. Exposure rate and photopeak counts were computed from these data and plotted on aerial photographs of the survey area. Several ground-based exposure measurements were made for comparison with the,aerial survey results. Exposure rates in areas surrounding the plant site varied from 6 to 10 microroentgens per hour, with exposure rates below 6 microroentgens per hour occurring over bogs and marshy areas. Man-made radiation was found to be higher than background levels at the plant site. Radation due to nitrogen-1 6, which is produced in the steam cycle of a boiling-water reactor, was the primaty source of activity found at the plant site. Cesium-137 activity at levels slightly above those expected from natural fallout was found at isolated locations inland from the plant site. No other detectable sources of man-made radioactivity were found