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PUBLICATION OF REPORT "EXPOSURE RATE REDUCTION ON BIKINI ISLAND DUE TO CONCRETE DWELLINGS" The enclosed report is being considered for publication as an AEC Technical Information Document, TID. Please provide us your comments by November 1, 1973. Special Assistant to the Assistant Director for of Operational Safety
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EXPOSURE RATE REDUCTION ON BIKINI ISLAND DUE TO CONCRETE DWELLINGS Division of Operational Safety U.S. Atomic Energy Commissioti Radiological Operations Division Nevada Operations Office, Las Vegas U.S. Atomic Energy Commission
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DUE TO COXCPSTE ON BIKINI ZSLAND During the May 1972 AEC sponsored resurvey of Bikini Atoll measurements were made to determine the reduction of exposure rates at dwelling sites due to the shielding effect of the concrete structures being erected for occupancy by the returning Bikini people. Exposure rates were measured at several points around and within each dwelling using a Baird Atomic NE-148 Scintillation lfonitor904-148, sodium iodide system calibrated with respect to l%s. The dwellings are constructed of wood and concrete. The floors are concrete slab, not extending beyond the walls of the houses. The - concrete slab walls are pierced by windows and, on the longer sides, by entrance ways. The roofing is constructed of wood framing and Local sources of sand and coral aggregate suitable for use in making concrete were identified by AEC prior to construction as having the minimum radioactive material content of those available on the _ atoll. The architectural drawings of the dwellings that were developed by the Office of Trust Territory, Department of Interior, in consultation 'with the Bikini people, were reviewed by the AEC staff. Recommendations were made that would reduce radiation levels and thus keep exposures as low
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A total of 33 structures were examined. These were in various *tages of construction that varied from floor slab only to essentially complete and occupied (by the contractor supervisor). The locations of the structures are shown in Figure 1. Figure 2 is a sketch of a A typical building layout is indicated in Figure 3, showing the t points at which measurements were made: on the center line of each wall, 10 feet out from the wall, 3 feet above the surface of the ground; in the center of the building, at a height of 3 feet; and in the center of the building, on the floor. The exposure rates measured are indicated in Table 1, roentgcns per hour (pR/h). External exposure rates ranged to 55 pR/hr, with an arithmetic mean value of 20 pR/hr. Treated Data and Results Exposure rate reduction factors (RF) were computed for each dwelling except for~seven "slab only" sites where no external measurements were made. The reduction factor (RR) termined utilizing the following is expressed in percent and was deInterior Exposure Rate) x 100 Exterior Exposure Rate
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The interior exposure rate is that which was observed at the center of the dwelling at a height above the floor of three feet or at contact with the floor. Both values were-investigated. The exterior exposure rate used in the above equation was the arithmetical average of the four external exposure rates measured around each dwelling site. Exposure rate reduction factors for each dwelling are indicated in Table 2 for the floor and three foot height situations. The measurements are stratified according to each aspect of construction encountered. The average interior exposure rate at floor level and at three feet in the center of the dwellings (exluding those filled with masonite and those having Dnly a slab) is about 11 pR/hr. On Bikini Island, exposure rates present from radioactivity remaining post nuclear testing are reduced within the concrete dwellings by a signif icant amount. Upon completion of the housing construction effort, an exposure reduction factor of about 50% may apply. This is about what was expected provided materials of construction contained low levels of radioactivity, Even greater reduction can be expected - when the housing area is covered with one to two inches of coral gravel as has been- recommended. Depending‘on the occupancy time for residents of these houses, total exposure to be reduced accordingly. to external radiation can be The authors wish to recognize the role of the Department of the Interior and particularly the Office of Trust Territories of
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Islands in obtaining favorable results of exposure rate reduction in construction of dwellings to be occupied by the Bikini people when
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BIKINI ISLAND HOUSING GAMMASURVEY SURVEY LAYOUT INTERIOR OFISLAND SIDE READINGS OBTAINED AS INDICATED AT 3 FOOT HEIGHT EXCEPT AT CENTER OF HOUSE WHERE ACONTACT READING WAS ALSO OBTAINED.
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Slab, Walls and Roof l Table 2 House External Interior Floor Interior Reduction Factor % Slab, walls, roof Slab, walls and roof,