Thesis Abstracts 2001
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Assessment of Canadian Forces Aircrew Radiation Exposure
By: Bernard M Ellaschuk, M.Eng. (Nucl. Eng.)
Supervisors: Dr. B.J. Lewis & Dr. L.G.I Bennett
Abstract
The International Commission on Radiological Protection recommended in its Publication 60 (1990) that radiation exposure limits for personnel be reduced, that aircrew be acknowledged as occupationally exposed and that their exposure levels be monitored.
Recently, a semi-empirical computer model, PC-AIRE, was developed at the Royal Military College to predict the ambient dose equivalent for global flight routes. The model was based on data spanning altitudes from 8800 to 11 900 m. In this thesis, the altitude function in PC-AIRE has been revised and validated with flights conducted in NASA ER-2 aircraft flying at ~ 20 700 m. As stated, the PC-AIRE code provides a prediction of the ambient dose equivalent, H*(10); however, regulations identify exposure limits in effective dose, E. Consequently, an E/H*(10) scaling ratio was developed for PC-AIRE. The model was then applied to a flight database for the Canadian Forces aircrew flying the Airbus A310 aircraft. This activity determined how their annual exposure for 1999 compared to the proposed regulations.
Additionally, Canadian Forces aircrew flying onboard NATO and US Air Force Airborne Warning and Control System (AWACS) aircraft were studied to ascertain their exposures. Unlike commercial air traffic, AWACS aircraft do not fly standard flight patterns, but orbit set locations for extended periods. Currently, models like PC-AIRE cannot predict exposures for such routes. Neutron-sensitive bubble detectors were utilized to predict their cumulative annual dose equivalent.
In this thesis, two E/H*(10) ratios were developed, one using Monte Carlo transport theory and the other using Boltzmann transport theory. When coupled with PC-AIRE, both ratios provided effective dose values that were within 20% of other industry accepted models. Also a high-altitude function was developed to improve the ability of PC-AIRE for route dose prediction that extended its capability from altitudes of 9 to 12 km to an upper range of 20.7 km. Application of the modified model to the Airbus database revealed that 68% of pilots, 90% of flight stewards and 92% of flight attendants exceeded the 1 mSv annual effective dose limit with mean annual effective doses between 2.44 and 2.47 mSv.
Analysis of the AWACS aircrew revealed their mean annual exposures (657 ± 122 µSv) to be only slightly higher than those of aircrew onboard lower flying transports such as the Hercules aircraft. In this assessment, for a typical 340-hour operating year, no AWACS aircrew met or exceeded the 1 mSv y-1 dose limit.
