Radiation exposure risk analysis

Two types of models are often used for conducting statistical analysis of cancer risks (1) absolute-risk models and (2) relative-risk models. With absolute-risk models, the excess risk due to exposure to radiation does not depend on the normal risk that would arise when there is no radiation exposure. With relative-risk models, the relative risk is a multiple of the normal risk. Unlike absolute risk, which is measured on a scale that starts at 0 and goes to 1, relative risk values begin at 1 and go to infinity (i.e., very large numbers). A value of 1 for the relative risk means that there is no excess risk. 

Risk analysis and comparison is very difficult due to the high concern of radiation exposure. It is advisable to contact USACHPPM or other trained Nuclear Medical Science Officers for guidance before making any risk analysis for radiation. The BEIRV committee estimated that the risk of dying of cancer for a low-level exposure to radiation is about 8% per sievert or 0.08% per rem or roughly 10 4 per mrem. 

In most quantitative risk analysis methods (Uijt de Haag 2006, purple book 1999), persons present in the hazardous area are assumed to be exposed for a fixed amount of time. Assumptions for fixed exposure times are 30 minutes for a toxic exposure and 20 seconds for exposure to heat radiation. Furthermore, persons are assumed to stay on the same place. The reahty is different in case of an emergency, every person capable of escape will try to rescue himself. In case of a toxic release it is possible that a safe location (for example inside a building) is reached within the prescribed 30 minutes. On the other hand, in case of fire in crowded places, it can be expected that people are unable to escape within 20 seconds. 

Schubach (1995) provides a review of thermal radiation targets for risk analysis. He concludes that (1) the method of assuming a fixed intensity of 12.6 kW/m to represent fatahty is inappropriate due to an inconsistency with probit functions and (2) a thermal radiation intensity of 4.7 kW/m is a more generally accepted value to represent injury. This value is considered high enough to trigger the possibility of injiuy for people who are unable to be evacuated or seek shelter. That level of heat radiation would cause injury after 30 s of exposure. 

Land, C.E., Boice, J.D., Jr., Shore, R.E., Norman, J.E., and Tokunaga. M. (1980). Breast cancer risk from low-dose exposures to ionizing radiation Results of parallel analysis of three exposed populations of women, J. Natl. Cancer Inst. 65, 353. 

Based on the results of the hazard analysis, the accidents posing the greatest risk involve direct exposure to radiation (workers) and airborne releases of radioactive material (the public). Accident analysis entails the formal quantification of a limited subset of accidents as design basis accidents (DBAs). These accidents are to represent a complete set of bounding conditions as noted in DOE 5480.23 (DOE 1994a). Further, as stated in DOE-STD-3009-94,... 

In common with all techniques involving radioactivity, particular care is taken to ensure that the hazard from the irradiated samples is minimized. The electronics of the y-ray spectrometry systems used in this technique cannot work at very high count rates and so it is not usually necessary or even advisable to induce high levels of radioactivity in samples for activation analysis. There is now a greater stress on the principle of keeping risk as low as possible, and so use is made of automation to reduce the contact time for radiation workers. Figure 9 shows a totally automated system for the irradiation and analysis of samples, avoiding any exposure to radiation for the operator. 

Airborne radiation monitors are described in CESSAR-DC Section 11.5.1.2.4, and include a portable unit that can be moved to areas where work or surveillance activities are at an unusual risk of airborne exposure. This monitor includes detector channels for particulate, iodine, and gaseous activity. All equipment is assembled on a mobile cart, and the design allows for transfer of the particulate sample filters and iodine sample cartridges to the Station Counting Room for further sample analysis. 

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