Optimization of mobile monitoring methodology for the detection of orphan sources and assessment of environmental radioactive contamination

Radioactivity release to the environment from nuclear facilities during the normal operation is extremely small to create any radiological impact on the environment or on the members of public. The engineered safety features incorporated in the design and the safe operating procedures adopted in the operation of the nuclear plants ensure that probability for major nuclear accidents is extremely small. Nevertheless, as a part of emergency preparedness for implementing protective measures, monitoring methodologies and systems are developed to assess the radiological impact, if any, in case of an unlikely sever nuclear accident in Indian Nuclear Power Plants (NPP's) or major release of radioactivity into the environment. Systems installed in a mobile platform with appropriate calibration factors for the monitors and optimized monitoring methodology can detect and qualitatively and quantitatively assess the contamination even if the spread is over an extremely large area. Mobile radiation monitoring can be ground based or aerial based. Compared to ground based mobile monitoring, aerial radiation monitoring has got the following advantages (i) quick monitoring and assessment of large area contamination/search of orphan sources from a large area (ii) systems totally free from contamination and minimized exposure to the monitoring personnel. At the same time limitations of aerial survey are the dependence on the weather conditions, topography and availability of aircrafts in short notice. Aerial Gamma Spectrometry System (AGSS) developed by BARC was used in many mobile ground based as well as aerial based-radiation monitoring exercises using simulated ground. The established Air to Ground Correlation Factor (AGCF) of the AGSS helps in computing the level of contamination on ground based on the altitude of flying, number of detectors used etc. Depending on the urgency of radiation monitoring required as well as the type and size of area to be scanned, the required monitoring systems, vehicle/air craft to be used, speed of the vehicle/air craft, altitude of flying in case of aerial survey etc are to be optimized. This paper describes how the experience gained during the environmental radiation mapping around Emergency Planning Zone of NPP's, major cities, and aerial survey exercises are utilized for radiological impact assessment during nuclear/radiological emergencies. (author)