Abstract
On the 12th of March 2011, The Great Tōhoku Earthquake occurred 70 km off the eastern coast of Japan, generating a large 14 m high tsunami. The ensuing catalogue of events over the succeeding 12 d resulted in the release of considerable quantities of radioactive material into the environment. Important to the large-scale remediation of the affected areas is the accurate and high spatial resolution characterisation of contamination, including the verification of decontaminated areas. To enable this, a low altitude unmanned aerial vehicle equipped with a lightweight gamma-spectrometer and height normalisation system was used to produce sub-meter resolution maps of contamination. This system provided a valuable method to examine both contaminated and remediated areas rapidly, whilst greatly reducing the dose received by the operator, typically in localities formerly inaccessible to ground-based survey methods. The characterisation of three sites within Fukushima Prefecture is presented; one remediated (and a site of much previous attention), one un-remediated and a third having been subjected to an alternative method to reduce emitted radiation dose.
Highlights
Following the accident at the Fukushima Daiichi Nuclear Power Plant (FDNPP) initial measurements of radiation intensity, dose and distribution were performed using manned military and civilian aircraft at high altitudes of 150e700 m to provide early quantifications across the east of Japan (MEXT, 2011; Sanada et al, 2014b)
Utilising the unmanned aerial vehicle (UAV) over the roof of the main school building, is was possible to examine the effectiveness of this remediation
The work presented here further demonstrates that such a small unmanned aerial system is capable of being utilised to produce radiation distribution maps at greater than 1 m resolution
Summary
Following the accident at the Fukushima Daiichi Nuclear Power Plant (FDNPP) initial measurements of radiation intensity, dose and distribution were performed using manned military and civilian aircraft at high altitudes of 150e700 m to provide early quantifications across the east of Japan (MEXT, 2011; Sanada et al, 2014b). Utilising these survey methods it was possible to quickly understand the approximate distribution of radio-caesium contamination across a very large area, independent of terrain. In addition to exposing themselves to radiation whilst undertaking the survey; individuals can attenuate circa 30% of the incident gamma-rays - affecting the survey's results (Jones and Cunningham, 1983)
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