Levels of Radioactivity in the Terrestrial Environment. Annex III of Technical Volume 4

Monitoring of radioactivity in the environment was carried out in Japan before the accident situation developed at the Fukushima Daiichi nuclear power plant (NPP), and soon after the accidental releases began, additional monitoring commenced and is continuing. Of particular note are measurements of ambient dose equivalent rates for external exposures, activity concentrations in air and deposited on the ground, and levels of radionuclides in the terrestrial and marine environments, including activity concentrations in food and drinking water. As discussed in Section 4.2 and Annex I of this volume, direct monitoring of activity concentrations in people was also carried out. Some of the monitoring infrastructure was severely damaged by the earthquake and tsunami, particularly on the site of the Fukushima Daiichi NPP. Despite this, steps were taken to carry out measurements on the site. For example, ambient dose equivalent rates were measured at fixed locations using a monitoring car as of 11 March. From 19 March onward, ¹³¹I and ¹³⁷Cs activity concentrations in air were measured using a portable sampler mounted on a car that was capable of measuring both airborne particulates and gases. On 23 March, continuous radiation measurements were restarted using temporary equipment at three locations