The accident of the Fukushima Daiichi (First) Nuclear Power Station (FDNPS) of the Tokyo Electric Power Company (hereafter, Fukushima accident) transpired after the Tohoku Region Pacific Coast Earthquake occurred in March 2011. Table 1.1 summarises the main events of the accident. After the earthquake occurred at 14:46 on 11 March 2011, tsunami waves of 13 m in height arrived at the FDNPS (TEPCO, 2011); the diesel power engine stopped at 15:41. Due to this electricity loss, the nuclear reaction became uncontrollable. The Fukushima Daini (Second) Power Station was able to make a controlled stop for cooling even after the intrusion of seawater from a tsunami wave with a height of 9 m. The estimated maximum height in the design of the Daiichi and Daini Power Stations was 5.1 m. In contrast, the estimated maximum tsunami height in the design of the Onagawa Nuclear Power Station of the Tohoku Electric Power Company, which avoided serious damage, was 14.8 m (Matsumoto, 2007).

The environmental consequences of the atmospheric release of radioactive materials from the accident at the Fukushima Daiichi Nuclear Power Station (FDNPS) were not sufficiently determined in the early stages of the accident, causing serious problems related to off-site countermeasures. One of the key questions faced not only by inhabitants in the affected areas but also by the public, including experts of relevant fields, is whether the confusion and problems in the emergency responses could have been avoided if the spatial extent and temporal evolution of the radioactive plume had been captured by monitoring. In this chapter, we will review the situation of the emergency preparedness related to the monitoring infrastructure at the time of the accident by examining whether the monitoring infrastructure was capable of coping with a large-scale nuclear disaster to determine an appropriate state of preparedness.

Radioactive substances were released from the TEPCO Fukushima Daiichi Nuclear Power Station (FDNPS) accident into the environment, beginning on 11 March 2011. A large amount of radioactive material was released into the atmosphere from the three damaged cores and 80% of it was deposited into the ocean. Radioactive materials also discharged directly into the ocean as leaked stagnant water from the reactor housing. River runoff and groundwater discharge can also be considered as minor sources of the FDNPS-derived radioactivity in the ocean.

In nuclear power plant accidents, enormous amounts of radioactive substances are released over a relatively short period of time (several hours to days). The direction and range over which the substances are dispersed and the amount deposited on the ground surface are influenced not only by the amount that is released but also by meteorological conditions at the time of and immediately following an accident. The most important meteorological factors include wind direction, wind speed and precipitation. Whereas wind direction and speed directly affect the atmospheric transport of radioactive substances, precipitation is the predominant factor that controls the removal of these substances from the atmosphere by wet deposition.

SPEEDI, the System for Prediction of Environmental Emergency Dose Information, is an emergency response system to predict the atmospheric dispersion of radioactive materials and radiological doses in the case of an atmospheric release of substantial radioactive materials from nuclear facilities in Japan. It has been operated by the Nuclear Safety Technology Center on consignment from the Ministry of Education, Culture, Sports, Science and Technology (MEXT) and local governments (Suda, 2006). After the accident at the Fukushima Daiichi Nuclear Power Station (FDNPS) of the Tokyo Electric Power Company (TEPCO) due to the Great East Japan Earthquake on 11 March 2011, which caused a substantial discharge of radioactive materials into the atmospheric and oceanic environments, SPEEDI became recognised by not only the nuclear emergency community but also the public at home and abroad, and the issue of its utilisation was discussed by the government, the Diet and independent accident investigations (Independent Investigation Commission on the Fukushima Nuclear Accident, 2012; Investigation Committee on the Accident at Fukushima Nuclear Power Stations of Tokyo Electric Power Company, 2012; National Diet of Japan Fukushima Nuclear Accident Independent Investigation Commission, 2012).

Radioactive materials emitted from the Fukushima Daiichi Nuclear Power Station (FDNPS) were deposited on soils and trees in forested areas, agricultural land and urban areas. It is expected that the radioactively polluted soils and radioactive materials would spread through erosion of soils from mountains and rivers. In this chapter, we first examine the behaviour of radioactive materials deposited on the ground in upcountry districts. Second, we discuss the movement of radioactive materials from various types of flatlands and forests in mountainous areas based on their chemical forms in soils and on trees. Finally, we report on the accumulation and transfer of radioactive materials to vegetation such as trees.

The accident of the Fukushima Daiichi (First) Nuclear Power Station (FDNPS) of the Tokyo Electric Power Company (hereafter, Fukushima accident) transpired after the Tohoku Region Pacific Coast Earthquake occurred in March 2011. Table 1.1 summarises the main events of the accident. After the earthquake occurred at 14:46 on 11 March 2011, tsunami waves of 13 m in height arrived at the FDNPS (TEPCO, 2011); the diesel power engine stopped at 15:41. Due to this electricity loss, the nuclear reaction became uncontrollable. The Fukushima Daini (Second) Power Station was able to make a controlled stop for cooling even after the intrusion of seawater from a tsunami wave with a height of 9 m. The estimated maximum height in the design of the Daiichi and Daini Power Stations was 5.1 m. In contrast, the estimated maximum tsunami height in the design of the Onagawa Nuclear Power Station of the Tohoku Electric Power Company, which avoided serious damage, was 14.8 m (Matsumoto, 2007).

There has been much reflection on the issue of access to and sharing of data and information among the different agencies involved in emergency response both in the country where an accident happened and among third-party countries. A universal data exchange format has been proposed by the International Atomic Energy Agency (IAEA) as a result (IRIX Steering Committee, 2013). The creation at the start of an emergency of a database containing exhaustive entries for all measurements (e.g. location of measuring devices, measuring device types, measurement errors, producers) would facilitate the work of the different bodies while removing the burden of communication from the affected country. A public database of this kind would also improve transparency in relation to the public. In France, for example, a shared database is currently being created. The same logic could also be applied to meteorological observations, to the parameters defining the state of the facility and even to the outcomes of expert assessments.