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.

The radioactive materials that were released into the atmosphere due to the Fukushima Daiichi Nuclear Power Station (FDNPS) accident not only spread within Japan but also dispersed over the entire globe through atmospheric flows. As described in Chapter 3, there were strong westerlies and a low pressure that passed over the Tohoku region when the accident occurred, which transported most of the released radioactive materials towards the east in the form of gas and/or aerosol particles. Previous studies on atmospheric trace materials (e.g. Okada et al., 1992; Husar et al., 2001; Uno et al., 2009) have shown that aerosol particles can be transported over long distances. A good example is the air pollution originating over East Asia, such as the Asian dust that arises from the dry land of China and Mongolia, which has been identified in the USA as well as over the Pacific Ocean. Therefore, to understand the entire picture of the radioactive pollution caused by the accident, it is necessary to clarify how the radioactive materials were transported, as well as deposited, over Japan and around the world. The radioactive materials that were produced by the FDNPS accident have been detected throughout the world. To date, numerical simulations of the transport of radioactive materials over large areas have been carried out by various organisations. In this chapter, we will discuss the global transport of the radioactive materials caused by the accident by examining their detection around the world, the characteristics of the atmospheric transport of radioactive materials using global numerical simulations, and estimations of the release of the radioactive materials using observations and numerical simulations.

The Fukushima Daiichi Nuclear Power Station (FDNPS) accident in Japan on 11 March 2011, which was triggered by a magnitude 9.0 earthquake that resulted in a tsunami, caused a month-long discharge of radioactive materials into the atmosphere. However, in the first stage of the accident, only monitoring cars near the FDNPS could collect monitoring data because of damage to the monitoring posts and stack monitor. The limited survey data from the monitoring cars from 12–13 March 2011 (NISA, 2011) showed that radioactive caesium and iodine were already detected at Okuma-machi and Namie-machi, close to the FDNPS around 8:00 JST on 12 March due to leakage from the containment vessel. In addition, increased air dose rates due to the deposition of radionuclides discharged by a hydrogen explosion at unit 1 were observed north of the FDNPS on 13 March.

The things we learned from the responses to the Fukushima Daiichi Nuclear Power Station (FDNPS) accident are as follows. (1) If experts had been properly placed in the Nuclear Emergency Response Headquarters and the Fukushima Prefectural Disaster Response Headquarters, the data calculated by SPEEDI or the results obtained from the airborne survey conducted by the US Department of Energy (DOE) might have been more effectively utilised, and people would likely not have been evacuated to areas with high dose rates. (2) If experts had been properly placed in the Fukushima Prefectural Disaster Response Headquarters, the distribution and administration of stable iodine preparations could have been performed in a similar manner by different local governments. (3) In the case of an emergency disaster, if special budgetary actions had been taken for the investigation of radioactive contamination, the collection of soil samples could have started earlier, and detailed maps could have also been created. These situations occurred because the government asked us to follow procedures to budget according to a normal situation. They requested a list including all items with unit prices and exact numbers of necessary items for soil sampling for about 11 000 samples from about 2200 locations. The list also had to include travel expenses for persons who took part in the soil sampling project, taxi fares for the transfer of persons from the headquarters to the sampling points, etc. This job took about one month because we had to get information from participants from 98 organisations. If we could have used the budget to pay for necessary items with receipts by drawing money from a special account, we could have started the soil sampling project one month earlier.

Fukushima University is the only national university in Fukushima Prefecture that is located near the earthquake and nuclear accident. The university provided much of the correspondence about the earthquake and the nuclear accident. Moreover, the highest dose rate from the radioactive material released into the environment by the nuclear accident was measured at the public facilities of the university. Putting aside the reality of crisis management, here we describe several thoughts for a safer society.