Monitoring Activity and Data of Local Governments

External Exposure

5.2.1.1 Targets and Methods

Main targets of the surveillance at the northwest of Chiba prefecture are the ambient radiation dose (μSv h−1, microsieverts per hour) at all the schoolyards, public parks, and representative measuring points selected by the local governments. This activity has been based on the decision of a local forum of six cities including the two cities of Kashiwa and Nagareyama as the “Conference on Radiation Countermeasures in the Tohkatsu Area (CRCT)” [1].

The ambient dose equivalent rate around the Tohkatsu area, northwest of Chiba, was elevated after the accident, as already mentioned. The public strongly requested their local governments to monitor the ambient dose equivalent rate precisely and officially. In addition, many questions, requests for consultation, and feelings of fear assaulted the local governments. Six local governments (Kashiwa, Nagareyama, Matsudo, Noda, Abiko, and Kamagaya) in the Tohkatsu area decided to establish a new organization, CRCT, to solve the total situation officially and in cooperation. The CRCT started its official activity on June 8, 2011, after a preparation period of about 1 month. A chair of the conference is the mayor of Kashiwa City. Three specialists of radiation protection, radiation measurement, and medical science in the radiation field are also involved in the conference as supporting members for its activity. We think this is a preparation step or first step toward the real stakeholder engagement and involvement procedure in local governments for the optimization of protection. ICRP Publication 111 [2] recommends “(71) Authorities should facilitate the setting-up of local forums involving representatives of the affected population and relevant experts (e.g., health, radiation protection, agriculture authorities, etc.). These forums will allow gathering and sharing of information and favor a common assessment of the effectiveness of strategies driven by the population and the authorities.”

Based on the guideline determined by the CRCT, the ambient dose rate has been monitored in the cities of Kashiwa and Nagareyama. The latest dose distribution data at the height of 5 cm (for identifying contaminated areas), 50 cm (for dosimetry of children), and 100 cm (for adults) from the ground in the cities can be seen against the background of a Google map on the government web pages. Monitoring targets are all schoolyards (nursery schools, kindergartens, child centers, elementary schools, and high schools), parks and sports grounds, the exterior of local government institutions, bus terminals, city streets, city pools, and around sewage adjustment ponds and waste disposal sites. These sites are monitored by energy-response compensation gamma survey meters with NaI(Tl) or CsI(Tl) scintillation detectors. These survey meters are also selected based on the CRCT guideline. The monitoring frequency for each investigation point was more than once monthly. These monitoring activities have also been conducted by Bunkyo ward in Tokyo.

The local governments distributed one (or two) electric personal dose meter(s) to all the public/private schools in Kashiwa City and Nagareyama City. The purpose was to announce the monthly dose of children for their routine activities to the citizens, and to determine an actual annual dose based on the measured results; this is representative of a child's personal dose, not the ambient dose. Unfortunately, at the early stages the citizens tended to worry about the effects of an extremely small area's high contamination, a so-called micro hot spot. The cities would like to do a quantitative analysis to show the actual level of the exposure dose around the micro hot spot rather than a qualitative explanation. Electric personal dose meters in each school were given to a representative staff member, and the meters were worn at the chest height of a typical child. The personal dose meter was operated all day long (24 h). At nights and on holidays the dose meters were placed in rooms of the schools.

5.2.1.2 Data and Information

The following data are major results of activities conducted by the three local governments as described in the earlier section.

The ambient radiation dose in the cities has been surveyed since around May 2011. The highest value of the ambient radiation dose was 0.65 μSv h−1 in Kashiwa City, 0.58 μSv h−1 in Nagareyama City and 0.22 μSv h−1 in Bunkyo ward at the height of 1 m from the ground among all the monitoring points. These values include the natural background dose rate (0.04–0.08 μSv h−1).

Figure 5.1 shows an example of annual average dose at schools in Kashiwa City

measured by personal dose meters from September 1, 2011 to August 31, 2012. The data recorded in this project have been announced on the official website in the city every month. This activity and information greatly reduced the number of questions or requests for consultations from citizens living around the “micro hot spot” area.