Development of a Carborne Survey System, KURAMA
Abstract A carborne survey system named KURAMA (Kyoto University RAdiation MApping system) has been developed for the establishment of air dose rate maps in Fukushima and the surrounding area as a response to the nuclear accident at the TEPCO Fukushima Daiichi Nuclear Power Plant. KURAMA is a γ-ray survey system with Global Positioning System (GPS) and up-to-date network technologies developed for the primary use of carborne surveys. The monitoring data tagged by GPS location data are shared with remote servers over the cloud network, then processed by servers for a real-time plot on Google Earth and other various purposes. Based on the success of KURAMA, KURAMA-II, an improved version of KURAMA with better handling and ruggedness, was developed for autonomous operation in public vehicles. About 200 KURAMA-II systems now serve for continuous monitoring in living areas by local buses as well as the periodic monitoring in Eastern Japan by the Japanese government. The outline and present status of KURAMA and KURAMA-II are introduced.
Keywords γ-Ray • Air dose rate • Carborne survey • Fukushima Daiichi Nuclear Power Plant • Mapping • Radiometry
The magnitude 9 earthquake in Eastern Japan on 11 March 2011 and the following massive tsunami caused a serious nuclear disaster at the Fukushima Daiichi nuclear power plant, which Japan had never experienced before. Huge amounts of radioactive isotopes were released in Fukushima and the surrounding prefectures.
In such nuclear disasters, air dose rate maps are quite important to take measures to handle the incident, such as assessing the radiological dose to the public, making plans for minimizing public exposure, or establishing procedures for environmental reclamation. The carborne γ-ray survey technique is known to be an effective method to make air dose rate maps . In this technique, continuous radiation measurement with location data throughout the subject area is performed by one or more monitoring cars equipped with radiation detectors. Unfortunately, the existing monitoring system did not work well in the disaster. Such monitoring cars tend to be multifunctional; thus, it is too expensive to own multiple monitoring cars in a prefecture. Fukushima was such a case, and worse, both the only monitoring car and the data center were contaminated by radioactive materials released by the hydrogen explosions of the nuclear power plant. Monitoring cars owned by other prefectures were then collected, but these monitoring cars were too heavy to drive on the roads in Fukushima, which were heavily damaged by the earthquake. Thus, daily measurements of the air dose rate in the whole area of Fukushima were eventually performed by humans. The measuring personnel drove around more than 50 fixed points in Fukushima Prefecture twice a day by sedan cars, and they measured the air dose rate of each point by portable survey meters. Airborne γ-ray surveys were performed by the Ministry of Education, Culture, Sports, Science and Technology of Japan (MEXT) and the United States Department of Energy, but difficulties in arrangements for the aircraft and their flight schedules prevented immediate and frequent surveys in the areas of interest.
KURAMA and its successor KURAMA-II were developed to overcome such difficulties in radiation surveys and to establish air dose rate maps during the present incident. KURAMA and KURAMA-II were designed based on consumer products, enabling much in-vehicle apparatus to be prepared within a short period. KURAMA/ KURAMA-II realize high flexibility in the configuration of data-processing hubs or monitoring cars with the help of cloud technology. In the present chapter, an outline of KURAMA/KURAMA-II as well as their applications are presented.