Development of KURAMA-II and its operation in Fukushima

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Abstract

A carborne survey system, named as KURAMA (Kyoto University RAdiation MApping system), was developed as a response to the nuclear accident at TEPCO Fukushima Daiichi Nuclear Power Plant in 2011. Now the system has evolved into KURAMA-II, characterized by its compactness, autonomous operation, and acquisition of pulse-height spectrum data. A two-year field test of radiation monitoring by KURAMA-II on local buses, performed by Kyoto University, has successfully proceeded to the phase of official operation by the Fukushima prefectural government, supported by Kyoto University and JAEA (Japan Atomic Energy Agency). An outline and the current status of KURAMA-II, including some results of the continuous monitoring by KURAMA-II on local buses in Fukushima, are introduced.

Introduction

The magnitude-9 earthquake in eastern Japan and the following massive tsunami caused a serious nuclear disaster of Fukushima Daiichi nuclear power plant. Serious contamination was caused by radioactive isotopes in Fukushima and surrounding prefectures. KURAMA [1] was developed to overcome the difficulties in radiation surveys and to establish air dose-rate maps during and after the present incident. KURAMA was designed based on consumer products, and enabled a large number of in-vehicle apparatus to be prepared within a short period owing to its high flexibility in the configuration of data-processing hubs or monitoring cars. KURAMA has been successfully applied to various activities in the radiation measurements and the compilation of radiation maps in Fukushima and surrounding areas.

As the situation was stabilized, the main interest in measurements moves to the tracking of the radioactive materials that have already been released into the environment surrounding the residential areas. KURAMA is not suitable for such purposes. Even though KURAMA enables measurements with a large number of monitoring cars over a wide area at one time, it still requires a trained operator and a driver in each monitoring vehicle. This means that a huge amount of resources and efforts will be required once the surveillance is changed into long-term (several tens years) and detailed monitoring in residential areas. Such monitoring can be realized efficiently if vehicles that periodically move around the residential areas, such as city buses, delivery vans or motorcycles for mail delivery, have compact and full-automated KURAMAs onboard. KURAMA-II is designed for such a purpose.

In this paper, a system outline and the development of KURAMA-II as well as the results of continuous monitoring using KURAMA-II will be introduced.

Section snippets

System outline of KURAMA-II

The system outline of KURAMA-II is shown in Fig. 1. KURAMA-II basically stands on the architecture of KURAMA [1], but the in-vehicle part has been totally re-designed. In KURAMA, a notebook PC was used in an in-vehicle unit, but KURAMA-II is based on the CompactRIO series of National Instruments [2] to obtain better toughness, stability and compactness. The 3G/GPS module for CompactRIO by SEA [3] provides time and location data as well as connection to a 3G network. The radiation detection part

Continuous monitoring by city buses

Recent applications of the KURAMA series are mainly with KURAMA-II because of its autonomous operation and ease of handling. One of such applications is continuous monitoring with KURAMA-II on city buses (Fig. 5). City buses are suitable for continuous monitoring purpose in residential areas because of their fixed routes in the center of those areas, and their routine operations.

Following the success of a field test in Fukushima city in 2012, the coverage area has been expanded to other major

Conclusion and future prospects

KURAMA-II has been developed to enable the long-term monitoring of the air dose rate in residential areas. A test operation throughout the year successfully observed the trends of air dose rates in residential areas, e.g., the shielding effect due to snowfall and reductions due to decontamination activities. Pulse-height spectra obtained by KURAMA-II provide important information concerning radioactive nuclides composing the air dose rates in residential areas. No severe troubles, such as the

Acknowledgments

The authors are grateful to Dr. Mizuno, Mr. Kimura, Mr. Ito and Mr. Kojima of the Fukushima prefectural government for a continuous support to field tests of KURAMA-II and the establishment of a monitoring scheme based on KURAMA-II on city buses. The authors are indebted to Dr. Saito, Mr. Yoshida and Dr. Takemiya at JAEA for discussions concerning the operation of KURAMA, and to Dr. Tsuda at JAEA for evaluating the G(E) functions of C12137 series. Mr. Nakamura at Hamamatsu Photonics offered the

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