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Okoshi, Minoru
Dekomisshoningu Giho, (31), p.32 - 44, 2005/03
The International Atomic Energy Agency (IAEA) published a Safety Guide (RS-G-1.7) on the application of the concepts of exclusion, exemption and clearance in 2004. In this Safety Guide, the IAEA proposes the activity concentrations can be applied to clearance. The Nuclear Safety Commission reevaluated their clearance levels to reflect the new technological information given in the IAEA Safety Guide and other reports. The Regulatory Authorities have been investigating and discussing regulatory rules on clearance including the verification system of clearance levels. And the Atomic Society of Japan has deliberated the technological standards for the verification of clearance levels performed by nuclear operators. In this paper the activities and outcomes by those organizations are outlined, and the issues to be solved on clearance are listed and the basic ideas for solution are discussed.
Tsutsumi, Masahiro; Oishi, Tetsuya*; Yamasoto, Kotaro; Yoshida, Makoto
JAERI-Research 2004-021, 43 Pages, 2004/12
JAERI-Research-2004-021.pdf:8.55MB
We have designed and developed a 
measurement system to certify radioactive wastes below the clearance level. By advancing non-destructive -ray assay technology, it aims at quantitative determination of radionuclides contained in 200 litter drum/container wastes. Unlike the waste from a nuclear power plant, you have to assume that the waste originating from radioisotope usage and nuclear research laboratory have a variety of contents and a complex mixture of radionuclides, and furthermore the uniformity of activity concentration is unknown. To cope with the problems, we have developed the -ray measuring instruments (units) with effective improvement of capability against each problem. They are (1) germanium spectrometry unit for enhanced peak identification, (2) positioning detection unit for positioning of interactions and (3)high-efficiency detection unit for separation of low-energy component. This report summarizes the direction of the clearance level measuring system and the three developed measuring units with their performances.
Okoshi, Minoru
Dekomisshoningu Giho, (26), p.2 - 12, 2002/11
The concept of clearance has been introduced by the International Atomic Energy Agency in 1996 and is very useful for the management of very low-level solid materials generating from the decommissioning of nuclear facilities. Therefore, the European Commission (EC) derived the specific clearance levels for metals, buildings and building rubble in RP 89 and 113, respectively. The EC also derived the general clearance levels for all solid materials generating from the regulated facilities in RP 122. Comparing the clearance levels of Japan with the unrounded levels of EC, the differences of levels are small. The biggest difference is found in Fe-55 and the EC's clearance level is about one fifth of Japanese clearance level. This is caused because the EC considers the direct ingestion of cleared building rubble by children and used the conservative ingestion rate of it. EC's discussions related to the clearance levels are very useful for Japan to derive our own clearance levels and to clear materials from regulatory control.
Sato, Shinichi*; Araki, Masanori; Omori, Junji*; Oono, Isamu*; Sato, Satoshi; Yamauchi, Michinori*; Nishitani, Takeo
JAERI-Tech 2002-083, 126 Pages, 2002/10
JAERI-Tech-2002-083.pdf:4.07MB
It is one of the foremost goals for ITER to demonstrate the attractiveness with regard to safety and environmental potential. This implies that the radioactive materials and waste at decommissioning phase should carefully be treated with prescribed regulations. As possible activities during the Coordinated Technical Activity (CTA), Japanese Participant Team (JA-PT) has proposed a study for searching the possibility of more reduction in the activated level by taking account of minimum material changes while keeping original design concept and structure. Based on it, reassessment of the activation level and the amount of activation volumes will give us positive aspects for public acceptance.
Okoshi, Minoru
Hoken Butsuri, 37(3), p.197 - 207, 2002/09
The concept of clearance has been introduced by IAEA in 1996 and is very useful for the management of very low-level solid materials generating from the decommissioning of nuclear facilities. Therefore, the Nuclear Safety Commission of Japan started the derivation of clearance levels for solid materials arising from nuclear reactors in 1997 and published the reports in 1999 and 2001, respectively. EC also published the several guides to clear metals, concrete, building and other solid materials from regulatory control. Some organizations including IAEA and USNRC are still discussing how to derive the clearance levels. In this exposition, the present status of clearance in Japan and other organizations and countries is summarized. And some information to realize the concept of clearance is given, and the problems related to the clearance are also discussed.
Tsutsumi, Masahiro; Oishi, Tetsuya; Kinouchi, Nobuyuki; Sakamoto, Ryuichi; Yoshida, Makoto
Journal of Nuclear Science and Technology, 39(9), p.957 - 963, 2002/09
Times Cited Count：3 Percentile：23.41(Nuclear Science & Technology)An anti-Compton spectrometer with semi-2
Compton suppression is designed to identify the photons emitted from low-level radioactive wastes from radioisotope usage and nuclear research laboratory. Since the objective sample is massive and large, the system has a full opening towards the sample position. The characteristics and features of the system concerning Compton suppression and reduction of the background component due to natural radioactive source are estimated by the Monte Carlo simulations. The anti-Compton technique is shown to be quite advantageous for the reduction of the surrounding natural background radiation, as well as the suppression of the background for the higher energy photons.
