천연방사성물질 취급 국내 주요산업체에 대한 안전관리 방안 연구

Abstract

ABSTRACT

Study of the NORM Safety Management for Major Domestic NORM Industry

Kim Ha Im Advisor : Prof. Lee Gyeong Jin, Ph.D. Department of Nuclear Engineering Graduate School of Chosun University

In 2011, low level radiation dose was detected from the asphalt on the road of Weolgae-dong in Seoul. The asphalt was made of recycled scraps of imported steel which is categorized as NORM(Naturally Occurring Radioactive Material). Since then, it has become an emerging environmental and social issue of ensuring radiation safety in the neighborhood of individual life. The government enacted the‘NORM Safety Management Law’ in 2012 to protect the environment and people from radiation exposure in their everyday life. As ‘NORM Safety Management Law’was established and implemented, it became a radiation safety issue for the NORM industries which handle large amount of raw materials with NORMs and process residues(technically enhanced NORM, TENORM) to understand the behavior of the industrial NORM and manage the NORM processes and radiation exposures of the workers. Therefore, it is necessary to perform on-site survey for major NORM industries thus improving the working environment in order to protect workers from radiation exposure. Until now, studies on the safety management of NORM process residues are performed by analyzing first radionuclide behavior and then the safety management practices of the NORM industries. Two steps were developed for the on-site radiation survey and characterization of the NORMs; Preliminary discussions with NORM industry for the needs of the on-site radiation survey for the NORM safety management and developing procedures for the on-site radiation survey after reviewing the process flows and work environments. On-site radiation survey methodology has been developed for a chemical plant manufacturing aluminum hydroxide and calcined aluminium from Bauxite as follows: (1) Real-time radiation dose measurement of raw materials and NORMs using Inspector 1000-NaI γ-ray detector; (2) Measurement of ambient particle size distribution and radioactive nuclide concentration using Cascade Impactor at work places with dust using Cascade Impactor; (3) Measurement of accumulated doses of workers using Glass Dosimeter in places where the workers are exposed to NORMs for a long period of time; (4) Quantitative analysis of radioactive nuclide and radioactivity concentrations of the raw materials as well as the field NORM samples including process residues and scales. As a result of the on-site measurements and quantitative analyses of NORM sample for the aluminum hydroxide and calcined aluminum manufacturing plant, a maximum of 0.46 mSv/y radiation dose was measured at the open residue storage. This is lower than the 1.0 mSv/y annual dose limit for the general public. The measured radioactivity concentration of the Bauxite was 0.1056 Bq/g for 238U and 0.1625 Bq/g for 232Th, respectively, which are higher than the raw material radioactivity concentration of 0.1 Bg/g. For pipe scales, the measured radioactivity concentration was 0.8575 Bq/g for 238U, which is higher than the definition of NORM, which is 0.5 Bg/g. Both Bauxite and pipe scales of the chemical plant manufacturing aluminum hydroxide and calcined aluminum from Bauxite can be defined as raw material and NORM as defined in the “NORM Safety Management Law” but not required for the registration since the annual total radioactive concentrations are less than the limit set by Article 4 of “NORM Safety Management Law” The NORM process characteristics and safety management practices of the NORM industry were studied through on-site radiation survey and quantitative analyses for a chemical plant manufacturing aluminum hydroxide and calcined aluminum from Bauxite. Through the investigation of the on-site radiation survey and quantitative analyses of a major NORM industry, important NORM safety management issues were identified and comprehensive NORM safety management strategies were proposed in this study. In the future, this study can be further applied to investigate the NORM process characteristics and develop NORM safety management and regulatory guidelines for he domestic NORM industries. Therefore, the results of the study can be utilized to improve working environment as well as the workers’ radiation exposures at the NORM industries and thus promotes public acceptance of the NORM safety.