Distribution of sealed sources in use or stored by user on-site in Republic of Bulgaria

Full text: Distribution of the sealed sources (SS) in use or stored by user on-site in Republic of Bulgaria has been determined by using the categorization system proposed by Institut National des Radioelements (IRE), Belgium. The criteria used to categorize the SS were the handling and monitoring equipment needed for dismantling, checking and treatment of spent sealed sources (SSS) before storage and/or final disposal. The categorization system was proposed as a basis for estimation of the needs of equipment for the new treatment and storage facility for SSS in the site of Novi Han radioactive waste repository. The categorization used to evaluate the distribution of SS in use or stored by user on-site is shown in Table I. Sealed sources are widely used in Bulgaria for industrial, medical, domestic and scientific purposes. Presently, the list of registered users of sealed beta-gamma and neutron SS consists of 387 industrial users, 78 research and control users and 14 medical users. In addition there are 48 registered users of Pu-239 static eliminators and an estimated number shows about 1000 users of Pu-239, Am- 241 or Kr-85 sources in smoke detectors. Wide range of activities with SS is controlled by CUEAPP, as license is required for use and/or storage by user of every single source. An electronic data base of the licenses for use of atomic energy is operated by CUAEPP. The investigation covered the sealed sources registered in the data base. The number of sources in different categories, their use and typical activity have been determined. The same approach has been used separately for sealed sources in use, as well as for spent sources stored by user on-site. Special attention has been paid to high activity gamma-sources used in teletherapy and irradiators, as their activities were corrected for radioactive decay (reference date: March 2001); the exact location and conditions of use or storage of every such source were established. As a result of the investigation the following main conclusions has been made: an enormously big share of spent sealed sources stored by user on site was determined, as for some types stored SSS are more than SS in use; big number of never used sources with expired recommended working life are stored by presently not working manufacturers of original equipment or construction companies; Pu-239 sources are widely used in smoke detectors and static eliminators, as Pu-239 was the preferable radionuclide for those purposes in the past; the problem of 'historical' Ra-226 in Bulgaria is insignificant; a relatively big number of Kr-85 sources are used, as the main use is in smoke detectors; big number of 'medium activity' (in the range of several TBq up to tens of TBq) Co-60 and Cs-137 sources are used in gamma-irradiators opposite to the Western practice of use of less number of sources with higher activity (hundreds of TBq). In addition improvements to the methodology of database handling were provided, and recommendations for future development were made. The results will be used by IRE, Belgium to prepare an assessment of the proposed design for a spent sealed sources treatment and storage facility at Novi Han as well as for planning the future management of SS in the country. (author)