Tendencies of occupational exposure at Ignalina NPP

Full text: Throughout the world, occupational exposures at nuclear power plants have been steadily decreasing for over a decade. Regulatory pressures, technological advances, improved plant designs, and improved operational procedures have contributed to this downward trend. However, with the ageing of the nuclear power plants the task of maintaining occupational exposures at low levels sometimes may become increasingly difficult. Lithuania has one nuclear power plant - Ignalina NPP, which contains two RBMK- 1500 reactors (actual thermal power output - 4200 MW, electrical power capacity - 1500 MW). The first Unit of Ignalina NPP went into operation at the end of 1983, the second Unit in August 1987. Due to unique construction, the occupational exposure doses for the reactors RBMK type are one of the highest if compared with other types of reactors. Due to effective implementation of the radiation protection programme, ALARA programme, use of work management (work planing) programmes and modernization of equipment used at the Ignalina NPP, occupational exposure doses have been decreasing during the period 1997 to 2001 (from total collective dose in 1997 - 18.51 man Sv to 6.27 in 2001). In 2002 the total collective dose was 7.33 man Sv, and 2003 - 8,53 man Sv. In the last two years a small increase of collective dose due to modernization and implementation of safety measures and larger amount of repair works has been observed at the first Unit of Ignalina NPP. The main work which contributed to the highest collective doses during last two years were: in the reactor vessel: maintenance, repairs, replacement of the reactor fuel channels; installation of the system of the additional emergency reactor protection; main circulation circuit: inspection of the primary system pipes d=300mm, d=800 mm, of drum separators, repairing of the primary system pipes; repairing of the reactor equipment and refuelling; insulation works; installation of the temporary shielding; rooms decontamination; other general work. Proper implementation of work cannot be guaranteed without effective implementation of a valid radiation protection programme. Basic regulations which establishes requirements for radiation protection of workers working at the nuclear power plant and for radiation protection of members of the public during the nuclear power plant operation, is the 'Lithuanian Hygiene Standard HN 87:2002, Radiation Protection at Nuclear Power Plant'. It was approved by the Order of the Minister of Health and came into force on 1 April 2001. According to this Hygiene Standard, practices at the nuclear power plant shall be authorized and conducted in accordance with the basic radiation protection principles: justification of the operation of radiation sources, optimization of exposure and limitation of doses. The license holder shall ensure that doses of NPP workers do not exceed the determined limits of occupational exposure, with the exception of cases, when special conditions are applied. The daily effective dose constraint established by the license holder for Ignalina NPP workers is 0.2 mSv. According to the requirements set out, the radiation protection programme shall be established at the plant. Following items shall be included in the programme: classification of working areas and access control; local rules, measures of supervision of safety at work and order of organization of work; procedures of monitoring of workplaces and individual monitoring of workers; individual protective equipment and rules for their application; main premises, control systems for assurance of radiation protection; requirements for management of radioactive waste; radiation protection in the case of accident; application of optimization principle (ALARA) and measures on exposure reduction; programs of health surveillance; mandatory training of workers and their instructions. The charts, dose analysis and implemented measures for reducing occupational doses will be presented in the poster. (author)