Radiological work management aspects influencing dose reduction at the Ignalina NPP during outages and coming decommissioning

Lithuania has few nuclear facilities. There are two non-upgradable nuclear reactors of RBMK-1500 series [light water-cooled graphite-moderated channel type reactors, LWGR (RBMK)]. Also one on-site dry spent nuclear fuel interim storage facility is located at Ignalina NPP. All these facilities are located in the north-eastern part of Lithuania, near the borders with Belarus and Latvia, 160 km distance from the capital city Vilnius, on the banks of the lake Druksiai. The first Unit of Ignalina NPP went into operation at the end of 1983, the second Unit in August 1987. Lithuania signed a Nuclear Safety Grant Agreement in 1994 stating, inter alfa, the commitment of the Republic of Lithuania to close both units of the Ignalina NPP at the time of so called 'gap closure' and therefore not to use the designed technical lifetime of the reactor units by re-channeling the fuel channels. The decision to shut down the Unit 1 is already taken by law, and it is planned to stop the Unit 1 before the 1 January 2005. in November 2002 the Government of Lithuania adopted the decision which states that preferred option for the decommissioning of Unit 1 is the immediate dismantling. It means that the process of dismantling of the Unit 1 will start right after shutdown of the reactor and the process will continue at least for 30 years. From the radiological point of view, this process can be treated as big extended outage of the unit with constantly changing working environment that might cause high individual and collective doses to the workers. The draft of the Final. Decommissioning Plan, as a part of the licensing requirements needed to start the decommissioning process, already exists. It has been preliminary estimated by the operator that during immediate dismantling of the Unit 1, the total exposure approximately will result in 35 manSv. Due to unique construction, the occupational exposure results for the reactors of RBMK (LWGR) type are one of the highest if comparing with reactors of other types. The outages of both units each year usually last 2-4 months. The main 'contributors' to the annual collective dose are the annual outages of the units. Keeping the occupational exposure in accordance with legal requirements, the operator needs to establish an effective radiological work management programme during the outage periods, which shall serve as a part of the radiation protection programme. Both legal requirements and practical experiences applied at Ignalina NPP related to radiological work management aspects influencing close reduction during outages and radiation protection measures planned to be applied during coming decommissioning of both units is discussed in the paper. (author)