On the 19th of June 2017, the first domestic commercial reactor Kori-1 in Korea was shut down after 40 years of operation since April 1978. Nuclear decommissioning of the Kori-1 will proceed for at least 15 years in the future, and according to the current plan proposed, fuel cooling will be perform...
On the 19th of June 2017, the first domestic commercial reactor Kori-1 in Korea was shut down after 40 years of operation since April 1978. Nuclear decommissioning of the Kori-1 will proceed for at least 15 years in the future, and according to the current plan proposed, fuel cooling will be performed during 2018~2022, decontamination and dismantling of reactor will be performed during 2022~2028, and site restoration will be done by 2032. The Kori-1 reactor is largely composed of a primary system and a secondary system. The primary system is composed of a nuclear reactor which operates fission reactions, a steam generator which delivers generated heat from the nuclear reactor to the coolant, a pressurizer, and a coolant pump. The secondary system is composed of a turbine, a generator, a condenser, and a feed water pump. Among the diverse devices and parts, the steam generator was selected for research. The reasons as to why are listed as follows:
1) It is a huge structure with a height of about 20 m, a top diameter of 6m and weighing about 700 tons.
2) It is a large metal waste, which changes in value depending on its dismantling and decontamination methods.
3) There is a relatively low level of radioactivity compared to reactors, which makes it possible for workers to work directly.
4) It is difficult to secure the data, the situation, and the environment since the contents such as the arrangements and specifications of the equipment inside the nuclear power plant are confidential. However, in 1998, the steam generator of the Kori Unit 1 was replaced, and further research, calculation, and evaluation could be conducted. Considering these four points in a comprehensive manner, the steam generator in the first line of Kori Unit 1 was selected as the main analysis and evaluation subject.
Necessary information such as the radioactive nuclides and nuclide radioactivity contamination level to calculate exposure dose of worker, was secured with reference to the ‘surface radiation dose rate evaluation of steam generator in Kori-1 for replacement’. Another necessary information to calculate the external and internal exposure dose, working hours and working distance between contamination object and worker, was secured from a steam generator replacement plan and steam generator replacement operation licensing documents and from the real decommissioning operation, proceeding in the V1 reactor in Slovakia. Based on these materials, I postulated the working hours and working distance for each working process. The Kori-1 steam generator nuclear decommissioning work is largely divided into 3 parts, which includes decomposition, cutting, and decontamination of the fixed steam generator. External and internal exposure dose of workers about each virtual operation was calculated, and in the case of external exposure, VISIPLAN produced by SCK∙CEN in Belgium was used, and in the program, the geometry of the steam generator was described and needed information such as the 13 nuclides’ radioactivity and worker’s working time and distance for every operation was included.
Using a simulation function in VISIPLAN, the external exposure dose result was calculated for each work operation. Internal exposure dose was calculated by using information like the internal exposure dose calculation formula for cases of inhalation and ingestion, provided by the IAEA safety guide. Radioactivity level change of nuclide in cutting or decontamination process was also reflected in exposure dose calculation. For the cutting operation, consideration to additional exposure by inner tube contamination was set with reference in radioactivity measurement of collected tube sample in steam generator of Dampierre 1 reactor in 1992, France. Applying the same ratio radioactivity contamination and assuming tube inner contamination level, worker exposure dose calculation was conducted for the cutting operation. For the decontamination operation, using the decontamination factor by each decontamination technologies and process, and radionuclide partitioning factors, the radioactivity level was postulated per radionuclides.
Through these processes, the expected kori-1 steam generator decomposition, cutting, and the decontamination operation was set, and worker external and internal exposure dose and radioactivity contribution rate per radionuclide was calculated. By doing these, understanding the upcoming steam generator decommissioning operation process was possible, and utilization of worker exposure calculation and evaluation could be helpful to an uncertain decommissioning operation plan establishment, operation risk evaluation, possible operation classifications, worker participation rate control and so on. Finally, I hope the first domestic nuclear power plant decommissioning would be successful, and taking the head of the world nuclear decommissioning market by outstanding techniques and safety measures.
On the 19th of June 2017, the first domestic commercial reactor Kori-1 in Korea was shut down after 40 years of operation since April 1978. Nuclear decommissioning of the Kori-1 will proceed for at least 15 years in the future, and according to the current plan proposed, fuel cooling will be performed during 2018~2022, decontamination and dismantling of reactor will be performed during 2022~2028, and site restoration will be done by 2032. The Kori-1 reactor is largely composed of a primary system and a secondary system. The primary system is composed of a nuclear reactor which operates fission reactions, a steam generator which delivers generated heat from the nuclear reactor to the coolant, a pressurizer, and a coolant pump. The secondary system is composed of a turbine, a generator, a condenser, and a feed water pump. Among the diverse devices and parts, the steam generator was selected for research. The reasons as to why are listed as follows:
1) It is a huge structure with a height of about 20 m, a top diameter of 6m and weighing about 700 tons.
2) It is a large metal waste, which changes in value depending on its dismantling and decontamination methods.
3) There is a relatively low level of radioactivity compared to reactors, which makes it possible for workers to work directly.
4) It is difficult to secure the data, the situation, and the environment since the contents such as the arrangements and specifications of the equipment inside the nuclear power plant are confidential. However, in 1998, the steam generator of the Kori Unit 1 was replaced, and further research, calculation, and evaluation could be conducted. Considering these four points in a comprehensive manner, the steam generator in the first line of Kori Unit 1 was selected as the main analysis and evaluation subject.
Necessary information such as the radioactive nuclides and nuclide radioactivity contamination level to calculate exposure dose of worker, was secured with reference to the ‘surface radiation dose rate evaluation of steam generator in Kori-1 for replacement’. Another necessary information to calculate the external and internal exposure dose, working hours and working distance between contamination object and worker, was secured from a steam generator replacement plan and steam generator replacement operation licensing documents and from the real decommissioning operation, proceeding in the V1 reactor in Slovakia. Based on these materials, I postulated the working hours and working distance for each working process. The Kori-1 steam generator nuclear decommissioning work is largely divided into 3 parts, which includes decomposition, cutting, and decontamination of the fixed steam generator. External and internal exposure dose of workers about each virtual operation was calculated, and in the case of external exposure, VISIPLAN produced by SCK∙CEN in Belgium was used, and in the program, the geometry of the steam generator was described and needed information such as the 13 nuclides’ radioactivity and worker’s working time and distance for every operation was included.
Using a simulation function in VISIPLAN, the external exposure dose result was calculated for each work operation. Internal exposure dose was calculated by using information like the internal exposure dose calculation formula for cases of inhalation and ingestion, provided by the IAEA safety guide. Radioactivity level change of nuclide in cutting or decontamination process was also reflected in exposure dose calculation. For the cutting operation, consideration to additional exposure by inner tube contamination was set with reference in radioactivity measurement of collected tube sample in steam generator of Dampierre 1 reactor in 1992, France. Applying the same ratio radioactivity contamination and assuming tube inner contamination level, worker exposure dose calculation was conducted for the cutting operation. For the decontamination operation, using the decontamination factor by each decontamination technologies and process, and radionuclide partitioning factors, the radioactivity level was postulated per radionuclides.
Through these processes, the expected kori-1 steam generator decomposition, cutting, and the decontamination operation was set, and worker external and internal exposure dose and radioactivity contribution rate per radionuclide was calculated. By doing these, understanding the upcoming steam generator decommissioning operation process was possible, and utilization of worker exposure calculation and evaluation could be helpful to an uncertain decommissioning operation plan establishment, operation risk evaluation, possible operation classifications, worker participation rate control and so on. Finally, I hope the first domestic nuclear power plant decommissioning would be successful, and taking the head of the world nuclear decommissioning market by outstanding techniques and safety measures.
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