atw - International Journal for Nuclear Power | 05.2019

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atw Vol. 64 (2019) | Issue 5 ı May DECOMMISSIONING AND WASTE MANAGEMENT 272 Therefore, in the preliminary DP it is necessary to identify all construction and operation data that are important to evaluate the radiological characteristics of facility and site, and describe the method of systematically managing these data in operation stages. These data are used as the important input for radiological characterization during the decommissioning phase. According to experience of decommissioning at home and abroad, the following data are expected to be necessary for the evalu ation of radiological characteristics [5, 6]. pp Radiation distribution inside and out side the decommissioning facility. pp Contamination degree and contamination distribution. pp Nuclide inventory. pp Radionuclide type, radioactivity and distribution. pp Justification of measurement point through prior sampling. In particular, the design provisions should be reflected in the reduction of radiation exposure of workers and the ease of sampling when performing these radiological characterization works. 3.5 Decommissioning strategy and method 3.5.1 Decommissioning strategy The decommissioning strategy is a general plan to achieve the successful decommissioning, and is set con sidering the decommissioning policy, the decommissioning method and the final goal of the decommissioning [3]. The decommissioning operator may determine ‘immediate decommis sioning’ or ‘delayed decommissioning’ as the decommissioning strategy through a review of the adequacy evaluation considering the following factors or may decide a third alter native that combines ‘ immediate’ and ‘delayed decommissioning’. National decommissioning policy. pp Laws, regulations and standards to be applied to the decommissioning activity. pp Facility characteristics, operation history, radioactivity inventory and its change with time. pp Radiological and conventional safety assessment. pp Spent fuel and decommissioning waste management. pp Change of facility physical conditions during the decommissioning period. pp Appropriateness and availability of decommissioning resources. pp Availability of experienced personnel and proven technologies. pp Lessons learned from past decommissioning projects. pp Residents’ concerns, including their social and economic impact on the community. pp Influence of several units within the site. pp Plan of reuse of site or facility (part of facility) after completion of decommissioning. pp Stakeholder interaction. The decommissioning operator should show in the preliminary DP that the strategy has been established by appropriately reflecting all above factors necessary for the strategy establishment. 3.5.2 Decommissioning method and schedule The decommissioning method and the schedule should be described roughly in accordance with the selected decommissioning strategy in the preliminary DP. It is necessary to define the decommissioning activities for each decommissioning step based on the decommissioning method, and the decommissioning schedule should be provided as the project milestone level [5]. The comprehensive decommissioning schedule as the milestone level can show the optimal timetable for decommissioning sequences considering the decommissioning stra tegy, the execution of major activities, and legal requirements. This should enable us to understand the overall decommissioning activities to be carried out during the entire decommissioning period. The schedule development helps to efficiently utilize decommissioning resources and is also useful for estimating decommissioning cost. Therefore, the following key factors should be considered when establishing the schedule. pp Decommissioning strategies and methods, experience/knowledge data. pp Decommissioning waste management. pp Decommissioning scenario. pp Spent fuel transportation schedule and availability of transport/storage casks. pp Availability of domestic decommissioning technology/manpower. pp Availability of decommissioning supply chains. pp Financial constraints. pp Political and social environment. 3.6 Design characteristics and measures for the decommissioning facilitation 3.6.1 Design characteristics The preliminary DP should describe the information related to the “design characteristics for the decommissioning facilitation” as follows [3]. pp Access way for equipment maintenance and laydown space for equipment replacement, which can be used as a decommissioning work space in the decommissioning phase. pp Design characteristics to minimize the radioactive contamination and the leakage of radioactive materials from the radioactive systems. pp Minimization of concrete buried pipes and ducts. pp Minimization of underground radioactive waste tanks, sumps and pipes. pp Impurities management in steel and concrete materials to prevent the generation of activation products that affect decommissioning work. pp Equipment layout considering ALARA guideline when replacing equipment. Therefore, the preliminary DP should also outline the following management plans and explain how to maintain its design characteristics. pp Management plan of the facility configuration management system (CMS) and their records during the operation phase. pp Management plan of the radioactive material leakage management system and their records during operation phase. pp Management plan of the design characteristics for the decommissioning facilitation during the operation phase. 3.6.2 Design measures to minimize radioactive material leakage, radioactive contamination and radioactive waste generation during the operation Actions to be performed at the construction and operation phase of a nuclear facility should be provided to confirm the minimization of radioactive material leakage, radioactive contamination and radioactive waste generation, which can be prepared for the future decommissioning as follows [5, 6]; pp Design information on on-site surveillance systems that can detect leakage and contamination Decommissioning and Waste Management Guideline to Prepare a Preliminary Decommissioning Plan for Nuclear Facilities in Republic of Korea ı Byung-Sik Lee and Kyung-Woo Choi
atw Vol. 64 (2019) | Issue 5 ı May from underground and concrete buried pipes early. pp Design information on separation and collection of radioactive waste and non-radioactive waste. Such information is used as input data such as “safety assessment” and “ radioactive protection plan” establishment. Therefore, it is needed to describe the information such as incidents and accidents that contaminated a facility and a site during the operation period of nuclear facility, which can affect decommissioning activities. 3.7 Safety assessment Existing safety related systems and engineered safety features are dismantled and altered through the decommissioning of a nuclear facility. Therefore, the safety assessment of the decommissioning phase is limited to the effects of dismantling equipment, installing new systems, or changing existing systems. According to the overseas decommissioning experience, the decommissioning stage generally carries out a safety assessment of the following events [3, 7]: pp Fire in facility. pp Leaks from container or system. pp Heavy material drop. pp Supply system failure. pp Criticality accident. pp Intrusion of water into a facility with delayed decommissioning. pp External accidents (that is earthquakes, storms, floods etc.). Radioactive material leakage prevention and mitigation systems, which are operating at the operational stage of a nuclear facility, are not operated any more due to power supply interruption or demolition at the disassembly stage. Therefore, it is necessary to partially localize the contaminated area during dismantling work or to install an additional mobile exhaust system. Especially when the exhaust system fails due to fire, “fire” will become a radiological representative design basis accident. It is necessary to describe the development of scenarios for these various accidents, the evaluation methodology for them, and describe the methods of preventing and mitigating accidents. 3.8 Radiation protection A radiation protection plan during the decommissioning phase should be established to identify major issues affecting worker exposure by decommissioning activities. In general, the radiation protection plan should include the following [3, 4]: pp Prediction and minimization of radiation exposure of workers. pp Radiation safety management plan during decommissioning work. pp For the various decommissioning options, prediction of the expected dose and measures to comply with the ALARA guidelines through decommissioning radiation management. When establishing the preliminary DP, the radiation protection plan is described as follows by establishing a radiation safety management plan that minimizes the workers’ exposure. pp Establishment of radiation protection policy and application of ALARA guidelines. pp Radiation Safety Plan during decommissioning activities. pp Monitoring plan of special radiation dose and air contamination in the workplace. pp Plan for entry and exit of workers and equipment. pp Evaluation and selection of radiation protection tools. 3.9 Decommissioning activity There are many decontamination, dismantling and demolition techniques necessary for the decommissioning of nuclear facilities, which depends on the type of facilities (types of radioactive contaminations, degree of contamination), regulatory clearance and removal of radionuclides. Therefore, proper decommissioning techniques should be selected considering the characteristics of decommissioning activities and contents of each decommissioning stage [4]. When decommissioning techniques (or potential decommissioning techniques) are selected, consider the following points. pp Safety, pp Efficiency, pp Cost-effectiveness, pp Waste minimization, pp Feasibility of industrialization. The decommissioning operator should identify the status of proven decommissioning technologies and potential decommissioning technologies, and periodically review these decommissioning technologies from the viewpoint of technology availability. Therefore, it is necessary to investigate the optimal decommissioning techniques from the above five perspectives based on the time of preparation of the preliminary DP, and describe them in the preliminary DP. And it is necessary to outline the decommissioning execution plan using these techniques. 3.10 Radioactive waste management In Korea, the decommissioning waste management cost accounts for about 40% of total decommissioning cost. Therefore, it is necessary to establish a decommissioning waste management plan and make every effort to minimize the amount of radioactive waste generated during the decommissioning phase. To this end, decommissioning waste management in the preliminary DP is considered for the as following points, and they should be outlined in the preliminary DP [3]: pp Management plan of radioactive waste generated during operation of nuclear facilities including spent fuel before entering decommissioning activity. pp Review of decommissioning waste management plan including sorting/disposal method, recycling method, volume reduction method by cost/benefit analysis. pp Operation plan review of decommissioning waste comprehensive treatment facility. pp Estimation and confirmation of total decommissioning wastes. pp Comprehensive plan for removal and disposal of large-sized equipment. The decommissioning waste management plan is closely related to the national waste management policy and should therefore be taken into account. The preliminary DP outlines the radioactive waste management based on the following technical review: pp Waste classification. pp Evaluation of liquid/solid waste treatment technology. pp Evaluation of waste characteristics technology. pp Utilization and disposal plan of clearance wastes. pp Management plan of non-radioactive waste in the decommissioning of nuclear facilities. 3.11 Environmental impact assessment The population exposure is assessed in the radiological environmental impact assessment due to the release of radioactive materials to the environment during the decommissioning phase. In the assessment, it is necessary to evaluate the environmental impacts of decommissioning period by using survey data of environmental characteristics such as terrain and DECOMMISSIONING AND WASTE MANAGEMENT 273 Decommissioning and Waste Management Guideline to Prepare a Preliminary Decommissioning Plan for Nuclear Facilities in Republic of Korea ı Byung-Sik Lee and Kyung-Woo Choi
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