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Abstract: This paper suggests the estimation algorithm for life time of structure, system and components (SSCs) for decommissioning safety of nuclear facilities using the performance data of linguistic languages and fuzzy theory. The fuzzy estimation algorithm of life time can be easily applicable but the estimated results depend on the relevant membership functions and performance characteristic functions. This method will be expected to be very useful for maintenance and decommissioning of nuclear facilities’ SSCs as a safety assessment tool. [Copyright &y& Elsevier]

Abstract: This paper proposes a model for the quantification and estimating the radiological risks of decommissioning processes in nuclear facilities. Based on fuzzy linguistic variables, the membership function and inference rules were developed for quantifying the radiological risks of nuclear decommissioning processes. Also, the fuzzy inference system was developed and the proposed method was applied to the process of concrete decommissioning. The proposed model and system is flexible in that it allows a fast-computation of the subjective expert opinion when one or several input factors change. It is believed that the suggested model and system can be applied to evaluate the safety of complex systems by only changing the variable and inputs. [Copyright &y& Elsevier]

Abstract: This paper proposes the estimation method on probability of decommissioning hazards for nuclear facilities. Evaluation method of decommissioning hazardous accidents is based on fuzzy and event tree method. Expert’s knowledge was considered as state of the basic variable with a normal distribution, which was considered to represent the membership function. The proposed method has been successfully applied to the removal of rotary specimen rack in KRR-2. [Copyright &y& Elsevier]

Abstract: A decommissioning plan should be followed by a qualitative and quantitative safety assessment of it. The safety assessment of a decommissioning plan is applied to identify the potential (radiological and non-radiological) hazards and risks. Radiological and non-radiological hazards arise during decommissioning activities. The non-radiological or industrial hazards to which workers are subjected during a decommissioning and dismantling process may be greater than those experienced during an operational lifetime of a facility. Workers need to be protected by eliminating or reducing the radiological and non-radiological hazards that may arise during routine decommissioning activities and as well as during accidents. The risk assessment method was developed by using risk matrix and fuzzy inference logic, on the basis of the radiological and non-radiological hazards for a decommissioning safety of a nuclear facility. Fuzzy inference of radiological and non-radiological hazards performs a mapping from radiological and non-radiological hazards to risk matrix. Defuzzification of radiological and non-radiological hazards is the conversion of risk matrix and priorities to the maximum criterion method and the mean criterion method. In the end, a composite risk assessment methodology, to rank the risk level on radiological and non-radiological hazards of the decommissioning tasks and to prioritize on the risk level of the decommissioning tasks, by simultaneously combining radiological and non-radiological hazards, was developed. [ABSTRACT FROM AUTHOR]

Abstract: As part of a fundamental research for the volume reduction of dismantled concrete, an investigation was carried out addressing the separation of the aggregates and the distribution of the radioactivity into the aggregates of contaminated concrete generated from dismantled nuclear facilities. Radioisotope 60Co was artificially used as a model contaminant for non-radioactive crushed heavy weight concrete taken from the Korea Research Reactor 2 (KRR-2) and light weight concrete from the uranium conversion plant (UCP) by thermal and mechanical treatment. The results showed that most of the 60Co nuclide was easily separated from the gravel and aggregate, and concentrated mainly into the porous fine cement paste. By thermal and mechanical separation treatment, the clean aggregate can be recovered up to 80% from radioactively contaminated concrete waste. The final wastes of formed cement paste were produced by thermal and mechanical treatment. Heavy and light cement pastes were vitrified. Volume reductions of the cement pastes were achieved at about 1/3 and 1/2.5, respectively. [Copyright &y& Elsevier]

Abstract: Vertical electrokinetic-flushing equipment suitable to the geological characteristics of Korean nuclear facility sites was developed for the decontamination of some real radioactive soil. The optimum reagent and electric current were chosen through vertical electrokinetic-flushing experiments. The effect of the particle size of some soil and the radioactive concentration of some soil on the removal efficiencies of the nuclides from said soil were analyzed. The experimental results are as follows. The removal efficiencies of 60Co and 137Cs by nitric acid were increased by 3.3% and 2.0% more than those by acetic acid. And, moreover, when nitric acid instead of acetic acid was used, it had the advantage of a reduction of the electricity consumption due to its higher electrolytic conductivity. The higher the radioactivity concentration of the soil was, the higher the removal efficiencies of 60Co and 137Cs were. Namely, the removal efficiencies of 60Co and 137Cs from the soil of a high concentration (2850Bq/kg) were increased by 13.7% and 3.9% more than those from the soil of a low concentration (135Bq/kg). The larger the particle size of the soil was, the higher the removal efficiency of 137Cs was. Namely, the removal efficiency of 137Cs from the soil of average 1.2mm particle size was increased by about 2% more than that from the soil of average 0.6mm particle size. Also, the removal efficiencies of 60Co and 137Cs by the application of an electric current of 20mA/cm2 were increased by 1.3% and 4.2% more than those by the application of 10mA/cm2. The removal efficiencies of 60Co and 137Cs from the radioactive soil of 1825Bq/kg were 99.9% and 94.3% by an electrokinetic-flushing decontamination by the application of an electric current of 20mA/cm2 for 50 days. [Copyright &y& Elsevier]