[en] As part of a fundamental study on the volume reduction of contaminated concrete wastes, the separation characteristics of the aggregates and the distribution of the radioactivity in the aggregates were investigated. Radioisotope ⁶⁰Co was artificially used as a model contaminant for non-radioactive crushed concrete waste. Volume reduction for radioactively contaminated dismantled concrete wastes was carried out using activated heavy weight concrete taken from the Korea Research Reactor 2 (KRR-2) and light weight concrete from the Uranium Conversion Plant (UCP). The results showed that most of the ⁶⁰Co nuclide was easily separated from the contaminated dismantled concrete waste and was concentrated mainly in the porous fine cement paste. The heating temperature was found to be one of the effective parameters in the removal of the radionuclide from concrete waste. The volume reduction rate achieved was above 80% for the KRR-2 concrete wastes and above 75% for the UCP concrete wastes by thermal and mechanical treatment

[en] The evaluation of decommissioning scenarios is critical to the successful development and execution of a decommissioning project. This paper presents the logical method that is the analytic hierarchy process for selecting a decommissioning scenario. The AHP provides a structure on decision-making processes where there are a limited numbers of choices but each as a number of attributes. In this study, the AHP model to evaluate decommissioning scenarios reflecting quantitative and qualitative considerations is presented. This AHP model is implemented for the two candidate scenarios of the thermal column in KRR-1 to find the better scenario. The weightings of each criteria and subcriteria and the quantitative figures about both scenarios were obtained

[en] At present, two research reactors are operated at the Korea Atomic Research Institute, namely, one being a TRIGA Mark-II reactor of 250-kW power rating and the other a TRIGA Mark-III reactor of 2 MW, both of General Atomic design. Design characteristics and operations for the reactors are reviewed

[en] Optimum solidification for slurry waste, produced during the operation of KRR-1 and 2, with ordinary Portland cement was investigated. Waste form was prepared by changing the ratio of slurry waste/water/cement. Waste forms were evaluated by workability test, compressive strength test, free standing water test, and immersion test. The experimental results showed that the optimum mixing ratio of slurry waste (dry wt)/water/cement(dry wt) was found to be 0.32/0.34/0.34. The effect of the chemical (EDTA complex, low conc.) in water on waste forms was insignificant

[en] During the decommissioning activities of the KRR-1 and 2 (Korea Research Reactor 1 and 2) and UCP (Uranium Conversion Plant), all information and data, which generated from the decommissioning project, were record, input and managed at the DECOMMIS (DECOMMissioning Information management System). This system was developed for the inputting and management of the data and information of the man-power consumption, operation time of the dismantling equipment, the activities of the radiation control, dismantled waste management and Q/A activities. When a decommissioning is planed for a nuclear facility, an investigation into the characterization of the nuclear facility is first required. The results of such an investigation are used for calculating the quantities of dismantled waste volume and estimating the cost of the decommissioning project. That is why, the DEFACS (DEcommissioning FAcility Characterization DB System) was established for the management of the facility characterization data. The DEWOCS (DEcommissioning WOrk-unit productivity Calculation System) was developed for the calculation of the workability on the decommissioning activities. The work-unit productivities are calculated through this system using the data from the two systems, DECOMMIS and DEFACS. This result, the factors of the decommissioning work-unit productivities, will be useful for the other nuclear facility decommissioning planning and engineering. For this, to set up the items and plan for the decommissioning of the new objective facility, the DEMOS (DEcommissioning work Modeling System) was developed. This system is for the evaluation the cost, man-power consumption of workers and project staffs and technology application time. The factor of the work-unit productivities from the DEWOCS and governmental labor cost DB and equipment rental fee DB were used for the calculation the result of the DEMOS. And also, for the total system, DES (Decommissioning Engineering System), which is now developing for the decommissioning design and plan

[en] Experimental result on power control for a research reactor is presented. Considering various design features for reactor safety, we developed a simple and easy-to implement controller with a limiting function of power change- rate as well as fine tracking performance. The proposed controller has been designed, simulated, and applied to TRIGA-II type research reactor successfully. A power control method for a TRIGA-II type research reactor has been designed, simulated, and applied to actual reactor. The control performance during commissioning test shows that the proposed controller provides fine control performance for various changes in reference values (PDM). Further research may include model-based approach with proper robustness to disturbances.

[en] The computer system for the characterization on the nuclear facilities is established as the name of the DEFACS (DEcommissioning FAcility Characterization DB System). his system is consist of the four main part with the grouping of the items and it's code creation and management system, data input system, data processing and data out put system. All the data was processed by a simplified and formatted manner to provide useful information to the decommissioning planner. The four nuclear facilities are objected for the system; the KRR-1 and 2 (Research reactor), Uranium conversion plant (Nuclear chemical plant), UF4 pilot plant and the North Korea nuclear facility (5MWe Research Reactor). All the data from a nuclear facility was categorized and inputted into the several data fields in the input system, which were chosen by considering the facility characteristics. All the hardware is workstation for Web and DB server and PC grade computers for the users and the software 'ORACLE, RDBMS 11g' operated on the WINDOW 2008 O/S, was selected

[en] Irradiated graphite arising from the decommissioning of KRR-2 (Korean Research Reactor 2) have shown to include somewhat degree of Wigner energy, specific radioactivity and the resulting radioactive chemicals/nuclides in the study of bulk mode of graphite structure. Plans of annealing and disposal of the irradiated graphite stored Wigner energy in its internal matrix of rearranged carbon structures due to neutron dose might depend on whether the storage stability of the graphite is attainable or not. That is, because the Wigner energy as a latent explosive energy in the graphite structure was caused by carbon atomic rearrangements or dimensional distortions in the graphite crystal lattice is very labile at higher temperature conditions than that of its formation, why it is of importance to forecast the thermal stability of the graphite in a long term storage. Moreover, since the nuclide emissions are directly related to the thermal stability of the graphite at the same time in view point of graphite disposal, the control of Wigner energy content in a lower level or naught in the waste program of the irradiated graphite might be necessary in the near future. A study on fire accident model as an emergency case analysis at a sudden external fire exposure of the irradiated graphite was proposed to assess the feasibility of the disposal storage of the graphite without any physical and/or chemical treatment of Wigner energy in the form of box disposal. In this study a fire accident model of the irradiated graphite, that is to be disposed in the radioactive waste storage facility in the forthcoming time, was considered to estimate the thermal stability of graphite, whether the Wigner energy of the irradiated graphite has an effect on the storage stability or not, in front of a sudden fire accident

[en] KAERI is the only expert group which has decommissioning experiences and KAERI is trying to develop computer code to converge all the data which has been accumulated during KRR (Korea Research Reactor)-1 and 2 and UCP (Uranium Conversion Plant) decommission. This paper contains validation results of the KAERI DES by using KRR-2 decommissioning data. As a responsible leading group of Korean decommissioning research field, KAERI has been developing DES application program. One of decommissioning experience data, KRR-2 was used for KAERI DES validation and it successfully is reflected in KAERI DES

[en] The first research reactor in Korea, KRR 1, is a TRIGA Mark II type with open pool and fixed core. Its power was 100 kWth at its construction and it was upgraded to 250 kWth. Its construction was started in 1957. The first criticality was reached in 1962 and it had been operated for 36,000 hours. The second reactor, KRR 2, is a TRIGA Mark III type with open pool and movable core. These reactors were shut down in 1995, and the decision was made to decommission both reactors. The aim of the decommissioning activities is to decommission the KRR 2 reactor and decontaminate the residual building structures and site, and to release them as unrestricted areas. The KRR 1 reactor was decided to be preserve as a historical monument. A project was launched for the decommissioning of these reactors in 1997, and approved by the regulatory body in 2000. A total budget for the project was 20.0 million US dollars. It was anticipated that this project would be completed and the site turned over to KEPCO by 2010. However, it was discovered that the pool water of the KRR 1 reactor was leaked into the environment in 2009. As a result, preservation of the KRR 1 reactor as a monument had to be reviewed, and it was decided to fully decommission the KRR 1 reactor. Dismantling of the KRR 1 reactor takes place from 2011 to 2014 with a budget of 3.25 million US dollars. The scope of the work includes licensing of the decommissioning plan change, removal of pool internals including the reactor core, removal of the thermal and thermalizing columns, removal of beam port tubes and the aluminum liner in the reactor tank, removal of the radioactive concrete (the entire concrete structure will not be demolished), sorting the radioactive waste (concrete and soil) and conditioning the radioactive waste for final disposal, and final statuses of the survey and free release of the site and building, and turning over the site to KEPCO. In this paper, the current status of the TRIGA Mark-II type reactor decommissioning projects was introduced