[en] DLC (Diamond-like carbon) thin film-deposited polycarbonate specimens were irradiated by high level gamma-ray and made observation of their irradiation effects. In order to do that, diamond-like carbon thin films were deposited on polycarbonate specimens by plasma-enhanced chemical vapor deposition, and then those specimens were irradiated in the high level irradiation facility in KAERI at the same dose rate of 10⁶ rad. Relative concentration of free radicals generated during irradiation of the DLC-deposited and undeposited specimens was determined by the analysis of EPR (electron paramagnetic resonance) spectrum at the elapsed time of 4 hours and 2 months after irradiation of those specimens. As a result of the analysis, it was found that the radical concentration in the DLC-undeposited specimen at the elapsed time of 2 months reduced rapidly in 4 % compared with that at the elapsed time of 4 hours, whereas the concentration in the DLC-deposited specimens decreased slowly in the vicinity of 60 %. Consequently, DLC thin film-deposited polycarbonate specimens resulted in the increase of radiation-oxidation resistance

[en] Purpose: This study investigates the validity of the interval method to determine the anisotropy factors of high dose rate (HDR) ¹⁹²Ir sources. Methods and Materials: A calculation method, which is one of the various numerical implementations of the Sievert integral and known as the interval method, is applied to determine the anisotropy factors of a HDR ¹⁹²Ir source. Calculated results from r = 1 cm to 10 cm are compared to published data. Results: The comparison shows that the error resulting from the interval method increases from 1.3 to 28.1% as the radial distance increases from r = 1 cm to 10 cm and is significantly smaller than that previously reported. Conclusions: The interval method might be considered as a method that provides a very rough estimate of the anisotropy of HDR ¹⁹²Ir sources whenever no conclusive anisotropy data is available

[en] Currently, the economic advantage of any known approach to the back end fuel cycle of a nuclear power reactor has not been well established. Thus the long term storage of the spent fuel in a safe manner is one of the important issues to be resolved in countries where the nuclear power has a relatively heavy weight in power production of that country. At KAERI, as a solution to this particular issue midterm storage of the spent fuel, an alternative approach has been developed. This approach includes the decladding and pulverization process of the spent PWR fuel rod, the reducing process from the uranium oxide to a metallic uranium powder using Li metal in a LiCl salt, the continuous casting process of the reduced metal, and the recovery process of Li from mixed salts by the electrolysis. We conducted the laboratory scale tests of each processes for the technical feasibility and determination for the operational conditions for this approach. Also, we performed the theoretical safety analysis and conducted integral tests for the equipment integration through the Mock-up facility with non-radioactive samples. There were no major issues in the approach, however, material incompatibility of the alkaline metal and oxide in a salt at a high temperature and the reactor that contains the salt became a show stopper of the process. Also the difficulty of the clear separation of the salt with metals reduced from the oxide became a major issue

[en] The research on spent fuel management focuses on the maximization of the disposal efficiency by a volume reduction, the improvement of the environmental friendliness by the partitioning and transmutation of the long lived nuclides, and the recycling of the spent fuel for an efficient utilization of the uranium source. In the second phase which started in 2001, the performance test of the advanced spent fuel management process consisting of voloxidation, reduction of spent fuel and the lithium recovery process has been completed successfully on a laboratory scale. The world-premier spent fuel reduction hot test of a 5 kgHM/batch has been performed successfully by joint research with Russia and the valuable data on the actinides and FPs material balance and the characteristics of the metal product were obtained with experience to help design an engineering scale reduction system. The electrolytic reduction technology which integrates uranium oxide reduction in a molten LiCl-Li₂O system and Li₂O electrolysis is developed and a unique reaction system is also devised. Design data such as the treatment capacity, current density and mass transfer behavior obtained from the performance test of a 5 kgU/batch electrolytic reduction system pave the way for the third phase of the hot cell demonstration of the advanced spent fuel management technology

[en] Safety limits such as trip-set-points of Reactor Protection System (RPS) and Engineered Safety Feature Actuation System (ESFAS) of nuclear power plants directly effect on safety so that surveillance tests are periodically performed to verify drift of trip-set-points. We have performed drift analysis of RPS/ESFAS with respect to relaxation of surveillance test intervals(STIs) to gain resonable basis of relaxation of STIs. We gather the data from surveillance test procedures and then analyze 95% confidence /95% reliability of analog channel for 1 month, 3 month and 6 month STI, respectively. The result shows that the maximum drift is 0.21% and the drift does not depend on STIs. Therefore, we reach the fact that the relaxation of STIs of RPS/ESFAS is feasible from a viewpoint of analog channel drift

[en] The object of this study is to improve the stability and the economic profit by reducing the radiation-induced degradation rate of polymer material used under the radiation environment. So far, the resistance to radiation-induced oxidation of a polymer has been improved by the stabilizers. They can play an important role in the anti-oxidants that interrupt the radical-mediated oxidation chain reaction. The stabilization effect could be larger than that achieved in an inert-atmosphere irradiation. Stabilization is a function of stabilizer concentration up to a certain threshold, but it is not further improved above this concentration. Beyond the threshold, the rate of radiation-induced oxidation goes up to the rate that is characteristic for the unstabilized polymer. To make up for this weakness, a technique depositing a thin layer of diamond-like carbon (DLC) on the polymer surface was developed for protecting the radiation-induced oxidation in the air

[en] The probabilistic effects on the online maintenance of safety related equipment have been reviewed only in view of the core damage frequency at power operation. It is because full scope shutdown and low power(SDLP) PSA has scarcely been performed. For APR1400, an extensive SDLP PSA is being performed. This paper is to introduce the methodology of SDLP PSA for APR1400 at design phase and to present how much the CDFs of SDLP and full power operation change, if preventive maintenance of the safety related equipment such as EDGs and ESW pumps is performed during full power operation instead of SDLP. The result shows that SDLP CDF reduces as much as 82%, and total CDF 44%, if preventive maintenance of all the EDGs and ESW pumps is performed during power operation

[en] KEPCO is planning to install Anticipated Transient Without Scram(ATWS) Mitigating System for Westinghouse type plants in Korea. In order not to perform plant specific analyses for each plant, the major parameters are compared to those of generic safety analysis results which were performed by Westinghouse owners group. Per the evaluation results, the most conservative results are obtained at Kori unit 2 loss of load/ turbine trip event with ATWS and the peak RCS pressure becomes 3072 psia which is less than the limit of 3200 psig. Therefore, the generic safety analysis results are applicable to Westinghouse type plants in Korea

[en] For the development of the advanced spent fuel management process based on the molten salt technology, it is essential to choose the optimum material for the process equipment handling a molten salt. In this study, corrosion behavior of Fe-base superalloy, Ni-base superalloy, non-metallic material and surface modified superalloy were investigated in the hot molten salt under oxidation atmosphere. These experimental data will suggest a guideline for the selection of corrosion resistant materials and help to find the operation criteria of each equipment in aspects of high temperature characteristics and corrosion retardation

[en] The object of this project is to improve the stability and the economics by reducing the radiation-induced oxidation as a factor of degradation of polymer materials used under the radiation environment. In order to attain the objective of this study and to check the effect of diamond-like carbon(DLC) coating on the anti-oxidation reaction, polymer specimens such as ABS, Acryl, Polycarbonate, Polyethylene, Polypropylene, PVC coating DLC thin layer were exposed to high-level gamma radiation, and their irradiation effects were investigated. A plasma-enhanced chemical vapor deposition method was adopted in fabricating a DLC thin film on the polymer specimens, which were irradiated with the non-DLC film deposited specimens under the gamma radiation emitted from Co-60 source from 1x10⁵ to 1x10⁸ rads exposure. According to the characterization of irradiated specimens from the elapsed time of minimum 4 hours to a maximum of 105 days after the irradiation, the DLC deposition on the polymer surface was revealed to contribute to the improvement on the resistance of the radiation-induced oxidation in this study