An Evaluation on the Applicable Adequacy of CONTAIN Code for a CANDU Containment

After the accident at TMI (1977) and Chernobyl (1986), the safety evaluation during the anticipated severe accident of a nuclear power plant has been continuously emphasized. In PWRs, the experimental and numerical analysis have been performed for a mitigation and phenomenon examination of the severe accidents. On the other hand, the analysis has been partly performed for PHWRs. Hence, this study has performed to evaluate the applicability CONTAIN 2.0 code for a CANDU containment and to simulate the phenomenon during the severe accident. In this thesis, it has been carried out the analysis of the phenomenon inside the containment during LBLOCA (Large Break Loss of Coolant Accident) without ECCS (Emergency Core Cooling System) injection. The 29-cell model was used to evaluate the thermal-hydraulic response and the 40-cell model was done to do the hydrogen concentration. Before evaluating the applicability of CONTAIN 2.0 code for the CANDU containments, the spray system and the fan cooling system which affect on the thermal-hydraulic behavior were assessed on the basis of the information of Wolsong 2, 3, 4 in FSAR (Final Safety Analysis Report). One of the major factor, which has an effect on the heat removal rate of the spray system and the fan cooler, and concentration removal rate in atmosphere, is the mole fraction in atmosphere. Since the most discharged mass flow rate of the steam mixture through the break piping occurs during the early accident period, the pressure, temperature, and hydrogen concentration decreased significantly by operating spray system during this period. After drying out the water in the spray system after 300 sec, the effect by the fan cooler for the decrease of pressure, temperature, and hydrogen concentration appears. Finally, the calculation results of CONTAIN 2.0 code were compared with the result of Wolsong 2, 3, 4 in FSAR. The pressure and temperature is over-predicted in the early accident but under-predicted in the late accident. The hydrogen concentration is continuously under-predicted. The first reason of these trend is supposed to be the difference of the operating process of the spray system, and heat and energy removal rate. The second reason of these trend is done to be the difference of considering of the generating hydrogen source. But, in general, the result of FSAR and CONTAIN 2.0 code is concluded to show similar trend and the use of CONTAIN 2.0 code for the analysis of PHWR containment is evaluated to be promising