국제 기준에 따른 RMS 성능검증 및 효율적인 설비 개선방안에 관한 연구

Abstract

In Fukushima nuclear power plant accident in 2011, people's interest in the management of radioactive materials emitted from nuclear power plants to the outside environment increased. For this reason, the role of radiation monitors is becoming important to the credibility of nuclear power plants to the public. As this result, the effectiveness of the value measured by the radiation monitor becomes very important. ANSI N13.1, a global technical standard for monitoring substances emitted through radiation monitors, was changed in 1999. However, there has been no conformity assessment of the revised regulations for radiation monitors already installed and operated. The key to validation is to demonstrate the representativeness of the airflow of the gaseous samples collected for analysis to the RMS equipment within the discharge line of the air conditioning system as collection samples. Verification of the conformity of the revised technical standards shall ensure that the sample collection position, i.e. velocity distribution coefficient of variation, average flow angle, tracking gas concentration distribution COV, and trace gas maximum concentration in the HVAC duct meet the technical standards. It is also important to ensure that the transfer rate of the sample transfer piping from the HVAC duct to the RMS facility is at least 50%. To verify the validity of the sampling location, one kind of emission radiation monitors installed and operated at the "B" nuclear power plant were verified using computational fluid dynamics (CFD). it was confirmed that the revised technical requirements were not satisfied. For RMS plants where the sampling location did not meet the revised technical standards, the CFD analysis was used to find an effective sampling location for the HVAC vent ducts at intervals of 0.5 m. Fundamentally, the flow rate through the exhaust venting capillary for each system is significantly different for different modes of operation. In addition, a plurality of discharge pipes for exhaust are connected to one capillary, and the exhaust gas behavior is different for each position. This study confirms that it is not possible to obtain representative air samples for all operating conditions at the sampling location. The transfer rate of the sample pipeline is checked by NRC and other countries using a transfer rate calculation program to confirm that the ratio is 50% or more. Sample transfer piping transfer rates were evaluated for currently operating RMS installations, but did not meet the technical standards. Accordingly, it was confirmed that it was necessary to increase the transfer rate by more than 50 % by means of RMS facility differations and simplified transport piping. Installation of pre-inspectors was not easy due to various steel structures and various fluid piping. This study confirms that these obstacles are concerned with the improvement of the sample transfer piping. This study will be of great help to improve the reliability of power plants by studying whether existing facilities meet the revised technical standards for gas effluent radiation monitors. In addition, this study attempted to present design criteria for equipment that does not meet the new technical standards. In order to meet this technical standard in the future, it was recognized that additional research is needed such as "Study for establishing sample transfer piping per operation mode" and "Development of correction factor according to sample transfer rate difference".