이온교환법을 적용한 원전의 방사성폐액 처리방법 개선방안 연구

Abstract

Liquid radioactive waste treatment method of using evaporator was widely used from Kori 1 to Uljin 3&4, but a liquid radioactive waste treatment method that uses an ion exchange method instead of an evaporator was adopted aiming to minimize amount of radioactive waste and radiation exposure. However, the same equipment was introduced and applied for the first time in Korea and had experienced difficulties in securing credibility for the equipment and handling of liquid radioactive waste with inadequate data about performance and experience in operation and maintenance. In this study, examination, application, and effect analysis was performed on the optimization measure for handling liquid radioactive waste of Yonggwang Nuclear Power Unit 5 and 6(YGN 5&6) that applies an ion exchange method. When special liquid radioactive waste or high level radioactive waste are flowed into the Liquid Radwaste System(LRS), concentration of the processed liquid waste only satisfies design basis value(1.85E-01Bq/cc) of LRS but intermittently can't satisfy plant standard(1.85E-02Bq/cc) of YGN 5&6. Therefore domestic and overseas application cases were studied to improve performance of an ion exchange equipment through the pretreatment of liquid radioactive waste flowed into LRS. The distillate water occurring during operation of Boric Acid Concentrator(BAC) should be collected with Reactor Makeup Water Tank(RMWT), however it is transferred to LRS and processed because of high concentration of dissolved oxygen within the distillate water as RMWT limits the concentration of dissolved oxygen to 0.1ppm. This is because fuel cladding can be damaged if BAC distillate water that includes with RMWT and used as supplementary water for a Reactor. However, there is a possibility of operation failure of LRS if the distillate water, which is created about 109㎥ per day when BAC is operated consecutively, is flowed into LRS with liquid radioactive waste occurring during normal operation as it exceeds capacity of LRS. In order to solve this problem, installation of a new dissolved oxygen removal equipment was promoted and it was set as that the dissolved oxygen concentration the entrance must satisfy less than 100ppb when the dissolved oxygen concentration of the BAC distillate water flowed based on the design standard is less than 1000ppb. Cooling water remaining in the bottom of tank or the pipe located under the pump at the time of drainage for maintenance operation at the primary cooling water that contains the boric acid water can't be collected to the collection tank and drained to the floor of building, so it increasing amount of liquid radioactive waste. Therefore the boric acid water was collected with Refueling Water tank(RWT) by developing a 3D drawing program using AUTO CAD and a compulsory drainage method through compressed air pressurizing in order to collect boric acid water that is disposed. Effects according to improvement of the liquid radioactive waste treatment method were analyzed as follows. First, LRDPS filling exchange volume had decreased after installing the pretreatment equipment. If it is converted into the 200ℓ waste drum, it is so about 30drums are reduced yearly. Second, installation of the dissolved oxygen removal equipment to collect BAC distillate water to RMWT and to resue it can reduce about 10 million won of demineralized water supplementary cost per 1Rx-year(based on 1 unit). Third, if boric acid is collected by applying the 3D drawing program and the compulsory draining method then more than about 700 million won of financial benefits can be gained through reduction of drainage time when the relevant operation is the main process of the maintenance period.