원자력발전소 배출수에 포함된 붕산 제어 연구

Abstract

In a nuclear power plant, boric acid is used in the primary system to control the reactor reactivity, and the reactivity is controlled by changing the boron concentration. Boric acid exists in the form of Ortho Boric Acid[B(OH)3] and ionized Mono-borate Ion [B(OH)4-] inwater, and the presence ration of the two chemical species depends mainly on pH. Most of the waste boric acid-containing water generated during the operation of the power plant is recycled through a recovery process, but some boric acid water is discharged through the ion exchange resin of the Liquid Radioactive waste treatment System(LRS). In order to increase the efficiency of removing boric acid discharged, the pH in the discharged water must be maintained at 10 or more, but the pH limit value of the discharged water of nuclear power plants is between 6 and 9, so it is difficult to maintain the pH more than 10 in reality. Inaddition, a large amount of waste is generated when chemicals are added to increase the pH. In other words, the ion exchange resin loses its performance prematurely due to the overdosing of the chemical. Therefore, most of the boric acid in the discharged water from nuclear power plants is being discharged without being removed. Of course, there is currently no regulation on boric acid in the discharged water from nuclear power plants, but the National Institute of Environmental Sciences recently designated boric acid(containing more than 0.3%) as a toxic substance. This means that boric acid is highly harmful to humans and the environment, and regulations on handling and use are expected to be strengthened in the future. Therefore, in this paper, various methods to meet the pH of the NPP discharge and ionize and remove boric acid were studied, and a pilot-scale boric acid control device was developed through the final verification test. The main core of this device is to ionize boric acid with an oxidizing agent (H2O2) and then inject sodium hydroxide (NaOH) to adjust the pH to increase the ionization efficiency of boric acid. Next, after coagulation and precipitation of boron ions using a coagulant (CaCl2), the precipitation is recovered and the residual boron ions in the supernatant is removed by using a filtration membrane(RO). As a result of the experiment, the boron concentration was measured to be less than about 5ppm, satisfying the target value (less than 5ppm).