Zinc injection into the coolant system of nuclear power plants is an effective method for reducing corrosion and improving performance. The effectiveness of this method is influenced by various factors such as zinc concentration and injection rate. This paper provides an overview of the factors affecting the effectiveness of zinc injection in nuclear power plants, with a focus on zinc concentration and injection rate, and discusses various research results on the effects of these factors on corrosion reduction and coolant system performance. Zinc concentration is an important factor affecting the effectiveness of zinc injection. The research results show that gradual increases in zinc concentration are more effective for coolant system stability. However, the concentration should not exceed the recommended levels as high zinc concentrations can have negative effects on the system. Injection rate is also an important factor affecting the effectiveness of this method. The research results show that gradual increases in injection rate are more effective for coolant system stability. However, excessive injection rates can have negative effects on the system such as overload of the zinc injection facility and chemical shocks within the coolant system, and therefore, should be optimized. In conclusion, zinc concentration and injection rate are important factors affecting the effectiveness of zinc injection in nuclear power plants. The optimal concentration and injection rate should be determined based on specific reactor conditions and system requirements, and efforts should be made to maximize corrosion reduction and performance improvement.

Radioactive products generated by long-term operation at NPP can become deposited on the surfaces of the system and equipment, leading to radiation exposure for workers during the decommissioning process. Chemical decontamination is one of the methods to reduce radiation exposure of workers, and there are HP CORD UV, CITROX, CAN-DECON. In the chemical decontamination process, organic acids are generally used, and representative organic acids include oxalic acid and citric acid. There are various methods for removing residual organic acid in decontamination liquid waste, such as using an oxidizing agent and an ion exchange methods. However, there is a problem in that oxidizing agent is used excessively or secondary wastes are generated in excess during organic waste treatment. However, when organic acid is decomposed using a UV lamp, the amount of secondary waste is reduced because it tis decomposed into CO2 and H2O. In this study, organic acid decomposition was evaluated as the contact time of the UV lamp. The experimental equipment consists of a UV reactor, a mixing tank, a circulation pump. The experimental conditions involved preparing 60 L of organic liquid waste containing oxalic acid, hydrogen peroxide and iron chloride. Test A was conducted using one UV reactor, and Test B was performed by connecting two UV reactors in series. As a result of the experiment, a decomposition rate of over 95% was shown after one hour for oxalic acid, and it was confirmed that the initial decomposition rate was faster as the contact time increases. Therefore, in order to increase the initial decomposition rate, it is necessary to increase the contact time of the UV lamp by connecting the UV reactors in series.

It is reported that 48 pressurized heavy water reactors (PHWRs) are in operation, and 10 PHWRs including Wolsong-1 NPP have been permanently shut down in the world. In the case of PHWRs, which have been permanently ceased, they are managed through the delayed decommissioning method, but there are no cases of dismantling. Therefore, technology development is urgent for the effective decommissioning of PHWRs. Unlike PWRs, PHWRs are separated into coolant system and moderator system. Most of pipes and systems of coolant system are mainly composed of carbon steel, expect of the steam generator tubes which are composed of nickel alloy. On the other hand, the moderator system is composed of stainless steel. In the case of stainless steel, the inner layer of the oxide film is composed of chromium oxide, and the outer layer is composed of iron and nickel oxide in enriched. To remove two oxide layers, it is needs to different decontamination method, the coolant system can perform the system decontamination process through a reduction process, but in the case of the moderator system, the oxidation/reduction process is required because it has a material and oxide film similar to PWRs. In this study, this is evaluated the oxide film removal rate according to the type of stainless steel and temperature in order to remove the oxide film deposited in the moderator system. The experiments were carried out at temperatures of 60, 70, 80 and 90°C, with a concentration of 200 ppm of permanganic acid and nitric acid, and 2,000 ppm of oxalic acid, respectively. The results of the oxide film removal rate test for SUS304 showed 29% at 60°C, 38% at 70 and 80°C, and 41% at 90°C. For SUS403, the oxide film removal rate experiment results showed 62% at 60°C, 85% at 70°C, 94% at 80°C, over 99% at 90°C. The results showed that the removal efficiency of the oxide film increased as the temperature increased. Following the results of experimental, the optimum temperature of oxide removal in composed of the stainless steel material is to be 90°C for decontamination of PHWR.

고리 1호기는 원전해체 계획에 따라 영구정지 이후 가능한 한 빠른 시일 내에 원자로냉각재계통의 화학제염을 수행할 계획으로, 계통제염 기술 확보를 위해 한수원에서는 2014년부터‘원전 해체설계를 위한 냉각재계통 및 기기제염 상용기술 개발’연구과제를 통해 화학제염기술을 개발하고 있다. 본 연구를 위해 Lab. 규모 계통제염 공정장치를 제작하였으며, 계통제염 대상의 주요재료인 STS304, 316, 410, Alloy600, SA508을 사용하여 화학제염 공정실험을 수행하였다. 화학제염 공정실험의 목적은 산화-환원공정의 최적시간, 최적제염제 및 공정횟수를 도출하기 위함이다. 화학제염 공정실험은 과망간산-옥살산 기반의 단위공정 및 연속공정 실험, 과망간산+질산-옥살산 기반의 연속공정 실험으로 나누어 수행하였다. 그 결과 단위공정실험을 통해 최적공정 시간인 산화공정 5시간, 환원공정 4시간을 도출하였으며, 연속공정실험을 통해 최적제 염제와 공정횟수를 도출하였다. 최적제염제는 산화제의 경우 200 mg·L-1 과망간산 + 200 mg·L-1 질산이고, 환원제는 2000 mg·L-1 옥살산이며, 공정횟수는 STS304와 SA508의 경우 2 cycle, Alloy600의 경우 3 cycle 이상 수행하는 것이 적절할 것 으로 평가되었다.