[논문]Application of Electromagnetic Fields to Improve the Removal Rate of Radioactive Corrosion Products

Kong, Tae-Young; Lee, Kun-Jai; Song, Min-Chul

Application of Electromagnetic Fields to Improve the Removal Rate of Radioactive Corrosion Products 원문보기

Journal of the Korean Nuclear Society = 원자력학회지, v.36 no.6, 2004년, pp.549 - 558

Kong, Tae-Young (Korea Advanced Institute of Science and Technology) , Lee, Kun-Jai (Korea Advanced Institute of Science and Technology) , Song, Min-Chul (Korea Institute of Nuclear Safety)

Abstract ▼ AI-Helper

TTo comply with increasingly strict regulations for protection against radiation exposure, many nuclear power plants have been working ceaselessly to reduce and control both the radiation sources within power plants and the radiation exposure experienced by operational and maintenance personnel. Many research studies have shown that deposits of irradiated corrosion products on the surfaces of coolant systems are the main cause of occupational radiation exposure in nuclear power plant. These corrosion product deposits on the fuel-clad surface are also known to be main factors in the onset of axial offset anomaly (AOA). Hence, there is a great deal of ongoing research on water chermistry and corrosion processes. In this study, a magnetic filter with permanent magnets was devised to remove the corrosion products in the coolant stream by taking advantage of the magnetic properties of the corrosion products demonstrated a removal efficiency of over 90% for particles above 5${\mu}m$. This finding led to the construction of an electromagnetic device that causes the metallic particulates to flocculate into larger aggregates of about 5${\mu}m$ in diameter by using a novel application of electromagnetic flocculation on radioactive corrosion products.

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문제 정의

An electromagnetic filter of about 5 ㎛ in diameter was set up as a cohesive device before the PMF, causing the corrosion particles to flocculate into larger aggregates and improving the corrosion product removal rate to over 90%. This paper focuses on the application of electromagnetic flocculation to radioactive corrosion products and presents the results of several experiments that show how the proposed cohesive device results in the successful agglomeration of corrosion products.
This study involved the design and manufacture of a magnetic filter with permanent magnets to reduce the risk of occupational radiation exposure(ORE) and to help meet increasingly demanding safety requirements in nuclear power plants. Previous research papers [2, 3] have demonstrated that the general removal efficiency of permanent magnet filters (PMF) is greater than 80% for various corrosion products.

제안 방법

Experiments were usually carried out at room temperature and atmospheric pressure since, in this study, the PMF was devised for preliminary research in the laboratory. Nickel ferrite (NiFe₂O₄), cobalt ferrite (CoFe₂O₄), magnetite (Fe₃O₄), and hematite (Fe₂O₃) were used to simulate corrosion products.
However, performing the experiment with such a low concentration is difficult since many factors, particularly the residual impurity in the fluid channel, can result in incorrect values. In this study, several experiments were carried out to obtain reasonable data values; incorrect values were eliminated.
In addition, the EMF offers more design flexibility for the filter elements to achieve the required efficiency related to the number of magnetic trapping sites per unit filter volume. In this study, the primary objective of the cohesive device was to cause the very fine suspeeded magnetic particles to flocculate into larger aggregates that could be separated easily in the PMF.
Several experiments were performed with changes to the following variables: the class of particles, the flow rates, the concentration of the input solution, the operation time of the electromagnets, and the applied magnetic field. Experiments were normally carried out at room temperature and atmospheric pressure.
The PMF devised in this research adopts the wiggler configuration and uses cylindrical magnet bars. The arrangement of the magnet assembly is shown in Figure 2 [2].
The cohesive device designed in this study is composed of three main parts: a vessel with inlet and outlet pipe connections, which are fitted to the inside with a solenoid to generate a background magnetic field and a structure to cool the magnet coils; the magnetizable matrix assembly; and the control panel. The whole vessel is supported concentrically to an electromagnetic solenoid (Fig.
Another advantage of permanent magnets is that they can be fabricated with a wide range of structural properties, geometric shapes, and magnetization patterns, owing to the rapid growth of manufacturing techniques for such magnets. Therefore, in this study, a permanent magnet filter (PMF) was devised that can separate metallic particles from the main stream and, applying the principle of OGMS, can remove the corrosion products in the coolant stream.

성능/효과

Preliminary experimental results showed that the removal efficiency was higher if the flow rate of the fluid stream was lower and the size of the particles was larger. Although the rotating velocity of the magnet assemblies had a slight influence on the removal efficiency, the flow rate and the particle size were the main parameters for determining removal efficiency in this study. The PMF was found to achieve a high removal efficiency of qver 90% for particles with diameters of 4 ㎛ and over.
After passing through the cohesive device, most corrosion particles within a range of 2 to 3 ㎛ in diameter were aggregated into particles of 4 to 8 ㎛.Experiments with magnetite and cobalt ferrite displayed outstanding results as the average size of aggregates was approximately 8 ㎛ in diameter due to the high magnetic susceptibility of those materials. The flow rate did not play an important role in the agglomeration of particles, and there was no difference in the particle sizes of high and low flow rates.
9 gallon/min (gpm) flow rate and 50 rotation/min (rpm) rotating velocity of the magnet assembly. The experimental results also reflect that the hydrodynamic drag force and the gravitational force, and not the magnetic force, are the major forces influencing very small particles. Some differences in separation efficiency are attributed to the disparities in the magnetic susceptibility of particular particles, especially hematite.

참고문헌 (9)

Cohen, P. The ASME Handbook on Water Technology for the Thermal Power System, American Society of Mechanical Engineers, pp. 1237-1289, (1989)
Song, M. C. A Study on the Method and Process for Removal of Radioactive Corrosion Product from NPP using its Magnetic Property, Ph. D thesis. Korea Advanced Institute of Science and Technology, pp. 72-74, (2004)
Song, M. C., Kim, S. I., and Lee, K. J. 'Development of a magnetic filter system using permanent magnets for separating radioactive corrosion products from nuclear power plants' , Journal of Separation Science and Technology, Vol. 39, Issue 5, pp. 1039-1059, (2004)
Reitz, J. R., Foundations of Electromagnetic Theory, 4th edition. Addison Wesley Longman, (1993)
Kim, S. I. A Study on the Moving Alternative Magnetic Filter for Radioactive CRUD Removal, MS thesis. Korea Advanced Institute of Science and Technology, pp. 11-14, (2001)
Nakajima, H., Kaneko, H., Oizumi, M., Fukui, S., Yamaguchi, M., Sato, T., Oizumi, M., Imaizumi, H., Nishijima, S., and Watanabe, T. 'Separation characteristics of open gradient magnetic separation using high-temperature superconducting magnet', Journal of Physica C: Superconductivity, Vol. 392-396, Part 2, pp. 1214-1218, October (2003)

상세보기
Selvaggi, J. A., Cottrell, D. L., Falconer, T. H., Daugherty, M. A., Daney, D. E., Hill, D. D., and Prenger, F. C. 'High gradient magnetic separation using a high temperature superconducting magnet', Journal of Applied Superconductivity, Vol. 6, Issue 1, pp. 31-36, January (1998)

상세보기
Furlani, E. P. Permanent Magnet and Electromechanical Devices. New York: Academic Press, p. 329, (2001)
Song, M. C., Kong, T. Y., and Lee, K. J. 'Conceptual Design of the Filter using Electromagnet and Permanent Magnets for Removal of Radioactive Corrosion Products,'Journal of the Korean Radioactive Waste Society, Vol.1 [1], pp. 73-79, December (2003)

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