Hee Reyoung Kim

Design and Performance Test of Photosensitive Glass–Based Nonfocused X-Ray Antiscattering Grid by Using MCNP Simulation

Abstract A design and performance test of an antiscattering X-ray grid that is based on photosensitive glass was conducted using MCNP simulation. The simulation was designed in three parts: source, scatterer, and grid. The source was a cone type with a single energy of 50 keV, and the scatterer was designed as a box with elemental composition and density the same as those of a human body. Three types of grid were tested: ideal, injection, and electroplating. The ideal-type grid was generally known and contained only a shielding wall, the injection-type grid had the shielding material injected into the glass, and the electroplating-type grid had the shielding material electroplated on the glass lattice skeleton. The ideal-type grid showed a scattered and primary photon ratio (SPR) of 0.106, and the nongrid type showed an SPR of 0.159. The injection-type grid had an SPR of 0.126, which corresponded to 119.3% of that of the ideal type. The electroplating-type grid had an SPR of 0.0964, which corresponded to 93.7% of that of the ideal type. It was understood that the electroplating-type grid showed the most effective reduction of the scattered photons in terms of SPR.

AN INVESTIGATION INTO RADIATION LEVELS ASSOCIATED WITH DISMANTLING THE KOREA RESEARCH REACTOR

We confirmed that the dismantling of two research reactors with thermal power of 2MW th and 100kW th , respectively, reveals no significant difference between the radiation levels of the research reactor site and the surrounding environment far away from it, from the radiation level aspect. Radiation dose and radioactivity were measured at monitoring points around the research reactor site of the Korea Atomic Energy Research Institute (KAERI) in Seoul and comparison points 0.5 km to 3.3 km from the site. To grasp trends in the radiation levels during dismantling from the end of 2002 to the end of 2007, the gamma radiation dose rate, the accumulated dose, and the radioactivity of the strontium, tritium, and gamma isotopes were statistically treated and estimated. The averages of these items between the two groups, the research reactor site and comparison points, were assessed by applying a T-test with a significance level of 0.05. P-values found by using the T-test were from 0.12 to 0.83 where the values were much higher than the significance level. As a result, no difference was observed between the radiation levels at the research reactor site and at the comparison points by this T-test. This study showed that dismantling activity of the Korea Research Reactor of the Seoul site did not expose the public or the environment to harmful levels of radiation.

Radiation Dose Assessment of the Uranium Rich Regions in Korea

The radiation dose was assessed for the inhabitants living in the Kumsan, Geosan and Miwon regions which belong to an Okchun metamorphic belt with plenty of uranium resources. The grain, vegetable, milk, and water, which the inhabitants generally ate or drunk, were sampled to reflect the dose effects. And TLD (Thermoluminescence dosimeter) was used for measuring the external dose in the sampled area. An external exposure includes the accumulated gamma dose measured by TLD and an internal exposure includes an ingestion ofthe food, and an inhalation of the air and radon gas. The radionuclides such as 137Cs, 7Be, 40K as well as 238U were included for measuring the radioactivity concentrations of the samples. Radioactivity concentrations for the samples were calculated as averaged annual values. The effective dose by TLD analysis was similar to the domestic average when considering that it was between 0.63 mSv/y and 0.71 mSv/y. The 222Rn concentration of indoor air significantly contributed to the total effective dose where the concentration of these uranium belt regions was more or less higher than the average domestic one. This study revealed that the dose level for the inhabitants ofthe uranium rich regions in Korea was similar to that of the other regions except for the effect by radon.

The Establishment of an In-Situ Real Time Radiation Contour Mapping Technique

The goal of this study is to present that an in-situ radiation dose distribution on an area measured by using a gamma radiation measuring instrument is grasped without a delay. Fundamentally, the test includes an area map as well as real numerical data from the measured area. The map is a computer file with a format of ‘bmp’ which is used in the gamma radiation measuring instrument, and the data is a text file which has numerical values of the latitude, longitude and radiation dose rates of the measured points. The radiation dose rates of the unmeasured points in the area are displayed through an interpolation with those of the measured ones. A 2D plot shows the contour lines with an overlapped map image and a 3D one gives contour lines on the z-axis for an immediate understanding of the radiation level. It is available to optionally display the numerical values of the radiation dose rates and to zoom up and down the image of a certain part for a detailed view. This contour mapping method programmed by using a commercial software requires only a mouse click to show in-situ in a real time the radiation distribution on the corresponding map in a laptop window screen.

Radiological Dose Assessment for Clearance of Biological Shield Concrete from KRR-2

A large amount of radioactive concrete waste was generated during the decommissioning work of the Korean Research Reactor #2 (KRR-2). More than 85% of the dismantled concrete waste will be disposed of by a recycling or landfill by the application of a clearance principle. Currently, the Korean Atomic Energy Act and relevant regulation comply with the international recommendation of the sources/practices meeting an individual dose criterion 10μsv/y and a collective dose criterion of less than 1 man.Sv/y. A variety of radionuclides was generated in the biological shield concrete by a neutron reaction during the operation of a reactor. The specific activities of these radionuclides were measured by using the developed methods and procedures. For the evaluation of a radiological dose, seven scenarios were selected which encompassed a realistic situation of a recycling such as a road construction and landfill disposal route. The external and internal exposure doses of each scenario were calculated by using the MCNP4C code and a mathematical model respectively. The dose assessment regarding the residents and industrial workers was evaluated by using the RESRAD code for the landfill disposal scenario. The maximum individual dose rate was 7.21 μSv/y and the maximum collective dose was 0.05 man. Sv/yr for the landfill disposal scenario.

The Radioactivity Analysis of 14C in the Graphite Samples From the Dismantled KRR-1&2 Sites by a High Temperature Furnace and a LSC

The radioactivity of 14 C of the graphite samples from the dismantled Korea Research Reactor 1&2 (the KRR-1&2) site was analyzed and proposed to be disposed of as a low level radioactive waste rather than self-disposed of. The graphite wastes, with a weight of seven tons, have been generated during the dismantling of a research reactor with a capacity of one MW from 1995 to 2006. The graphite was used as a moderator for the research reactor and so has been radioactivated by thermal neutron. It was thought that the graphite wastes mainly included a radioisotope of stable carbon, 14 C, a pure beta emitter with a half life of 5,730 years and with a maximum decay energy of 156 keV. Therefore, it has been requested to see whether the dismantled graphite radioactive wastes including 14 C can be self-disposed of or not. In the present study, the radioactivity of 14 C in the graphite sample used in the research reactor was analyzed by using a commercialized high temperature furnace and a Liquid Scintillation Counter (LSC). The combustion temperature of the furnace was five hundred degrees centigrade and especially the temperature in the catalyst region was eight hundred degrees centigrade. The recovery from the furnace was 95% for 14 C and the LSC had a quenching efficiency of approximately 66%. Carbosorb was used as a trapping solution for 14 C. The radioactivity of 14 C was measured by a LSC through the procedure of a pre-treatment such as the combustion of a sample in the temperature range of 500–800 degrees centigrade by a high temperature furnace, trapping of 14 C into carbosorb and cocktailing it with a scintillator. The radioactivity was analyzed to have a concentration with a value of much more than a domestic legal limit for a self-disposal. And an individual effective dose rate estimation was also carried out. Finally, it is suggested that the graphite wastes from the dismantled research reactor should be disposed of at a low level radioactive waste disposal site and monitored.Copyright

Design and preliminary test of an annular linear induction electromagnetic pump for a sodium-cooled fast reactor thermal hydraulic experiment

ABSTRACT An annular linear induction electromagnetic pump (ALIP) with a flow rate of 2265 L/min and a developed pressure of 4 bar was designed and fabricated to test the performance of the components of a sodium-cooled fast reactor (SFR) in a sodium thermal hydraulic experimental loop. The design characteristic of the ALIP was calculated using the electrical equivalent circuit method typically used for analyzing linear induction machines. Preliminary tests, such as verification of the moving function using an annular Al pipe, were carried out. The linearity between the input voltage, current, and magnetic flux density was verified. The developed force demonstrated an increase proportional to the square of the input current, whereas the velocity was linearly proportional to the input current. The main design variables of the pump were calculated theoretically for the SFR thermal hydraulic experimental loop. The pump was optimized for the design variables including input frequency, and the characteristics of the optimized pump were compared with those of the pump at the commercially used frequency of 60 Hz.

The Radioactivity of 3H in Metals by a High Temperature Furnace and a Liquid Scintillation Counter

The radioactivity of 3 H of the metal samples from the nuclear sites was analyzed by using a commercialized high temperature furnace and a Liquid Scintillation Counter (LSC). The 3 H activity of the sample was measured according to the duration of the high temperature combustion and the oxidation temperature. Basically, the recovery from the furnace was 90% for 3 H and the LSC had a quenching efficiency of approximately 30 %. HNO3 was used as a trapping solution for 3 H and the solution was cocktailed with a scintillator. The activity extracted from the sample was increased till the combustion time elapsed 60 minutes and the increasing rate was reduced continuously thereafter at 600 °C whereas 80% of radioactivity was extracted during the first 15 minutes at 900 °C. Also, the pretreatment for the metal sample, which included a high temperature combustion and trapping, had the time required of at least four hours at 900 °C. Finally, it was suggested that this high temperature combustion method could be applied to analyze the activity of the radioactive metal waste from the nuclear power plants.© 2010 ASME

Radiological Dose Assessment and Survey of a Radioactive Contamination in Foodstuffs

Radiological dose assessments and surveys of a radioactive contamination have been performed for domestic and imported foodstuffs since 2003. The following samples among the imported foodstuffs were selected from open markets; one group is imported foodstuffs and the other group is domestic foodstuffs produced from around nuclear facilities. These included imported samples from a country associated with the Chernobyl nuclear accident, samples produced around nuclear power plants or nuclear tests, and foodstuffs reported as radioactively contaminated materials in a foreign country. After pretreatments such as a drying and homogenization, the samples were analyzed. Only the 137Cs radionuclide was measured from among the regulation radionuclides(137Cs, 134Cs, 131I) of the Korea food code. All foodstuffs except Inonotus Obliquus (Chaga mushooms) were less than 25.24 Bq/kg or below the minimum detectable activity (MDA). The average activity concentrations of 203 mushroom samples was 38.60 Bq/kg but the effective dose was also far less than 1 mSv/yr. Based on the radiological dose assessments and surveys of a radioactive contamination, the radioactivity of the domestic and imported foodstuffs has not shown any significant levels during recent years in Korea.