C.S. Kim

Plutonium isotopes in seas around the Korean Peninsula

239+240Pu concentrations and 240Pu/239Pu atom ratios in coastal seas adjacent to the Korean Peninsula were determined, during the period 1999 to 2002, to assess the current distribution and to identify sources of Pu isotopes. 239+240Pu concentrations in surface waters ranged from 3.1 to 22.3 mBq m(-3) with higher concentrations in winter than in summer. 239+240Pu concentrations in seawaters around the Korean Peninsula are greater than that in the western North Pacific. 240Pu/239Pu atom ratios ranged from 0.18 to 0.33 with an average value of 0.25+/-0.03, which is significantly higher than the global fallout average. The 240Pu/239Pu atom ratios of the 2000 m deep entire water column in the south western part of the East Sea (Sea of Japan) was comparable to that observed in waters near Bikini Atoll. The higher 240Pu/239Pu atom ratios than that of global fallout may be explained by the hypothesis that the earlier input signal of low 240Pu/239Pu atom ratio (0.18-0.19) of global fallout plutonium in seas adjacent to the Korean Peninsula is being gradually diluted by the high 240Pu/239Pu atom ratio plutonium transported from the tropical Pacific Proving Grounds via prevailing ocean current.

Rapid determination of 99Tc in environmental samples by high resolution ICP-MS coupled with on-line flow injection system

High resolution inductively coupled plasma mass spectrometry coupled with an on-line flow injection system (FI-HR-ICP-MS) was applied to determine the ultra-trace level 99Tc in soil. The flow injection system (PrepLab™) was composed of two TEVA-SpecÒresins, reduced remarkably the sample amounts and the analysis time, compared to the conventional analytical methods. In the flow injection system, Mo and Ru were sufficiently eliminated by using the flow injection system, with the decontamination factors of 1.6.104 and 9.9.105, respectively. With the present method, it was possible to determine ultra-low level of 99Tc in 3-6 g soil at 3–5 hours of analysis time per sample. The relative standard deviation for each sample was less than 4%. The detection limits for 99Tc was 85 fg.ml–1 (0.05 mBq.ml–1), which was calculated from the three times standard deviation of the count rate of the blank.

240Pu/239Pu atom ratios in the bottom sediments of the NW Pacific Ocean

Abstract239+240Pu concentrations and 240Pu/239Pu atom ratios in bottom sediments of the Yellow Sea, Korea Strait, East Sea (Sea of Japan), Sea of Okhotsk, and Northwest Pacific Ocean were determined. In coastal sediments near the Korean Peninsula, 239+240Pu concentrations varied from 0.02 to 1.72 Bq.kg-1, and their 240Pu/239Pu atom ratios from 0.15 to 0.24, with an average of 0.20±0.03. 240Pu/239Pu atom ratios of bottom sediments in the deep NW Pacific Ocean and its marginal seas (East, Okhotsk seas) were in the range of 0.15-0.23. A little elevated 240Pu/239Pu atom ratios in the bottom layer sediment may be due to Pu released into the environment during the pre-moratorium period, having high 240Pu/239Pu atom ratios and low 238Pu/239+240Pu activity ratios.

Distribution of3H,137Cs and239,240Pu in the surface seawater around Korea

The concentrations of3H,137Cs and239,240Pu were determined in surface seawaters collected at 21 sampling stations around Korea from October of 1994 to May of 1995. The results were consistent with the past data observed in the North Pacific. The concentrations of3H and137Cs did not show much difference no matter where the samples were taken. Due to the limited distribution of sampling points, no systematic change in3H and137Cs levels with latitude was observed. On the other hand,239,240Pu concentration in the East Sea (Japan Sea) was somewhat higher than that in the South and the Yellow Seas, although the data on239,240Pu concentration were not enough to explain the reason. The activity ratios of239,240Pu/137Cs in surface seawater ranged from 0.13% to 0.44% with a mean of 0.25±0.08%. The activity ratios were lower than those of the global fall-out level, 1.1%. This result presumably arose from the different behavior of the two radionuclides in seawater.

The new IAEA reference material: IAEA-434 technologically enhanced naturally occurring radioactive materials (TENORM) in phosphogypsum

A reliable determination of Technologically Enhanced Naturally Occurring Radioactive Materials in phosphogypsum is necessary to comply with radiation protection and environmental regulations. In this respect, a new phosphogypsum reference material was produced and certified to assist in the validation of analytical methods and the quality assurance of produced analytical results. This paper presents the sample preparation methodology, material homogeneity assessment, characterization campaign results and assignment of property values, and associated uncertainties. The reference values and associated uncertainties for Pb-210, Ra-226, Th-230, U-234 and U-238 were established based on consensus values calculated from analytical results reported by three National Metrology Institutes and five expert laboratories.

Technically enhanced naturally occurring radionuclides (TENORM) in phosphogypsum: Comparison CCRI(II)-S5

Within the frame of mutual cooperation between the IAEA and the BIPM, the Consultative Committee for Ionizing Radiation Section II—Measurement of Radionuclides accepted an IAEA-organized interlaboratory comparison in 2008 on the determination of technically enhanced naturally occurring radionuclides in phosphogypsum. The study was piloted by the Chemistry Unit at the IAEAs Laboratories in Seibersdorf (Austria). This report presents the methodology applied in conducting this comparison and the results. Activity results for Pb-210, Ra-226, Th-230, U-234, U-235 and U-238 were reported by three national metrology institutes (NMI) and five other expert laboratories or designated institutes. Four different approaches were used to calculate the nominal value of the reported results and associated uncertainties, and the results from each individual participant were evaluated and compared with this nominal reference value. The reported evaluation of the measurement results demonstrated agreement amongst the participating laboratories. Main text. To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/. The final report has been peer-reviewed and approved for publication by the CCRI Section II, according to the provisions of the CIPM Mutual Recognition Arrangement (MRA).

Evaluation of abundance of artificial radionuclides in food products in South Korea and sources

Food samples are collected nationwide from January 2016 to February 2017 and their contents of artificial radionuclides are measured to address the growing concerns regarding the radioactive contamination of food products in Korea. Specifically, 900 food samples are collected for this study and their contents of representative artificial radionuclides 134Cs, 137Cs, 239,240Pu, and 90Sr are analyzed. The analysis shows that the activity concentrations of 137Cs in fish range from minimum detectable activity (MDA) to 340 mBq/kg of fresh weight. The concentration factor (CF) determined for 137Cs as a measure of its bioavailability is calculated to be ca. 74 and found to be very similar to that (100) recommended by the International Atomic Energy Agency. With an MDA of <0.221 mBq/kg, the results reveal that 239,240Pu values in fish are below the MDA. The activity concentrations of 137Cs and 90Sr are lower than the MDA in both shellfish and seaweed, while the activity concentrations of 239,240Pu in shellfish range from 0.26 to 2.18 mBq/kg, and for seaweed samples range from 2.07 to 3.38 mBq/kg. The atom ratios of 240Pu/239Pu in shellfish caught at the Korean coast vary from 0.209 to 0.237, with a mean of 0.227. The higher 240Pu/239Pu atom ratio determined in shellfish is thought to be caused by the plutonium transported from the Pacific Proving Grounds rather than other sources such as the Fukushima nuclear power plant accident. The activity concentrations of 137Cs in mushrooms are found to vary from 1.0 to 21.4 Bq/kg, with the highest concentrations observed in the Oak (shiitake) and Sarcodon asparatus. 134Cs is detected in three mushroom specimens collected from Jeju Island and about 3-3.6% of 137Cs present in the wild mushrooms native to the Jeju Island are introduced as a result of the Fukushima nuclear plant accident. The annual effective doses of 137Cs received through consumption of mushrooms and fish are 2.0 × 10-4 mSv yr-1 and 3.9 × 10-5 mSv yr-1, and those values are negligible compared to the annual effective doses limit of 1 mSv yr-1.