Chang-Kyu Kim

Radiological impact in Korea following the Fukushima nuclear accident

The pathway and radiological impact of the radioactive plume released at the Fukushima nuclear accident site on the Korean Peninsula has been studied. On March 28, 2011, only (131)I was first observed at all 12 regional monitoring stations in Korea, and the highest activity concentrations in aerosol were 3.12 mBq/m(3) for (131)I at Gunsan, 1.19 mBq/m(3) for (134)Cs and 1.25 mBq/m(3) for (137)Cs at Busan on April 7, 2011. These radionuclides were also detected in dry and wet deposition samples, while the significant increase of (131)I, (134)Cs and (137)Cs activity concentrations were not observed in seawater and marine biota samples.

Simultaneous determination of 226Ra and 210Pb in groundwater and soil samples by using the liquid scintillation counter – suspension gel method

A method for the simultaneous determination of 226Ra and 210Pb in groundwater and soil samples by liquid scintillation counting was developed. Radium and lead were separated together from the samples as Ba(Ra) x PbSO4 co-precipitate, which was centrifuged and dissolved with 0.1 M EDTA solution (pH 9.0). Radium was separated as Ba(Ra)SO4 co-precipitate by adding ammonium sulfate and adjusting the pH of the solution to 4.2. Lead remaining in the solution was separated as PbSO4 precipitate by adding 9 M sulfuric acid. These Ba(Ra)SO4 and PbSO4 precipitates were purified with EDTA solution and used for measurement. To save time and to make counting samples simpler, direct counting of Ba(Ra)SO4 and PbSO4 precipitates instead of the phosphoric acid fusion method was attempted. Ba(Ra)SO4 and PbSO4 precipitates were suspended in the scintillation gel, and measured. Two liquid scintillation cocktails, Instagel XF and UltimaGold AB were used to prepare the counting samples. A mixture of water (40%), Instagel XF (40%) and UltimaGold AB (20%) formed a stable gel. Activities of 226Ra and 210Pb were calculated from the alpha spectrum of Ba(Ra)SO4 and beta spectrum of PbSO4, respectively. The long-term stability of the suspension gel was good. The analytical results of 226Ra and 210Pb in spiked groundwater samples were in good agreement with the known concentrations of 226Ra and 210Pb. The analytical values of 226Ra and 210Pb in the soil reference samples were within 11.5 and 1.6% of the relative error from the reference values, respectively.

Determination of226Ra in environmental samples using high-resolution inductively coupled plasma mass spectrometry

A time-saving and accurate technique for determining226Ra in groundwater and soil was examined, using high-resolution inductively coupled plasma-mass spectrometry (HR-ICP-MS). The technique was applied to the determination of226Ra in groundwater and soil samples and compared with the conventional liquid scintillation counting method. This technique was capable of completing226Ra counting within 3 minutes, without the in-growth period to allow radon and its progeny to achieve secular equilibrium with the parent226Ra. The detection limits of HR-ICP-MS for226Ra in groundwater and soil were 0.19 mBq·1−1 and 0.75 Bq·kg−1, respectively, which were about 10 times lower than that of the liquid scintillation counter. The results obtained from HR-ICP-MS in groundwater and soil were in accordance with those of LSC within a relative error of about 13%.

Environmental distribution and behavior of 3H and 14C around Wolsong Nuclear Power Plants.

Abstract—To estimate of the dispersion trend of 3H and 14C discharged from the Wolsung Nuclear Power Plants, the present level of 3H and 14C in environmental samples in the vicinity of the Wolsong site was studied. Tree-ring cellulose analyses were carried out for retrospective evaluation of 3H and 14C in the environment around the Wolsong Nuclear Power Plants. 3H released from the Wolsong Nuclear Power Plants has affected an area up to a 25-km radius from the site, while almost all 14C was deposited within a 2-km radius, reaching to a natural level over 2 km. Organically bound tritium concentrations in tree rings were strongly correlated with the gaseous tritium discharge rate, while &dgr;14C (excess) in tree rings ranged from 204‰ to 460‰, which did not significantly vary with year.

Fluctuations of exposure rate at regional radiation monitoring stations in Korea

Based on hourly means of exposure rate between August 2000 and July 2001 at nine Regional Radiation Monitoring Stations (RRMS) in Korea, we analyzed spatio-temporal characteristics of exposure rate. The mean and fluctuations of exposure rates were 99 and 3.8 nGy h(-1), respectively. The hourly exposure rate over 9 RRMS indicated a diurnal pattern with the exposure rates reaching a maximum between 5:00 and 8:00 a.m. in the early morning and a broad minimum between 4:00 and 10:00 p.m. in the afternoon. The fluctuations of exposure rate in the inland areas were less than 3.2 nGy h(-1), and those of exposure rate in coastal areas were larger than 3.9 nGy h(-1). The frequency distribution of exposure rates had one peak around the mean and was to be skewed to the right or positively skewed and its tails were fatter than those of a normal distribution. The interrelations of exposure rates at each station generally decreased with the distance between the stations. Empirical orthogonal function (EOF) analysis showed that almost all (99.9%) of exposure rate fluctuations were described by simultaneous variations. The spatial distribution of the first EOF modes of actual, low-pass (periods longer than one month) and high-pass (periods shorter than one month) exposure rate series were similar to each other.

230,232Th in milk, meat, and grain in korea

The concentrations of natural radioisotopes 230Th and 232Th in Korean foods were measured by the method of calcium oxalate co-precipitation in addition to the conventional anion-exchange method and alpha spectroscopic measurement. The 230Th concentrations(mBq/kg-fresh) in Korean foods were found to be as follows: milk 0.14~2.45, pork 2.98~8.97, beef 1.94~9.80, chicken 1.22~13.0, rice 0.43~2.35, wheat 0.53~14.4, and soybeans, 8.44~91.6. The 232Th concentrations(mBq/kg-fresh) in Korean foods were found to be as follows: milk 0.01~2.46, pork 0.28~9.32, beef 1.02~5.34, chicken 0.56~4.98, rice 0.32~2.54, wheat 0.53~20.0, and soybeans, 2.30~42.2. The annual internal dose of Th was also estimated. The annual internal dose of 230Th and 232Th in milk was about 0.006 uSv/yr and much lower than that of other countries because of the low intake of milk in Korea compared to other countries. The annual internal dose of 230Th and 232Th in the rice was about 0.043 pSv/yr and highest because rice is the staple food of Koreans.