The Evaluation on the Environmental Radiation around the Nuclear Facilities in Ulsan

Abstract

This research, centered around (Shin) Kori Nuclear Power Plant (NPP) near Ulsan, which is the area with the highest centration of nuclear power plants in Korea, evaluated the effects nuclear facilities have on the surrounding environment through total of 18 sites, 47 sample examinations and t-test comparison verification method with non-nuclear power plant area. For the sample examination, 18 sites were selected considering the isotropy and easy grab of sample at 5 km interval from 5 km to 30 km from the nuclear facility and the 47 total samples were collected, which include soil, surface water, gamma dose rate, moss, pine needles, rice, and cabbage. Based on it, the distribution of radionuclide out of the environment was analyzed according to the distance from the nuclear facility From the result, gamma dose rate using the portable dosimeter, FH-40G, counts mode and dose rate mode showed a radioactivity level of a background level with the average of 174±21, 173±19 nSv/h each. From the soil sample, out of the artificial gamma ray emission nuclide, only 137Cs showed an average of 13.1 Bq/kg-dry, <1.10 ~ 38.2 Bq/kg-dry. Also, from the indicator plant, at the 2 pine needle sites (20 km, 25 km), 137Cs was found to be 58.8, 80.8 mBq/kg-fresh each, from the Moss, 137Cs 3.34 ~ 22.1 mBq/kg-dry was detected from all 3 samples, but at one sample (10 km), a small amount of 134Cs at 1.34±0.18 mBq/kg-dry was detected. However, in the surface water, all the activity was less than the MDA. Also, artificial radionuclide was not detected at all samples of the vegetables and grains harvested in the places within 5 km (short distance) and more than 10 km (above 30 km) from nuclear facility. Excluding the moss sample, the tendency of radioactivity concentration according to the distance from the nuclear facility was not found in other samples. And in soil, pine needle, moss samples 134Cs (half-life 2.06 years) and 137Cs (half-life 30 years), which show similar behavior in case of accidents, were detected. The activity concentration of 137Cs from the soil, was ranged between 4.5 and 145 Bq/kg-dry in Korean soil. Moss showed a similar level to the result (15.0 ~ 40.9 Bq/kg-dry) of the research conducted on the Jeju area without nuclear facilities. In other samples, artificial emission nuclide was not detected or the detected activity, where it was less than MDA, was too infinitesimal to be considered as an effect due to the nuclear facilities. Therefore, it thought that to be the effects from the atmospheric nuclear tests conducted since 1960s in the past or Chernobyl nuclear accidents. Also, using the 2013 surveillance results of local radioactivity monitoring station, the difference of the radiation/radioactivity level of the soil samples and gamma dose rate between the nuclear facility and the non-nuclear facility area was comparatively analyzed using the statistical t-test. The P-value of the soil was 0.15, which is three times higher than 0.05 of the significance level at the 95% confidence interval. For the gamma dose rate, compared to the non-nuclear facility area of Gunsan, P-value was 0.17 at the dose rate mode, which is approximately three times higher than 0.05 of the significance level, and 0.16 at the counting mode. The study showed the level of environmental radiation in Ulsan had the background. It was thought that the nuclear facilities in Ulsan had little effects on the surrounding environments and, therefore, the nuclear facilities were being operated safely.