S. Korea unaffected by Japan's reactor blasts

SEOUL, March 14 (Yonhap) -- The explosions of two Japanese nuclear reactors have not affected radiation levels in South Korea mainly due to the direction of winds in the region, the government said Monday.
The Ministry of Education, Science and Technology and the state-run Korea Institute of Nuclear Safety said radiation levels on Ulleung Island in the East Sea, which is closest to the two Fukushima reactors, have remained virtually unchanged in the past three days.
"The winds that affect the region of the nuclear power plant usually blow from west to east, so all radioactive materials are being sent out over the Pacific Ocean," the ministry said.
The Unit 1 reactor at the earthquake-damaged Fukushima No. 1 nuclear power plant experienced a hydrogen blast on Saturday. The Unit 3 reactor exploded earlier in the day as critical cooling systems for the reactor core malfunctioned after a record magnitude 9 earthquake took place off the northeastern coast of Honshu Island on Friday.
As of 1 p.m. Monday, the radiation level on Ulleung stood at 138 nanosievert (nSv) per hour, effectively unchanged from 137 and 139 nSv per hour checked on Saturday and Sunday, respectively.
"Overall levels have not changed at all from normal that is around 140 nSv," the ministry said. "There has been no difference in the readings collected from the 70 detection devices scattered throughout the country that are being monitored every five minutes around the clock."
The ministry also said South Korea's 21 operational atomic reactors have not been affected by the Japanese tremor.
The Uljin nuclear plant, located 1,164 kilometers from the epicenter of Friday's quake, reported a peak ground acceleration of just 0.0006g. This is way below the 0.2g that the reactors at the plant can withstand.
A 0.2g ground acceleration number translates into the plant being designed to withstand a 6.5 magnitude earthquake right under its bedrock. South Korea is located 1,000 kilometers from the nearest major tectonics fault line and rarely gets quakes over a magnitude of 3.
Despite the relative safety, the ministry said it will enhance its countermeasures so alerts will be issued if ground acceleration exceeds 0.01g. Reactors, in addition, will automatically go offline when a tremor from a quake reaches 0.1g, it added.