Regarding the incident of a radiation source coming loose at a nondestructive testing worksite in South Chungcheong, it was confirmed that one on-site worker's hand exposure dose exceeded the annual dose limit.
The Nuclear Safety and Security Commission said that while investigating the radiation source detachment incident that occurred on Apr. 29 at company A's nondestructive testing worksite in South Chungcheong, the dose assessment for one worker found the equivalent dose to the hand to be at least 1.3 Sv (sievert). That far exceeds the annual dose limit for the hand of 0.5 Sv.
The incident occurred at about 4:50 p.m. on Apr. 29 during an outdoor gas pipeline radiographic inspection. Because the remote control of the gamma irradiator did not operate properly, the radiation source, selenium-75 with an activity of 1.4 TBq (terabecquerel), became stuck outside the shielding container.
Company A reported to the Nuclear Safety and Security Commission that the radiation source became stuck outside the irradiator on the day of the incident but was retrieved immediately. The Nuclear Safety and Security Commission dispatched a Korea Institute of Nuclear Safety (KINS) investigation team to the site that day to conduct an initial probe, including the sequence of events and response measures, worker interviews, verification of direct-reading dosimeter values, and an urgent readout request for personal dosimeters.
The direct-reading dosimeter values confirmed on site for six workers were all below the dose limit, with a maximum of 2.38 mSv (millisievert). The urgent readout of personal dosimeters also showed all six workers were below the dose limit.
However, the Nuclear Safety and Security Commission confirmed that during the retrieval of the radiation source the worker wore protective gear such as a lead apron and lead gloves but did not use a retrieval tool like tongs. Accordingly, it requested a blood test for the worker and began assessing the dose to the hand using an exposure dose evaluation program.
The blood test showed no abnormalities, and so far the worker has not exhibited any notable symptoms such as skin erythema or swelling on the hand. The Nuclear Safety and Security Commission asked the company to report immediately if abnormal symptoms occur.
The Nuclear Safety and Security Commission said, "The radiation source in question is currently stored safely, so there are no additional effects," and added, "We will investigate the detailed cause of the incident and whether radiation safety management procedures were violated, and will ask company A to draw up measures to prevent a recurrence."