Cause of radiation exposure was failure of safety device due to unauthorized operation
Unable to confirm details of unauthorized operation... Prosecutors' investigation referral under review
Operator report and initial response not violations of regulations
The Nuclear Safety and Security Commission (NSSC) has decided to impose corrective measures and fines regarding the radiation exposure incident that occurred last May at Samsung Electronics' Giheung plant. Additionally, it is considering requesting a prosecution investigation into the unauthorized manipulation whose circumstances have not been confirmed.
At the 201st NSSC meeting held on the 25th, the commission reported the investigation results and action plans concerning the radiation exposure incident at Samsung Electronics' Giheung plant.
This agenda pertains to an incident on May 27, when two maintenance workers at Samsung Electronics' Giheung plant were directly exposed to radiation due to a safety device (interlock) malfunction while servicing an 'X-ray fluorescence analyzer.' Both workers are currently receiving hospital treatment following the accident.
Both exposed workers exceeded the annual dose limit (0.5 sieverts/year) for equivalent dose to the skin (hands). Among them, one exceeded the dose limit (50 millisieverts/year) for effective dose (whole-body absorbed radiation). For reference, the radiation dose from a typical chest X-ray is 0.1 millisieverts (mSv).
The NSSC concluded that this exposure incident resulted from the operator's overall management negligence and decided to impose corrective actions along with fines.
"Lack of supervision and procedural adherence in radiation equipment maintenance work"
According to the NSSC investigation, the two workers were performing maintenance with the radiation device powered on when the accident occurred. This equipment, introduced from Japan in 2001, uses X-rays to inspect the condition of wafers. It has shielding to prevent X-ray exposure under normal circumstances, and the safety device is designed to activate automatically when the shielding is removed.
However, on that day, the safety device did not operate, resulting in the radiation exposure of the two maintenance workers.
The NSSC investigation found that prior to the incident, someone had manually altered the wiring, causing the safety device to malfunction. However, the exact time and person responsible for the wiring change remain unidentified. The NSSC speculates that at some point in the past, when X-rays were not emitted despite normal wiring, someone altered the wiring to enable X-ray emission.
An NSSC official explained, "We interviewed all workers who had maintenance experience over the past three years, but there was no record of any arbitrary manipulation of the safety device," and added, "We judged that supervision was significantly inadequate." There are a total of eight such devices at Samsung Electronics' Giheung plant, and three, including the accident device, were confirmed to have been arbitrarily manipulated.
Additionally, although the equipment had warning lights for radiation exposure, the two exposed workers did not notice the warning lights during their work. Originally, these warning lights used filament bulbs but were replaced with LEDs, which were less noticeable. The NSSC judged that this was not simply a personal error of the workers.
The NSSC investigation also revealed that the maintenance procedures at Samsung Electronics' Giheung plant were inadequate. According to the NSSC, Samsung Electronics had internal manuals related to maintenance and upkeep, but there was no procedure for how to respond when maintenance issues arose. In other words, there was no manual requiring reporting to the radiation safety manager, followed by review and approval before commencing maintenance.
An NSSC official stated, "There was no involvement of the radiation safety manager during this incident," and explained, "This is not so much the radiation safety manager's responsibility as it is the operator's fault for not granting such authority to the radiation safety manager."
Samsung Electronics also failed to properly utilize materials provided by the seller regarding the use, operation, maintenance, management methods, and handling prohibitions of the radiation equipment. Overall, the NSSC assessed that "the incident occurred due to inadequate management and supervision procedures for radiation safety, arbitrary manipulation of safety devices, non-compliance with safety rules, and lack of maintenance work review."
Accordingly, the NSSC determined that Samsung Electronics' Giheung plant violated the Nuclear Safety Act by failing to comply with radiation device handling technology and radiation hazard prevention measures, and decided to impose fines. The maximum fine applicable for these violations is 10.5 million KRW. Furthermore, the NSSC plans to order Samsung Electronics to improve organizational and procedural operations so that radiation safety managers can effectively perform management and supervision. The case of unauthorized manipulation of radiation equipment, for which the circumstances have not been confirmed, will be considered for referral to the prosecution for investigation.
Separately, the NSSC plans to promote system improvements for reportable radiation devices and conduct inspections of institutions possessing such devices. The NSSC will pursue radiation safety supervision and on-site inspections for institutions holding 30 or more reportable devices and identify additional necessary system improvements.
"Operator reporting and initial response are difficult to view as regulatory violations"
The NSSC judged that the operator's reporting and initial response are difficult to consider as violations of related regulations. Samsung Electronics became aware of the suspected exposure when the maintenance workers reported it on May 28 around 3 p.m. Later that day, at 5:47 p.m., the company reported the incident to the Korea Institute of Nuclear Safety (KINS). After medical examination at the Korea Institute of Radiological & Medical Sciences (KIRAMS) at 7:44 p.m. on May 28, radiation exposure symptoms were confirmed, and an initial written report was submitted around 3 p.m. the following day.
The NSSC explained, "Since the written report was submitted within the next working day after recognizing and reporting the suspected exposure, it is difficult to view this as a violation of reporting regulations."
Samsung Electronics also arranged for the exposed workers to receive medical diagnosis promptly by transferring them to the company hospital (4:20 p.m. on May 28), Ajou University Hospital (5:30 p.m.), and KIRAMS (7:44 p.m.). The NSSC stated, "Since the exposed individuals received medical diagnosis on the day they reported suspected exposure, it is difficult to consider this a violation of initial response regulations."
Meanwhile, Samsung Electronics' Giheung plant manages a total of 694 radiation devices, including one licensed device, under the supervision of two radiation safety managers. The equipment involved in this incident is a reportable device. Reportable devices are those that, when used according to the manufacturer's instructions, rarely cause accidents.
The NSSC investigation found that the radiation-emitting devices at the Giheung plant were used in licensed and reported locations, but the practical management and supervision system by radiation safety managers was insufficient. Violations of the Nuclear Safety Act were also found regarding education, health examinations, and exposure management for radiation workers handling licensed radiation-emitting devices.
Since July 25, the NSSC has been inspecting all radiation-emitting devices (147 units) across all Samsung Electronics plants to check the operation of safety devices and other factors.
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