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Lost Source Accident in NanJing, China
Baowei CHEN1) ， Qipu ZHOU2)
1) China Institute for Radiation Protection
2) Nuclear and Radiation Safety Center ( Affiliated
to Chinese Department of the Environment )
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Contents
Source
Accident Process
Dose Calculation
Clinical Manifestation
Source
Source: Ir-192 Usage: industrical defect detection Activety: about 0.94TBq (25.5Ci)
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Process
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On 7th, May
Four workers had done industrial defect detection work in a workshop of a factory which locates in NanJing, a big city in the southeast of the China.
The work had been finished, the detection instruments needed to be collected and taken away from the workshop.
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Process
7th May, about 3:00 a.m.
When the workers collected the instruments, they found that the remote control cable can’t be unloaded.
According to the machine’s design, only when the radiation source locates in the machine, the remote cable can be unloaded. Otherwise, the cable’s unloading is impossible.
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So, the radiation source was suspected still had located in the source guide tube, yet.
The workers shook the guide tube wanted to find the source, but there wasn’t source in the tube.
(Indeed, the source had slid off tube when they had picked the tube up, before they shook it.)
Process
Guide Tube
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Process One worker took a dosimeter to detect the dose near the surface of the machine.
The dose rate indication was high, so he thought the source must be located in the machine.
(indeed, if there had been a source in the machine, the dose rate near the machine can’t be so high. The machine’s radiation shield is thick enough. The exposure actually came from the radiation source near the machine.)
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Process Because the workers believed that the source had located in the machine,
they took the machine with the unloaded cable away from the workshop.
About at 7:00 a.m. ,7th, May
Other employees went into the workshop and begun their work. One worker found the source. He picked it up, looked it carefully. He didn’t know what it was, then he thrown it out of the workshop.
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ProcessAbout at 8:00 a.m. ,7th, May Another worker, named Wang(who received the most radiation dose in this accident), found the source near the workshop’s door. He thought it was beautiful and attractive, so he picked it and put it into his pocket.
Then Wang took a rest with source in his pocket in a rest room about one hour. There was a workmate of Wang in the room, The workmate was also irradiated.
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ProcessAbout at 9:00 a.m. ,7th, May Wang had done his normal work till 11:30, some his workmates near him had been irradiated.
Wang had finished his work and went his home with the source in his pocket at about 11:30 . Then he put the source in a warehouse locates in his backyard.
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Process
At night, 8th, May
The formal four workers took the inspection instruments into the workshop again. The film wasn’t photo sensitized after the “exposure”. So the radiation source was found lost!
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ProcessAt 2:00, 9th, May
The radiation source lost accident was reported to environment protection bureau and police bureau of NanJing city.
At 3:00, 9th, May
Environment protection bureau’s employees went to the workshop where the source was lost.
At 8:00, 9th, May
The policemen went to the workshop and asked everyone worked in the factory. They promised 20,000 RMB Yuan to the people who provided the corresponding information. But the policemen didn’t tell that the lost item is harmful.
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Process Mr. Wang felt fearful. He had not the knowledge about radiation source, and he thought the item he had picked up must be very expensive, otherwise the policemen can’t provide so much money for it’s information. He thought policemen maybe regard him as thief who stolen the “very expensive treasure”. So he didn’t tell policemen the truth, and he telephoned his wife to transfer the source to his parents’ home.
Mr. Wang feared and feared at that night. The next morning(10th, May), he went to his parents’ home, wrapped the source with a dark blue plastic bag and thrown it to a grass 100 meters away from his parents’ home.
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Finding the source
The approximate position of the source was found through gamma-ray detection instruments at morning 9:00 a.m. on 10th May, after Wang had thrown it 3 hours late. But the precise position’s determination was difficult, because the source was too small and the radiation was too strong near the source. Finally, a metal-detector was used to find the precise position of the source.
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Process
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Calculation Mr. Wang’s DoseLocal Dose ： Thigh ： D=157Gy
(t=3.5h,r=5cm,D5cm=50Gy/h)
Hands ： (picked up and looked up the source, loaded the source, took the source)
D=D1+D2+D3=14.33Gy
Whole Body Dose ： 2.55 Sv （ Bladder, gonad, red marrow and skin are mainly considered. ）
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Calculation Other People’s DoseWang’s Wife ： Hands Dose(Carrying source ) ： 0.16Gy; Whole Body Dose(Carrying source and close
contact source at home ）： 270mSv
The person who first picked up the source ： Hands Dose ： 0.83Gy; Whole Body Dose ： 8.3mSv 。
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Other people working in workshop ： 9 person （ 3-5m from source ）， Dose ： 2.5-6.25mSv
4 person （ 6m from source ）， Dose ： 1.74mSv
7 person （ 15m from source) ， Dose ： 0.28mSv
20 person (20-40m from source) ， Average Dose ：
0.07mSv
The road construction workers near the warehouse:
20 person (10-20m from source) Dose ： 0.78~ 3.125mSv22
Calculation Other People’s Dose
The workmate rested along with Wang in rest room
Average range from source ： 3meters ， Dose ： 13mSv
Wang’s family and tenant:
Dose ： 25~37.5mSv
Wang’s parents and sister:
Wang’s Father ： 0.09mSv;
Wang’s Mother ： 1.22mSv
Wang’s Sister ： 0.22mSv
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Calculation Other People’s Dose
Two tenants lived in second floor up the
source’s room
Dose ： 5.12-6.4mSv;
The constructors near the place where the
source was found
11 constructors （ 30-80m from the source ），
Maximum Dose ： 0.42mSv24
Calculation Other People’s Dose
Conclude of the calculation Near 100 people(More than 80) had been
irradiated in this source lost accident. The person who accepted the most dose is
Wang. His local dose are more than 100 Cy, and his whole body dose is about 2.5Sv. This dose is very harmful, but not fatal.
Wang’s wife had once carried the source and close to the source long time at home, her dose maybe about 270 mSv.
All of the other people’s dose are little than 50mSv.
These data come from calculation used by physical method, the uncertainties of the data maybe large.
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Clinical Manifestation
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Wang is in the hospital and undergoing treatment at present. An abscess had been taken placed on his right thigh. No life threatening temporarily.
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Thanks ！
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