Gamma radiography: serious accidents abroad The number and consequences of gamma radiography accidents in France have remained limited since March 1979, when a worker had to have a leg amputated after having picked up a 518 GBq source of iridium-192 and put it in his pocket. This incident had led to a tightening of the regulations in effect at the time. This must not be taken for granted. ASN keeps a watchful eye on accidents occurring abroad which have sometimes had serious effects. Over the last few years (in 2024, no accidents have been reported to date), examples brought to ASN’s attention confirming the risks to which operators can be exposed as a result of inappropriate actions, include: • In 2023 in South Korea, a radiographer was exposed (116 millisieverts – mSv – for the whole body, 1,957 mSv to the hand) when manipulating a gamma ray projector whose irridium-192 source was no longer connected to the remote control cable. Owing to a lack of adequate radiation protection equipment, the radiographer did not notice the situation until the work was finished and the developed images were found to be overexposed. • In 2023 in Germany, a radiologist was exposed to a dose of 71.5 mSv after entering a facility when the electrical device emitting ionising radiation used in that facility was still in operation. The causes of the event are still being investigated. Another radiologist was exposed (230 mSv for the whole body, 546 mSv to the lens of the eye) when he placed his head in an X-ray beam for two minutes in order to align the part being X-rayed, despite the radiation protection measures in place (flagging tape, flashing signal light and audio warning from the active dosimeter). • In 2023 in the United States, a trainee radiographer was exposed several times to a source of iridium-192 on a worksite when carrying out various operations (replacement of the film, movement of the guide tube) while the source was still positioned in the irradiation endpiece due to the detachment of the source holder In the course of this incident, several radiation protection barriers were not observed, notably by the lack of supervision of the trainee radiographer (particularly during the source holder connection phase), failure to wear a dosimeter or use a radiation meter and verify that the source had returned properly into the projector (check of the indicator light, measurements, etc.). The trainee radiographer only noticed the problem when the guide tube became disconnected from the source projector. The dosimetric reconstruction (as no dosimeter was worn) gave an effective received dose estimate of 75 mSv and 258 mSv at the extremities. • In 2022 in the United States, a team of three operators of a non-destructive testing company was performing gamma radiography work. One of the operators was close to the cobalt-60 source when it was ejected by his colleague who did not have direct visual contact with him. Given the very noisy environment of the worksite, the operator did not hear the alarm of his monitoring devices and was exposed to a dose of 55 mSv for about one minute. • In 2022 in Belgium, a radiographer was exposed (14 mSv whole body, extremity dose not specified) to a selenium-75 source for a short period (60 to 90 seconds) when he tried to disconnect the device collimator while the source was still present in it. The alarm of his active dosimeter did not function because its battery was discharged; furthermore, the operator was not wearing his radiation meter. It was the triggering of his assistant’s active dosimeter alarm when he approached the source that signalled the incident. • In 2022 in Hungary, an operator was exposed to about 134 mSv when handling the collimator and the guide tube, as the selenium-75 source was not retracted into the safe position in the projector. • In 2021 in the USA, an employee of a non-destructive testing company was exposed to a dose of 70 mSv (whole body) while carrying out gamma radiography exposures within a dedicated facility. The procedures in force at the time of this accident authorised the operator to be present inside the facility even when the source was in the irradiation position. An employee of another non-destructive testing company was exposed to a dose of 93 mSv (whole body) when manipulating a defective gamma radiography projector whose source was not in the safe position. These two events were rated level 2 on the International Nuclear and Radiological Event Scale (INES). • In 2021 in Serbia, an iridium-192 source became detached from the remote control cable during an outdoor non-destructive test. The two operators did not check that the source had returned to the safe position at the end of the inspection and did not notice its absence until they got back to their company base. The source was found the next day after the intervention of a specialised laboratory. The two operators were exposed to doses of 451 mSv and 960 mSv. • In 2021 in Spain, an employee of a non-destructive testing company was exposed after entering a gamma radiography bunker when the iridium-192 source was not in the safe position (source jammed). The passive dosimeter of the first employee indicated a dose of about 70 mSv, and that of the second about 3 Sieverts (Sv). The event was rated level 2 on the INES scale. The data for earlier incidents can be consulted in the previous issues of this annual report, which are available on asn.fr, under the headings “ASN informs”, “Publications”, “ASN Reports”. Selenium-75 gamma radiography The use of selenium-75 in gamma radiography has been authorised in France since 2006. Implemented in the same devices as those functioning with iridium-192, selenium-75 offers significant radiation protection advantages. This is because the equivalent dose rates are about 55 millisieverts per hour and per terabecquerel (mSv/h/TBq) one metre from the selenium-75 source, as opposed to 130 mSv/h/TBq for iridium-192. Yet it can be used in place of iridium-192 in numerous industrial fields, especially the petrochemical or boilermaking industry, and it enables the cordoned-off safety area to be significantly reduced and facilitates intervention in the event of an incident. In France, about 11% of the devices are equipped with selenium-75 sources. The use of selenium-75 has stagnated over the last few years and has even been decreasing since 2023 (20% in 2022 and 15% in 2023). More specifically, the current geopolitical context (sanctions against Russia because of the war in Ukraine) is resulting in a restructuring of the global supply chain for gamma radiography sources, accompanied in particular by delays in delivery. Nevertheless, new procurement routes have been set up by the source suppliers in the last few years, and new ones are being explored in order to reduce procurement times and restore the 2022 level. ASN therefore still encourages the use of selenium-75 whenever possible. 264 ASN Report on the state of nuclear safety and radiation protection in France in 2024 Sources of ionising radiation and their industrial, veterinary and research applications
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