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IAEA International Atomic Energy Agency Radiation Sources in Industrial and Research irradiators Overview and Accidents Day 6 – Lecture 1.

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Presentation on theme: "IAEA International Atomic Energy Agency Radiation Sources in Industrial and Research irradiators Overview and Accidents Day 6 – Lecture 1."— Presentation transcript:

1 IAEA International Atomic Energy Agency Radiation Sources in Industrial and Research irradiators Overview and Accidents Day 6 – Lecture 1

2 IAEA To understand the uses of research and industrial irradiators and the potential for accidents to occur with their use. Objective 2

3 IAEA Beneficial uses of ionizing radiation. Categories of irradiation facilities. Need for an adequate radiation safety program Consequences of radiological accidents Contents 3

4 IAEA Beneficial uses of ionizing radiation in irradiators Sterilization of medical products (e.g. insulin syringes); Used in more than 160 gamma irradiation facilities and over 1300 electron beam facilities (2003) Sterilization of blood products; Sterilization of pharmaceutical products; Preservation of foodstuffs (spices etc); Eradication of insects; Synthesis of polymers; Irradiation of cell cultures for research purposes. 4

5 IAEA Types of Irradiators Gamma Irradiation Facilities The total source activity in an irradiator may range from a few Terabecquerels (10 12 Bq) to more than 100 Petabecquerels (> Bq). 5

6 IAEA Types of Irradiators (cont) An irradiator in which the sealed source is:- Category I (gamma) and where human access to the sealed source and the volume undergoing irradiation is not physically possible in the designed configuration. [IAEA Safety Series 107] is shielded at all times; completely enclosed in a dry container constructed of solid materials, 6

7 IAEA Types of Irradiators (cont) 7

8 IAEA Category II (gamma) A controlled human access irradiator in which the sealed source is:- Types of Irradiators (cont) is fully shielded when not in use; and is exposed within a radiation volume that is maintained inaccessible during use by an entry control system. [IAEA Safety Series 107] enclosed in a dry container constructed of solid materials; 8

9 IAEA Types of Irradiators (cont) Personnel access door Control panel Source holder Turntable 9

10 IAEA Category III (gamma) An irradiator in which the sealed source is:- Types of Irradiators (cont) Sample or product container Product hoist cable Demineralized water pool approx 7 m Source array Source rod is shielded at all times, and where human access to the sealed source and the volume undergoing irradiation is physically restricted in the designed configuration and proper mode of use. [IAEA Safety Series 107] contained in a water filled storage pool, 10

11 IAEA Category IV (gamma) A controlled human access irradiator in which the sealed source is:- Types of Irradiators (cont) is fully shielded when not in use; and is exposed within a radiation volume that is maintained inaccessible during use by an entry control system. [IAEA Safety Series 107] contained in a water filled storage pool; 11

12 IAEA Types of Irradiators (cont) 2 m concrete shielding Hoist cable Source hoist cylinder Access for source transport container Product Conveyor Shielding pool Guide cable Control panel Source array (safe position) Personnel access door Source transport container 12

13 IAEA Types of Irradiators (cont) 13

14 IAEA Electron Beam Facilities Category I An integrally shielded unit with interlocks where human access during operation is not physically possible owing to the configuration of the shielding IAEA Safety Series107 divides electron irradiation facilities into two categories. Category II A unit housed in shielded rooms that are maintained inaccessible during operation by an entry control system 14

15 IAEA Electron Beam Facilities (cont) Lead shield Product conveyor High voltage transformer Controls Single stage electron beam source 15

16 IAEA Electron Beam Facilities (cont) Scan horn Concrete shield High voltage system Oscillator cabinet Access labyrinth Product conveyor 16

17 IAEA Accidents Need for an adequate radiation safety program 5 fatal accidents were reported to the IAEA between 1975 and Deaths from exposure to radiation from irradiators Incident 1DosePrime causes 1 to 4 minutes to 500 TBq 60 Co 12 Gy to the bone marrow Untrained, unsupervised and unauthorized worker gained access to the irradiation cell The source had been left exposed [Lessons learned from accidents in industrial irradiation facilities. IAEA, 1996] 17

18 IAEA Need for an adequate radiation safety program Deaths from exposure to radiation from irradiators (cont) Incident 2DosePrime causes “Several minutes” to 2.43 PBq 60 Co 22 Gy. Died 13 days later. Faulty GM monitor dismantled leaving only one non-redundant interlock safety system connected to the entrance door. Continued operation of the facility nevertheless was permitted by management. Operator failed to use a portable survey meter [Lessons learned from accidents in industrial irradiation facilities. IAEA, 1996] 18

19 IAEA Need for an adequate radiation safety program Death from exposure to radiation from irradiators (cont) Incident 3DosePrime causes 23 TBq 60 Co Three workers exposed; one died 8.3, 3.7 and 2.9 Gy. One death after 6.5 months Lack of regulatory control No contact with persons having radiation safety expertise Inadequate worker training Key safety features were not repaired. Some removed [Lessons learned from accidents in industrial irradiation facilities. IAEA, 1996] 19

20 IAEA Need for an adequate radiation safety program Death from exposure to radiation from irradiators (cont) Incident 4DosePrime causes 1 ½ - 2 mins to 12.6 PBq 60 Co Gy. Died 36 days later Faulty limit switch indicating “source down”; safety interlocks were by-passed Gamma monitor ignored (failed previously) Management had not installed the shroud recommended by the manufacturer to prevent product jamming. Operating instructions not in local language [Lessons learned from accidents in industrial irradiation facilities. IAEA, 1996] 20

21 IAEA Need for an adequate radiation safety program (cont) Electron irradiator accidents Incident 1OutcomePrime causes Gy to R hand; Gy to R foot; 290 Gy to parts of R leg from 10 MeV electrons Right arm amputated above elbow 138 days later Right leg amputated above knee 6 months later Worker knowingly entered the room by an unauthorized method (under the door through which the conveyor passed) thus effectively bypassing interlocks [Lessons learned from accidents in industrial irradiation facilities. IAEA, 1996] 21

22 IAEA Need for an adequate radiation safety program (cont) Electron irradiator accidents (cont) Incident 2OutcomePrime causes Exposed during maintenance procedures to Gy/s over 1-3 mins from “dark current” from 3 MeV electrons. 4 digits of R and L hands amputated after 3 months Hair thinning after 2 weeks. No regrowth after 6 months Worker not aware of “dark current” Worker did not use any radiation survey meter Worker did not have personal dosimeter Untrained assistant [Lessons learned from accidents in industrial irradiation facilities. IAEA, 1996] 22

23 IAEA Need for an adequate radiation safety program (cont) Electron irradiator accidents (cont) Incident 3OutcomePrime causes Hands in 15 MeV beam while adjusting an experimental sample. Dose difficult to estimate R hand and 2 fingers of L hand amputated 8-15 months later Facility had no interlocks or warning signals (1991) A physicist (who was responsible for radiological protection) entered the irradiation chamber to adjust a sample. A co-worker activated the irradiator without checking. [Lessons learned from accidents in industrial irradiation facilities. IAEA, 1996] 23

24 IAEA Need for an adequate radiation safety program (cont) 24

25 IAEA Need for an adequate radiation safety program (cont) 25

26 IAEA Major causes of radiological accidents Flaws in the initial design. Redundant and diverse safety systems could have prevented most accidents. Access barriers based on radiation activated interlocks had either not been installed, had been removed, or were easily defeated. When trying to resolve problems, personnel were tempted to circumvent barriers if they could be easily bypassed with ladders, by stooping or crawling, or by manipulating switches, using tape, etc. In several facilities, personnel had employed tricks to circumvent the safety systems. 26

27 IAEA Personnel involved in accidents generally failed to follow instructions to alert radiation safety supervisors when alarms indicated that the source was not in the safe “shielded” position. Major causes of radiological accidents (cont) Personnel had usually failed to use a demonstrably operational portable radiation survey meter when entering the irradiation chamber. The incidents suggest that not following this obvious and simple safety precaution may be common practice. (Most operators involved in incidents also had not worn their personal monitoring device.) 27

28 IAEA In some incidents, management tolerated the removal or the defeat of radiation activated interlocks. In at least one accident, management apparently approved the installation of a switch to bypass an interlock and the removal of the only passive detection system that could not be circumvented easily by stooping or crawling. Major causes of radiological accidents (cont) Several accidents occurred after management had received the manufacturer’s recommendation to install a protective shroud that could have prevented the accident, but had failed to do so. 28

29 IAEA Many of the accidents occurred during shifts with only one trained worker on duty or on call. Employee behavior appeared to reflect a management policy of having one person undertake as many tasks and responsibilities as possible. Major causes of radiological accidents (cont) Workers and operating personnel performed inappropriate actions based on available information and instructions given. In some cases, the personnel involved were not adequately trained to understand the hazards, or those who were trained made bad judgments 29

30 IAEA Lessons learned from radiological accidents Diverse safety systems could have prevented most accidents. Safety is compromised if the facility is not carefully audited to identify conditions critical to safety.  This requires consideration of redundancy, avoidance of single mode failures and human factors.  Where these considerations were not adequately taken into account, unsafe conditions resulted. 30

31 IAEA The management of the operating organization can quickly lose control of the employees’ level of knowledge and performance unless systematic audits are conducted and frequent training is provided. Lessons learned from radiological accidents (cont) Management practices or attitudes resulted in degradation of the safety systems and operating procedures. It appears that sometimes product and production costs took precedence over safety. This was particularly evident when oversight from the Regulatory Authority was absent or weak. 31

32 IAEA Personnel involved in accidents sometimes lacked an understanding of the fundamental principles of the devices with which they were working. e.g. the cold discharge current for electron sources or the connection between a strong odor of ozone and the interaction of ionizing radiation with air. Lessons learned from radiological accidents (cont) 32

33 IAEA Prevention and remedial actions If implemented, the following would greatly improve the safety performance of industrial irradiators and reduce the frequency and mitigate the severity of accidents when they do occur. 33

34 IAEA Funding Organizations Organizations have provided funds for the installation of irradiators in developing countries in which the radiation protection infrastructure is not yet strong or in countries that are not sufficiently experienced in the licensing and inspection of irradiators Prevention and remedial actions (cont) Such organizations must recognize their safety responsibilities and promote the development and implementation of radiation protection programs for irradiators 34

35 IAEA Licensees:- are responsible for the operation of the irradiator and the security of radiation source(s) in accordance with the requirements of the legislation imposed by the Regulatory Authority; Prevention and remedial actions (cont) have primary responsibility for radiation safety. Senior management must recognize the potential hazards associated with an irradiator’s operation and must exercise leadership in developing and maintaining a strong safety culture throughout the entire organization. 35

36 IAEA Designers, Manufacturers, Suppliers and Installers Prevention and remedial actions (cont) should provide sufficiently detailed information for the development of local operational and maintenance procedures, to enable a hazard assessment to be carried out and for emergency instructions to be prepared. must provide safety information in the local language bear a primary responsibility for carrying out research, testing and examination to ensure the safe design and performance of facilities, equipment and systems. 36


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