Presentation on theme: "Radiation Sources in Industrial and Research irradiators"— Presentation transcript:
1 Radiation Sources in Industrial and Research irradiators Overview and AccidentsDay 6 – Lecture 1
2 ObjectiveTo understand the uses of research and industrial irradiators and the potential for accidents to occur with their use.
3 Contents • Beneficial uses of ionizing radiation. Categories of irradiation facilities.• Need for an adequate radiation safety program• Consequences of radiological accidents
4 Beneficial uses of ionizing radiation in irradiators Sterilization of medical products (e.g. insulin syringes);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.Used in more than 160 gamma irradiation facilities and over 1300 electron beam facilities (2003)
5 Types of Irradiators Gamma Irradiation Facilities The total source activity in an irradiator may range from a few Terabecquerels (1012 Bq) to more than 100 Petabecquerels (> 1017 Bq).
6 Types of Irradiators (cont) Category I (gamma)An irradiator in which the sealed source is:-completely enclosed in a dry container constructed of solid materials,is shielded at all times;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]
8 Types of Irradiators (cont) Category II (gamma)A controlled human access irradiator in which the sealed source is:-enclosed in a dry container constructed of solid materials;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]
9 Types of Irradiators (cont) Personnel access doorControl panelSource holderTurntable
10 Sample or product container Demineralized water pool Types of Irradiators (cont)Sample or product containerProduct hoist cableDemineralized water poolapprox 7 mSource arraySource rodCategory III (gamma)An irradiator in which the sealed source is:-contained in a water filled storage pool,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]
11 Types of Irradiators (cont) Category IV (gamma)A controlled human access irradiator in which the sealed source is:-contained in a water filled storage pool;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]
12 Types of Irradiators (cont) 2 m concrete shieldingHoist cableSource hoist cylinderAccess for source transport containerProduct ConveyorShielding poolGuide cableControl panelSource array (safe position)Personnel access doorSource transport container
14 Electron Beam Facilities IAEA Safety Series107 divides electron irradiation facilities into two categories.Category IAn integrally shielded unit with interlocks where human access during operation is not physically possible owing to the configuration of the shieldingCategory IIA unit housed in shielded rooms that are maintained inaccessible during operation by an entry control system
15 High voltage transformer Single stage electron beam source Electron Beam Facilities (cont)Lead shieldProduct conveyorHigh voltage transformerControlsSingle stage electron beam source
16 Electron Beam Facilities (cont) Scan hornConcrete shieldHigh voltage systemOscillator cabinetAccess labyrinthProduct conveyor
17 Accidents Deaths from exposure to radiation from irradiators Need for an adequate radiation safety programDeaths from exposure to radiation from irradiators5 fatal accidents were reported to the IAEA between 1975 and 1994.Incident 1DosePrime causes1 to 4 minutes to 500 TBq 60Co12 Gy to the bone marrowUntrained, unsupervised and unauthorized worker gained access to the irradiation cellThe source had been left exposed[Lessons learned from accidents in industrial irradiation facilities. IAEA, 1996]
18 “Several minutes” to 2.43 PBq 60Co Need for an adequate radiation safety programDeaths from exposure to radiation from irradiators (cont)Incident 2DosePrime causes“Several minutes” to 2.43 PBq 60Co22 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]
19 Need for an adequate radiation safety program Death from exposure to radiation from irradiators (cont)Incident 3DosePrime causes23 TBq 60CoThree workers exposed; one died8.3, 3.7 and 2.9 Gy. One death after 6.5 monthsLack of regulatory controlNo contact with persons having radiation safety expertiseInadequate worker trainingKey safety features were not repaired. Some removed[Lessons learned from accidents in industrial irradiation facilities. IAEA, 1996]
20 Need for an adequate radiation safety program Death from exposure to radiation from irradiators (cont)Incident 4DosePrime causes1 ½ - 2 mins to PBq 60Co10-15 Gy.Died 36 days laterFaulty limit switch indicating “source down”; safety interlocks were by-passedGamma 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]
21 290 Gy to parts of R leg from 10 MeV electrons Need for an adequate radiation safety program (cont)Electron irradiator accidentsIncident 1OutcomePrime causesGy to R hand;3-290 Gy to R foot;290 Gy to parts of R leg from 10 MeV electronsRight arm amputated above elbow 138 days laterRight leg amputated above knee 6 months laterWorker 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]
22 Need for an adequate radiation safety program (cont) Electron irradiator accidents (cont)Incident 2OutcomePrime causesExposed 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 monthsHair thinning after 2 weeks. No regrowth after 6 monthsWorker not aware of “dark current”Worker did not use any radiation survey meterWorker did not have personal dosimeterUntrained assistant[Lessons learned from accidents in industrial irradiation facilities. IAEA, 1996]
23 Need for an adequate radiation safety program (cont) Electron irradiator accidents (cont)Incident 3OutcomePrime causesHands in 15 MeV beam while adjusting an experimental sample.Dose difficult to estimateR hand and 2 fingers of L hand amputated 8-15 months laterFacility 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]
24 Need for an adequate radiation safety program (cont) Hands – blistering of the right hand palmar surface of the 2ns, 3rd, 4th and 5th fingers (13 April 1999)Thigh – Extended superficial erosion surrounded by a large dusky inflammatory area in the rear surface of the right thigh (1 March 1999)Thigh – Hyperpigmented reaction of the lesion. The lesion edges are well defined, and the skin is peeling off in some areas surrounding the central lesion (15 March 1999)
25 Need for an adequate radiation safety program (cont) Severely superinfected large ulceronecrotic lesions spreading to the whole perineum (14 December 1999)
26 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.
27 Major causes of radiological accidents (cont) 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.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.)
28 Major causes of radiological accidents (cont) 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.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.
29 Major causes of radiological accidents (cont) 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.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
30 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.
31 Lessons learned from radiological accidents (cont) 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.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.
32 Lessons learned from radiological accidents (cont) 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.
33 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.
34 Prevention and remedial actions (cont) Funding OrganizationsOrganizations 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 irradiatorsSuch organizations must recognize their safety responsibilities and promote the development and implementation of radiation protection programs for irradiators
35 Prevention and remedial actions (cont) 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;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.
36 Prevention and remedial actions (cont) Designers, Manufacturers, Suppliers and Installersbear a primary responsibility for carrying out research, testing and examination to ensure the safe design and performance of facilities, equipment and systems.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