Safety and Work Procedures in Radiation Processing Facilities

National Committee for the Certification of Radiation Protection Officer

Safety and Work Procedures in Radiation Processing Facilities


ContentContent Introduction

Gamma Irradiation Facilities Types of Irradiator Basic Components of Gamma Irradiation Facilities Operating Procedure Maintenance Procedure Leakage Test Procedure

Electron Beam Irradiation Facilities Types of Irradiator Basic Components of Gamma Irradiation Facilities Operating Procedure Maintenance Procedure


Radiation processing facilities are specially designed facilities that use ionizing radiation to improve quality of products.

Source of radiation: High activity gamma sources High energy irradiating apparatus

Safety a prime concern in the operation of the facilities. A good working practice should be introduced and

implemented.

IntroductionIntroduction


Types of irradiator:

Category I:

• A dry storage, self-shielded type, with radiation sources in fixed position.

• Co-60 is mainly used while Cs-137 is used only occasionally.

• Main application is for research.

Gamma Irradiation FacilitiesGamma Irradiation Facilities


Example of Category I Gamma

Irradiation




Category II:• A dry storage, panoramic irradiation type with movable

source. • The source is safely kept inside a container and raised to

the working position for irradiation.• The irradiation area is surrounded by concrete shielding

and access is strictly controlled and possible only with the source in safe position.

• Main applications are for research, pilot studies and commercial irradiations.



Example of Category II

Gamma Irradiation




Category III:

• A panoramic irradiation type with radiation source fixed at the bottom of a water pool.

• Samples for irradiation are inserted into the radiation field by any convenience method.

• Main application is for research.



Example of Category III Gamma Irradiation




Category IV:

• Similar to category II facility except that it is a wet type.

• The source is kept in a water-pool for safe storage.

• Main applications are for commercial irradiation.



Example of Category IV

Gamma Irradiation



Category IV Gamma Irradiation



Basic components of gamma irradiation facilities: Gamma radiation source Source handling system Source safe storage Irradiation room or chamber Radiation safety system Product or material handling system



Gamma radiation source:

• Usually use very high activity sealed sources:o A few GBq up to about 7.4 x 105 GBq for Category Io 3.7 x 105 GBq up to 1.85 x 107 GBq for Category IIo 3.7 x 105 GBq up to 7.4 x 105 GBq for Category III o 3.7 x 106 GBq up to 3.7 x 108 for Category IV

• The most commonly used radionuclide is Co-60.



Source handling system:

• A special system designed to handle radiation sources used by the facilities.

• For Category II and IV facilities, the system is used to move gamma sources from their storage place to an exposure condition during operation and back to the storage place after the operation.



Source handling system (cont.):

• For Category I and III facilities it is used only to handle the sources during source replenishment.

• For Category II and IV facilities, the system should be interlocked with safety systems installed at all openings and access doors to the irradiation room.

• The system is designed that whenever there is an interruption of power supply, the sources can be moved back to their storage place.



Source safe storage:• It is designed to safely keep the sources when they

are not in use. • For some facilities, it is also used to facilitate source

changing during source replenishment.• It should be provided with adequate shielding to

minimize the radiation.• For Category III and IV source storage is in a wet

form.• For Category I and II source storage is in dry form.



Irradiation room or chamber:• Is a place where the products or materials are

exposed to gamma radiation over a preset exposure time.

• It should be provided with adequate thickness of shielding.

• For big facilities (Category II, III and IV) concrete is usually used as shielding.

• For Category I irradiators steel and lead are used as shielding.

• Should be provided with a number of access doors and openings.



Radiation safety system:

• Safety philosophy:

o The design and operation of the facilities are in accordance with international standards practice.

o Safety analysis of the facilities should demonstrate that main objectives of building and operating the facilities are achieved under all predictable normal and abnormal operating conditions of the facilities.



Radiation safety system (cont.):

• Safety philosophy (cont.):

o The design and operation of the facilities should be made based on multiple levels of protection (defense in depth):

– Any function which is critical to safety should not depend on only one component (redundancy).

– Utilization of different systems, components, principles, etc to achieve the same goal (diversity).

– The operation and functionality of individual elements of the systems should not be effected by malfunction of other component (independence).



Radiation safety system (cont.):• Safety components:

o The minimum requirements for safety system are:– The radiological (biological and physical) shield or

barrier of sufficient thickness;– Warning system;– Monitoring system;– Interlock system or safety interlock;– Documentation;– Written procedures; and– Training




• Alarm system:

o Alarm systems provided are: - Access and Egress Alarm

- Source Movement Alarm

- Water Treatment Alarm

- Fire Alarm

- Low Water Level Alarm



Product or material handling system:

• To bring the materials or products into the irradiation room and to bring them back right after completion of irradiation.

• The dose absorption is maximized by narrowing the gap between the sources and the product handling system.



Operating procedures:

Procedures are different at different facilities and for different category.

The following descriptions are typical procedures for Category IV facilities.



Operating procedures (cont.):

Irradiation room entry procedures:

• Irradiation room is a controlled and high radiation area which requires personnel access to be minimized and avoided.

• If access is unavoidable and necessary, strict entry procedures must be observed.

• The first step of the entry procedures is to confirm that the radiation room monitor is functioning and the indicated radiation level is normal.

• Subsequently proceed as described in the figure below for Category IV facilities.



Entry procedures for Category IV

Facility



Source exposure procedures:

Actuate the SAFETY DELAY TIMER key-switch.

Leave the room, hook the air interlock of the source hoist and close the personnel access door on the way out.

Check that all green start–up indicators are illuminated and there are no red FAULT INDICATORS.



Source exposure procedures (cont.):

Insert the key into the MACHINE keyswitch on the Machine Control Panel of the Control Console.

Turn the key to the START position and release it.

Make a complete entry in a Log Book.



Source change/replenishment procedures:

Transportation of radiation sources:

• A consignee should be designated to receive transport packages containing radiation sources from the supplier/manufacturer.

• Upon receipt of the transport packages, he shall do the followings:

o Inspect all packages upon arrival for any sign of damage.o Check that the information provided which should agree with the order

acknowledgement. Otherwise, place it in a secure and safe area and notify the supplier.

o Notify receipt of the package to the RPO and update the inventory record for radiation sources.

o If the package is not opened immediately provide a suitable secure and safe storage place.



Source change / replenishment procedures:

Transportation of radiation sources (cont.):

• Most source manufacturers require the EMPTY transport packages to be returned.

• Instructions for return of such packages are usually supplied by the source manufacturer and they should be followed closely.

• A consignor should be designated to oversee off-site transportation of radiation sources including return of EMPTY transport package.

• Shipment of the radiation sources including EMPTY packages should comply with the requirements of Radiation Protection (Transport) Regulations.




• In making the arrangement to return EMPTY transport package, the consignor shall carry out the following responsibilities:

o Ensure that the package is empty.o Check that the package is free from external contamination. o Ensure that the package is securely closed.o Remove or cover up all previous shipping and transport

labels.o Complete and firmly attach the supplier address label on to

the package.




• In cases where the package is returned with radiation sources, the consignor should carry out the following:

o Obtain a written approval from the supplier and the AELB. o Check the package for any damage and its condition. If

found to be faulty contact the supplier.o Load source into the package as described in the

instructions supplied by the source manufacturer.o Make the necessary arrangement for packaging, labeling

and marking the package.




o Use the appropriate and proper shipping name ‘Radioactive Material, special Form N.O.S. UN 2974’.

o Lock and seal the container with wire and security seal.

o Ensure that all shipping documents and the relevant certificates are available and should accompany the package.



Unloading and installation:

• Sources must be unloaded and installed by persons who are trained, competent and authorized to handle.

• If specific instructions have been supplied, they must be carefully read and fully understood before commencing to unload the package.

• For wet type of irradiators, the unloading and installation is carried out in the pool under certain thickness of water so that the personnel involved is protected.

• Dry-storage type of irradiation facilities is normally loaded by supplier’s engineers.



Radiological protection:

• Before any source movement is carried out, a detailed plan of the operation must be prepared to assess any potential hazard caused.

• All source movements must be recorded and records maintained for a period specified in local rules.

• A controlled area may be required to be established. • All personnel must be adequately protected from

gamma radiation as appropriate. • A suitable means should be provided to prevent

inadvertent entry of personnel into high radiation areas during replenishment work.



Radiological protection (cont.):

• A survey meter must be used to check actual dose rates to personnel in the vicinity.

• Check for contamination using a survey meter in the working area after each operation.

• If a source is damaged during installation, use or an accident or exposed to adverse conditions, actions must be taken according to emergency plan.

• Always handle the sources with extra careful and avoid the possibility of bending, dropping or crushing.

• Sources must not be modified, re-worked or interfered with unless agreed in writing by the supplier.



Report and operation log book:

• All movements of radiation source must be recorded. • All tests, maintenances, modifications or changes

made to the irradiator facility shall be recorded in a logbook and kept.

• The results of all tests described above shall be verified by the RPO.

• The records should be kept for inspection by AELB over a period prescribed by the authority.

• All normal and abnormal shutdowns as well as abnormal occurrences should be recorded in the operation logbook.



Maintenance procedures:

The irradiator shall not be used until all maintenance tasks have been completed.

Regular maintenance should be done according to the manufacturer’s instruction.

Operator on-duty is responsible for all checks and for completing the checklist at the specified intervals.

Any deviation from normal condition should be reported to the Facility Supervisor and the RPO.

Maintenance schedule is established to ensure that all systems/equipment are safe for operation.

The maintenance is carried out in accordance with the requirements of the manufacturer and the AELB.



Leakage test procedures:

Leakage of exposure room:

• Radiation leakage test is performed in areas where there is a significant radiation leak to occur.

• Radiation leakage test should be performed:o Before initial use of radiation shield.o Whenever source manipulation is carried out.o Periodically (at an interval prescribed by the AELB).



Leakage test procedures (cont.):

Leakage of exposure room (cont.):

• The radiation survey must be carried out with the presence of RPO.

• Results of the radiation survey must be maintained and kept for an appropriate period.




Leak test of radiation source:

• Radiation sources are first tested for leakage right after they are manufactured. Tests are usually carried out in accordance with the manufacturing standards.

• User should carry out periodic leak test in accordance with the test standards recommended by the manufacturer and recognized by AELB.

• For dry type facilities, the leak test can be performed by drawing the sources out of the facilities and checking inside of the loading tube for contamination.




Leakage of radiation source (cont.)

• For wet type facilities, the test is done by continuous monitoring of the resin filters in the pool water deionization system and testing of the pool water for radioactivity presence.

• Leak test should a carried out:o Before initial use (by supplier).o Periodically (at interval prescribed by the AELB).o Whenever damage of capsule or seal is suspected.o Whenever contamination of handling the source is detected.

• Results of the tests must be maintained and kept for a period prescribed by the AELB.



They are facilities or machines specially designed to cater for effective delivery of electron energy to induce changes in materials or products for improvement of their quality.

This improvement of quality is achieved through sterilization, preservation or introduction of physical or chemical changes.

Electron Beam Irradiation Facilities



Types of electron beam irradiation:

Category I, low energy, self shielded, accelerator (E < 0.5 MeV)

Category II, medium and high energy accelerators (0.5 MeV < E < 10 MeV)




Category I Irradiator:

• It is an electron beam accelerator with energy up to about 0.5 MeV.

• Usually designed and manufactured in such a way that radiation shield is an integral part of the machine.

• A system of interlock switches disables the machine if part of the shielding is removed.

• No additional shielding is required and the accelerators need a very small space.




Example of Category I

Electron Beam Irradiator




Category II Irradiator:

At energies above 0.5 MeV, it is impractical and costly to include shielding as an integral part of the machine.

These machines are installed in areas surrounded by concrete shield and shielded entrances (labyrinth or thick door).

Shielding design is concerned only with X-ray generated by attenuation of electrons in target material (usually steel).




Example of Category II

Electron Beam Irradiator




Basic components of electron beam irradiation facilities:

Electron beam source Irradiation room or chamber Radiation safety system Product or material handling system




Electron beam source:

• It is the most important part of the facilities both in term of usefulness and safety.

• Use very high-energy electron beam because of high dose required in short exposure time and for better penetration into the products.

• The electron energy involved varies between a few hundreds keV to 10 MeV, depending on capability of the machines.

• The disadvantage about these facilities is the generation of X-rays as a result of electron interaction with the materials or products being irradiated.

• This secondary radiation is more hazardous and requires more elaborate protection because of its penetrating nature.




Irradiation room or chamber:

• Irradiation room is a place where materials are going to be exposed to electron beam over a preset exposure time.

• The room should be made spacious enough to accommodate the products, their handling system and other support systems.

• The room should be provided with adequate shielding to ensure X-rays leakage is below the acceptable level.




Irradiation room or chamber (cont.):

• Category II facilities usually use thick concrete as shielding while Category I facilities normally use steel and lead. The shielding can also be a combination of concrete, steel and lead.

• The room should be provided with access doors and openings to allow for personnel, products and utilities into the room.

• Such openings and doors should be properly designed and interlocked to limit radiation leakage to below the acceptable levels and to avoid unauthorized access.




Radiation safety system:

• The same safety philosophy for gamma irradiators applied.

• Safety components:

o Radiological shield of sufficient thickness to reduce radiation intensity to acceptable level.

o Warning systems to mark the restricted and radiation areas, imminent or ongoing radiation, beam and high voltage status etc.

o Monitoring system to indicate current radiation levels.o Interlock system for precluding exposure of an individual by preventing access

to the radiation area when the facilities are in operation.o Documentation, which comprises a set of management and operation

documents, inspection and maintenance schedules, records, etc.o Procedures for normal operation and emergency situations.o Training and retaining of personnel involved in the operation, maintenance and

use of the facilities.





• Alarm system:

o Category II facilities are typically provided with the following alarm systems:– Access and Egress Alarm to prevent opening of the door

and triggers alarm if the radiation level inside the room is abnormal.

– Electron Beam Alarm to indicate that the beam is on. – Fire Alarm which usually consists of smoke detectors

and heat sensors that will activate warning systems and fire fighting systems in case of fire. The fire alarm system is also connected to the ventilation system, which will be shutdown automatically to avoid fire propagation.




Product or material handling system:

• Is provided to bring the materials into the irradiation room and to bring them back right after completion of irradiation.

• In some facilities, the system is connected to an automatic control system so that withdrawal of the materials from the irradiation room is done immediately to avoid them from being overexposed.




Operating procedures:

Radiation room entry procedure:

• Has no special requirement to observe. • Only ensure that the machine is off before

entering the radiation room.




Source exposure procedure:

• Leave the irradiation room and close the personnel access door on the way out.

• Turn on the key switch and select the operation mode.

• Push ‘start’ button, the starting alarm works for about 30 seconds. After starting alarm stop, the accelerator voltage ramps up to the preset value follow by the beam ramps up automatically and gradually to the preset value.




Maintenance procedure:

The irradiator shall not be used to irradiate product until all maintenance tasks have been satisfactorily completed and recorded.

Regular maintenance of the facility should be done according to the manufacturer’s instruction.

Operator on-duty shall be responsible for the required checks and for completing the checklist at the specified intervals.

Any deviation from normal condition should be reported to the Facility Supervisor and the RPO for further action.

Maintenance schedule is established to ensure that all systems are safe for operation and the maintenance is done according to the requirements of the manufacturer and the appropriate authority.




Summary


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Safety and Work Procedures in Radiation Processing Facilities