8. SOURCE HANDLING
8.4. Equipment and tools for source handling
In routine operation, radioactive sources are handled in the original devices, transport containers or in other shielding which protect the operators from high radiation doses. The packages can be handled manually or using a forklift. When, for specific reasons, bare radioactive sources have to be handled, the operator should be as far away as possible from the sources in order to minimize the dose.
Handling of sealed sources can be deceptive in terms of contamination control. Even old sources that have been in use for years can maintain the appearance of a new source. It is not uncommon for experienced operators handling sources to become careless, assuming that the sources being handled are intact and there is no leakage.
Users should encourage an attitude that sources and devices containing sources are contaminated until proven otherwise.
8.4.1. tongs and temporary shielding
Low activity sources emitting low energy radiation typically can be handled manually (Fig. 47) or with short handling tools such as tongs or forceps (Fig. 48). Sources of this type include calibration sources, sources used in medical applications, check sources, and some sources used in industrial devices. Handling such sources normally does not require any shielding.
FIG. 47. Source manipulation by hand. FIG. 48. Short tools for manual handling of sources.
Some sources of higher activity and dose rates than the ones described above can also be handled manually with suitable tools as long tongs (Fig. 49) but shielding of these sources is needed to reduce the doses received by the operator (Fig. 50). The most common sources in this group are LDR brachytherapy sources containing caesium and the sources in thickness gauges (85Kr, 90Sr), fill level or thickness gauges (137Cs), density gauges (137Cs), moisture density gauges (241Am–Be–137Cs), bone densitometry (109Cd), and static electricity eliminators.
FIG. 49. Long tongs and manipulation of source with them.
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FIG. 50. Installation of lead shield and lead glass and source manipulation.
Temporary shielding can be employed effectively during source handling operations to reduce dose to workers. When selecting and employing shielding, users should consider:
— Shield in excess or located in ways that impede work activities can actually increase dose to workers. Work performance against the potential dose reduction offered by shielding should be carefully evaluated to find an effective balance.
— Appropriate shielding materials should be selected for use.
— Leaded glass or other windows through which users can see when employing shielding between them and the source should be provided.
8.4.2. fume cupboard
If leaking/contaminated low activity or radium sources are to be handled, a fume cupboard (or a glove box) is a simple, safe and effective means of protecting the operator and preventing the spread of contamination. A fume cupboard is a safety cabinet with an opening through which the operator can carry out manipulation inside the cabinet and with air being continuously exhausted from the cabinet at sufficient rate to prevent the escape of airborne contamination generated within the cabinet (Fig. 51). Temporary shielding in the form of lead bricks could be assembled inside the fume cupboard to reduce operator dose when handling high dose rate sources. This approach would minimize cost and maximize the flexibility of providing a safe working environment for operators.
FIG. 51. Glove box handling of low activity sealed sources.
In the fume cupboard, where space is at a premium, the maximum separation of operator from sources can be achieved by the use of forceps or long tongs (Fig. 52).
FIG. 52. Moving a sealed source using long handled tongs.
It must be recognized that handling work using tongs and forceps makes it possible to lift only small masses (maximum 2 kg in comfort).
8.4.3. Hot cells
It is not always possible to remove the high activity source from the equipment at the user’s premises. This may be because the equipment was designed to be de-sourced in a shielded cell, or because insufficient technical information is available to do this safely outside a shielded cell. In such cases, it is necessary to transport the source in its operational shielding to be de-sources on receipt at a shielded facility such as a hot cell. Hot cells equipped with remote/slave manipulators vary widely in sophistication and complexity, but most of them are perfectly adequate depending on the sources to be handled (Fig. 53).
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FIG. 53. Hot cells with remote/slave manipulators.
8.4.4. Containers
When relocating the disused sources on the site of the licensee, it is important that they are kept in the original container. In case of radiography or teletherapy equipment, the disused sources need to be properly kept in their shielded location. If other than original containers are used, the new container design should take into account the geometry of the source, radionuclide, its activity, and handling requirements. An example of a typical container used for on-site relocation is shown in Fig. 54.
FIG. 54. A container for sealed beta–gamma sources.
Containers or devices used to relocate an SRS on-site need to be appropriately labelled to warn of the potential hazard. It is important that the warning sign is in the local language, as well as the manufacturer’s language. The use of the trefoil symbol on its own is not sufficient as people may not understand its meaning.
The main design requirements applicable to containers used for the relocation of SRSs on-site are as follows:
— The package shall retain containment and shielding integrity during the relocation process. The container needs to be mechanically closed when subjected to the physical stresses associated with transfer during relocation.
— The maximum dose rate on the container is required to be ALARA and in accordance with the licensee radiation protection requirements. In either case, the maximum dose rate should not exceed the dose rate limits stated in the IAEA Transport Regulations, i.e. <2 mSv/h on the surface and <0.1 mSv/h at 1 m from the surface of the package at any time during the transfer [47].
— Radioactive contamination of the container surfaces should be as low as possible and in accordance with the licensee radiation protection requirements. In either case, the radioactive contamination should not exceed limits stated in the IAEA Transport Regulations: 4 Bq/cm2 for beta and gamma emitters and low toxicity alpha emitters, and 0.4 Bq/cm2 for all other alpha emitters.
8.4.5. Lifting and transfer equipment
Various lifting and transferring equipment is used for disused sources depending on their activities, size and weight. An example of the lifting equipment used for a heavy teletherapy head is shown in Fig. 55.
FIG. 55. Rigging and lifting of a teletherapy head.
Normally, a hand pulled trolley, with a 500 kg capacity would be adequate for the transfer operation. A manually operated forklift with drum grab attachment would be required in the store to off-load the source from the trolley. An electric forklift (Fig. 56) would certainly require less manual effort, and would be most appropriate for heavy disused sources and if a large number of sources were to be handled in a short space of time. In addition to a fork lift, a jib attachment to it will allow the lifting of heavy sources (Fig. 57), their transfer around the facility and for removing shielding pots from transport containers, as well as lifting straps, shackles, chains and eye bolts.
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FIG. 56. An electric forklift truck.
FIG. 57. Handling a 200 L waste drum with a forklift truck.