IAEA
RADIATION PROTECTION IN NUCLEAR MEDICINE
PART 10. RADIOACTIVE WASTE
1.
INTRODUCTION
Radioactive waste needs to be safely managed because it is potentially hazardous to
human health and the environment. Through good practices in the production and
use of radionuclides, the amount of waste can be significantly reduced but not fully
eliminated. Inadequate management after use or loss of radioactive material,
especially sealed radiation sources, has resulted in radiation exposure of members of
the public or extensive contamination of equipment, buildings or land. In some cases
uncontrolled radiation exposure has been lethal. It is important that safe waste
management, in full compliance with all relevant regulations, is considered and
planned for at the early stages of any projects involving radioactive materials. It
should be established from the outset that the waste could be properly handled,
treated and ultimately disposed of.
The radioactive waste in hospitals comprises many different types of waste. It
may be of high activity such as a technetium generator and sources used in
radionuclide therapy, or low activity waste from biomedical procedures or research. It
may be in solid, liquid or gaseous form. The radioactive material may be mixed with
different chemicals, in itself hazardous or flammable. Moreover some of the waste is
mixed with biological substances such as blood and may be infectious subsequently
special precautions must be taken for disposing of such items as needles used for
injection. All these aspects must be accounted for in the planning of waste treatment
in a hospital.
2.
BASIC REQUIREMENTS AND LEGAL FRAMEWORK
According to the Basic Safety Standards: “Registrants and licensees shall:
(a)
ensure that the activity and volume of any radioactive waste that results from
the sources for which they are responsible be kept to the minimum practicable, and
that the waste be managed, i.e. collected, handled, treated, conditioned, transported,
stored and disposed of, in accordance with the requirements of the Standards and
any other applicable standard
(b)
segregate, and treat separately if appropriate, different types of radioactive
waste where warranted by differences in factors such as radionuclide content,
half-life, concentration, volume and physical and chemical properties, taking into
account the available options for waste disposal.
Furthermore the Standards require that Registrants and licensees shall ensure that
radioactive substances from authorized practices and sources not be discharged to
the environment unless:
(a)
either clearance has been granted for the radioactive substance or the
discharge is within the discharge limits authorized by the Regulatory Authority;
(b)
the discharges are controlled;
(c)
the public exposures committed by the discharges are limited as specified in
the Standards; and
(d)
the control of the discharges is optimized in accordance with the Standards.
Other international recommendations concerning radioactive waste such as those of
the International Commission on Radiological Protection and the publications within
the lAEA's RADWASS Programme on the safe management of radioactive waste
may be useful.
Safe management of radioactive waste requires a proper national
infrastructure, which should include appropriate legislation, a regulatory organization,
a competent operational body and properly trained staff. It is important that waste
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PART 10. RADIOACTIVE WASTE
management is considered and planned for at the early stages of any projects
involving radioactive materials.
3.
WASTE COLLECTION, SEGREGATION AND STORAGE
Waste management starts already with the application of unsealed sources. In order
to simplify the waste management the selection of unsealed sources in a certain
application should consider:




the half-life of the radionuclide, which should be as short as is consistent with
the application,
the type and energy of the radiation
the activity, which should be as low as is consistent with the application
selection of materials that minimise the number of operations required to
prepare them for the specific application.
The management of the waste may be divided into six different steps: pre-treatment
(collection and handling), conditioning, storage, treatment, transportation and
disposal. For practical reasons the waste may be divided into solid, liquid and
gaseous form. In every step the national and international standards and legislation
should be taken into account.
The thorough pre-treatment of the waste is the most important step towards a
rational (both practical and economical) and safe handling of the waste. It includes
steps such as collection, segregation, chemical adjustment and decontamination.
The segregation is crucial and should be done taking account the different aspects
of the waste with a clear view of the final treatment and/or disposal. The segregation
of wastes into appropriate categories should take place during the waste collection.
Conditioning includes those operations that produce a waste package
suitable for handling, transportation, storage and/or disposal. It may include the
conversion of the waste to a solid waste form, enclosure of the waste in containers
and, if necessary, providing an overpack.
Interim storage of radioactive waste may be needed in different stages of the
waste management process. For many of the wastes generated in hospitals, storage
for decay is a useful option because the radionuclides have short half-lives. This can
be done in the hospital and may include some treatment of the wastes to ensure safe
storage. After a sufficient storage time, the final step, disposal as exempt waste, can
also be performed at the hospital. Other types of waste containing radionuclides with
longer half-lives must be transferred to a special waste treatment, storage and
disposal facility outside the hospital.
4.
WASTE TREATMENT AND DISPOSAL
Disposal is the emplacement of waste in an approved specified facility (for example,
near surface or geological repository) without the intention of retrieval. Disposal may
also include the approved direct discharge of effluents (for example, liquid and
gaseous wastes) into the environment with subsequent dispersion.
There are two main approaches to the disposal of radioactive waste. One is
characterized as "dilute and disperse" and the other as "confine and contain". By the
"dilute and disperse" concept, radioactive material, in aqueous or gaseous form, is
released into the environment in such a way that the material is diluted and
distributed over a large volume so that the final concentration of radionuclides is
acceptably low. In the "confine and contain" approach, the waste is collected and
converted into a form such that, when placed in a repository, it will retain the
radionuclides until the activity has decayed, or at least will ensure that the leakage of
radionuclides from the repository does not give rise to unacceptable concentrations
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PART 10. RADIOACTIVE WASTE
anywhere in the environment. This approach is always used for longer-lived solid
radioactive waste.
During transportation, safety management includes appropriate packaging,
labelling, transportation of documents including sender, retriever, content of the
waste, categorisation, and information to possible rescue personnel. The packages
and containers should always be strong enough to ensure a safe, sometimes rough,
handling. The transportation should follow the IAEA guidelines.
.
5.
EXAMPLES OF WASTE MANAGEMENT IN NUCLEAR MEDICINE
The solid waste generated in nuclear medicine includes cover papers, gloves, empty
vials and syringes, radionuclide generators, items used by hospitalised patients after
radionuclide therapy, sealed sources used in therapy, sealed sources used for the
calibration of instruments, animal carcasses and other biological waste. In the liquid
waste category one can find residues of radionuclides, patient excreta, liquid
scintillation solutions, and in the gaseous waste exhausted gas from patients in
nuclear medicine.
Depending on the final handling or disposal, the waste could be divided into
different categories. One category where the waste will end up in a public waste
treatment system with or without incineration, the next where it will be poured out in
the public sewage system, and the third where it will be disposed of in a national
plant or recycled.
The segregation could be done in the following categories:
Solid waste which after proper treatment and conditioning can be handled in the
public waste treatment system. Solid waste should be immobilised by surrounding it
with a matrix material in order to produce a waste form suitable for storage and
transportation governed by the properties of the waste, the transport regulations and
the specific waste treatment or disposal acceptance requirements. Incineration is
recommended for combustible solid waste because it achieves the highest volume
reduction and dilutes and disperses the radionuclide content. Total sterilisation of
biological waste will be achieved. Discharge limits given by the regulatory authority
should be followed.
Liquid waste which after proper treatment and conditioning can be handled in the
public waste treatment system. For aqueous waste evaporation, chemical
precipitation and ion exchange may be considered. For organic and infectious liquid
waste incineration is a suitable method. The residues of the treatment process
should be handled as solid waste. Treated aqueous effluents can be discharged in
the environment via the sewage system if either clearance has been granted for the
radioactive substance or the discharge is within the limits authorised by the
regulatory authority.
Solid waste containing short-lived radionuclides capable of being stored for
decay. Thereafter it may be handled in the public waste system if the discharge is
within the limits authorised by the regulatory authority
Liquid waste containing short-lived radionuclides capable of being stored for
decay. Thereafter it may be handled in the public waste system if the discharge is
within the limits authorised by the regulatory authority.
Sealed sources with high activities which will be disposed of in a national plant or
recycled.
Biological waste, which may undergo decomposition. A suitable treatment method
is incineration.
Infectious waste requiring sterilisation possibly by incineration prior to disposal.
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PART 10. RADIOACTIVE WASTE
Broken glass-ware, syringes etc, requiring collection in separate containers to
prevent personnel being injured. Depending on other content, radionuclide type,
biological, infectious etc. it should be appropriately handled, treated and stored.
Radionuclide generators should after storage for decay be checked for
contamination and dismounted or, preferably, returned to the producer.
Bed linen and clothing from hospital wards, which are contaminated, could be
stored for decay if the nuclides are short-lived. Otherwise it is treated as solid waste.
Patient excreta. For diagnostic patients there is generally no need for collection of
excreta. Ordinary toilets can be used. For therapy patients there are different policies
in different countries. Either to use separate toilets equipped with delay tanks or an
active treatment system, or allow the excreta to be released directly into the sewage
system.
Liquid scintillation solutions, which due to its flammable organic solution, could
preferably be disposed of by incineration. New types of liquid scintillation solutions
are less flammable and hazardous to the environment could otherwise be handled in
the public waste treatment system.
Containers to allow segregation of different types of radioactive waste should
be available in areas where the waste is generated. The containers must be suitable
for purpose (volume, shielding, leak proof, etc.) Each type of waste should be kept in
separate containers properly labelled to supply information about the radionuclide,
physical form, activity and external dose rate.
A room for interim storage of radioactive waste should be available. The room
should be locked, properly marked and if necessary ventilated. Flammable waste
should be placed apart. It is essential that all waste be properly packed in order to
avoid leakage during the storage. Biological waste should be refrigerated or put in a
freezer. Records should be kept where the origin of the waste can be identified.
6.
REFERENCES
1. INTERNATIONAL ATOMIC ENERGY AGENCY. International Basic Safety
Standards for Protection Against Ionizing Radiation and for the Safety of
Radiation Sources. Safety Series No.115, IAEA, Vienna (1996).
2. INTERNATIONAL ATOMIC ENERGY AGENCY. Model Regulations on Radiation
Safety in Nuclear Medicine. (in preparation).
3. INTERNATIONAL ATOMIC ENERGY AGENCY. Management of radioactive
wastes produced by users of radioactive materials. Vienna, International Atomic
Energy Agency, 1985 (IAEA Safety Series No. 70).
4. INTERNATIONAL ATOMIC ENERGY AGENCY. Principles for limiting releases of
radioactive effluents into the environment. IAEA, Vienna, 1986 (IAEA, Safety
Series No. 77).
5. INTERNATIONAL ATOMIC ENERGY AGENCY. Principles for the exemption of
radiation sources and practices from regulatory control. IAEA,Vienna, 1988 (IAEA
Safety Series No 89).
6. INTERNATIONAL ATOMIC ENERGY AGENCY. Management of radioactive
waste. IAEA, Vienna,(IAEA Safety Series No.111).
7. INTERNATIONAL ATOMIC ENERGY AGENCY. Report on radioactive waste
disposal. IAEA, Vienna, 1993 (IAEA Technical Report Series TRS No.349).
8. INTERNATIONAL ATOMIC ENERGY AGENCY. Guidance for regulation of
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underground repositories for disposal of radioactive wastes. IAEA, Vienna, 1989
(IAEA Safety Series No 96).
9. INTERNATIONAL COMMISSION ON RADIOLOGICAL PROTECTION. Handling
and disposal of radioactive materials in hospitals, ICRP Publication No. 25.
Oxford, Pergamon Press, 1977 (Annals of the ICRP No. 2).
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