2.4.2. Medicine, industry and research

2.4.2.1. Medicine

Radionuclides used in nuclear medicine can be categorised into two forms:

Open sources which have relatively low activity and consist of radioactively labelled chemical compounds used for imaging of internal organs, studying of bodily functions and localised irradiation of cancer cells.

Sealed sources (Fig. 2.10) that generally have high activity and are used for irradiation of tumours. Sealed sources are used in two applications: the first is ‘‘brachytherapy’’, where the source is placed directly in, or very near, the tumour; the second is ‘‘teletherapy’’, where very highly active sources of Co-60 or Cs-137 are used externally.

The medical use of radioisotopes (open sources) for diagnosis and treatment results in the generation of mainly L/ILW-SL. Typically, this waste consists of paper, rags, tools, clothing and filters which are contaminated with small amounts of mostly short-lived radioactivity. The majority of these wastes undergo decay storage for periods of months to a few years before being disposed of in conventional landfill sites.

When sealed sources have decayed to a point where they are no longer emitting enough penetrating radiation for use in treatment, they are considered as radioactive waste. Sources such as Co-60 (half-life =5.24 a) are treated as L/ILW-SL, whereas sources containing significant amounts of Ra-226 (half-life =1620 a) are treated as L/ILW-LL as they require storage and geological disposal due to the long-lived radioactivity.

2.4.2.2. Industry

Industries use radioactive sources for a wide range of applications (e.g., Fig. 2.11). When these sources no longer emit enough penetrating radiation for them to be of further use, they are treated as radioactive waste. Sources used in industry are generally short-lived and any waste generated can be disposed of in near-surface disposal facilities. However, if a sufficient number of sources are disposed of together, e.g., thousands of smoke detector Am-241 sources compacted into steel tubes, then this may be classified as L/ILW-LL

As mentioned previously, some industrial activities involve the handling of raw materials such as rocks, soils and minerals that contain NORM.

The main industries that generate these types of wastes are:

Fig. 2.10. Typical sealed medical sources – radium needles and radium Crowe probe (image courtesy of ANDRA).

Fig. 2.11. Typical sealed industrial sources and smoke detectors (utilising americium).

Oil and gas exploration and production – minerals including a wide range of radionuclides, but especially Ra-226, are deposited as scale in piping and oil field equipment, or left as residues in evaporation lagoons or dumps below offshore oil rigs. In fact, it is interesting to note that the oil and gas industry is the main source of radioactive releases to the waters of northern Europe.

Coal contains uranium and thorium, as well as other radionuclides. These radionuclides become more concentrated than in the original coal when this is burned to produce fly ash.

The wastes from the processing of rock containing phosphates to produce phosphate fertilizers result in enhanced levels of naturally occurring uranium, thorium and potassium radionuclides.

Water treatment – some waters, especially mineral waters, contain low levels of uranium and thorium. These radionuclides become concentrated as a result of purification processes that are used to treat the water before its consumption, e.g., filter sludges, ion-exchange resins, granulated activated carbon, etc.

Metal smelting slags, especially from tin smelting, may contain enhanced levels of uranium and thorium series radionuclides.

2.4.2.3. Research

Universities and research establishments use both open and closed sources that require appropriate management and disposal. The majority of sources are of low activity and/or short half-life. However, some exceptions include high-level long-lived sources such as radium-226 and americium-241 used in biological and/or agricultural research, as well as large but shorter-lived Co-60 sources used for radiation research.

Research reactors produce similar wastes to a commercial nuclear power plant, although on a smaller scale, i.e., operational, decommissioning and spent fuel (if not reprocessed).

Due to the continuing development of particle accelerators (e.g., Fig. 2.12), the current generation have beam currents that are now high enough to result in the production of a significant amount of neutrons (leakage of the proton beam results not only in a cascade of nuclides from spallation reactions but also produces secondary neutrons), leading to the activation of a large amount of the materials used in their construction. Following a 40-year operating lifetime of one of the new generation of particle accelerators, the volume of decommissioning waste and its activity is expected to be in the same order of magnitude as for a 1 GW(e) nuclear power plant which has operated over 40 years.