Risks from radiation sources

Risks from radiation sources
Introduction Accidents involving radiation sources Lost sources causing contamination incidents
Introduction The small but nonzero probability of a catastrophic accident makes nuclear power seem especially dangerous in the public mind. Radiation-invisible and poorly understood by most people-makes the environmental and health effects of nuclear power seem particularly insidious. And its relation to nuclear weapons makes nuclear power seem far from benign.
The important question is not whether nuclear power is safe but how it compares with other energy sources-especially its main competitor, coal. Coal mining accidents regularly kill as many people as did Chernobyl, and the latter's excess cancer fatalities are no match for the 10,000 deaths that occur each year in the United States alone as a result of air pollution from coal-burning power plants. And the continued use of fossil fuels, especially carbon-rich coal, has started us on the path of irreversible climatic change that could bring environmental disaster in the twenty-first century.
Statistically, the risks from nuclear power seem low compared with those of its fossil-fuel alternatives. And those risks are orders of magnitude lower than others many people willingly endure, like smoking, failing to wear seat belts, or persisting in high-fat diets. Nevertheless, unanswered questions about the long­term effects of low-level radiation, about nuclear waste disposal, and most significantly about the proliferation of nuclear technology in a politically unstable world, raise doubts even for those who agree that nuclear power is statis­tically quite safe. Many take the compromise position that views nuclear fission as a bridge to a time when safer, more economical, and more sustainable power sources become available. We argued that solar photovoltaic cells may soon be one such source. Nuclear fusion, may be another.
In normal everyday use, radiation sources and technologies are used by professionals in well managed, properly regulated institutions. As described previously, radiation sources can be generating devices, such as X ray machines or particle accelerators used in medicine. The sources can also be radioactive materials sealed in a secure capsule or housing. Some sources, particularly those used in nuclear medicine and research are radioactive materials in an unsealed form. Problems can arise if radiation sources are involved in accidents, and if they become damaged or lost.
Accidents involving radiation sources
Radiation sources are widely used in industry and accidents can occur either as a result of poor management or sometimes because of bad judgement. A common denomina­tor of the major accidents is a breach of safety or security requirements. Another common thread is that for the most part they could have been prevented through the enforcement of international safety standards that were developed and issued for that purpose. Between 1945 and 1999 there were some 140 serious reported accidents involving excessive radiation exposure in the nuclear industry, military facilities, hospitals, research facilities, and general industry. The most frequent occur­rence (about 70 in total) is the mishandling or misappropriation of sealed sources used for radiography in industry and radiotherapy in hospitals. Some of the most serious health consequences have been caused by therapy sources being taken from discard­ed hospital equipment by people who did not appreciate the acute radiation hazard that could result. Unfortunately, there are also cases of unintentional overexposures of patients from radioactive sources in medicine, usually caused by human error or inappropriate calibration procedures.
An example of radiation injury is shown as a blistering of the right hand in the following figure.
The following table gives information on the most serious accidents that resulted in fatalities reported between 1987 and 2001.
Year Location Type of Source Deaths caused by radiation exposure Workers Public Patients 1987 Goiana, Brazil Removed teletherapy Source 4 1989 San Salvador, El Salvador Industrial sterilizer 1 1990 Zaragoza, Spain Radiotherapy accelerator Several 1990 Soreq, Israel Industrial sterilizer 1 1991 Nesvizh, Balarus Industrial sterilizer 1 1992 China Lost cobalt-60 source 3 1990 USA Brachytherapy 1 1994 Tammiku, Estonia Source removed from waste repository 1 1996 San Jose, Costa Rica Radiotherapy Several 1997 Sarov, Russian Federation Critical assembly 1 1999 Tokaimura, Japan Criticality accident 2 2000 Thailand Lost cobalt-60 source 3 2000 Egypt Lost cobalt-60 source 2 2001 Panama Radiotherapy overexposures Several Table (18): Recent Fatal Radiation Accidents (1987-2001) ( In each case, overexposure is considered likely to be a direct or major cause of several deaths.) ( Radiation, People And The Environment IAEA, Vienna 2003 )
Lost sources causing contamination incidents
Many sources are sealed devices, with the radioactive material firmly contained or bound within a suitable capsule or housing; others consist of radioactive materials in an unsealed form. Sealed radioactive sources should only present a risk of exposure to external radiation. However, damaged or leaking sealed sources, as well as unsealed radioactive materials, may lead to radioactive contamination of the environment and the intake of radioactive substances into the human body. Melting of disused radioactive sources accidentally sent with scrap metal for recycling is of particular concern. The table below gives an assessment of the major contamination incidents that have involved sources appearing in the recycled metal industry.
Type of source mislaid Number of reported incidents worldwide (1983-1998) Recycled metal industry involved Cobalt-60 15 Steel (14), Copper Caesium-137 30 Steel (27), Aluminium (2), Lead Iridium-192 1 Steel Radium-226 3 Aluminium (2), Steel Thorium-232 3 Aluminium (2), Steel Americium-241 3 Aluminium, Copper, Gold Others 4 Aluminium, Copper, Zinc, Lead Total 59 Table (19): Major contamination incidents involving lost sources (Radiation, People And The Environment IAEA, Vienna 2003)
Each of these incidents had a significant economic impact on the industry involved, and some also led to environmental and health consequences. In addition to those listed, there are many more cases of lost sources being discovered by radiation moni­toring equipment installed by the metal recycling industry. The installation of radiation detectors at recycling facilities is becoming common practice in many countries, and, therefore, the number of serious contamination incidents is expected to decrease.