Radiation Source Use and Replacement Abbreviated Version (2008) / Chapter Skim
Currently Skimming:
3 RADIATION SOURCE RISKS
3 RADIATION SOURCE RISKS
Pages 43-66
The Chapter Skim interface presents what we've algorithmically identified as the most significant single chunk of text within every page in the chapter.
Select key terms on the right to highlight them within pages of the chapter.
From page 43... ...
NRC reexamine its security-based orders and decisions for materials licensees, considering the potential consequences of area-denial RDDs. For the purpose of prioritizing radiation source replacements and considering options for implementing those replacements, the committee concludes that radioactive cesium chloride is the greatest concern among the materials used in radiation sources in the United States because it is used in significant quantities in urban areas in a powdered, dispersible form.
|
From page 44... ...
The committee was equipped to evaluate hazards or, from the risk formalism, some of the potential consequences, parts of the vulnerabilities, and none of the threats associated with misuse of radiation sources. Further, it is the role of policy makers to decide what levels of risk are acceptable and how to achieve those levels (e.g., through deterrence, detection, denying access, interdiction, mitigation, or reduction of the hazard)
|
From page 45... ...
Accidental exposures resulting from inadvertent access have resulted in some of the worst incidents involving radionuclide radiation sources, so many of the commission's security measures were designed to prevent inadvertent access. Since September 2001, in response to the changing threat environment, the U.S.
|
From page 46... ...
Poisoning large numbers of people to achieve near-term health impacts would be difficult because in food, for example, the radioactive material must be fairly highly concentrated to have a deterministic effect on any individual -- bacteria are much more effective at causing harm -- so to affect many people requires a very large amount of material. Soluble radioactive material could be introduced into water reservoirs, but almost any plausible number of radiation sources would become too dilute to have much health impact.
|
From page 47... ...
. The quantity of radioactive material required to cause economic consequences is somewhere between the large amount needed to cause deterministic health effects and the small amount that might trigger psychological impacts.
|
From page 48... ...
. Twenty mSv is much lower than the doses required to cause deterministic health effects (immediate or near-term effects, such as those considered in establishing the IAEA source categories)
|
From page 49... ...
The committee has not reviewed the studies of direct or indirect costs in detail and so draws no conclusions about the reliability of the results, but notes that these are commonly cited figures. To appreciate the hazards associated with Category 1 and 2 radiation sources, one has to understand the actual devices in which the sources are used.
|
From page 50... ...
Requirements for radioactive material quantities of concern (RAMQC) apply to these shipments.5 Self-contained Irradiators As noted previously, the form of the cesium-137 in self-contained irradiators is the same as the source in the Goiânia radiation dispersal accident: radioactive cesium chloride powder.
|
From page 51... ...
The U.S. NRC's Nuclear Material Event Database lists a number of incidents in which radiography devices containing radionuclide radiation sources were lost or stolen.
|
From page 52... ...
NRC analysis to identify sources and quantities of concern did include area contamination, it was a single threshold criterion. That is, it could have affected which radionuclide radiation sources are in Category 2, but there would have been no distinction, in terms of the potential for contamination, between Category 2 and Category 1.
|
From page 53... ...
The system has been used to establish new regulations on the import/export of radioactive material. It is also used both domestically and internationally to help prioritize the recovery of orphaned and unwanted radiation sources.
|
From page 54... ...
Americium-beryllium sources, such as those used in oil-well logging, typically are formed by sintering mixtures of americium oxide and beryllium powders to form a pellet which is then either diffusion bonded to a metal strip or sealed in a welded stainless steel container. The committee does, however, conclude that consequences other than deterministic health effects, especially the consequences of area-denial RDDs, should be factored into decisions about security for radiation sources.
|
From page 55... ...
When evaluating the potential harm that could be caused by different radionuclides in radiation sources, radioactive cesium chloride sources emerge as a major concern. Cesium chloride is soluble and highly dispersible (other forms of cesium-137 mentioned in Chapter 2 are not as dispersible)
|
From page 56... ...
NRC, 2006a) : A specific area of concern is the widespread use of cesium chloride (CsCl)
|
From page 57... ...
because the power plant is located in the Ukraine. 9 The cesium-137 deposited as fallout during the accident was not in the form of cesium chloride, but once deposited in a moist environment, the cesium behavior is similar.
|
From page 58... ...
FIGURE 3-4 Cesium-137 ground contamination zones from the Chornobyl accident. SOURCE: Image adapted for black-and-white reproduction from De Cort et al.
|
From page 59... ...
The easy dispersal was facilitated by the form of cesium-137 used in these and other highactivity devices in use throughout the world, then and now. As described in Chapter 2, the cesium-137 is in the form of radioactive cesium chloride.
|
From page 60... ...
Picture of a sealed source holder, which is approximately three times the size of the sealed source itself: ~ 2.5 cm diameter ~ 50.9 TBq (1375 Ci) cesium chloride powder Schematic view of a teletherapy machine similar to the one in Goiania.
|
From page 61... ...
The cesium-137 sources provided by DOE were much larger than typical cesium chloride radiation sources sold today. DOE had Sandia National Labortories carry out tests with the capsules in wet-load, dry-storage, dry-irradiator mode.
|
From page 62... ...
NRC, 2001) : The Commission determined that the safety hazards associated with leaks of dispersible cesium chloride, even though the leaks were infrequent, justified restricting its use.…The Staff argues that the longer half-life and decay time of cesium-137, combined with its dispersibility, could actually present an increased risk in comparison with cobalt-60 if a leak or other safety problem occurred, including the possible increased risks associated with a proliferation of smaller (non-cobalt)
|
From page 63... ...
The U.S. NRC has ranked radiation sources in terms of hazard using the IAEA system of five source categories, determining that the Category 1 and 2 sources are "high-risk sources." The IAEA analyses supporting its source categorization system consider only deterministic health effects (such as early fatalities)
|
From page 64... ...
Having taken an essential first step in considering deterministic health effects from possible radiation exposure from an incident involving radiation sources, the U.S. NRC should now include economic and social disruption in its risk analyses of radiation sources.
|
From page 65... ...
Finding: Government action is required to implement replacement of radioactive cesium chloride sources because the alternatives cost more and the liabilities or social costs of the sources are not borne by the end users. There is no indication that replacement of devices containing Category 1 and 2 radioactive cesium chloride sources with lower hazard alternatives will improve or worsen the performance of the devices in their standard and proper uses.
|
From page 66... ...
In Chapter 10, the committee offers several suggestions as its lead candidates for how to implement the replacement, and they are summarized here. First, to stop the addition of new Category 1 and 2 cesium chloride sources to the nation's inventory, the U.S.
|
Key Terms
This material may be derived from roughly machine-read images, and so is provided only to facilitate research.
More
information on Chapter Skim is available.