Answer to Question #7440 Submitted to "Ask the Experts"
The following question was answered by an expert in the appropriate field:
- Are there any specified limits for the concentrations and radiation doses of naturally occurring radioactive materials in ceramic tiles as a consumer product and in ceramic waste sludge out of the industry?
- If these limits exist, what are these limits and what are the countries that apply these limits?
- Are there any precautions that should be taken into account in ceramics industry for the safety of workers and public against radiation doses from naturally occurring radioactive materials that exist in the components used in and waste coming out of the industry?
Answer to Question 1. Yes.
Answer to Question 2: It depends. We believe that this question is too broad in scope to answer satisfactorily, but we will try to answer it nevertheless.
There are many different types of naturally occurring radionuclides, e.g., hydrogen-3, carbon-14, potassium-40, radium-226, thorium-232, uranium-235, and uranium-238.
In a given situation, some of these might be regulated while others would not be. In addition, how they are regulated can depend on the nature of the radioactive material. For example, in the United States how uranium is regulated can depend on whether or not it has been chemically processed. If the uranium has not been processed but is natural ore, its regulation will depend on the concentration of uranium.
In the United States, the regulatory responsibility might fall to a state regulatory agency or the federal government (usually the Nuclear Regulatory Commission [NRC]). The various states take different approaches to regulating this material. Needless to say, how the material is regulated also varies from one country to another.
To make this discussion manageable, I will limit our consideration to the United States and the NRC's regulations pertaining to a particular category of natural radioactive material, source material.
The NRC defines source material as follows:
"(1) Uranium or thorium or any combination of uranium and thorium in any physical or chemical form; or
(2) Ores that contain, by weight, one twentieth of 1 percent (0.05 percent), or more, of uranium, thorium, or any combination of uranium and thorium. Source material does not include special nuclear material."
The relevant NRC regulations, from Part 40 of Title 10 of the U.S. Code of Federal Regulations, are as follows.
"§ 40.13 Unimportant quantities of source material.
(c) Any person is exempt from the regulation in this part and from the requirements for a license set forth in section 62 of the Act to the extent that such person receives, possesses, uses, or transfers:
. . . .
(2) Source material contained in the following products:
. . . .
(iv) Glass enamel or glass enamel frit containing not more than 10 percent by weight source material imported or ordered for importation into the United States, or initially distributed by manufacturers in the United States, before July 25, 1983."
The glass enamel mentioned in the regulation refers to the glaze used on the tile. The source material of primary interest is the processed uranium in the glaze. As long as the uranium (essentially the mass of the uranium-238) constitutes less than 10 percent of the mass of the glaze, possession of the tile should not require a license.
You can refer to the complete text of Part 40 of Title 10 of the Code of Federal Regulations.
For more general information about these regulations and related issues, refer to Section 3 in the NRC publication "Systematic Radiological Assessment of Exemptions for Source and Byproduct Materials" (NUREG 1717, June 2001).
For information about regulations and other issues related to the concentration of natural radioactive material in waste streams, a type of technologically enhanced naturally occurring radioactive material (TENORM), check out the TENORM page.
Similar information can be found at the Environmental Protection Agency (EPA) website.
With regard to the situation in other countries, a rather nice discussion of how the European community is addressing this issue can be found in "A Review of Consumer Products Containing Radioactive Substances in the European Union."
The key document from the European Union can be found at "Radiological Protection Principles concerning the Natural Radioactivity of Building Materials"—Note its use of a screening index for various nuclides.
Also see "Effluent and dose control from European Union NORM industries: Assessment of current situation and proposal for a harmonised Community approach."
And finally, see an International Atomic Energy Agency (IAEA) document that addresses radioactive tiles, Radiation Protection and NORM Residue Management in the Zircon and Zirconia Industries.
Answer to Question 3: Yes, but there are too many to identify all of them here. The general approach is to keep exposures as low as reasonably achievable (ALARA).
Regarding the workers, their external exposures can be minimized by maximizing the distance between the worker and the material, minimizing the time the worker is around the material, and (when appropriate) employing shielding. Inhalation and ingestion of radioactive material in the workplace can be minimized by a variety of means, e.g., minimizing the use of dry dusty operations and employing proper ventilation.
As far as exposures to the public are concerned, the simplest approach is to minimize the amount of radioactive material ending up in consumer products. But there are limits as to what is appropriate or possible, e.g., should we get into the business of regulating the sale of granite kitchen countertops because of the elevated levels of uranium they might contain?
Orhan H Suleiman MS, PhD