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Answer to Question #554 Submitted to "Ask the Experts"Category: Radioactive Waste Disposal — Non-U.S. Waste Issues The following question was answered by an expert in the appropriate field: Q
Regarding the setting up of a possible nuclear waste site here in Australia, what thickness of sand or soil would be sufficient to provide complete shielding from high-energy gamma radiation? Thank you. A
I am pleased to help you with this question. In short there is no simple answer. The shielding values of soils depend on soil type and water content and the degree of compaction with which they are placed over wastes. Water content depends on climate as well. The natural environment plays a part, as does the site's design and operational characteristics. Also, waste packaging offers some shielding value as well and this influences cover thickness. Finally, the mix of radioactive materials that are included in low-level radioactive wastes (LLRW) also determine what shielding is required. I recommend the Web site "South Carolina Department of Health and Environmental Control Radioactive Material License Supplementary Sheet," which has the license for the LLRW disposal facility in Barnwell, South Carolina. This facility has been in operation since 1971. I turn your attention to condition 98D, which states: "Direct gamma radiation from buried wastes should be essentially background." This is accomplished in different ways depending on the different waste classes that are disposed. In no case is the minimum thickness of cover less that five feet and in most cases it is more. The focus is on the result that "direct gamma radiation from buried wastes should be essentially background," not on the thickness itself. The license gives a lot of detail for a variety of requirements. It gives all the requirements that the operator and users of the site must meet. There is a document that describes additional information of how wastes must be prepared and shipped to the site. These requirements can be found in a document called "Disposal Site Criteria." The regulations that also govern the operation along with the license are found at the Bureau of Land and Waste Management's Radioactive Waste Regulations Web page. I hope this answer is useful to you. Please do not hesitate to call our editors if you wish further help from me. They will contact me. Michael T. Ryan PhD, CHP
Answer posted on 19 December 2000. The information and material posted on this Web site is intended as general reference information only. Specific facts and circumstances may alter the concepts and applications of materials and information described herein. The information provided is not a substitute for professional advice and should not be relied upon in the absence of such professional advice specific to whatever facts and circumstances are presented in any given situation. Answers are correct at the time they are posted on the Web site. Be advised that over time, some requirements could change, new data could be made available, or Internet links could change. For answers that have been posted for several months or longer, please check the current status of the posted information prior to using the responses for specific applications.
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