Below are the first 10 and last 10 pages of uncorrected machine-read text (when available) of this chapter, followed by the top 30 algorithmically extracted key phrases from the chapter as a whole.
Intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text on the opening pages of each chapter. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.
Do not use for reproduction, copying, pasting, or reading; exclusively for search engines.
OCR for page 351
E Origin of Radioactivity in Fuel-Cycle Facilities Fuel-cycle facilities are involved in the extraction and processing of uranium to produce fuel for nuclear reactors. Consequently, the most im- portant radioactive effluent releases from these facilities involve uranium and its decay products (Table E.1). Uranium and its decay products are present in equilibrium at mining and milling facilities (Figure E.1). The uranium decay products are removed during the milling process1 and disposed of onsite as mill tailings (Fig- ure E.2), which are potential sources of radioactive particulate and radon gas effluent releases from these facilities. Other radioactive isotopes are sometimes present in effluent releases from enrichment and fuel fabrication facilities, usually at trace levels. These include cesium-137, technetium-99, as well as a number of actinide iso- topes, most notably uranium-236, neptunium-237, and plutonium-239/240. These isotopes are produced by fission and neutron-capture reactions (these reactions are described in Appendix D). Their presence in an effluent release indicates that the facility has processed uranium that was previously irradi- ated in a nuclear reactor.2 1 However, the decay products “grow back” into the uranium with time, especially those decay products near the top of the uranium decay chains, which have short half-lives (see Figure E.2). 2 For example, recycled uranium (i.e., uranium obtained from reprocessing spent nuclear fuel) was enriched at the Paducah Gaseous Diffusion Plant between 1953 and 1975. This plant is still reporting releases of radioactive effluents from this recycled uranium. 351
OCR for page 352
352 APPENDIX E TABLE E.1 Typical Effluent Releases from Fuel-Cycle Facilities Facility Type Typical Radioactive Effluents Mining (in situ leaching) Uranium, radon, and progeny Milling Uranium, radon, and progeny Conversion Uranium, radium-226, thorium-230 Enrichment Natural uranium, uranium-235, thorium-230, technetium-99, neptunium-237, plutonium-239, 240 Fuel Fabrication Uranium-234, 235, 236, 238 FIGURE E.1 Schematic illustration of the uranium-235, thorium-232, and ura- Figure E.1.eps nium-238 decay chains showing decay modes (i.e., alpha or beta decay), half-lives, and progeny. SOURCE: U.S. Geological Survey, http://gulfsci.usgs.gov/tampabay/ bitmap data/2_biogeochem/images/decaychain.gif.
OCR for page 353
353 APPENDIX E FIGURE E.2 Aerial view of the White Mesa Uranium Mill near Blanding, Utah. The Figure E.2.eps mill facilities can be seen in the upper right quadrant of the photo. The filled and active mill tailings ponds cells occupy bitmap remainder of the photo. SOURCE: most of the Elise A. Striz (USNRC) presentation at the Atlanta committee meeting.
OCR for page 354