Long-term criticality control in radioactive waste disposal facilities
Journal Article
·
· Nuclear Safety
OSTI ID:642365
- Oak Ridge National Lab., TN (United States). Chemical Technology Div.
Plant photosynthesis has created a unique planet-wide geochemistry--an oxidizing atmosphere with oxidizing surface waters on a planetary body with chemically reducing conditions near or at some distance below the surface. Uranium is up to four orders of magnitude more soluble under chemically oxidizing conditions than it is under chemically reducing conditions. Thus uranium tends to leach from surface rock and disposal sites, move with groundwater, and concentrate where chemically reducing conditions appear. The earth`s geochemistry concentrates uranium and can separate uranium from all other elements except oxygen, hydrogen (in water), and silicon (silicates, etc.). Fissionable isotopes, isotopes that can form a critical mass, include {sup 232}U, {sup 233}U, {sup 234}U, {sup 235}U, and many higher actinides that eventually decay to one of these uranium isotopes. The potential for nuclear criticality exists if the precipitated uranium from disposal sites has a significant fissionable enrichment, mass, and volume. The earth`s geochemistry suggests that isotopic dilution of fissionable materials in waste with {sup 238}U is a preferred strategy to prevent long-term nuclear criticality in and beyond the boundaries of waste disposal facilities because the {sup 238}U does not separate from the fissionable uranium isotopes. Geological, laboratory, and theoretical data indicate that the potential for nuclear criticality can be minimized by diluting fissionable materials in each package with {sup 238}U to less than 1 wt % {sup 235}U equivalent, or nearly the 0.71 wt % {sup 235}U found in nature.
- OSTI ID:
- 642365
- Journal Information:
- Nuclear Safety, Journal Name: Nuclear Safety Journal Issue: 1 Vol. 38; ISSN 0029-5604; ISSN NUSAAZ
- Country of Publication:
- United States
- Language:
- English
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