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Affordable Cleanup? Opportunities for Cost Reduction in the Decontamination and Decommissioning of the Nation's Uranium Enrichment Facilities (1996) / Chapter Skim
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G: NUCLEAR CRITICALITY
Pages 236-243

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From page 236...
... of the GDPs is that most accidents have occurred during cleanup operations. A chain reaction such as the fission of 235U to release energy is triggered by the reaction of the 235U nucleus with a neutron of the proper energy level.
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From page 237...
... " The factors above can limit the extent and duration of a criticality accident through their effects on the system of the large energy release. In a liquid system, for example, there can be rapid boiling, and, as the moderating liquid evaporates, the system reverts to subcritical.
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From page 238...
... Multiple-parameter controls provide significant relief from the extremely restrictive single-parameter limits of Table G-1. Control of solution concentration is one of the most useful ways to relax the single-parameter limits, but this immediately entails administrative control to ensure that the concentration is kept within specified limits.
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From page 239...
... Criticality is not possible in unmoderated uranium with less than 5 percent by weight 23su. Subcritical limits for various 23sU enrichment levels are shown in Table G-3.
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From page 240...
... 10.00% 1.071.47 5.00% 1.643.30 4.00% 1.986.50 3.00% 2.75 2.00% 8.00 Cylinder diameter (cm) 10.00% 20.1025.20 5.00% 26.6042.70 4.00% 30.2048.60 3.00% 37.40 2.00% 63.00 Slab thickness (cm)
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From page 241...
... considers 350 grams of 235U as "always safe" for any enrichment of 235U. Nuclear Regulatory Commission licensing of the special nuclear material burial site in Washington State allows a maximum of 500 grams (a critically safe quantity)
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From page 242...
... from metal parts requires criticality controls: restricting 235U amount and geometry (e.g., to occur only in thin layers) , and possibly using neutron poisons.
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From page 243...
... 1994. Gaseous Diffusion Plants Decontamination and Decommissioning Assessment Review Issue Papers (predecisional draft)
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Key Terms

  • subcritical limits
  • enriched uranium
  • gaseous diffusion
  • diffusion plant
  • enrichment level

  • enrichment levels
  • slab thickness
  • criticality safety
  • chain reaction
  • critical limits

  • aqueous solution
  • critically safe
  • using neutron
  • thin slab
  • highly enriched

  • nuclear society
  • criticality accident
  • enriched material
  • american nuclear
  • issue papers

  • maximize neutron
  • assessment review
  • remove enriched
  • conditions occur
  • fissionable materials

  • considered critically
  • aqueous washing
  • ensure subcritical
  • uranium results
  • thin layers


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