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IAEA Sources of Radiation Nuclear Fuel Cycle – Enrichment Day 4 – Lecture 6(2) 1.

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Presentation on theme: "IAEA Sources of Radiation Nuclear Fuel Cycle – Enrichment Day 4 – Lecture 6(2) 1."— Presentation transcript:

1 IAEA Sources of Radiation Nuclear Fuel Cycle – Enrichment Day 4 – Lecture 6(2) 1

2 IAEA Enrichment 2

3 IAEA Gaseous Diffusion  Two enrichment processes:  Gaseous Diffusion  Gas Centrifuge 3

4 IAEA Basic Theory of Gaseous Diffusion Gaseous Diffusion uses molecular diffusion to separate the isotopes of uranium Three basic requirements are needed Combine Uranium with Fluorine to form Uranium hexafluoride (UF 6 ) Pass UF 6 through a porous membrane Utilize the different molecular velocities of the two isotopes to achieve separation 4

5 IAEA Enrichment of 235 U through one porous membrane (or barrier) is very minute Thousands of passes are required to increase the enrichment of natural uranium (0.711%) to a usable assay of 4 or 5% for use in reactors Basic Theory of Gaseous Diffusion 5

6 IAEA Cylinder Filled with Solid UF 6 6

7 IAEA Gaseous Diffusion Enrichment of 235 U through one porous membrane (or barrier) is very minute 7

8 IAEA Tails Condensation and Withdrawal Tails are the depleted UF 6 stream UF 6 is compressed and condensed into a liquid Withdrawn into 10- or 14-ton cylinders Cooled at ambient conditions until UF 6 is solid, taking at least 5 days Typical assay of tails is between 0.2% and 0.4% 8

9 IAEA Potential Hazards Primary overall hazard is a major UF 6 release Liquid cylinder drop is most credible When UF 6 reacts with water, it forms hydrofluoric acid Both corrosive and toxic 9

10 IAEA UF 6 – Uranium Hexafluoride HF – Hydrogen Fluoride Cl 2 - Chlorine NH 3 - Ammonia ClF 3 – Chlorine Trifluoride Significant Hazards 10

11 IAEA Gaseous Diffusion 11

12 IAEA Gas Centrifuge 12

13 IAEA Why Gas Centrifuge?  Large enrichment effect per stage  > 1.05 vs for GDP  More compact design  Reduced uranium inventories in cascades  Better energy efficiencies  < 5% of GDP energy typically stated  More rapidly achieves equilibrium/steady state  about a day instead of “weeks” for GDP 13

14 IAEA Gas Centrifuge View of a Urenco cascade 14

15 IAEA Safety Comparison: GC vs GDP  Centrifuge  Lower pressures, less inventory, more isolation  Newer facility  Liquid UF 6 areas comparable  Conclude GC risk probably lower 15

16 IAEA What is Depleted Uranium?  Definition:  Depleted uranium (DU) is uranium that contains less than the natural assay of uranium-235  Natural assay = approximately 0.712% U-235  “Normal DU” is around % U-235  DU comes as a “byproduct” - some say “waste” from enrichment 16

17 IAEA DU Background  Generated by every enrichment process  DU generation cannot be avoided  Perceived hazards  old and rusting containers  chemical - UF 6, F 2  liability for cleanup, accidents 17

18 IAEA A DUF 6 Cylinder 18

19 IAEA UF 6 Tailings Cylinders 19

20 IAEA Little U ‑ 235 remains in the tails (usually less than 0.3%) so it is of no further use for energy. Depleted uranium is used in metal form in yacht keels, as counterweights, and as radiation shielding, since it is 1.7 times denser than lead. Military uses include defensive armor plating and bullets. Depleted uranium 20

21 IAEA Depleted uranium – hazards External exposure to radiation from pure depleted uranium is less of a concern because the alpha radiation emitted by its isotopes travel only a few cms in air or can be stopped by a sheet of paper. Further, the low concentration of uranium-235 that remains in depleted uranium emits only a small amount of low energy gamma radiation. The chemical toxicity of depleted uranium is about a million times greater in vivo than its radiological hazard. 21

22 IAEA What are the potential hazards with DUF 6 ?  DU more chemically toxic than radiotoxic  heavy metal  ingestion equivalent to about 1 rem dose can be fatal  DUF 6 readily reacts with atmospheric water vapor to form UO 2 F 2 and Hydrogen Fluoride (both “bad”)  DUF 6 corrosive (+ HF effect)  DUF 6 reacts violently with most organic materials 22

23 IAEA Reference  International Atomic Energy Agency, Postgraduate Educational Course in Radiation Protection and the Safety of Radiation Sources (PGEC), Training Course Series 18, IAEA, Vienna (2002) 23


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