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The waste is not the issue

The waste is not the issue. Russell J Hand Immobilisation Science Laboratory Department of Engineering Materials University of Sheffield. Nuclear power. Utilises the binding energy of the nucleus Not chemical energy 1 t natural U produces ~ 44 GWh(e) = 158 TJ(e)

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The waste is not the issue

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  1. The waste is not the issue Russell J Hand Immobilisation Science Laboratory Department of Engineering Materials University of Sheffield

  2. Nuclear power • Utilises the binding energy of the nucleus • Not chemical energy • 1 t natural U produces ~ 44 GWh(e) = 158 TJ(e) • 1 t coal (Drax) produces ~ 2.6 MWh(e) = 9.4 GJ(e) • ~ 17000 times difference!

  3. Waste • All human activities produce waste • E.g. Burning fossil fuels produces CO2 as a waste • Nuclear reactors produce radioactive waste • What we do with the waste depends on the level and type of hazard posed • Biological • Chemical • Physical • Radiological • Radioactive wastes are a hazard BUT we have technologies for dealing with them

  4. UK radioactive wastes Very low level waste (VLLW) < 400 kBq / 0.1m3β and γ Not considered as radioactive waste and may be treated as conventional waste Low level waste (LLW) < 4 MBq kg1α, < 12 MBq kg1β Largest volumes – Smallest hazard Cemented Intermediate level waste (ILW) Greater activity levels than LLW but not significantly heat generating Cemented High level waste (HLW) Wastes in which are self-heating due to radioactive decay Smallest volumes – greatest hazard Vitrified 2007 data

  5. Origin of wastes • Contaminated materials • Nuclear fuel • During fission in a nuclear reactor a wide range of (often radioactive) fission products are generated • Some fission products are particularly efficient at capturing neutrons • Other fission products may change the structure of/pressurise the fuel • Eventually fuel removed from the reactor and is placed in cooling ponds

  6. Currently in the UK spent nuclear fuel is re-processed to recover re-usable U and Pu • Re-processing leads to high level liquid waste • However re-processing is not an essential element of nuclear power programmes • The spent nuclear fuel (SNF) can simply be stored and eventually placed in a repository • This is the approach currently used in e.g. the US and Sweden

  7. Total 106 Fission & activation products Actinides and daughters 105 Activity /U ore activity Radioactivity of mined uranium ore 104 103 102 10 1 0.1 0.1 1 10 102 103 104 105 106 Time /years Activity of SNF relative to U ore (SKB)

  8. Cement encapsulation in UK • Used for LLW and ILW • Can incorporate a number of different species • Alkaline environment immobilises many species

  9. High level waste Heat generating wastes Contains both short- and long-lived radionucleides e.g.137Cs – half-life 30.07 years – heat generating Smallest volumes – greatest hazard Vitrification is used to immobilise high level liquid waste Waste is chemically bonded into the glass matrix Each canister is 42 cm in diameter and 1.3 m high and holds ~400 kg glass

  10. Spent nuclear fuel • Initial above ground storage • For disposal SNF would be emplaced in canisters • Swedish/Finnish model is for external copper canisters with internal cast iron linings

  11. Current wastes versus future wastes • Current waste arisings are not representative of future waste arisings • Even reactors of the same nominal type involved changes in design • Particularly an issue with Magnox reactors • Magnox reactors used fuel less efficiently than current designs

  12. Final disposal • Deep repositories • Typically designed to be ~0.5 km beneath the surface of the earth • These involve multiple barriers to prevent he radionuclides reaching the biosphere again • Deep borehole disposal • Burial at 4-5 km depth

  13. Multiple engineered barriers • Wasteform • Cement, glass, SNF • Canister • Stainless steel, cast iron surrounded by copper • Backfill • Bentonite • Engineered repository walls • Rock FEBEX experiment – Grimsel URL

  14. In general under static conditions where saturation is possible we get Interdiffusion V II I III IV Resumption of alteration r(t): rate drop rf:: residual or final rate B Hydrolysis Na Concentration of leached species Si End of alteration or phase precipitation Possible phase precipitation Time Final rate - ~1μm/50 yr at 90ºC ~1μm/170 yr at 50ºC Initial rate - ~1μm/day at 90ºC ~1μm/50 day at 50ºC

  15. Natural analogues http://www.ocrwm.doe.gov/factsheets/images/0010_gabongeology.gif • Basaltic glasses • Last in the environment for millions of years • Surface palagonisation • Maqarin, Jordan • Hyperalkaline conditions • Analogue of a cementitious repository • Oklo natural reactors, Gabon • U deposits found with unusually low levels of 235U • ~1.7 billion years ago 16 reactors operated • Probably operated intermittently for ~ 1 million years • At least 10 tonnes U reacted • Pu formed in reactor zones has moved ~ 3 m from where it was formed in 1.7 billion years

  16. Summary • Nuclear power provides low carbon baseload electricity generation • We have technologies and solutions for the safe handling and ultimate disposal of nuclear waste • Vitrification – HLW • Cementation – ILW • Canisters for spent nuclear fuel • Final disposition of the waste • Other countries are developing repositories • The issues here are not technical they are political

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