Gif Reactor technologies

Gas-cooled fast reactors

Like other helium-cooled reactors which have operated or are under development,these will be high — temperature units — 850 °C, suitable forpower generation, thermochemical hydrogen production or other processheat. For electricity, the gas will directly drive a gas turbine (Brayton cycle).Fuels would include depleted uranium and any other fissile or fertilematerials. Spent fuel would be reprocessed on site and all the actinides recycledto minimize production of long-lived radioactive wastes.While GeneralAtomics worked on the design in the 1970s (but not as fast reactor),none has so far been built.

Lead-cooled fast reactors

Liquid metal (Pb or Pb-Bi) cooling is by natural convection. Fuel isdepleted uranium metal or nitride, with full actinide recycle from regionalor central reprocessing plants. A wide range of unit sizes is envisaged,from factory-built "battery" with 15 — 20 year life for smallgrids or developing countries, to modular 300 — 400 MWe units andlarge single plants of 1400 MWe. Operating temperature of 550 °C isreadily achievable but 800 °C is envisaged with advanced materials andthis would enable thermochemical hydrogen production.

This corresponds with Russia's BREST fast reactor technologywhich is lead-cooled and builds on 40 years experience of lead-bismuthcooling in submarine reactors. Its fuel is U+Punitride. More immediatelythe GIF proposal appears to arise from two experimental designs:the US STAR and Japan's LSPR, these being lead and lead-bismuthcooled respectively.

Molten salt reactors

The uranium fuel is dissolved in the sodium fluoride salt coolant whichcirculates through graphite core channels to achieve some moderation and anepithermal neutron spectrum. Fission products are removed continuously andthe actinides are fully recycled, while plutonium and other actinides can beadded along with U-238. Coolant temperature is 700 °C at very low pressure,with 800 °C envisaged. A secondary coolant system is used for electricitygeneration, and thermo chemical hydrogen production is also feasible.

Sodium-cooled fast reactors

This builds on more than 300 reactor-years experienced with fastneutron reactors over five decades and in eight countries. It utilises depleteduranium in the fuel and has a coolant temperature of 550 °C enablingelectricity generation via a secondary sodium circuit, the primary

one being at near atmospheric pressure. Two variants are proposed: a150 — 500 MWe type with actinides incorporated into a metal fuel requiringpyrometallurgical processing on site, and a 500 — 1500 MWetype with conventional MOX fuel reprocessed in conventional facilitieselsewhere.

Early in 2008, the USA, France and Japan signed an agreement toexpand their cooperation on the development of sodium-cooled fast reactortechnology. The agreement relates to their collaboration in theGlobal Nuclear Energy Partnership, aimed at closing the nuclear fuel

cycle through the use of advanced reprocessing and fast reactor technologies,and seeks to avoid duplication of effort.

Supercritical water-cooled reactors

This is a very high-pressure water-cooled reactor which operatesabove the thermodynamic critical point of water to give a thermal efficiencyabout one third higher than today's light water reactors fromwhich the design evolves. The supercritical water (25 MPa and 510 —550 °C) directly drives the turbine, without any secondary steam system.Passive safety features are similar to those of simplified boiling waterreactors. Fuel is uranium oxide, enriched in the case of the open fuelcycle option. However, it can be built as a fast reactor with full actiniderecycle based on conventional reprocessing. Most research on the designhas been in Japan.