I've never considered the cost of the graphite as signicant. djw1, how much would you expect to spend per GWe-yr replacing graphite? I think the bigger issue is to ensure that the reactor down time is minimized.Owen T wrote:It's not just sintering. I believe it will need to be cooked for a while in vacuum to get any adsorbed xenon and krypton out and then re-densified with chemical vapor deposition to get the outer surface to be smooth and nonporous again.djw1 wrote:Current theory is that moderator life is a function only of fluence and temperature.
Assuming fixed temperature, you can only get so much energy out of a kg of graphite.
From an economic point of view, everything else being equal, high power density
and short moderator life is cheaper than low power density and long moderator life.
You want to turn over your expensive inventory of graphite rapidly,
Reactor grade graphite costs up to $20/kg. It seems to me that the way forward
is high power density, short moderator life, and after a decay period recycle. Re-sintering
moderately radioactive graphite can't be that big a problem.
Cooking radioactive stuff in high pressure flammable gas? Sounds like fun. Should be feasible, but it's not going to be too cheap.
Talking with ORNL they suggest that in essence we would have to grind the graphite back to dust, add a binder and then reform it (pressure, temperature, and vacuum). I think there is no chance that reformed graphite is cheaper than new stuff. But PERHAPS if the machine can be sealed and automated and built in a low throughput form we could put such a machine at each site and over four years reform the graphite from the previous cycle. That would be a way to reduce the graphite waste and sounds politically attractive. Note that this will not reduce the total number of 14C atoms created but it will reduce the total volume of waste graphite. It is my presumption that the waste graphite will be treated as high level waste but very low radiation and heat generation so it should be quite suitable to geological disposal.