E Ireland wrote:
Ive thought about using fusors to pump neutrons into cores myself - largely in an attempt to consume tritium produced by a CANDU in a way that can significantly improve fuel economy - and/or provide extra reactivity to allow xenon override without boosters or adjusters.
How much tritium is produced in CANDU, or any fission reactor? Is that enough to fuel to make a fusion reactor worth the trouble? Is tritium even a good fuel to use? Or, are you simply suggesting that a fusion reactor is just one means to dispose of tritium?
I did some reading on how fission-fusion hybrid reactors could work and I'm still not convinced of the merits. I will say that a fission-fusion hybrid system does make fusion look a lot more attractive. I say this because fusion is hard, and a way to make it easier is to find a way to deal with one big problem it has, containing neutrons.
Confinement systems for fusion largely rely on the electric/magnetic properties of a plasma. We know how to confine charged particles, but neutrons don't have a charge. One means to deal with this is a choice of fuel that produces as few neutrons as possible under fusion, but this has a cost. Aneutronic fusion requires exotic fuels that are not as reactive as more easily obtained neutron producing fuels. By placing a blanket of material that can capture those neutrons, and do something useful with them, then one problem is solved. Then the problem is making use of those neutrons that were captured.
By using fissionable material to capture the neutrons lost in fusion this can possibly make fuel choices for a fission reactor simpler. Neutron bombardment can turn worthless U-238 into valuable Pu-239, or thorium into U-233. Or maybe Li-6 into Li-7. A fusion reactor does not have to be used to produce electricity or fuel for fission. It's value could be from it's ability to produce neutrons for bombarding all kinds of materials. I remember a Youtube video from Dr. Stephen Boyd where he talked about the chemistry applications of a molten salt reactor, well I believe a lot of that could apply to a fusion reactor too.
Using deuterium as fuel can make the fusion reactor much smaller than what would be required from, as an example, an aneutronic protium-boron reactor. The neutrons released can bombard a molten salt blanket/coolant/target material. This material can carry away the heat produced and run a turbine, not to produce electricity for sale but to minimize energy losses from heat. Any electricity produced would be used to drive the fusion containment. The material soaking up the neutrons could be fission fuel, fission products for disposal, or for producing any of a number of isotopes that have value in medicine and industry.
The example of dealing with xenon can be dealt with, IMHO, with things less complex than a fusion reactor. This is doubly so if we're talking about coupling this fusion reactor with a molten salt reactor. I can see the value in using a fusion reactor in dealing with some problems from fission reactors, and vice versa. What I have trouble seeing is the need to couple the two reactors directly.
We can achieve the same benefits of having both fusion and fission by having them as independent reactors. For example the tritium produced in a CANDU can be collected and shipped to a fusion reactor. The fusion reactor can use the tritium as fuel to bombard thorium, which would be collected and shipped to a CANDU. By tying the two directly, such as sharing the same coolant system, means if one goes down for maintenance then the other must be shut down too.
Perhaps these latest proposals allow for some level of independent operation of the fission and fusion reactors, but that was not apparent from what I've seen. I'm a bit frustrated at their lack of detail in their proposals so far but I do see the need to not give out information to potential competitors.
Again, I wish them success but I'm not convinced that they will find it. Even a failure can teach us a lot, so we will get value from their efforts either way.