I do not believe u233 neutron capture without fission creates a problem. The same can be said for U235. One of the well know neutron poison created is U232 (can be created by multiple reactions, but is only created in small amounts). In fact, U233 neutron capture has much higher probability of fission compared to U235 neutron capture and is an advantage of the thorium fuel. I am only talking about thermal reactors, not fast reactors, which have different neutron energy spectrum and poison generate may not be a problem.
Tritium generation you mentioned is not a thorium fuel specific issue, it is caused by your coolant selection. If you replace thorium with uranium you'd still have the same problem. Tritium is an issue even for existing plants.
I am not promoting thorium type of reactors, except if you have uranium supply problems (I believe India and China have the largest thorium deposits). However, thorium cycle is viable and have advantages, especially if you have re-processing. I have evaluated once through hybrid fuel designs that use both U and Th in the past and this concept does produce more energy overall without increasing peak reactivity (I work in the nuclear industry). At the time the nuclear industry was limited to 5% U-235 enrichment. Since the benefit is not large and in the absence of thorium fabrication facility the concept could not be pursed. Now the commercial nuclear industry is moving to enrichment above 5%, a once through hybrid U-Th fuel may work better, but the ability to use higher enrichment mitigate the need for a combined uranium-thorium design.
