Jim L. wrote:
Would annular fuel pellet/fuel rods also help with uprating the BWR? I think that flow and heat transfer would be improved while also keeping the centerline fuel temps down.
Yes, it should be about as good as with PWR. Limits are similar - limits to dryout, critical heat flux, cladding temperature, cladding strain etc.
The cladding is the limit. BWRs operate with peak fuel temperatures below 1200C. The fuel melting point is >2800C so no issues here.
If you provide 50% more surface area, you can get 50% more power with the same cladding margins.
Big question with natural circulation is whether this would still work. Pressure drop rises much faster with power density. So this annular fuel may not be much use for ESBWR. It would be more interesting for ABWR-II and Kerena reactors.
If we are going to change the fuel rods we should make other changes. The fuel assemblies are too many. 1132 for the ESBWR. Making them twice the diameter means the number drops to 283 assemblies. Much faster refuelling, many fewer (albeit bigger and wider) control rods.
But I don't think we should do any of this. I think we should build ESBWRs as they are right now, no changes to the nuclear island, only incremental changes to the non nuclear, turbine and steam systems. Changing the fuel design just delays eveything 15-20 years. Not worth the gain. We needed a thousand ESBWRs decades ago.