Lars wrote:Just finished reading the report and learned a lot. There are several ideas that would be common with a LFTR. Question 2 is applicable in the context of a LFTR and would love to discover that it isn't a problem at all.
I have a few questions.
1) Was thorium considered as a burnable poison - would it work?
2) It seems like Smahtr will have virtually the same tritium production as a LFTR. It seems to me that the main tritium transfer path will be through the heat exchangers especially if a steam turbine is used. What is the forecast tritium release rate?
3) Your fissile consumption of 1600 kg LEU20 every 3 years for 125 MWth => 2.1 tonnes fissile / GWe-yr so at the end of life roughly half the fissile must still be in the fuel. Is it correct that the spent fuel contains roughly 10% enriched uranium? Is the plan that this is treated as once-through or is the plan to recycle the fuel in some form?
4) From the drawings it looks like an aircraft could take out all three passive cooling towers. Is this a plausible scenario? If so, how does the system handle it?
Thanks for your feedback Lars. It's great to get these comments and questions as they will help us in the next iteration of the design. Let me try to provide some answers to your questions and Sherrell can also chime in:
1) We discussed thorium as an option for burnable absorbers, but frankly did not have time to look at it and for the report section on reactivity control had just considered more traditional poisons. All of the analysis for cycle length was performed without reactivity control. One of our next steps is to design the control system including the burnable absorber and control rods.
2) On tritium, you are correct. As you can read in the the report we plan to have a tritium clean up system to control the tritium. We are not planning on using a steam power conversions system, our preferred approach is SCO2 and in addition to the intermediate loop, one option is the use a "salt vault" head storage system which will represent another barrier to release. We have not gone far enough with this to calculate a tritium release rate.
3) This concept is purposefully focused on just energy production, much as the NGNP, and therefore at this conceptual stage it is best to keep the fuel cycle as simple as possible, which means a one-batch, once-through core design. In order to maximize the cycle length we are using 19.75% enriched uranium. I don't have the number handy regarding the end of life enrichment, but it may very well be in the 10% range. The one-batch core certainly hurts our fuel utilization, but we selected it for simplicity to allow a cartridge core design that is removed in once piece. The fuel could certainly be reprocessed and re-enriched or used in other reactors, and there is some R&D going on in this area. We originally had a section in the report on fuel cycle, but decided to leave it out because we had not performed sufficient analysis. Certainly thorium is an option for these systems as is the deep-burn approach that is being proposed for HTGRs. For now using enriched uranium is a simpler starting point for the concept.
4) There are a couple of different drawings showing the DRACS towers. They would be positioned such that they could not be taken out by one aircraft. Note also that even if they are taken out by an aircraft that does not mean the primary system is not still functioning. This system has a six heat exchangers, 3 primary and 3 DRACS, only 2 (either 2 primary or 2 DRACS) are needed In fact, we didn't analyze it, but I suspect that for decay heat removal, only 1 primary heat exchanger would be sufficient.
Good questions/comments. Keep them coming!