Online Processing System for Molten Salt Reactors
David Barnett, Nathan Glaser, Joseph F. Specht IV
In a net-zero carbon energy future, advanced nuclear reactors will help satisfy growing energy demand. Among promising advanced nuclear reactor concepts, Molten Salt Reactors (MSRs) have high potential due to high outlet temperatures, fuel utilization, and processing capabilities. While operating MSRs, certain fission and transmutation products are controlled using fuel-salt processing. Traditionally, processing in MSRs is performed offline in batches — a portion of the fuel salt is (i) diverted from the main fuel-salt line, (ii) processed in isolation, and (iii) re-combined with
the main fuel line. Instead of offline processing, online processing operates on the entirety of the fuel-salt. In offline processing, the equilibrium concentrations of products is limited by the portion of the fuel-salt diverted. However, in online processing, the equilibrium concentrations can be much lower as all of the fuel-salt is operated on. Through online processing, the lower concentrations extended component lifetime, improve neutron economy, and enable load following with dramatic power differentials. Our design uses the Molten Salt Breeder Reactor (MSBR) as a template and
implements various elements to enable online processing and improve reactor performance. Through our design changes, we control noble metals plate-out, increase thermal efficiency, and reduce tritium levels.
Liquid Lithium Tritium Breeding Facility to Support the Fusion Fuel Cycle
Harrison Brosius, Riley Trendler, Sean Mahanes
Nearly all fusion power devices will utilize the deuterium-tritium reaction to generate power. It is estimated that a gigawatt fusion reactor would consume 55 kg of tritium per year, but the current global tritium supply is less than 40 kg, almost all of which is harvested as a byproduct of heavy-water fission reactors. As these reactors are decommissioned, the existing global supply will eventually be exhausted by ITER, decay, and other sales. The technology necessary for internal tritium production in fusion power devices is still in its infancy, and as such, these devices will likely require an external tritium supply. The proposed liquid lithium breeding facility aims to address this need for the long-term use of tritium in fusion systems. The facility is based on previous successful breeder reactor concepts, primarily the Experimental Breeder Reactor II (EBR-II). Primary objectives are to produce at least 10 kg of tritium per year, continuously extract tritium, remain in compliance with existing regulations, and meet thermal and structural design criteria. The breeding facility emulates a “pool-type” liquid metal-cooled fast reactor in which liquid lithium reacts with neutrons to produce tritium, which is extracted with a “permeator against vacuum” (PAV) system. Evaluation of this design includes a 1-D neutronic and thermal analysis for the core, as well as a steady-state tritium diffusion analysis for the intermediate loop and liquid lithium pool. In addition, a high-level economic analysis is performed under US and European siting scenarios. Initial neutronic and temperature predictions show that the design lies close to thermal design limits, but more refining is necessary to confirm the validity of the design. Corrosion and diffusion analyses suggest that degradation of steel components is unlikely, and tritium diffusion into the intermediate loop is negligible. Tritium extraction with the PAV method is highly efficient and prevents the formation of harmful hydrides in the coolant stream. Power production calculations confirm that the reactor will generate sufficient electricity to power itself and benefit from electricity sales. Based on these predictions, the design appears feasible under the prescribed constraints for yearly tritium production. Further work will focus on refining and updating geometric and neutronic models to describe the overall system more accurately.