Low enriched uranium and thorium fuel utilization under once‐through and offline reprocessing scenarios in small modular molten salt reactor

Abstract

Summary Using low enrichment uranium as driver fuel under once‐through mode in molten salt reactor (MSR) attracts more and more attention because of its fuel availability, no new technology, and nuclear nonproliferation. It is regarded as a wise research and development road to shorten deployment time of MSRs and to prepare techniques and experiences for thorium‐uranium breeding of MSRs in the future. However, this fuel management is still faced with some different technical routes, such as the selection of carrier salts, the enrichment of uranium, with or without thorium, and the recycle necessary of spent nuclear fuel. Therefore, various fuel cycle schemes were compared and analyzed using an in‐house developed fuel management code MOBAT. Different graphite assemblies were optimized by changing the salt volume fraction in core and dimension to find a region for best fuel utilization and negative temperature reactivity coefficient. Prismatic block with 10% volume fraction of molten salt is considered as a good assembly type because of its significant space shielding effect of U‐238. For carrier salts, LiF‐BeF2 with 99.995% enriched Li‐7 displays higher fuel utilization and lower cost of fuel cycle than NaF‐BeF2, while the tritium production at the beginning of life will be two orders of magnitude higher. For fuel enrichment, 20% enriched uranium is recommended because the background of neutron absorption from carrier salt and graphite will be more significant in lower enrichment condition. Importantly, it shows that thorium is a good breed and burned fuel in situ and could improve the fuel utilization by 20%. Also, offline reprocessing to recover the uranium is a commendable scheme when the cost of offline reprocessing is lower than 400 $/kgHN.

Neutronic effect of graphite dimensional change in a small modular molten salt reactor

“…Small modular‐MSRs 18‐20 are small power level MSRs combined with modular technology for multi‐purposed applications, such as electricity generation, seawater desalination, hydrogen production, supply of supercritical steam for industrial use, and the production of medical radionuclides. One of the modular philosophies is to integrate the high radioactive primary loop into a power module with advantages of easy transportation, assembly, and disassembly in remote regions.…”

“…Compared with the fuel salt channel in the center of one prismatic graphite block, this structure benefits the lateral connection between channels and block gaps, and further favors the heat conduction from narrow gaps. The salt VF in active core is near 10% according to the analysis of fuel utilization and TRC 18 . As a result, even a 3% averaged volume shrink of graphite will have an about 30% volume increase of fuel salt in active core.…”

“…In addition, the spatially dependent change of fuel salt may make power density distribution more centralized and hence reduce the time interval between graphite replacements. Those phenomena could be significant in small modular MSR (SM‐MSR), 18‐20 in which the best fuel salt VF in active core is only about 10%, lower than ~20% VF in MSBR. Therefore, it is necessary to take the dimensional change into account either in neutronic or thermal‐hydraulic analysis.…”

Parametric study on minor actinides transmutation in a graphite‐moderated thorium‐based molten salt reactors

“…With many remarkable characteristics such as inherent safety, excellent neutron economy, no fuel fabrication, online refueling and reprocessing, and so on, MSR can attain high burnup and is considered to have the ability to operate in a thorium–uranium fuel cycle and the potential to burn transuranic elements 16‐19 . Up to now, many different types of MSR have been designed to serve as the burner, converter, or breeder in any of the thermal, epithermal, or fast spectrum reactors using enriched U‐235, U‐233, or transuranic elements as the fissile fuel 20‐24 . In 2011, China initiated a pioneer program of research and development (R&D) for thorium‐based molten salt reactors (TMSRs) at the Shanghai Institute of Applied Physics, Chinese Academy of Science (SINAP, CAS) 25,26 .…”

Comparison of homogeneous and heterogeneous thorium fuel blocks with four drivers in advanced high temperature reactors

“…With the development of nuclear energy, the utilization of thorium has been discussed in various types of reactors with varying intensity, particularly in pressurized water reactors (PWRs), boiling water reactors, heavy water reactors, Canadian deuterium natural uranium reactors, molten salt reactors (MSRs), hybrid systems, accelerator‐driven systems, high temperature reactors (HTRs), breeder reactors, as well as in fast reactors . Thorium has gained considerable amount of interest because of its many advantages that;characterize it as fuel.…”