Molten Salt Reactors Explore New Designs

Julia Lebovitz
June 11, 2018

Submitted as coursework for PH241, Stanford University, Winter 2018


Fig. 1: Fig 1. Possible MSR design. (Source: Wikimedia Commons)

Molten Salt Reactors (MSRs) seem to be on the forefront of cutting edge technology for achieving a more efficient and safe approach to nuclear energy. MSRs use either liquid fuel or solid fuel to provide safe and sustainable benefits. MSRs differ from more conventional nuclear technology, because the majority of the whole reactors volume resides in its core. This allows for their compact technology to introduce new levels of predictability, reliability, and economies of scale to an industry thats become synonymous with billion-dollar cost overruns and years of delays. [1] After first being introduced in the late 1900s, MSRs have helped to create a more efficient and sustainable approach to nuclear technology. Currently, one of the main problems with advancing nuclear technology is their price. However, these smaller reactors could provide a more cost-efficient means for production. There are around 50 designs for possible Small Modular Reactors that can solve this cost issue. Nevertheless, until MSRs can be fully approved and completely transform modern technology, scientists must develop a model that ensures all the benefits of these reactors. Scientists are working with both liquid and solid fuel designs in hope to find the most efficient and well-balanced model.

Liquid Fuel Utilizing the Thorium Fuel Cycle

Liquid fuel reactors can use either uranium or thorium fuel. In this section, I will focus on Thorium fuel as it is currently thought to be the most cost-effective due to its abundance. The purpose of using thorium-based fuel in the MSR design is to find the most efficient, clean, and accessible way of obtaining energy that can be transformed into electricity. [2] Most in-use fuel models are Uranium based. However, by 2025, it is predicated that 95% of Uranium would need to be produced instead of predominately being recycled. Fortunately, thorium can provide a comparable alternative. Using Thorium-Based fuel could help to acquire the same amount of energy, but doing so in a cleaner and more environmentally-sustainable manner. Liquid reactors using thorium would have a small and compact reactor cores that would significantly reduce the economic costs of producing nuclear energy (see Fig. 1). Liquid fuel MSRs utilizing the thorium fuel cycle have many safety, economic, and environmental advantages. [3] Because their reactor cores are much smaller and more compact, they are less expensive to produce. They do not need to shut down for refueling and their fuel lifetime is not limited by radiation damage. Because thorium is much more abundant and accessible than uranium (four times), using thorium for reactors can expand the supply of nuclear fuel, therefore expanding the environmental advantages. Additionally, the liquid fuel would allow the reactors to operate at low pressures with less chemical reactivity.

Solid Reactor

Other research is being spent on solid fuel reactors. MIT more specifically has proposed a Thermal-hydraulic design for MSRs. Like the liquid fuel reactor, this solid fuel design would have a compact reactor core allowing the reactor to be more transportable. In total, this reactor would only have a height of 2.9 m, diameter of 3.0 m, volume of 20.50 m3, and would be made of 12 symmetrical parts. [4] This reactor would also have a fuel cycle of 540 EFDP and thermal power of 20 MWth. Because there have been previous studies showing the plausibility and safety that this solid-fuel reactor could provide, it may currently be the best idea to keep perusing.


As laid out above, technological advancements are outdating the currently-used reactors and creating a design that addresses economic, environmental, and safety concerns. Both the liquid fuel and solid fuel reactors address this issue and has potential to transform nuclear technology.

© Julia Lebovitz. The author warrants that the work is the author's own and that Stanford University provided no input other than typesetting and referencing guidelines. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.


[1] J. Temple, "Small Reactors Could Kick-Start the Stalled Nuclear Sector," Technology Review, 17 Jul 17.

[2] E. Holmvik, "Augmentation of Traditional Uranium Nuclear Fuel Cycles with Thorium," Physics 241, Stanford University, Winter 2017.

[3] T. J. Dolan, Molten Salt Reactors and Thorium Energy (Woodhead Publishing, 2017).

[4] C. Wang et al., "Thermal-Hydraulic Design and Analysis of a Small Modular Molten Salt Reactor (MSR) with Solid Fuel," Int. J. Energy Res. 42, 1098 (2018).