IMSR® Technology

Advanced Reactor power plant based on proven molten salt reactor technology

How it Works

The fundamental engineering challenge of nuclear fission-reactor design is the safe dissipation of fission heat in every conceivable set of circumstances. The fundamental economic problem with solid-fuel reactors, which have been used for the past 60 years, is that a solid-fuel solution to this central challenge leads to a nuclear plant that is too complex and too challenging to finance and build. It is time to revisit this fundamental challenge of heat dissipation with different technology choices and with 21st century energy-market needs in mind.

The IMSR® is a liquid-fuel reactor system, rather than a solid-fuel system, as is used exclusively in conventional reactors. The IMSR® dissipates heat using a molten salt. Salts are thermally stable and excellent heat-transfer fluids, ideal for dissipating heat from the fission process simply and safely. In a molten salt reactor (MSR), salt provides a fluid medium to carry a nuclear fuel—in the case of the IMSR®, a low-enriched-uranium fluoride salt. The IMSR® provides simple, safe, and natural mechanisms for heat dissipation. It is a far superior system for the simple passive dissipation of fission heat. The use of a molten salt is at the heart of many engineering and commercial virtues of the IMSR®.

An IMSR® power plant generates 400 MWth of thermal energy (190 MWe) with a thermal -spectrum, graphite-moderated, molten-fluoride-salt reactor system, fueled by low-enriched uranium (less than 5% 235U). It incorporates the approach to MSR design and operation researched, demonstrated and proven by the ARE and MSRE test reactors at Oak Ridge National Laboratory (ORNL); these were further developed under the DMSR program.

The IMSR® improves upon the earlier ORNL MSR designs through various innovations that are pragmatic and commercial. The key challenge to MSR commercialization is graphite’s limited lifetime in a reactor core, which is a function of reactor power. Commercial power reactors require high core energy densities to be economical, but high power densities significantly reduce the lifetime of the graphite moderator requiring its replacement; this is challenging to do simply, safely and economically in an industrial environment. The key IMSR® innovation is an elegant solution to this challenge – the integration of the primary reactor components, including the graphite moderator, into a sealed and replaceable reactor core, the IMSR® Core-unit, which has an operating lifetime of 7 years. The IMSR® Core-unit is simple and safe to replace, it supports high utility factors for IMSR® power plants and high capital efficiency. It also ensures that the materials’ lifetime requirements of all other reactor core components are met; the challenge of achieving these requirements is often cited as an impediment to immediate commercialization of MSRs. The result is a power plant that delivers the combination of high energy output, simplicity and ease of operation, and cost-competitiveness essential for widespread commercial deployment. IMSR® power plants are a new clean energy alternative.

More reasons the IMSR®  power plant is the planet’s smart and clean energy alternative