US-based Terrestrial Energy and Netherlands-based NRG have begun an irradiation programme to analyse the behaviour of graphite under the conditions it will experience in a Terrestrial Energy Integrated Molten Salt Reactor (IMSR) core. The work is part of a wider test programme supporting the IMSR design.

The programme will provide data that demonstrates to nuclear quality standards the structural changes of graphite under the irradiation conditions experienced during the seven-year life of an IMSR Core-unit.

Terrestrial Energy and NRG presented the programme at the 20th International Nuclear Graphite Specialists' Meeting in Brugge, Belgium. NRG operates the European Union-owned High Flux Reactor at Petten, and is providing technical services to support Terrestrial Energy for "in-core" materials testing and development the IMSR power plant.

Molten salt reactors (MSRs) use fuel dissolved in a molten fluoride or chloride salt, which functions as both the fuel (producing the heat) and the coolant (transporting the heat away and ultimately to the power plant). Terrestrial's IMSR, based on MSR experience at the USA's Oak Ridge National Laboratory, integrates the primary reactor components, including the graphite moderator, into a sealed and replaceable reactor core unit with an operating lifetime of seven years.

The graphite irradiation programme should enable Terrestrial to select the most suitable graphite grade for use in the IMSR reactor, and will qualify graphite for IMSR use. Different graphite grades will be subjected to neutron irradiation at elevated temperatures and characterised on a range of material properties. The data will cover the lifespan of the graphite components in the IMSR.

The collaboration between Terrestrial Energy and NRG is part of a wider partnership between Terrestrial and the European Union’s scientific community, following a March 2018 technical services agreement with the European Commission's Joint Research Centre (JRC) in Karlsruhe, Germany to perform confirmatory studies of the fuel and primary coolant salt mixture for the IMSR.

Photo: NRG's High Flux Reactor in Petten (Credit: NRG)