US-based Terrestrial Energy and NRG PALLAS are starting the final phase of their graphite irradiation programme for Terrestrial Energy’s Integral Molten Salt Reactor (IMSR). The tests will enable Terrestrial Energy to finalise the qualification of graphite for licensing and future operation of its IMSR plant. The tests are conducted at the High Flux Reactor (HFR) Research Centre of NRG PALLAS in Petten (the Netherlands). Using the HFR, NRG PALLAS simulates ageing processes of reactor materials in an accelerated manner. This allows the effects of irradiation on materials to be measured in order to support reactor design and licensing.
The IMSR design is for a 442 MWt per Core-unit (IMSR400) small modular molten salt fuelled, graphite moderated, thermal spectrum reactor. Terrestrial Energy has developed a two-unit configuration which can deliver 884 MWt/390 MWe. The design features a completely sealed reactor vessel with integrated pumps, heat exchangers and shutdown rods all mounted inside a single vessel. IMSR is a thermal spectrum reactor that uses around 125 tonnes of graphite as the neutron moderator.
The sealed Core-unit is replaced completely at the end of its useful service life (nominally seven years). This allows factory production levels of quality control and economy, while avoiding any need to open and service the reactor vessel at the power plant site. The IMSR400 does not depend on operator intervention, powered mechanical components, coolant injection or their support systems such as electricity supply or instrument air in dealing with upset conditions. It operates at the high temperature required for broad industrial relevance and is designed to use standard assay low enriched uranium fuel.
The completion of tests at HFR will confirm the predicted performance of selected graphite grades. Material tests enable the selection of graphite type and licensing for the Generation IV Integral Molten Salt Reactor (IMSR) core technology. This technology is designed to deliver high-temperature heat and electrical energy, for industrial purposes among other things.
Terrestrial Energy’s goal is to build, license and commission the first IMSR plants in the early 2030s. Since 2020 Terrestrial Energy works with several suppliers of nuclear graphite in western markets on a test program for the selection and qualification of the most suitable graphite grade.
“Comprehensive irradiation tests are essential for advanced reactor development and reactor licensing, as they validate the performance of critical materials under actual operating conditions. The tests are providing the data needed to make our final graphite grade selection for the IMSR,” said Simon Irish, CEO of Terrestrial Energy. “This work will be a major step toward Terrestrial Energy’s goal of achieving early fleet deployment.”
Arjan Vreeling, Manager R&D Nuclear Fuels & Materials at NRG PALLAS said: ” We have been collaborating with Terrestrial Energy now for 5 years and are delighted to be moving to the final stage of irradiation testing of IMSR graphites. Terrestrial Energy is the first developer to begin such tests for this type of molten salt reactors.”
