Molten Salt Reactor Research Program

SALIENT-01 was the world’s first MSR-specific fuel salt irradiation experiment in 45 years and has gained notoriety in the MSR community.

The main objective of SALIENT-01 is to acquire experience with performing molten salt irradiation, including the design of a rig containing liquid fuel and the handling of fresh and irradiated fuel salts in inert environments.

In a nutshell, mixtures of lithium fluoride and thorium fluoride salts contained in graphite crucibles are exposed to high neutron and gamma radiation levels in the High Flux Reactor in Petten. After generating burn-up in the reactor, the samples are inspected for material compatibility and fission product behavior.

SALIENT-03 is the successor of the SALIENT-01 experiment. This project focuses on the determination of corrosion rates of structural materials when they are exposed to molten fuel salts under irradiation, and introduces in-pile measurement of fission gas release. Lessons learned from the SALIENT- 01 project are incorporated in the design.

The SALIENT-03 experiment is performed in cooperation with JRC-Karsruhe, which produces the thorium salts.

Nickel-based materials are foreseen to be used in MSR systems for their high corrosion resistance. Nickel is however sensitive to thermal neutron irradiation, producing helium which may consequently weaken the material. The ENICKMA project is performed to study the effect of helium embrittlement in nickel-based materials such as Hastelloy N, that are candidates for use in Molten Salt Reactors.

100 tensile, stress relaxation and low cycle fatigue samples are irradiated at MSR-relevant temperatures. Test results for the irradiated materials are then compared with results for reference samples.

The objective of SAGA is to study the gas formation that can take place if fluoride salt specimens are exposed to gamma (and alpha and beta) radiation at temperatures up to about 150 ^oC. This phenomenon may represent an issue when molten salt waste is temporarily stored before waste treatment and final disposal.

The re-usable SAGA facility contains 6 gastight sample holders attached to pressure sensors. The pressure sensors register pressure build-up due to gas formation while the facility is bombarded with gamma rays using spent fuel from the HFR Petten.

The Lumos waste project anticipates the need for safe and secure disposal of the radioactive waste that is generated during irradiation of fuel-bearing salts in a molten salt reactor.

For this purpose NRG consults the Dutch central organization for radioactive waste (COVRA) to determine the criteria for acceptance of this type of waste. generated during experiments in the HFR. Complete characterization of the composition of the waste is a prerequisite. The process that is currently explored, includes stripping of the most aggressive agents from the waste by chemical separation, followed by vitrification and cementation of the resulting waste streams.

For design support and safety analyses one should know the molten salt flow and heat transport in the reactor vessel and/or the cooling system. For this, so-called thermal-hydraulics system codes were used. The nuclear reactor is modelled in such codes by ways of 0- or 1-dimensional elements. Originally, such codes were developed for water cooled reactors.

The simulation code needs to be adapted for molten salt reactors. Besides, validation is required to gain trust in the simulation outcomes. The SPECTRA code of NRG has been adapted for the specific and unique requirements put forward by modelling molten salt reactors. The following models are now available in the code:

Besides, the flow in the reactor vessel demands 3-dimensional modelling. For that reason, NRG started to prepare also a 3-dimensional tool for simulation of molten salt reactors.