NRGDutch Institute NRG in Petten began irradiation experiments in August to investigate the safe operation of molten salt reactors (MSRs). NRG said on its website that MSRs had the potential for increased passive safety and decreasing the production of long-living radioactive waste compared with existing NPPs, which use enriched uranium as the fuel and water at high pressure as the coolant. 

MSRs are suitable for operation with thorium-based fuel carried by a liquid salt mixture which is also the coolant. The design of a molten salt reactor removes the risk of core melt.  NRG said meltdown could be avoided in molten salt reactors because they operate at low pressure, the fission chain reaction is stopped when the temperature in the reactor increases and the salt is automatically flushed to a safe location if needed. Within the framework of the Dutch government’s undertaking to reduce CO2 emissions, NRG is studying molten salt technology as part of a nuclear research programme funded by the Ministry of Economic Affairs.

On 10 August, NRG started irradiating a mixture of lithium and thorium fluoride salts, using the High Flux Reactor (HFR) in Petten. The experiment seeks to investigate the stability of the salt mixture during and after irradiation, as well as the evolution of (fission) gases, and the effect of the salt on surrounding materials. This type of information is important for designers of future MSRs, and can be used to answer questions on the materials that are suitable for use in containment as well as the most suitable salt mixtures. 

The experiment was originally planned to begin last year, but because of a lack of previous experience at NRG with molten salt irradiations, additional research was carried out to ensure safe operation under all circumstances. “Safety is of overriding priority at NRG. We have used an extra year to investigate different scenarios in which safety and/or quality of the experiment could be compromised. Now that we know that the design of the irradiation facility is adequate, we can start the experiment”, said project manager Irene Bobeldijk.   

In the 1960s an experimental molten salt reactor operated for five years at the Oak Ridge National Laboratory in the USA.  “It has been some time since a similar molten salt fuel has been irradiated," Bobeldijk noted. 

"Our research can contribute to the renewed interest by providing well-founded data." 

The research is being carried out in collaboration with the European Commission's Joint Research Centre in Karlsruhe, which produced the fuel and will investigate samples in its laboratories after irradiation. All findings will be shared with the international community. According to the IAEA, molten salt technology will require at least a decade of intensive research, validation and qualification before it can be considered for commercialisation.

Photo: Courtesy NRG