The first phase of a Salt Irradiation Experiment (SALIENT) has begun at the Nuclear Research and Consultancy Group in Petten, a nuclear research facility along the North Sea coast in the Netherlands.
The experiment is being carried out with the cooperation of the European Commission Laboratory Joint Research Center-ITU (JRC) in Karlsruhe, Germany with the initial aim of producing cleaner reactor fuel. The researchers will later look into materials for reactor construction.
It has been 45 years since this type of experiment has been undertaken. The last research into Molten-Salt thorium reactors was carried out in the 1960s at the Oak Ridge National Laboratory (ORNL) in the United States. The ORNL’s Molten-Salt Reactor Experiment (MSRE) was constructed in 1964, went critical in 1965 and was in operation until 1969.
First Stage of Experiment
Scientists at the Petten facility will use the high-flux reactor, one of two reactors on-site, under the management of Sander DeGroot and lead scientist Ralph Hania.
The team will be melting a sample of thorium salt fuel — a mixture of lithium fluoride and thorium fluoride inside an insulated graphite crucible.
Inside the crucible, neutron bombardment will trigger a nuclear reaction that changes the thorium salts into uranium isotopes that will undergo a nuclear reaction. The purpose of this part of the experiment will be to remove what’s called “noble metals,” those metals that are not involved in a nuclear reaction.
To find the most efficient fuel production, two processes will be used. To test this, the scientists will place nickel foil in one crucible and a cube of highly porous nickel in another crucible, in both cases, hoping the noble metals will preferentially precipitate out onto the nickel. This part of the experiment is crucial in that the tests will determine the path of the next phase of the research project.
The use of an insulated graphite crucible in the Petten experiment is important because it tells us just how far we have come in the development of a graphite material. ORNL scientists wanted to use graphite in the 1960s, knowing the thorium salt would not permeate graphite in which the pores were on the order of a micrometer.
But they only had a few small experimental pieces. Difficulties were encountered when a manufacturer set out to produce a new grade of pyrolytic carbon (CGB) to meet the MSRE requirements. Actually, the research being done today can date back to earlier molten salt reactor research for the Aircraft Reactor Experiment. Yes, we were looking to build a nuclear-powered aircraft.
Second Stage of Experiment
During the next phase of the experiment, scientists will be using a different fuel mixture also containing beryllium, known as TFLIBe. TFLiBe is a molten salt made from a mixture of lithium fluoride (LiF) and beryllium fluoride (BeF2). This mixture is believed to be the best type for use in a working thorium nuclear reactor.
This experiment will help in testing the resilience to corrosion and high operating temperatures of materials to be used in the construction of molten salt thorium reactors, such as the different grades of steel, the nickel alloy Hastelloy, which was used at ORNL, and titanium-zirconium-molybdenum alloys.
Molten-salt reactors (MSRs) may be our answer to future energy production that will be safer and cleaner. MSRs are a class of generation IV reactors capable of running at higher temperatures than water-cooled reactors for a higher thermodynamic efficiency.