Researchers at NRG, a Dutch nuclear materials firm, have begun the first tests of nuclear fission using thorium salts since experiments ended at Oak Ridge National Laboratory in the early 1970s.
Thorium has several advantages over uranium, the fuel that powers most nuclear reactors in service today.
1. it’s much harder to weaponize.
2. Reactor design with fuel in liquid form can be self-regulating and fail-safe.
The inside of the Petten test reactor where the thorium salt is being tested is shining due to charged particles traveling faster than the speed of light in water.
The team at NRG is testing several reactor designs on a small scale at first. The first experiment is on a setup called a molten-salt fast reactor, which burns thorium salt and in theory should also be able to consume spent nuclear fuel from typical uranium fission reactions.”
Sander de Groot from NRG explains that their interest for MSR’s at NRG originated while working on several large scale programs, dedicated to the High Temperature Reactor (HTR) and transmutation. “There was both internal and external support for our idea to start the SALIENT (its name derived from SALt Irradiation ExperimeNT) experiments”, he says. “This is a technology with much perspective for large scale energy production. We want to have a head-start once the technology will break through. We see this as a commercial opportunity for the long-term. It also gave us the opportunity to cooperate with the European Commission laboratory Joint Research Center-ITU located in Karlsruhe, a cooperation that we see as very important.”
Sander de Groot and Ralph Hania say this will build up experience with the use of fission fuel in the form of a molten salt.
First Experiment: SALIENT – 1
The materials chosen for the first experiment, a lithiumfluoride/thoriumfluoride mixture, stem from the European concept for a waste-burning MSR, the Molten Salt Fast Reactor.
There will be four small crucibles that contain the LiF/ThF mixture. They are placed within a set of concentric steel tubes that are about 50 cm high. At the start of the experiment, the tubes will be brought into a selected radiation field of the High Flux Reactor. After a while, thorium will be transmuting to uranium and the uranium will start to fission. The salt content of the crucibles is identical at the start, but within one, a small nickel sponge will be placed, and in another one is a nickel foil. During the fission reaction, fission products will form and a part of these are noble metals. The goal is to find out if these noble metals precipitate on the nickel and the TMSR salt can be cleaned in this way.
For SALIENT-02, a different material mixture will be used that contains beryllium, forming a mixture also known as FliBe.
Further experiments will focus more on the interaction between the salt and the containment materials. Corrosion resistance is very important for those materials: they should be mechanically strong, and able to resist chemical corrosion and intense radiation. This corrosion resistance will be the next focus of the experiments with tests for 316 stainless steel, Hastelloy, the nickel alloy that ORNL used in the 1960s, and TZM – a titanium/zirconium/molybdenum alloy. Molybdenum has the potential to neutronically be much more attractive but there is no history of testing it at these temperatures
China, India and Indonesia are developing TMSRs of various kinds. Indonesia together with ThorCon want to skip the entire test reactor scaling up process and directly build a radiation-free full-scale reactor and test it to the maximum before loading it with fuel.
India has two TMSR types in the planning but doesn’t seem to prioritize construction since they are going for their AHWR utilizing thorium.
China has a streamlined TMSR effort with government support and funding. They take an intermediate step by developing and building a molten salt cooled pebble bed reactor, a technology which they are world leaders in, as a rather quick test reactor towards their TMSR prototype.
If the NRG loop experiment proves feasible, this has the potential to give Europe, showing up from nowhere, a major head-start in Thorium Molten Salt Reactor (TMSR) development further speeding up the race.