This tiny set of crucibles is the world's first thorium molten salt reactor (TMSR) experiment in over 45 years.
“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.”
- Sander de Groot, NRG
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.”
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It’s important to notice that SALIENT is not a single experiment but really a series, and we’ll build that up step by step.
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. That hasn’t been done for decades and we’re also doing it to train ourselves. It’s important to notice that SALIENT is not a single experiment but really a series, and we’ll build that up step by step.
We need highly purified salts for SALIENT and JRC is one of the very few places in the world that have the expertise to produce them while NRG has designed the irradiation part of the experiments.
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.
The idea is to stick to standard materials wherever possible and therefore the tubes are made of ordinary stainless steel. The suitability of steel remains to be determined. Corrosion may be a problem, and it is not yet know if it can be controlled by managing the salt chemistry. The high temperatures in MSRs might also be problematic, even if the pressure inside the system is low.
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.
What makes SALIENT and NRG unique?
United States, France and perhaps Japan has national laboratories that have the same infrastructure as will be used at NRG. So of course, if their government would give this priority, they would be able to prepare for similar experiments.
Another major ingredient is that you need a regulator that has some flexibility.
Ralph says that “what we are doing here is new, it hasn’t been done before. If you have a regulator that simply says ‘this is something we don’t know, we won’t allow you to do it’, then you cannot possibly innovate. We have the good fortune of having a regulator that we can communicate with. That is not to say they’re not strict, they are! Even though we only use a couple of cm3 of salt, they checked every detail and we had to redo our homework quite a few times.”
Interestingly, the zones on the left of the ‘checkerboard’ form a ‘pool side facility’ that will become relevant in a next phase of experimentation. This pool side facility is a high flux region on the outside of the reactor core with enough room to accommodate a larger molten salt reactor experiment, in which a ‘salt loop’ can be tested. The intention is to fill this ‘salt loop’ with molten salt fuel. Due to the high neutron flux, a fission reaction will start and the loop will become a test-scale molten salt reactor. This pool side facility of the HFR is unique.
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.
Gijs Zwartsenberg at the local Thorium organization (ThMSR.nl) did the interviews and deserves all the Dutch support you can give!