Gates has been talking up a storm around MSR(s) lately.
It's hard for me to believe, however, that they're going to get a prototype reactor in the 2024-2028 time frame if they haven't decided which halogen to use in their fuel salt.
MSRs have many good points but there is a lot of development left to do. For instance, a thermal reactor using thorium/uranium and fluoride salts will probably have a graphite moderator, but the lifetime of that moderator is limited by exposure to neutrons. This material can stand the chemical environment
but it does not hold up as well under neutrons as we'd like.
It's a complicated problem because the question of "what happens to the fission products" is a complicated one. Some fission products will stay in the salt, where you hope they won't absorb neutrons and 'poison' the reaction. Others will condense on the colder parts of the system. Others are released in gas form, especially the noble gases Xe-131 and Kr-85. The reactor vessel has to not just hold up to the molten salt, but it has to hold up to a molten salt which contains random fission products from across the periodic table.
A group of enthusiasts took up the cause of the thorium/uranium cycle 15 years ago. There has been a lot of research on it since, certainly people are much more aware of the challenges there.
People were less interested in Chloride salts and the uranium/plutonium cycle back in the day but that interest is increasing now for quite a few reasons. One of them is that the materials challenges seem less severe (no moderator, more neutrons to start with, less neutron loss to reactor materials.)
The other advanced technology to make that work is
It's hard for me to believe, however, that they're going to get a prototype reactor in the 2024-2028 time frame if they haven't decided which halogen to use in their fuel salt.
MSRs have many good points but there is a lot of development left to do. For instance, a thermal reactor using thorium/uranium and fluoride salts will probably have a graphite moderator, but the lifetime of that moderator is limited by exposure to neutrons. This material can stand the chemical environment
https://www.steelforge.com/hastelloy-n/
but it does not hold up as well under neutrons as we'd like.
It's a complicated problem because the question of "what happens to the fission products" is a complicated one. Some fission products will stay in the salt, where you hope they won't absorb neutrons and 'poison' the reaction. Others will condense on the colder parts of the system. Others are released in gas form, especially the noble gases Xe-131 and Kr-85. The reactor vessel has to not just hold up to the molten salt, but it has to hold up to a molten salt which contains random fission products from across the periodic table.
A group of enthusiasts took up the cause of the thorium/uranium cycle 15 years ago. There has been a lot of research on it since, certainly people are much more aware of the challenges there.
People were less interested in Chloride salts and the uranium/plutonium cycle back in the day but that interest is increasing now for quite a few reasons. One of them is that the materials challenges seem less severe (no moderator, more neutrons to start with, less neutron loss to reactor materials.)
The other advanced technology to make that work is
https://en.wikipedia.org/wiki/Closed-cycle_gas_turbine
which is necessary for any kind of economically competitive nuclear energy because the cost of a steam turbine is outrageous.