CK,
I want to make a couple of comments based only of the technical merits of the design I read.
So I looked at the article a little bit and it appears to be a variant of the Liquid Metal Cooled Fast Reactor (LMCFR). These types of reactors have operated in the past and had some intriguing properties. First off, unlike virtually every other power generating reactor (as opposed to a research reactor or breeder reactor), the LMCFR operates in the fast spectrum. This requires a coolant other than water as water is an excellent moderator (or rather the hydrogen atoms in the water are excellent moderators). This poses some challenges but offers some potential benefits. The reactor used in your article appears to use liquid sodium, and not salt, as the primary coolant.
First the good part about sodium. It melts at just barely above room temperature, but boils at an extremely high temperature, giving a tremendous range of operating temperatures. Secondly, and importantly for a fast spectrum reactor, it barely interacts with neutrons, allowing them to pass right through almost unimpeded (a few will get captured and form Sodium-24 which has a 15 hour half-life. This is actually quite radioactive. The upside is that the Sodium-24 will decay into Magnesium-24 relatively quickly which is stable. More on this later). Third, sodium is extremely thermally conductive, exactly what one wants in any coolant. Fourth, being electrically conductive, liquid sodium can be pumped via magneto-hydrodynamic pumping. This means that a series of electromagnets can be set up outside the piping and move the fluid with no moving parts whatsoever. This is an extremely desirable quality. Finally, and related to point number 1, the boiling point of sodium is well above the operating temperature of the nuclear fuel. In fact, even in the (highly unlikely) event of a runaway reaction, the sodium stays in a liquid state.
But then there is the bad part. First, obviously, sodium is wickedly chemically reactive, so any sodium leak is likely to cause a chemical reaction/fire of some type. The third US nuclear submarine, (USS Seawolf) used a sodium cooled fast reactor. It was small, efficient, had a very high power output compared to water cooled reactors--all desirable qualities on a submarine. However, the sodium leaked frequently. Nothing disastrous happened from the sodium leaks, but after only a few years operation, the sub was re-fitted with a water cooled reactor which then operated normally for decades (decommissioned in the late 90's). Secondly, whenever reactor maintenance needs to be done, the reactor must be shut off completely and allowed to sit for about 9-10 days. The reason for this is to allow any highly radioactive sodium-24 to decay into stable magnesium-24. This is a perfectly doable operation, but it is just another step to go through.
Back in the 1950's, the United States experimented with a reactor called the Experimental Breeder Reactor #1 (EBR1). This was a test reactor and only ever produced a very modest amount of electricity--basically enough to run some
light bulbs. The reactor was basically a success. However, at the end of the reactor lifespan (a few years for that particular one), the reactor was deliberately allowed to undergo a loss-of-coolant event. The initial thinking was that the EBR1
should be resistant to meltdowns for reasons I will get to later. Instead, about the 1/3-1/2 top of the reactor (about the size of 2
coffee cans stacked on top of each other) did in fact melt down. Emergency alarms sounded, but there was no explosion, fire, or any loss of radioactive materials. It was a totally contained meltdown and in fact the reactor was rebuilt and continued to operate for years.
The reason for the partial meltdown is that Fast Spectrum reactors are extremely sensitive to the precise geometry of both the fuel and the reactor chamber. When the reactor fuel rods over-heated, they softened and bent towards each other. This increased the reactor output causing more softening and eventually a hot blob of molten metal worked its way down the core before the reaction stopped. The core itself was actually partially repaired and taught a lot about how nuclear designs fail. Importantly, there was no steam or hydrogen explosion like at TMI, Chernobyl or Fukushima.
Eventually, a second, modified reactor was built on similar principles but incorporating the lessons of the the partial meltdown of the EBR1. The EBR2 had the fuel contained in steel rods that were more heat resistant that in EBR1, but both the fuel and steel coating were designed to expand slightly outward under heat stress without softening. This is important because as the fuel and rods expand--even slightly--the geometry changes in such a way that fast fission becomes virtually impossible very quickly. The EBR2 had some other changes. The EBR1 had only a minimal amount of sodium acting as coolant. The EBR2 was completely immersed in a pool of liquid sodium to ensure that the core would always have coolant around even if the pumping were turned off completely. In 1986, just a couple of weeks before the Chernobyl disaster, an experiment was carried out to show the passive safety of the EBR2 design. The coolant pumps were deliberately turned off, the temperature of the core
rose and in doing so, the fuel rods themselves expanded, reducing the rate of fission to zero. In fact, this experiment was carried out twice, and each time the EBR2 stubbornly but politely refused to overheat. Being immersed in a pool of liquid sodium, the coolant continued to carry away waste heat via natural convection and the temperature of the entire reactor stayed well below the design limits. There was no core damage or damage of any type and after the experiment was over the coolant pumps were turned back on and the reactor resumed normal operation. The EBR2 continued to operate without incident until it was de-funded in 1994 and decommissioned.
CK, The design you showed does have intriguing properties and in general is much better than the solid fuel water-cooled reactors we use today. There is more intriguing reactor physics I could go into, but I will end my post here with this one. Personally, I still think that the molten salt reactors are the safest ones out there, but this is not a debate. It is a very interesting design with some very interesting potential properties. Hopefully such a design has the passive safety inherent to the EBR2.
Eric