3 ms·

I'm surprised the reactor needs a moderator, I would assume that a liquid fuel reactor could be controlled far better by controlling flow into and out of the cr

I'm surprised the reactor needs a moderator, I would assume that a liquid fuel reactor could be controlled far better by controlling flow into and out of the critical mass. It's all at normal pressures, just hot (temperature and radiation wise), so just bog standard plumbing practices for handling fluid levels should work. Being able to scramble the reactor by just dumping the contents through a set of diverters into separate flat bottom chambers to cool and eventually freeze is an awesome safety feature.

YakBizzarro 4y ago
A moderator is not used to control the reaction, but to make it possible. The neutrons produced by fission, have high kinetic energy, and fuel has a small cross section for neutrons at such high energy. A neutron moderator slows down the neutrons, making them more likely to interact with the uranium and split them. typically water is a good moderator, but here they use graphite for obvious reason (high temperature salts doesn't play well with water)
- mikewarot 4y ago
  That makes a lot of sense... thanks! As for molten salts and water... oh yeah. That gets into very dangerous territory.[1] A very similar reaction seems to happen even with just molten table salt, where it "shouldn't". 1 - https://www.youtube.com/watch?v=LmlAYnFF_s8
Rokid 4y ago
One of the great practical challenges with molten salt is to design a reliable valve. At temperatures this high and with the high corrosive properties of the medium, this is not trivial.
- mikewarot 4y ago
  I didn't realize that the viscosity stays high for molten salt[1], that makes everything abrasive, along with dealing with possible phase change if the salt solidifies... yikes! So, what we're dealing with is highly radioactive corrosive molasses with a constant stream of radioactive decay product gasses bubbling out of it, like Xenon and Iodine. Yeah, that seems more challenging that I first thought. 1 - https://www.powermotiontech.com/home/article/21144640/armoring-a-valve-against-molten-salt

YakBizzarro 4y ago

A moderator is not used to control the reaction, but to make it possible. The neutrons produced by fission, have high kinetic energy, and fuel has a small cross section for neutrons at such high energy. A neutron moderator slows down the neutrons, making them more likely to interact with the uranium and split them. typically water is a good moderator, but here they use graphite for obvious reason (high temperature salts doesn't play well with water)

mikewarot 4y ago
That makes a lot of sense... thanks! As for molten salts and water... oh yeah. That gets into very dangerous territory.[1] A very similar reaction seems to happen even with just molten table salt, where it "shouldn't". 1 - https://www.youtube.com/watch?v=LmlAYnFF_s8

Rokid 4y ago

One of the great practical challenges with molten salt is to design a reliable valve. At temperatures this high and with the high corrosive properties of the medium, this is not trivial.

mikewarot 4y ago
I didn't realize that the viscosity stays high for molten salt[1], that makes everything abrasive, along with dealing with possible phase change if the salt solidifies... yikes! So, what we're dealing with is highly radioactive corrosive molasses with a constant stream of radioactive decay product gasses bubbling out of it, like Xenon and Iodine. Yeah, that seems more challenging that I first thought. 1 - https://www.powermotiontech.com/home/article/21144640/armoring-a-valve-against-molten-salt