Chinese molten-salt reactor cleared for start up | Hacker News Reader

Chinese molten-salt reactor cleared for start up

world-nuclear-news.org

21 pointsbeefman9 comments

> As this type of reactor does not require water for cooling, it will be able to operate in desert regions. The Chinese government has plans to build more across the sparsely populated deserts and plains of western China, complementing wind and solar plants and reducing China's reliance on coal-fired power stations. The reactor may also be built outside China in Belt and Road Initiative nations.

Good news for reducing CO2 emissions around the world. Shame there's an evolving rift in international relations that will keep this technology out of the western sphere and it's allies (let alone political anxiety about Nuclear power)

This is just a research reactor. Far from production ready.

Here's a somewhat similar molten salt research reactor that has received support from the Department of Energy.

  Molten Chloride Reactor Experiment – Southern Company Services Inc. (Birmingham, AL) will lead a project to design, construct, and operate the Molten Chloride Reactor Experiment (MCRE) – the world’s first critical fast-spectrum salt reactor relevant to TerraPower’s Molten Chloride Fast Reactor. Total award value over seven years: $113 million (DOE share is $90.4 million)

Except that instead of being a "Thorium" reactor, it's a Uranium one. By the way, the Chinese reactor has some Thorium in it, but it's mainly Uranium. TerraPower's reactor is an Uranium one, but it's a fast reactor, which has all sorts of advantages, like higher efficiency and fewer waste products.

[1] https://www.energy.gov/ne/articles/energy-departments-advanc...

> TerraPower's reactor is an Uranium one, but it's a fast reactor, which has all sorts of advantages, like higher efficiency and fewer waste products.

I'm naive to the finer technical aspects of nuclear technology, but I was under the impression that a main advantage of thorium reactors is less nuclear waste?

> after a few hundred years, the waste from a thorium reactor can be less toxic than the uranium ore that would have been used to produce low enriched uranium fuel for a light water reactor of the same power

https://en.wikipedia.org/wiki/Thorium_fuel_cycle#Fission_pro...

I'm not sure how a 'slow' thorium reactor stacks up to a 'fast' uranium reactor

In a fast reactor neutrons are a few thousand times faster than in a slow one. They are more likely to zip by a nucleus than to interact with it, a few hundred times more likely. But when they do interact, they are very likely to just trigger fission, rather than be absorbed. For example a U-235 has a chance of about 82% to be fissioned by an incoming slow neutron and 18% to become U-236, which is a very nasty long-live waste product. Pu-239 has about a 30% chance to become Pu-240. This itself has a 99.9% to absorb a thermal neutron rather than undergo fission [1].

  When the isotope 240Pu captures a neutron, it is about 4500 times more likely to become plutonium-241 than to fission. In general, isotopes of odd mass numbers are more likely to absorb a neutron, and can undergo fission upon neutron absorption more easily than isotopes of even mass number. Thus, even mass isotopes tend to accumulate, especially in a thermal reactor.

Bottom line, in a thermal reactor a lot of neutrons get absorbed and transuranic elements get produced, which have a tendency to have very long half lives.

Thorium, being lighter than Uranium, will produce less of those, because it takes more successive neutron absorptions to become a transuranic isotope. So, yes, Thorium has an advantage over slow Uranium reactors.

But fast Uranium reactors produce much fewer transuranic isotopes to begin with, plus they can burn U-238, which is plentiful. Slow Uranium reactors use Uranium that only contains about 5% U-235, and they only burn a part of it. Fast reactors can burn a copious amount of the U-238 they have, and so they produce much more energy from the same amount of fuel. Which is a different way to say, they produce much less waste for the same amount of delivered energy.

[1] https://en.wikipedia.org/wiki/Plutonium-240#Nuclear_properti...

The way to get energy out of a nuclear reactor today is with a heat engine.

The nuclear reactor provides the heat for the hot side.

But you also need cooling for the cold side. Normally that's a river/lake/ocean or evaporative cooling.

All of those involve lots of water... So how does this work?

A heat engine needs a heat difference. If you operate the hot side, the reactor, at a very hot temperature, the cool side can be quite hot too and there is still enough temperature difference to generate electricity.

The hot running cool side can be air cooled, doesn't need water.

Traditional nuclear power plants operate at low temperature, hence the cold side needs to be cool for enough temperature difference. For that cool you need water cooling.

Thorium salts and other fluorides can go to high temperatures at low pressures. It's easy to make them high temperature.

Other high temperature liquids used for cooling include sodium and lead.

I'm naive to the topic, but I'm guessing the actual energy generation still requires water, it's just the coolant aspect consists of molten salts:

> Molten salt reactors (MSRs) use molten fluoride salts as primary coolant, at low pressure

https://world-nuclear.org/information-library/current-and-fu...

The primary coolant is used closed-loop, and therefore isn't used up anyway.

From a cursory google, it doesn't seem that water cooling is closed-loop:

> Direct or once-through wet cooling

> If a coal or nuclear plant is next to a large volume of water (big river, lake or sea), cooling can be achieved by simply running water through the plant and discharging it at a slightly higher temperature.

> Recirculating or indirect wet cooling

> Where a power plant does not have abundant water, it can discharge surplus heat to the air using recirculating water systems which mostly use the physics of evaporation.

> Cooling towers with recirculating water are a common visual feature of power plants, often seen with condensed water vapour plumes. Sometimes in a cool climate it is possible to use simply a pond, from which hot water evaporates.

> Dry cooling

> As the name suggests, this relies on air as the medium of heat transfer, rather than evaporation from the condenser circuit

https://world-nuclear.org/information-library/current-and-fu...

Reply on news.ycombinator.com