Small modular nuclear reactors

[billvon 2,427]

Modular/small reactors are nothing new; the first power reactors were small (60MwE) and over time they grew to today's gigawatt plus monsters. With the size though there have been some problems:

1) Lots of space needed
2) Cooling problems during rapid shutdown
3) Seismic issues since the reactor covers a larger area
4) Plants have to be built on site

Small reactors tend to overcome a lot of those problems. They need less space and are often installed in the ground; a typical installation with one of these takes about 40 acres of land rather than 200. Generally the reactor vessel is built somewhere else (in a controlled factory environment) then shipped to the site. Since it is physically small it is much more resistant to earthquakes.

But perhaps the biggest safety improvement is passive cooling. When reactors have to shut down rapidly they go from 100% to 2-3% power very rapidly. But that last 2-3% cannot be eliminated; all the short lived radioisotopes produced during nuclear fission are still decaying, and it can take weeks to months for them to start tapering off. This is not a problem when everything is going well; you just keep the coolant pumps running until the core reaches "cold shutdown" where it's still warm but not hot enough to boil water. You can then shut down the pumps, close the valves and let the core just sit there, dissipating all its heat through the walls of the reactor.

During a Fukushima type accident, though, you can lose power to the coolant pumps and then there's too much heat in too small a space to conduct away naturally. Small reactors are a lot better in this regard. Due to the square/cubed law, smaller reactors have an easier time radiating away their waste heat during a rapid shutdown. Many are designed so they can be shut down with all power removed for days or weeks; a few designs require nothing more than opening a few emergency valves internally to allow better circulation of the coolant INSIDE the core (no pumps or external coolant needed.) The remaining heat can be conducted out through the walls of the reactor without damage to the core.

This also adds to safety because it can more easily survive plant damage. You can close the valves on most of these plants, isolate external broken piping and use the internal cooling features to keep the core cool enough. Again the small size helps there.

Since they are thermal plants they generate a lot of waste heat. This is a problem in places like Phoenix (all thermal plants, including fossil fuels, have the same problems there.) But in places like Alaska/Canada this can be a big advantage; the waste heat can be used to heat buildings or provide low quality process heat.

Their one big problem is cost. Per megawatt hour they are more expensive because they generate less power overall (from around 10 to 300 megawatts.) And like all nuclear reactors, they would not be practical without extensive government subsidy coverage, primarily the Price-Anderson act.

Overall, though, they might serve as a pretty good source of baseline power, especially in places where the waste heat would also be useful. Several companies including General Electric and Toshiba, are now offering reactors ranging from 50 to 300 megawatts.

[quade 3]

Problems I see are that energy companies generally want economies of scale rather than safety of smallness. By building smaller plants they require more people to operate and manage. Businesses generally don't like that.

Smaller also means you can have competition from smaller companies who move into a territory and offer similar services for lower cost. Big companies HATE that. My guess is if small nuke plants were available, the large energy companies would fight to the death to keep "outsiders" from bringing any on-line.

quade -
The World's Most Boring Skydiver

[normiss 622]

How dissimilar are these designs to the type the Navy uses aboard vessels?

[billvon 2,427]

>How dissimilar are these designs to the type the Navy uses aboard vessels?

Fairly dissimilar. Naval reactors are generally built for low noise operation, high power densities and very long life, since you have to literally cut apart a submarine to refuel it. Naval reactors often use very highly enriched uranium, and as a result most can be forced to go prompt-critical (i.e. to explode like a nuclear bomb.) Commercial reactors are incapable of this even if someone tries to do this intentionally.

However the lessons learned from operating these small reactors have gone into a lot of these designs; the decades of experience with smaller reactors have been very valuable.

[billvon 2,427]

>Problems I see are that energy companies generally want economies of scale rather
>than safety of smallness. By building smaller plants they require more people to operate
>and manage. Businesses generally don't like that.

Yes, and that's one reason that smaller reactors are less cost effective. However, the lower up front construction costs and easier siting requirements may compensate for that.

>My guess is if small nuke plants were available, the large energy companies would fight
>to the death to keep "outsiders" from bringing any on-line.

When I say "small reactors" these are still massive power plants that would still be owned and operated by the large energy companies. These aren't something that a town is going to install and run their municipal buildings with.

[DanG 1]

Quote

When I say "small reactors" these are still massive power plants that would still be owned and operated by the large energy companies. These aren't something that a town is going to install and run their municipal buildings with.

Dammit. I though I'd found something to power the time machine. How am I going to generate the 1.21 gigawatts I need?

- Dan G

[quade 3]

billvon

When I say "small reactors" these are still massive power plants that would still be owned and operated by the large energy companies. These aren't something that a town is going to install and run their municipal buildings with.

Oh, I dunno. I can totally see it as something the Reedy Creek Improvement District might do in Florida.

quade -
The World's Most Boring Skydiver

[lawrocket 3]

The problem I see is the de facto ban on siting permits for nuclear power plants in places like Cali.

The small, modular systems I see a great benefit. Not in replacing larger facilities but in providing some buffer. Question: can these thing be powered on for high loads and shut down for lower loads?

My wife is hotter than your wife.

[billvon 2,427]

>Question: can these thing be powered on for high loads and shut down for lower loads?

Depends on the design. In general, no, for several reasons:

1) Poison generation. Most nuclear plants do not do well when started and stopped often because nuclear poisons build up during the first stages of shutdown, and these must be burned off during a restart, leading to problems with full power operation.

2) Cost. When nuclear plants are not generating power they aren't making money and there's no cost savings in plant operations when the plant is shut down. Indeed the pumping required generally means they are energy hogs when they're shut down.

3) Thermal cycling. Many components in thermal plants are rated for a certain number of thermal cycles, at the end of which you need at least a shutdown and detailed inspection.

However you can throttle nuclear plants to some degree; there are several methods to do this that do not significantly reduce operating temperature or interfere with poison burnup. Depending on design they can be throttled to 30 to 60% of max.

[livendive 8]

NuScale

Blues,
Dave

"I AM A PROFESSIONAL EXTREME ATHLETE!"
(drink Mountain Dew)

[rushmc 18]

billvon

Cost. When nuclear plants are not generating power they aren't making money and there's no cost savings in plant operations when the plant is shut down. Indeed the pumping required generally means they are energy hogs when they're shut down.

Something not really known
Even for the large scale coal plants, those plants biggest energy users is usually the plant itself
BTW
Thanks for the thread
Interesting

"America will never be destroyed from the outside,
if we falter and lose our freedoms,
it will be because we destroyed ourselves."
Abraham Lincoln

[winsor 187]

If the population was under control, we could work out viable solutions with renewable resources only.

Without control of the population, there is no solution.

All the efforts to produce more energy without addressing the other half of the equation can only forestall the inevitable, and amount to mental masturbation.

Carry on.

[NorrinRadd 0]

quade

Problems I see are that energy companies generally want economies of scale rather than safety of smallness. By building smaller plants they require more people to operate and manage. Businesses generally don't like that.

Smaller also means you can have competition from smaller companies who move into a territory and offer similar services for lower cost. Big companies HATE that. My guess is if small nuke plants were available, the large energy companies would fight to the death to keep "outsiders" from bringing any on-line.

You are right, alas. It is too bad.. smaller, decentralized is far more efficient. Tailoring energy production to local communities, using what resources they have on hand, if at all possible, would prove far more efficient. But profit over efficiency!

Why drive myself crazy trying to be normal, when I am already at crazy?

[billvon 2,427]

>If the population was under control, we could work out viable solutions with
>renewable resources only.

Fortunately it is; the second derivative of population is now negative and has been for some time. Thus the population will eventually peak and then start to decline, absent something that changes that trend.

[winsor 187]

billvon

>If the population was under control, we could work out viable solutions with
>renewable resources only.

Fortunately it is; the second derivative of population is now negative and has been for some time. Thus the population will eventually peak and then start to decline, absent something that changes that trend.

Nevertheless, we have so badly overshot sustainability by any measure that a soft landing is out of the question.

[NorrinRadd 0]

winsor

Nevertheless, we have so badly overshot sustainability by any measure that a soft landing is out of the question.

I don't know if that is true. Yes.. we are well past sustainability with our current rate and means of consumption. But a radical shift in the way we do things would still allow us to live sustainably, even at this population. In other words, I don't see it as a population issue. I see it as a consumption issue. As in the WAY we consume. We just don't need as much as we are taking.

Why drive myself crazy trying to be normal, when I am already at crazy?