Why big neuclear reactors rather than many smaller nuclear reactors?

For power in the public sector why big nuclear reactors rather than many smaller nuclear reactors? Not infrequently do we read of safety problems with the big nuclear reactor constructed to generate power for the public sector. Infrequently do we read of safety problems with the smaller reactors in submarines. Someone, somewhere must have decided for some reason to make relatively few giant reactors rather than relatively many smaller reactors.

I can conjecture cost, distribution, security, nimby, but have no clue as to why. Do you know how these decisions were made?

It is more expensive to keep them safe, on a per kilowatt/hr basis. Nuclear submarines are relatively safe because the Navy spends large amounts training technicians to keep them safe. The more reactors you have spread out all over the country, the more highly trained staff you need to maintain them. Several small reactors use more staff than one large reactor, so the power is more expensive on a per unit basis.

Smaller reactors do exist. The Proper Authorities in the US developed the SNAP-19 and its series as sort of a backup generator that runs on radioactivity. The CANDU-1 and -2 are also smaller and more or less the same from one plant to another. As you pointed out, naval plants are smaller and reactors on spacecraft are (I guess) the smallest of all.

I suppose the idea of a big plant is to spread the cost of containment and other overhead costs over the largest amount of kilowatts possible in order to try to make the thing pay.

Efficiency of scale, more than anything, along with the fact that thermodynamic efficiency increases as the temperature difference between your energy source and the cooling system increases. It’s easier to maintain one big, hot energy source and insulate and cool it than to try and do this with a lot of small ones. It also puts all of your complex control apparatus and support mechanisms in one place, and you only have one place to guard against theft or attack.

The only reason reactors in subs are smaller is because they have to fit on board the subs.

Yeah. Don’t confuse the relative safety records of naval ships with the size of the reactors themselves.

The US Navy nuclear power safety record is unequaled – cited by world nuclear authorities and held up as a gold standard by other US gov’t agencies [.pdf warning]. There are several reasons, but the key ones are relentless dedication to training, the authority inherent in military organizations to make people perform, and Hyman G. Rickover.

A big problem is that the NRC doesn’t have any procedure for licensing small reactors, so they would take as long and cost as much as a full sized reactor. There is some discussion about creating special procedures for small reactors.

Small reactors in 100-300 MW power range could potentially be much cheaper on a cost per kilowatt hour, since they could be factory built rather than site built. Building the reactors in a factory could also have better quality control.

A lot of the cost could be controlled by using a central control room and having a lot of small reactors on the same site so you don’t have a staff for each reactor.


Do we? (I know, I hate to be the guy that always shoots at the OP’s premise.)

Besides 3 “major” incidents (one of which was more recent), I don’t remember hearing about a lot of safety problems at nuclear power sites. Maybe I’m not reading the right newspapers.

I don’t believe spacecraft have nuclear reactors in the same sense as earthbound nuclear reactors. Whereas terrestrial/naval nuclear power plants rely on a mass of radioactive fuel being held at criticality by a complex, actively-controlled system using control rods and neutron moderator material, the nuclear reactors for spacecraft are thermoelectric batteries that rely on the decay heat from a subcritical mass of plutonium. There’s no complex control system involved to regulate the power output from the radioactive mass, so the power output decreases over time as the fuel decays, and they’re also quite inefficient compared to the typical terrestrial/naval nuclear power plant. But they last an awful long time, which makes them a suitable choice for deep-space probes that need to operate for decades without being serviced.

American nuclear reactors are very safe. The issue of size is that a larger plant can operate with about the same overhead as a smaller plant.
The plants being designed now are failsafe-they are designed to shut down automatically in the event of an accident.

Yeah, for now, but I’m sure we’ll find a way around that.

This has been my understanding as well: Paperwork. Apparently you can’t do it in bulk. It’s per reactor/site (whatever) so it’s cost prohibitive to build anything less than big.

Too bad. I wouldn’t mind a little 20-25KW generator for … well, all my power :slight_smile: Skip the grid (or feed back into it).

Yes, you’re not reading the right newspapers.

Here’s something from yesterday:

Please ignore the the alarmist quotes from activists, I’m just using the article to cite the NRC.

A much more serious incident was the 2001 Davis-Besse corrosion.

Ten years on, safety is not really improving at Davis-Besse, is it?

I tend to notice these stories when they appear because of professional interest; I’m guessing a lot of people glance over them but do not remember them later.

Do you live near a nuke plant? Little things happen that don’t make national news. Our local plant had a tritium leak about a year and a half ago. Not national news or a “major” incident by far, but something nonetheless. Of course, who knows if we would even hear about something of a similar scale happening on a sub.

Cost because there are huge economies of scale as far as capex and licensing. Going to less efficient economies of scale can literally cost ratepayers billions of dollars (not an exaggeration).

Public utility commissions and regulated utilities are charged by state legislatures with providing safe, reliable energy at the lowest cost to serve, so they have a strong bias towards economies of scale.

For non-regulated markets, they must still pursue economies of scale, otherwise their energy becomes too expensive relative to regulated jurisdictions and industries won’t locate new plants in the territory, and in fact may relocate existing plants to jurisdictions with cheaper operating costs.

post-Fukushima, do any of them have even the slimmest hope of going into service? Or are we condemned to limp along on 50-year-old reactors (the one closest to me is the same gen. BWR as the Fukushima ones) forever?

It seems like the Westinghouse AP1000 is still on track to geting approved.