CANDU reactor miniaturization

[Ted C]

For those who have some experience with such things, is a CANDU-style reactor something that can be scaled down in size?

I was just thinking that with oil prices so high, nuclear-powered civilian cargo ships might be worth investigating. A CANDU reactor doesn't require enriched uranium, which would be preferrable in such an application, but I don't know if that feature would also forces it to have a minimum size in order to get a powerful enough reaction going.

Logistical concerns are a separate issue. Assuming that such power plants would be technologically feasible, implementation would require a plan for keeping the fuel reasonably secure from terrorists; if that's not feasible, the idea would still be a washout.

[Darth Wong]

CANDU reactors were always designed for commercial power generation, with features like the ability to refuel without shutting down the reactor. The kind of ultra-compact reactor you put on a commercial vessel wouldn't need any of that. They're often sealed units with an integral fuel supply that lasts a few years, which you just run until it peters out and then return to source. I don't think you can really make a CANDU reactor as small as some of these other designs.

[The Duchess of Zeon]

For those who have some experience with such things, is a CANDU-style reactor something that can be scaled down in size?

I was just thinking that with oil prices so high, nuclear-powered civilian cargo ships might be worth investigating. A CANDU reactor doesn't require enriched uranium, which would be preferrable in such an application, but I don't know if that feature would also forces it to have a minimum size in order to get a powerful enough reaction going.

Logistical concerns are a separate issue. Assuming that such power plants would be technologically feasible, implementation would require a plan for keeping the fuel reasonably secure from terrorists; if that's not feasible, the idea would still be a washout.

It would be cheaper to simply provide the nuclear cargo ships of the future with a security squad and some 30mm autocannons.

[Vehrec]

Or a solid impact resistant cask and some scuttling charges.

[Patrick Degan]

I would imagine the reactor vessel for such an application would be sealed with its fuel core, with an outer jacket through which the circulation pipes for cooling and steam generation would run. A few hookups for something which would require very heavy machinery to haul out of the ship and which would not be easy to cut into to get at the fuel within. Not something a terrorist cel or a gang of pirates can easily make off with.

The reactor room could be sealed off and its entrances locked by a dual-key system, with one located on the ship's bridge and the other in the engine control centre which have to be turned simultaneously to allow access, or the locks jam shut.

[Ted C]

CANDU reactors were always designed for commercial power generation, with features like the ability to refuel without shutting down the reactor. The kind of ultra-compact reactor you put on a commercial vessel wouldn't need any of that. They're often sealed units with an integral fuel supply that lasts a few years, which you just run until it peters out and then return to source. I don't think you can really make a CANDU reactor as small as some of these other designs.

I was less concerned about the refueling process than about the type of fuel used. I know that a CANDU doesn't require enriched uranium, so the whole centrifuge process isn't necessary. For a ship, a system that's designed to stop in port every few years for a refueling stop would be fine, but I don't know if a reactor that uses unenriched fuel could be made small enough to fit on a ship and operate it. I know that US Navy warships with nuclear power use enriched uranium, since the fuel is made in Tennessee.

A small reactor will obviously have a relatively small volume/mass of fuel compared to a large, inland power plant. My main question is whether that smaller reactor will need enriched fuel in order to generate enough power.

EDIT: I guess the point is that if terrorists do manage to get hold of the fuel supply from one of these reactors, it won't be something easy to weaponize.

[Darth Wong]

The thing is, enriched fuel is kind of a design shortcut, which is why even the smaller Canadian reactor designs use moderately enriched fuel. It just makes it easier to build a really small, simple reactor.

[Ted C]

The thing is, enriched fuel is kind of a design shortcut, which is why even the smaller Canadian reactor designs use moderately enriched fuel. It just makes it easier to build a really small, simple reactor.

So an enriched fuel system is probably going to be preferred for this application, which would affect the supply chain.

Of course, if sealed fuel supplies for navy vessels are already normal, that's probably not a big deal, anyway.

[fnord]

Does it absolutely have to be a water cooled (whether light or heavy) CANDU-style reactor?

[fnord]

Whoops, hit return too quickly. Are other fuel and coolant forms and choices ok to consider?

[Darth Wong]

Does it absolutely have to be a water cooled (whether light or heavy) CANDU-style reactor?

You need the heavy water moderator to get the heavy neutron moderation that you need in order to sustain a reaction with non-enriched uranium fuel.

[Ted C]

Whoops, hit return too quickly. Are other fuel and coolant forms and choices ok to consider?

I suppose so. I'm not sure what alternatives would power a cargo ship at an acceptable speed, though.

Presumably the power plant would need to have the capacity of a naval version, since a cargo ship wouldn't have the same high-end performance requirements, nor all the high-powered communications and radar equipment to run.

Someone with a navy background have an idea what kind of wattage this would need? On-board maintenance requirements?

[Sea Skimmer]

A big medium speed container ship needs in the range of 100,000 shaft horsepower and maybe 4 megawatts of electrical capacity, so your looking at needing a reactor with something like 240-280 megawatt thermal output to power the thing. You'll also still need diesels or gas turbines for auxiliary and emergency power. Even with high oil prices its going to be hard to make economical nuclear merchant ships. After all a giant diesel engine or marine gas turbine can burn just about anything including some types of raw crude so they aren’t as handicapped as gasoline car motors which can only be converted to run on a few types of alternative fuels.

[Ted C]

Hmm... if Wikipedia is to be believed, civilian nuclear ships were tried from the 1960's to 1990's, with little commercial success.

Can't help wondering if that would change with current oil prices, though.

[Ted C]

Related article on the N/S Savannah

Apparently, this ship saved 29 million gallons of fuel oil over 5 years in the 60's and 70's.

By my quick table-napkin estimate, that's over $15 million a year at current crude oil prices (I don't know the difference in cost between crude and fuel oil).