Wednesday, November 18, 2009

Floating nuclear plants for cheap power and desalination

Russia has started work on the first of its floating nuclear power plants. It's a pretty simple concept; they've been using nuclear-powered icebreakers since the 1970s, and this is essentially just a nuclear-powered barge that can be hooked up to a city's power grid. It uses a newer version of the same reactors they've been using on ships for a while.

The economics of floating nuke plants are intriguing. They can be manufactured at a central location, sent out to where they're needed, and then sent back for maintenance and refueling periodically. This lets you centralize the manufacturing, scheduled maintenance, and waste management, which has traditionally happened at the site of each power plant.

Perhaps even more interesting is the cooling. It uses seawater as coolant, and the waste heat can be used to desalinate the water, making it drinkable. One of the 70 MWe Russian power boats could produce more than a million gallons of drinkable water every day, if it was equipped with desalination equipment.

Now consider the number of countries that are short on fresh water but located next to the sea. Most of the Middle East has this problem; they're more likely to fight over water than over oil. Turkey, southern Australia, and west Africa are all running dangerously low on fresh waster, despite sitting next to vast amounts of salt water. And all these regions need more electricity, preferably in small increments. Floating nuclear plants are a perfect fit.

One disadvantage here is energy security. It would put these countries' power and water supplies at the mercy of whoever owns the power boats. (Most of Europe is already dependent on Russia for their natural gas, and they're cheerfully increasing this reliance.) The obvious solution here is competition: another country, like the US or China or Japan, needs to get into the floating nuke plant market, too. All three countries are well-equipped for this. The US has a number of advanced reactor designs which would be ideal, as well as naval reactors which could be adapted to civilian power. China has a well-developed pebble-bed reactor program. Japan has a strong nuclear industry and the US would probably jump at the chance to team up with Japan to put some of those advanced reactor designs into production.

So, brief summary: floating nuclear plants can give economical power and desalination, and there will be a huge demand for them in the coming years, but we need competition.

Friday, November 6, 2009

Nuclear reactors for space: safety issues

Propulsion and science in space requires a lot of energy, but we pay dearly for every kilogram that we launch. Nuclear reactors are an obvious power source, since they combine large power outputs and a long supply of fuel into a very small package. NASA is designing a 40 kW reactor to power a moon base, most of the high-efficiency ion drives require more electricity than they're going to get from solar panels, and both the US and the Soviet Union launched several nuclear-powered satellites back during the Cold War. The technology isn't too difficult, and it works like nothing else.

But how do we keep them safe? What if a rocket explodes while carrying a nuclear reactor up into space? This is the most common objection: nobody wants to have chunks of highly radioactive debris raining down on them. Nobody. So let's look at the sequence of events when we're launching, say, a nuclear-powered ion-propelled probe to Jupiter's moons.

  1. The reactor is loaded onto a conventional chemical rocket. It hasn't been turned on yet, so it's not radioactive. The radioactivity in nuclear reactors doesn't come from the uranium fuel; it comes from the reaction and from the radioactive isotopes that the reaction produces. At this point, you can handle the fuel with your bare hands.
  2. The rocket is launched into orbit. The reactor still hasn't been turned on, so it's still not radioactive. If the rocket explodes at this point, there will not be a release of radioactive material because we don't have any yet.
  3. The rocket reaches orbit and stops firing.
  4. The reactor turns on. Now it's radioactive. Good thing it can't just fall out of orbit!
  5. The ion drive has power now, so it turns on and starts thrusting. It leaves Earth's orbit and heads for Jupiter.
If the rocket blows up, the reactor will just be an especially heavy chunk of metal.

The only serious safety issue is if we use reactors to fuel satellites. Satellites may decay in their orbit and eventually fall to Earth. The Soviet Union did this; one of their reactors was even so rude as to break up in re-entry over Canada. I'm not saying that having nuclear-powered satellites is inherently unsafe; just that it is not trivially safe. Using nuclear reactors to power ion drives and moon bases, on the other hand, is trivially safe: there is literally no way for them to rain radioactive debris on us without violating basic physics.