Thoughts on nuclear power

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Recent events in Japan have caused me to think again about the issue of nuclear power generation, having consigned it to the too-hard basket some time ago. Besides, it’s been off the agenda here in Australia for a while now. It’s one of those topics on which I’ve found it difficult to have a clear view either way.

On one hand, it’s an abundant source of clean energy as far a greenhouse issues go, as well as having some romance attached to it as a result of the early promise reflected in older sci-fi literature. Even sewing machines were to run on nuclear energy, and of course it would be indispensable for our jet packs.

On the other hand, the potential harm if poorly managed (or mis-used) is enormous. I liken it to flying – I’d like to learn to fly a plane, but the price of a simple mistake can be very high, and I’m not sure I trust myself enough.

While I have faith in the engineering profession, it comes down to a risk analysis – is the generous amount of power available worth the potential harm, not only to this generation but to hundreds of generations to come? Mankind has proceeded with nuclear power in the face of these risks, with only the odd mishap along the way, such as Chernobyl and 3-mile Island. The indications have been, until now, that we had engineered sufficient protection into nuclear power plants to account for most disaster scenarios.

But this latest round of issues in Japan reminds us of the fine line between success and failure; between clean, cheap power, and disaster. Japan has received a double-whammy, earthquake + tsunami, which has been sufficient to completely destabilise a number of power plants in the affected region.

In case you’re interested in the technical details, here’s a potted summary of the story so far:

First some basics:

1. Nuclear power plants operate by heating water, to create steam, to spin turbines, to create electricity.

2. The water is heated by splitting uranium atoms (fission), releasing large amounts of energy.

3. Uranium atoms can be split by assembling a sufficient quantity (or critical mass) of Uranium 235 in one place. Once critical mass is reached, the splitting of atoms by high speed neutrons is self-sustaining, and indeed can run away if not controlled. The runaway version is called a bomb. The controlled version is called a power station.

4. The uranium fuel is manufactured in rods about 4 metres long, and between them are inserted rods of the element Boron which are good at absorbing neutrons and hence controlling the amount of atom splitting. These are all mounted in a vessel, known as the reactor.

5. Also required to prevent runaway reactions is copious water cooling, of both the reactor and of big pools in which spent fuel rods are stored.  Why is is necessary to store spent fuel in water? Because the fuel rods are only 3-4% Uranium 235 which is fissionable. The balance is Uranium 238, which is not fissionable, but slowly decays releasing neutrons and changing into other elements such as Plutonium. The decay produces significant amounts of heat which must also be controlled. Electricity is required to keep pumps running to keep both the reactor and spent fuel cooled.

OK, now you know the basics, here’s what’s happened.

1. When the earthquake hit, the power grid in the area was disrupted, resulting in the power station losing its power (which sounds strange, but it gets its power from the grid, and not straight out of its turbines, since the power needs to go through transformers – that’s another story).

2. Fortunately, engineers foresaw this eventuality, and built in dedicated diesel-powered generators to run the pumps, which then kicked in and allow the cooling water to continue pumping.

3. Now for the bad news. Some time later, the tsunami hit, flooding the region with sea water. The sea water engulfed all of the generation equipment, distribution cables and instrumentation, and basically killed it. Now we have no power to cool the fuel, and things start to heat up, literally. Because the spent fuel rods are just in a big pool, the water slowly evaporates as it heats, exposing the spent fuel, allowing radiation to propagate further. It turns out that as well as cooling the fuel, the water is also a great insulator against radiation.

4. Subsequently we see frantic efforts to re-establish cooling without being able to get too close, by spraying from riot hoses, and water bombing with fire-fighting aircraft. Finally, they try hooking up a huge extension lead to get power there.

5.  More bad news. These efforts are hampered by a series of explosions – but what caused them? It seems that the fuel rods are encased in Zirconium, which in addition to making great fake diamonds, is also a great material to provide robustness to the the fuel rods. However, this material only behaves this way up to 500-600 degrees. By now, temperatures have reached around 1100 degrees. Guess what happens at this temperature? Zirconium reacts with water, producing Zirconium dioxide, and, hydrogen, which explodes from the heat when it is vented into the atmosphere, producing more damage to the containment vessels, and making it harder to get near.

6. As at today, the huge extension lead has worked, and sea water is being pumped in, but not before significant levels of radiation have escaped prompting warnings to evacuate for tens of kilometers around the plants. In a further development, this report discloses that seawater is now contaminated with a range of radioactive isotopes of Iodine and Caesium, which is nasty stuff.

Are we having fun yet?

Admittedly, the technology in this plant is 60-70’s  vintage. But it illustrates the perils of taking on risks. Just like climate change, many argue for ignoring the risk because of financial factors, but, the key question is, are we prepared to pay the price if the risk is realised?

Don’t get me wrong. I believe that science and engineering can build nuclear power plants that are more robust than the above story would indicate.  However, the economic drivers involved mean that compromises have to happen – there is a trade-off in cost for some level of risk, in order to make it economic, so that corporations can make money. It is the trade-offs which expose the risk, and it is those same trade-offs which  have me now leaning toward the side of ‘no more nuclear’.

My jet pack will just have to wait.

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