Saturday, April 14, 2012

Getting Greedy,and Stupid

I have not joined in on the hyperventilating about the San Onofre nuclear power station because the only known fact is that it is shut down due to unexplained wear in the tubing of its primary heat exchanger. That is the device similar to a giant radiator that transfers heat from the water cooling the reactor to the water which becomes steam to drive the generators.

The thing that’s interesting about the wear, and which struck me when the problem was first reported, is that there are no moving parts in this device. It’s pretty much like your car’s radiator, just tubes with water on both sides, so wear should not be an issue. The pressurized water inside the tubes is very hot and at very high pressure, so it could be a bit “erosive,” but that did not seem to be the issue.

My thought was that there might be a problem with the metal from which the tubes were made; that it might be the wrong alloy, not be tempered properly, or have inclusions of some sort. As time went on with no report those issues seemed unlikely, because they are pretty easy to evaluate.

Now we find out that the new heat exchangers were redesigned to increase the number of tubes from 9,350 to 9,727 and that doing so “required the removal of supporting cylinder designed to prevent vibrations.” The report also says that the wear is not caused by water flowing through the tubes, as earlier reports have implied, but is caused by the tubes rubbing against each other and against support structures.

It seems pretty clear that these heat exchangers will need to be replaced, and that they will need to be redesigned; probably returned back to the original design, which worked very efficiently and lasted for thirty years.

I have been supportive of the nuclear power industry and the NRC, at least as it relates to the use of pressurized water reactors. I opposed the boiling water reactor design, the type that failed so disastrously in Japan, when it was first proposed and I think the ones still in use should be shut down. I have believed, however, that the PWR is an acceptably safe design and that the NRC does a reasonable job of maintaining safe operating standards. Given this report, though, I may have to rethink that.

The engineers made a redesign on this heat exchanger, and the NRC approved that redesign, which removed a “supporting cylinder designed to prevent vibrations” in order to add tubes which added a mere 4% to it’s heat transfer capability. To risk increased vibration, a risk which obviously was a very real one, for such a small return strikes me as sheer stupidity. If this is the caliber of our new generation of nuclear engineers, and if the NRC is either of equally low caliber or is so inattentive that they failed to notice, then I may have to join the ranks of those who oppose nuclear energy in its entirety.


bruce said...

So where is the "greedy" part from your headline? Perhaps just stupid is enough?

Jayhawk said...

Actually, greedy in two respects. Greedy for more power from the same-sized heat exchanger, for one, and monetary greed because more power translates to more electricity sold on a per kwh basis.

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