San Onofre shutdown will mean tight electricity supplies

[PamW]

99. Simplistic Analysis

Some here are doing a real simplistic analysis of how the seismic safety of a nuclear power plant is analyzed.

It's akin to saying that every car has a crash rating in miles per hour; say 35 mph. All crashes below 35 mph are survivable, and all crashes above 35 mph will be fatal. It's just not that simple. You could hit a large flat concrete wall at 37 mph, and the mass of the engine will help protect the passengers, and they can survive. On the other, hand, one could have a 33 mph crash with a narrow metal pole rooted in concrete, which crashes through the frontal structure, misses the engine, travels the length of the engine compartment, rips through the firewall, and kills the driver. Car crashes are much too varied to be characterized by a single number.

So too with nuclear power plants. That's not how their safety is analyzed. For all the faults in the area, one takes all the types of earthquake / tsunami effects that could be generated by any of the faults and analyze their effect on the plant. This requires massive structural mechanical modeling by big computer programs. One then determines what parts of the plant are damaged. Then one analyzes whether the damaged parts will create a safety problem. Not all components of the plants are equal critical to safety. ( In the car accident, an oblique collision may take out the front bumper and demolish the left front quarter panel; but that structure isn't critical to protecting the driver. )

So one can't say that a plant can only withstand a 7.8 quake, and some nearby fault can generate an larger quake, and conclude the plant is unsafe. It's more complex than that.

Additionally, many anti-nukes don't realize that the Richter scale is common logarithmic. I've heard some say, "The plant was rated at 10 on the Richter, and the quake was 9; so they only had an 11% margin. They don't realize that a magnitude 10 is 10 TIMES as intense as a magnitude 9.

A magnitude 10 is 10X a magnitude 9, which is 10X a magnitude 8. So a magnitude 10 is 100X a magnitude 8. You take the difference between the two magnitudes you want to compare, eg. 10 - 8 = 2; and then you take the number 10 to that power. Eg. 10 to the power of 2 equals 100.

One can only speak in generalities when comparing different geographic regions. That's why I DID NOT say that there were "no subduction faults of California". There are small subduction faults. But just because a fault is a subduction fault doesn't mean it's automatically fatal to the power plant. Again, the subduction fault can be small and far away, and the tsunami it generates would have a small impact at the plant.

The major fault of concern off California is the San Andreas, a strike-slip fault; the motion of which will generally be more horizontal than vertical. In general, the California faults are not as tsunami-prone as those off Japan.

Even so, a tsunami is not automatically deadly to a nuclear power plant. A tsunami was deadly to Fukushima because of their poor design practices. In particular, the Fukushima plants put their diesel fuel tanks above ground at dockside for ease of filling; but the tsunami wiped those fuel tanks away. Additionally, the diesel-generators themselves were in a non-watertight basement, along with their switchgear, and the momentary flooding of the tsunami rendered the backup generators and switchgear inoperable.

In the USA, the NRC requires that the fuel tanks be buried or otherwise protected. Likewise for the diesel generators; which will be in watertight vaults or otherwise protected. When I was a graduate student at MIT, I toured Boston Edison's Pilgrim Nuclear power plant, a plant not too different in vintage from Fukushima. We were in the upper part of the reactor building when we came across these two large diesel engines that our guide pointed out to us as part of the backup electrical system. After looking over the engines, we got in a nearby elevator and rode about 2 stories up, and we were at the top floor of the reactor building.

So although many make a big deal out of the fact that Pilgrim and Fukushima are close in vintage, and general design; the details matter. Fukushima had diesel generators in a non-watertight basement which was vulnerable to tsunami, and Boston Edison's Pilgrim Nuclear plant has those generators high up in the reactor building so as to meet the NRC's mandate that those generators are protected.

In the recent past, we had rivers overflow their banks and inundate nuclear power plants like the Fort Calhoun plant with water. The area around the plant was flooded when their sandbag walls gave way. Having the area around the plant flooded with water is actually worse than getting momentarily flooded by a transient tsunami. However, Fort Calhoun survived with no difficulty since the diesel generators are protected, as mandated by NRC regulations.

One has to look at the DETAILS to determine whether a plant is safe, ( and that is done ); instead of comparing single numbers or making a big issue as to whether a given fault is a subduction fault or not.

The seismic safety analysis is much more involved and extensive than any of the "strawman" arguments the anti-nukes have presented here.

PamW