Thursday, June 21, 2012

San Onofre Debacle

The reactors at San Onofre nuclear power plant have been shut down for almost six months now, and it is uncertain when they will be restarted. Sempra Energy is assuring us that even if we have an unusually hot summer there will be no power shortages, but they are also publishing instructions on how to conserve power, so that’s a bit of a mixed message.

At issue are not the reactors themselves, but the steam generators which transfer heat from the “primary cooling loop” of high pressure, high temperature reactor cooling water to the lower pressure and lower temperature system which drives the steam turbines that generate electricity. These steam generators were replaced very recently, are a redesign over the originals that lasted for more than twenty years, and failed after only a few months in service. There are a lot of questions about the need for and the execution of the redesign, which added only a trifling percent to the capacity. My sense is that a lot of stupidity was involved.

The media covering this story really should send people to cover it who have at least some knowledge of nuclear reactors, because they keep spouting nonsense. They say, for instance, that some of the steam generator tubes are “corroded,” and talk about the piping that “carries radioactive water.”

According to sources at San Onofre, the leaks are not caused by corrosion, but by vibration causing tubes to rub against each other and against supports within the structure. It seems this is the result of ill-advised design changes for the purpose of increasing heat exchange capacity.

And there is no “radioactive water” in a nuclear reactor, because water cannot become radioactive. The primary cooling loop in the pressurized water reactor design type is separate and at higher pressure so that the water may be kept at a higher temperature, which allows the reactor core to operate at a higher efficiency and temperature. If there are any impurities in that water, which is inevitable, those impurities will become radioactive, so that water does contain some small traces of radioactivity, but it is not “radioactive water” as such.

The implication of saying it the way the reporters do is that the water is separate because it is radioactive, but if that were so there would not be the “boiling water reactor” type, in which the water which cools the reactor is turned into steam that drives the turbines. There is nothing inherently dangerous in this design from a radioactivity standpoint, although there are other really severe drawbacks to it which should result in it being banned.

I realize this sounds like nitpicking, but when a reporter starts talking about “radioactive water” it creates a sense of danger which is simply not accurate. My support for the NRC and the nuclear industry has taken a bit of a hit from reading about the stupidity involved in the design changes in these steam generators and the NRC’s approval of those changes, but we don’t need to add to the anti-nuclear hype with inaccurate reporting.

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