By Michael Mariotte

A couple decades ago, the Union of Concerned Scientists (UCS) published what it called the “bathtub curve.” This curve charted the expected and observed performance of nuclear reactors from initial operation until final shutdown. The main finding of note was that when a reactor first comes online, typically there are a large number of problems as the operators learn the technology of that specific reactor, issues resulting from construction deficiencies surface, etc. After a shakedown period of a year or two, reactor operations typically settle down for quite a while, with most reactors operating relatively efficiently. But as time goes on, problems associated with reactor aging–components being exposed to extraordinarily high heat and radiation as well as the simple reality that all things mechanical break down over time–begin to materialize and safety issues begin to mount again.

As we have been seeing at reactors across the nation, especially those in competitive markets, when aging-related safety problems arise, so do economic problems. It takes a lot of money to operate and maintain aging reactors, and some, like Crystal River, San Onofre, Trojan, Maine Yankee and more, have elected to close permanently rather than continue to pour money into them.

The other approach some utilities take to closing uneconomic and unsafe aging reactors is to try to ignore the problems and not make the necessary repairs and modifications.

That second approach–denial–is perhaps best exemplified by the Entergy Corp.’s Palisades reactor in Michigan. Decades ago–really–Palisades was identified by the NRC as being the reactor in the U.S. most vulnerable to Pressurized Thermal Shock (PTS). This nightmare scenario occurs when the reactor pressure vessel has become embrittled by exposure to heat and radiation over many years. When, for whatever reason–a pipe break for example–the reactor loses coolant, it begins to heat up quickly. Left unchecked, it will melt down. But emergency core cooling systems are designed to rush large amounts of cold water into the core and cool it down that way. The problem is that a reactor vessel susceptible to PTS could crack, and all that cooling water would simply drain out and the reactor would melt down. It’s like putting cold water in a hot wine glass.

The Palisades reactor on Lake Michigan. Photo from Wikipedia.

Our friends at Beyond Nuclear, Don’t Waste Michigan, and other groups have been challenging the license renewal of the Palisades reactor for years, based primarily on that NRC finding of its pressure vessel embrittlement. For its part, Entergy says the pressure vessel is just fine. Entergy’s statement is based not on direct observation of Palisdades’ vessel, however, but on a paper analysis of apparently generic pressure vessels. This ignores that how the pressure vessel was constructed and what materials were used in that construction, both of which vary from reactor to reactor, can greatly affect the rate of embrittlement. But in November, the NRC Commissioners overruled the Atomic Safety and Licensing Board established to hear the license renewal challenge and denied the groups a hearing …read more

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