Ohio Power Reactor Narrowly Avoids Nuclear Core Breech

You’ve heard about Chernobyl. You’ve heard about Three Mile Island. As reported today in Wired News, the Davis-Besse reactor in Oak Harbor, Ohio came very close to joining this rogue’s gallery when it was literally discovered to be a reactor with a hole in its head.

What happened? The Davis-Besse reactor core is cooled with water that has concentrated boric acid powder mixed in to help absorb neutrons produced by the reactor. This reactor coolant is presurized to 2500 pounds per square inch, allowing it to stay liquid at the operating temperature of 500-600 degrees. If this pressurization is lost, the water-boric acid mixture would instantly flash into radioactive steam. This would be very, very bad. Keeping the core pressurized is the job of the containment vessel which has walls 6 inches thick constructed of strong carbon steel. Boric acid easily eats through carbon steel, tho, so the containment vessel is lined with less than a half-inch of weaker stainless steel. This stainless steel liner is not a pressure barrier; instead, it is impervious to the boric acid and is only intended to protect the carbon steel walls from boric acid.

Too bad this plan got implemented by Homer Simpson. As determined by subsequent investigation, one of the water lines developed a leak in 1995 that went unnoticed for years. An incredible 900 pounds of dried boric acid residue subsequently collected on the top of the carbon steel vessel dome, or “head”, that was not noticed during visual inspections in 1998 and 2000. The resulting corrosion continuously contaminated the cooling water to a point where filters were being changed daily instead of quarterly by 1999; this anomaly became accepted as a routine instead of raising an alarm. These years of boric acid exposure resulted in a 6-by-5 inch hole that penetrated the full six inches of the containment vessel, dissolving 70 pounds of carbon steel and reaching the 3/8 inch thick stainless steel liner. Unbelievably, this liner did a job it was never intended to do and maintained the 2500 PSI pressurization required to prevent a core breech and subsequent nuclear disaster. The liner was bowed outward in an eighth-inch high blister when it was discovered in March 2002, the only thing separating the Davis-Besse radioactive core from the Ohio countryside.

Unfortunately this story is far from over. Ongoing inspections of other US power reactors have uncovered similar problems, tho not as severe, at two other reactors as well.

3 thoughts on “Ohio Power Reactor Narrowly Avoids Nuclear Core Breech”

  1. The Davis-Besse story, while grounded in truth, is so distorted as to render it meaningless. Facts, apparently, don’t matter so apparently the author decides to make them up.

    The Davis-Besse event _is_ an important one for the nuclear industry. It provides many lessons-learned from which the industry can improve. Just like TMI, and countless other minor events, the U.S. nuclear industry will learn and improve.

    Finally, the fact is not, “The liner … the only thing separating the Davis-Besse radioactive core from the Ohio countryside.” There were two additional, significant barriers preventing release of fission products to the atmosphere: fuel cladding and the containment itself. Actual facts are publicly posted.

  2. …maybe that line about “radioactive core and Ohio countryside” had a little bit too much poetic license, but boy oh boy, it’s hard to overstate what a fiasco Davis-Besse was / is.

    I disagree that the fuel cladding EVER represents radioactive containment – the cooling water is already radioactive from neutron absorption producing dissolved tritium gas, and that cladding is the first thing to go in a LOCA (loss of cooling accident). I agree that the concrete containment building stood between the radioactive core and the Ohio countryside, but I just don’t have a lot of faith in it after hearing what else happened there. Best case if the stainless steel liner had blown, the inside of the containment building would have been contaminated big time to a point where it would have been sealed off and we’d have another unreachable, untreatable messed up core like Three Mile Island. Let’s not even think about the worst case, which is what my aerospace safety training tells me to do.

    Don’t get me wrong, I’m actually pro-nuclear and have even worked a number of years in Oak Ridge, but I have a healthy dose of scepticism about the US power reactor program. There are LOTS of ways to design nuclear reactors and pressurized light water reactors (PLWRs) are just asking for trouble in my opinion. Historically, they were developed for the US Navy sub program, where they have an excellent record. In the 50s and 60s the nuclear companies tried to create a little bubble of ocean in the middle of dry land to house a scaled up version of a sub reactor big enough to power a city instead of push a sub so they could piggyback (i.e. save / make money) on their previous efforts. I personally think this was the wrong approach, but that’s water under the bridge now. The key to safe nuclear reactors are to build designs where the cooling depends on MASS, not pressurized water (or God forbid, liquid sodium), so that if a pump/fan/heat circulator goes out, the thing gets hot, maybe even really hot, but it’s DESIGNED to take that worse case until repairs are made on modular equipment that you can get at. Such reactors would be BIG and they would be more expensive than the ones we’ve got now – but they would be SAFE. Or at least much safer than current PLWRs.

    By the way, I clicked on your links but it didn’t seem to work – are there facts in the UCS and NRC links I provided in the story that you dispute? Friendly disagreement intended here, don’t mean to antagonize…

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