A large crack was discovered early in October 2009 in the outer containment wall of the Crystal River Nuclear Power Station during a scheduled refueling and maintenance outage. It is the latest in a series of alarming discoveries signaling the hidden deterioration in the “defense in depth” design concept of passive safety systems for US reactor containment structures which is very difficult, if not impossible, to catch by visual inspections.
A special inspection team from the United States Nuclear Regulatory Commission (NRC) was dispatched to the Crystal River on Florida’s west coast to look deeper into extent and root cause of the ½ inch (1.3 centimeters) wide horizontal crack that was discovered in the reactor’s 42-inch thick (106.7 centimeters) concrete containment wall. An official from the NRC estimated the crack to be at least 25-feet (7.62 meters) long. NRC’s Chairman Gregory Jaczko and Regional Director Luis Reyes made a tour of the cracked reactor on October 9 for a firsthand look.
Crystal River’s owner and operator, Progress Energy, reported the discovery to NRC on October 7, 2009 after maintenance workers began cutting a large hole through the concrete containment to provide passage for the removal and replacement of reactor’s worn steam generators. After cutting through the first 9-inches (22.9 centimeters) of the wall from the outside surface, workers found what was described as a “separation in the concrete” which is crisscrossed with steel reinforcing bars in the safety-related structure. The reinforced concrete containment shell is credited for safety by resisting and “containing” pressure-induced forces.
The Crystal River crack follows the April 2009 discovery of a hole that had corroded all the way through the steel inner liner of the containment system for the Westinghouse Pressurized Water Reactor at Beaver Valley station in Pennsylvania. The source of corrosion was determined to be a small piece of wet wood left behind from the original concrete pour decades earlier that bridged the inner wall of the concrete dome and the outer wall of the inner steel liner. The outer corrosion and through-wall hole was not discovered until a visual inspection found a blister in the paint on the inside of the reactor containment wall. When the paint and rust was removed, the inside wall of the concreted containment dome was visible through the hole. Similarly, NRC reports the same outside-to-inside corrosion-induced holes through inner steel liners for containments at the North Anna and Cook PWRs. The steel liner is credited for being leak tight to prevent the escape of radiation in the event of an accident.
In both cases, the deterioration in safety margins for the containment system components was not readily visible until the structure was compromised. The potential for the hidden convergence of corroded containment liners and cracks in containment walls is hard to ignore where it can be potentially revealed in the entire containment system failure during a nuclear accident.
The Crystal River reactor is a Babcock & Wilcox Pressurized Water Reactor similar in design to the notorious Three Mile Island Unit 2 that melted down in 1979 and the Davis-Besse reactor near Toledo, Ohio, which was discovered to be potentially weeks away from a core melt accident in 2002 due to leaking borated coolant corrosion that had eaten a deep cavity into the carbon steel head of the reactor pressure vessel. (see Nuclear Monitor 565, 22 March 2002: "Millimeters from disaster")
A NRC official was quoted to say “The discovery of this crack in the concrete does not appear to represent a major reduction in safety, and there are no immediate concerns because the plant is shut down.” The emphasis should be placed on the fact that the reactor is shut down. Progress Energy officials are now seeking to bring the reactor back on line by December 2009 but conceded that the outage might be extended depending on the findings and conclusions of the NRC special inspection. At present, neither the company nor the NRC were able to determine the cause of the crack or if it was present at the completion of the reactor construction 32 years ago. NRC did not know if the company would be required to fix the crack or allowed to bring the reactor back on line with the cracked containment. The NRC did acknowledge that it was looking into Crystal River’s crack for generic implications for reactors of similar design.
Crystal River’s has made application to NRC to extend its 40-year operating license by an additional 20 years.
Chief among public safety concerns voiced by nuclear power critics is whether or not more cracks are present and perhaps linked throughout containment and how containment integrity can be assured. Given that the crack was only discovered by workers destroying the containment wall to make a hole to replace the reactor’s steam generators, the watchdog community is eager to know how NRC and the industry plan to rule out further cracking and justify continued operations with uncertainty about any additional cracking in Crystal River and other PWR containments. The question arises whether or not an adequate analysis is even possible. One NRC containment specialist is quoted in an agency 2008 transcript to say, “It’s sort of difficult for us to do an independent analysis. It takes time. We’re not really set up to do it. The other thing you have to realize, too, for containment, which isn’t as true in the reactor systems area, is that we don’t have the capability.” In any case, the nuclear industry is likely to resist large scale non-destructive testing of its concrete containments to detect the presence of more cracking just as they have already resisted full scale ultrasonic testing measurements to determine remaining wall thickness on corroded steel liners in containments.
Beyond Nuclear, the public interest and safe energy group, has filed a request under the Freedom of Information Act for the release of documents and photographs regarding the Crystal River containment crack.
Source and contact: Paul Gunter, Director Reactor Oversight Project, Beyond Nuclear. 6930 Carroll Avenue Suite 400, Takoma Park, MD 20912.
Tel: +1 301 270 2209