Davis-Besse corrosion?

["Christoph Hofmeyr" <chofmeyr@nnr.co.za>]

Sandy, Radsafers,



I get the impression that there is a bit of questionable information

being distributed on the Davis-Besse problem.  Since when is "The acid

... a byproduct of the nuclear fission process inside the reactor"?

Boric acid is a design element of criticality control and part and

parcel of any PWR cooling system. It is also difficult to accept that

the stuff which is mild enough to be used as an eyewash has corroded

through six inches of steel.  At the temperature in question, the boric

acid would tend to dry to a solid in air. The question I heard mooted by

experts is whether a more realistic mechanism would not be that the

steam leak resulted in high pressure steam cutting of the metal.  The

rate of progress of that process could conceivably be quite different

from corrosion.

Chris Hofmeyr

chofmeyr@nnr.co.za





>News item in Sandy's list:



>NRC Blasts Nuclear Plant Vigilance

  

>OAK HARBOR, Ohio (AP) - An acid leak that ate through a steel cap 

over a nuclear plant's reactor vessel should have been spotted as 

long as four years ago, according to a Nuclear Regulatory Commission 

report released Friday. 



Inspectors said there were many opportunities for the operator of the 



Davis-Besse plant to find the problem, which wasn't discovered until 

the plant was shut down in February for refueling. 



``It should have been recognized,'' said NRC spokesman Jan Strasma. 



The NRC said the damage did not pose a safety threat but did order 

operators of all 69 pressurized water reactors in the United States 

to submit information on the structural integrity of their plant's 

reactor head. 



The NRC said it was the most extensive corrosion ever found on top of 



a U.S. nuclear plant reactor. Inspectors spotted a second cavity two 

weeks later. 



Plant employees found leaking boric acid created a 6-inch hole in the 



steel cap near a cracked control rod nozzle. The hole was stopped by 

a steel layer impervious to the acid. 



Significant corrosion began at least four years ago, according to 

preliminary findings of an NRC inspection. Inspectors said it was 

caused by cracked control rod nozzles. 



FirstEnergy Corp., which operates the plant, said it was not 

surprised by the findings and that its own investigators came to the 

same conclusion, said company spokesman Richard Wilkins. 



The plant had visual inspections over the years, but corrosion was 

overlooked because plant staff and management for years did not 

realize the significance of boric acid deposits on top of the vessel 

head, according to FirstEnergy's findings. 



The company said similar corrosion can be found or avoided at similar 



plants if engineers know how to look for it. 



The acid is a byproduct of the nuclear fission process inside the 

reactor. The reactor has 69 control rods. The nozzles are vertical 

tubes that house the rods, which absorb excess neutrons in the 

reactor core. 



The damage to the reactor's steel cap will keep the plant shut down 

until at least June. 



>The plant is along Lake Erie and about 25 miles east of Toledo. 



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