Problems at DavisBesse worse than expected

Davis-Besse reactor nozzle cracks highlight nuclear safety risks as NRC monitors ultrasonic inspections, corrosion, coolant leak pathways, and control rod housings during an extended shutdown and repairs to the stressed alloy reactor lid.

As many as 16 critical parts in the DavisBesse reactor lid are cracked or flawed, and the problem could get worse.

Engineers expect to find additional problems when they conduct a third round of hightech inspections in the coming weeks.

The cracks can lead to radioactive coolant seeping into reactor lid, corroding it and ultimately, as seen in pipe leak concerns at other plants, leaking into the heavywalled building containing the reactor. Thats what happened to DavisBesse in 2002.

The reactor has been shut down since February 28 for what owner FirstEnergy Corp. initially thought would be a fairly routine refueling and safety inspection. There is no restart date at this point because of the timeconsuming repairs that have barely begun and the planned additional inspections.

The Nuclear Regulatory Commission dispatched a special inspection team to DavisBesse weeks ago, echoing the Browns Ferry safety plan framework, to keep an eye on the company inspections as well as its repairs. The team is also looking into how the company has operated the plant since federal authorities allowed it to restart in 2004.

The Union of Concerned Scientists, a watchdog group that does not oppose nuclear energy, has cited watchdog criticism in similar cases and has petitioned the NRC to force FirstEnergy to keep DavisBesse shut down until it can prove the reactor can be safely operated.

The NRC team plans a public meeting with the company to explain its preliminary findings, a commission spokeswoman said. No date has been set.

The troubleprone components in the reactor lid are corrosionproof alloy tubes or cylinders tightly fitted and welded into the heavy steel lid.

Called nozzles because they resemble hose nozzles, the 69 tubes carry critical control rods into and out of the reactor, allowing operators to control the nuclear fission and operate the reactor.

Ultrasonic inspection of the nozzles turned up 12 nozzles with definite cracks and four more with indications of flaws that could become cracks, company spokesman Todd Schneider said.

So far, only three nozzles have been completely repaired, he said, a complicated, robotic procedure that includes nozzle modifications and involves grinding away the cracked nozzles and welds, sealing them into the lid, rewelding the affected area, grinding the new welds and then instrumenttesting to make certain the repairs have been done correctly.

After the ultrasonic scans revealed the 16 nozzles with problems, the company dyetested eleven of the 16, a procedure designed to reveal whether the cracks have allowed reactor coolant to leak into the center of the carbonsteel lid.

Schneider said two of the nozzles had such cracks, but testing revealed that only one showed a definite leak path into the carbon steel.

Engineers also plan to do an electromagnetic test of the welds of about 50 of the remaining nozzles in order to detect weld flaws that could become cracks. Were doing the final test to ensure all the nozzles have structural integrity to allow safe and reliable operations, he said, mindful of how a power line failure can force shutdowns elsewhere.

Undetected nozzle cracks in the past caused unprecedented corrosion that ate a pineapplesized hole through the 61/2inch thick carbon steel, leaving only a 3/8inch stainless steel liner to hold back pressures of more than 1 ton per square inch.

The NRC kept DavisBesse shut down from February 2002 to March 2004 while the company installed another lid and made plantwide repairs and design changes to many of the reactors safety systems, amid oversight that paralleled a water discharge permit lapse review at a TVA reactor.

The company ordered a new reactor head from Europe but has not yet taken delivery on it. FirstEnergy installed a lid purchased from a Michigan utility that never finished building its reactor in the 1970s that lid is identical to the one being replaced.

And that is apparently the problem. The nozzles in the oldbutneverused reactor lid are made of the same nickelsteel alloy that has cracked in numerous reactors across the nation. New reactor lids have nozzles made of a different alloy that is engineered to take the heat stress.

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