NRC urges US nuclear plants be checked for leaks
Date: 12-Aug-02
Country: USA
Author: Tom Doggett
The NRC said it issued the bulletin in response to cracked and leaking nozzles found at several reactors and significant corrosion discovered in the reactor vessel head at the Davis-Besse nuclear power plant in Oak Harbor, Ohio.
Instead of relying only on visual inspections to find any problems, the agency said reactor operators should also use ultrasound, electric currents and liquid dyes to check for cracking and corrosion in a reactor's metal head.
"Inspection programs that primarily rely on visual examinations may need to be supplemented," the NRC said in a statement.
The NRC asked plant operators to file their future inspection plans with the agency within 30 days.
During a scheduled refueling outage at the Davis-Besse plant last February, the plant's engineers found boric acid had leaked at the base of several of the control rod nozzles that penetrate the reactor. The plant has been shut down since then.
Boric acid is used in the primary coolant bath surrounding uranium rods in the reactor core.
At one of the nozzles, the acid had eaten all the way through the vessel head, which was 6 inches (15-cm) thick. The vessel head is a massive piece of carbon steel 17 feet (5.2 meters) wide that is bolted down on top of the reactor to prevent any radioactive material from escaping.
The corrosion was so severe that a stainless steel liner 3/8-inch (1 cm) thick inside the reactor was the only barrier left between the reactor core, which operates under enormous pressure, and the metal shroud surrounding the reactor vessel.
The 25-year-old Davis-Besse plant is owned by FirstEnergy Corp.
Of the 103 nuclear reactors operating in 34 states, 69 facilities are of the pressurized-water type.
With a pressurized reactor, water is kept in the reactor under high pressure so it does not boil. The heated water flows from the reactor through pipes to a nearby steam generator. The pipes are surrounded by a second water supply that boils and produces steam to spin the turbine generator and produce electricity.
The water then returns to the reactor, where it is reheated and sent back to the steam generator in a continuos loop.
Agency staff will meet at NRC headquarters in Rockville, Maryland on Aug. 23 with the Nuclear Energy Institute and power plant operators to discuss the new inspection guidelines. The meeting is open to the public.
