RALEIGH, N.C. (AP) -- A nuclear plant near North Carolina's capital city was shut down after operators reviewing ultrasonic tests from last year found the results showed tiny marks of corrosion and cracking that need repair, the Nuclear Regulatory Commission said.
Operators at the Shearon Harris plant on Wednesday found a quarter-inch flaw in the covering of the reactor vessel, which contains superheated steam produced by the nuclear reaction's energy.
The crack did not penetrate the vessel head and there is no evidence of radiation leakage, an NRC incident report said. The discovery did not affect the health and safety of employees or the public at the New Hill plant, federal regulators said.
NRC inspectors will want to ask plant owner Duke Energy Corp. — which acquired the 26-year-old plant through its buyout last year of Progress Energy — why the testing performed during a spring refueling outage last year didn't find the problem, agency spokesman Roger Hannah said Thursday.
"I think that's a question, from our perspective, that we'd like to have answered," Hannah said. "We'll follow up on that to see if it was something that should have been seen."
Spokesmen for Charlotte-based Duke Energy said it would evaluate why the problem was missed last year. Data from last year's test were being reviewed ahead of an upcoming planned refueling outage.
"During refueling outages, we collect and analyze a lot of plant data," spokeswoman Rita Sipe said in an email. "The reactor is shut down and our repair plans are in progress."
She said Duke has reserves that can meet customers' needs during the shutdown.
The company expects to have the unit back online within a matter of weeks, Duke Energy said Thursday in a filing with the U.S. Securities and Exchange Commission.
The "minor repairs in a nozzle that penetrates the top of the reactor vessel" has been performed successfully at other nuclear reactors around the world, the company said.
The reactor vessel head is commonly checked because the metal is "subject to very high pressure and very high temperatures over a long period of time," Hannah said.
The shutdown comes days before the Harris plant's annual assessment meeting, at which NRC staffers discuss plant operations with the public. The meeting is Monday in nearby Holly Springs.
Progress Energy was cited last year for two safety violations considered to be of low to moderate significance, which Hannah said have since been corrected. Regulators found problems with ventilation systems that would be needed if there were a nuclear emergency.
Since the two North Carolina utilities merged to make Duke Energy the country's largest electric company, the Charlotte-based company has cut back on plans for Progress Energy nuclear plants.
Duke said earlier this month that it will not build two new reactors at Shearon Harris, reversing plans put in place by Progress Energy executives.
In February, Duke Energy said it will permanently close the Crystal River nuclear plant in Florida after botched repairs while it was operated by Progress Energy Florida. Estimates for repairing the nuclear plant shut down since 2009 were between $1.3 billion and $3.4 billion.
Duke Energy Chairman and Chief Executive Jim Rogers told North Carolina regulators last year that former Progress Energy CEO Bill Johnson was dumped within hours of becoming CEO of the merged company in part because of dissatisfaction over his handling of Crystal River's problems. Johnson is now CEO of the Tennessee Valley Authority.
Emery Dalesio can be reached at https://twitter.com/emerydalesio