LACEY TOWNSHIP Measurements of a radiation barrier at the Oyster Creek nuclear power plant show the structure will be able to last another two years.

But federal regulators aren't saying whether the 100-foot-tall drywell liner will be safe for another 20 years if the operating license is extended for the oldest operating commercial nuclear plant in the U.S.

The U.S. Nuclear Regulatory Commission issued the preliminary assessment of the barrier. Officials for AmerGen Energy Co., which operates the plant and has proposed a monitoring program to find degradation, agree with the findings.

AmerGen is a subsidiary of Chicago-based Exelon Corp.

Measurements were taken during the plant's scheduled outage, which takes place approximately every 24 months for maintenance and refueling purposes.

Exterior sections of the drywell became rusted and thinner in the mid-1980s, when GPU Nuclear owned the facility, because of a water leak. Steps were later taken to stop the corrosion, but the liner remains one of the biggest questions in renewing the plant's license.

"We are far from done in regard to the drywell liner in regard to the extension period," NRC spokesman Neil Sheehan told The Press of Atlantic City for Saturday newspapers. "This is more immediate in looking for operational issues. We didn't find any."

Opponents of the plant's license renewal say the recent assessment isn't enough to assure safety at Oyster Creek.

"Even if there is not evidence of deterioration, it doesn't mean that everything is fine," Richard Webster, an attorney assisting renewal opponents, told The Asbury Park Press.

Oyster Creek's scheduled outage started Oct. 16. An Exelon spokeswoman did not immediately return a call Saturday on whether the plant had reopened.