LOWER ALLOWAYS CREEK TWP. -- "Degradation" to about 2 percent of the bolts that secure a metal liner inside the core of the Salem 1 nuclear reactor has caused its operator to extend the plant's current shutdown for additional inspections and repairs, a utility official said.

Salem 1 was taken off line on April 15 for what was expected to be a routine refueling outage. It was during a visual inspection of the reactor core that issues with a number of bolts were discovered.

"Like all inspections, this inspection was conducted to identify potential issues early so they do not impact our ability to operate the plant safely," said Joe Delmar, a spokesman for the plant's operator, PSEG Nuclear on Wednesday. "Safety is our number one priority and this issue has no impact to public health and safety."

This illustration shows the location of the baffle bolts inside a nuclear reactor's core. (Special to the Times/Entergy and PSEG Nuclear)

What's being termed "degradation" was found on 18 of the 832 baffle bolts inside the reactor core, Delmar said. The utility didn't elaborate.

Nuclear Regulatory Commission Spokesman Neil Sheehan said the "degradation" found on the bolts was cracking.

Some of the bolt heads had actually broken off and a number of the bolt heads have been recovered from the reactor core, but an exact number was not available, he said Wednesday.

"There was no imminent danger of these bolts failing," he added.

According to Sheehan the condition was not a risk to plant operations because there were "no instances where the bolts were missing."

NRC resident inspectors along with specialist inspectors and metallurgical experts from the federal agency are monitoring the situation, Sheehan said.

The bolts are called "baffle bolts" because they hold metal plates called baffles in place inside the reactor core. These plates form a liner which keeps the uranium fuel assemblies in place during the reactor's operation and helps direct water flow through the reactor.

There are 28 baffle plates more than 13 feet tall and 1.125 inches thick that form the liner. The 832 stainless steel bolts that hold the plates in place are 2 inches long and the bolt heads measure more than half an inch in diameter, according to Delmar.

Because of issues with baffle bolts at other nuclear plants, PSEG workers focused special attention on them during this reactor inspection, Delmar said.

Ultrasonic testing of baffle bolts at Salem 1 had been scheduled for 2019 as one of the conditions of having its operating license extended for 20 years.

"Based on the visual inspections, we made the decision to conduct ultrasonic testing of the bolts now to determine the full extent of condition and to make appropriate repairs," Delmar said.

Any damaged bolts are expected to be replaced with one made of stronger metals.

Salem 1 is one of three reactors operated by PSEG Nuclear at its Artificial Island generating complex in Lower Alloways Creek Township along the Delaware River. Along with Salem 1 are the Salem 2 and Hope Creek reactors.

Delmar said this is the first time baffle bolt issues have been identified at either Salem 1 or 2, Delmar said. Salem 2 is scheduled for ultrasonic testing of its baffle bolts in 2020, but that could now change.

Refueling outages at nuclear power plants are generally scheduled every 18 months and last about a month.

During that time workers replace about one third of a reactor's fuel. They also perform inspections -- like the one which uncovered the bolt issue -- and maintenance work that generally can't be completed while the plant is in operation.

Delmar said said there was no estimate when Salem 1 inspections and repairs would be complete and it could return to service.

"Salem Unit 1 plays a significant role in providing clean energy," said Delmar. "This issue is fixable and our employees have rallied together to execute repairs. It is their commitment and dedication that will ensure Salem Unit 1's continued safe operation for many years to come."

The bolt issue is not unique to the Salem 1 reactor built by Westinghouse, Sheehan said. At New York's Indian Point 2 reactor, inspections found 227 of its 832 baffle bolts degraded and in need of replacement.

This is not the first time that bolts have been an issue for Island plants. In 2014 the Salem 2 reactor was shut down for three months after sheared-off bolt heads were found in the bottom of key reactor coolant pumps.

Wednesday morning Salem 1's neighboring reactors, Salem 2 and Hope Creek, remain operating at full power.

The bolt issue isn't expected to impact Hope Creek because that reactor is of a different design from Salem 1 and 2, Delmar said.

The three plants comprise the second-largest commercial nuclear generating complex in the U.S.

Last week PSEG Nuclear was granted an Early Site Permit from the Nuclear Regulatory Commission, the federal agency which oversees the operation of the nation's nuclear power plants.

That permit, which is good for 20 years, is the first of many approvals the utility needs to build a new nuclear reactor at its Artificial Island site, but PSEG Nuclear currently has no plans to build a new plant.

Bill Gallo Jr. may be reached at bgallo@njadvancemedia.com. Follow Bill Gallo Jr. on Twitter @bgallojr. Find NJ.com on Facebook.