READSBORO, Vt. (AP) – Officials have discovered that a 250-foot retaining wall was built with concrete blocks from the now-closed Yankee Rowe nuclear power plant and they are slightly radioactive.

Tests of the retaining wall behind the Readsboro General Store, conducted in February by the Vermont Department of Health, show it is contaminated with the radioactive isotope tritium. State and federal officials say the wall poses no health risk. The tritium has a half-life, or remains radioactive, for 12.3 years.

The retaining wall was built along the West Branch of the Deerfield River behind the store, located on Vermont Route 100.

It was built with 35 large, interlocking concrete blocks taken from the reactor building of the nearby nuclear plant in Rowe, Mass., about three miles from the southern Vermont town of Readsboro in Bennington County. The blocks were once part of a concrete shield around the reactor core.

The blocks were taken from the site – with the company’s permission – by employee Tom Dente of Readsboro, who owns the Readsboro General Store with his wife, Brenda.

“It made a beautiful retaining wall; it was the cheapest thing I could build,” Dente said.

He has worked at Yankee Rowe for most of the past 20 years, the past 13 years for a subcontractor at the plant in the shipping department.

The reactor’s owner, Yankee Atomic Electric Co., tested the blocks in 1999 as part of a decommissioning and demolition process and found them free of radioactivity, said the company and Nuclear Regulatory Commission.

Yankee Atomic spokeswoman Kelley Smith said the retaining wall was the only case of recycled building material from the reactor building at Yankee Rowe being released to the public.

NRC spokesman Neil Sheehan said the commission was investigating whether the handling of the waste material was a violation of federal policies.

Tests in Readsboro in February showed the wall was releasing one millirem of radioactivity a year above normal background levels of radioactivity exposure, which is estimated at 360 millirems a year, Sheehan said.

For comparison, a chest X-ray adds 20 millirems of radioactivity a year to normal background levels; a cross-country airplane ride adds 4 millirem.

“One millirem does not pose a radiological health risk,” said Robert Stirewalt, programs and policy coordinator for the Vermont Department of Health.

Jonathan Bloch, a Putney attorney who represents the Citizen Awareness Network, an anti-nuclear group based near Yankee Rowe, said he was not surprised about the tritium problem.

“We are of course outraged, but not surprised,” he said. “This material was put in a public place and the public was exposed to it. What else is out there? Perhaps something more dangerous? This happened in 1999 and they’re telling us now?”