The federal agency responsible for overseeing the nuclear power industry has continually rewritten rules to allow aging plants to continue running even as they fall into disrepair, an investigation by the Associated Press found.

No new nuclear reactors have been built in the U.S. since the 1970's, placing the burden for generating nuclear energy on a network of aging facilities. According to the AP report, the nuclear industry enjoys a close relationship with regulators, who frequently adapt rules to retroactively cover up violations by determing that the existing rules are overly conservative.

The process of manipulating data in order to make plants compliant, known as sharpening the pencil or pencil engineering, has become prevalent. As a result, safety lapses that include cracked nozzles, malfunctioning cooling components and leaky valves have proliferated as plants deteriorate over time.

It's a philosophical position that [federal regulators] take that's driven by the industry and by the economics: What do we need to do to let those plants continue to operate? said Paul Blanch, an engineer who worked in the nuclear industry.

They somehow sharpen their pencil to either modify their interpretation of the regulations, or they modify their assumptions in the risk assessment.

President Obama was an early supporter of expanding nuclear energy by building new plants in the U.S.