Federal regulators are halting a five-year study of the risk of cancer in communities around six U.S. nuclear plants and a nuclear fuel site.

The Nuclear Regulatory Commission said Tuesday remaining work on a pilot study would take too long, at more than three years, and cost too much, at $8 million. It's already spent $1.5 million. Completing the pilot study and subsequent nationwide reviews could take eight to 10 years.

The commission said radiation releases, when they occur, are too small to cause observable increases in cancer risk.

Anti-nuclear power group Beyond Nuclear said halting the study is outrageous and that funding it is a legitimate cost.

Nuclear sites to be studied included active and decommissioned plants in California, Connecticut, Illinois, Michigan and New Jersey and a nuclear fuel fabrication plant in Tennessee.