The Nuclear Regulatory Commission will face daunting challenges in updating current assessments of cancer risks for individuals living near the country's 104 operating reactors, a National Academy of Sciences panel said in a report released today.

The National Research Council report found that NRC will face data limitations in conducting a new study to determine if there is a link between living near nuclear reactors or other nuclear facilities and higher risk of cancer.

"Finding scientific evidence of whether people who live near nuclear facilities have a greater risk of developing cancer than those who live farther away is a challenge," John Burris, chairman of the committee that wrote the report, said in a statement. "There are issues of whether scientists can get the information needed to carry out the study."

Burris, who is also president of the Burroughs Wellcome Fund, said scientists may not be able to get the information they need to carry out the study because some state cancer registries have only recently attained quality data.

"Information about cancer risks might also be insufficient to estimate the amount of radioactive material released from nuclear facilities, especially during early years of operations," he said. "This makes it much more difficult to determine risks from decades ago when radiation releases from nuclear facilities were larger."

Limited information on the movement of populations and other external factors may also complicate findings, the council said. Such factors would include exposure to cigarette smoke, access to health care, contact with toxic chemicals and exposure to other sources of radiation such as from medical procedures like CT scans, they said.

"The impact of these other possibly immeasurable factors on cancer incidence and mortality could overwhelm the expected effect from the releases of radiation from nuclear facilities," the council said.

Nuclear facilities licensed by NRC sometimes release small amounts of radioactivity during normal operations, and NRC ensures operators monitor and control the releases to meet radiation dose limits. Plant operators are also required to publicly report releases to the commission.

NRC asked the academy to conduct the study because the agency is currently relying on a 1990 National Cancer Institute survey, which is now "outdated and has limitations," according to the council. The 1990 study found that cancer mortality rates were not elevated in populations living near nuclear plants.

"Obviously, the further we get into the future, the more important it is to have an updated study available to provide the most recent information to reply to those sorts of questions," said NRC spokesman Scott Burnell.

The council said doses resulting from "monitored and reported radioactive releases from nuclear facilities are expected to be low" and cancer risks, if any, will likely be minimal. "It is not certain whether a full-scale study would have sufficient statistical power to detect such small effects, if present," the council said.

If NRC does decide to move forward with updating its assessment, the council recommended that the agency first conduct a pilot study at six different nuclear plants in Illinois, Connecticut, New Jersey, Michigan, California and Tennessee to determine whether certain approaches could be conducted on a large-scale.

The council said NRC could use two approaches during the pilot study. The first approach would involve investigating the rates of cancer in small geographic areas within approximately a 30-mile radius of nuclear facilities. Another approach would study how close the mothers of children younger than 15 lived in relation to a nuclear plant during pregnancy.

The council said both approaches would focus on leukemia, the cancer associated with radiation exposure in children.

The report will now be open to public comment for 60 days to inform the design of the next phase of the study, the council said.

Rep. Edward Markey (D-Mass.) applauded the study. "I look forward to continued work on this important issue, and I hope that the next phase of the study will proceed quickly so as to best inform our public health and nuclear energy policies," he said in a statement.