Correction appended.
An outdated model for health risks from radiation is hampering the nuclear energy industry, experts warn. They want rules that recognize new scientific findings to help speed the arrival of a new generation of fission power plants.
Nuclear energy’s potential as a weapon in the fight against climate change remains contentious, however. Some climate scientists warn that it’s going to be difficult to keep warming in check without a zero-carbon-emissions baseload power source to replace the nation’s aging nuclear power plants (ClimateWire, Dec. 4).
Opponents argue that reactors take years to build, with each plant costing in the billions of dollars. Both of these problems are heightened by traditional safety worries about radiation.
In high doses, radiation is deadly, with effects ranging from burns to cancer to organ failure. However, much of the time and money involved in building a nuclear power plant goes toward keeping radiation in check at much lower levels, a practice that some scientists say is not supported by their research.
At issue is the "linear no-threshold" model for radiation safety, which measures the harm from high radiation doses and extrapolates in a straight line to zero, giving rise to the argument that there is no level of exposure below which radiation is harmless, let alone helpful.
The model emerged as a standard in the early days of the nuclear energy industry, when radiation’s impact on health was uncharted territory.
"They basically said there was no lower radiation limit that wouldn’t cause damage," said Carol Marcus, a professor of radiation oncology, nuclear medicine and radiological sciences at the University of California, Los Angeles, medical school. "As the years have gone by, you can imagine the amount of bureaucracy that’s grown up to protect you from a single atom."
Marcus said the Nuclear Regulatory Commission, which licenses and oversees safety in nuclear power plants in the United States, has become bloated from an unfounded fear of low-level radiation. This thinking spread to other agencies and their dealings with radiation, like the Food and Drug Administration’s regulations for medical devices.
"In order to save their jobs and their funding, they invented a national crisis. ‘My God, CT [computed tomography] scans are killing people!’ And there’s no data to support it," Marcus said.
Beneficial effects of low levels of radiation
There are several ways to quantify radiation. For the medical sector, the main unit is the sievert, a measure of the probability of cancer or genetic damage resulting from a quantity of ionizing radiation. One sievert is equal to 1 joule per kilogram of absorbed energy, though a millisievert (mSv), or one one-thousandth of a sievert, is the more practical unit.
More than 100 mSv of radiation exposure each year leads to a statistically significant increase in cancer risk. Around 500 mSv, you start to see symptoms of radiation poisoning.
On average, an American receives a radiation dose of 3.1 mSv each year from natural sources, according to the NRC. A chest CT scan results in a radiation dose of 7 mSv.
NRC requires its licensees to limit radiation emissions to 1 mSv above background radiation each year, and the annual limit for nuclear workers is 50 mSv. Even so, the agency pushes nuclear energy firms to keep radiation levels even lower under a standard known as ALARA, short for "as low as reasonably achievable."
Marcus said the science doesn’t support these rules and a growing body of research seems to indicate that low levels of radiation may actually have health benefits, stimulating the activation of repair mechanisms that protect against disease.
In February, Marcus sent a letter to the NRC to ask it to change radiation protection rules under a regulation known as 10 CFR Part 20, which was last updated in 1991. She cited several studies that showed that low levels of radiation exposure actually reduced health risks.
Studies on atomic bomb survivors in Japan showed that low exposures to radiation reduced cancer risks below a 500-mSv threshold. A study of 400,000 nuclear industry workers across 15 countries showed a decrease in risk from all cancers.
Another analysis of 36,000 hyperthyroidism patients showed leukemia rates dropping among those treated with radioactive iodine compared to those treated with surgical thyroid gland removal. The radioactive iodine resulted in a dose of 130 to 140 mSv to tissues outside of the thyroid gland.
The mechanism behind this is uncertain, but Marcus said it is likely that low levels of radiation trigger cellular repair mechanisms without doing any damage, helping the body repair wear and tear from other sources like oxidation, chemical exposure or accumulated mistakes in the genome.
Marcus added that spurring the body to repair itself is one of the foundational principles of radiation oncology. Focusing radiation narrowly to a tumor kills off rapidly growing but fragile cancer cells while leaving healthy cells intact to heal the tissue.
Stricter radiation limits would hamper interventional radiologists since they would hit their annual exposure limits earlier.
Regulators should therefore build their safety standards around the evidence instead of pushing for zero radiation exposure, according to Marcus. "The first thing NRC can do is throw out ALARA," she said.
‘This is a controversial rule’
Mary Lou Dunzik-Gougar, chairwoman of the nuclear engineering and health physics program at Idaho State University, said the current radiation limits are too restrictive for the nuclear energy industry, adding time and costs to reactor designs and raising personnel costs.
"The regulations say that no nuclear facility can expose a person to a fraction of what people are exposed to living in the world," Dunzik-Gougar said. "We live in a radioactive world. If it was so dangerous, we would be seeing different effects.
"There has to be a sort of refocus on basing laws and regulations on what we actually know," Dunzik-Gougar added.
She noted that when it comes to health risks, air pollution is more dangerous than radiation. The World Health Organization attributes 7 million deaths to air pollution each year. As such, nuclear energy is a favorable option compared with dirtier fossil fuels.
Meanwhile, coal-burning power plants actually pump more radiation into the environment than nuclear power plants since trace radioactive elements like thorium and uranium end up concentrated in fly ash waste. But these fossil fuel plants are outside NRC’s purview.
"It’s important that, if we’re considering air pollution, to be realistic about what sources of power there are that can provide the power we need," Dunzik-Gougar said.
Maureen Conley, a spokeswoman for NRC, acknowledged that the linear no-threshold model for radiation was cautious. "This is a very conservative model that is necessary because while a dose-response relationship has been documented for high doses, there is not enough data on health effects at low doses to provide a definitive picture," she said, adding that every other nuclear regulatory agency in the world uses this framework.
She said the agency is taking Marcus’ comments and similar petitions under advisement and is reviewing comments on the proposal for a new radiation rule. "This is a controversial rule," Conley said. "We’re really only in the early phases of going through those comments."
The next step for NRC is to determine whether it will take action based on petitions to revise the linear no-threshold model for radiation safety. Conley said she could not estimate a timeline for this.
Correction: An earlier version of this story misframed a source’s comments about a federal agency. The story has also been revised to clarify the results of the thyroid study and to specify the medical specialty affected by proposed radiation rules.
