How Foolproof Air Cleaning Systems at Nuclear Power Plants Protect Public Health

Effective air cleaning systems can make all the difference in preventing a nuclear or radiological disaster.

Air cleaning systems are often the final line of defense in the event of radiological release or nuclear disaster. The role of air cleaning systems in nuclear accidents is vital in minimizing public exposure to radioactive material and protecting public safety. When nuclear accidents occurred in the past, air cleaning systems successfully prevented disaster by mechanically filtering out particulate matter, and chemically removing gaseous radioactive material from the air, thereby mitigating technical fallout and retaining radiation. Yet, even the most advanced air cleaning systems can malfunction at any time, without warning. The ongoing implementation of rigid testing standards, filter maintenance, and stringent adherence to operational demands is necessary to keep air cleaning systems running smoothly—both during a nuclear power plant’s day-to-day operation and in a nuclear emergency.

Air Cleaning Systems Prevent Radioactive Release

When potentially dangerous nuclear accidents occurred in the past, radiological release was successfully prevented thanks to smoothly-operating air cleaning systems.

Ronald R. Bellamy, PhD, Co-Program Director of the In-Place Filter Testing Workshop at the Harvard T. H. Chan School of Public Health, spent three years cleaning up Three Mile Island—a historic nuclear power plant accident that occurred on March 28, 1979 in Pennsylvania.

“Operators did not realize a valve was stuck open on top of the reactor vessel. Pumps that would have kept the nuclear reactor cooled were mistakenly shut off, and the reactor core partially melted,” Bellamy explains. “But safety systems at the plant operated as designed to protect public health and safety and radioactive releases into the environment were very minimal.”

When nuclear accidents occurred in the past, air cleaning systems successfully prevented disaster.

Nuclear air cleaning systems must be designed to function as intended during dire circumstances such as equipment failure or unexpected power loss, extreme weather including tornados that would drastically impact air pressure, human error, or training deficiencies—even when all backup systems malfunction, says Bellamy. “You design the plant so if something goes wrong, there’s a system that will compensate for that deficiency. You then make sure the system you designed to compensate for the deficiency has a backup system,” Bellamy states. “You design it so that second backup system has a third backup system. You may wind up with 8 different backup systems to make sure the plant can shut down safely.”

Emphasized Bellamy, air cleaning systems must function with redundancy so that what happens to one system will not affect what happens to another. As Bellamy stated last year in an article from the American Society of Mechanical Engineers, “The technical fallout, as well as the emotional response of the public, could be catastrophic. The necessity to protect public health and safety and the environment are of paramount importance, and cannot be overstated.”

Air Cleaning System Components Ensure Protection and Safety

Following the Three Mile Island incident, the business, design, and regulatory facets of nuclear power plants shifted to ensure adherence to rigorous regulations and criteria, says Bellamy. Nuclear power plant components are designed to minimize radioactive release to the public.

Activated carbon is one such air cleaning system component, says Bellamy. “Activated carbon removes gaseous material before it is released in the plants—primarily radioactive iodine,” he explains. “Significant amounts of iodine 131 may cause thyroid cancer. So the activated carbon does a similar job for the iodine as high efficiency particulate absolute (HEPA) filters do for particulate material.”

Following the Three Mile Island incident, the business, design, and regulatory facets of nuclear power plants shifted to ensure adherence to rigorous regulations and criteria.

Bellamy says there is little need to be concerned about radioactive iodine exposure from the operation of a nuclear power plant, since we are all exposed to radiation every day. “Bananas, for example, are very rich in Potassium-40, a radioactive material known to set off radiation detectors at airports,” he adds. A person in a normal year averages about 600 millirem—the unit of measurement used for absorbed radiation dose, says Bellamy. “The calculated doses from exposure due to radiation released from a nuclear power plant for an individual are around 2 to 5 millirem—a very small fraction of 600,” he says.

Another component of air cleaning systems designed to meet rigid standards are the HEPA filters that remove particulate material. “Each filter is tested independently at the manufacturer before they are allowed to ship it to a facility for use,” says Bellamy. “The filters are required in this laboratory test to remove at least 99.97% of particulate material.”

Regulatory authorities use the air cleaning systems in helping to predict what the radioactive material available for release after an accident might be—referred to as a radioactive source term, says Bellamy. “You can define how much material the radioactive source term is that might be released to the public. You then take that radioactive source term and apply the efficiency of the filter so you can calculate how much radioactive material actually is released from the plant,” he states.

“You can take the source term and reduce it by the efficiency of the filters. You can look at meteorology and use health physics factors to calculate the doses. The doses allowed to members of the public are required to be small fractions of the radioactive exposure an individual would get normally,” states Bellamy. “Even in a nuclear incident, the public would be adequately protected,” he emphasizes.

Air Cleaning System Regulations Increase Protection, Right Down to the Nanoscale

Ensuring greater protection of public health and safety means continuously meeting evolving industry regulation standards. According to John M. Price, PhD, CIH, CSP, PE, Co-Program Director of the In-Place Filter Testing Workshop at the Harvard Chan School and Director of Environmental Health and Safety at Northeastern University, strict ongoing controls are implemented to ensure successful contamination control across greater health and healthcare industries, such as clean room technology, micro-manufacturing, and pharmaceuticals.

It is critical that systems are tested periodically, equipment is properly maintained, and the integrity of filters is intact on a day-to-day basis.

One such regulation involves the labor-intensive process of changing out filters. “Filters used for emergency systems tend to stay in place for a long time. But when you’re not using them, they may degrade over time,” Price explains. “At clean rooms within the biotech industry, they’re probably changing the filters if not on an annual basis, probably within a few years. Typically, this is the last stage of filtration. And they have pre-filters to remove a lot of the larger-sized particles so they don’t end up clogging HEPA filters,” Price says.

It is critical that systems are tested periodically, equipment is properly maintained, and the integrity of filters is intact on a day-to-day basis, Price states. One critical filter testing component is contamination control. “There was an issue a few years ago with drug compounding where drugs were to be used intravenously, but they weren’t done in clean environments. Several people died from contaminated drugs,” states Price. “Research and manufacturing processes are highly dependent on a clean environment. These environments typically have different ratings regarding how they measure toxic contamination and airborne particulate matter that interferes with their processes since they’re going down to the nanoscale,” he adds.

Global Standards and the Greater Future of Nuclear Power

Bellamy says the 500 nuclear power plants worldwide rely on the evolution of global air cleaning regulatory standards. Global standards and codes may be different compared to the United States, but they are likely just as stringent, adds Price. “The basic methodology, principles, and theory of air flow measurements and filter testing is not different anywhere else in the world,” Price says. “Although we do have American national standards with the American Society of Testing and Manufacturing, they recognize there are international, European standards. They want to harmonize a lot of that criteria.”

“Domestically speaking, nuclear power is responsible for a sizable part of the country’s electricity. One hundred operating plants in the United States provide nearly 20 percent of the nation’s electricity,” Bellamy says. “The future of nuclear power is probably brighter overseas than it is in the United States now, but that 20 percent of the electricity needs to come from somewhere,” he stresses. Here in the United States, the federal government has long advocated for air cleaning guides and standards to be published and converted into legally binding international codes and standards. For example, the international ASME AG-1 Code document, “Code on Nuclear Air and Gas Treatment,” as Bellamy noted in his article, took hundreds of nuclear air cleaning experts 40 years to complete. Bellamy is the Chair of the ASME Committee responsible for the AG-1 Code, and notes that their work is continuing.

The manufacturing of filters and other system equipment will continue to drive the international market, Price predicts. “Manufacturers have a global market and they’re very interested to make sure not only do we meet American standards, but we meet European or international standards.”

Criteria is becoming much more stringent as demand for cost-effective technology rises, he adds. “The filter manufacturers are constantly looking at new applications for technology and trying to enhance the materials they work with to make the filters,” Price says. “It’s cutting-edge because we’re trying to remove the smallest of particles,” he stresses.

Air cleaning systems are perhaps the last ray of hope for the human race when radiological release or nuclear catastrophe strikes. That being said, the popular belief that nuclear power plants themselves are dangerous is invalid, says Bellamy, who has lived with his family in close proximity to power plants. “The risk of dying from a nuclear power plant is equivalent to the risk of being hit by a meteor,” he says. “So if you’re not worried about being hit by a meteor tonight, don’t be worried about dying from a nuclear power plant tonight.”

Harvard T.H. Chan School of Public Health offers the In-Place Filter Testing Workshop, which focuses on testing and certifying systems containing HEPA filtration and gas adsorption systems for nuclear and non-nuclear applications.