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Radioactive Waste Safety

Nuclear Regulatory Commission to reexamine how to safely store a mountain of radioactive waste for decades to come

by Jeff Johnson
November 4, 2013 | A version of this story appeared in Volume 91, Issue 44

Credit: NRC
Most U.S. spent nuclear fuel is held in pools next to power plant reactors.
A pool is surrounded by orange industrial equipment. At the bottom of the pool is a large array of circular holes.
Credit: NRC
Most U.S. spent nuclear fuel is held in pools next to power plant reactors.

With no place to call home, some 70,000 metric tons of high-level radioactive waste in the U.S. will stay where it is today, piling up at 75 sites in 33 states. The waste is mostly highly radioactive spent fuel remaining from decades of nuclear power plant operations. It is likely to double during the next 30 years, says an analysis by the Government Accountability Office, the investigative arm of Congress. GAO calls the waste “one of the most hazardous substances created by humans.”

Roughly 70% of the high-level radioactive waste currently resides in 40-foot-deep swimming-pool-like steel-lined cement tanks; the rest is in cement-and-iron shrouded dry casks on concrete slabs. Both temporary homes are adjacent to the power plants where the radioactive waste was generated and where it has been since the power plants were put in operation. The pools, casks, and reactors are found near urban and rural communities.

In the 1950s and ’60s, nuclear waste management received little national attention, reports GAO. But in 1982, Congress passed the Nuclear Waste Policy Act that required the Department of Energy to find a geological repository for radioactive waste and begin accepting waste by 1998. However, politics, money, and technology have blocked that path. Meanwhile, nuclear power plant owners have slowly shifted the waste from pools to more stable aboveground dry casks.

Late in November, the Nuclear Regulatory Commission will hold a hearing to take up an NRC staff draft report examining whether the spent fuel should be moved more quickly to dry casks, which some think are safer than pools. The draft report shows, as have past NRC reports, that the commission’s engineers and scientists are satisfied with the status quo.

However, some non-NRC scientists say the pools are dangerously filled beyond their design capacity, and they want an expedited move to what they believe is safer dry-cask storage. Several of the critics are former colleagues of current NRC Chairman Allison M. Macfarlane, and they say her past research backs their view. They point to a 2003 research paper that was coauthored by Macfarlane when she was a Massachusetts Institute of Technology researcher. That paper warned that if the cooling water were to leak out of a damaged storage pool, a fire would result, causing radioactivity to be released that could rival that from the 1986 Chernobyl disaster in Ukraine.

Spent-fuel safety concerns have grown in the past few decades, driven by fears of terrorist attacks at a nuclear facility or the possibility of earthquakes and tsunamis like those that devastated Japan’s Fukushima Daiichi nuclear reactor complex in 2011. In either case, the potential to release radioactivity from a drained spent-fuel pool has been recognized by all stakeholders as potentially a serious problem, particularly as the amount of spent fuel stored at reactor sites has grown. This increase has been triggered by the long-running failure to construct a U.S. radioactive waste repository and by President Barack Obama’s 2008 decision to cancel development of the Yucca Mountain nuclear waste repository in Nevada.

Credit: NRC
Spent nuclear fuel rests in dry casks at Diablo Canyon Nuclear Power plant in California.
Several concrete cylinders sit on a concrete pad in a grid, mixed in with flat metal rings of the same diameter.
Credit: NRC
Spent nuclear fuel rests in dry casks at Diablo Canyon Nuclear Power plant in California.

Shortly after that decision, the President called for and appointed an expert commission to develop a whole new plan for how the U.S. should address reactor waste issues. After the commission completed its report, DOE produced an implementation plan for the commission’s report. It recommended a fresh start in the search for a permanent repository, as well as construction of an interim radioactive waste storage facility. This plan would further put off action on an interim facility for at least a decade, and a permanent repository would wait until 2048 or later (C&EN, Feb. 13, 2012, page 33).

DOE’s plan also requires legislation, and Congress is hopelessly divided. A handful of senators have proposed legislation, but in the House of Representatives, Republican leadership remains wedded to a restart of the Yucca Mountain project, which Democrats oppose (C&EN, Jan. 21, page 6).

Meanwhile, the spent-fuel tonnage is expected to reach 140,000 metric tons by 2055, according to GAO. By then, experts say, nearly all the nuclear power plants that created this waste will be in the process of being shuttered, with their owners starting billion-dollar cleanup and decommissioning operations. With spent fuel increasing by some 2,200 metric tons per year, a disturbing image emerges of waste from the past left next to decommissioned nuclear power plants long into the future.

Since the early 1980s, utilities have realized they were running out of space for spent fuel rods. Most of the 12- to 15-foot-long fuel rods are kept in on-site pools some 20 feet below the water’s surface, isolating the radioactivity and cooling the thermally hot bundled rods. Water circulates through the pool, helping keep the rods cool and the pool temperature at around 49 °C (120 °F).

Without water, the spent fuel rods would jump in temperature, reaching 1,000 °C, according to NRC and DOE laboratory studies, a temperature high enough to ignite the rods’ zirconium cladding and cause the release of the radioactivity remaining in the spent fuel through a self-sustaining zirconium fire.

Spent-fuel pools contain the highest concentration of human-generated radioactivity on the planet, says Robert Alvarez, senior scientist with the Institute for Policy Studies, a Washington, D.C.-based think tank. Alvarez is a former top DOE waste official and a coauthor of the 2003 study with Macfarlane.

Alvarez says today the pools contain four to five times more spent fuel than they were originally designed to handle. He urges NRC to forbid industry to continue to “rerack” and tighten up spent fuel rods, as it has done in the past, and to move the rods to dry casks within five years of leaving the reactor core, a quicker move than is now the industry norm. After those five years of pool time, the spent fuel is sufficiently cool and radioactively stable enough to move to dry-cask storage.

Much of the spent fuel in pools has been there for a long time. In another study, the Union of Concerned Scientists estimates that more than 80% of spent fuel in pools today has cooled sufficiently that the rods could be moved to dry-cask storage, reducing the heat load in the pools and allowing the waste to be kept passively safe without external systems needing electricity, which is required for the pools.

NRC is well aware of the problem. Documents and officials acknowledge that radiation exposures from a spent-fuel pool accident could exceed that of releases from a reactor core meltdown. Studies show spent-fuel pools now store significantly more fuel assemblies than does a reactor core. Also, spent-fuel pools are not isolated from the environment like reactor cores, which are held within a reactor’s containment structure.

But NRC staff say expedited transfer of spent fuel to dry-cask storage wouldn’t increase the overall protection of public health and safety nor would any other benefit warrant the added implementation costs. The rods, they say, are safe where they are. NRC maintains that a loss-of-coolant accident is highly unlikely and mitigation efforts such as monitoring and backup water supplies for the pools would prevent disaster.

The Nuclear Energy Institute, an industry trade association, adds that more rapid movement of spent fuel from the pools would, in fact, increase risks, including higher occupational doses to workers from handling “hotter” fuel and higher numbers of casks as well as the increased potential for cask drop accidents.

Although industry and NRC defend the status quo, the seemingly endless delay in addressing waste is not lost on those who oppose nuclear power and are likely to testify at the upcoming NRC hearing. One group, Beyond Nuclear, puts its concerns bluntly, noting that last year marked the 70th anniversary of the creation by Enrico Fermi and his team of the first radioactive waste from the Manhattan Project.

“What this date should remind us is that no permanent safe location or technology has ever been found to isolate this waste from the biosphere,” says Kay Drey, a Beyond Nuclear board member who supports dry-cask use.

When Macfarlane was quizzed on her position, she released only this statement: “The back-end of the fuel cycle highly interests me. I strongly encourage our staff to closely and carefully study the research underway here at the NRC and fully explore all the options.”


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