There have been recent reports of problems at the Boone Dam in Tennessee, which is upstream of seven nuclear reactors. Although the indications are that the problems will be solved, the seepage at the dam means that the potential failure of such dams, and associated threats to nuclear facilities, should be reexamined. The problems include the fact that dams can fail, and that seepage can be evidence of potential failure, that excessive flooding may result from dam failure, and that downstream nuclear plants may not be resilient in the face of such an event. There is also recent evidence, from the Mineral, Virginia earthquake, that the Eastern United States is more vulnerable to earthquakes than has previously been considered and that the effects of earthquakes in the region can travel for very long distances from the epicentre. The US has a large number of inland nuclear plants, some of which are around 40 years old. There is continuing argument as to the safety of the design of older US reactors in the light of the failure at Fukushima Daiichi. In this article I have tried to present some of the issues for consideration, without making judgement.
The American Society of Civil Engineers has stated that, “The average age of the 84,000 dams in the country [USA] is 52 years old. The nation’s dams are aging and the number of high-hazard dams is on the rise. Many of these dams were built as low-hazard dams protecting undeveloped agricultural land. However, with an increasing population and greater development below dams, the overall number of high-hazard dams continues to increase, to nearly 14,000 in 2012. The number of deficient dams is estimated at more than 4,000, which includes 2,000 deficient high-hazard dams. The Association of State Dam Safety Officials estimates that it will require an investment of $21 billion to repair these aging, yet critical, high-hazard dams.”
A Press statement by the U.S. Nuclear Regulatory Commission (NRC) stated that “On October 30, 2014, at 1100 EDT, TVA conducted a briefing for government officials and other stakeholders regarding the decision to accelerate the Boone Reservoir annual drawdown after discovery of a sink hole near the base of the embankment and a small amount of water and sediment found seeping from the river below the dam. TVA is continuously monitoring the dam and conducting an investigation to determine the source of the water seepage. The dam is located upstream of all three TVA nuclear sites. There are currently no nuclear plant operability or safety issues, and TVA is assessing the impacts on the plant licensing bases.”
On the 30th October 2014 The Johnson City Press had reported: “When an Oct. 20 inspection of the dam revealed a sink hole — a common occurrence — TVA workers repaired it quickly. Six days later, an uncommon occurrence happened when seepage was found near the location of the sink hole at the base of the dam.” Boone Dam is near the border with Virginia, where a M5.9 earthquake occurred in 2011. This earthquake was important because the USGS found that, the farthest landslide from the 2011 Virginia earthquake was 245 km (150 miles) from the epicenter. The USGS stated that: “This is by far the greatest landslide distance recorded from any other earthquake of similar magnitude. Previous studies of worldwide earthquakes indicated that landslides occurred no farther than 60 km (36 miles) from the epicenter of a magnitude 5.8 earthquake.” Jibson and Harp stated that “The 23 August 2011 Mineral, Virginia, earthquake (Mw 5.8) was the largest to strike the eastern U.S. since 1897 and was felt over an extraordinarily large area.”
Randall Jibson, USGS scientist and lead author of a study published in the December 2012 issue of the Bulletin of the Seismological Society of America, said, “What makes this new study so unique is that it provides direct observational evidence from the largest earthquake to occur in more than 100 years in the eastern U.S. Now that we know more about the power of East Coast earthquakes, equations that predict ground shaking might need to be revised.” The USGS said that. “It is estimated that approximately one-third of the U.S. population could have felt last year’s earthquake in Virginia, more than any earthquake in U.S. history. About 148,000 people reported their ground-shaking experiences caused by the earthquake on the USGS “Did You Feel It?” website. Shaking reports came from southeastern Canada to Florida and as far west as Texas.” They added that, “In addition to the great landslide distances recorded, the landslides from the 2011 Virginia earthquake occurred in an area 20 times larger than expected from studies of worldwide earthquakes. Scientists plotted the landslide locations that were farthest out and then calculated the area enclosed by those landslides. The observed landslides from last year’s Virginia earthquake enclose an area of about 33,400 km2, while previous studies indicated an expected area of about 1,500 km2 from an earthquake of similar magnitude.” Edwin Harp, USGS scientist and co-author of the study said, “The landslide distances from last year’s Virginia earthquake are remarkable compared to historical landslides across the world and represent the largest distance limit ever recorded. There are limitations to our research, but the bottom line is that we now have a better understanding of the power of East Coast earthquakes and potential damage scenarios.” According to the USGS, “The difference between seismic shaking in the East versus the West is due in part to the geologic structure and rock properties that allow seismic waves to travel farther without weakening.”
Boone Dam was well outside the area affected by the Mineral, Virginia earthquake, it is 436 km, or 271 miles from Mineral, but the USGS report and 2012 study indicates that the risk factors associated with East Coast earthquakes are higher than normally planned for. The concerns associated with the Boone Dam are the possible consequences of any failure of the dam to the seven nuclear plants down-stream of the dam.
In September 2012 Tom Zeller, Jr., writing in The Huffington Press, reported that, “Richard H. Perkins, a reliability and risk engineer with the agency’s division of risk analysis, alleged that NRC officials falsely invoked security concerns in redacting large portions of a report detailing the agency’s preliminary investigation into the potential for dangerous and damaging flooding at U.S. nuclear power plants due to upstream dam failure. Perkins, along with at least one other employee inside NRC, also an engineer, suggested that the real motive for redacting certain information was to prevent the public from learning the full extent of these vulnerabilities, and to obscure just how much the NRC has known about the problem, and for how long. “What I’ve seen,” Perkins said in a phone call, “is that the NRC is really struggling to come up with logic that allows this information to be withheld.” Another engineer, interviewed by Zeller, added real concerns about the Oconee nuclear plant. “Among the redacted findings in the July 2011 report — and what has been known at the NRC for years, the engineer said — is that the Oconee facility, which is operated by Duke Energy, would suffer almost certain core damage if the Jocassee dam were to fail. And the odds of it failing sometime over the next 20 years, the engineer said, are far greater than the odds of a freak tsunami taking out the defenses of a nuclear plant in Japan.”
There are currently 61 commercially operating nuclear power plants with 99 nuclear reactors in 30 states in the United States. Thirty-five of these plants have two or more reactors. The majority of US nuclear reactors are dependent on rivers for cooling. In the light of the Fukushima Daiichi disaster there have been growing concerns about nuclear safety, especially for older reactors, some reactors, like Oyster Creek in New Jersey, are over forty years old.
Accordingly, it is reasonable that the possible impacts of earthquakes and floods are better understood, as the risk of catastrophic failure of nuclear plants is one of the most serious threats our societies face today. It is also important to understand that dams can fail, and as Patrick J. Regan said in Hydro Review (1st June 2010), “Dam safety professionals must be ever vigilant in their efforts to assure the safety of dams and other water retention or control structures under their charge; whether owner, regulator or consultant, none can be complacent when it comes to dam safety. And yet, all too often complacency creeps in when a dam has had a lengthy history of apparent successful operation. How many times have we heard, or used the words, ‘The dam’s been OK for 50 years. Why are you worried about it now?’ During many Potential Failure Mode Analysis sessions conducted by the [US] Federal Energy Regulatory Commission, this reasoning came up as a way to lower the categorization of a potential failure mode. We seem to forget that dams are subject to many of the affects of aging and exposure that we are all subject to.” Regan added, “Seepage related incidents are the most common modes of failure in the early years of a dam’s life and continue to be an important potential failure mode over the longterm.”
Which brings us back to the seepage problems at Tennessee’s Boone Dam. There have also been growing concerns about the poor state of repair of key infrastructure elements in the United States, with the failure of bridges, the poor state of repair of highways, railways with speed restrictions, very poor airports and so on. See http://www.infrastructurereportcard.org