Two outside lines of defense against flooding failed Sunday at Fort Calhoun Nuclear Station, shifting the plant to backup electricity for 12 hours.
On Monday, the Omaha Public Power District was studying whether it could patch and refill the temporary water dam that burst. When the dam ruptured, it allowed floodwater to fill in around the plant to a depth of more than two feet, said OPPD spokesman Jeff Hanson.
Sunday's development offers more evidence that the relentlessly rising Missouri River is testing the flood-worthiness of an American nuclear power plant like never before. The now-idle plant, 19 miles north of Omaha, has become an island. And unlike other plants previously affected by high water, Fort Calhoun faces months of flooding.
Also on Monday, the head of the nation's nuclear regulatory agency, his lieutenants and congressional representatives toured the plant.
“It's pretty jarring to see a boat tied up to the nuclear power plant. ... It's an intense operation going on there, particularly with water surrounding all the buildings,” said U.S. Rep. Jeff Fortenberry of Lincoln, who toured the plant Monday with Rep. Lee Terry of Omaha. “There's no water inside; they have multiple, redundant systems in place.”
The plant disconnected from the electrical grid Sunday morning and ran on electricity supplied by its main, on-site backup source: two diesel-fueled generators. Federal regulators require nuclear plants to have generators to keep a plant running in case its main power source is interrupted.
Hanson said a piece of heavy equipment moving sand on the dry side of the water-filled dam, “brushed up” against it, causing it to rupture. The utility disconnected from the grid because the river water leaked through a cement barrier installed to protect the plant's main transformer.
“It did not work; it did not keep the water out,” he said.
Floodwater rose a couple of feet inside that barrier, Hanson said. Crews switched off the electricity feeding it to assure that it wouldn't be damaged, and it was not, he said. They pumped out the water, sealed the leaks in the cement barrier and restarted the transformer.
Disconnecting from the grid “gave us time to ascertain that all was fine,” he said.
The 2,000-foot-long water-filled dam that ringed the plant collapsed about 1:25 a.m. Sunday.
The dam itself was not part of OPPD's federally required flood defenses, both federal and utility officials say. Instead, it was an extra line of defense OPPD installed to protect equipment outside the reactor building from damage and to make it easier to get around the plant's immediate exterior.
“It was nice to have. It was a new, first line of defense against the river,” Hanson said, explaining why the utility hopes to refill it.
Victor Dricks, spokesman for the U.S. Nuclear Regulatory Commission, agreed that nothing else had changed at the plant as of Monday morning.
Because of the collapsed water-filled dam, river water surrounds the main reactor building, mechanical building, spent fuel pool building and other structures.
Barriers at entrances to the buildings are keeping that water from entering, Hanson said. A “minor” amount of water did seep into the plant's turbine building, he said, and was pumped out.
The buildings themselves and associated pumps and electrical equipment are designed to handle flooding up to 1,014 feet above sea level. The river is a little over 1,006 feet now and is forecast to reach a crest of 1,008 feet, barring extraordinary rains.
Federal nuclear regulators are monitoring the plant, which has been shut down since early April for refueling. Flooding will remain high at Fort Calhoun through at least August, as the U.S. Army Corps of Engineers continues releasing unprecedented amounts of water from upstream dams.
Regulators say their inspectors were at the plant when the water-filled dam failed and have confirmed that the flooding has had no impact on the cooling of the idled reactor or the spent fuel pool.
The NRC said there is a separate earthen berm to protect the electrical switchyard, which is in a different area of the plant site.
Last week, federal regulators augmented their inspection staff at Fort Calhoun. In addition to the two resident inspectors, three more inspectors and a branch chief were added to provide around-the-clock coverage.
Both the plant's operator, OPPD, and federal regulators say the plant remains safe.
But what happens if the river keeps rising?
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In the past, floods have had limited effect on U.S. nuclear plants, said Scott Burnell, spokesman for the Nuclear Regulatory Commission.
In 2008, the Duane Arnold Energy Center near Cedar Rapids, Iowa, temporarily lost its land line phones during a flood on the Cedar River.
In 1982, the Dresden Generating Center outside of Chicago was shut down for 24 hours as a precaution after the Kankakee River sent almost 6 inches of floodwater into the pump house that feeds water to the plant.
But neither of those plants faced months of flooding.
“Fort Calhoun is in a unique situation,” the NRC's Burnell said. “But let me stress again that the plant is in a safe condition and is expected to remain so.”
Fort Calhoun's chief nuclear officer, David Bannister, is equally emphatic.
“Let me be clear. The Fort Calhoun Station is safe, and it will continue to be safe throughout the duration of this event.”
The situation at Fort Calhoun can be told in part by the numbers.
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Monday, the Missouri River stood at about 1,006.3 feet above sea level at Fort Calhoun.
The nuclear plant is required to be offline when water rises above 1,004 feet, which occurred June 9.
The Nuclear Regulatory Commission expects flooding — based on current release rates and with normal to higher-than-normal rainfall — to peak between the current level and 1,008 feet at Fort Calhoun, said spokeswoman Lara Uselding.
That would give OPPD a little room to breathe.
New problems could start in the 1,010- to 1,012-foot range.
At around 1,010 feet, water would overflow an earthen levee protecting the electrical switchyard, based on the levee's current height.
The switchyard is important because it transfers electricity to the plant from the power grid. Even though the reactor is shut down, electricity is crucial for operating pumps and other equipment that circulate water to cool both the fuel in the nuclear reactor and the plant's spent fuel pool.
Bannister, OPPD's chief nuclear officer, said equipment inside the switchyard is further protected by sandbags to a height of about 1,011 feet. The utility is in the process of raising the earthen levee around the switchyard because that type of levee remains strongest if water does not reach the top few feet.
Should enough water get into the switchyard to damage the electrical equipment, the plant could lose power from the grid, and OPPD would again fire up its two primary backup generators. That's what the company did Sunday, when water got into a different area of the plant.
Bannister said the generators have weeks of fuel on site. The generators are protected against flooding to 1,014 feet above sea level, which means they should be able to provide energy to the plant if the river rises 7.5 feet above its current level.
At another location on the plant site, a temporary levee has been built around the storage area where casks containing older and cooler used nuclear fuel are kept. At some point above 1,014 feet, the Missouri River would overflow that berm, according to OPPD. Hanson said the 88-ton casks are anchored and will not float.
Also at 1,014, floodwater would incapacitate OPPD's backup generators if they were still being used. The utility has developed plans for tying directly into the transmission lines above the plant, if necessary, Bannister said. It also could shift to secondary backup generators, which are stationed about 22 feet above the worst-case design standard — at an elevation of 1,036 feet, Bannister said.
Water would have to rise to 1,038.5 feet above sea level to reach the spent fuel pool, a water-filled pool that holds the plant's most recently used uranium fuel.
If floodwater made it to the reactor, Bannister said, it couldn't get inside. That's because the reactor is itself a watertight vessel that holds nuclear fuel in its own deep pool of water.
Gary Gates, president and chief executive officer at OPPD, said the utility has been developing contingency plans to ensure that off-site electrical power is maintained to Fort Calhoun.
“We have literally been working around the clock,” Gates has said. “We do have a plan for a long-duration event, we're not anticipating that this will be a short-term effort.”
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Despite the hand dealt by the flooding, public safety has a few good cards to draw from. Among them:
» The maintenance shutdown.
Because the reactor went offline in April for routine maintenance, nuclear fission hadn't taken place for weeks when it became apparent that flooding would prevent restarting the plant.
As a result, the reactor had cooled to about 80 degrees, whereas normally it would have been about 560 degrees, Bannister said. Should something catastrophic happen, OPPD would have more time to act because it would take longer for water in the reactor to heat to a dangerous level.
» An aggressive federal inspection of Fort Calhoun in June 2009.
That inspection uncovered problems with OPPD's flood preparedness.
As a result, the utility was required to modernize its flood-fighting arsenal, including better and easier-to-install watertight doors and barriers, additional pumps and sandbagging equipment.
OPPD had put the finishing touches on those protections and was preparing for what it hoped would be a final inspection this June when floodwaters arrived.
» Discovery of erroneous flood calculations.
NRC review uncovered a mistake in calculating the level of catastrophic flooding that could occur, an error that OPPD has acknowledged.
According to the NRC review, OPPD was prepared for flooding up to a level of 1,009 feet above sea level — five feet below what the NRC required. Additionally, the federal agency said, OPPD's plans for protecting the plant to the required 1,014 feet were flawed and subject to failure.
The error was more than an academic exercise, said David Lochbaum, director of nuclear safety for the Union of Concerned Scientists. Lochbaum is a leading critic of the regulation of commercial nuclear plants and is among the people Congress turns to for advice.
An NRC risk analysis released last year determined that under OPPD's now-discarded plans, flooding above 1,010 feet would have led to a 100 percent chance of a fuel damage if the emergency gasoline pumps didn't work.
Bannister said those pumps had been tested and were working, and workers would have been able to deploy them. With the pumps in place, the NRC calculates that the pumping plan had a 97.5 percent chance of success of protecting the reactor core.
In response to the NRC's criticism, Bannister said the utility has doubled the number of pumps in question.
“Whatever threat the current flooding poses to the Fort Calhoun nuclear plant in Nebraska, that risk is lower today due to actions taken by the NRC,” Lochbaum said.
» The 9/11 terrorist attack, the Fukushima crisis in Japan and other catastrophes.
Experts in the industry universally agree that U.S. nuclear plants are more prepared for catastrophe because of the overhaul that took place after 9/11. All plants, including Fort Calhoun and Cooper, expanded their emergency capabilities so they could operate for the short-term with no outside help.
In addition, the NRC has required plants to go beyond their original safety standards. This is a reason why Fort Calhoun has plans and equipment in place should waters rise above 1,014 feet.
In the weeks after the Fukushima-Daiichi disaster — and thus just before this flooding — U.S. nuclear plants, including Fort Calhoun and Cooper, were required to inventory and test emergency equipment and undergo emergency drills to make sure safety systems were in place and working properly.
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The U.S. Climate Prediction Center has said the odds favor a rainier-than-normal summer for the upper Missouri River basin, which could worsen flooding.
However, Dave Pearson, a hydrologist with the National Weather Service, said the river has gotten so wide from flooding that it rises more slowly after rainfall or dam releases.
Fort Calhoun and Nebraska's other reactor, Cooper Nuclear Station, aren't being factored into the Army Corps of Engineers schedule of dam releases, said Erik Blechinger, corps spokesman.
“Flood-risk reduction is our priority right now,” he said. “We are working closely with OPPD and NPPD, so I would never say that we wouldn't consider adjusting releases, but I can't imagine all the possible scenarios. Currently, there is just no flexibility in the system.”
Sitting above Nebraska's nuclear plants are six upstream dams, part of one of the nation's largest reservoir systems. Failure of any of those dams would send devastating amounts of water downstream.
Could the dams fail?
“The short answer is no,” said Brig. Gen. John McMahon, who oversees the corps' 12-state northwestern division.
“It's not to say there aren't issues at different places that we're monitoring closely. But in terms of the integrity of the dams, that absolutely is not a concern.”
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