Historic flooding in the Midwest along the Missouri River occurred in the sum-mer of 2011. According to the National Weather Service, the flooding was due to a combination of an estimated 212 percent of nor-mal snowpack in the Rocky Mountains and nearly a year’s worth of rainfall in the upper basin of the Mis-souri river during the second half of May. The flood devastated homes, businesses and many square miles of farmland in Montana, North Dakota, South Dakota, Iowa, Nebraska, Missouri and Kansas. The Fort Calhoun and Cooper nuclear stations are located in the flooded region. Both plants took precautions to implement and bolster flood protection measures and ensure safety would be maintained as water lev-els rose.
Fort Calhoun had shut down for a scheduled refuel-ing outage before the flood. It remains in a safe shutdown condition pending NRC permission to re-start. Flood protection measures included sandbags, aqua berms and additional testing of emergency die-sel generators and loss of off-site power procedures. The NRC detailed additional inspectors to Fort Cal-houn during the peak of the flood, and NRC Chair-man Gregory Jaczko visited the plant to view the flood protection measures.
Cooper station used more than 5,000 tons of sand to create additional flood barriers. The plant continu-ously monitored the flood waters and coordinated with the Army Corps of Engineers regarding plans to release dams, but was not required to shut down the reactor since flood waters did not exceed technical specifications.
On April 16, 2011, an EF3-rated tornado touched down in the switchyard of the Surry nuclear power station in Virginia, damaged equipment and severed off-site electric pow-er. The station shut down automatically and back-up diesel generators started immediate-ly to provide electricity to maintain both units in a stable condition. The National Weather Service reported that the tornado had a “nearly continuous damage path ranging from around 200 yards to as much as a half mile wide.” Over 200 homes were damaged and numerous trees were downed or sheared.
Three waves of storms in the Southeast on April 26 and 27 generated an un-precedented 226 tornadoes in a 24-hour period. These tornadoes killed ap-proximately 330 people, obliterated entire towns and devastated the Tennessee Valley Authority (TVA) transmission system in this region. TVA’s Browns Ferry reactors in Alabama suffered a loss of off-site power when the storm damaged the station’s transmission lines. The layers of protection for nuclear units en-sure that even though the station had diverse off-site power feeds, the next
layer of defense, the emergency diesel generators, were available when the unlikely combination of storms occurred. Due to the extensive damage to the transmission system (337 damaged structures, 96 lines out of service) off-site power was not restored for five days. All three reactors shut down safely and were maintained in safe shutdown condition during this period.
The weather in the U.S. was particularly cruel in 2011. A series of natural phe-nomena challenged nuclear stations across the country, yet the nuclear plants managed and mitigated the events per the emergency response procedures and guidelines, resulting in no danger to health and safety of the public. The layers of protection provided at nuclear stations demonstrated the effectiveness of training, procedures and planning in the face of floods, tornadoes, earth-quakes and hurricanes.
The Great East Japan earthquake of March 11, 2011, and the resulting tsunami had a profound impact on nuclear power operators worldwide. The policy discussion on nuclear energy changed from the benefits of this clean energy technology to safety and security—issues that, informed by decades of safe operation, had been largely resolved in the minds of the public.
Within one week of the Fukushima accident, operators at the 104 U.S. reactors were reviewing systems and com-ponents to ensure that the designed features and measures could mitigate the effects of a seismic event, flood or complete loss of AC power. The U.S. nuclear industry has pooled resources to ensure the lessons from Japan are systematically gathered, analyzed and imple-mented. This process has already identified near-term actions that will add further to the margin of safety. In addition, the industry will take action to satisfy appropri-ate and additional requirements imposed by the NRC.
For U.S. nuclear operators, safety is always in the fore-front of operations and planning. The U.S. Nuclear Reg-ulatory Commission (NRC) is one of the world’s largest independent regulators. With over 4,000 employees and an annual budget of $1 billion, the NRC is the most intru-sive and prescriptive regulator in the world.