The risks associated with flooding of nuclear plants are as follows [1,2]:
- The presence of water in many areas may be a common cause of failure for safety related systems, such as the emergency power supply systems or the electric switchyard, with the associated possibility of losing the external connection to the electrical power grid, the decay heat removal system and other vital systems.
- Considerable damage can be caused to safety related structures, systems and components by the infiltration of water into internal areas of the plant. Water pressure on walls and foundations may challenge their structural capacity.
- The dynamic effect of the water can be damaging to the structure and the foundations of the plant as well as the many systems and components located outside the plant.
- A flood may transport ice floes in very cold weather or debris of all types which may physically damage structures, obstruct water intakes or damage the water drainage system.
- Flooding may affect the communication and transport networks around the plant site. The effects may jeopardise the implementation of safety related measures and emergency planning by making escape routes impassable and isolating the plant site in a possible emergency, with consequent difficulties in communication and supply.
- Flooding can contribute to the dispersion of radioactive material to the environment.
A 2005 Greenpeace International report lists examples of flooding of nuclear plants:
- India, 2004: Kalpakkam-2, also known as Madras Atomic Power Station (MAPS), was operating at nominal power when the December 2004 tsunami sent seawater into its pump house. Operators brought the unit to safe shut-down. The tsunami swept away 59 people from Kalpakkam town, including five employees of the nuclear plant.
- France, 2003: EDF shut down two reactors at Cruas in December 2003 in response to torrential rainfall along the lower Rhone River, prompting French nuclear safety authority DGSNR to activate its emergency response centre. Filters on heat exchangers between the component cooling system and the essential service water system at Cruas 3 and 4 were clogged, hindering operation of the residual heat removal system. At the nearby Tricastin site, clogging of filters on the conventional site caused two more power reactors, Tricastin 3 and 4, to scram.
- Ukraine, 2000: reactor 3 at Chernobyl was shut down due to flooding caused by a storm. Workers had to pump water out of the reactor building.
- France, 1999: The electricity grid was hit hard by storms on December 27. One of many problems was the loss of auxiliary power for the four reactors at Blayais as well as a loss of the 400 kV power grid at Blayais units 2 and 4. The load shedding design that allows the units to self-supply with electrical power after disconnection from the grid failed. This led to an automatic shut-down of these two units. The diesel generators were started and functioned until the connection to the 400 kV power grid was restored, after about three hours. Furthermore, a flood resulted in the partial submergence of the Blayais site. Invading the site through underground service tunnels, water flooded the pumps of the essential service water system to unit 1, and one of the two trains (with two essential service water system pumps each) was lost because the motors were flooded. Other facilities were also flooded, including rooms containing outgoing electrical feeders (indirectly leading to the unavailability of certain electrical switchboards); the bottom of the fuel building of units 1 and 2 leading to the unavailability of safety-critical pumps (arising from a breach of French safety standards).
- In July 1993, the operator of the Cooper nuclear power plant on the Missouri River, Nebraska, was forced to shut down the reactor as dykes and levees collapsed around the site closing many emergency escape routes in the region. Below grade rooms in the reactor and turbine buildings had extensive in-leakage with rising water levels. The NRC inspectors noted that plant personnel "had not established measures to divert the water away from important components".
Case Study: Fort Calhoun
A flood assessment performed by the Nuclear Regulatory Commission (NRC) in 2010 indicated that the Fort Calhoun nuclear power plant in Nebraska "did not have adequate procedures to protect the intake structure and auxiliary building against external flooding events."
In June 2011, Missouri River floodwaters surrounded the Fort Calhoun plant. The reactor had been shut down in April 2011 for scheduled refueling, and has remained shut down ever since for a variety of reasons.
A fire on June 7 caused electricity to shut off in the spent fuel pools resulting in 90 minutes without cooling, and resulting in a partial evacuation. NRC inspectors were concerned that faulty design and faulty maintenance contributed to the fire; workers were unable to quickly get into the electrical room; and plant operator Omaha Public Power District was slow to notify emergency officials.[4,5]
This was followed by allegations that an NRC manager tried to override inspectors' conclusions about the fire and that he misrepresented their findings, and further allegations that senior NRC management made only token efforts to address NRC staff concerns.
On June 23, a helicopter contracted by Omaha Public Power District to survey transmission lines made an unplanned landing 2.4 kms from the plant; reports described it as an unplanned landing but photos showed it on its side in a field.
On June 26, a water-filled rubber flood berm surrounding part of the plant was punctured by a small earth mover and collapsed, allowing flood waters to surround the auxiliary and containment buildings at the plant, and forcing the temporary transfer of power from the external electricity grid to backup generators.[8,9]
On June 30 one of the pumps used to remove seepage caught fire when a worker was refilling it with gasoline. The worker put the fire out with a fire extinguisher but was burned on his arms and face.
Beyond Nuclear summarises several examples of NRC whistleblower revelations about inadequate protection against flood risks.
In July 2011, with flood waters along the Missouri River rising around Nebraska's Fort Calhoun nuclear power station, David Loveless, a NRC Senior Reactor Analyst, concluded that the reactor would not survive the gross failure of the Oahe dam. Loveless cited analysis that a dam break would hit the reactor with a wall of water knocking out electrical power systems and water pumps vital for reactor cooling.
In September 2012, Richard Perkins, an NRC engineer, accused the NRC of deliberately covering up information relating to the vulnerability of US nuclear power facilities that sit downstream from large dams and reservoirs, and failing to act to correct the vulnerabilities despite being aware of the risks for years.[11,12,13]
Perkins asked the NRC's Office of Inspector General to investigate his allegations that NRC "staff intentionally mischaracterized relevant and noteworthy safety information as sensitive, security information in an effort to conceal the information from the public" where "agency records that show the NRC has been in possession of relevant, notable, and derogatory safety information for an extended period but failed to properly act on it. Concurrently, the NRC concealed the information from the public."
Perkins, along with at least one other NRC engineer, suggested that the real motive for redacting information was to prevent the public from learning the full extent of the vulnerabilities and to obscure how much the NRC has known about the problems and for how long.
Perkins was the lead author of July 2011 report, "Flooding of U.S. Nuclear Power Plants Following Upstream Dam Failure". The report concluded that the failure of one or more dams sitting upstream from several nuclear power plants "may result in flood levels at a site that render essential safety systems inoperable." Floodwaters could undermine all power sources including grid power, backup generators, and battery backups. The report concluded: "The totality of information analyzed in this report suggests that external flooding due to upstream dam failure poses a larger than expected risk to plants and public safety."
"My estimation," Perkins told The Huffington Post, "is that if people saw the information that we have, and if they knew for how long we've had it, some might be disappointed at how long it's taken to act, and some might be disappointed that, to date, we haven't really acted at all."
Another NRC engineer told The Huffington Post that the Department of Homeland Security had signed-off on releasing the July 2011 report without redactions, undermining arguments made by some NRC officials that certain information should be withheld because upstream dam vulnerability could be exploited by terrorists.
Several nuclear experts have expressed concern about the three-reactor Oconee nuclear plant in South Carolina, which sits on Lake Keowee, downstream from the Jocassee Reservoir. The plant would almost certainly suffer core damage if the Jocassee dam were to fail, according to redacted findings in the July 2011 report. "The probability of Jocassee Dam catastrophically failing is hundreds of times greater than a 51 foot wall of water hitting Fukushima Daiichi," an NRC engineer said.
Nuclear engineer Dave Lochbaum from the Union of Concerned Scientists notes that improvements have been made at some US plants in the aftermath of the flooding of the Fukushima plant in March 2011. However he questions why the steps were not taken sooner:
"For decades, these design deficiencies left these reactors more vulnerable to floods than necessary. The Fukushima disaster prompted reactions in the United States that found and fix these longstanding impairments. That's good. But what if these reactors had experienced the flood prior to March 2011 that it was supposed to be protected against, but was not? ...
"Why weren't these design problems found in the 2000s, 1990s, 1980s, or 1970s? Lots of people spent lots of time allegedly looking for them. For example, the NRC has inspection procedure 71111.06 titled "Flood Protection Measures" that requires two plant areas to be examined each year. The procedure explicitly guides NRC inspectors to give priority to "Sealing of equipment below the floodline, such as electrical conduits" in "areas that can be affected by internal flooding, including water intake facilities." ...
"Again, why didn't these or other NRC inspections find at least some of these design problems in the 2000s, 1990s, 1980s, or 1970s? It's not a case of one NRC inspector having a bad week – it's a case of a regulatory agency having four bad decades. The NRC should review its inspection efforts in light of all these reports and make changes necessary to improve their effectiveness.
"And the NRC could take a complementary approach. ... The NRC has the authority to fine owners for violating federal safety regulations. The NRC should take its federal safety regulations seriously by sanctioning owners who have violated them for decades."
UK: 12 of 19 nuclear sites at risk of flooding
As many as 12 of Britain's 19 civil nuclear sites are at risk of flooding and coastal erosion because of climate change, according to an unpublished analysis by the UK Department for Environment, Food and Rural Affairs obtained by the Guardian. Nine of the sites are vulnerable now, while others are at risk from rising sea levels and storms in the future. The sites include all of the eight coastal sites proposed for new nuclear power reactors, and numerous radioactive waste stores, operating reactors and defunct nuclear facilities.
A 2007 study by the UK Met Office, commissioned by nuclear firm British Energy, said that "increases in future surge heights of potentially more than a metre could, when combined with wind speed increases, threaten some sites unless existing defences are enhanced."
 Hirsch, Helmut, Oda Becker, Mycle Schneider and Antony Froggatt, April 2005, 'Nuclear Reactor Hazards: Ongoing Dangers of Operating Nuclear Technology in the 21st Century', Report prepared for Greenpeace International, www.greenpeace.org/international/press/reports/nuclearreactorhazards
 IAEA, 2004, 'Flood Hazard for Nuclear Power Plants on Coastal and River Sites Safety Guide', http://www-pub.iaea.org/books/IAEABooks/6731/Flood-Hazard-for-Nuclear-Po...
 NRC, 16 May 2011, 'Licensee Event Report 2011-003, Revision 1, for the Fort Calhoun Station', http://pbadupws.nrc.gov/docs/ML1113/ML111370123.pdf
 Nancy Gaarder, 11 May 2012, 'NRC staff criticizes official's handling of Fort Calhoun', www.omaha.com/apps/pbcs.dll/article?AID=/20120511/NEWS01/705119889
 Ryan Tracy, 8 June 2011, 'Nebraska nuclear plant lost cooling system after fire', http://online.wsj.com/article/SB1000142405270230477830457637401196302228...
 Ryan Tracy and Keith Johnson, 9 May 2012, 'NRC Manager Blocked Safety Concerns, Letter Says', http://online.wsj.com/article/SB1000142405270230407030457739419248788652...
 Jodi Baker, 23 June 2011, 'No One Hurt In Emergency Helicopter Landing', www.wowt.com/news/headlines/124434274.html
 Matthew Wald, 27 June 2011, 'Nebraska Nuclear Plant's Vital Equipment Remains Dry, Officials Say', www.nytimes.com/2011/06/28/us/28nuke.html?_r=2
 NRC, 'Event Notification Report for June 27, 2011', http://nrc.gov/reading-rm/doc-collections/event-status/event/2011/201106...
 KETV, 30 June 2011, 'Worker Burned At Nuclear Plant', www.ketv.com/r/28412417/detail.html
 Beyond Nuclear, 11 Oct 2012, 'NRC whistleblowers warn of nuclear accidents caused by dam failures and effort to suppress disclosure', www.beyondnuclear.org/nuclear-power/2012/10/11/nrc-whistleblowers-warn-o...
 Tom Zeller, 14 Sept 2012, 'Flood Threat To Nuclear Plants Covered Up By Regulators, NRC Whistleblower Claims', www.huffingtonpost.com/2012/09/14/flood-threat-nuclear-plants-nrc_n_1885...
 Richard Perkins, 14 Sept 2012, Letter to the NRC Office of the Inspector General: Concealment of Significant Nuclear Safety Information by the U.S. Nuclear Regulatory Commission, http://big.assets.huffingtonpost.com/igletter.pdf
 Dave Lochbaum, 19 February 2013, 'Fission Stories #130: Fukushima's Dividends or Mea Culpas', http://allthingsnuclear.org/fission-stories-130-fukushimas-dividends-or-...
 Rob Edwards, 7 March 2012, 'UK nuclear sites at risk of flooding, report shows', http://www.theguardian.com/environment/2012/mar/07/uk-nuclear-risk-flooding
 Nick Mathiason, 13 January 2008, 'Nuclear plants 'need better flood protection'', The Observer, www.guardian.co.uk/business/2008/jan/13/nuclear.nuclearpower