Sustainable Development / International
Renewable Energy and International Development
U.S. Nuclear Flooding
Q. Do hydrogen explosions happen in U.S. nuclear power plants?
Q. Can natural disasters result in flooding of U.S. nuclear power stations?
A. It has already happened… Examples from one nuclear plant - a long way from the ocean
The extensive cooling systems that are required for nuclear plant operation dictates these facilities are built close to large water supplies – rivers, lakes, and oceans. Consequently these locations are typically in a 100 year flood plain. 
A 100 year flood has a 1% probability of occurring in a given year (i.e. 1 chance in 100) and is described as a 100-year flood event. This suggests the common but mistaken notion that there should be an interval of 100 years between such events. In fact the probability of having two 100-year floods within 10 years is almost 10%.[1]  
The average age of the nuclear power plants in the U.S. is over 30 years. A 100 year flood has a 26% chance of happening in 30 years - that's why you buy flood insurance with your mortgage if your house is in a flood plain.[2]  
Nebraska Cooper Nuclear Power Station
The Cooper Nuclear Power Station was built near Brownville, Nebraska on a 100-year flood plain with additional protective dikes and levees. The plant was first put into operation in July 1974. In mid-July 1993 upstream dikes and levees collapsed causing rapidly rising flood waters on the Missouri River forced the operator to shutdown the reactor. The flooding closed many emergency escape routes in the region. 
“…below grade rooms in the reactor and turbine buildings had extensive leakage with rising water levels.” 
 “… the floor drain system backed up so that standing water from within areas known to be radiologically contaminated had migrated out into designated clean areas.”
 “…water levels rising inside the reactor building impinged on electrical cables and equipment such as the Reactor Core Isolation Cooling (RCIC) pump room causing the circuitry to ground out.”  [3]
   
Photo: Diane Krogh/Lighthawk
A 1993 flood collapsed dikes and levees on the Missouri River upstream from the Cooper Nuclear Power Station and forced the operator to shutdown the reactor. 
Are hydrogen explosions uncommon? Apparently not…
The first close call. The Brownville, Nebraska Cooper Nuclear Power Plant: On November 5, 1975 the plant had been operating a year and a half. Hydrogen gas leaking from the reactor core exploded from an air sampler spark and injured and contaminated two workers, and damaged the plant boiling water reactor and an auxiliary building. [4]
The second close call. On January 7, 1976, two months after the hydrogen gas explosion that injured two men, an ice plug formed at the top of the 325 foot off-gas stack, producing a back pressure and build up of hydrogen in the building. The building was evacuated, and shortly thereafter an explosion completely demolished the building; the reactor was shut down immediately. There were no personnel injuries. There was some release of radioactivity on site, but it did not reach the site boundary. “…levels of activity at the site boundary were below maximum permissible concentrations throughout the accident.” [4]
The third close call. A news release in mid-September, 1999 described a hydrogen gas explosion at the Cooper Nuclear Power Plant, causing the shutdown of the reactor. An electrical problem in sump pumps at the base of the plant’s gas release towers caused the hydrogen explosion. [5]
TVA Browns Ferry Nuclear Station
 
The TVA Browns Ferry Nuclear Station is located on the Tennessee River near Decatur and Athens, Alabama, on the north side of Wheeler Lake. On Saturday, March 28, 2011 a safety spokesperson for TVA assured a CNN reporter that the dikes and levees for this nuclear plant were designed for ‘a million year flood’. 
Q. For the regulators - What is the condition of upstream dikes and levees?
There are over 100 nuclear plants in the U.S. average age 30 years older.
Q. For the statisticians –what are the odds in the first 100 years of operation that one of these plants will have a 500, 1,000, 10,000, or 1,000,000 year flood? 
Teaching Quantitative Skills in the Geosciences - Recurrence Interval - Quantitative concepts: probability
Note – In calculating your answer you may ignore any future changes in the climate, rain fall, water use, construction on the river, maintenance, etc. - over the next 1,000,000 years.
[3] Nuclear Information and Resource Service article “Natural Disasters and Safety Risks at Nuclear Power Stations” November 2004 by Paul Gunter http://www.nirs.org/factsheets/naturaldisaster&nuclearpower.pdf 
[4] “Descriptions of Selected Accidents that Have Occurred at Nuclear Reactor Facilities” Nuclear Safety Information Center, April 29, 1980. Department of Energy’s (DOE) Information Bridge: DOE Scientific and Technical Information. http://www.osti.gov/bridge/
[5] Environment News Service Ameriscan: September 21, 1999 http://www.mail-archive.com/nativenews@mlists.net/msg04368.html
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